Contents of Monthly Reports

All information contained in these reports is preliminary and subject to change.

All times are local (= UTC + 1 hour)

06/1968 (CSLP 11-68) Explosive activity on 16 June follows two months of lava flows

Notification Report (16 June 1968) Explosive eruption follows two months of lava flows

Eruption accompanied by two sharp earth tremors, clouds of dense black smoke. Additional information obtained from UPI dispatch, 1948 EST: Streams of red-hot lava on Etna for last two months. Today's tremors registered II on XII-point Mercalli scale (with IV registered in some villages) and second tremor, less than two hours later, registered between VI and VII. Eruption location undetermined because of heavy clouds.

Information Contacts: BBC; UPI.

Information Report 1 (18 June 1968) Explosions and lava flow from Northeast Crater

Current Etna activity scarce. Medium explosive activity from Northeast Crater. Seven-hundred-meter-long lava tongue from new opened vent below Northeast Crater.

Information Contact: F. Cugusi, Rome, Italy.

Jump to Index of Monthly Reports

07/1968 (CSLP 11-68)

Information Report 2 (17 July 1968)

Information Report 3 (24 July 1968)

Jump to Index of Monthly Reports

07/1969 (CSLP 11-68) Report of activity during a week of fieldwork at Bocca Nuova

Card 0656 (10 July 1969) Report of activity during a week of fieldwork at Bocca Nuova

Our mission of nine scientists and a 12-man support team, spent 7 days at the Bocca Nuova experimenting new devices to continuously measure and record the values of temperature, pressure and speed of the gases; chemical determinations, closely grouped (separated by the order of 10 seconds from one another), provided curves of the variations of the different constituents of the gas phase. Some figures can be given a indicative of the very rare phenomenon presented by this blow-hole: temperatures varied from ~800 to 1,100°C, speed from zero to ~20% in weight, CO₂ content from 4 to 60%. The permanently eruptive state of Mt. Etna is presently characterized by: 1) lava fountaining in the NE crater with "bombs" hurled up to 250 m above the crater rim from any of the three vents opened in the bottom. 2) lava flows being poured out from a fissure opened on the W side of the NE cone; lava supplies vary up to 10 or 12 m³/s the flows do not exceed 1 km in length. 3) lava fountaining in the bottom of the deep (>400 m) main crater pit (so-called "la voragina"). 4) hot (>800°C) gas rhythmic activity at the June 1969 born blow-hole (so-called Bocca Nuova) on the west side of the cone containing "la voragina."

Information Contacts: Haroun Tazieff, Paris, France; Centre National de la Recherche Scientique, France; Commissariat a L'Energie Atomique, France; Office National d'Etudes et Recherches Aerospatiales, France.

Jump to Index of Monthly Reports

10/1969 (CSLP 11-68) Review of typical activity; diagram of Northeast Crater

Card 0777 (06 October 1969) Review of typical activity; diagram of Northeast Crater

Since January 1967, Mt. Etna (figure 1) is in persistent activity. This activity can be observed if the vent of the volcano is open (the NE Crater of Mt. Etna) and the column of the fluid magma stands high in it. The gases escape through the crater producing intermittent explosions by which spatters and lumps of liquid lava are thrown in the ai sometimes as high as about 200 m. This explosive activity undergoes strong fluctuations in intensity. The intervals between consecutive explosions vary between a few seconds to many hours and even some days. It happens that during a long interval the scories lying on the inner slopes of the funnel glide down and cover the surface of the lava lake within the vent. For a while, only "smoke" issues quietly from the crater, till a new, somewhat stronger explosion throws the detritus our in the form of an "ash clouds" (crumbled scories but no real "ash"), and the usual persistent activity begins again, presenting often impressing spectacle, particularly at night.

It seems that some tourists observed the opening of a new "bocca" on the lower slopes of the NE Crater and believed that they were seeing the beginning of a new eruption, not knowing that during the normal persistent activity such ephemeral secondary boccas form very often – if the magma column stand high in the vent – and die out in a few days. In this case the degassing takes place at the surface of the magma column where trains of rising bubbles explode at intervals, throwing spatters out of the crater. The degassed epimagma descends along the wall of the vent while the foaming pyromagma rises in its central part. During the 2-phase-convection, the hydrostatic pressure may cause an intrusion of the epimagma between the strata of the more or less welded spatter and cinder cone of the NE Crater. At a certain distance form the vent, the increasing hydrostatic pressure in the downwards tended intruding epimagma becomes higher than the load and the resistence of the overlaying strata which are then uplifted giving way to the epimagma to the surface. A bocca forms without any explosive activity and the lava flows out quietly. Such a subterminal effusion is a common feature of the persistent activity of Mt. Etna. These small lava flows cool down rapidly and are covered by a slightly socriasceous glassy crust, under which the liquid lava continues to flow in a tunnel.

Fluctuations in the supply of epimagma, due to oscillations of the magma level in the vent, cause the formation of new lava channels and the ceasing of the former ones. In time, a great lava cake will form, covered by a consolidated crust. Here and there through this crust new secondary boccas are formed, from which ephemeral small lava flows are poured out. Such an activity may last for months and even for years without any paroxismal climax, i.e., without a true eruption, characterized by its violent character and by a following period of exhaustion with almost only fumarolic activity.

The only particular aspect of the actual activity of Mt. Etna is the existence of a large blow hole at the western part of the central crater from which, at short intervals, roaring gases escape violently. My friend and collaborator, Tazieff, with a team of specialists are studying this event carefully using new equipment which permits measurement of temperature, pressure and the speed and composition of the gases. All the qualities very widely within very short time intervals. The maximum temperature measured was 1070°C. During the night, large flames of burning gases are seen. Tazieff and his team will come to Catania within a few days to continue their research."

Information Contact: S. Rittman, Institut Internazionale Ricerche Vulcanologiche, Italy.

Jump to Index of Monthly Reports

04/1971 (CSLP 33-71) New craters, cones, and lava flows; lava surrounds observatory

Card 1167 (06 April 1971) Lava flows from fissure approach observatory

"A fissure opened a little above and halfway between the Volcano Observatory and the water condensation fumaroles. Lava flows, comparatively wide and swift, have almost reached the Observatory. Two points of emission and strong degassing craters on these fissures are delivering huge quantities of scoria and cinders with thunderous noise. The altitude of the activity is approximately 3,000 m. A party of six volcanologists will be there for field investigations on 7 April."

Information Contact: Haroun Tazieff, Paris, France; Sr. Antonio Nicoloso.

Card 1169 (08 April 1971) Activity from two radial fractures; three new cones built

Mount Etna thundered in new activity on 8 April 1971. Half a million persons watched to see whether it would threaten them. "For now it is not possible to determine whether the phenomenon will pose a threat to the countryside and the cities", said Swiss volcanologist A. Rittman, chief of the Volcanological Institute Center. The University of Catania Volcanological Institute said each of two radial fractures of the volcano's surface opened since 6 April near the 9,700-foot [(2,950-m)] level had 10 or 12 explosive centers hurling burning rock, ash, and steam into the air, and pushing molten lava down the mountainside. A report on 7 April said the more westerly of the two centers of activity already had thrown up three volcanic cones which were about 65 feet high. "It is the center of a violent uninterrupted explosive activity throwing hunks of lava and incandescent rock mor that 650 feet into the air accompanied by thunderous explosive noises." Lava flow from that eruption has surrounded three sides of the Volcanological Observatory, perched a half mile from Etna's main crater at 9,679 feet. The Etna cableway was halted because lava surrounded several of its supporting pillars. Etna's upper slopes are bare or snow-covered, but the rich soil of the lower elevations yields bountiful fruit and vegetable crops and has one of the highest population densities. The triangle between Catania, Nicolosi, and Acierale on Etna's southern flank supports more than 3,200 persons per square mile.

Information Contact: A. Rittman, Instituto Internationale di Volcanologia, Catania, Italy; David Haskell, UPI.

Card 1170 (12 April 1971) Very active lava flows almost surround observatory

Two apparently radial fractures ~200 m apart; the W one 100 m long from 3,000 m elevation, the E one 100 m long from ~3,100 m elevation (figure 2). Presently two lava flows issuing from E fissure proceed ~3 km down W slope of Valle del Bove. One lava flow is presently flowing out lower end W fissure. It is fed by a small fountaining breached spattercone; its speed ~2 m/s, width 10-12 m, thickness up to our knees. One offshoot of western flow is leaning against north, east, and western walls of University of Catania Observatory. Other lava offshoots seriously threaten cableway. Length evening 8 April about 2 km with lava thickness 2-10 m, heights reached by observable molten lumps up to 300 m, speeds up to 200 m/s. Central crater big chasm and usually actively erupting; bocca nordest presently quiet and filled by whitish sulphur oxide smelling fumes.

Information Contact: A. Rittman and H. Tazieff, Instituto Internationale di Volcanologia, Catania, Italy.

Card 1171 (12 April 1971) About 150,000 m² were covered by noon on 6 April

Maximum temperature estimated ~1,030°C. volume emitted lava about 10-20 m³/s. Area covered at noon 6 April about 150,000 m². Prevailing winds were ~100 km/hour in strength from northwest direction carrying volcanic gases plus steam from snow and condensed atmospheric water plus ash from both volcanic and phreatic explosions. 10 April: Activity continues, heavy fog prevents observations.

Information Contact: H. Tazieff and R. Romano, Instituto Internationale di Volcanologia, Catania, Italy.

Card 1173-1174 (19 April 1971) Lava covers 1 km² by 17 April; observatory and cableway damaged

"This is a report of the eruption between 15 April and 17 April. The two radial fractures are covered by lava flows. On the place of the E fracture, there is a single volcanic cone now 70 m high. There were violent explosions about every 20 minutes. At the foot of the active center there is a small cone delivering hot steam. Some ten meters below there is a vent with a lava flow which was going toward the Valle del Bove with a speed of 1 m/hour. This lava flow stopped Friday morning 16 April. The water condensation fumarole is preserved by the lava. The activity has momentarily stopped on the eastern sector fracture zone.

"On the place of the W fracture there are now two big cones, 40 m high on a N-S direction throwing incandescent rocks more than 200 m high. The southern one has on it flank a vent emitting 1 m³ of lava per second. This lava flow, after having entirely destroyed the observatory, has surrounded four pylons of the cableway, and the cable was broken by the lava Thursday morning, 15 April. The lava flow is still following its way at about 1 meter per hours. It is a typical block lava. Between Thursday evening, 15th and Saturday morning, 17th, the lava has moved about 50 m towards the intermediate station of the cableway which is now about 150 m from the lava. The northern cone stopped activity Thursday morning. According to the local guides it was during the night between 15 and 17 April that the explosive activity was the biggest since the beginning of the eruption. The observatory is surrounded on its four sides by four-meters-high lava products. The lava is threatening the north wall of the observatory and penetrated inside the observatory. The area covered by lava Saturday noon is about 1 square kilometer, and the damage is estimated to be about 1 million dollars."

Information Contact: M. Krafft, Centre Vulcain, Mulhouse, France; Roland Haas.

Card 1183 (30 April 1971) Three new craters formed; lava flows advancing on the S flanks

"Etna activity which commenced 5 April continues. Three craters have formed S of the central crater. Two are currently active with frequency of 25-30 explosions per minute per crater, with ejecta being hurled up to 300 m. Lava flows were advancing to the SE (Valle del Bove - 3 km) and continue to advance to the S (cable car lines - 4 km), and SW (Frumento - 2 km).

"The first chemical analysis of lava indicates a phonolitic tephrite. Gas from active craters shows an excess of CO₂ over SO₂; gas from lava flows shows an excess of SO₂ over CO₂. N-S fractures have been observed on the E side of Monte Frumento and between Central Crater and Northeast Crater. Central Crater continues to smoke, mostly white, occasionally brownish-black. Northeast Crater shows no activity. Presently no danger exists for populated area."

Information Contacts: T. Casadevall, F. LeGuern, and R. Romano, Instituto Internazionale di Vulcanologia, Catania, Italy; CNRS, France.

Card 1184 (30 April 1971) Observatory surrounded, but not destroyed, by lava flows as of 25 April

The following corrects statements made on cards 1173 and 1174: "The observatory was not ‘entirely destroyed' nor lava penetrated neither on April nor ... 25 April, when we last reached it (but to reach it, one has to cross the thick and still hot lava flows which do completely surround the building); the outpour of lava is an average of 25,000 m³ per hour presently emitted, at speeds varying from 0.5 to 4 m/s.; it is not a ‘typical block-lava' but a quite typical aa flow with accessory pahoehoe streams."

Information Contact: H. Tazieff, Instituto Internazionale di Vulcanologia, Catania, Italy.

Card 1185-1186 (30 April 1971) Two new explosive vents on the E fissure; cone growth continues

"The [E] fissure, which was the most active from the start, stopped all explosive and apparently effusive activity (although there are still some small and slow lava flows progressing on the big one which has flowed into the Valle del Bove. On the other hand, the [W] fissure extended upwards (northwards) for about 250 m with two new explosive vents starting on 19 April; they were still very active yesterday when we eventually reached them to collect gases (F. Le Guern). This fissure is now approximately 2.5 km long, extending en echelons from the very base of the central cone (alt. ca 3,050 m) down to the NW foot of Mt. Frumento Supino. Only its upper half km is active. The direction of this open fracture is N10-15°W. It is also the direction of the fault which worked last week (earthquake intensity 6-7 on the Mercalli scale) in the Giarre region, on the E foot of Mt. Etna. Exceptionally, some sort of relationship between an eruption and a tectonic earthquake could perhaps be considered as existing here.

"Presently, explosive degassing is continuously going on at the three lower and two upper main vents left open in the fissure. The lava lumps do not reach higher than about 200 m above crater rims. The cones are steadily growing up. The effusive activity decreased during the third week of the eruption and is more awkwardly estimated, the major part of the lava being now emitted through tunnels within the body of the main flow. This allows the lava keeping its heat content almost intact until its exit point, this meaning it being able to flow further down than the preceding ones in spite of decreased output and temperatures, as compared with the bigger flows of the first week of the eruption.

"R. Romano, assistant to A. Rittmann's I.I.V. magmatological laboratory, Catania, is carrying on daily analyses of emitted lavas. S. Cuccuzza-Silvestri, from the University of Catania, together with C. Sturiale and Riuscetti, also do watch the developments of the eruption. The two physicists of our eruptive gas-investigating group, P. Zettwoog and C. Vavasseur, will join F. Le Guern on 3 May. The violent degassing with related lava bombing, together with the strenuous access over fresh lava-flows, make it somewhat difficult to carry on P, T, and V measurements of the erupting gases as well as chemical analyses. The probes and protecting suits developed so far are suitable for the comparatively mild permanent eruptive activity of Mt. Etna (or Stromboli as well), but do not suffice for more violent eruptions."

[Corrections of fissure locations by H. Tazieff, Card 1229].

Information Contact: H. Tazieff, Instituo Internazionale di Vulcanologia, Catania, Italy.

Jump to Index of Monthly Reports

05/1971 (CSLP 33-71) Additional vents and fissures open; very active lava flows

Card 1195 (06 May 1971) Activity continuing in early May at high levels

"The activity of Etna has shown some increase during the past few days. A new fracture opened ... 4 May at the eastern base of the terminal cone between about 2,870 and 2,840 m above sea level and about 1 km from the crater's rim. Scoria cones were formed. An effusive bocca produced lava flowing with a velocity of about 20 m an hour at 1500 (local time) the 5th of May, along the W slopes off Valle del Bove. Explosive activity at the main focus of the eruption continues with somewhat reduced intensity, but the lava flows continue to be well supplied, the fresh material spewed through units on top of the old lava or sometimes running alongside. The lava is advancing in three main branches. The first south to southwest joined by the second moving south toward the central part of Piano del Lago about 2,880 m above sea level, while the third moving SSE flanks the main flow reaching down to 2,270 m above sea level by 1600 hours, travelling with an average velocity of 150 m an hour. Small lava flows running S or SSW continue to be emitted from the bocca above the principal eruptive focus at the higher level of 3,020 to 3,040 m above sea level."

Information Contact: A. Rittmann and R. Romano, Instituto Internazionale di Vulcanologia, Catania, Italy.

Card 1198 (10 May 1971) Eruption stops at some locations, but opens new vents and emits more lava flows

"Early on the morning of 7 May activity suddenly ceased at the two eruptive centers above the former observatory, and at the four small bocche situated on a fissure to the E which had opened on 4 May. Towards the evening of 7 May, two new bocche opened to the NNE of the center of 4 May, one at a height of 2,700 m above sea level and the other a little to the N, and ca. 2,580 m. A little later, a third fissure with four orifices opened at ca. 2,540 m. All are emitting lava flows directed toward the Valle del Bove. In contrast to the earlier centers, the rather less explosive activity leads to the formation of hornitos rather than cinder cones."

Information Contact: A. Rittmann, R. Romano, and F. LeGuern, Instituto Internazionale di Vulcanologia, Catania, Italy.

Card 1200-1201 (13 May 1971) Details of lava-flow activity during early May

"Present volumetric output of lava was estimated this past week as follows: 5 May, ~140,000 m³/hour; 6 May, ~90,000 m³/hour; 9 and 10 May, <10,000 m³/hour. A new fracture system did open on 4 May about 2200 on the E foot of the central main cone of Mt. Etna along a trend perpendicular to the initial N-S one at an altitude of 2,890 m above sea level. High pressure gases without lava fountaining fumed at the upper part of the main new fracture. Intense fountaining, a big spatter cone approximately 30 m high about 100 m downslope, and a lava flow averaging 10 m in width and [a speed of about 9 km/hour] around was discovered on the down slope end of the fountaining crater. These eruptive fissures, perpendicularly opened during one [same] eruption and exactly one month apart, constitute a rather exceptional phenomenon. It is in fact really quite interesting. On 6 May former activity . . . located on the N-S fissure completely stopped and the big chasm in the central crater started emitting big ash-laden puffs. On 7, 8, and 9 May the new easterly trending fissure extended downward towards Pizzi Deneri across the Valle del Leone which is the upper part of the Valle del Bove.

"[Henceforward, explosive activity is concentrated in the new collapse-chasm formed in the E foot of Mt. etna's central cone, at the upper end of the fracture zone. Effusive activity] of 4-6 May stopped at the upper part of this fissure as similar although much lighter activity resumed at altitudes several hundreds of meters lower down.

"We were able to simultaneously make recorded measurements of speed by way of special speedometers, temperature by way of a thermocouple gage, and pressure by way of a special Pitot tube, and make a large series of gas samplings for chemical analyses which are being (analyzed) now. The temperatures were usually about 1,000°C and the speed (it is not yet exactly calculated) was about 400 km an hour. These gas samplings and measurements were made on maybe the best possible place just at the head of the erupting fissure where the degassing of the magma is optimum."

[Corrections of fissure locations by H. Tazieff, Card 1229].

Information Contacts: F. LeGuern, P. Zettwoog, C. Vavasseur, and H. Tazieff, Paris, France.

Card 1202 (13 May 1971) Two additional eruptive vents open on 11-12 May

"Two new eruptive vents opened at an altitude of only 1,800 m above sea level S from [Rifugio] Cetelli. The first vent opened ... 11 May at 1137 exactly, and the second vent opened at 0400 [on] 12 May. These two vents have very slight explosive activity and the molten lava lumps are hurled only about 20 m high. The lava flows had already entirely crossed the forest zone and had reached the cultivated areas after having [crossed the road leading to Rifugio] Citelli. So, it's only an effusive . . . type of activity. All other activity stopped several days ago on the volcano, [but for the strong explosive degassing, without any fresh lava but with old ash- and rock-laden puffs at the new chasm, at an altitude of circa 3,000 m on the E foot of Etna's central cone.]

"The fissures system on the upper part of the volcano is always moving, and the fissures are extending, widening, and steam and hot gasses escape from an altitude of 2,670 m up to the very top of Etna at 3,300 m."

[Corrections of fissure locations by H. Tazieff, Card 1229].

Information Contacts: F. LeGuern, French Atomic Energy Commission; T. Huntington, Reading University, England; H. Tazieff, Paris, France.

Card 1208 (17 May 1971) Lava flow from 11-12 May centers cuts highway

"During the night 11-12 May two new effusive centers opened on a fissure directed NW-SE on the E slope of Mt. Etna at about 1,800 m elevation outside of Valle del Bove. The lower bocca is emitting a big lava flow which in 30 hours reached 1,100 m elevation cutting the highway Fornazza-Cabancitelli (Mare Niri). The effusive centers of 7 May on the inner slope of Valle del Bove are still very active. Up to now, no danger for inhabited places."

Information Contact: R. Romano, C. Sturiale, and A. Rittmann, Instituto Internazionale di Vulcanologia, Catania, Italy.

Card 1211 (18 May 1971) New fissure on the S flank emits lapilli and fumes

The following report was telephoned to the Center by H. Tazieff. "The fissure system with a trend N63°E is extending on about all the upper part of the E flank of Mt. Etna and at an altitude of 1,800 m above sea level it presently delivers two lava flows: the first one is approximately . . . . . . speed about 4 km/hour and an estimated output of 10,000 m³/hour; the second flow is approximately 8 m wide with a speed of 15 km/hour and an output of 10,000-15,000 m³/hour. Both flows coalesce lower down and proceed with decreasing speed down to 20-40 m/hour . . . . . the town of Formazzo which is still 5 km away from the lava front. Trees are burning and the menace becomes really important now.

"On the other hand, a new fissure opened today at an altitude of 3,000 m above sea level on the S flank just N from the new mountain hut called 'Il Torre del Filosofora' and this fissure starts throwing lapilli and fumes up into the air."

Information Contacts: F. Le Guern and H. Tazieff, Paris, France.

Card 1213 (19 May 1971) Farm houses destroyed by lava flow; strong explosions on 18 May

The following was telephoned to the Center by A. Rittman. "Emission of lava from the bocche near Cabancitelli is continuing and supplying copiously the great lava flow which advances slowly on a front about 700 m large towards the road Fornazzo-Lingualossa. Some farm houses and a vast area of cultivated land have been destroyed. In the early morning of 18 May strong explosions started to open a new sub-terminal crater which at 1000 was already more than 150 m wide and violently emitting dark clouds charged with ashes and white vapor. The new crater is situated at the place where on 4 May a small eruption center had opened on the E slope of Mt. Etna at about 2,900 m altitude. The activity of the bocche in the Valle del Bove continues much reduced; the Central Crater and the Northeast Crater quietly emit white vapor."

Information Contacts: R. Romano, E. Lo Giudice, and A. Rittman, IIV, Catania, Italy.

Card 1215 (21 May 1971) Summary of activity during 4-12 May

"A flank eruption has occurred on the E slope of Mount Etna, after 30 days of strong effusive and explosive activity located on the upper S zone of the volcano. The eruption started in the evening of 4 May by the opening of a new fissure at the E foot of the Central Crater about 2,900 m above sea level. The discharge of highly fluid lava increased during the night, and the strong and almost continuous degassing throwing lava lumps and incandescent scoriae 250 m began to build an elongated, sharp-shaped cone 30-35 m high. This cone was open toward the E, where a big lava flow was flowing with an initial speed of 10-15 km/hour. in a few hours the new lava reached a zone S of Monti Centenari in Valle del Bove near the 2,000-m level.

"This new activity apparently does not affect the S vents (figure 3), which remained active until 6 May. on this day, however, the explosive and effusive activity was somewhat decreasing. At midnight, the activity of the E vent began to decrease considerably and completely ceased on the 7th of May at 0200. In the morning of 7 May all was quiet on the volcano, excepting small cooling lava flows toward the S and some increased emission of gas from the Central Crater accompanied by rumblings and occasionally throwing brown cinder clouds.

"By the 8th of May at 0100 we were able to observe a large red glow toward the E on the Valle del Bove, where a flank eruption was starting on the slope between Valle del Leone and Vale del Bove (level 2,700 to 2,400), near the 1950 eruption vents. Six or seven lava flows were vigorously active, but explosive activity was almost negligible. In the 9 May morning at 1100, our team reached the vents. There was a continuous cracking of ground between the now inactive upper E vent and the location of the flank eruption. This flank eruption had broken by two en echelon fissures, the upper being between 2,680 and 2,650 m, and the lower near 2,500 m. Several lava flows were moving at an initial speed of 1-2 m/s, while continuous degassing (but without violent explosions) was building small eruptive conelets (hornitos).

"In the morning of 12 May, the magma erupted at a more lower point by the aperture of a new vent near Rifugio Citelli, around 2,000 m level, and the lavas from this new outbreak could be dangerous for the inhabitants of the Etnean E zone. This flank eruption is of the 1928 eruption type, and is even located approximately on the same fracture line as the 1928 eruption was. The maximum lava temperature recorded by both thermocouple and optical pyrometers is between 1,100 and 1,130°C. The viscosity, as estimated by Jeffreys' formula, appears very low, from 1,000 to 10,000 poises only."

Information Contacts: C. Archambault, F. Gauthier, A. Nicoloso, and O. Nicoloso, Instituto Internazionale di Vulcanologia, Catania, Italy; J.C. Tanguy, Laboratoire de Geomagnetisme du Parc Saint-Maur 94, Saint-Maur-des-Fosses, France.

Jump to Index of Monthly Reports

06/1971 (CSLP 33-71) Crater enlargements; corrections to previous reports

Card 1229 (03 June 1971) Crater enlargements; corrections to previous reports

"Important developments are the engulfments which recently did enlarge both the central crater's big chasm (la Voragine) and the new eastern chasm, as well as the extent, in length, width, and throw, of the fracture zone which is responsible for the second phase of the present eruption."

[H. Tazieff also submitted a number of corrections to his previous reports and comments about other reported aspects of the eruption. The corrections have been made to cards 1185, 1200, 1201, and 1202, above. Additional comments regarding card 1195 are included below. Comments disputing the interpretation and information presented by A. Rittman in a 3 May 1971 report not published by SI, included on the original card, are not reproduced here.]

Regarding Card 1195 (06 May 1971): "The velocity of the lava flow escaping through the newly opened N63°E fracture was approximately 9 km/hour (see Card 1200) and the mentioned speed of 20 km/hour can only be that of some flow-front."

Information Contact: H. Tazieff, Paris, France.

Jump to Index of Monthly Reports

09/1971 (CSLP 33-71) Activity starts again after 100 days of quiescence

Card 1294 (23 September 1971) Activity starts again after 100 days of quiescence

"[After] 100 days [of} complete quiescence, Mt. Etna volcanic activity started again. Lava column raised up to 200 m from Main Crater's rim. Two explosive boccas are located at the bottom of the crater."

Information Contact: A. Rittman, Istituto Internazionale di Vulcanologia, Catania, Sicily, Italy.

Jump to Index of Monthly Reports

12/1971 (CSLP 33-71) Periodic explosions from La Voragine crater

Card 1332 (21 December 1971) Periodic explosions from La Voragine crater

"After a few months of complete quiescence -- last activity occurred around the end of September -- Mt. etna activity started again. Two explosive boccas are located at the bottom of the main summit crater named La Voragine. They emit periodically volcanic sands and ashes mixed with fragments of molten lava that reach about 400 m elevation falling into a surrounding area of about 300 m radius."

Information Contacts: R. Romano and L. Villari, Istituto Internazionale di Vulcanologia, Catania, Sicily, Italy.

Jump to Index of Monthly Reports

02/1974 (CSLP 20-74) W-flank eruption rapidly builds cone; explosions and lava flows

Card 1791 (06 February 1974) First W-flank eruption of this century rapidly builds cone

"The eruption started [on 30 January] at an altitude of 1,800 m on the W flank of Mt. Etna. A new fissure was observed. The activity is essentially explosive. Only very short and thick tongues of lava seep slowly (less than 0.1-2 m/hour) to the E foot of a new rapidly built-up cinder cone about 50 m across the base and 100 m high. After initial, almost continuous lava fountaining which lasted throughout the first day, explosions occurred at the rate of 30-50 per minute. Lumps of a few kilograms were hurled 300-500 m high. Blocks weighing several tons have been observed reaching about 100 m above the crater rim. The lava temperature is estimated to be over 1,100°C in the crater and under 1,000°C in the lava flows. The viscosity is exceptionally high and probably due to a high degree of crystallization. The excepotionally high proportion of pyroxene accounts for the impoverishment of the lava in several magnesium elements and its relative enrichment in alumina and silica.

"Geophysical teams from the IIV in Catania, from the Observatorio Vesuviano, and from the Polytechnical School, Milano, started measurements on 4 February. It is totally impossible to reach the crater due to dense and continuous bombardment. I am presently sampling the eruptive gas phase. No eruption has occurred on the W flank of Mt. Etna this century. Local people called the quickly built-up new cone ‘Mt. Rapido.' The latest report states that the 'explosions are stronger but still no lava flow.'"

Information Contact: H. Tazieff, Chairman, Science Council, IIV, Catania, Italy.

Card 1795 (12 February 1974) Vigorous and frequent explosive activity from the new crater

The eruption that began on 30 January 1974 on the W slope of Mt. Etna was visited by J.C. Tanguy from 2 to 8 February.

According to Rittmann's classification, this should be an eccentric eruption with little or no relation to the main vent. It is mostly characterized by a highly explosive crater situated at an elevation of 1,680 m, which quickly built a cone over 100 m high. During the first days of activity, a restricted lava flow very slowly travelled about half a kilometer westward.

On 3 February, a very small lava tongue seemed to progress towards the SE, but next morning all effusive activity had stopped. The explosive crater, however, was vigorously active with continuous ejections (40-50 per minute) of big lava lumps and scoriae 400-600 m high. From time to time, the vent was blocked for a few seconds and the successive outbreak was accompanied by a strong air-shock percussion. Impressive also were the numerous earth tremors, especially E of the crater where the cone is partly open. Optical temperature at the vent is about 1,020-1,030°C, but measurements are probably too low as the top of the magma column cannot be observed. Another typical feature of this kind of eruption is the intense seismic activity the preceded the opening of the vent. Numerous earth tremors were felt from 14 January even at Rifugio Sapienza, 1,900 m high on the S flank of the volcano.

On 7 February the eruption was still continuing with some fluctuations. Explosions were 15-30 per minute, somwhat irregular in power and frequency. A new small but thick lava flow issued the day before from the N foot of the cone and is progressing as slowly as the former towards the NW. Earth tremors are persistent E of the crater.

Information Contact: J.C. Tanguy, Laboratoire de Geomagnetisme du Parc Saint-Maur, France.

Card 1807 (25 February 1974) Eruption ended on 17 February

"The eccentric eruption on the W slope of Mt. Etna ended on the 17th of February. On 8 February, the explosive activity began to decrease, although exceptionally strong recrudescences occurred from time to time. The outpouring of lava, however, was more important than at the beginning of the eruption. Nevertheless, it was still restricted in area and characterized by the sluggishness of the effusions. A flow starting on 9 February slowly reached a maximum length of about 2 km over the next few days. On the morning of 16 February, the explosions stopped at the vent and all outflow of lava ceased on 17 February.

"A run of lava temperature measurements was made using two chromel alumel thermocouples and a Schneider digital voltmeter. Although the eruption was coming to an end, temperatures as high as 1,075-1,085°C were recorded in both thermocouples. The optical surface temperature was 1,015-1,020°C. It can be compared to the measurements made at the explosive vent during the first phase of strong activity.

"The viscosity was high, but not measured (10⁵ poises?), However, this high value can be partially understood with respect to superficial cooling connected with the slow rate of lava discharge."

Information Contacts: J.C. Tanguy, Laboratoire de Geomagnetisme du Parc Saint-Maur, France; Guy Kieffer, Institute de Geographie, Clermont-Ferrand, France.

Jump to Index of Monthly Reports

03/1974 (CSLP 20-74) New vent SW of the 1974 cinder cone opens on 10-11 March

Card 1814 (14 March 1974) New vent SW of the 1974 cinder cone opens on 10-11 March

"After 22 days of quiescence, eruptive activities started again on the W flank of Mt. Etna during the night of 10-11 March 1974. A new volcanic vent opened about 200 m SW from the cinder cone built up during the period of the earlier 1974 activity. The area is located about 8 km W of the summit crater. The vent is characterized by highly explosive activity which brought about the formation, during the first two days, of an 18-19-m-high cinder cone. A viscous lava tongue is flowing out [of] the vent very slowly, proceeding westward. The length of the lava flow was about 700 m after 14 hours from the opening of the vent. From an approximate examination of the erupted material the rate of emission during the first 14 hours approached 10-12 m³/s."

Information Contact: CNR, Instituto Internazionale di Vulcanologia (IIV), Catania, Italy.

Jump to Index of Monthly Reports

10/1974 (CSLP 20-74) Lava lake drains and lava flows about 1 km

Card 1954 (10 October 1974) Lava lake drains and lava flows about 1 km

"The NE side of the terminal crater that stopped its activity at the beginning of the April 1971 eruption was opened again during the night of 28-29 September 1974 with strong explosive activity. During the night of 9-10 October 1974, following the collapse of the ring on the SW side, the lava lake that had formed in the base began to flow out. After 20 m, the flow changed its direction to the NNW for about 1 km. At the present time the activity is of irregular explosions and a slow flow of lava going for about 2,000 m."

Information Contacts: E. Lo Giudice and D. Condarelli, IIV.

Jump to Index of Monthly Reports

02/1975 (CSLP 10-75) Eruption on NW flank produces spatter cones and lava flows

Card 2092 (26 February 1975) Eruption on NW flank produces spatter cones and lava flows

An eruption began on the NW flank of Mt. Etna during the night of 23-24 February 1975, 24 hours after normal summit activity stopped. The eruption continues at the present time. Several spatter cones with fountaining activity have formed along the fissure which opened at an altitude of 2,500 m above sea level on the NW slope of Mt. Etna. A lava flow fed by the lowest vent has already reached a length of about 1 km. The front of this lava flow is presently about 10 km from the village of Maletto, to which it seems to be directed at the moment. The NE crater has stopped its activity, while the central crater is erupting dense clouds of ashes and sand.

Information Contacts: D. Condarelli, IIV.

Jump to Index of Monthly Reports

03/1975 (CSLP 10-75) New eruptive center on the North Rift zone

Card 2124 (19 March 1975) New eruptive center on the North Rift zone

On 24 February 1975, the persistent activity of the NE summit crater (altitude about 3,300 m) shifted towards the North Rift zone of Mt. Etna. Thus, a moderate outpouring of lava occurred at the 2,600-m level, accompanied by weak explosive activity that formed small so-called "hornitos." This new eruptive center was visited again on 13 March. The upper, sharp-shaped hornito (altitude 2,590 m) was continuously emitting white vapors and tiny pieces of scoriae only a few meters above the magma level. The lower hornito was inactive, being partly buried by early lava flows. The liquid lava itself poured out slowly 100-150 m downward from beneath a consolidated crust, forming several short-lived flows that did not exceed a few hundred meters in length. Emanations of gas were occurring also from a fissure near the 2,550-m level on the right edge of the lava field.

A maximum temperature of 1,065°C was recorded on chromel-alumel thermocouples inserted to 60 cm into the lava of the uppermost source. This temperature was nearly the same as those (1,075°C) measured in the lavas of the NE crater before 1971.

At the summit craters system there was on this day a strong continuous emission of dense white vapors from the NE crater and heavy clouds of brown ashes from the "Voragine" (chasm) of the central crater.

Information Contacts: G. Kieffer, Department of Geology, University of Clermont-Ferrand, France; A. Nicoloso, Capo Guida dell'Etna, C.A.I., Catania, Italy; J.C. Tanguy, Laboratoire de Geomagnetisme du Parc Saint-Maur, University of Paris VI, France.

Jump to Index of Monthly Reports

11/1975 (SEAN 01:02) Continuous activity for most of 1975; new lava vent

Continually active throughout most of 1975, lava began flowing from a new opening on the NW side of the volcano on 29 November [originally reported as 21 November].

Information Contact: G. Nappi, IIV.

Further Reference: Pinkerton, H., and Sparks, R.S.J., 1976, Formation of the 1975 subterminal compound lava flow, Mount Etna: JVGR, v. 1, p. 167-182.

Jump to Index of Monthly Reports

05/1976 (SEAN 01:08) Lava eruption stops in mid-May

In mid-May, Etna [temporarily] ceased erupting lava. For several days prior to 15 May, the volcano's two lateral craters were inactive, and only a thin column of vapor rose from the central crater. A team of scientists, led by Haroun Tazieff, was on the scene conducting investigations.

Information Contact: IIV, Catania.

Jump to Index of Monthly Reports

06/1976 (SEAN 01:09) Explosions from Bocca Nuova and The Chasm; lava flows on N-flank

Observations were made by the University College group and R. Romano of the IIV, 16 May-4 June 1976. Until this time weather conditions had been very bad on the volcano and reports of activity were sporadic. In the summit region, Bocca Nuova was fuming strongly and had a depth estimated to be in excess of 200 m. This pit was exploding throughout the period of observation, at rates varying from one explosion per 3 minutes up to 2 or 3 explosions/minute. Incandescent material was occasionally thrown above the level of the crater rim and vesicular scoria and Pele's hair fell close to the crater down-wind. The Chasm was also fuming strongly, and although its bottom was not seen, it had a depth of several hundred meters. During the afternoon of 25 May the Chasm started deep violent explosions at a rate of 20-25/minute. No bombs were seen from these explosions, and the activity died down over the next few days. The new pit on the W side of Northeast Crater was fuming quietly but not exploding. The area around this new pit contained large amounts of sublimates and its total depth was around 50 m. The Northeast Crater itself is now inactive, the vent being plugged by scree; but there is still heavy fumarolic activity high on the W inside wall.

The effusive activity during the period was occurring from new vents on the N side of the mountain (near Punta Lucia). A 40-m-high cone formed at about the 2,900 m level. Inside this cone was a conelet from which mild strombolian explosions of fresh gassy lavas were occurring on 26 May, though it was quiet on 31 May. Lava emissions were taking place farther downslope in the new lava field, from a number of boccas with positions that changed from day to day in an area above the 2,500 m contour. The rate of emission from one bocca was measured to be 0.4 m³/sec. and the total emission for the whole field was 2 m³/s.

Information Contacts: J. Guest, J. Murray, S. Scott, and W. O'Donnell, Univ. of London; R. Romano, IIV.

Jump to Index of Monthly Reports

07/1977 (SEAN 02:07) Lava effusion and explosive activity from a new vent

Lava effusion and explosive activity, from a new vent at 3,200 m elevation just N of the Northeast Crater, began during the early morning of 16 July. A small lava lake, first observed at 0400, occupied the new vent, which was the source of two lava flows. The larger moved E into the Valle del Leone, and the smaller to the N. By 18 July, the flows had reached 2 km and 800 m length respectively. Strombolian activity began at 0515 on 16 July and rapidly increased in frequency and power. Ejecta reached 600 m in height and fell over an area ~1 km in diameter. The explosions had ended by 20 July and lava extrusion ended on 23 or 24 July.

Precision leveling two weeks before the eruption by John Guest and co-workers showed a 1-cm inflation of the S flank since September 1976, but strong deflation under aa fields on the N flank.

Information Contacts: J. Guest, Univ. of London; R. Romano, and G. Frazzetta, IIV.

Jump to Index of Monthly Reports

08/1977 (SEAN 02:08) Two eruptions in August generate fountaining and lava flows

"After a period of quiescence since the beginning of this year, Etna erupted again on 16 July. New explosive and effusive boccas opened on the lower flank of the Northeast Crater cone at an altitude of 3,200-3,270 m. The first signs of eruption occurred in early July when a small pit opened on the N edge of the Northeast Crater Cone. Initially this pit emitted high-temperature gas which during the night was seen to be incandescent.

"The first sign of lava emission was seen by a guide at 0400 on 16 July when he observed a small 'lake' of lava in the bottom of the pit. An hour later weak explosive activity started and increased to become stable at about 15 explosions/minute by 1000. Incandescent material was thrown 300 m above the vent, with a maximum height of 500 m. The maximum range of the bombs was 400-500 m. During this early period of explosive activity, a fracture opened at about 3,240 m on the lower slopes of the cone and flows were emitted from the end of the fracture (at 3,220 m), first towards the NE and later to the E. At the same time ephemeral boccas (3,200 m) opened below the main fracture and fed a small flow in a northerly direction. Explosive activity reached its peak during the night of 17 July. During the early hours of 18 July collapse occurred in the Northeast Crater itself, causing great clouds of dust and ash. The explosive activity at the new vent then diminished both in frequency and intensity, becoming extreme1y variable.

"On 18 July the flows had reached a length of 800 m to the N and 2 km to the E. From then onwards the explosive activity continued to diminish, as did the effusion of lava to the N flow. The E flow reached the edge of Valle del Leone and continued as the principal flow, reaching a total length of 4 km by the end of the eruption. The N flow stopped with a total length of 1 km. Explosive activity ended at 1000 on 22 July and the lava flows stopped in the late afternoon.

"The area covered by lava was 0.16 km², the volume of lava was 4.8 x 10⁵ m³ and volume of pyroclastic material 500 m³. Microseismic activity was noted before and during the eruption.

"The Northeast Crater started erupting again on 5 August at 1430. The activity began with strong explosions from the July vent, with lava fountains being thrown to 400 m in the early stages. One lava flow formed, advancing N from a fracture on the N slope of the Northeast Crater Cone. The fracture was oriented approximately NNE. The lava was fluid and travelled about 3 km. Seismic activity was observed just before and during the eruption, which ended at 0630 on 6 August."

UPI reported that a third eruption began early 14 August and lasted only 14 hours. Fountains or strombolian ejecta rose 200 m above the vent, and two lava flows, each about 200 m wide, moved about 4 km down the volcano.

Information Contacts: R. Romano, G. Frazzetta, and D. Condarelli, IIV; J. Guest, Univ. of London; UPI.

Jump to Index of Monthly Reports

11/1977 (SEAN 02:11) Eruption from the NE crater, the fourth since mid-July

Etna's fourth eruption since mid-July began during the night of 2 November from the Northeast Crater Cone, site of the three previous events. Two lava flows were extruded, but (in contrast to the earlier events) explosive activity was very weak. The larger flow traveled 2.5 km NW from the vent and the smaller 1 km to the N, before the eruption ended about noon on 4 November.

Information Contacts: R. Romano, IIV; J. Guest, Univ. of London.

Jump to Index of Monthly Reports

12/1977 (SEAN 02:12) Frequent eruptions from Northeast Crater continued into January

Frequent eruptions from Etna's Northeast Crater continued through early January (table 1). Since the 2-4 November activity, progressively briefer 1-day eruptions occurred on 7, 22, and 25 November. On 6 December, extrusion of a single lava flow began at about 1100 from a NNE-trending fissure on the N side of the Northeast Crater. The flow traveled 4.5 km down the E flank before the eruption ended at 2200. On 24 December, tephra was thrown 1,000 m above the vent, and renewed activity 5 days later, accompanied by small earthquakes felt in nearby villages, projected tephra several hundred m above the vent. Lava extrusion resumed 2 January and the flow had advanced 1 km on a 150-m-wide front by evening. The eruption was continuing as of the morning of 4 January.

Table 1. Summary of Northeast Crater activity since November 1977. Courtesy of R. Romano.

    Month      Dates of Eruption

    Nov 1977   2-4, 7-8, 22 (10 hrs), 25 (7-8 hrs), 27 (10 hrs)
    Dec 1977   6 (8 hrs), 10-(?)13, 18, 24-25, 29
    Jan 1978   2-3, 4, 5, 7
    Mar 1978   25-26, 27-28

Information Contacts: R. Romano and L. Villari, IIV; J. Guest, Univ. of London; New York Times; UPI.

Jump to Index of Monthly Reports

03/1978 (SEAN 03:03) New lava flow and ash on 25 March

Etna erupted for the first time since January on 25 March [originally reported as 26 March], extruding a lava flow, destroying trees on the flank, and emitting ash, that was blown S towards Catania (25 km from the summit) by a strong wind.

Information Contact: UPI.

Jump to Index of Monthly Reports

04/1978 (SEAN 03:04) First SE flank activity since 1971

An eruption began 29 April and continued as of 3 May. Lava was extruded from four new vents, on the SE flank, and had reached the 1700 m level near Monti Centenari, the 1852 cone by the morning of the 3rd. Explosive activity ejected bombs to 300 m above the largest of the vents (near the 1819 crater; figure 4) and built a 50-m cone. Explosions had declined by early 3 May, but vigorous lava effusion continued.

Frequent brief eruptions from Etna have occurred since July 1977, but all have originated from vents on the Northeast Crater cone. The last SE flank eruption occurred 5 April-12 June, 1971, destroying the Etna Observatory.

Reference: Rittman, A., Romano, R., and Sturiale, C., 1971, L'Eruzione Etnea dell'Aprile-Giugno 1971: Atti della Accademia Gioenia di Scienze Naturali in Catania, Serie Sestima, v.3.

Information Contacts: J. Guest, Univ. of London; R. Romano, IIV.

Jump to Index of Monthly Reports

05/1978 (SEAN 03:05) SE-flank eruption continues through May

R. Romano reported the eruption started on 29 April at about 2000-2030 from bocca 1 (figure 5). Explosive activity built a cone that was 50 m high by 2 May. Lava flowed from the E side of the cone into the Valle del Bovee. Fissures opened, extending into the 1819 crater, where they intersected another fissure set which runs along the wall of the Valle del Bove.

"During the afternoon of 1 May new boccas 2 and 3 opened on the existing fissures, then early the next afternoon bocca 4 opened, emitting a small lava flow that stopped the same day. Activity at bocca 1 also ended on 2 May, but the main flow front advanced at 100 m/hour. Bocca 3's activity diminished 6 May and ended by 7 May."

John Guest and J.B. Murray arrived at the volcano on 10 May and reported: "Lava effusion was limited to bocca 2, marked by a hornito 10 m high. The rate of eruption was 10 m³/s through midday 13 May when bomb ejection began at a rate that increased to 40-50 m³/s, but decreased to 20-30 m³/s by the next day and had returned to 10 m³/s by 15 May.

"Although bocca 1 was not emitting lava during this period, there were several collapses in the vent, producing billowing brown smoke. Occasional big explosions began 14 May, throwing bombs as much as 100 m above the vent. Explosions intensified on 27 May, but activity quickly returned to the 15 May level, and the eruption was continuing on 31 May.

"These eruptions have completely changed the Northeast Crater and surrounding area; the highest point on the volcano is now the Northeast Crater. Strong explosive activity during several eruptions has covered much of the summit area with ash, and during the Easter eruptions (March 25-28) there was a light ashfall as far away as Catania (25 km SE). Lava flows were extensive, one reaching as far down as 1,700 m elevation of the NW flank."

Information Contacts: R. Romano, IIV; J. Guest, Univ. of London.

Jump to Index of Monthly Reports

06/1978 (SEAN 03:06) SE-flank eruption ended by 14 June

The eruption of Etna, which began 29 April, had ended by 14 June. [This date was later corrected to 5 June, and the report was removed completely from GV 75-85.]

Information Contact: J. Guest, Univ. of London.

Jump to Index of Monthly Reports

07/1978 (SEAN 03:07) Persistent SE flank activity resumes 26 May-5 June

Etna's SE-flank eruption, which began on 29 April, stopped for about 12 hours on 26 May, then resumed and continued until the evening of 5 June. When visited by John Guest and others in late July, the main SE flank vents contained glowing red fissures and emitted jets of gas at high pressure. Occasional deep explosions could be heard inside Bocca Nuova (the W vent of the central crater), accompanied by rumbling and frequent collapse activity. The Chasm (the larger E vent of the central crater), normally continuously active, was largely filled with ash and snow, and showed no signs of activity. Steam emission continued from the Northeast Crater, site of a series of brief eruptions between July 1977 and March 1978.

Information Contact: J. Guest, Univ. of London.

Jump to Index of Monthly Reports

08/1978 (SEAN 03:08) New SE flank eruption

Activity resumed on Etna's SE flank during the night of 24-25 August. The initial activity consisted of ejection of spatter bombs and ash from one of the 1971 eruption craters, at 3,000 m altitude on the SE flank of the summit cone. Lava extrusion from this crater began the night of 25-26 August and had ended by the next morning. Lava flowed eastward into the Valle del Bove, traveling 2.5 km to 2,000-2,100 m elevation. During the afternoon of the 26th, a second vent opened at 2,725 m altitude, on the wall of the Valle del Bove. Its flow moved 3 km in 12 hours, reaching 1,650 m altitude.

The explosive activity that started 24-25 August began to decrease on 27 August, but 7 more vents opened that afternoon on the walls of the Valle del Bove, between 2,800 m and 2,500 m. By 29 August, the number of active vents had decreased to four with a notable diminution of lava effusion, and explosions had ended.

Information Contact: R. Romano, IIV.

Jump to Index of Monthly Reports

09/1978 (SEAN 03:09) SE flank eruption ends; occasional central crater explosions continue

The SE flank eruption ended on the morning of 30 August. Activity since then has been confined to occasional explosions from Bocca Nuova. Two distinct sets of fissures formed during the eruption. The active vents trended NE-SW, parallel to the 1971 vents. No lava was extruded from the second set, which trended N-S. Fault throws of up to 3 m were observed.

Information Contact: J. Guest, Univ. of London.

Further Reference: Mackey, M., and Scott, S.C., 1980, The eruption of Mt. Etna in August 1978, in Huntingdon, E.T., and others, eds., 1980, U.K. Research on Mt. Etna; Royal Society of London, p. 43-44.

Jump to Index of Monthly Reports

11/1978 (SEAN 03:11) New SE-flank eruption

A new SE flank eruption began on 18 November. Initial activity consisted of ejection of ash and wallrock from one of the spatterspatter cone cones formed in the August eruption. Ejection of incandescent ash and larger tephra from this cone started during the morning of 23 November, and was accompanied by minor lava effusion on the crater floor. Lava fountains rose 500 m above the August cone during the afternoon of 25 November and lava began to flow eastward into the Valle del Bove. That night, two new vents opened on the wall of the Valle del Bove at about 2,600 m altitude, extruding flows that traveled 4 km E, to an altitude of 1,500 m. Strong ash emission from the August cone was visible from 40 km away on 26 November.

Two more vents opened in the Valle del Bove on 27 November at 1700 m above sea level, and another vent opened nearby the next day, at 1,800 m altitude. Lava flows from these vents had traveled 4 km into the Valle Calanna, a steep valley extending SE from the E end of the Valle del Bove, by the evening of the 27th. A sixth vent opened that night at 1,650 m altitude, extruding lava that advanced slowly toward the town of Zafferana Etna (population 7,000), a few km S of Milo. The eruption ended during the night of 29-30 November.

Information Contacts: R. Romano, IIV; UPI; AP.

Jump to Index of Monthly Reports

07/1979 (SEAN 04:07) Eruption from summit and SE flank

By early July, activity had resumed at the Chasm in Etna's central crater. The Chasm had been continuously active for many years but had become quiescent and largely filled with ash during the 1978 eruptions. John Guest and coworkers arrived at the volcano 11 July and observed small, sharp, strombolian explosions from a small pit that had formed in the floor of the Chasm. When visited again on 27 July, the pit was filled with lava, covered by a thin crust that swelled prior to frequent Strombolian explosions. The lava lake had grown further by the next day. Large blisters formed in the lake, then burst, throwing bombs 200 m or more high. Some fell 50-60 m outside the rim of the Chasm.

Bocca Nuova, adjacent to the Chasm, was quiet on 11 July. However, collapse activity deep in this crater could be heard 27 July, and billowing clouds of dust were emitted.

Guest and coworkers observed the beginning of activity at a third site during the morning of 16 July, when strong gas emission started from a vent at the bottom of one of the 1978 craters on the upper SE flank (figure 5). Ejection of lithic blocks and a little fresh magma soon commenced, with the proportion of juvenile material increasing steadily. By afternoon, strong strombolian activity was occurring from the vent. The next day, bombs from many of the spasmodic explosions rose 200-300 m above the rim of the (100-m deep) 1978 crater. Most bombs fell back inside the crater, but a few landed as much as 50 m outside the rim. Another vent, on the side of the 1978 crater, emitted ash, building a small conecone. Similar activity continued until the night of 22-23 July, when the explosions became stronger and more frequent. The stronger activity continued through the morning of the 23rd, then declined to the more moderate levels of 17-22 July. Six vents were active at various times, two of which were dominant. This activity persisted, with some fluctuations in intensity, through 28 July, when Guest and coworkers left the volcano.

After a series of felt earthquakes 29-30 July, strong explosions from the Chasm began during the night of 3-4 August. Heavy ashfall took place in Catania, closing the airport, and ash fell as far away as Syracusa, about 80 km to the SSE. Unusual lightning accompanied the explosions, which were visible from the mainland, 75 km from Etna. Two fissures opened early 4 August near crater l, at 2950 m and 2875 m altitude. By afternoon, fluid lava from these fissures had traveled 13 km down the E flank, threatening the village of Fornazzo and forcing its evacuation. However, about 300 m from Fornazzo the lava changed direction, and damage was limited to about 1,000 acres of fruit and nut orchards. By late 4 August, summit explosions had apparently ceased.

Several new fissures opened the next day. The first was 1 km long, located at 1,800 m altitude in the Valle del Bove, on the SE flank. Others opened later on the NE flank, producing lava that flowed down two valleys. Lava effusion from some of these vents was continuing as of the morning of 7 August.

Information Contacts: J. Guest, J. Murray, Univ. of London; R. Romano, IIV; UPI; Reuters.

Jump to Index of Monthly Reports

08/1979 (SEAN 04:08) Lava extrusion from several SE flank vents; ashfall to 70 km away

The following report was prepared by John Guest and Romolo Romano from observations by E. LoGiudice, D. Condarelli, and A. Pellegrino.

"In the afternoon of 3 August, lava fountaining up to a height of 300 m started in the 1978 crater, which we are now calling the Southeast Crater. This crater has been active since the middle of July. Ash from this explosive activity fell over the E flank of the volcano, then later that day fell over the SW flank as far as Syracusa, some 80 km away. During the evening of 3 August, an eruptive fissure opened near the 1819 Crater. Lava erupted that night reached Monte Centenari, some 2 km away. Fifty-four earthquakes were recorded with magnitudes up to 3.5-4.

"At 0545 on 4 August, another fissure opened in the Valle del Bove, SE of Monte Simone from 1,800 m to about 1,700 m elevation, 1 km long. Two flows were erupted quietly from the fissure. The flow from the top of the fissure moved SE (towards Rocca Musar-ra). The second, from the lower part of the fissure, traveled along the N wall of the Valle del Bove past Rocca Caora and reached the Torrente Fontanelle by midday. At 1430 the flow front was advancing at 100 m/hour and cut the Rifugio Citelli-Fornazzo road. The flow continued to advance, stopping in the evening 50 m from the N-S road through Fornazzo, just N of the town at 870 m above sea level.

"In the central crater area, large explosions had occurred from the Chasm during the end of July. At 1000 on 4 August, the magma level in the Chasm dropped, and in the Southeast Crater explosive activity was greatly diminished. At 1130 on 5 August there were again large explosions from the Southeast Crater and fountaining resumed at 1345 with heights of up to 400 m.

"At 1615 on 5 August, a new fissure opened just NW of the 1819 Crater, with fountaining. A lava flow from this fissure reached the foot of the wall of the Valle del Bove. At 1715, another eruptive fissure opened SE of the 1819 Crater, again with fountaining, and a flow moved into the Valle del Bove. Ash from this eruption also fell in the region of Catania and Syracusa. At 1730, a fissure with a NE trend opened at 2,500 m above sea level in the Valle del Leone. During the night of 5-6 August, lava from this fissure traveled 3 km.

"Early in the morning of 6 August, many earthquakes of up to M 3.5-4 were recorded until about 1218. In the afternoon, activity increased from the fissure near Monte Simone, which had been active on 4 August, and lava flows overlapped the earlier ones from this vent. The 6 August flow traveled some 1.5 km. At 2030, yet another fissure opened, with an ENE trend, at an altitude of 2,150 m, coinciding almost exactly with the 1928 fissure on the outer flank of the Valle del Bove. A sluggish flow followed the path of the 1928 lava, stopping on 8 August, 50 m from the Rifugio Citelli road, having traveled 1 km. Flows from vents in the Valle del Bove stopped on 9 August."

Information Contacts: J. Guest, Univ. of London; R. Romano, IIV.

Jump to Index of Monthly Reports

09/1979 (SEAN 04:09) Nine killed and 23 injured by explosion

Activity resumed during the night of 1-2 September, with a collapse of part of the wall of Bocca Nuova and small explosions from the neighboring summit crater, the Chasm, the following day. The volcano then remained quiet until a 30-second explosion from Bocca Nuova killed nine persons and injured 23 at 1747 on 12 September. Some of the 150 tourists in the area at the time of the explosion were on the crater rim, and others were at a parking lot 400 m to the NW, where a large number of blocks about 25 cm in diameter fell. The explosion was apparently somewhat directed, because the distribution of blocks was dominantly to the NW of Bocca Nuova and no blocks traveled as far as 200 m in directions other than NW. No fresh magma was ejected by the explosion. The next day, considerable quantities of fine ash were emitted from Bocca Nuova and one or two small deep explosions were heard, but activity since then has been limited to weak emission of vapor containing SO₂.

Information Contacts: J. Guest, Univ. of London; UPI.

Further Reference: Kieffer, G., 1981, Les explosions phreatiques et phreatomagmatiques terminales a l'Etna: BV, v. 44, p. 655-660.

Jump to Index of Monthly Reports

10/1979 (SEAN 04:10) Thermal anomaly on SE flank

The following thermal anomaly report is from C. Archambault, J. Stoschek, and J. C. Tanguy.

"The existence of a N-S elongated thermal anomaly about 10 km has been determined on the upper half of Mount Etna, both by field measurements and infrared satellite imagery. It is believed that this high temperature anomaly is symptomatic of storage of magma at shallow depth within the rift zones of Etna. However, the magnitude of the thermal anomaly is expected to change with respect to volcanic activity (four flank eruptions have occurred from this zone during the past 2 years). Since 26 June, ground temperatures have been continuously recorded at the end of the thermal anomaly (figure 6). The results in this part of the volcano are considered the most significant because no volcanic activity has occurred in this zone for 70 years, therefore, the abnormal temperature cannot be due to cooling of residual magma. In order to eliminate the climatic effect, the data are presented (figure 7) as the difference between recordings of the central part of the thermal anomaly (Monte Calcarazzi Station) and those of a "reference station" (Sapienza) located at the same altitude about 1 km outside the anomalous zone.

"There had been considerable temperature increase (3°C) at the Monte Calcarazzi station during the month that preceded the flank eruption of 3 August. On 10 August the temperature at 120 cm depth, checked by direct measurements, was 9°C higher than the normal (Sapienza). Such a variation may be either a transient response to the August eruptive phenomena on the SE, E, and NE flanks, or the indication of magma motion southward - a problem that should be solved in the months to come.

References: Mise en évidence de zones thermiquement anormales sur le massif de l'Etna. 7éme R. ann. Sci. Terre, Lyon, Avril 1979, p. 15.

Mise en évidence d'anomalies thermiques dans la basse zone du secteur Sud de l'Etna, Note technique CNET 110/79.

Etablissement d'une carte thermique du massif de l'Etna à partir des données transmises par le satellite météorologique NOAA V...: Note technique CNET 111/79.

Information Contacts: C. Archambault and J. Stoschek, CNET, France; J. Tanguy, Univ. de Paris VI; PIRPSEF, CNRS-INAG.

Further Reference: Guest, J.E., and Murray, J.B., 1980, Summary of volcanic activity on Etna, 1977-1979, in Huntingdon, E.T., et al., eds., 1980, U.K. Research on Mt. Etna: Royal Society of London, p. 50-52.

Jump to Index of Monthly Reports

01/1980 (SEAN 05:01) Reduced thermal anomaly; small ash eruption

[Some elements of this report were excised at the authors' request.] "Since the August flank eruption, no major volcanic event has occurred on Mount Etna, although on 12 September a moderate phreatic explosion resulted in nine casualties near the W vent Bocca Nuova. On 11 January 1980, ashes were emitted from both Bocca Nuova and the Southeast Crater, where activity has preceded all the flank eruptions for the past two years.

"However, ground temperature measurements made on 21 January in the S part of Etna (Sapienza, Monte Silvestri, Monte Calcarazzi) show that the thermal anomaly has been reduced to a very low level (1-2°C, in contrast to 9°C in August 1979). This is the lowest temperature recorded in this zone since temperature measurements were initiated in September 1978.

Information Contacts: C. Archambault and J. Stoschek, CNET, France; J. Tanguy, Univ. de Paris VI; PIRPSEF, CNRS-INAG.

Jump to Index of Monthly Reports

02/1980 (SEAN 05:02) Red glow in SE crater

During the night of 29 February-1 March, red glow was visible in the Southeast Crater. No glow was reported the next two nights, but cloud cover may have obscured the crater.

Information Contacts: J. Guest, Univ. of London; R. Romano, IIV.

Jump to Index of Monthly Reports

04/1980 (SEAN 05:04) Explosions from summit and SE craters; thermal anomaly on S flank

During the evening of 14 April, explosions began from Etna's summit area and red-hot gases were emitted from the Southeast Crater. Explosions continued for the next several days. Residents of Zafferana, 11 km SE of the summit, saw large explosions on 16 and 17 April that were especially spectacular at night because of incandescence or perhaps lightning. Poor weather prevented observations from the IIV in Catania.

Etna guides who climbed the volcano, probably on 17 April, saw large fresh bombs near the Chasm and Bocca Nuova craters. Bombs were particularly prominent on the N and W sides of the central crater area. On 27 April at 1705, a large summit explosion produced a 3-km-high ash cloud. Renewed explosions began during the afternoon of 29 April and continued through the night from the Southeast Crater.

Information Contacts: R. Romano and L. Villari, IIV; J. Guest, Univ. of London; C. Archambault and J. Stoschek, CNET, France; J. Tanguy, Univ. de Paris VI; G. Scarpinati, Acireale.

Jump to Index of Monthly Reports

05/1980 (SEAN 05:05) Incandescent tephra ejected; temperature anomaly on S flank

"After a 3-month period of stabilization, ground temperatures in Etna's S-flank fissure zones (6 km S of the summit) began to increase again in March (figure 8). However, station 3, only 25 m from station 2, continued to show a nearly constant temperature. Variations in temperature are calculated by comparison with Sapienza reference station 1, located outside the fissure zones, 0.5 km WNW of stations 2 and 3, and 1.25 km from station 5.

"The increase in temperature preceded renewed activity from the summit crater system. On 14 April, red-hot gases were emitted from the Southeast Crater and on the following days fresh lava lumps were ejected from the Chasm.

"On 20 April, S flank temperatures were stationary or even slightly lower. Between 20 April and 1 May, temperatures strongly increased again. A large explosion on 27 April (probably at Bocca Nuova) and strong lava fountaining on 29 April at the Southeast Crater were followed by moderate magmatic activity until at least 3 May. After a short period of stabilization (1-4 May), temperatures were still increasing, although more slowly.

[Archambault, Stoschek, and Tanguy added the following paragraph to replace explanatory material excised from 5:1]. "It was initially believed that the thermal anomaly fluctuations were related to the reopening of cracks caused by increases in volcanic pressure. Further investigations showed this hypothesis to be incorrect, with the systematic seasonal increase of surficial temperatures being mainly the consequence of a microclimate (Bourlet and Bourlet, 1982). A volcanic effect does occur, but its influence cannot be simple and is probably linked to the circulation of hot waters through the S flank. From this standpoint, a striking example is the rapid temperature increase measured in November 1982 at 6 m depth (figure 8, 08:04), where a climatic effect cannot be invoked. Such a variation was not observed the following years (November 1983 and 1984). It may have resulted from the heating of meteoric waters by an intrusion of magma into the S flank a few months before the March 1983 eruption.

"The Southeast Crater was intermittently active throughout May. On 31 May, two vents were observed inside the crater with moderate ejections of incandescent magmatic material up to 50 or 100 m, with some bursts occasionally reaching 200 m. As of 3 June, activity had increased noticeably, and explosions were stronger and more frequent. The number of explosions per hour reached 165 and the ejecta reached heights of 200-300 m."

References: Bourlet, Y. and Bourlet, F., 1982, Etude microclimatique de 5 stations sur le versant sud de l'Etna: Bull. PIRPSEV, no. 63.

Bourlet, Y. and Bourlet, F., 1983, Etude des anomalies thermiques et hydriques sur le versant NE à Citelli et sur le versant sud à la Montagnola: Bull. PIRPSEV, no. 73.

Information Contacts: J. Tanguy, Univ. de Paris VI; C. Archambault and J. Stoschek, CNET, Lannion, France; G. Scarpinati, Acireale (direct measurements and observations); PIRPSEV, CNRS/INAG, France.

Jump to Index of Monthly Reports

07/1980 (SEAN 05:07) Incandescent tephra ejection; decreased gravity readings

Activity increased gradually between 13 and 20 July in the Southeast Crater, site of lava fountaining in late April, intermittent eruptions in May, and stronger explosions in early June. No information was available on activity between 4 June and 12 July [but explosive activity was persistent from the SE Crater and Bocca Nuova]. In mid-July, many small explosions were observed on some days, while other days were characterized by fewer but larger explosions. After a period of poor weather, renewed observations of the Southeast Crater on 31 July revealed four active vents, located 25 m below the lowest portion of the crater rim. The two larger vents steamed continuously, and exploded about every 2 seconds, ejecting incandescent tephra to heights of 25 m. At approximately 2-minute intervals, stronger explosions sent tephra upward 100 m. A small spatter cone surrounded the vents. The two smaller vents ejected juvenile material only occasionally.

Explosions from deep within Bocca Nuova were heard about every 2 seconds on 31 July. No tephra reached the rim. Since last September, Bocca Nuova's diameter [corrected from radius] has increased by as much as 80 m, bisecting a small crater formed in 1964. Most of the increase occurred during the winter, but further crater growth took place in June.

The Chasm, E of Bocca Nuova, was filled with solidified lava to within 25 m of its rim on 31 July. Large amounts of spatter and many bombs surrounded the crater as a result of activity in April (05:04).

Gravimeter readings made in late July by Tim Sanderson on the S flank yielded values that were significantly lower than in September 1979, indicating a loss of mass on that flank. July 1980 N flank gravity values were very similar to those of the previous September.

Information Contacts: J. Guest, J. Murray, C. Kilburn, and R. Lopes, Univ. of London; T. Sanderson, Imperial College.

Jump to Index of Monthly Reports

08/1980 (SEAN 05:08) Two one-day eruptions

Relatively weak activity similar to that of late July continued through August at Etna. A 1-day eruption on 1 September deposited ash on the E flank and extruded two lava flows.

John Guest climbed the volcano on 18 August. As on 31 July, explosions occurred deep within Bocca Nuova. The Chasm remained quiet. Mild strombolian activity continued from the Southeast Crater, but reportedly weakened the following week. Romolo Romano reported that a swarm of local seismic events began on 21 August.

At 0957 on 1 September, a pale brown plume was seen rising from the Northeast Crater, which last erupted in March 1978 (03:05). By 1130, explosions were ejecting large bombs or blocks every 10-15 minutes. An increase in seismicity at about 1700 was followed at 1730 by stronger explosions that were audible in Fornazzo, 10 km E of the crater. A large black eruption column rose to 6 km above the crater. By 1800, ash was falling on Fornazzo and the entire E flank. Geologists reached the eruption area by about 2000 and saw nearly continuous strombolian explosions from two vents in the Northeast Crater ejecting tephra to 500-600 m above the rim. Lava from the Northeast Crater flowed to the N and NW. By the next morning, the eruption had stopped. Heavy fog made mapping of the two lava flows difficult, but the NW flow had moved past Punta Lucia, about 3/4 km from the Northeast Crater.

A second brief eruption from the Northeast Crater began early 6 September, ending at about 1500 the same day, after an estimated 10 hours of activity. A small lava flow was extruded. No further information was available at press time.

Information Contacts: J. Guest and C. Kilburn, Univ. of London; T. Sanderson, Imperial College; R. Romano, IIV; G. Kieffer, Univ. de Clermont-Ferrand.

Jump to Index of Monthly Reports

09/1980 (SEAN 05:09) Ashfall to coast; lava flow; bombs

The 6 September eruption began at about 0500. Vigorous strombolian activity continued for 10 hours, ejecting bombs to 500 m above the same Northeast Crater vent that had erupted 1 September. Bombs 20 cm in diameter or larger fell as far as 750 m away. A lava flow, extruded from the same vent at a rate of 10-20 m³/s, traveled 2 km to the N, directly over the main lobe of the bifurcated 1 September flow, which extended about 1/2 km farther to the N. Ash fell on the coastal towns of Acireale and Taormina, 20 km SE and 30 km NE of Etna. Observations after the eruption showed the vent completely filled by lava and slumped debris. As of 3 October, no further eruptions had been reported.

Rumbling and deep explosions continued in September from Bocca Nuova. The Chasm remained inactive. Mild strombolian activity at the Southeast Crater stopped in September, with only infrequent gas emission and small collapse events reported.

Tim Sanderson collected gravity data before the 1 September eruption and after the 6 September one. Frequent ground temperature measurements by J. C. Tanguy and associates continue (05:05).

Information Contacts: C. Kilburn, Univ. of London; T. Sanderson, Imperial College.

Jump to Index of Monthly Reports

02/1981 (SEAN 06:02) Explosions and lava flow from Northeast Crater

The IIV reported explosions and extrusion of lava from the Northeast Crater. After a period of ash emission at the end of January and the beginning of February, stronger activity began with intense explosions the evening of 5 February. Lava flowed through a breach in the W-to-NW side of the Northeast Crater cone, forming three lobes that moved W, NW and N, covering the upper NW slope of the volcano. The N lobe, the largest, traveled ~2 km to 2,600 m elevation where it had a 1.2 km front. The eruptive activity stopped the evening of 7 February.

Information Contacts: R. Romano, IIV; J. Guest, Univ. of London.

Jump to Index of Monthly Reports

03/1981 (SEAN 06:03) Large lava flows cause severe damage

An eruption 17-23 March extruded lava from several fissures on the NNW flank. Initial estimates indicate that the main flow reached 7.5 km in length, lava flows covered an area of 6 km², and 30-35 x 10⁶ m³ of lava were extruded [but later calculations from topographic measurements by Murray (1982) yield 18 x 10⁶ m³] at a rate of 58-70 m³/s. Damage was estimated at about $10 million. Of the 90 historic eruptions of Etna for which location data are available, only three (1614, 1764, and 1918) occurred on the NW or NNW flanks.

Etna began to erupt on 17 March after a 2-day swarm of about 500 earthquakes, including a M 4-5 event during the morning of 16 March. On 17 March at 1337 an eruption fissure opened at about 2,550 m [corrected from 2,250 m] above sea level on the NW flank, trending approximately NW-SE. Lava fountains rose 100-200 m from this fissure and lava flowed rapidly westward. In the next 4 hours, three more fissures opened, the first and third also trending NW, the second WNW. All showed strong lava fountaining and were the source of lava flows. As fissures formed at lower altitudes, those higher on the volcano ceased to be active.

At 1855 on 17 March, another fissure opened at 1800 m elevation on the NNW flank, trending NW at its upper end, but after a short distance changed direction to more directly downslope. A large lava flow that originated from this fissure traveled 5 km within 4 hours, cut a railroad and highway (at 730 m altitude) during the night, and crossed another railway line and road (at 680 m altitude) early on 18 March. The lava destroyed orchards and farm buildings, and passed very close to the village of Montelaguardia, forcing the evacuation of its 250 residents. The fissure propagated downslope to 1,300 m altitude at 1130 on 18 March. The lower section extruded a small lava flow that briefly threatened Randazzo (population 15,000) but did not force its evacuation. By 1630, the center of the main flow was more than 1 km wide and its front had reached 650 m altitude, 100 m from the bed of the Alcantara River.

At 2200, another fissure opened between 1,235 and 1,140 m altitude extruding flows that moved toward Randazzo. By this time, the system of eruptive fissures had a total length of about 7.5 km. The main flow reached the Alcantara River bed (600 m above sea level) on 19 March at 1100, while the flows extruded from the fissure between 1,235 and 1,140 m altitude continued to advance slowly. By noon on 20 March, this fissure was characterized by mild spatter ejection that continued to feed slow-moving lava flows. However, the main flow had nearly halted. Sporadic activity between 1235 and 1140 m continued 21-22 March, finally ending during the evening of the 23rd. The longest flow from this fissure stopped at 900 m elevation, 2 km from Randazzo. More than 25 small earthquakes were recorded on 23 March, centered around the eruption fissures.

Throughout the period of lava extrusion, more or less intense emission of sand-size tephra occurred from Bocca Nuova, enlarging it to the W. Strong winds caused flank ashfalls on 22 March [as the Northeast Crater briefly ejected juvenile cinders; Tanguy and Patané, 1984].

Information Contacts: R. Romano, IIV; UPI; AP.

Further References: Murray, J.B., 1982, Les Déformations de l'Etna à la suite de l'eruption de Mars 1981: Bull. PIRPSEV, no. 57.

Sanderson, T.J.O., Berrino, G., Corrado, G., and Grimaldi, M., 1983, Ground deformation and gravity accompanying the March 1981 eruption of Mount Etna: JVGR v. 16, p. 299-316.

Guest, J.E., Kilburn, C.R.J., Pinkerton, H., and Duncan, J.M., 1987, The evolution of lava flow-fields: Observations of the 1981 and 1983 eruptions of Mt. Etna, Sicily: BV v. 49, p. 527-540.

Jump to Index of Monthly Reports

04/81 (GV 1975-85) Photograph from Space Shuttle

The fissures and lava flows on the NNW flank resulting from the March 1981 activity (figure 9) were visible to astronauts aboard the Space Shuttle in April 1981.

Information Contact: Charles A. Wood, NASA Johnson Space Center.

Jump to Index of Monthly Reports

07/1981 (SEAN 06:07) Ash ejection, probably caused by central crater collapse

On 29 July, a dense ash cloud was ejected for more than 30 minutes from Bocca Nuova. The ash emission may have been produced by collapse within the crater; no significant explosions were associated with the activity. Similar events have occurred on several occasions since the March eruption.

Information Contacts: J. Guest, Univ. of London; R. Romano, IIV.

Jump to Index of Monthly Reports

09/1981 (SEAN 06:09) Collapse in the central crater; ash ejection

Collapse activity deep within Bocca Nuova has been frequent since the 17-23 March fissure eruption. No fissuring or other evidence of surface collapse has been observed around Bocca Nuova. Explosions associated with the collapse activity ejected fine ash, caused strong ground vibrations 300 m from the crater, and could be heard as much as 10 km away. Plumes produced by this activity could sometimes be seen on the satellite images returned once daily by the NOAA 7 polar orbiter. Images returned shortly after noon on 3 and 4 October showed narrow, well-defined plumes extending ~75 km downwind from Etna. A smaller, less dense plume extending outward only about 20 km was present on the 6 October image.

Information Contacts: J. Guest, Univ. of London; M. Matson, NOAA.

Jump to Index of Monthly Reports

10/1981 (SEAN 06:10) Small plumes on satellite images

Images returned by the NOAA 7 polar orbiting satellite continued to show occasional plume emission: on 9 October at 1442 plume roughly 75 km long, drifting to the SE, and on 1 November at 1329 a much smaller plume, roughly 20 km long was moving to the SW. No other activity was seen on the almost daily imagery between those dates.

Information Contact: M. Matson, NOAA.

Jump to Index of Monthly Reports

12/1981 (SEAN 06:12) Collapse continues in central crater; ash plumes

As of mid-January, collapse on Bocca Nuova's inner walls was almost continuous, producing plumes that contained fine ash but no fresh magma. At times of little or no wind, the plumes rose 3-4 km above the crater. There was no evidence of collapse beyond the crater rim. No changes have occurred in seismicity or tilt.

Images from the NOAA 7 satellite showed plumes emerging from the summit area on 4 and 6 January. A plume observed on 4 January at 1431 extended ~80 km to the SE, beyond the coast. Infrared data showed that the plume's apparent temperature was comparable to that of the sea water beneath it, and thus it probably remained at a relatively low altitude. The next image of the area, at 1408 on 6 January, showed a fairly diffuse linear plume ~55 km long, drifting SE. A plume from Etna had last been observed on satellite imagery (available most days for the Etna area) on 1 November.

Information Contacts: L. Villari, IIV; M. Matson, NOAA.

Jump to Index of Monthly Reports

05/1982 (SEAN 07:05) Small central crater explosions follow earthquakes and higher ground temperatures

[Some elements of this report were excised at the authors' request.] Since the fissure eruption of 17-23 March 1981, explosions associated with collapse activity deep within Bocca Nuova have produced small to moderate ash plumes. Magma was observed in the bottom of Bocca Nuova in mid-May, mid-July, and early September 1981, and incandescence was seen there in February 1982. All activity from Bocca Nuova stopped 8 May, but resumed about a week later at around a time of unusual seismic and thermal activity on the NE flank. Incandescent scoria rose above the crater rim 20-22 May.

Seismicity increased during the third week of May and culminated with an explosion, possibly at 1515 on 27 May, when the summit seismometer operated by the Univ of Catania detected a M 3.5 earthquake that was felt by local residents. The next day, geologists found blocks of old lava that had been ejected more than 300 m from the Chasm. Blocks up to 1.5 m across were found in small impact craters at the rim. Many blocks larger than 10 cm occupied elongated depressions, implying relatively oblique impact, oriented radially to the crater. The greatest concentration of blocks was immediately N of the crater, although the pattern of smaller blocks suggested a NW orientation. The depth of the Chasm had increased from ~50 m in March to ~100 m after the explosion, by removal of material that had filled it since 26 May 1980 [explosive activity had begun in mid April], and vents in its walls were steaming. However, activity 28 May was concentrated in Bocca Nuova, where occasional detonations could be heard and the crater floor was obscured by sulfurous steam. On 29 May, Bocca Nuova ejected black ash, containing fresh magma, every 2-3 minutes. Ash clouds rose 200-300 m above the crater rim and were blown a few hundred m to the south. Only fumarolic activity was observed in the Northeast and Southeast craters.

Information Contacts: R. Romano, IIV; M. Malin and M. Sheridan, Arizona State Univ.; J. Sheridan, Tempe, AZ; C. Archambault and J. Stoschek, CNET, France; J. Tanguy, Univ. de Paris VI; R. Basile, S. Scalia, and G. Scarpinati, Gruppo Ricerca Speleologica; M. Cosentino, S. Gresta, G. Lombardo, and G. Patane, Ist. di Scienze della Terra, Catania.

Jump to Index of Monthly Reports

07/1982 (SEAN 07:07) Eruption cloud; lava in main crater

Etna erupted on 8 August, when a black tephra column was emitted from Bocca Nuova and lava rose to 150-200 m below the crater rim. The activity was accompanied by a marked increase in minor earth tremors. Sicilian authorities have restricted tourist access to the volcano.

Information Contacts: J. Guest, Univ. of London; Reuters.

Jump to Index of Monthly Reports

09/1982 (SEAN 07:09) Strombolian activity on central crater floor

Strombolian activity on the floor of Bocca Nuova was observed in September. Fine ash fell on the crater rim. Since summer 1981, continuing collapse activity at Bocca Nuova has widened the crater by nearly 100 m, to 250 m in SW-NE dimension. Poor visibility prevented determination of the crater's depth. Just to the E, vapor emission was continuous from the Chasm, site of an explosion in late May that removed ~50 m of debris that had choked this vent for 2 years (07:05).

Information Contact: J. Guest, Univ. of London.

Jump to Index of Monthly Reports

11/1982 (SEAN 07:11) Small explosions, but tephra to 12 km

A C-141 cargo plane pilot observed tephra from Etna at ~12 km altitude on 6 December at 1800. Romolo Romano reported there had been many small explosions from Bocca Nuova throughout the day. No eruption plume was visible on the only satellite image of Etna that was available on 6 December, from a NOAA polar orbiter at 1530. Poor weather and heavy snow make access to Etna's summit area difficult during the winter.

Information Contacts: R. Romano, IIV; M. Matson, NOAA.

Jump to Index of Monthly Reports

12/1982 (SEAN 07:12) Incandescent tephra from central crater

Explosive activity of varying intensity continued through early January from the floor of Bocca Nuova. Large ash emissions were sometimes observed. During the night of 24-25 December, intense explosions ejected incandescent tephra. Most of the tephra fell back within the crater, but some was deposited outside the crater rim.

Press sources reported emission of large quantities of gray and white "smoke" from the Northeast Crater but Romolo Romano noted that the Northeast Crater activity was fumarolic and no ash was ejected. The Northeast Crater last erupted in February 1981, producing a lava flow and ash (06:02).

Information Contacts: R. Romano, IIV; UPI.

Further Reference: Scarpa, R., Patane, G., and Lombardo, G., 1983, Space-time evolution of seismic activity at Mt. Etna during 1974-1982: Ann. Geophysicae, v. 1, no. 6, p. 451-462.

Jump to Index of Monthly Reports

03/1983 (SEAN 08:03) Lava from S-flank fissure; central crater enlarged

A destructive S-flank fissure eruption began on 28 March, preceded by a series of strong earthquakes first felt during the night of 26-27 March. At about noon on the 27th, a strong smell of H₂S was noted from an old cone (Monte Silvestri) roughly 2 km S of the initial eruption, although H₂S is not normally present in that area. Seismicity continued through the following night. At about 0845 on 28 March a NNE-SSW-trending eruptive fissure opened from about 2,450 to 2,250 m altitude, roughly 4 km S (bearing ~170°) of the central crater (between the eruption fissure of 1910 and La Montagnola). The base and E side of this fissure fed several lava flows that initially moved to the SSE and SSW then turned S. Weak explosive activity along the entire fissure ejected modest quantities of lava fragments. By evening, the main flow had cut a road and overrun several buildings.

During the morning of 1 April, vigorous emission of gas, ash, and old lava, accompanied by occasional phreatic explosions, began from two explosion craters upslope at 2,700 m altitude. At the end of the day, explosions from the southern vent ejected lava fragments. On 2 April, nearly constant lava production fed numerous superposed flows that formed a 500-m-wide lava field extending to 1,900 m altitude. As of 3 April, the lava had not advanced below 1,450 m altitude, 3.5 km from the fissure. At least four principal effusive vents were active along the 750-m fissure, and from its upper part strong gas emission with sporadic explosions occurred at about 30 hornitos.

Bands of open fractures, oriented about N-S, extended from the central crater area to the eruptive fissure. A substantial widening was noted at the S rim of Bocca Nuova, site of frequent collapse activity since Etna's last eruption (from N flank fissures in March 1981). Strong vapor emissions from Bocca Nuova sometimes included abundant ash. There was no activity from the Northeast and Southeast craters.

The temperature of the lava was less than 1,100°C and its chemistry (alkali basalt) [corrected from phonolitic tephrite] was similar to that from some of the more recent eruptions. An area of more than 1 km² was covered by lava and the volume emitted was estimated at about 8-10 x 10⁶ m³. The IIV considered the eruption to be a typical slow subterminal type. The last activity of this type on the S flank was in 1780. As of 8 April, effusive activity had diminished, but the eruption had not yet ended.

The lava destroyed ski lifts [the cable car system originally reported destroyed survived until March 1985] and destroyed or seriously damaged nine privately-owned huts and 11 small buildings owned by local authorities, including restaurants, chalets, mountain refuges, and a first aid station. Lava remained 8 km from the village of Nicolosi, its closest approach to a village or town.

Information Contacts: R. Romano, IIV; M. Krafft, Cernay, France; UPI.

Jump to Index of Monthly Reports

04/1983 (SEAN 08:04) Lava effusion continues; central crater explosions; deformation, temperature and self-potential data

The eruption was continuing as of 6 May. J. C. Tanguy noted that temperature station cables in the S part of the summit zone broke on 27 March between 0530 and 0946, probably because of the opening of the eruption fracture. Fissures extended S from 2,700 m (where two explosion vents formed on 31 March) to 2,450 m, then turned SSW along the trend of the 1910 eruption. Small hornitos and spatter cones formed between 2,450 and 2,350 m. The main effusive vent was at 2,280 m altitude. On 31 March, the temperature of lava at this vent was 1,067°C at 60 cm depth, and the same value was measured in the main flow 30-40 m downslope on 4 April. F. Mousnier-Lompre and G. Scarpinati recorded a lava temperature of 1,078°C on 1 May. J.B. Murray and A. Pullen reported that lava flow surface velocities measured 17-30 April were in the 1.17-3.41 m/s range. Using surface velocities, Murray and Pullen calculated an average effusion rate of 22 m³/s if flow thickness was 3 m and 44 m³/s if the thickness was 5 m.

Romolo Romano reported that lava flowed S and SW, forming a wide, complex field as much as 1 km across and 40 m thick. On the E side of the field, the fronts of the longest flows were about 6 km from the vent and reached 1,150 m altitude before stopping. On 23 April, the principal flow shifted to the W side of the field, and advanced to about 6.5 km from the vent, stopping at 1,100 m altitude only 30 m from a road. On 4 May the primary flow was again moving down the E side of the lava field and had reached 1,450 m altitude as of early 6 May. Lava flowed from the vent at about 2 m/s, a rate of about 10 m³/s, and had a temperature of about 1,030°C [but note 1,067° and 1,078° above]. The rate of advance of the flow fronts was quite variable and dependent on the gradient; estimated velocities ranged from a very few meters per hour to ~60 m/hour. The area covered by the lava was about 4 km² on 6 May and the volume of lava emitted was ~40 x 10⁶ m³.

Earlier in the eruption, small hornitos and spatter cones had formed above the main effusive vent and small quantities of lava fragments were ejected. Vapor emission continued from this portion of the eruption fissure but no lava fragment ejection has been noted since 10 April. Two explosion vents [not one as originally reported] at 2,700 m altitude ejected ash during the morning of 1 April [not 28 March as originally reported; Tanguy and Patané (1984), Frazzetta and Romano (1984)], but only vapor emission has been observed at this vent since then.

Throughout the eruption, ash was ejected at varying intensity from Bocca Nuova. More vigorous ash ejection 2-5 May sent plumes to 2 km above the crater and caused ashfalls on the mainland (Calabria coast) at least 60 km from the volcano. On 4 May, a polar orbiting satellite image showed the beginning of an ash emission episode at 0453. By the next image at 0606, a narrow plume extended nearly 1,000 km SE from Etna at an altitude of about 7.5 km. Venting was continuing at 0945 but the plume was smaller; at 1603, it was 100-150 km long. Another image, at 0705 on 6 May, showed a plume ~100 km long. From the Chasm, weak emission of gas that sometimes contained reddish ash has been observed during the eruption. In the Northeast and Southeast craters, eruptive activity was limited to weak fumarolic emissions, but new concentrations of large fractures were seen in these craters as well as small internal collapses.

Murray and Pullen reported that vertical ground deformation during 1981-82 was characterized by summit deflation and S flank inflation. Reoccupation of a precise leveling network 20-22 April 1983 showed large changes on the upper S flank (near Piccolo Rifugio) since September 1982: 42 cm of uplift W of the eruption fissure, 12 cm of uplift E of the fissure, and a drop of 126 cm on the fissure itself. Large and complex movements had occurred elsewhere, including deflation of 76 cm above the eruption fissure at about 2,900 m altitude (near Torre del Filosofo). Horizontal measurements across the fissure showed an E-W extension of 1.3 to 2 m since August 1981, with contraction of 17 cm and 6 cm at 500 m and 1 km W of the fissure. A network of 25 dry-tilt stations occupied 24-29 April 1983 showed no general inflation or deflation of the edifice since 1982.

Ground temperature measurements at 6 m depth on the S flank at 1,900 m altitude showed a strong increase in November 1982 (figure 10). In the summit zone, ground self-potential increased at roughly the same time and again in mid-January. A very steep rise occurred in early April, after the start of the eruption (figure 11). Immediately before the eruption a geophone in the S summit zone registered strong seismic activity, up to 134 events/hour during the morning of 27 March.

Information Contacts: R. Romano, L. Villari, S. Gresta, and O. Consoli, IIV; J. Tanguy and J. Murray, PIRPSEV; A. Pullen, Imperial College; M. Matson, NOAA; C. Archambault and J. Stoschek, CNET, France; S. Scalia and G. Scarpinati, Acireale; J.Bartaire J. and N. Bartaire, St. Maur des Fossés; R. Cristofolini, M. Cosentino, G. Lombardo, G. Patanè, A. Viglianisi, and P. Villari, Ist. di Scienze della Terra, Catania; P. Mousnier-Lompré, Servizio Sismico Regionale.

Further References: Frazzetta, G., and Romano, R., 1984, The 1983 Etna eruption: event chronology and morphological evolution of the lava flow: BV, v. 47, p. 1079-1096.

Tanguy, J., and Patané, G., 1984, Activity of Mount Etna, 1977-1983: volcanic phenomena and accompanying seismic tremor: BV, v. 47, p. 965-976. (both in Barberi and Villari, eds., 1984, cited after 8:07)

Jump to Index of Monthly Reports

05/1983 (SEAN 08:05) Lava production slows; lava partially diverted; central crater explosions continue; self-potential data

The continuing eruption showed signs of a progressive decline on some days. The velocity of the lava flow from the vent at about 2,280 m altitude decreased from ~1.7 m/s on 28 May to <0.5 m/s in early June, with a reduction in the rate of outflow to ~3 m³/s. In early May, the velocity at the vent had been about 2 m/s and the effusion rate was about 10 m³/s. New flows, most of which moved S and SW, continued to add to the S flank lava field that has accumulated during the eruption. On 25 May a flow advanced beyond the edge of the lava field, reaching 1,240 m altitude by the 27th, ~5.5 km from the vent. From 28 May, all of the lava flowed toward the interior of the lava field or approached its W side. In early June, frequent and impressive overflows occurred from both sides of the main lava channel at about 2,200 m altitude. Within the lava field, effusive pseudo-vents at around 1,800-1,980 m altitude have remained numerous. As of 8 June the area covered by lava was estimated at 6 km² and the volume of lava produced by the eruption was ~75-80 x 10⁶ m³.

Explosions of varying intensity continued, particularly from Bocca Nuova and primarily ejected reddish ash. On 15 May and 1-4 June the explosions were quite large. A NOAA 7 satellite image at 1529 on 15 May showed a strong plume (as large or larger than the 4 May plume; 8:04) that extended 100-150 km to the SE. Pilots reported that the plume had emerged from the summit area at about 1100. on 1 June at 0800, pilots estimated the height of a plume at about 5 km and reported that it was drifting SSE. In May and early June, only vapor emission was observed from an explosion crater at 2,700 m altitude and a fissure between 2,450 and 2,300 m altitude that were active early in the eruption. On 3 June, deep felt shocks (M 3.3) occurred near the active vent; these events continued the next day.

Because the advancing lava flows threatened additional property damage, efforts were made to divert the lava. Explosive charges were detonated at 0409 on 14 May to blast a passage from the W side of the main lava flow at 2,100 m altitude into a previously prepared artificial channel. Initially 20% of the total lava flux was diverted into the artificial channel, but by 16 May lava had ceased to flow in this channel after reaching 700 m length. After the explosions, however, there were numerous substantial overflows from the main natural channel, particularly from the W side, and these slowed the advance of the most distant flow. Artificial embankments have also been constructed E and W of the main natural channel, allowing control of the overflows from this channel that were moving over earlier flows.

Pham Van Ngoc and D. Boyer obtained self potential data during a PIRPSEV mission to Etna 27 April to 3 May. The following is a report from Pham Van Ngoc.

"Five self potential (SP) profiles were carried out from 2,350 to 2,700 m elevation. These profiles straddled the open fissure that trends NNE-SSW below Piccolo Rifugio (at 2,500 m altitude on the S flank) and the N-S fractures above it. The profiles were located upstream from the lava emerging at 2,320 m altitude. Figure 12 shows the results of the SP profiles.

"The shape of the SP anomalies was very different S and N of Piccolo Rifugio. To the S, profiles I, II, and III show huge (more than 50 mV) and sharp anomalies suggestive of superficial origin. it is notable that the maxima of these anomalies were not located just above the open fissure, but 40-50 m westward. The detail of profile III, just below Piccolo Rifugio, indicated clearly that the axis of the underground flow lies 40 m W of the active fissure (under the ski lift building W of Piccolo Rifugio). These results confirm that the pressure exerted by underground flow induced an E-W extension, creating a small graben clearly visible in the area of Piccolo Rifugio. The open fissure corresponds to a normal fault on the E edge of the graben and caused the collapse of the W part of Piccolo Rifugio.

"Above Piccolo Rifugio, profiles IV and V show much smaller Sp anomalies (~250 mV). Furthermore, these anomalies widen, thus indicating a deeper origin. It is notable that the shape of the SP anomalies changed completely from profile III to profile IV in a distance of ~300 m.

"SP results suggest that: 1) above Piccolo Rifugio, the magma flowed deeply in a N-S direction; and 2) level with Piccolo Rifugio (2,500 m altitude), the magma suddenly approached the surface and followed a shallow underground NNE-SSW channel that ran some 50 m W of the open fissure, then came to the surface at about 2,320 m altitude. Arrows in figure 12 indicate the path inferred from the lava."

Information Contacts: R. Romano, IIV; Pham Van Ngoc, Ecole Nationale Supérieure de Géologie; M. Matson, NOAA.

Jump to Index of Monthly Reports

06/1983 (SEAN 08:06) Lava production continues but at lower rate; central crater explosions; lava temperatures

Romolo Romano reported that the velocity of the lava flow from the main vent, at about 2,280 m altitude on the S flank, continued to decrease in early July, from somewhat less than 0.5 m/s in early June, to an estimated 0.1 m/s on 7 July. The rate of outflow, ~3 m³/s in early June, had dropped to ~0.5 m³/s by 7 July. Lava flowed SE, S, and SW onto the S flank lava field that has accumulated since the eruption began, but the flows were smaller than in previous months and reached a maximum length of 1 km. Between 1,800 and 1,950 m altitude, some flows approached the E edge of the lava field and effusive pseudo-vents remained numerous. Moving lava was visible through many small windows. Between the main vent and the lava field, numerous overflows occurred from the E and W sides of the main lava channel from 2,270 to 2,100 m altitude. As of 8 July, the volume of lava erupted since 28 March was estimated at 100-110 x 10⁶ m³.

J.C. Tanguy reported that on 14 June, the temperature of a slow (~0.15 m/s) lava outflow at 2,280 m altitude was determined to be 1,071-1,073°C using both Cr-Al and Pt-Rh thermocouples inserted at 40 cm depth. This temperature was identical to that measured in the main lava flow 12 May by P. Mousnier-Lompre. Lava velocity at the vent began to increase 14 June and reached almost 4 m/s 18-21 June. Gas pressure increased during the same period and new hornitos were built just below the main vent between 2,280 and 2,260 m altitude. Lava overflows occurred in this zone 18 and 20 June. On 21 June, gas pressure decreased and the lava velocity at the vent decreased to <1 m/s. The level of lava in the main channel dropped again, leaving impressive grottoes where gas combustion produced temperatures as high as 1,137°C (thermocouple) - 1,165°C (infrared measurements) on 21 June.

Moderate to violent explosions have continued to occur from Bocca Nuova. Explosions on 20, 24, and 26 June, and 8 July were especially strong. On 24 June, emission of white vapor had been increasing since at least 0700, culminating in an explosion at 1015 that ejected old material, including reddish cinders and large blocks, that fell as much as 250 m from the vent, primarily to the W. A polar orbiting satellite image 26 June at 0606 showed a low-altitude plume that extended ~100 km ESE, and a similar plume, ~150 km long, trended SSE on 4 July at 0640. Larger plumes were seen on satellite images 8 July at 1427 and 1609 (more than 500 km long, to the ESE), 10 July at 0615 (500 km, to the SSE) and 2036 (150 km, to the SE), and 11 July at 0554 (300-500 km, to the SSE). On 12 July at 1415, the U.S. Navy reported a cloud extending 250 km to the SE with a base at 1 km altitude and a top at ~5 km altitude. Only weak vapor emission has been observed from the Chasm, and from vents at 2,700 m on the S flank active earlier in the eruption.

Information Contacts: R. Romano, IIV; J. Tanguy, PIRPSEV; R. Clocchiatti, CEN, Saclay, France; F. De Larouziere, CNRS; R. Cristofolini, M. Cosentino, G. Patane, A. Viglianisi, and P. Villari, Ist. di Scienze della Terra, Catania; M. Matson, NOAA.

Jump to Index of Monthly Reports

07/1983 (SEAN 08:07) Eruption ends after four months of lava extrusion

After 131 days of activity, the eruption stopped during the morning of 6 August. The July activity was similar to that of the second half of June. The main lava channel was almost completely roofed over, but moving lava was visible through four "windows" in the channel roof. Numerous overflows from the upper "windows" produced modest lava flows of short duration during the first 10 days of July. Through the end of the month, lava emerged from scattered short-lived pseudo-vents at about 1,860-1,800 m above sea level and flowed onto the S flank lava field that has accumulated during the eruption (figure 13). These small superposed flows approached the E and W edges of the lava field; one advanced beyond the field's W margin on 13 July but stopped quickly. Efforts to contain the lava flows continued with the construction of new small embankments. None of the July flows moved below 1,600 m altitude.

Ash emissions occurred at irregular intervals from Bocca Nuova, but were not as strong as in the previous month. High-altitude winds carried ash to Catania (~30 km to the SSE) on 9, 10, and 11 July. No significant activity stoccurred from other vents.

Preliminary estimates suggest that the 131-day eruption extruded ~100 x 10⁶ m³ of lava, at a rate of 10 m³/s. Lava flowed a maximum of 7 km from the vent, reaching 1,100 m altitude (E of Mt. Mazzo), and covered an area of ~6 km².

Information Contact: R. Romano, IIV.

Further References: Kieffer, G., 1983, L'Eruption de l'Etna commencée le 28 Mars, 1983: sa place dans l'exceptionnel cycle eruptif en cours (1971-1983): Comptes Rendus Acad. Sci. Paris, Ser. II, v. 296, p. 1689-1692.

Barberi, F., and Villari, L., eds., 1984, Special issue on Mt. Etna and its 1983 eruption: BV, v. 47, no. 2, p. 877-1177 (22 papers).

Lockwood, J.P., and Romano, R., 1985, Diversion of lava during the 1983 eruption of Mount Etna: Earthquake Information Bull., v. 17, no. 4, p. 124-133.

Jump to Index of Monthly Reports

08/1983 (SEAN 08:08) No new activity

No additional activity has been reported since 4 months of lava extrusion ended 6 August. [Corrections were made to the figure caption from the previous issue; this report was removed for GV 75-85.]

Jump to Index of Monthly Reports

01/1984 (SEAN 09:01) Incandescent tephra from central crater; seismicity

"Beginning in December, numerous seismic crises were recorded, mainly connected to the degassing of the magma column through the central vents. In the same period, ejections of reddish ash (old material) or dark ash (fresh material) occurred from the central crater. At times (14, 16, and 28 January) these have been rather significant, depositing thin layers of ash on the E flank. Some nights, pulsating flashes, due to the ejection of incandescent material from Bocca Nuova were observed. Tiltmeter variations were also recorded."

Information Contact: R. Romano, IIV.

Jump to Index of Monthly Reports

04/1984 (SEAN 09:04) Strombolian activity and small lava flows from Southeast Crater

"During the night of 27-28 April, an eruptive fissure oriented approximately NW-SE opened inside the Southeast Crater, near its NE margin. This crater, which is at ~3,000 m elevation behind the SE side of the central crater, formed in May 1971 and had numerous eruptive episodes in 1978 (April-July, August, November), 1979 (July-August), and 1980 (January-September, explosive activity only).

"Initially, moderate activity was observed from three explosive vents along the fissure, which ejected lava fragments. At the same time, small lava flows emerged from the fissure, remaining inside the Southeast Crater. During the next few days, strombolian activity increased with the ejection of lava fragments to 250 m or slightly more in height. During the morning of 1 May, lava flowed over the NE rim of the crater then turned SE, covering the E side of the Valle del Bove and quickly reaching a length of 2 km. Feeding of this flow was continuous but of variable volume, resulting in numerous superposed and parallel subflows but little advance of the flow front after its initial rapid movement. On 6 May, lava overflowed the SE rim of the crater, advancing NE and later E. This flow, which was fed until the morning of 8 May, reached a length of about 1 km. As of 10 May, both the strombolian activity (which formed a scoria conescoria cone inside the Southeast Crater) and the effusive activity appeared to be decreasing.

"Starting 5 May, strong ash ejections from the Chasm were observed, while from Bocca Nuova only emission of gas under pressure was detected. In the past months, a lava lake 150 m from the rim of Bocca Nuova has been noted."

Information Contact: R. Romano, IIV.

Jump to Index of Monthly Reports

05/1984 (SEAN 09:05) Continued lava production; Strombolian activity

"The Southeast Crater eruption was continuing in early June. The explosive strombolian activity from the small new cone within the Southeast Crater had been diminishing, and stopped almost completely 13 May. Starting that day, ash ejections have been observed at more or less regular intervals, while slow emission of gas and vapor usually occurred. The strombolian activity started again in late May; at times (25 May and 4 June) it was particularly violent.

"The effusive activity has been continuous, with alternating phases of greater or lesser vigor. The lava field has grown noticeably toward the S (reaching a maximum dimension of more than 500 m) and by early June had in its interior, many ephemeral effusive vents, which generated small lava flows that advanced over earlier ones. The main flows (generally one to the S and another to the N), which originated from convergence of the small flows, barely got below 2,700 m elevation.

"At irregular intervals, more or less violent ejections of reddish ash from the Chasm have been noted, while from Bocca Nuova there have only been gas emissions."

Information Contact: R. Romano, IIV.

Jump to Index of Monthly Reports

06/1984 (SEAN 09:06) Explosions and lava production continue from Southeast Crater; central crater explosions

Tanguy and Clocchiatti reported that in late May and early June explosions, usually 10-30/minute, ejected lava fragments and scoria to 50-200 m above the inner cone that had formed inside the Southeast Crater. Explosive activity sometimes declined to weak puffs of gas without much tephra, but at other times the ejecta were rich in large fragments of magmatic material. During periods of more vigorous activity, occasional bursts hurled the smallest tephra to 500-600 m height. In contrast, lava effusion occurred at a steady rate of a few (perhaps 2-5) cubic meters per second, significantly lower than in paroxysmal eruptions (>10 m³/s) but probably higher than in typical subterminal persistent activity (1 m³/s). The maximum temperature measured at small effusive vents on 31 May and 5 June was 1,075-1,076°C (at 60 cm depth).

Romolo Romano reported that explosive activity at the Southeast Crater in June and early July was limited to ejection of incandescent tephra at varying intervals, occasionally accompanied by ejection of dark ash. Effusive activity continued, resulting in further enlargement of the lava field, especially to the N. Lava flows did not extend much below the 2,800 m level. During the last 10 days of June, lava overflows occurred from the SE side of the Southeast Crater, but did not flow over the edge of the Valle del Bove. On 4 July, an overflow of very thin (0.5 m thick) fast-moving lava occurred from the still-active SE side of the Southeast Crater. Tanguy and Clocchiatti reported Bocca Nuova was filled with lava to within ~100 m of its rim in April, but by early June the lava column was again very deep (> 300 m) and activity was limited to quiet emission of large amounts of SO₂. Romano reported that violent ejection of reddish ash from Bocca Nuova was observed beginning in the second half of June. Recently, the ash has been gray (indicating presence of new material). On 3 and 9 July, violent explosions ejected lava fragments that fell outside the crater rim, especially on the SW flank. During this period, strong emission of gas under pressure was noted at the Chasm.

Tanguy reported that in late April seismicity recorded by Christian Archambault from a geophone about 1 km SSE of the Southeast Crater increased from less than 500 to more than 2,200 events/day (figure 14). A seismic crisis was also recorded January-March, accompanied by lava filling and strombolian activity at Bocca Nuova. The temperature at 3 cm depth at the station about 400 m SSE of the Southeast Crater decreased before the 1983 flank eruption but increased before the current eruption began in April 1984.

Information Contacts: R. Romano, IIV; J. Tanguy, Univ. de Paris VI; R. Clocchiatti, CEN, Saclay, France; C. Archambault, CNET, France.

Jump to Index of Monthly Reports

07/1984 (SEAN 09:07) Lava production and Strombolian activity continue from Southeast Crater; strong explosions from Central and Northeast craters

"The Southeast Crater eruption was continuing in early August with more or less intense strombolian activity, accompanied at irregular intervals by violent expulsions of dark ash. This activity produced a scoria cone (~50 m high) higher than the rim of the Southeast Crater. The effusive activity took place from vents around 3,000 m above sea level that changed their positions continuously. On 6 August, two effusive vents were active along the old rim of the Southeast Crater, one on the NE edge, the other on the S edge. Some rather well-fed flows originated from these vents. The final flow direction was always E, toward the Valle del Bove. During this period, the lava flows never advanced below 2,600 m. The lava field that formed from this continuous and variable (in terms of intensity and position) effusive activity was larger than 1 km in extent. The volume of lava emitted can be estimated at around 8-10 x 10⁶ m³.

"An increase in central crater eruptive activity was recorded in July. From Bocca Nuova, violent expulsions of gray ash continued at irregular intervals, while on the vent floor, violent and continuous strombolian activity continued. At times, incandescent lava rose higher than the crater rim. The Chasm, after showing activity similar to that at Bocca Nuova in mid-July, was the source of violent activity on 19 July between 1300 and 1700. Very violent strombolian activity ejected incandescent lava fragments about 1 m in diameter to 500 m from the crater rim. The S and N flanks of the central crater were most often impacted by the lava fragments (their average diameter was ~30 m, they fell within an average radius of 300 m)."

The pilot of an aircraft flying near Etna at 1542 on 19 July observed an eruption cloud that reached ~6.5 km altitude. At 1613, the NOAA 7 polar orbiting satellite showed a plume extending 100 km E from Etna.

"After this, the Chasm remained obstructed until 1 August, when it reopened (at 1900) with the expulsion of old material that fell outside the crater rim. On 6 August, this vent was once again obstructed (around 1300) as the result of internal landslides."

"The Northeast Crater, inactive since February 1981, had a violent explosion that ejected old material on 20 July at 1715. Since then, strong emissions of gases occurred from the small vent that formed near the summit."

Information Contacts: R. Romano, IIV; M. Matson, NOAA.

Jump to Index of Monthly Reports

08/1984 (SEAN 09:08) Lava production and ash emission continue

"The Southeast Crater strombolian activity was intense at times (23 August, 1 and 6 September) and almost absent at other times (afternoon of 7 September). Violent expulsions of dark ash still occurred, at irregular intervals. The effusive activity took place through various vents along the edge of the Southeast Crater (around 3,000 m elevation). In August the effusive activity occurred mainly on the SE side producing lava flows variable in number, position, and rate of feeding. At first they were directed toward the S; later they turned E, rarely (on 23 August) advancing below the edge of the Valle del Bove (about 2,700 m elevation). On 31 August, one of these flows advanced to ~200 m from the rifugio Torre del Filosofo at 2,910 m elevation. The flow then turned E and stopped 1 September at 2,780 m elevation.

"August activity from Bocca Nuova was similar to that of the previous month, mainly showing emission of gas and steam. The Chasm remained obstructed by landslides within the conduit. During the first few days of September, isolated expulsions of reddish ash from the Northeast Crater were noted, always in the afternoon. The last one was observed on 5 September. Usually, strong emissions of gas occur from this crater."

On 16 August at 0606, a weather satellite image showed a plume extending ~200 km SE from Etna at about 5.5 km altitude. The next morning at 0726, a similar plume was present on the imagery. Low sun angles in the early morning improve the visibility of eruption plumes.

Information Contacts: R. Romano, IIV; M. Matson and J. Paquette, NOAA.

Jump to Index of Monthly Reports

09/1984 (SEAN 09:09) Lava flows, Strombolian activity and ash emission

Continuing strombolian activity, particularly intense at times (on the 14th and 20th) and very irregular in intensity and duration, marked the activity in September. Beginning 27 September, this activity was nearly replaced by expulsions of reddish ash at irregular intervals, rarely accompanied by the ejection of incandescent material (bombs and incandescent lava fragments). Lava flows, rarely thick (20 September), usually emerged from effusive vents on the S rim of the Southeast Crater at 3,050 m elevation, and were directed mainly SE, E, S, and ENE. A lava flow advanced S to about 100 m from the rifugio Torre del Filosofo. The flows moved across the lava field, rarely advancing below 2,700 m elevation, within the Valle del Bove.

"Strombolian activity occurred at the bottom of Bocca Nuova. The activity was particularly violent at times with ejection of incandescent lava fragments above the level of the crater rim (24 and 27 September). Generally, only gas emissions were observed. The Chasm usually remained obstructed. Rarely (11 and 24 September), incandescent gas under pressure was observed emerging from a small vent. From the Northeast Crater, isolated expulsions of reddish ash continued, but activity was usually limited to quiet gas and vapor emissions."

Michael Matson reported that a weather satellite image on 14 September at 0740 showed a plume at 4.5 km elevation or higher extending SE from Etna. Ejection of the plume was estimated to have begun 1-2 hours earlier. No plume was evident on an image at 0946.

The following report by Christopher Kilburn, is based on observations 25 August-1 October.

"Since the eruption began in late April, a cone has developed inside the upper E rim of the Southeast Crater, roughly coincident with the position of the most northerly vent active in 1979 (figure 15). On 1 October the cone was ~120 x 100 m at its base (the longer axis oriented roughly NNW) and some 30-40 m high. Until 20 September, the strombolian activity consisted of intermittent violent explosions, with peak frequencies of 14/minute and bomb trajectories ranging from subvertical to directed. Lower-angle ejections were mainly to the E and S, but occasionally to the N and W. Bombs of the order of 0.04 m³ had maximum ranges of ~300-400 m. After 20 September, the violence of the explosions markedly decreased. Weak ejections every few minutes or hours were interspersed with periods of inferred internal collapse that generated small convection columns of pale brown ash and dust. This change in explosive behaviour followed a brief period of rapid lava discharge to the E on 20 September as well as a period of heavy precipitation. Enlargement of the vent at the top of the new cone, which occurred sometime between 13 and 24 September, may have been associated with the 20 September lava discharge.

"Lava discharge was virtually continuous from ephemeral vents S and E of the base of the new cone. Lava flowed S, SE, and E over low points in the Southeast Crater rim. Activity typically alternated between the S and E vents at intervals of one to several days. The successive aa flows, few of which were longer than 1.5 km with frontal thicknesses rarely exceeding 5 m, created a compound flow field with an estimated area that approached 1.5 km² by 1 October (figure 16). By 23 September, ponding inside the Southeast Crater had reached a maximum accumulated thickness of more than 45 m, raising the level of its bottom to ~3,065 m above sea level. Assuming a conservative average thickness of 5 m, and including the material within the Southeast Crater, a provisional estimate of the minimum volume of the flow field on 1 October is 8.5 x 10⁶ m³, yielding a minimum average effusion rate of ~0.64 m³/s. Estimates of the eruption rate, made near the vent 17-28 September, were 0.5-1.0 m³/s for lava discharged toward the S. The chief uncertainties in these discharge rates are the velocity profiles across the flow surface and with depth, and the thickness of the flow; for the minimum value, parabolic velocity profiles and a flow depth of 3-4 m have been assumed, the maximum (central) surface velocity and lava channel width being estimated in the field.

"The Strombolian activity at Bocca Nuova was accompanied by the emission of large quantities of SO₂-rich fumes. Until at least 24 September, magma was probably roughly 100-200 m below the W rim; observations were obscured by fumes. An apparently fresh bomb was found ~20-30 m from the NW rim 24 September, while others, up to 70 cm across, were seen being expelled toward the N and NW 28-29 September to a maximum estimated range of ~100-120 m. It is not known whether ejection of material outside the crater indicated a rise in level of magma within Bocca Nuova or an increase in explosive vigour due to changes in the physical state of the magma, notably in its vesicle content."

Information Contacts: R. Romano, IIV; C. Kilburn, Univ. of London; J. Murray, D. Decobecq, and C. Delmotte, Univ. Paris Sud; P. Briole, PIRPSEV; M. Matson, NOAA.

Jump to Index of Monthly Reports

10/1984 (SEAN 09:10) Earthquake swarm starts as lava production ends

After 172 days of activity, the eruption in the Southeast Crater stopped during the evening of 16 October, although activity continued at the Northeast and central craters. On 17-18 October, only violent ejections of ash at rather long intervals occurred from the small cone that had formed inside the Southeast Crater. The ash ejections stopped completely the morning of 18 October. During the last week of activity from the Southeast Crater, there was a gradual decrease in lava effusion, which was limited to vents along the S rim, and ash ejection from the small cone inside the crater. The lava flows were directed mainly toward the SE, generally stopping after only a few hundred meters.

"During the late morning of 16 October, strombolian activity began from a vent at the bottom of The Chasm. Activity was extremely violent during the evening. At times, lava fragments were ejected above the crater rim, falling back within a 100-m radius. The strombolian activity diminished during the night but continued, with alternating phases, through 17 October. During the morning of 18 October, the crater was obstructed by consolidated lava. It reopened 25 October with the ejection of old lava and ash, and more or less intense emission of gas has continued since then. Bocca Nuova alternated phases of slow emission of gas with periods of intense emission of vapor mixed, at times, with mainly reddish ash.

"Ejections of vapor mixed with reddish ash that had started at the beginning of September from the Northeast Crater intensified during the final phase of the Southeast Crater eruption. During the night of 19 October, weak strombolian activity from the Northeast Crater was recorded at irregular intervals. This activity was succeeded by almost continuous ejection of dark ash, followed during the night of 21 October by the collapse of the crater's summit area. This enlarged the central part of the crater and ejected old lava to a distance of about 500 m, mainly toward the W. Discontinuous and more or less intense emission of vapor mixed with reddish ash started 21 October from this crater, while continuous emission of dense white vapor occurred from a small vent to the N.

"During the afternoon of 16 October a seismic crisis began, with earthquakes mainly occurring in the middle and upper parts of the E flank. The strongest shocks (M ~3.5-4.5), which were felt, were all shallow (around a few kilometers)."

A few of the largest earthquakes in the swarm are described below. Date, time, epicenter, and some casualty and damage data are from Romolo Romano; intensity values and the remaining casualty/damage information are from press sources.

18 October, 1258: centered near Piano Pernicana (15.5 km NE of the summit): Intensity reached MM V-VII, causing ground fracturing and some cracking of roofs and walls.

19 October, 1843: centered near Zafferana Etnea (11.5 km SE of the summit): 1 person was killed and others injured. Intensity reached MM VII-VIII. More than 400 buildings were damaged, including 50% of the historic district, and about 500 people were left homeless. Damage also occurred in Milo (11 km ESE of the summit), Fornazzo (10.5 km E), Santa Venerina (14 km SE), and Giarre (16.5 km ESE).

25 October, 0211: centered near Fleri (14 km SE of the summit), where it reached MM VIII, injured 12-15 people, destroyed 80% of the houses, and left 900 homeless. Ground cracking was observed in the area. Mt. Ilice, a 350-m-high prehistoric cone roughly 1.5 km upslope from Fleri, lost about 20 m of height during the earthquake. The shock was also felt in Catania.

7 November, 0956, centered near Pedara (15.5 km SE of the summit), where a few buildings were damaged.

Information Contacts: R. Romano, IIV; La Stampa, Torino; Corriere della Sera, Milano.

Jump to Index of Monthly Reports

11/1984 (SEAN 09:11) Occasional ash emission; flank seismicity continues

No major eruptive activity has occurred since the Southeast Crater eruption ended in mid-October. From the Northeast Crater, emission of white vapor was more or less continuous and consistent. Sporadic expulsions of reddish ash were observed 27 November and 3 December. Ejection of mainly reddish ash observed at Bocca Nuova was particularly violent 22-24 November. Ash ejected 23 November was mainly dark in color, but on succeeding days was mostly reddish older material that had fallen into the conduit. Ash fell on the lower SE flank. Only weak emission of gas and vapor occurred from The Chasm.

Flank seismicity began as the Southeast Crater eruption ended in mid-October (09:10). Isolated tremors continued in November. Both felt and located events were mainly on the N and NE flanks. No additional damage was reported.

Information Contact: R. Romano, IIV.

Jump to Index of Monthly Reports

02/1985 (SEAN 10:02) Seismicity, then Strombolian activity and lava flows from Southeast Crater; ashfall on coast towns

Weak strombolian activity started 8-9 March in the Southeast Crater. Lava began to flow from the Southeast Crater the morning of 10 March and advanced E (toward the Valle del Bove), stopping that night as feeding ended. Mudflows were also observed in the Valle del Bove; heavy rains had caused flooding in Sicily during the previous week. On 11 March, fissures opened on the upper S flank (in Piano del Lago Alto). The press reported that temperatures in some of the fissures were high enough to melt plastic at nearby cable car stations. Ash fell on the towns of Acireale and Fiumefreddo (~20 km SE and 20 km ENE of the central crater). During the morning of 12 March, lava emerged from vents that opened at progressively lower elevations (from 2,620 to 2,500 m above sea level) and flowed S and SSW, reaching 2,250 m elevation by the next morning. Numerous mudflows preceded the lava flows.

An 11 March newspaper article citing the National Institute of Geophysics reported that microtremors with epicenters in the W part of the Valle del Bove had been recorded for the past few days. A M 3.4 event near the central crater occurred 9 March at 1523, and a shock with a focus at 5 km depth was felt 10 March at 1101 in the towns of Linguaglossa, Milo, and Sant Alfio (16 km NE, 11 km ESE, and 13 km E of the central crater). No magnitude was reported for the 10 March earthquake but both events were said to reach MM IV-V intensity.

Information Contacts: R. Romano, IIV; Il Progresso, New York; Corriere della Sera, Milano, UPI.

Jump to Index of Monthly Reports

03/1985 (SEAN 10:03) S-flank fissure eruption preceded by seismicity and tilt

The following is a report from Romolo Romano. Additional information about the eruptive activity from French volcanologists has been inserted in parentheses in this section. Their report of seismicity and tilt associated with the eruption is presented below.

"Explosive and effusive activity occurred 8-10 March from the Southeast Crater (French volcanologists noted that a strong but short-lived phase of the Southeast Crater activity started 10 March at 1100, with vigorous lava fountaining and overflow of lava toward the Valle del Bove). After numerous fractures formed 11 March on the upper S flank between 3,000 and 2,600 m above sea level, an exclusively effusive vent opened 12 March at 2,620 m elevation, with no recorded seismic activity. The same day, three more effusive vents opened at lower elevations (2,600, 2,510, and 2,490 m); only the last two (near Piccolo Rifugio) remained active. The lava flows that originated from these vents moved mainly toward the S and SW, giving rise to numerous individual lobes. Near the vent at 2,510 m elevation, weak explosive activity occurred, soon creating several small spatter cones and hornitos.

"On 14 March, the lava flows moving S destroyed two Etna cableway pylons; the cable broke the next day. The longest flow stopped 15 March at 2,080 m elevation. Along this trend, superposing lava flows were noted during the following days, until the effusive activity from the vent at 2,490 m ceased on 23 March.

"The lava flows that moved SW created an extensive lava field (maximum width 500 m). At 2,100 m elevation the lava field split into at least five lobes. The longest (and easternmost) flow had descended to 1,850 m elevation by 4 April, covering a distance of ~3 km.

"As of early April, the main lava channel had become a lava tubelava tube between 2,450 and 2,300 m above sea level. Short-lived effusive vents opened near the lower end of the tubelava tube, with lava flows approaching the E side of the lava field or flowing over it. The velocity of the lava flows varied from a few meters per hour to ~30 m/hour. The surface covered by the lava can be estimated at around 2.5 km² and the volume of lava at ~12 x 10⁶ m³. The temperature of lava at the vents was around 1,050°C.

"Particularly during the first few days of the eruption, because of the snow cover, several mudflows formed ahead of the lava flows. Phreatic explosions, violent at times (25 March) were also observed. During the eruption, more or less vigorous emission of vapor, gas, and rarely ash occurred from the central crater vents. (French volcanologists reported a strong explosion from the Chasm on 1 April at about 1625). Isolated expulsions of dark ash from Northeast Crater were observed.

"Collection of information on the eruptive activity was possible thanks to the cooperation of the following Italian Alpine Club rescue team guides and volunteers: G. Baglio, A. Cariola, A. Cristaudo, C. Ferlito, A. Nicotra, G. Puglisi, and F. Zipper."

Later newspaper reports described a swarm of about 30 earthquakes, some reaching intensities of MM IV-V, that started 7 April and continued until early on the 9th. The events were felt most strongly in the towns of Santa Venerina, Acireale, and Giarre (14.5 km SE, 20 km SE, and 17 km ESE of the central craters). After the swarm, the rate of lava production increased by a factor of about 1/3.

The following report, on activity monitored through the ARGOS system, is from PIRPSEV, CNRS-INAG, in the context of French-Italian cooperation.

"Two geophones and a Blum pendulum inclinometer, connected with ARGOS for telerecording of the data, operate near the summit (TDF) and on the south flank (SLN) (figure 17). The geophones record both earthquakes and pulses of volcanic tremor as seismic events, and appear to be good indicators of seismic activity linked to volcanism. The eruption was preceded by an increase in seismic activity (mainly tremor energy) as indicated by the two geophones (TDF and SLN, figure 18). However, after the Southeast Crater eruption, the tremor energy returned to very low levels (figure 19), although effusive vents subsequently opened on the S flank.

"The SLN inclinometer showed continuous tilt toward the WSW during early February, consistent with inflation on the site of the 1983 (and March 1985) eruptions (figure 18). Since mid-February, however, tilt has been mainly westward (figures 20 and 21), thus indicating inflation lower on the S rift zone. This change appears almost synchronous with the appearance of new frequencies of volcanic tremor (personal communication by S. Gresta)."

Information Contacts: R. Romano, IIV; C. Archambault and C. Pambrun, CNET/PIRPSEV; P. Blum, IPG/PIRPSEV; P. Briole, IIV/IPG/PIRPSEV; G. Kieffer, Centre de Recherches Volcanologiques, Clermont-Ferrand/PIRPSEV; J. Tanguy, PIRPSEV; La Stampa, Torino.

Jump to Index of Monthly Reports

04/1985 (SEAN 10:04) South-flank lava production continues; tremor energy increases

"The S flank activity that began 12 March was continuing in early May. During April, the main lava channel was transformed to a continuous lava tube (with at least three 'windows') from 2,510-2,320 m elevation. Around 2,300 m elevation numerous ephemeral effusive vents formed, variable in number and location, from which several lava flows originated and advanced over the lava field or along its E edge.

"The lava flows, directed mainly SE, S, and SSW, have not advanced much, generally stopping at 2,150-2,050 m above sea level. The lowest elevation reached during this period was 1,950 m (20 April). At times (19 and 21 April and 6 May), because of an increase in the production rate, lava overflows occurred following roof collapses in the upper parts (2,510 and 2,485 m elevation) of the lava tube, giving rise to small lava flows of short duration.

"No gas emission was noted from the mid-April hornitos. More or less intense emission of gas and vapor continued from both of the central crater vents; ash emission was very rare. The Northeast Crater generally emitted vapor and rarely (10 April and 9 May) ejected reddish ash.

"The surface covered by lava can be estimated at around 3 km² and the volume at ~20 x 10⁶ m³. In this period there has been almost a total absence of earthquakes. However, during the week of 8-14 April, 20 shocks with magnitudes less than 3 were recorded. Afterwards, a variation in the main spectral peaks of the tremor was observed. A gradual increase in the tremor energy was observed during the entire month of April (S. Gresta, personal communication).

"The Etna Guides and volunteers from the Italian Alpine Club rescue team cooperated in the collection of information about eruptive activity."

Information Contact: R. Romano, IIV.

Jump to Index of Monthly Reports

05/1985 (SEAN 10:05) Lava flows toward SW and SE; strong gas and vapor emissions

"The eruption continued through May without significant changes from last month. The main lava channel has been transformed into a lava tube, between 2,510 and 2,320 m elevation, that has at least four windows through which it was possible to see the lava flow. The lava has maintained a constant velocity during the last few weeks. On 23 May another lava overflow occurred as a result of roof collapse along the upper portions of the lava tube (2,485 m elevation), generating small lava flows of brief duration.

"The numerous short-lived vents inside the lava field (from 2,320 to 2,150 m elevation) were variable, as usual, in number and position. The lava flows that originated from these short-lived vents have increased the size of the lava field on both the W and E sides to a maximum width of ~1.5 km.

"Beginning 10 May the lava moved mainly toward the SW (Monte Rinatura and Monte Nero). Around the beginning of June there were numerous lava flows toward the SE (1910 craters area). Lava continued to flow toward the south (Monte Castellazzi area), but these flows were not strongly fed. None of the lava flows descended below 2,000 m elevation.

"The more or less intense emission of gas and vapor from both vents of the central crater and from the Northeast Crater continue. Emissions of ash are rare and inconsistent. Gas under pressure emerged from a small opening at the southern base of the 1984 cone inside the Southeast Crater (P. Briole, personal communication). R. Clocchiatti conducted temperature measurements with a thermocouple; the temperature ranged between 1053°C and 1,088°C (CEN-SACLAY).

"M. Cosentino and G. Lombardo reported that no particular seismic activity was recorded. Instead, an increase in the average amplitude of harmonic tremor was noticed, probably connected to the degassing of the central and Northeast craters.

"The Etna guides and rescue volunteers from the Italian Alpine Club (A. Cristaudo and A. Nicotra) helped with information on the activity."

Information Contact: R. Romano, IIV.

Jump to Index of Monthly Reports

06/1985 (SEAN 10:06) Continued S-flank lava production

"After a brief period of quiescence from 11-13 June, the eruption continued. Only one effusive vent remained active (2,485 m elevation) with major lava flows originating from it. From 9 to 11 July, following a brief increase in activity, four effusive vents were present at high elevation (2,490-2,480 m). The velocity of the lava produced in this period ranged from 20 to 7 cm/s, volume 2.5 to 0.5 m³ /s.

"The directions of the lava flows were mainly toward the S, SSE, and SE. In the last few weeks, lava flows of significant size were also present, and were directed toward the SSW, S, and SW. The short-lived vents were still present and numerous, scattered on the lava field from 2,350 to 2,250 m elevation. As usual, they varied in number and location. Recently, the lava field enlarged on the E side, but the lava flows have not descended below 2100 m elevation. The emission of gas continued and was sustained from the central craters, and the Southeast Crater. At times, expulsion of generally reddish ash from Bocca Nuova was noted. From the Northeast Crater, violent expulsions of old material (28 June), and emission of reddish ash (10 July) were observed.

"The temperature of the lava flow at the main effusive vent was around 1,080°C (P. Briole). During this period seismicity remained at low levels. On 12 June at 1848, a seismic event (M 2.5) with an epicenter in the lower E flank (14 km depth) was recorded. On 7 July, three events of low magnitude (<2.8) with epicenters on both the E and W flanks were also recorded.

"On 9 July at 0430, the amplitude of harmonic tremor increased abruptly, coinciding with the increase in effusive activity. During the following 24 hours, the amplitude of the harmonic tremor returned to normal levels (communications with M. Cosentino and G. Lombardo). The Etna guides and rescue volunteers from the Italian Alpine Club have cooperated in the collection of information."

Information Contact: R. Romano, IIV.

Jump to Index of Monthly Reports

07/1985 (SEAN 10:07) Four-month eruption ends in mid-July

"The eruption ended 13 July. The first phase (12 March-11 June) lasted 92 days, the second phase (13 June-13 July) lasted 31 days.

"The effusive activity that had shown new strength during the last days of the eruption greatly diminished on 12 July. Only one main effusive vent at 2,490 m elevation and two short-lived effusive vents in the lava field (at 2,300 and 2,600 m) remained active. The flows from the upper vent never descended below 2,400 m elevation and those from the lava field vents never below 2,100 m. From preliminary estimates, the area covered by lava was ~2.2 km² and volume of lava produced was ~30 x 10⁶ m³. The maximum width of the lava field is 1.5 km, the maximum length of flows, 1,830 m (figure 22).

Information Contact: R. Romano, IIV.

Jump to Index of Monthly Reports

12/1985 (SEAN 10:12) SE-flank fissure eruption follows seismic swarm and deformation

Eruptive activity. (Romolo Romano) "Strombolian activity started from the Southeast Crater on 19 December. The activity occurred at irregular intervals, becoming increasingly intense and continuous in successive days. Since the end of the 12 March-13 July 1985 eruption, more or less intense strombolian activity had been observed from several explosive vents (variable in number and position) on the floor of Bocca Nuova at variable depths (from 100 to 300 m or more from the rim of the vent).

"On 25 December at 0340 an eruptive fissure opened on the W side of the Valle del Bove (on Etna's SE flank), beginning at 2,750 m above sea level. The opening of this E-W-oriented fissure was preceded by a seismic crisis (see below). Strombolian activity soon started along this fissure from at least three explosive vents, while a lava flow began from the lower end of the fissure, covering, in a period of 18 hours, a distance of 1.5 km. The lava flow stopped at a point NE of Monte Centenari, at about 1,700 m elevation, within the Valle del Bove. Eruptive activity from the fissure stopped early the next morning. Activity resumed from the same place early 28 December. This second eruptive phase was characterized by weak strombolian activity from the three explosive vents, and created small spatter cones. The effusive activity decreased; a very viscous lava flow moved ~300 m from the origin, branching at ~2,600 m elevation. The eruptive phase ceased during the early morning of 31 December. A violent expulsion of ash and lapilli from the summit craters (E and W vents of the central crater, Southeast Crater, and Northeast Crater) during the first hours of the eruption was succeeded by more or less continuous and consistent emission of reddish ash.

"The Etna Guides (S. Carbonaro, O. Consoli, A. Mazzaglia, A. Nicotizza, and volunteers of the Alpine Rescue Team of the Italian Alpine Club (A. Cristaudo) have collaborated in collecting information about the eruptive activity.

Seismic activity. (M. Cosentino, M. DiFrancesco, and E. Lombardo) "A seismic crisis began during the early morning of 25 December with shocks located mainly between Piano Provenzana (NE flank) and the Valle del Bove. The shocks were very shallow (2 km or less). At the same time, the amplitude of harmonic tremor increased sharply. The shock that destroyed the hotel Le Betulle at Piano Provenzana, killing one person and injuring seven others, occurred on 25 December at 0338 and had a magnitude of 3.5. During the following 48 hours, about 200 more tremors with magnitudes of 1-4 were recorded. The strongest, M 4, occurred on 26 December at 0334, with its epicenter at Piano Provenzana. Focal depths were 2-3 km. The area of the epicenters remained between Piano Provenzana and Valle del Bove. Beginning 27 December, seismicity decreased in frequency, energy, and number of events, and stabilized to values of ~5-6 shocks/day. Their location was mainly in the eruptive area and on the E and W flanks (especially in early January). Similar activity was continuing on 10 January."

Newspapers reported that continuing seismicity included an event on 12 January at 0037, centered in the Zafferana Etnea area (11 km SE of the summit), that reached MM 6 and damaged some buildings. At least 3-4 minor shocks (one of MM 3) were felt the previous day.

Ground deformation. (G. Nunnari and R. Velardita) "During the second half of December, the tilt stations (Pizzi Deneri, NE flank, elevation 2,850 m; and Serra Pizzuta Calvarina, S flank, elevation 1,650 m) recorded a progressive inflation of the upper E flank. At the Pizzi Deneri station the variation was 13 µrad radially and 22 µrad tangentially between 20 December at 0900 and 23 December at 0900. The same stations recorded a variation of 45 µrad radially and 42 µrad tangentially between 24 December at 0900 and 25 December at 0900. The deformation produced during the first hours of 26 December reached a level that remained substantially unchanged as of 10 January."

Information Contacts: R. Romano, G. Nunnari, and R. Velardita, IIV; M. Cosentino, M. DiFrancesco, and G. Lombardo, Ist. di Scienze della Terra, Catania; La Stampa, Torino.

Jump to Index of Monthly Reports

01/1986 (SEAN 11:01) Strong flank seismicity

Seismicity has continued since Etna's SE-flank fissure eruption in late December. The following is from R. Romano. "Beginning 1 February, a series of shocks occurred on all ... flanks (table 2). The most energetic events occurred 1 and 2 February ~ 15 km SE of the summit (in the Dagala zone, in the area of Santa Venerina and Linera), with magnitudes between 3.0 and 3.6 and depths within 1 km. During the week, 50 shocks were also recorded by instruments, mainly on the E flank."

Table 2. Largest of a series of earthquakes on Etna's flanks, February 1986.

    Date    Location (and                Magnitude   Depth
            distance from summit)

    3 Feb   E of S. Pizzuta                 3.0       1 km
    4 Feb   between Linera and
              Guardia Mangano (16 km SE)    2.5       1 km
    5 Feb   E of Mt. Pomiciaro (15 km NE)   3.2      16 km
    6 Feb   N flank, E of Malvagna          3.1       4 km
    7 Feb   between Mt. Pomiciaro and
              Linguaglossa (15 km NE)       3.0      16 km

Information Contact: R. Romano, IIV.

Jump to Index of Monthly Reports

02/1986 (SEAN 11:02) Ash and bombs from Northeast Crater

While spending the night of 5 March at the foot of Northeast Crater, geologists observed ash emission every 5-15 minutes with ejection of glowing red bombs 6-7 times/hour. Bombs reached the base of the crater. Significant degassing occurred from both of the central craters (The Chasm and Bocca Nuova). However, there were no explosions, nor was glow visible at night.

Information Contacts: F. Le Guern, CNRS; Compagnie Republicaine de Securité de Briancan.

Jump to Index of Monthly Reports

05/1986 (SEAN 11:05) Strombolian activity and gas emission

Explosive activity has continued from both central crater vents since the end of the SE flank fissure eruption. Strombolian activity could be seen from within ~ 100 m of the W vent (Bocca Nuova) rim, but ejected lava fragments rarely rose above the crater rim. Active vents within Bocca Nuova varied in position and number. Since the end of April, a vent on Southeast Crater has emitted hot pressurized gas. Northeast Crater has been partially obstructed by internal landslides; weak fumarolic activity occurred along the crater walls.

Information Contact: R. Romano, IIV.

Jump to Index of Monthly Reports

09/1986 (SEAN 11:09) Strombolian activity and lava flow, then strong explosion

Strombolian activity and lava production, late July-23 September. Strombolian activity began from Northeast Crater at the end of July and continued with periods of greater (19 August) and lesser intensity. In early September, 20-30 explosions occurred/minute, with ejection of bombs and scoria to 100-250 m above the vent. A scoria cone ~ 40 m high formed inside the crater. Strombolian activity increased in the late afternoon of 13 September, and lava overflowed Northeast Crater's W rim early the next morning, feeding a modest-sized lava flow that moved NW. By 16 September, the flow had descended to 2,920 m altitude (~ 1.5 km from the main effusive vent at 3,190 m altitude) after crossing a trail (maintained by the Società Turistica Star). During the following days, small lava flows advanced a few hundred meters NW, NNW, WNW, and W, beside or on top of the first flow. This slow and discontinuous activity built a small lava field, with a volume that was estimated at a maximum of 0.25 x 10⁶ m³. On 22 September, the temperature of the flowing lava near the vent was 1,094°C at 40 cm below its surface. During the effusive phase, Strombolian activity varied in strength but generally remained at rather low levels. While sampling high-temperature gases and measuring oxygen fugacity on 22 September, Patrick Allard and others noted that the floor of the crater oscillated, rising by as much as 1 m with every explosion. During a summit-area leveling traverse the next day, a very strong tremor made automatic level readings difficult. Strombolian activity increased considerably, with bombs rising to 200 m above the vent and falling 300 m away. Strombolian activity also occurred at the bottom of the E and W vents (The Chasm and Bocca Nuova) of the central crater. This activity was of variable intensity, with changing numbers and locations of vents. Only rarely were lava fragments ejected above the vent rims.

Cessation of activity, early 24 September. During the early morning of 24 September, the scoria cone and a portion of the wall inside Northeast Crater collapsed into the vent area, leaving a fuming pit ~50 m deep. Effusive and explosive activity ended almost immediately, between 0600 and 0700. That morning, activity was limited to expulsions of reddish ash and white vapor. Steaming fissures and a small graben (~ 1 m wide and 1 m deep in places, wider nearest the crater) opened to the SW and NE (figure 23), with fissures reaching the Valle del Leone (1.5 km ENE of Northeast Crater) and the Piano delle Concazze, 2 km to the ENE. Activity from Bocca Nuova had also ceased. A leveling team in the summit region and N of Northeast Crater detected some intermittent tremor and measured substantial deflation that had occurred since the previous day.

Because of the abrupt cessation of summit activity and the possibility of violent vent-clearing explosions, the summit area was closed to tourists.

Resumption of explosive activity, afternoon of 24 September. A prolonged period of ash ejection accompanied by thunder and lightning started at about 1215, causing a light ashfall on the upper SE flank (figure 23). At 1312, large dark ejecta were seen rising to ~ 40-50 m above the vent, with stronger expulsion of small brown ash clouds, but no discrete explosions were heard. Episodic eruptions continued for the next 3.5 hours. Periods dominated by quiet emission of pink-brown ash alternated with periods characterized by ejection of black cypressoid and columnar ash jets, and expulsion of large tephra to ~200-350 m above the vent (figure 24). Electric discharges were common. Thick white convecting vapor clouds emerged separately from the S part of the vent area, at increasing rates. Continuous tremor and occasional stronger shocks were felt after 1515 by a gas sampling team working ~ 200 m S of Northeast Crater. There was no apparent time relation between the seismicity and eruptive activity.

The following preliminary observations have been extensively updated by J.B. Murray.

Ash emission began to increase gradually at about 1645, changing to violent phreatomagmatic explosions. Black clouds, again cypressoid and columnar, initially rose to 400 m above the vent, merging by 1743 to produce a convective cloud that reached a relatively consistent height of ~ 1,000 m. Stronger falls of ash and small lapilli occurred SE of the summit, and bombs reached heights of 600-700 m. No [sounds] were heard, [apart from frequent dry cracks of] electrical discharges in the cloud [and the rushing of air in the rising column]. Incandescent ejecta were first seen at about 1800, and within 40 minutes lava fountains had developed at the center of a much wider column of dark ash. Heat from the fountains could be felt from a distance of ~ 800 m. ... Between 1815 and 1843, bombs fell progressively farther SW from the vent, with maximum ejection distance increasing from ~300 to 700 m, and maximum heights building from ~600 to 1,500 m.

Paroxysmal explosion, evening of 24 September. The paroxysmal phase began about 1845 with continuous louder rumbling and the sudden rise of a vertical lava fountain, ~ 300 m across, to 800-1,000 m. A dense black cloud surged down the E flank of Northeast Crater into the Valle del Bove. [Dense bombs up to 50 cm in diameter fell as far as 2,700 m to the SW, suggesting to Murray that they reached 2-3 km height]. ... The eruption cloud moved SSE, and ... the tephra fallout [rapidly] advanced ~2 km, showering observers [fleeing in vehicles] on the S flank (near the Torre del Filosofo; figure 23) with a dense blanket of ... scoria and ash [with occasional heavy bombs falling from 2-3 km height]. In a short time, the entire SE flank of the volcano was covered by pyroclastic material of sizes that varied with distance from the vent (figure 23). [Differential winds at higher altitude carried some scoria SW as far as Biancavilla (~ 15 km SW), where fragments measuring a few cm fell]. Tephra fall continued for almost 20 minutes.

[Subsequent topographic mapping] showed that pyroclastic material (scoria, lava fragments, and lithic blocks) [reached 4 m thick near the edge of Northeast Crater, and 5 cm thick] at a distance of 2 km (Torre del Filosofo). Scoria and lithic blocks up to a meter in diameter could be found within a radius of 0.5 km; at 2 km, scoria a few tens of centimeters across were observed. Hot scoria 11 cm in diameter melted roof tar 4 km S of the crater (at Piccolo Rifugio); hot lapilli to [7.5] cm across [scratched car windshields at] the tourist complex around Rifugio Sapienza and the base station of the cable car system 6 km from the vent; some scoriae as large as 15 cm were found 7 km from Northeast Crater at 1,700 m altitude (Serra La Nave); and 1.9-[cm] lapilli fell at Nicolosi (17 km to the SSE). Lapilli [0.5 cm in size reached Catania, 27 km away, where light ashfalls also occurred]. Catania airport (35 km from the summit) was closed from that evening until late the next morning.

[Bond, Décobecq, Kilburn, Murray, and Obreski] estimate that the tephra column reached 10-13 km altitude during the paroxysmal phase, in agreement with an independent estimate by Mueller [from Nicolosi. However, photos by J.P. Delouche, approaching the volcano from Siracusa, show maximum column height to be 6-7 km above the summit (9-10 km altitude)]. The press reported that the tephra column was visible from the Aeolian Islands (95 km N), and Agrigento (100 km WSW). At [1900] on 24 September, the explosive activity ceased completely. During the following days, Northeast Crater slowly emitted gas, vapor, and (rarely) reddish ash.

[Nearly 200 depths measured by Murray, Décobecq, and Bond yield a tephra deposit volume of 2.6 x 10⁶ m³, mostly of pumice density, or 0.4 x 10⁶ m³ dense rock equivalent (DRE)]. The volume of material emitted was estimated by IIV geologists at around a few million cubic meters ... . If most of the tephra were assumed to have been erupted during the final phase, the mean paroxysmal eruption rate was [~500] m³ DRE/s (2.7 x 10⁶ kg/s). Kilburn notes that the independently determined values for eruption rate and column height are consistent with the column height model of Wilson et al., 1978. Total energy release was [~9 x 10²¹] ergs. Vigorous explosive eruptions are relatively uncommon at Etna; [this century only four comparable events have occurred, in 1917, 1940, 1947,and 1960].

Minor activity, late September-early October. Strombolian activity from the two central crater vents, which ended 24 September with the collapse in Northeast Crater, resumed on the morning of 29 September. Gas, at times under pressure, was also emitted from Southeast Crater and a nearby gas vent before, during, and after the paroxysmal explosion. Emission of gas with fragments of old lava and/or incandescent lapilli was observed at times. The frequency of these ejections was very irregular, varying from a few minutes to several hours. As of 9 October, no significant changes in the activity of the summit craters have been noted.

Seismicity. Beginning 13 September, the seismic activity consisted only of explosion earthquakes probably related to the onset of the increased Northeast Crater activity. During the night of 22 September, three isolated seismic shocks with a maximum magnitude of 2.9 were recorded on the NW flank. Minor shocks were recorded until the night of 2 October, when a swarm of 30 events (maximum magnitude 3.3) occurred on the lower NW flank (between Maletto and Randazzo) at variable depths of ~ 20 km. A second swarm started during the morning of 5 October, again on the W flank, at the same depth. The strongest shock (M 3.8) occurred at 1228, and was felt at numerous locations on the volcano. The swarm ended that night, after ~ 40 weak shallow events were recorded on the W flank (Monte Minardo area). Another swarm of ~ 10 shocks occurred the morning of 7 October, also on the W flank, with a maximum magnitude of 3.3.

Harmonic tremor increased during the first phase of Northeast Crater eruptive activity (13 September). Similar tremor energy values were observed until ~ 5 hours before the 24 September eruptive event, when tremor energy began a gradual increase of about an order of magnitude. Energy values returned to normal around 2000 and no significant variations occurred in the following days.

Reference: Wilson, L., Sparks, R.S.J., Huang, T.C., and Watkins, N.D., 1987, The Control of volcanic column heights by eruption energetics and dynamics: JGR, v. 83 p. 1829-1836.

Information Contacts: R. Romano, G. Budetta, T. Caltabiano, D. Condarelli, O. Consoli, and E. Lo Giudice, IIV; G. Luongo, IIV and OV; G. Ricciardi and G. Forgione, OV; S. Gresta, Univ di Catania; R. Clocchiatti, P. Gillot, G. Kieffer, J. Murray, and J. Tanguy, PIRPSEV; P. Allard, G. Benhamou, and M. Pennisi, Centre de Faibles Radioactivites; A. Bond, Univ of Lancaster; D. Décobecq, Univ Paris-Sud; C. Kilburn, Univ di Napoli.

Further References: Amore, C., Giuffrida, E., Scribano, V., Lowenstern, J., and Müller, W., 1987, Emplacement and textural analysis of some present-day pyroclastic deposits of Mt. Etna (Sicily): Boll. Soc. Geol. It., v. 106, p. 785-791.

Murray, J., Décobecq, D., and Bond, A., 1989-90, L'Eruption paroxysmale du cratère Nordest de l'Etna du 24 Septembre 1986: LAVE Bulletin, no. 22, p. 11-23; no. 23, p. 5-18; and no. 24, p. 11-21.

Jump to Index of Monthly Reports

10/1986 (SEAN 11:10) Lava flows and Strombolian activity from SE fissures and crater

A new system of eruptive fissures opened at the base of the central crater on 30 October. The new eruption was marked by vigorous Strombolian activity and intense seismicity. Several new lava flows emerged from the fissures.

The seismic activity observed during the first several days of October continued during the following days. Both shallow and deep earthquakes occurred, mainly on the W flank of the volcano. The deepest earthquakes were at 20 km and maximum magnitude was 3.0.

An intense but brief seismic swarm that included > 40 shocks in one hour began at 2345 on 29 October. The strongest event (M 3.7), centered on the NE flank (at Piano Provenzana), occurred ~1/2 hour later at 0018. Only a few events were recorded during the following days.

Harmonic tremor remained at late September-early October levels until 30 October, when the seismic swarm was joined by a brief, ten-fold rise in tremor amplitudes, between 0000 and 0400, that accompanied the opening of a system of eruptive fissures. The 2-km-long fissure system, oriented ENE, stretched from the base of the central crater to the Valle del Leone (from 2,900 to 2,500 m above sea level (asl), on the W flank of the Valle del Bove). Several explosive vents that formed along the upper part of the fissure system were the source of gas and vapor emission, strong ash expulsions, and occasional phreatic explosions. Weak Strombolian activity occurred from the lower part of the fissure system (~ 2,500 m altitude) and several lobes of lava flowed away from the fissures. Eight hours after the start of the eruption, two main flows were moving SE. The southern flow had advanced ~ 2.5 km and reached the Valle del Bove at 1,750 m altitude.

During the early afternoon the fissure system continued to propagate downslope, creating a new eruptive fissure NW of Mt. Simone, around 2,300-2,200 m altitude, just behind and to the side of the N "wall" of the Valle del Bove. Violent explosive Strombolian activity started immediately, as four eruptive vents formed. Lava flows from the two lower vents coalesced into a single lobe that moved SE. In the late evening, strong lava fountaining began along a few hundred meters of the central part of the fissure system (around 2,600-2,500 m altitude). The ash and lapilli from this activity were transported by the wind 30 km to the SW.

Similar explosive activity was continuing the next morning. Lava formed three main flows (around 2,700 m altitude), that moved SE and ESE. Tremor amplitude decreased significantly, but increases were later recorded during various periods of increased eruptive vigor. Strong Strombolian activity from Southeast Crater began in the early afternoon. Isolated but violent explosions continued until the next day (1 November) when lava overflowed from Southeast Crater and moved SE for a few hundred meters. Southeast Crater lava effusion ended during the morning of 2 November and ash expulsions, sometimes violent, began.

During the first few days of November, violent explosions audible on the entire SE flank marked periods of intense ash expulsion from the new eruptive vents (particularly those around 2,300-2,200 m altitude). The numerous lava flows remained above 1,500 m altitude, forming a large lava field.

Strombolian activity from the bottom of the 2 central crater vents had continued through October. From the beginning of the 30 October eruption, vapor emission of fluctuating intensity alternated with expulsions of significant amounts of dark ash from these vents. Fumarolic activity occurred along the edges of Northeast Crater.

On 3 November a M 3.5 earthquake, the strongest since 30 October, occurred at 0833 in the lower part of the Valle del Bove. As of the morning of 10 November, weak Strombolian activity was occurring from six explosive vents, two around 2,500 m altitude, and four around 2,300-2,200 m. Lava from the two eruptive systems merged and formed a single flow. It advanced 200 m past Rocca Musarra (on the N side) and penetrated farther inside the Valle del Bove than any other flow, to 1,450 m. At least two large scoria cones were forming over the vents.

Information Contacts: R. Romano, G. Budetta, T. Caltabiano, D. Condarelli, and O. Consoli, IIV; G. Luongo, IIV and OV; S. Gresta, Univ di Catania.

Jump to Index of Monthly Reports

11/1986 (SEAN 11:11) Fissure eruption continues

"The eruption ... was continuing in early December. As of 9 December, two eruptive vents were still active, as was a pit crater at ~ 2,850 m altitude (figure 25) that generally showed strong gas emission but at times (15 November) violent expulsions of ash and/or sporadic ejection of incandescent material. A substantial spatter cone has formed at the eruptive vent at 2,600 m altitude, from which strong gas emissions have occurred since mid-November. The main lava channel originated at the base of the cone, and since the end of November has been an essentially continuous lava tube (with at least seven skylights in its roof) down to 1,900-2,000 m altitude, where a few ephemeral effusive vents have formed. Several lava flows fanned out from these vents, rarely going below 1,500 m and remaining within the Valle del Bove. The more active lava flows have generally moved E. On 19 November one of these reached 1,325 m altitude, ~ 5 km from the vent.

"A large spatter cone (called Monte Rittmann in memory of our beloved teacher) formed around 2,300-2,350 m, and reached a height of ~ 100 m. From its base, a lava overflow started at the beginning of December and fed a flow that advanced ~700 m before stopping behind Monte Simone. Monte Rittmann has shown almost continuous Strombolian activity, more or less violent and often accompanied by strong explosions. Expulsions of ash have also been observed. The eruptive vents at lower elevation have not been active since 25 November. These vents, one exclusively explosive (at ~ 2,250 m altitude) and two primarily effusive (2,200 and 2,190 m altitude) were very active during the first weeks of the eruption, helping to form a large lava field. The flow fronts were generally wide (at times > 100 m) and high (at times > 10 m). An initial estimate, still to be confirmed, suggests that the volume of lava is around 25 x10⁶ m³. It is difficult at this time to evaluate the surface covered by the lava, but it should be > 4 km².

"From the E vent of the central crater (the Chasm) more or less violent emissions of reddish ash have continued without interruption. Only emissions of gas and vapor were recorded from the other summit-area vents.

"Only a few weak earthquakes were recorded during November and the first few days of December. Volcanic tremor remained at high levels (5-10x normal), with variations related to changes in the eruptive activity."

Information Contacts: R. Romano, T. Caltabiano, D. Condarelli, and O. Consoli, IIV; S. Gresta, Univ di Catania.

Jump to Index of Monthly Reports

12/1986 (SEAN 11:12) Lava flows; Strombolian activity; ash emission

"The eruption was continuing in early January. Strong gas emissions continued from the eruptive vent at ~ 2,600 m altitude. Lava continued to flow into a tube that extended from the base of the vent to ~ 1,800 m altitude, where there were ephemeral effusive vents that varied in number and position. The lava flows that originated from these ephemeral vents did not advance below 1,500 m altitude, and remained in the center of the Valle del Bove.

"The Strombolian activity at Conetto Rittmann (2,350-2,300 m altitude), at times from as many as three explosive vents, included periods of greater or lesser activity, but diminished gradually. From the beginning of January, the Strombolian activity was almost totally replaced by more or less violent explosions of gray ash. Lava flows originating at the base of Conetto Rittmann (recently more than two lobes have been noted) usually reached 1450 m altitude, passing N of Rocca Musarra, where they stagnated. The rate of lava production varied considerably with time. At the pit crater at ~ 2,850 m altitude, only gas emissions were observed. More or less violent explosions of reddish ash continued from the E vent of the central crater (La Voragine) alternating with periods (more rare) of vapor emission. Gas emissions from the other summit vents (Bocca Nuova, and Southeast and Northeast craters) were continuous but of varying strength.

"During this period, no seismic shocks were recorded. Volcanic tremor remained at rather high levels, with sporadic variations associated with the trend of the eruptive activity."

Information Contacts: R. Romano, T. Caltabiano, and D. Condarelli, IIV; S. Gresta, Univ di Catania.

Further Reference: Kieffer, G., and Tanguy, J.C., 1987, L'activité de l'Etna en 1986: Bull. Sect. Volcanol. Soc. Géol. Fr., no. 3 (January 1987), p. 3-6.

Jump to Index of Monthly Reports

01/1987 (SEAN 12:01) Lava flows in tubes; Strombolian activity and seismicity decline

"The eruption ... continues. Gas emission and rarely (12, 13, and 18 January) strong expulsions of ash occurred from the pit crater at ~ 2,850 m altitude. Only gas emission was observed from the spatter cone at ~ 2,600 m altitude, and it appears that lava effusion from its base ceased at the end of January.

"The Strombolian activity from Conetto Rittmann (2,350-2,300 m altitude) has decreased gradually, almost completely replaced since mid-January by more or less violent expulsions of gray ash, and irregular intervals in which only gas emission was observed.

"The effusive activity that originates from the base of Conetto Rittmann continued with alternating phases of greater or lesser intensity. Between 9 and 23 January several lava flows (four at times) were noted. These were fed at a moderate rate and descended to 1,500 m altitude, after passing Rocca Musarra to the N and S. As of mid-February, a lava tube extended from the base of Conetto Rittmann down to 2,000 m altitude. From there, small lava flows originated from many ephemeral vents, variable in location and duration. These flows moved mainly SE and E, covering lava from previous days, but remained inside the Valle del Bove, and never descended below 1,700 m altitude.

"Expulsions of reddish ash were observed at irregular intervals from both vents of the central crater (mainly from the E vent), while from Southeast Crater only gas emission of variable intensity was recorded. Weak fumarolic activity occurred from Northeast Crater.

"During the first two weeks of January no earthquakes were recorded. Tremor remained at high levels until the morning of 16 January, when tremor energy was reduced to 1/4 that of the preceding days. Seismicity resumed 27 January and continued for 5 days with weak, sporadic shocks on the N flank, at ~ 10 km depth. At the same time, tremor energy descended to levels typical of quiet periods at the volcano.

"Two strong earthquakes (M 4.2, depth 20 km) were recorded on 2 February at 1648 and 1659. Epicenters were ~ 40 km NW of the volcano and the events were felt in much of eastern Sicily. No additional significant earthquakes had occurred as of mid-February, and tremor remained at low levels."

Information Contacts: R. Romano, T. Caltabiano, and D. Condarelli, IIV; S. Gresta and C. Sturiale, Univ di Catania.

Jump to Index of Monthly Reports

02/1987 (SEAN 12:02) 120-day eruption ends

"The eruption that began 30 October 1986 ceased at the end of February, probably on the 27th, after 120 days. The effusive activity that had originated from Conetto Rittmann diminished gradually. Only two lava flows, poorly fed, were noted around 20 February. These were moving across the lava field that had formed in previous months within the Valle del Bove, and did not advance below 1,800 m altitude. At the end of February, only gas emission, very vigorous at times, was noted at Conetto Rittmann. More or less impressive gas emission, mixed at times with a little ash, occurred from the two central crater vents. Consistent ash expulsion was rare. Gas emission continued from Southeast Crater. During the eruption, Northeast Crater had shown weak fumarolic activity, but emission of gas that sometimes contained a little ash was noted in early March.

"After the two earthquakes of 2 February, no significant shocks had occurred in the area as of 6 March. Throughout February, tremor energy remained at the low levels reached at the end of January. The presumed date of the end of all eruptive activity (27 February) is in accord with a decline in tremor energy, when values reached those typical of quiescence at the volcano."

Information Contacts: R. Romano, T. Caltabiano, and D. Condarelli, IIV; S. Gresta and C. Sturiale, Univ di Catania.

Further References: Caltabiano, T., Calvari, S., and Romano, R., 1987, Rapporto sull'attività eruttiva dell'Etna nel periodo Gennaio 1986-Febbraio 1987: Bolletino del Gruppo Nazionale per la Vulcanologia, p. 215-231.

Carveni, P., Rasa, R., Scribano, V., and Sturiale, C., 1987, L'Eruzione Etnea del 1986-1987: Aspetti Fenomenologici e Dati Petrologici: Boll. Accad. Gioenia Sci. Nat. Catania, v. 20, p. 197-217.

Jump to Index of Monthly Reports

04/1987 (SEAN 12:04) Phreatic explosions from Southeast Crater kills two, injures seven

An explosion from Southeast Crater on 17 April ejected tephra that killed two people and injured seven others.

During the first half of March, Northeast Crater occasionally emitted gas and vapor, sometimes with ash. During the second half of the month only weak fumarolic activity occurred from Northeast Crater, but more or less intense gas emission episodes that occasionally ejected ash occurred from the central crater's Bocca Nuova. Low-level volcanic tremor occurred during the same period but no earthquakes were recorded. Ten microshocks (M 1.0) occurred 23-25 March.

Sudden increases in sporadic tremor, lasting ~ 10-15 minutes, began 1 April. Geologists attributed the tremor to deep phreatomagmatic explosions. Activity increased during the first few days of April, reaching a maximum of 10 episodes of sporadic tremor on the 6th. The episodes lasted 30-40 minutes each and occurred at ~ 2-hour intervals. On 8 April > 50 microearthquakes were recorded. Only weak gas emission occurred from the central crater's E vent through early April. However, on 8 April at 0835 a violent phreatic explosion from that vent fed a 1-km-high eruption column. Abundant tephra was strewn to 300 m from the crater rim, with maximum dispersion to the NE. Geologists believed that similar explosions had probably occurred during the second half of March. The 8 April explosion was followed by a long period of relative seismic quiescence when only weak sporadic tremor was recorded. Beginning 12 April, 4-5 episodes of sporadic tremor were recorded daily.

Following several days of forceful gas emissions from Southeast Crater, tremor duration increased to a maximum of 30 minutes on the morning of 17 April. At 1335 a moderate-intensity phreatic explosion launched tephra SSE, killing two and injuring seven of the ~ 30 tourists who, the press reported, were standing ~500 m from the crater. A similar explosion on 12 September 1979 had killed 9 tourists and injured 23 others near the central crater's Bocca Nuova (04:09). The 17 April ejecta appeared to be older volcanic material. Tephra fragments 150 m from the crater rim reached diameters of 15 cm and at 250 m were a maximum of 5 cm. IIV geologists suggested that conditions for the 8 and [17] April explosions resulted from the collapse of the internal vent walls and subsequent gas accumulation.

Immediately after the [17] April explosion an increase in tremor was noted. The next day, three episodes of periodic tremor were recorded, each lasting ~ 90-120 minutes. Levels of tremor 2-3x normal continued through the end of the month. Only small quantities of gas were emitted from the central crater during the days following the fatal explosion. Weak Strombolian activity [from Southeast Crater] was observed during the night of 25 April and the morning of 26 April [and 10-16 May]. Vapor emission resumed after the end of the Strombolian activity.

Information Contacts: R. Romano, T. Caltabiano, D. Condarelli, O. Consoli, and G. Frazzetta, IIV; S. Gresta and C. Sturiale, Univ di Catania; La Republica, Rome; AP.

Jump to Index of Monthly Reports

03/1988 (SEAN 13:03) Inflation and seismicity

The following is from a joint French (CNRS/PIRPSEV)-Italian (CNR) monitoring program.

Ground deformation and microseismicity data are transmitted by an ARGOS satellite station, 1 km SSE of the central craters at 2,920 m asl (near the Torre del Filosofo). Two tiltmeters and a vertical geophone are installed inside a 50-m-long lava tube.

From November 1987 through January 1988, no ground deformation was detected and microseismicity was at a low level (100 events/day). In February, ~ 3 µrads/day of nearly continuous inflation was measured by the N-S component of the tilt instrumentation, but E-W tilt remained essentially flat (figure 26). Microseismicity remained at a low level until 25 February, when both the number of events and noise amplitude began to increase (figure 27). A sharp (30 µrad) N-S deflation occurred 29 February-1 March, with a further increase in the number of events (to 700-950/day) and noise amplitude.

Seismicity continued to build 1-5 March, to 1,100 earthquakes/day. An additional 15 µrad of N-S deflation 5 March was accompanied by the onset of 20 µrad of rapid uplift to the E. From 5 March through early April, NNE-trending inflation has continued at ~ 4 µrad/day, and microseismicity has remained strong, reaching a maximum of 2,700 shocks/day on 8 April. Since the end of February, the 10-station ARGOS seismic network has located many shallow earthquakes in the NE quadrant of the volcano. Local and regional networks have recorded many earthquakes on Sicily's E coast, especially near Etna. Some reached M3 with hypocenters deeper that 10 km. One was felt during the night of 1-2 April by residents of Santa Venerina (15 km SSE of the summit) and Guardia-Mangano (18 km SSE). The ground deformation and microseismicity data suggested to the French/Italian team that significant stress modifications had been located beneath the central craters, and these have since moved to the E flank. No magma had reached the surface as of early April and degassing activity from Bocca Nuova and Southeast Crater remained normal.

Information Contacts: C. Archambault, Centre National d'Etudes des Telécommunications; F. Barberi, Univ di Pisa; R. Basile, Osservatorio Sismologico, Acireale; P. Briole and C. Pambrun, IPGP; J. Glot, IRIGM; J. Liparski, ICSC World Laboratory; O. Nicoloso, Nicolosi.

Jump to Index of Monthly Reports

01/1989 (SEAN 14:01) Strombolian activity from summit craters: inflation

After the October 1986-February 1987 eruption, activity has been confined to the summit craters. In the following report, frequent observations by IIV personnel with help from Italian Alpine Club guides are supplemented by data from geologists who reoccupied ground deformation networks 20 May-24 June and 16 September-7 October.

Bocca Nuova. Since the end of April 1988, Strombolian activity and/or degassing has continued at varying intensity. Explosive vents were active at different points on the crater floor, 150-250 m below the rim. Lava fragments only rarely reached the crater rim. Ash and lapilli ejections were occasionally observed, especially during periods of stronger and more continuous activity. In May and June, small explosions or gas bursts could be heard deep within the crater at a rate of 30-50/minute, with larger explosions about every 5 minutes. Loudness of the explosions varied considerably; they usually were not audible 400 m from the crater, but on 23 June, 4 were heard from Rifugio Sapienza, 5.5 km S, between 1214 and 1226. In September and October, the explosion rate was 30-40/minute. Strombolian explosions from three active vents on the crater floor, roughly 150 m below the rim, were observed about once every 5 minutes. Louder series of explosions were heard up to 3 km away on 23 and 28 September and 1 October. During the night of 1-2 October, a few fresh bombs landed just outside the crater rim and the next day bombs were rising to ~ 10 m below the rim. Violent activity that included lava fountaining was observed from a distance on 31 January 1989 from 1930 to 2100. Bocca Nuova was relatively quiet in early February.

La Voragine. The vent was partially obstructed until July, with activity limited to weak gas emission. Strombolian activity of variable intensity then started at the bottom of the crater, at more than 250 m depth. Ejecta only rarely reached the rim. On 23 August between 1610 and 1650, a series of pyroclastic explosions ejected juvenile material (lava fragments, scoria, lapilli, and ash) to a few hundred meters height. The tephra fell mainly on the E flank, to 400 m from the rim. Explosive activity ceased completely from the end of August until the beginning of September. During visits on 28 September and 6 October, Strombolian explosions were occurring from vents that appeared to be higher in the crater than those at Bocca Nuova. About 30 explosions/minute were counted on the 28th, with ~1/minute strong enough to eject bombs visible to the geologists, who could see 50-80 m into the crater. At night on 2 October, no noises could be heard from the rim, although faint glow was visible. In early February 1989, little activity was occurring from the crater.

Southeast Crater. Gas emission, sometimes under pressure, continued from a vent near the center of this complex of cones and depressions. By 4 October the gas emission had strengthened, ejecting blocks, apparently from the wallrock, and sublimates. Weak and irregular Strombolian activity began in early October. A small new vent opened between 24 and 25 November E of the previous vent, ejecting ash and other tephra. Some of the explosions were fairly vigorous, as on 27 November. The activity changed gradually from ash ejection to a nearly continuous explosive Strombolian activity, with periods of greater and lesser intensity. At times, lava fragments reached 250 m height, falling within a few hundred meters of the crater. Similar Strombolian activity was continuing in early February 1989.

Northeast Crater. Only fumarolic activity was observed until the end of July, varying in intensity with weather conditions. A small vent opened inside this crater on 24 July and grew with time. Very hot pressurized gases emerged, particularly soon after the vent opened. The vent was glowing at night in September. Smoke rings were occasionally emitted in September and October, similar to those observed from Bocca Nuova early in its development.

The following deformation and seismic data are from J.B. Murray.

Despite the increased seismicity and deformation recorded February-April 1988 (13:03), the June levelling traverse showed an unusually small amount of movement since September 1987. Subsidence of recent lava around Northeast Crater was <2 cm, an order of magnitude less than usual and the smallest recorded since the line was installed in 1975. Inflation of 1.6 cm measured 3.5 km NE of the summit was also unusual. Recently active areas generally showed subsidence, with downward movement of slightly > 1 cm at the 1983, 1985, and September 1986 dikes, and isolated larger movements of -6.6 cm at the 1986-87 fissure and -19 cm at the edge of Southeast Crater. The very large amounts of subsidence measured in recent years in the Valle del Leone have diminished considerably.

A very different pattern was measured during the September traverse, with broad inflation centered just SW of Bocca Nuova. Inflation extended over the entire traverse, reaching +5.3 cm at the center when compared to the southern reference station 2.5 km away, or +8.5 cm compared to stations at the N end of the traverse, 5 km away. This inflation was the largest recorded at Etna when no eruption had occurred between measurements. Most dry-tilt stations showed typical small, more or less random, tilts of apparently local origin. However, 4 stations 4-9 km to the SW showed westerly tilts of 20-30 µrad, suggesting that inflation may extend farther in that direction. Murray noted that summit inflation preceding summit eruptions was measured in May 1976, June and September 1977, September 1978, July 1980, October 1983, September 1984, and June 1986. Inflation episodes centered just SW of the summit have tended to precede Southeast Crater activity.

Small local shocks that were apparently related to summit activity were detected optically during measurements of the levelling line and dry tilt stations. Using the automatic level, relative amplitudes were obtained by noting the amount of crosshair movement against the levelling rod and correcting for distance. In June, seismicity was very quiet, with only four events noted in a week of levelling, all within 450 m of Bocca Nuova. The largest had an amplitude of ~ 60 µrad.

In September and October, seismicity had increased dramatically. On 23 September, 73 shocks were noted in 1 hour while levelling W of Bocca Nuova at a mean distance of 330 m from the rim. The shocks were much stronger than in June, with largest amplitudes reaching 250 µrad. Seismic events were detected as much as 4.6 km from the summit. W of Piccolo Rifugio, ~ 3 km from the summit, three shocks were detected in 1 hour, the largest of 35 µrad.

Information Contacts: R. Romano, T. Caltabiano, and O. Consoli, IIV; J. Murray and D. Norman, Dept of Photogrammetry and Surveying, Univ College London; D. Décobecq, Paris; J. Miller, T. Elliott, and B. Van Wyk de Vries, Open Univ; B. Bone, Lancaster.

Jump to Index of Monthly Reports

05/1989 (SEAN 14:05) Explosions from summit craters; small lava flow; high SO₂

The following, from IIV, describes activity March-April 1989.

Summit activity. (S. Calvari, M. Coltelli, and M. Pompilio.) Vigorous Strombolian activity at the two central craters (Bocca Nuova and La Voragine), persisted through March and April. At Southeast Crater, Strombolian ejections became strong and continuous during the last 10 days of March, similar to those of 24 December-24 January and 29 January-22 February. Strong explosions continued through April. A small lava flow emerged from the base of Southeast Crater's cinder cone on 15 April at 2300 and flowed over the crater's S rim. Lava effusion stopped early the next morning. Degassing continued at Northeast Crater.

Seismicity. (E. Longo, A. Montaldo, M. Patanè, E. Privitera, and S. Spampinato.) A total of 71 tectonic earthquakes (M >1.0 and S-P <5 seconds) were recorded on the Serra Pizzuta Calvarina seismic station (~ 13 km S of the summit craters) in March, compared to 194 events during all of 1988. The highest seismic energy release and the largest number of events (9, with two of M 2.7) occurred on 17 March. Tectonic events were fewer and smaller (M<=2.7) in April than in the first three months of 1989. Most of the largest events (M>=2) were located on the W flank at depths of ~ 15-25 km. High-energy volcanic tremor episodes were recorded 9-16 April and represent the only seismic evidence of the Southeast Crater eruptive episode on 15 April. After the effusive episode, the spectral amplitude of tremor greatly decreased, but remained higher than in March.

SO₂ emissions. (T. Caltabiano and R. Romano.) During the first half of March, SO₂ emissions from the summit craters were similar to relatively high February values at ~ 6,000 t/d. During the last half of March, SO₂ emissions increased to ~ 8,000 t/d, then decreased to ~2,000 t/d. After the lava effusion of 15-16 April, SO₂ emission rates rose to ~12,000 t/d, but decreased to ~3,000 t/d during the remainder of the month.

Ground deformation. (O. Campisi, G. Falzone, B. Puglisi, G. Puglisi, and R. Velardita.) Ground deformation at the Serra Pizzuta Calvarina borehole tilt station showed no significant variations during March and April.

Information Contacts: R. Santacroce, IIV.

Jump to Index of Monthly Reports

06/1989 (SEAN 14:06) Summit explosive activity

The following, from IIV, describes activity May-June 1989.

Summit activity. (S. Calvari, M. Coltelli, and M. Pompilio.) Vigorous activity at the two central crater vents (Bocca Nuova and La Voragine) continued in May. On the 4th, La Voragine ejected bombs and lapilli that fell as far as the rim of Cratere del Piano (roughly 300 m away), choking the crater bottom with tephra. In late May, explosive activity diminished and continued at a normal level throughout June. Discontinuous effusive activity was observed in May within Bocca Nuova, and bombs accumulated in the crater to ~ 100 m from the rim. From late May through most of June, many bombs, some of considerable size, fell outside the crater. This activity suddenly stopped in late June, when the small cone inside the crater collapsed, and was succeeded by sporadic scoria ejection from two vents. Mild Strombolian activity at Southeast Crater in May slightly eroded the scoria cone that had formed in April (14:05). Strombolian activity continued at a medium-low level in June, with occasional pulses ejecting small numbers of bombs over wide areas. The vent on Northeast Crater's floor continued to degas through May and June.

Seismicity. (V. Longo, A. Montaldo, M. Patané, E. Privitera, and S. Spampinato.) The frequency of tectonic seismicity in May and June was generally similar to that of the past year, with occasional seismic swarms. During the last two days in May, low-energy events were detected ~ 10 km below the volcano's central area. A seismic swarm, recorded 19-24 June on the W flank, was 13-15 km deep and included the largest events (M 3.1-3.2) of the month. One of the earthquakes (on the 24th at 0230) was felt by area residents. On 28 June, a small mainshock-aftershock sequence (11 events) was recorded, with the largest earthquake located near the S portion of the Valle del Bove at <5 km depth. From late June to 1 July, events with M 2.5-3.0 occurred 10-15 km beneath the summit. No significant variations in the volcanic tremor pattern were observed during May or June.

Ground deformation. (O. Campisi, G. Falzone, B. Puglisi, G. Puglisi, and R. Velardita.) Ground deformation measured at the Serra Pizzuta Calvarina borehole tilt station showed no significant variation in May or June. Measurements in May using the S trilateration network showed little deformation since l June 1988.

SO₂ emissions. (T. Caltabiano and R. Romano.) The average value of SO₂ flux in May 1989 was the lowest of the past year, but moderately high values returned in June. SO₂ flux was measured 3, ll, 17, and 24 May and 1, 7, 15, 22, and 29 June. Emissions fluctuated in May, with high values on the 3rd and 17th and low values on the 11th and 24th, reaching only 2,500 t/d on the latter date.

Tephra composition. (S. Calvari, M. Coltelli, and M. Pompilio.) January 1989 activity produced hawaiite tephra, with petrography and chemical composition similar to tephra from the previous year. Tephra emitted from Southeast Crater during 1988 had relatively more evolved compositions, but early 1989 tephra was less differentiated than material emitted by the other summit craters.

Information Contacts: R. Santacroce, IIV.

Jump to Index of Monthly Reports

07/1989 (SEAN 14:07) Summit Strombolian activity; little deformation in past year

Geologists observed Strombolian activity at three summit area craters (Bocca Nuova, La Voragine, and Southeast Crater; figure 28) and an incandescent gas vent in Northeast Crater during field work 26 May-1 July. Fresh-looking tephra was abundant W and SW of the summit craters, to 800 m from Bocca Nuova.

Bocca Nuova. Vigorous Strombolian activity from two vents on the crater floor, both building cones, was observed 29-30 May, 5, 18, 19, and 30 June, and 1 July. Small explosions and gas bursts averaged ~70/minute. Larger explosions ejected incandescent cowdung bombs, some of which fell 100 m beyond the crater rim. Crater depth was estimated at > 120 m. On 5 June, another glowing vent was visible on or near the flank of the largest active cone. Toward the S end of the crater floor, there was an irregularly shaped area of glowing lava, possibly a ponded flow or passive lava lake. Lava in one of the intracrater vents had a maximum brightness temperature of 1,019°C when measured with a 0.8-1.1 mm infrared thermometer. On 30 June, heat from one of Bocca Nuova's active vents was felt from the observation point on the NW rim.

La Voragine. Strombolian activity occurred from crater floor vents. Loud detonations were heard from the crater rim on 29 May; 17 were counted in 2 minutes. Ejecta were heard falling on the crater floor. During observations the evening of 5 June, four vents were visible, two of which were active. The largest of the 72 explosions counted in a 2-minute period sent bombs to 30 m above the rim. On 1 July, juvenile bombs were ejected by a glowing hornito or small cone on an apparent solidified lava lake. The 0.8-1.1 mm thermometer recorded a peak temperature of 821°C.

Southeast Crater. Strombolian eruptions continued from Southeast Crater's new cone 29 May-30 June, frequently ejecting incandescent tephra above the crater rim. On 4 June, bombs rose to 100 m above the cone. During a 10-minute period around noon, geologists counted 28 eruptions that projected bombs higher than the rim.

Northeast Crater. On 8 June, a vent 2-3 m in diameter was degassing near the middle of the crater floor. A peak brightness temperature of 462°C was recorded by an 8-14 mm infrared thermometer pointed at the vent's inner wall from ~ 50 m distance. Geologists noted that this instrument probably significantly underestimated the gas temperature (see 1 July data). There was no sign of fresh tephra. On 12 June at about 0850, four white "smoke rings" rose slowly from Northeast Crater. On 1 July, glow from the vent was visible during observations in low light shortly after 0600. A 0.8-1.1 mm infrared thermometer yielded a maximum temperature of 644°C, compared to 491° with the 8-14 mm instrument. Eight gas puffs and two more vigorous exhalations were counted in 1 minute.

Geodetic measurements. Very little vertical deformation has occurred since September 1988 (14:01). Slight subsidence was measured E of the summit, with a maximum displacement of 3 cm near the 1987 fissure (relative to a reference station 2.5 km SSW of the summit). A 3.5-cm swelling was measured on the Northeast Rift. A trilateration network on the upper E flank was reoccupied for the first time since June 1988, revealing movements of as much as 4 cm to the NE at stations in the Valle del Leone. The station on Monte Simone (4 km E of the summit) showed an anomalous displacement of 2 cm to the S since September 1987. Stations at Punta Lucia (1.5 km NNW of the summit) and Belvedere (2 km SSE of the summit) were assumed to be stable. Etna's summit elevation was determined at 3,318.4 m, using the base station near Piccolo Rifugio (2,516 m altitude) as a datum. Seismicity was detected optically through the levelling instrument, as in 1988 (14:01). During the early June levelling traverse, 36 shocks were observed, all within 2.2 km of the summit. The largest amplitudes noted were 70 µrad (1.5 km NE of the summit), 111 µrad (near Southeast Crater), and 123 µrad (400 m from Bocca Nuova).

Information Contacts: J. Murray and C. Oppenheimer, Open Univ; A. Jones, Univ of Lancaster; P. Cruddace, Univ of Newcastle; P. Aragno and S. Haefeli, SVG.

Jump to Index of Monthly Reports

08/1989 (SEAN 14:08) Explosions and lava flows; tephra reaches the coast

The following preliminary data is from R. Romano.

Strong Strombolian activity from La Voragine and Southeast Crater was followed by an explosive eruption from La Voragine during the late morning of 10 September. Tephra rose 600-700 m, and the resulting plume, carried E by the wind, deposited ash and lapilli along a narrow, well-defined, path that extended to the coast. After strong explosive activity and lava fountaining, lava spilled over the rim of Southeast Crater early the next morning, forming fluid, fast-moving flows that reached the Piano del Lago (on the upper S flank). During the nights of 11, 12, and 13 September, four more episodes of strong activity occurred, feeding lava flows that advanced SE, S, and SW; these were also very fluid and descended ~ 2 km to 2,640 m elevation. During this period, with brief exceptions, a small lava lake remained visible within Southeast Crater, and was the location of lava fountains that reached average heights of a few hundred meters.

A violent explosive episode that began at about 0900 on 13 September ejected incandescent pyroclastic material to more than 1 km height. Winds again carried the plume toward the E, leaving a narrow band of scoria, lapilli and ash that reached the coast. Press reports said that tephra fall lasted for ~ 15 minutes and some of the lapilli reached walnut size. No injuries were reported, but numerous cars were damaged, and traffic was slowed by nearly 4 cm of ash on the lower flanks. During the explosive activity, felt seismicity on the upper flanks increased substantially but subsided after a few hours.

The plume from the explosion at 0900 was not evident on weather satellite images, but data returned 4 hours earlier, at 0500, showed a plume 15-20 km wide extending ~ 100 km E from Etna. The plume had dissipated by about 0800. During the day on 14 September, no eruptive episodes occurred, and the magma column remained low.

Preliminary estimates suggest that an area of ~0.5 km² was covered by ~ 5x10⁵ m³ of lava. No estimates of the volume of pyroclastic material were available at press time. Similar activity occurred at the NE crater in 1977-78.

Information Contacts: R. Romano, IIV; A. Brown, NOAA/NESDIS; UPI.

Jump to Index of Monthly Reports

09/1989 (SEAN 14:09) Strong tephra emission; lava fountains >1 km; lava flows

The following supplements the preliminary report in 14:08.

Through 26 September, the eruption was dominated by vigorous Southeast Crater activity that fed upper-flank lava flows and ejected tephra that reached the coast. Fissures opened on the upper E flank 27 September, producing lava flows that advanced ~ 6 km before activity stopped on 9 October.

[Fourteen] strong eruptive episodes that occurred 11-26 September included vigorous explosive activity from Southeast Crater with lava fountains that rose > 1 km. Violent Strombolian activity alternated with periods limited to ash ejection, particularly during the first days of the eruption. Winds initially carried eruptive clouds E and S, then E and NE, with ashfalls reaching Catania (roughly 30 km SSE of the summit). Very fluid lava flows moved S and SSE (Piano del Lago), SE and E (Valle del Bove), and NE (Valle del Leone). The lava flows reached 2,600 m elevation (~ 2 km from the crater) in the Piano del Lago, and the base of the Valle del Bove's W wall at ~2,000 m (3-4 km from the crater).

A team from the Open Univ (P. Francis, C. Oppenheimer, and D. Rothery), the Jet Propulsion Laboratory (L. Glaze and D. Pieri), and IIV (T. Caltabiano) carried out field work 22-29 September. Lava fountaining and Strombolian activity occurred about every 10-12 hours from Southeast Crater. The activity fed many aa flows ~ 100 m long in addition to the more fluid flows that advanced farther downslope. Their detailed chronology of a 24 September Southeast Crater eruptive episode, apparently typical of 23-28 September activity, is shown in table 3.

Table 3. Description of the 24 September 1989 eruptive episode at Etna's Southeast Crater, observed by L. Glaze, C. Oppenheimer, and D. Rothery from 900 m away at the Torre del Filosofo. Temperatures were measured with a Cyclops 33 infrared thermometer (8-14 mm bandpass), but were lower than true values because the 1° field of view always included some air or cold ash.

    Time       Description of activity

    0940-0955  Gray ash clouds rose 50-100 m above the rim every few minutes.
                 The Central Crater was fuming strongly, but produced no ash.
    0955-1035  Sustained gray ash eruption to 100 m above the rim.
    1038       Ash column production ceased, but explosions were audible. Peak
                 column base temperature, 288°C.
    1040       Bombs began to rise above the rim.
    1050       Semi-continuous Strombolian ejection with some red
                 incandescence. No distinct tephra column.
    1103       50-m lava fountain; maximum temperature of 443°C at its visible
                 base.
    1105       Onset of fine ashfall at the Torre del Filosofo (TDF).
    1108       Continuous noise; fountain to about 80 m above the rim.
    1115-1117  Temperature at the fountain's visible base, 280-882°C. Brown
                 smoke rose E of the crater, probably from lava advancing
                 toward the Valle del Bove.
    1120       Lava fountained to 160 m above the rim, surmounted by a
                 convectively rising ash/scoria column.
    1124       Maximum temperature of the visible column base 693°C with the
                 Cyclops 33, but 983 with a Cyclops 52 (0.3 field of view,
                 0.1-1.1 micron bandpass).
    1126       Centimeter-size scoria fall began at the TDF.
    1129       Incandescent material rose above the rim from a second western
                 source within the crater. The two sources soon joined to feed
                 a single lava fountain with a sustained height of 250 m above
                 the rim.
    1136       A clast-fed lava flow began on the crater's SW flank. 2-cm
                 tephra fell at the TDF a minute later.
    1145       Brick-size bombs fell 100 m E of the TDF, where 4-cm tephra was
                 falling 2 minutes later.
    1200       Lava fountained to more than 300 m above the rim with jet
                 engine roaring. A convective ash/scoria column rose to
                 considerable (but undetermined) altitude.
    1205       A fissure developed on the crater's SE flank, and lava
                 fountaining from the fissure fed a flow. The fountain's
                 infrared temperature  was 614° C at 1211. By 1224, the
                 fissure had become the source of the main column, with
                 incandescent material rising 200-300 m.
    1233       Roaring noise stopped for about 3 seconds, then activity
                 declined and had virtually ceased by 1238.

Geologists from the Ruhr Univ visited Etna 22-30 September. Eruptive episodes that included lava fountains up to 500 m high, ash emission, and lava flows from Southeast Crater and associated fissures, occurred once or twice daily during their first five days. They provided the following chronology of activity observed from Nicolosi, 15 km to the S.

22 September, 2100-2330: Lava fountains to 500 m height, lava flows mainly directed toward the Valle del Bove.

23 September, 2000-2015: Vigorous lava fountains (probably higher than the previous night) and lava flows to the Valle del Bove.

24 September, 0930-1200: Initial small ash puffs from Southeast Crater were followed by high lava fountains. New fissures opened at the base of Southeast Crater, and lava flows moved S, cutting off the road to the Torre del Filosofo (900 m from Southeast Crater).

25 September, 0530-0900: Lava fountains rose 300 m, a 4-km vapor plume was ejected, and lava flowed into the Valle del Bove. Loud rumblings were heard from Nicolosi near the end of the activity. Strong ash emission from Southeast Crater and Bocca Nuova lasted from 0700 to 0900. 1900-2000: Lava fountained to 300 m height from at least four vents in Southeast Crater and a lava flow advanced toward the Valle del Bove.

26 September, 0600-0710: Lava fountains reached 400 m height and powerful ash ejection fed a column that rose 5-6 km above the summit within 30 minutes. Lava flowed into the Valle del Bove. At 0645, a brown, cauliflower-shaped ash cloud rose from the Valle del Bove, suggesting a possible flank outbreak. However, ash emission from that site ceased after a few minutes and no flank eruption was confirmed by other observers. 1210-1215: A series of ash puffs rose from Southeast Crater, but no additional eruption followed. 2000-?: High lava fountains were ejected, lava flowed to the Valle del Bove, and a new vent formed near Southeast Crater.

27 September, about 1200: Ash emission resumed from Southeast Crater. Dark gray ash clouds rose continuously to ~ 100 m above the vent before being carried E by strong winds. Ash emission continued through the evening. After nightfall, a bright glow was visible above the Valle del Bove and small fountains emerged from Southeast Crater once or twice/minute.

R. Romano reports that in the late evening of 27 September (around 2230) two new sub-parallel eruptive fissures opened on the upper E flank at 2,600 and 2,575 m altitude (between Valle del Leone and Valle del Bove, SE of Pizzi Deneri), preceded by a brief seismic crisis. Strombolian activity, violent at times, was initially continuous along the fissures, forming hornitos and scoria ramparts. Lava flows from the upper fissure did not extend beyond (but generally entered) the main lava channel formed by the primary effusive vent at the base of the lower fissure (2575 m altitude). The lava flows, moving generally SE, passed S of Monte Simone, widening at ~ 1,750 m altitude.

During the morning of 28 September an extensive field of NNW-trending non-eruptive fractures formed in the Piano del Lago, propagating in succeeding days to the W and S wall of the Valle del Bove. The fractures also extended downslope, past the edge of Serra del Solfizio, on a NW trend. By the morning of 2 October new fractures had opened to the Zafferana-Rifugio Sapienza road (route 92) ending around 1,500 m elevation, below the effusive vents of 1792. Total length of the fractures was ~6 km.

Ruhr Univ geologists climbed Etna on 28 September. Ash emission from Southeast Crater remained continuous. Around noon, brown ash plumes rose from the vent in pulses every 3-5 seconds, accompanied by block and bomb ejection. No glow was seen. Dense weather clouds obscured visibility during the afternoon, but a distinct increase in noise suggested the onset of Strombolian explosions. As night fell around 1800, weather clouds dissipated and Strombolian bursts were visible every 5-10 seconds, ejecting bombs and spatter to 300 m height. The lava flow in the Valle del Bove apparently emerged from a fissure in its NW part. The non-eruptive fractures that had opened parallel to and ~ 50 m W of the rim of the Valle del Bove during the morning, had vertical displacements that sometimes exceeded 1 m; some were 1.5 m wide and several meters deep. The next day, ash and bomb ejection from Southeast Crater increased considerably at about 0730, with dark gray columns rising 150-200 m despite a very strong W wind. Large bombs often rose higher, falling on the flanks of the cone that was rapidly growing around the vent. Expulsion of ash and blocks occurred every 5-10 seconds, accompanied by hissing and rumbling sounds. No glow was visible. Numerous impact craters as much as 1 m wide and 0.5 m deep, probably produced by the strong 13 September activity (14:08), were found at the site of the 1971 Observatory cone, 500 m SW of the active crater. At 1900, lava fountains were again visible in Southeast Crater, with bombs and spatter sometimes rising 350 m. Lava continued to flow into the Valle del Bove. Similar activity was continuing late 30 September.

R. Romano reports that during the following days a wide lava channel formed, extending E after passing Rocca Musarra to the S. Lava flows branched from this channel, passing a line connecting Monte Calonna and Monte Fontana on 6 October, and reached ~ 1,100 m elevation (~ 6 km from the fissure vents). The lava flows stopped ~ 3 km from the nearest town (Milo). Lava production from the vigorous effusive vent at 2,575 m altitude was very strong during the first days of its activity (30-40 m³/sec), started to diminish beginning 3 October, and stopped completely on 9 October.

Preliminary estimates indicate that a [3] km² area was covered by lava, and lava volume was [~24] x10⁶ m³ (within the Valle del Bove). No estimates are available for volumes of pyroclastic material and lava ejected by the Southeast Crater. Information remains preliminary and incomplete, and will be revised in coming months with more detailed reports, geophysical and geochemical data, and maps of the lava flows and fractures.

Information Contacts: R. Romano, IIV; B. Behncke, Ruhr Univ; D. Rothery, Open Univ.

Jump to Index of Monthly Reports

10/1989 (SEAN 14:10) Details of September-October eruption

The following report (quoted sections technically edited by F. Barberi, A. Bertagnini, P. Landi, and R. Rapuzzi) summarizes studies of Etna's recent activity.

Eruption chronology. "The vigorous Strombolian activity at three summit area craters (Bocca Nuova, La Voragine, and Southeast Crater) observed during May, June, and July (14:07) declined during the first 20 days of August, then progressively resumed in the last 10 days of the month. On 29 and 31 August, after some days of Strombolian activity, La Voragine emitted a 700-m-high tephra column with fallout of lapilli and ash that affected the SE flank to the coast, 19 km from the crater.

"In the first days of September, Strombolian activity also increased at Bocca Nuova and in the morning of 10 September an explosive eruption, identical to those of 29 and 31 August, occurred again at La Voragine. Beginning in the early hours of 11 September, Strombolian activity also resumed at Southeast Crater, then progressively evolved into lava fountaining. Lava spilled over the rim of Southeast Crater, forming two fluid, fast-moving flows that traveled ~2 km SE. Explosive activity and lava spillover then suddenly ceased, indicating lowering of the magma column in the conduit. On the evening of the same day, and 12 more times until 27 September (figure 29), new episodes of vigorous Strombolian activity, evolving into lava fountaining with effusion, were observed at Southeast Crater, each suddenly ceasing and giving rise to slow degassing followed by the resumption of less vigorous Strombolian activity. Lava flows emitted during these 14 effusive episodes were confined to the upper S and SE flank area (Torre del Filosofo-Cisternazza) and descended 2.5-3 km S and SE (figure 30)."

During fieldwork on the 23rd, geologists observed that the area between Southeast Crater and the TDF was covered by fresh aa, in a flow field that had advanced around the TDF and continued southward. The most distal lobes stopped moving on 22 September.

"Near the end of the lava fountaining phase, in at least six cases (13, 19, 22, 23, 25, and 26 September) a sustained tephra column was formed, with consequent lapilli and ash fallout over the E and SE flank to the coast. On [24] September, two fracture systems, trending [N40°E] and N140°E, opened on the flanks of the newly formed Southeast Crater cone, down to elevations of 2,800 and 2,900 m respectively. An appreciable quantity of lava spilled either over the Southeast Crater rim or from the two newly formed fractures on 25 September and in the following two days. In the morning of 25 September a lava flow from the NE fracture descended 3 km in the Valle del Bove, to 1,900 m (M. Simone area, figure 30). The last episode of lava fountaining and effusion at Southeast Crater occurred the morning of 27 September. Since that afternoon the crater has been characterized by Strombolian activity and ash emission."

On the evening of 27 September, the focus of activity shifted to the NE fracture system. "At about 2200 a small fast-moving flow was emitted from the terminus of the NE fracture, and descended 2 km in the Valle del Bove. The Strombolian activity of Southeast Crater then [temporarily] ceased, and between 2300 and 2330 a series of eruptive vents opened at 2,550 m elevation in the Valle del Leone (upper part of the Valle del Bove), preceded and accompanied by a vigorous seismic swarm. These vents were aligned along a N50°E fracture, on the extension of the fracture cutting the NE flank of the SE cone (figure 30). Lava poured from 3-4 vents, where degassing was minor with ejection of lava fragments to only a few meters height. The various lava tongues converged a short distance from the fracture into a main channel, 10 m wide, where lava advanced rapidly. At dawn on 28 September the flow had descended 5 km in the Valle del Bove, reaching Rocca Musarra at ~ 1,650 m elevation.

"That morning, the SSE fracture (extending N140°E from Southeast Crater) was also seen to have progressed downslope. This newly formed part of the fracture system affected a 100-m-wide sector, extending down 2.5 km (to Cisternazza) and to the upper (W) part of the Valle del Bove. Fracture propagation continued on 29 and 30 September, when the S scarp of the Valle del Bove was affected. On 1 October the fracture, accompanied by marked collapses along the fissure system, crossed the Valle del Bove scarp and propagated farther downslope, following the feeding fissure of the 1792 flank eruption. At 1200 on 2 October the fracture cut route SP92 connecting Zafferana to Rifugio Sapienza. The seismic activity that accompanied the entire fracturing process peaked at that time, with ~40 shocks/hour (figure 31). In the following hours, seismic activity rapidly declined and fracture propagation stopped at ~ 1,500 m elevation, 8 km from Southeast Crater. In the following three days only widening of single fissures was observed, with development of consistent compressive structures (uplift folding, reverse faulting) on both sides of the main extensional (open) fissure."

During fieldwork the night of 1 October (by C. Oppenheimer, M. Pompilio, M. Coltelli, and V. Scribano) the flow near the NE fracture's main vent was ~ 8 m wide, and its center was moving at faster than a walking pace. Blocks of lava tossed onto the flow welded instantly but did not sink. A maximum lava surface brightness temperature of 1,039°C was measured by a 0.8-1.1 mm bandpass infrared thermometer (recording for 10 minutes, 3 m from the flow top).

Guy Kieffer notes that the axes of the two fracture systems that opened during the eruption had both been frequently active during the eruptive cycle that began in 1971: the NE axis in 1971, 1978, 1979, and 1986-87; and the SSE axis in 1971, 1978, 1979, 1983, and 1985 (along a southward extension). The NE axis had also been active during the 1811, 1865, and 1928 eruptions, and the SSE axis in 1792, 1908, and 1910. As in the present eruption, fissures had opened from the SSE base of the central cone in 1874, 1911, and 1923 without producing any lava, while lava was emitted from N flank fissures. The 1989 eruption's SSE fracture had opened ~ 45 cm and had a right-lateral displacement of ~ 15 cm (on 7 October) where it crossed route SP92. Kieffer suggested that the SSE fracture was the result of an offset caused by intrusion below Southeast Crater, added to several years of accrued stresses as part of the E flank is forced eastward.

"Lava outpouring from the Valle del Leone fissure continued until 2 October without significant variation in the effusion rate. From 3 October, oscillations, but with a slow progressive decrease, were observed in the rate of lava effusion. During temporary phases of effusion rate increase, eruptive vents were reactivated at higher elevation on the NE effusive fracture. New hornitos were formed, 50 m above those at the 1,550-m vents, accompanied by a series of lava overflows. The effusion rate decreased further on 6 October and lava emission stopped during the night of 8-9 October.

"During the same period, explosive activity continued at Southeast Crater. After the late morning of 28 September ash-laden clouds were emitted from the crater, which also showed Strombolian activity of variable intensity." When observed by C. Oppenheimer on 29 September, discrete eruptions of ash and blocks about every 30 seconds were superimposed on continuous ash emission. Ballistic trajectories of incandescent bombs that rose >400 m above the crater were visible at night.

"Tephra were dispersed eastward by the wind, causing ash showers on Catania and eastern villages, especially on 3 and 4 October. Limited episodes of lava fountaining last occurred during the night of 3-4 October. Strombolian activity stopped during the night of 6 October, whereas discontinuous weak ash emission continued until 9 October. Southeast Crater appeared almost totally obstructed on 11 October. Ash emission and vigorous degassing continued, since 9 October, only at Bocca Nuova.

Lava flows. "Etna's 27 September-9 October flank eruption produced an aa flow field in the Valle del Leone-Valle del Bove ~ 6.5 km long and 5-10 m thick, with a volume of 10-20 x 10⁶ m³. The flows descended from ~2,550 to 1,100 m elevation. The average effusion rate is estimated at 10-20 m³/second, with peak daily average values during the first 4 days of eruption (until 2 October) of between 15 and 25 m³/second. Combinations of the overall emplacement characteristics (e.g. length-average effusion rate, length-volume, width/length-duration) of the flow fields lie within ranges typical for Etna's historic lavas. Velocity and dimension measurements of active overflows at the feeding vent (Valle del Leone, ~ 2,550 m asl) on 2 and 4 October suggest apparent viscosities for the initial lava of the order of 10,000 Pas, for bulk shear rates between 0.01 and 0.1/s. Thermocouple data yielded a surface temperature of 800°C on the overflow (after it had advanced ~ 50-75 m) on 2 October. Preliminary analysis of infrared data obtained on the ground on 5 October suggests a similar temperature for incandescent cracks in an active flow front ~ 6 km from the vent.

Petrology. "The lavas are porphyritic (P.I. = 30-40) alkali basalts with phenocrysts of plagioclase, clinopyroxene, and olivine, and microphenocrysts of Ti-magnetite. There are only minor differences, in size and relative abundance of phenocrysts, between the Southeast Crater flows and the Valle del Leone lavas. Two representative chemical analyses are shown in table 4. The 1989 lavas are slightly more mafic and magnesian than those of either the last Etna eruptions (1986-87 average) or Southeast Crater in 1988.

Table 4. Chemistry of 1989 lavas from Etna's Southeast Crater (11 September) and the Valle del Leone 93 October). Analyses by X-ray Flourescence at the Dipt. di Scienze della Terra, Univ. di Pisa, except Na₂O and MgO (Atomic Absorption Spectrophotometer) and FeO (titration) at IIV.

    Oxide   Southeast Crater   Valle del Leone

    SiO2        47.46              46.70
    TiO2         1.78               1.78
    Al2O3       18.11              17.36
    Fe2O3        2.83               4.30
    FeO          7.32               7.41
    MnO          0.19               0.20
    MgO          5.57               5.84
    CaO         10.39              10.25
    Na2O         3.45               3.51
    K2O          1.99               1.81
    P2O5         0.44               0.41
    LOI          0.48               0.44

Civil Protection aspects. "The lava flow emitted from the SE fractures in the Valle del Leone did not present any serious civil protection problem. Flow fronts advanced very slowly at elevations lower than 1,200 m. The flow was confined within the totally uninhabited Valle del Bove and never threatened villages or lifelines. However, the propagation of the SE fracture system from Southeast Crater downslope caused serious concern. Because of strong seismic activity and marked uplift on that sector of the volcano, route SP92 was closed to traffic 24 hours before it was cut by the fracture. The terminus of the fracture was located in a zone that had been affected by flank eruptions in the past (e.g. in 1792). It was at low elevation (~ 1,500 m) and only 5-6 km from villages (Malpasso, Fleri), a distance that could be traveled by a fluid lava flow in a dangerously short time, considering that magma was at the surface in Southeast Crater vent (3,000 m elevation) and hence there was a very high potential load (1,500 m of lava column) on the fracture apex.

"The more probable paths of lava flow in case of effusion from a vent at 1,500 m elevation were estimated on a morphological basis. People living on the potential lava trajectories were alerted to the potential risk and a plan was established for their prompt evacuation.

"Scientific monitoring at the fracture terminus was expanded and reinforced with a mobile seismic network, precision levelling, microgravimetry, geodimeter lines, and soil gas geochemistry. I gas;sampling Visual observation points (24 hours/day) were established near the fracture apex and along the expected flow path, radio linked with the army units responsible for the emergency plans.

"The alert system was maintained until 16 October. Then, with six days having passed since the end of eruptive activity and without any sign of potential volcanic activation of the SE fracture, the eruption was considered concluded.

Seismicity. "Seismic activity has been monitored since early summer 1989, using both the IIV's permanent array (8 stations) and a temporary array operated by the OV (up to 11 three-component telemetered digital stations). The daily frequency histogram is shown in figure 31.

Pre-eruptive period. "Five major seismic sequences were recorded from late July to late August; none of the events exceeded M 3.3. Focal depths, calculated with respect to the highest stations (at 2,900 m asl) ranged from ~ 15 km (3 August, 45 events) to <4 km (27 July and 17-18 August, 24 and 18 events respectively). On 21 and 28 August, two sequences, with 16 and 12 events respectively, were located at intermediate depths of 5-8 km. No remarkable microseismic activity was observed between 29 August and the start of the eruption.

Eruptive period. "On 23-24 September, a swarm of 84 events (M >3.2) was located at ~20 km depth. Three days later, during a period of large fluctuations in tremor amplitude, intense microseismic activity preceded and accompanied the opening of the eruptive fissures on the E flank. Because of its weakness (only 19 events of M>2), this activity was clearly observed only at the nearest station (PDN, ~ 1 km from the new vents).

"More than 1,000 shallow events (depth <2.0 km; M<=3.0) accompanied the propagation of the fracture system toward the SE between 28 September and 2 October. The geometry of the seismic arrays was quickly modified to obtain adequate coverage of the focal area; a small and dense array composed of three digital three-component, and three analog one-component stations, was installed across the S part of the fracture. The seismic crisis had nearly finished by 3 October.

Volcanic tremor. "Volcanic tremor was monitored at stations PDN (hourly analysis) and SLN (real-time analysis). A rapid increase in tremor energy was recorded during the morning of 10 September. The level of tremor remained high for four days, with an estimated daily energy release of 1017 ergs (1010 J), then dropped by about an order of magnitude (figure 32). Between 18 September and 6 October, near-periodic (daily/half-daily) oscillations could be distinguished in the tremor amplitude (minor peaks in energy release on 19, 22, 25, and 27 September, and 4 October). With the end of the eruption on 9 October, tremor amplitude dropped to the pre-crisis level. Energy spectra analysis of 5-minute samples from station SLN shows steady peaks in the 1.4-1.9 Hz band, independent of energy level, while spectral displacements to higher frequencies were occasionally observed at station PDN.

Ground deformation - tilt. "Tilt data have been collected at an IIV borehole biaxial tilt station (SPC), located along the SE flank at ~ 1,600 m elevation. Continuously monitored tilt signals indicated a positive variation of the radial component (crater up), clearly exceeding the signal confidence limit, since the beginning of June 1989. The tangential component of the tilt remained practically flat until the beginning of the fracturing phase affecting the SE flank by 2 October. Both radial and tangential tilt underwent a sharp variation by the afternoon of 1 October, suggesting a rapid inflation of the Valle del Bove's S outer flank, where the fracture later propagated. The almost constant ratio between the two tilt components throughout this phase of the deformation process depicts a resultant tilt vector trending approximately N25°E (up) and totaling 14 µrad by the end of the deformation phase.

"Additional tilt data were obtained by two stations (sensor made of a pair of horizontal pendulums) installed by IIV and IPGP. The two automated stations (GIA and TRE) recorded an uplift of the summit area since the first 10 days of June (radial component, figure 33). Marked variations were recorded during the SE fracture propagation, particularly at TRE station, only 200 m from the fracture.

Ground deformation - geodimeter. "A trilateration network on the SE flank area had been previously surveyed in 1987, 1988, and May 1989. Daily EDM measurements were made on some of the network benchmarks since 30 September, before the fracture propagated downslope. Horizontal strain solutions for the main deformation phase that occurred on 2 October indicated an overall areal contraction (~152 ppm) with a minimum extension axis of about -206 ± 80 ppm striking N30°E; maximum shear was 260 ppm. Distance measurements across the main fracture system, at ~ 1,700 m elevation, indicated a local extension of up to ~ 1 m between May 1987 and October 1989.

Ground deformation - levelling. "Precise levelling surveys around the circumference of the volcano and across the new fracture system where it cuts route SP92 were carried out 2-16 October. With respect to September 1988, the N part of the volcano had remained stable, while relative sinking had occurred at the station closest to the central crater (20 mm) and across the fault at Piano Pernicana (25 mm; figure 34). Along route SP92, repeated surveys 6-16 October indicated a relative sinking near the new fracture system of ~ 14 mm.

Microgravimetry. "On 3 October the pre-existing microgravimetric network (OV, IIV) was expanded near the fracture cutting route SP92. A new 2-km-long E-W line was established, with eight stations symmetrically arranged across the fracture, each coinciding with a precision levelling benchmark. Gravity measurements were carried out on 3, 4, 6, and 11 October. Differences from 3 to 4 October (figure 35) show a positive variation of the gravity field with a maximum (18 ± 7 microgal) corresponding to the fracture. Subsequent gravity variations remained mostly within the error range. Correction for levelling data does not appreciably modify these results.

Geochemistry - COSPEC data. "A slow increase in SO₂ output from the summit craters was observed in August 1989, with a transition from very low values (1,000 t/d) to medium-high values (~ 7,000 t/d). In the first half of September, SO₂ flux remained around medium values. Since 14 September, coinciding with the Valle del Leone effusive phase, SO₂ emission increased markedly with oscillation around 15,000 t/d, three times the average Etna values. [Measured rates of SO₂ emission exceeded 25,000 t/d on one day around 18 September and reached ~ 23,000 t/d on another day near 1 October].

Geochemistry - soil gases. "From 3 to 14 October, CO₂ was measured in the soil close to the terminus of the SE fracture. CO₂ concentrations were determined at a soil depth of 50 cm by an IR spectrophotometer, and varied from 0 to 1,500 ppmv, with a clear anomalous degassing at the fracture which showed a progressive decrease with time (figure 36). In addition, CO₂ concentration in the soil was measured continuously at one of the points. Two sharp peaks were recorded on 3 and 8 October, while later CO₂ concentrations remained quite constant (figure 37).

"From 9 to 13 October another soil-gas survey was carried out across the fracture. Data from 140-cm soil depths did not show any anomalous H₂ and CO degassing but the data from 60-cm depths were significantly higher than atmospheric: they ranged from 3 to 12 ppmv for H₂ and 0.3-58.8 ppmv for CO. The meaning of this difference of gas concentration between 140- and 60-cm-deep holes must be further investigated."

Information Contacts: Many scientists and technicians were involved in the September-October Etna eruption, coordinated by the National Volcanic Group.

Scientific coordination and Civil Protection problems: F. Barberi, Univ di Pisa; G. Frazzetta and R. Santacroce, IIV; F. Innocenti, Univ di Pisa; G. Luongo, OV; R. Mazzuoli, Univ di Cosenza; L. Villari, Univ di Messina.

Volcanological Observations: R. Azzaro, S. Calvari, M. Coltelli, G. Frazzetta, G. Lanzafame, M. Pompilio, and R. Romano, IIV; V. Scribano, Univ di Catania; F. Barberi, A. Bertagnini, F. Innocenti, and P. Landi, Univ di Pisa; C. Kilburn, OV; L. Glaze, JPL.

Petrology: P. Armienti and F. Innocenti, Univ di Pisa; S. Calvari, M. Carà, M. Coltelli, and M. Pompilio, IIV.

Seismicity (24-hour monitoring): E. Privitera, R. Allotta, C. Cardaci, O. Cocina, D. Condarelli, V. Longo, A. Montalto, D. Patanè, A. Pellegrino, S. Rapisarda, S. Spampinato, and O. Torrisi, IIV.

Seismicity (OV mobile network and tremor): F. Ferrucci, G.P. Ricciardi, M. Calì, M. Capello, M. Castellano, U. Coppa, R. D'Alessandro, J. Dorel, D. Ereditato, V. D'Errico, G. Gaudiosi, C. Godano, and G. Milano, OV.

Seismicity – Univ di Catania: S. Gresta, G. Lombardo, and G. Patanè, Univ di Catania.

Ground deformation (IIV tiltmetry and geodimetry): L. Villari, Univ di Messina; A. Bonaccorso, O. Campisi, O. Consoli, B. Puglisi, G. Puglisi, and R. Velardita, IIV.

IIV-IPGP tiltmetry: P. Briole, G. Nunnari, G. Puglisi.

OV levelling: F. Obrizzo, H.A. Ali Naghi, C. Del Gaudio, C. Ricco, V. Sepe, OV.

Microgravimetry: G. Budetta, IIV; M. Grimaldi, OV.

Geochemistry (COSPEC): T. Caltabiano and R. Romano, IIV.

CO₂: M. Valenza, G. Capasso, M. Carapezza, W. D'Alessandro, S. Giammanco, S. Gurrieri, J. Hauser, and F. Parello, IGF, Palermo.

H₂ and CO: R. Cioni, G. Chiodini, A. Pescia, B. Raco, and G. Taddeucci, IGGI, Pisa, and Univ di Perugia.

Others: G. Kieffer, Univ Blaise-Pascal; C. Oppenheimer and D. Rothery, Open Univ.

Further References: Barberi, F., Bertagnini, F., and Landi, P., eds., 1990, Mt. Etna: the 1989 eruption: CNR–Gruppo Nazionale per la Vulcanologia; Giardini, Pisa, 75 pp. (11 papers).

Briole, P., Nunnari, G., Puglisi, G., and Murray, J., L'Eruption de Septembre-Octoberobre 1989 à l'Etna (Italie): quelques informations quantitatives fournies par la géodesie et l'inclinométrie: Comptes Rendus de l'Académie des Sciences, v. 310, série II, no. 13, p. 1747-1754.

Jump to Index of Monthly Reports

11/1989 (SEAN 14:11) Summit tephra emission; strong, fluctuating SO₂ emission

The following, from IIV, summarizes the much milder activity in November.

Summit activity. (S. Calvari, M. Coltelli, and M. Pompilio.) November summit activity was limited to discontinuous tephra emission from Bocca Nuova. Tephra emission episodes were frequent during the first two weeks of the month, often associated with deep explosive activity. Tephra emission became sporadic in the second half of November, although continuous activity was observed on the 19th. No juvenile material was ejected. La Voragine and Southeast Crater remained closed, with only weak fumarolic activity on their floors. Degassing from the vent at the bottom of Northeast Crater continued from previous months.

Seismicity. (E. Privitera, C. Cardaci, O. Cocina, V. Longo, A. Montalto, D. Patané, A. Pellegrino, S. Rapisarda, S. Spampinato, and O. Torrisi.) Seismic activity was very low in November. The three most energetic events following the eruption seismicity occurred 31 Oct at 0752 (M 3.0, 9 km depth, in the S. Alfio area, ~ 13 km E of the summit), 10 November at 0319 (M 3.6, 14 km depth, S of the seismic network near Pantano di Lentini, roughly 50 km S of Etna), and 20 November at 0754 (M 2.4, 15 km depth, in the Sciara del Follone area on the N flank). Recorded tremor remained similar to the pattern observed by the end of the eruption.

Ground deformation. (A. Bonaccorso, O. Campisi, G. Falzone, B. and G. Puglisi, and R. Velardita.) No significant variation has been observed in data from a borehole tilt station (SPC) on the SE flank at ~1,600 m elevation.

SO₂ flux. (T. Caltabiano and R. Romano.) SO₂ flux stabilized at intermediate values (~ 5,000 t/d) at the end of October, but increased in November, reaching 12,000 t/d on the 17th. Rates then declined, to 2,000 t/d on 28 November. A similar fluctuating pattern was observed during the three months (June-August) preceding the recent eruption, and during the same period in 1988 (not followed by an eruption).

Information Contact: R. Santacroce, IIV.

Jump to Index of Monthly Reports

12/1989 (SEAN 14:12) Southeast Crater explosive activity drops tephra on nearby towns

Summit activity. (S. Calvari, M. Coltelli, O. Consoli, M. Pompilio, V. Scribano.) After only fumarolic emissions from Southeast Crater in November (14:11), renewed activity began on 16 December with continuous ejection of reddish cinders. The activity continued for the following two days, becoming weaker on the 18th. A new vent on the crater bottom, observed 21 December from the rim, exhibited strong explosive activity, but without visible tephra ejection. The activity became somewhat more intense during the following days. Only very small cinders (probably juvenile) reached the crater rim. Strong, deep, explosive activity was noted at Bocca Nuova, but there was no evidence of new tephra on the crater rim. La Voragine was obstructed and characterized by weak fumarolic emissions from the crater bottom. Gas emission from a vent on the floor of Northeast crater continued as before, but reddish cinders and gas were emitted on the 16th.

Seismic activity. (S. Privitera, C. Cardaci, O. Cocina, V. Longo, A. Montalto, D. Patane, A. Pellegrino, S. Spampinato.) Seismic activity in December returned to levels similar to those preceding the July-October seismic and eruptive activity (14:7-11). Five events with M>2 were recorded at 5-10 km depths on the Valle del Bove and the volcano's W sector. The most energetic event (M 2.8) occurred 9 December on the E part of the Valle del Bove at 9 km depth. The number and energy of low-frequency events increased, with maximum activity recorded on 16 December. Tremor amplitude also increased and was characterized by energy fluctuations, especially on the 18th and 19th.

Ground deformation. (A. Bonaccorso, O. Campisi, B. and G. Puglisi, R. Velardita.) Preliminary interpretation of the signal at the SPC borehole tilt station on the S flank showed no significant variation during December. Deformation measured on the NE trilateration network was characterized by shear, with almost equal moduli of the main strain axes. Distance measurements across the fracture on the volcano's S side indicate general stability relative to 7 October and 11 November surveys.

Summit crater SO₂ flux. (T. Caltabiano, R. Romano.) Samples collected 7, 20, and 29 December revealed that SO₂ flux had stabilized below the mean value of 4,000 t/d. A relatively low value (2,000 t/d) was recorded in late November. December 1989 SO₂ flux was slightly higher than the December 1988 trend, probably related to a longer-period flux component.

Early January activity. A seismic phase characterized by fluctuations in the mean amplitude of volcanic tremor began on 4 January at 1950 and was recorded at the ESP station of the permanent Mt. Etna seismic network. Iseismicity;amplitude By 5 January at 0120, the amplitude had stabilized at medium-high values. The most energetic phase was recorded between 0730 and 0922 on several seismic stations. During the following hours, tremor amplitude decreased, but sporadic 1-minute fluctuations brought the tremor amplitude to normal levels. The seismic phase was probably accompanied by lava fountaining at Southeast Crater, but bad weather prevented direct observation. The activity deposited lapilli and small scoria (up to 4 cm) on the NW side of the volcano in the Bronte-Randazzo area, with a dispersion axis oriented toward the town of Maletto (15 km NW of the summit crater). Scoria 13 km from the summit crater was 2-3 cm in diameter. Fieldwork in the following days revealed that a small amount of lava had poured over Southeast Crater's rim, probably due to lava fountaining. The 300-m lava flow, ~ 50 m wide and 1-2 m thick, reached the lowermost 1971 crater. As of 10 January, Southeast Crater showed no explosive activity.

Information Contact: R. Santacroce, IIV.

Jump to Index of Monthly Reports

01/1990 (BGVN 15:01) Renewed Southeast Crater Strombolian activity; flank tephra fall and small lava flows; increased seismicity and SO₂

Summit activity. (S. Calvari, M. Coltelli, O. Consoli, M. Pompilio and V. Scribano.) Eruptive activity that resumed in December at Southeast Crater continued in January, with explosive episodes of Strombolian activity and lava fountaining 4-5, 12, and 14-15 January. The first episode of Strombolian activity deposited 1 to a few cm of ash on the NW flank. Lava poured from the S crater rim, reaching the 1971 eruptive craters (at least 200 m from the vent). A smaller amount of tephra ejected by similar activity on 12 January was carried a few hundred meters WNW by the wind. Lava spilled over the N crater rim, producing a flow 1.5 km long and 20-30 m wide that traveled NE along the September-October fracture system to ~ 2,700 m altitude. When activity ceased, Southeast Crater was completely obstructed by a solidified crust of lava.

The next day, Strombolian activity gradually increased, reaching maximum intensity on the morning of the 15th. Observations from a helicopter on 16 January revealed a new lava flow 50-100 m wide (apparently erupted 15 January) that had flowed over the E crater rim and traveled about 2.5 km SE down the Valle del Bove, stopping at ~2,000 m altitude (S of Sierra Gianicola Piccola).

Sporadic Strombolian explosions with variable intensities resumed 19 January and continued throughout the month. Bad weather prevented field surveys at the other active summit craters, but observations by helicopter showed degassing at the two central vents (Bocca Nuova and La Voragine) and Northeast Crater.

Seismic activity. (E. Privitera, C. Cardaci, O. Cocina, V. Longo, A. Montalto, D. Patane, A. Pellegrino, and S. Spampinato.) January seismicity increased from previous months. Tremor amplitude fluctuated, with increases on 5, 11-12 and 14-15 January, associated with strong explosive activity and lava emission at Southeast Crater. The number of low-frequency events of M<=1 increased from the single shock recorded in December, often becoming more numerous before and after variations in tremor amplitude. A large increase in the number of low-frequency shocks was recorded 19-20 January, but was not accompanied by variation in the tremor amplitude or an increase in energy release. A sequence of 18 events on the NNW side of the volcano at 10-15 km depth had a large energy release. At least nine events reached or exceeded M 2, with 2 main shocks (at 1200 and 1336 on the 28th) reaching M 2.7.

Ground deformation. (A. Bonaccorso, O. Campisi, G. Falzone, B. Puglisi, and R. Velardita.) January tilt recorded at the SPC and CDV borehole tilt stations on the volcano's S flank showed no significant variation from the previous month. EDM surveys across the fracture on the S side (along SP92) and on the N part of the Etna Sud trilateration network showed variations within instrumental error limits.

Summit crater SO₂ flux. (T. Caltabiano and R. Romano.) Samples collected from the summit craters on 8, 12, 16-18, 24, and 31 January showed increased SO₂ emission preceding eruptive activity. Emissions rose from ~4,000 t/d on 29 December to ~ 26,000 t/d measured 16 January following Southeast Crater explosive and effusive activity on the 14-15th. Emissions returned to moderate values on 17 January (~5,000 t/d) and remained near that level during measurments on 18, 24, and 31 January.

Information Contacts: R. Santacroce, IIV.

Jump to Index of Monthly Reports

03/1990 (BGVN 15:03) Lava fountains and flow then strong block ejection from Southeast Crater

Summit activity. (S. Calvari, M. Coltelli, O. Consoli, M. Pompilio, and V. Scribano.) February activity was characterized by a single strong eruptive episode at Southeast Crater. Summit-area craters generally remained quiet through the rest of February and March. The 1-2 February eruptive episode was similar to several in January. A gradual increase in Strombolian explosions was followed by lava fountaining, and lava flowed over the crater's E rim for 5 hours beginning at 2200 on 1 February. The flow turned toward the Valle del Bove, advancing to ~ 2,000 m altitude, near the terminus of the mid-January flow. During the morning of 2 February, discontinuous Strombolian activity was followed by ejection of scoria that seldom reached a few tens of meters from the rim. Activity changed at about 1330 to energetic, discontinuous explosions that generated rumbling heard at a considerable distance. Blocks more than a meter across fell within a few hundred meters of the crater; much of the slightly vesicular ash was non-juvenile. Similar activity continued until about midnight. After the eruptive episode, the crater was completely obstructed, without any gas emission, until 27 February, when sporadic ejection of dark tephra began from two vents on the crater floor. February activity at other summit-area craters was limited to vapor emission from floors and walls. Emissions were particularly strong from Northeast Crater, where the active vent's walls were strongly incandescent.

Degassing was continuous at the summit craters in March but was not accompanied by Strombolian activity. Degassing occurred from an elliptical vent on the W floor of La Voragine accompanied by sporadic rumbling. Gas was also emitted from two sites on the SE and NW floor of Bocca Nuova. Weak fumarolic activity, from collapse steps that have formed along concentric fractures in Southeast Crater, was strongest from the center of the crater. Degassing also continued in Northeast Crater. On 29 and 30 March, sporadic tephra ejection and incandescence were observed, apparently from a sudden rise in the magma column.

Seismic activity. (E. Privitera, C. Cardaci, O. Cocina, V. Longo, A. Montaldo, M. Patanè, A. Pellegrino, and S. Spampinato.) Volcanic tremor amplitude began a progressive increase on 1 February at 1239, probably associated with increased Strombolian activity at Southeast Crater. Amplitudes peaked at 1940 that day, and at 0048 the next morning as activity was changing from Strombolian to lava fountaining. Other substantial increases in tremor amplitude occurred at 0600-1100, 1855, and 1935. The first of two sequences of discrete earthquakes on 2 February began at 0352. Eight of the events, centered at ~15 km depth on the volcano's N sector, were larger than M 1, the strongest at M 2.6 between 0424 and 0619. The second series of shocks started at 1321, with the two largest events (M 2.8) at 1322 and 1337. Hypocenters were on the Valle del Bove at <1 km depth. From 3 February until the end of the month, seismic activity was at very low levels, with little variation in tremor amplitude or the number of low-frequency shocks. Nine fracturing events exceeded M 1, with a maximum magnitude of 2.5.

Seismic activity in March was characterized by a significant increase in the number of fracturing events. Swarms on 16 and 18 March totaled 124 shocks (M>=1) and brought the month's recorded earthquakes to 153, ~ 3 times as many as in January and February. The 16 March swarm began at 0530 and continued until 0050 the next day. Of the 107 shocks stronger than M 1, 28 were of M>=2 and three of M>=3. The bulk of the most energetic events originated from the central to W part of the edifice at 10-20 km depth, although one (at 1052) was located just NNW of the central crater at ~5 km depth. The strongest shock of the 18 March sequence, which included 17 events, occurred on the SW flank (a few kilometers S of Monte Nero) at ~10-15 km depth. An M 3.3 earthquake on 22 March at 1159 was ~15 km deep, roughly 6 km SSW of the summit (just S of Monte Vetore). The March seismicity was not accompanied by changes in volcanic tremor amplitude, which remained low throughout the month. The number and amplitude of low-frequency events showed little change after 3 February. A new seismic station (PZF) was installed on the lower NW flank (near Maletto), replacing station RCC, stolen in August 1989. With the new site, IIV's Etna network numbers 8 stations.

Ground deformation. (A. Bonaccorso, O. Campisi, G. Falzone, B. Puglisi, and R. Velardita.) Two tilt stations (SPC and CDV) operated during February, both on the S side of the volcano. Data from station SPC generally remained within resolution limits through February and March. A weak anomaly was recorded on the tangential component 18-20 February, then tangential data returned to the normal range. Radial values from recently installed station CDV remained within resolution limits through February, while tangential data began a (negative) excursion on 18 February that totalled 5 µrad by the end of the month. All instruments from this station were stolen on 1 March. Reoccupation of sites that form a triangle along the fracture zone between 1,800 and 1,500 m altitude on the S-SE flank (between benchmarks Bocche 1792, Serra Pizzuta Calvarina, and Mt. Stempato) did not show significant deformation since the previous measurements on 19 January.

Summit SO₂ flux. (T. Caltabiano and R. Romano.) Rates of SO₂ emission during Southeast Crater's eruptive episode on 2 February were three times mean values. Measurements 7, 14, and 21 February showed considerable variation. The five March measurements yielded SO₂ flux of 2,500-14,000 t/d, increasing at the end of the month.

Information Contacts: R. Santacroce, IIV.

Jump to Index of Monthly Reports

10/1990 (BGVN 15:10) Strombolian activity and lava fountaining from central craters; earthquakes and tremor; deformation

The following, from IIV, covers April-September 1990.

Summit crater activity. Eruptive activity was at Bocca Nuova and La Voragine, while only degassing was observed at the SE and NE subterminal craters. At the beginning of July, the mild degassing that had characterized the central vents during previous months evolved to Strombolian activity, sporadically ejecting juvenile products that reached the rim of Bocca Nuova. An intense eruptive episode began at Bocca Nuova on 7 August at about 1130, lasting for ~ 40 minutes. Strong Strombolian activity alternated with lava fountaining, producing a thick deposit (~10 cm maximum) of vesiculated scoria and Pele's Hair that accumulated on the N and NW sides of the crater rim. Wind carried lighter tephra 10 km NE, where it reached the villages of Vena and Presa (figure 38). Weak Strombolian activity followed, stopping early the next day. During the same period, La Voragine was limited to moderate Strombolian activity that stopped on 8 August. Increased tremor amplitude was recorded during the night of 7-8 August (see below), then tremor declined to low levels.

Collapse of part of the wall between Bocca Nuova and La Voragine 9-10 August produced a landslide deposit that covered pre-existing vents on Bocca Nuova's floor. This deposit was soon penetrated by explosive activity, which formed two new vents characterized by weak Strombolian activity.

Throughout this period, activity at the SE subterminal crater remained limited to degassing. However, a considerable enlargement of the vent was observed in June, accompanied by strong incandescence of the inner walls. The temperature of the fumarolic gas, measured 8 August, reached 615°C. By the end of August, a larger degassing vent (~ 10 m across) had formed on the crater floor where fumarolic activity had previously been most intense. This vent produced only strong gas emission, without explosive episodes. Activity at the summit craters was limited to degassing of variable intensity in September.

Fault seismicity. Seismicity alternated between phases of relative quiet (April-June, September) and moderate to intense activity (July-August).

Moderate activity April-June was broken by four seismic sequences that occurred 25 April, 17-18 May, and 1-2 and 30 June (figure 39b). Seismic energy release (figure 39a) was also moderate (maximum M 3.0 on 17 May) and a total of 101 shocks of M >= 1 were recorded. The April-May seismicity mainly affected the W sector of the volcano, with seismic activity moving to the E (Valle del Bove) and NE flanks in June (figure 40). Average focal depths were ~15 km, except for the 1 June sequence, which had a focal zone at a depth of <=10 km (figure 41).

During the next two months, the most significant seismic episodes took place on 3 and 8 July, and 27 August. These sequences plus a general increase in background activity caused a significant change in the slope of the cumulative strain release curve. Energy associated with single events remained moderate, never exceeding M 3.1. The total of 148 events recorded in July decreased to 97 in August. The upper NE flank (10-25 km depth) and the Valle del Bove (6-12 km depth) were the areas most affected.

Another seismic sequence (78 events of M >= 1) occurred on the NW flank on 3 September; the average calculated focal depth was about 24 ± 4 km. Seismic activity then returned to moderate levels for the rest of the month.

Volcanic tremor. During April, May, and the first part of June, volcanic tremor amplitude recorded at a reference station (ESP) on the S flank fluctuated from low to moderate values (7-20 mV/_Hz). Beginning in the second half of June, an amplitude increase was observed (20-30 mV/_Hz) that lasted until 7 August. During the night of 7-8 August, a sudden further increase in tremor amplitude coincided with the violent Strombolian activity from Bocca Nuova (see above). After this episode, tremor amplitude returned to low levels (5-8 mV/_Hz), remaining at similar values until the end of September.

Ground deformation. EDM measurements were performed on two geodimeter networks, on the S and SW flanks. The southern network was measured in June, about a year after the last measurement in May 1989. The area covered by the network includes part of the main fracture system that affected the SE flank during the September-October 1989 eruption (14:8-10). Comparisons between May 1989 and June 1990 data showed significant distance variations, mostly for lines in the higher altitude sector of the network. The resulting deformation pattern was characterized by a significant areal contraction. The deformation ellipse was strongly polarized with the minimum extension axis (contraction) trending approximately N29°E. The southwestern EDM network was reoccupied in July, showing only minor slope distance variations from the previous measurements in June 1989. A weak areal contraction was observed. The calculated deformation ellipse had a minimum extension axis (contraction) striking approximately N7°E.

Tilt data were collected at a biaxial borehole station (SPC) on the S flank, close to the ESP seismic station. Recording was interrupted early April-early June by vandalism. The radial component indicated continuous inflation of the volcanic edifice from the beginning of July until early September, closely paralleling the seismic strain release (figure 39a). During the same period, the tangential component remained nearly flat, showing fluctuations within the confidence limit of about ± 2 µrads.

Information Contact: IIV.

Jump to Index of Monthly Reports

03/1991 (BGVN 16:03) Periodic summit explosions; brief earthquake swarms; deformation

The following, from IIV, describes activity October 1990-March 1991. Explosive and/or Strombolian activity with strong degassing characterized Bocca Nuova, while the other summit craters generally showed almost continuous mild degassing.

Bocca Nuova. Intense Strombolian activity occurred from 4 or 5 vents that formed on the crater floor between 10 and 15 November. Ejecta only sporadically reached or went beyond the crater rim; most of the pyroclasts were ejected to moderate height, falling within the crater, where they accumulated with minor intracrater lava flows. The activity stopped abruptly on 24 December (associated with a deformation change; see below), and was succeeded that afternoon by strong continuous ash emission that lasted until the beginning of January. Weak Strombolian activity resumed for a few days in early January, ending by the 12th.

Southeast Crater. Typically mild, sometimes pulsating, gas emission was accompanied in December by weak ash ejection during times of the most intense similar activity at Bocca Nuova. A short period of mild Strombolian activity 4-7 January was the first significant eruptive event since the opening of a vent on the crater floor in April 1990.

La Voragine. Only discontinuous Strombolian activity 4-12 January was reported.

Northeast Crater. Frequent explosions occurred, but did not eject any juvenile tephra. Gas emission became intense in October and November, producing continuous incandescence of the degassing vent's inner walls that persisted through the report period.

Only sporadic summit observations were possible during February. These were limited to Southeast Crater, which was characterized by vapor emission. No information about March summit activity is available.

Seismic activity. Seismicity was moderate during October and November. On 7 December, a sequence of 26 events was recorded in a few hours. All were centered on the N flank at 7-24 km depth. Energy release was low, with no shocks exceeding M 2.2. Seven events on 9 January, at ~9 km depth on the SSW flank, were followed by a second swarm (42 events) on 26 January, which was deeper (14-20 km) and distributed over a wider area on the same part of the volcano. A deformation episode was recorded the same day by a nearby tiltmeter (see below). Another, shallower sequence occurred on the SSW flank on 2 February, in the same area as a sharp deformation episode on 24 December. Instrument problems prevented accurate location of a swarm on 8-9 February. A series of moderate earthquakes, on the N flank at ~ 21 km depth, was recorded 19-20 February. Seismicity declined in March.

Tremor amplitude was low in October, but increased 5-6 November, followed by a period of frequent amplitude fluctuations. On 27 November, tremor was strong enough to be detected for a few hours at seismic stations far from the summit craters. It then declined but remained at slightly elevated amplitude. No change in eruptive activity was reported on 27 November. Tremor continued to fluctuate into early December, then remained at low amplitude through March.

Ground deformation. Tilt data were collected at three borehole biaxial stations (SPC, CDV, and MDZ) on the S and SSW flanks. Summit inflation continued from previous months (at SPC), but slowed in November, and had nearly stopped by December. At nearby CDV, no significant radial tilt was detected, but the tangential component showed inflation toward the SW in October that reversed in November and continued on that trend until 24 December. A sharp deformation event was recorded that day on all three tilt stations, and a sudden change from Strombolian activity to continuous ash emission occurred at Bocca Nuova (see above). The pre-24 December trend then resumed at CDV, continuing through January, while similar behavior was shown by the tangential component at SPC.

Another sharp deformation event was recorded 26 January at station MDZ during a seismic swarm centered nearby (see above); a less intense deformation signal was detected at CDV.

Information Contacts: R. Velardita, IIV.

Jump to Index of Monthly Reports

05/1991 (BGVN 16:05) Strong degassing

Nearly continuous degassing was observed ... on 24 May. Northeast Crater's active vent was slightly incandescent and weakly emitting gas. Normal degassing, with sporadic rumbling, occurred at La Voragine, whose elliptical vent E of the central crater floor had reopened. The floors of Bocca Nuova and Southeast Crater were not visible due to their strong degassing.

Information Contact: H. Gaudru, EVS, Switzerland; Franco Emmi, Etna guide.

Jump to Index of Monthly Reports

07/1991 (BGVN 16:07) Strombolian activity and continued strong degassing

Strong degassing continued .. during fieldwork in June and July. Strombolian activity was reported at a vent in the NE part of Southeast Crater. Small explosions occurred almost continuously, with more powerful blasts ejecting material to the level of the crater rim occurring every 10-15 minutes (in July). Meanwhile, a vent in the center of the crater gently degassed. In June, occasional emissions of small (<20 cm) sublimate-covered lithic blocks and scoria occurred from a 20 x 10 m pit in Northeast Crater. Lava was visible within the vent, which continued to glow through July. The vent widened internally, giving the appearance of a large chamber inclined in the direction of La Voragine. The elliptical vent at La Voragine crater (reopened prior to a 24 May visit; 16:05) showed incandescence in July, but not in June. Degassing continued from numerous fumaroles within the crater. The floor of Bocca Nuova crater was hidden by large quantities of gas in June, but in July two scoria cones were seen gently emitting vapor. At night, a strongly degassing vent on the SE side of the crater emitted tongues of incandescent gas at 15-minute intervals. A fumarole (56°C) was observed on the October 1989 fracture where it crossed the Canalone Della Montagnola at an altitude of ~ 2,200 m.

The following is from Steve Saunders. "A resurvey, in July, of an EDM network (67 lines) on the upper S flank showed a shortening of the majority of the lines (56), suggesting that minor deflation had occurred since the previous survey in July 1990. At that time, length increases along most lines were interpreted as resulting from minor inflation of the upper flanks since November 1989."

Information Contacts: H. Gaudru, EVS, Switzerland; T. De St. Cyr, Fontaines St. Martin, France; S. Saunders, West London Institute of Higher Education; W. McGuire, Cheltenham and Glouster College of Higher Education.

Jump to Index of Monthly Reports

09/1991 (BGVN 16:09) Summit-area Strombolian activity apparently ends; continued degassing

Strombolian activity in Northeast Crater had decreased by mid-July, and was no longer apparent on 23 August. Strombolian activity was observed in Southeast Crater in mid-July. All four summit craters were in a state of almost continuous mild degassing through August.

The following is from a report on activity 10-14 July, by J.P. Kloster in LAVE Bulletin no. 33, p. 4.

A network of curvilinear fissures, up to 2 m wide, covered the N, E, and SE parts of Southeast Crater. In the NW part of the crater, a vent 15 m in diameter emitted puffs of gas roughly every 3 seconds. Every half hour, a more violent explosion ejected lava fragments to 200 m above the vent, covering the walls of the crater and occasionally sending projectiles outside of the crater. The largest projectiles were estimated at around 5 kg, and were fluid enough to deform on impact. Two vents emitted slightly incandescent plumes at night. Each explosion was preceded by ~12 seconds of increased incandescence at the non-exploding vent, and corresponding intensification of glow at the exploding vent. On one occasion, a roughly 100-kg block of lava was ejected to 50 m height.

In the S part of Northeast Crater, a long-persistent vent, 5 m in diameter, emitted puffs of gas. At night, the emission was incandescent to 30 m height, with small lava fragments ejected during the most violent explosions. No projectiles fell beyond the crater rim.

About 70 m below Bocca Nuova crater's S rim, gas was strongly emitted from an E-W fissure, several meters wide and 12 m long, that probably formed in October 1989 (14:10). Explosions were heard emanating from the fissure area, roughly every 4-5 minutes. Night glow was visible at the fissure and at the vents of two coalesced scoria cones in the S part of the crater floor.

Very little activity occurred in La Voragine crater. One 20-m-diameter vent, on a small cinder cone, degassed quietly to several meters, and had night glow. Snow on the cone was largely covered by scoriae, suggesting recent activity.

No Strombolian activity or lava emission were observed during a 23 August visit to the summit by J. Dehn and B. Behncke. The vent in Northeast Crater had strong gas emission, accompanied by loud roaring noises, but no solid material was ejected. A dense continuous gas column was rising from Southeast Crater.

Information Contacts: J. Kloster, LAVE; J. Dehn and B. Behncke, GEOMAR, Kiel.

Jump to Index of Monthly Reports

10/1991 (BGVN 16:10) Minor Strombolian activity from several summit-area vents; little deformation

An 8-19 October resurvey of a 46-line EDM network on the upper S flank showed little movement since July, with maximum line-length changes of ~0.0015%. Activity at the summit craters was more energetic than in July but had the same general characteristics. Continued Strombolian activity in the NE sector of Southeast Crater periodically increased in strength, with large incandescent blebs of lava rising tens of meters above the crater rim. The open vent in Northeast Crater was degassing strongly and incandescent at night, while the two vents on the floor of Bocca Nuova had mild to strong Strombolian activity. E of Bocca Nuova, a single vent on the floor of La Voragine displayed weak Strombolian activity and daylight incandescence.

Information Contacts: S. Saunders, West London Institute; W. McGuire, Cheltenham and Gloucester College of Higher Education.

Further Reference: McGuire, W., Murray, J., Pullen, A., and Saunders, S., 1991, Ground deformation monitoring at Mt. Etna: evidence for dyke emplacement and slope instability: Journal of the Geological Society, London, v. 148, p. 577-583.

Jump to Index of Monthly Reports

11/1991 (BGVN 16:11) Brief SE-flank fissure eruption

Lava emerged from a fissure at 3,000 m altitude, apparently on the SE flank, for about an hour on 14 December. Light ashfalls occurred on small villages below the fissure. The eruption was preceded by hundreds of small earthquakes.

Information Contact: AP.

Jump to Index of Monthly Reports

12/1991 (BGVN 16:12) Lava from SE-flank fissures covers about 5 km²; barrier constructed

The following, from R. Romano with additional information from J.C. Tanguy, supersedes the preliminary press report in 16:11. Information from Tanguy about the beginning of the eruption was collected thanks to G. Patanè, S. Imposa, R. Cristofolini, A. & O. Nicoloso, and G. Scarpinati.

A SE-flank fissure eruption began near the base of Southeast Crater early 14 December. Activity ended that day from the initial vents, but fissures propagated downslope where more vigorous lava production began the next morning. The eruption produced a substantial lava field and was continuing in mid-January.

After intense Strombolian activity at ... Bocca Nuova and Southeast Crater, eruptive fissures opened during the early morning of 14 December. These extended ~ 1 km SSE from the base of Southeast Crater (figure 42). Strong harmonic tremor was recorded between 0220 and 0420 by Univ di Catania seismometers. Ejection of lava fragments built modest cones and scoria ramparts along the fracture system, while small lava flows were extruded from some vents. More consistent lava production at the end of the fracture system fed a flow that advanced down the W wall of the Valle del Bove, branching into two lobes. These moved E, but did not exceed 1 km in length, reaching ~2,400 m altitude. When chief guide A. Nicoloso reached the area at about 0800, lava production had nearly stopped, although strong gas emission continued at Bocca Nuova and Southeast Crater. Activity from the fissures ceased completely during the morning. Another modest-sized eruptive fissure, oriented NE-SW, opened at the NE base of Southeast Crater, ejecting hot pyroclastic material.

During the night, the NNW-SSE fissures that had been active the previous morning continued to propagate downslope. A second seismic crisis heralded the opening, at about 0245, of two sub-parallel eruptive fissures. These developed along a non-eruptive segment of the 1989 eruption's SE fracture, on the W wall of the Valle del Bove between roughly 2,400 and 2,200 m altitude, a total length of ~ 400 m. Strombolian activity began immediately along the new fissures and lava flowed E from the fissures' ends, extending ~ 1.5 km along the floor of the Valle del Bove by 0900 (observation by G. Scarpinati). The flows reached the base of the Valle del Bove during the afternoon, and advanced on the Piano del Trifoglietto, a plain at ~ 1,500 m altitude. That evening, at 2103, a strong shock was felt near Etna and to ~ 75 km SE (in the Siracusa area). Other isolated shocks and swarms of events with M <4 were recorded, particularly during the first few days of the eruption.

In the days that followed, Strombolian activity, sometimes intense, occurred from several points along the fissures, building small cones and scoria ramparts. Impressive phreatomagmatic explosions, accompanied by loud detonations, were clearly felt in towns at the foot of the volcano, especially during the eruption's first few days. The effusive activity created a system of lava flows, some with fronts hundreds of meters wide, which generally moved east, in the Piano del Trifoglietto.

By 20 December, lava had reached ~ 1,500 m altitude and superposition of lava flows began to be observed. During the evening of 23 December, a very wide lava front reached the Salto della Giumenta (at the head of the Val Calanna, ~ 4.5 km from the vent) and a few flows descended into it the next morning. Lava flows almost completely covered Val Calanna during the succeeding days, destroying orchards and drinking water facilities. On 2 January, a very wide flow front, ~ 10 m thick, had reached 950 m altitude (~ 5.5 km from the vent) and was advancing slowly. Construction began that day on a containment barrier along the E side of Val Calanna.

An extensive lava field had formed in the Piano del Trifoglietto, with individual lobes frequently superposing and combining. Overflows began from the N part of the lava field about 2 January, forming a separate flow around the N side of Monte Calanna on 5 January and rejoining the stagnant lava front in Val Calanna on the 7th. Flow fronts in Val Calanna had stopped by the morning of 9 January, while active superposed lobes were noted on the lava that had flowed N of Monte Calanna. The most advanced front was at ~ 1,100 m altitude and was tending to move E. The extensive (1-km-wide) main lava field fed numerous breakouts or ephemeral vents, from which modest flows advanced over earlier lava. The main lava channel, originating around 2,200 m altitude, was being vigorously fed and at times was tubed over.

By 14 January, Strombolian activity from the fissure vents had declined notably and explosions were no longer audible. Effusive activity was concentrated at a single vent, feeding a lava channel that subdivided into several flows at ~ 2,000 m altitude (at the base of the Valle del Bove's W wall). These moved onto the lava field formed earlier in the eruption but did not extend beyond 1,550 m altitude. The area covered by new lava had not grown since 9 January, but numerous ephemeral flows appeared on its surface. The containment barrier at the end of Val Calanna had not been tested as of 14 January, since the nearest flow had stopped ~150 m away (~6 km from the vent). As of 21 January the eruption was continuing, although apparently at a reduced rate.

Degassing from the summit craters has continued since the beginning of the eruption. Activity was sometimes intense, but ash was rarely mixed with the gas. Strombolian activity that was vigorous at times continued from various vents at the bottom of Bocca Nuova.

Romano noted that the activity has the characteristics of a classic "slow eruption" (Romano and Sturiale, 1982) and is very similar to the 1819 eruption that occurred in the same area of the Valle del Bove.

Preliminary estimates indicated that ~40 x 10⁶ m³ of lava had been ejected as of 9 January, with an effusion rate of around 15-18 m³/s. Measurements of the effusion rate on 11 January yielded a value of around 9 m³/s from the lava channel at 2,000 m altitude.

Reference: Romano, R., and Sturiale, C., 1982, The historic eruptions of Mt. Etna (volcanological data): Memoirs of the Geological Society of Italy, v. 23, p. 75-97.

Information Contacts: R. Romano and T. Caltabiano, IIV; P. Carveni and M. Grasso, Univ di Catania; J. Tanguy, Univ de Paris.

Jump to Index of Monthly Reports

01/1992 (BGVN 17:01) Lava production continues from SE-flank fissure but explosive activity declines

The following is from R. Romano. The SE-flank fissure eruption that began on 14 December was continuing as of early February. No notable decrease in the rate of lava effusion has been observed. Explosive activity along the eruptive fissure, which has been highly variable in intensity and duration, has mainly declined to sporadic ejections of lava fragments, limited expulsion of dark ash, and rare phreatomagmatic explosions. Strong gas emission was generally evident. Seismic activity has declined to isolated weak events.

The lava field in the SE flank's Valle del Bove has grown considerably, reaching a maximum width of 1.5 km in a few places, as flows from the N (dominantly) and S merged. Most of the lava was carried through a complex system of tubes originating at the main effusive vent, and emerged onto the lava field surface through numerous ephemeral secondary vents. These varied daily in number and position, and were concentrated in the middle of the lava field (around 1,550 m asl), but some have recently appeared at ~ 1,450 m altitude (at the base of Monte Zoccolaro, just before the break in slope at the Salto della Giumenta). Lava flows from the secondary vents generally advanced along the Salto della Giumenta, and were sometimes relatively continuous. In early February one of these reached, but did not surpass, the front of the eruption's longest flow, at 1,000 m elevation (in Val Calanna, ~6 km from the active fissure). Preliminary estimates indicate that > 6 km² has been covered by ~55-60 x 10⁶ m³ of new lava, an average volume for Etna's "slow eruption" type (Romano and Sturiale, 1982).

The summit craters remained open, emitting gases from small vents. High-temperature gas release was sometimes observed (as at the central crater's E vent, La Voragine, on 11 February). A little dark ash was recently emitted from the central crater's W vent (Bocca Nuova).

Information Contacts: R. Romano and T. Caltabiano, IIV; P. Carveni and M. Grasso, Univ di Catania.

Jump to Index of Monthly Reports

02/1992 (BGVN 17:02) Continued flank lava production

The following is from a report by the Gruppo Nazionale per la Vulcanologia (GNV) summarizing Etna's 1991-92 eruption.

1. Introduction and Civil Protection problems. After 23 months of quiet, and heralded by ground deformation and a short seismic swarm, effusive activity resumed at Etna early 14 December. The eruptive vent opened at 2,200 m elevation on the W wall of the Valle del Bove, along a SE-flank fracture that formed during the 1989 eruption.

Since the eruption's onset, the GNV, in cooperation with Civil Protection authorities, has reinforced the scientific monitoring of Etna. Attention was focused on both the advance of the lava flow and on the possibility of downslope migration of the eruptive vent along the 1989 fracture system. The progress of the lava flow has been carefully followed by daily field inspections and helicopter overflights.

Because of its slow rate of advance, the lava did not threaten lives, but had the potential for severe property destruction. The water supply system for Zafferana (in Val Calanna; figure 43) was destroyed in the first two weeks of the eruption ($2.5 million damage). On 1 January, when the lava front was only 2 km from Zafferana, the Minister for Civil Protection, at the suggestion of the volcanologists, ordered the building of an earthen barrier to protect the village. The barrier was erected at the E end of Val Calanna, where the valley narrows into a deeply eroded canyon. The barrier was conceived to prevent or delay the flow's advance, not to divert it, by creating a morphological obstacle that would favor flow overlapping and lateral expansion of the lava in the large Val Calanna basin.

The barrier, erected by specialized Army and Fire Brigade personnel in 10 days of non-stop work, is ~ 250 m long and ~ 20 m higher than the adjacent Val Calanna floor. It was built by diking the valley bottom in front of the advancing lava and accumulating loose material (earth, scoria, and lava fragments) on a small natural scarp. On 7 January, the lava front approached to a few tens of meters from the barrier, then stopped because of a sudden drop in feeding caused by a huge lava overflow from the main channel several kilometers upslope.

A decrease in the effusion rate has been observed since mid-January. There is therefore little chance of further advance of the front, as the flow seems to have reached its natural maximum length. The eruptive fracture is being carefully monitored (seismicity, ground deformation, geoelectrics, gravimetry, and gas geochemistry) to detect early symptoms of a possible dangerous downslope migration of the vent along the 1989 fracture, which continues along the present fracture's SE trend. Preparedness plans were implemented in case of lava emission from the fracture's lower end.

Many scientists and technicians, the majority of whom are from IIV and the Istituto per la Geochimica dei Fluidi, Palermo (IGF) and are coordinated by GNV, are collecting information on the geological, petrological, geochemical, and geophysical aspects of the eruption.

2. Eruption chronology. On 14 December at about 0200, a seismic swarm (see Seismicity section below) indicated the opening of two radial fractures trending NE and SSE from Southeast Crater. Very soon, ash and bombs formed small scoria ramparts along the NE fracture, where brief activity was confined to the base of Southeast Crater. Meanwhile, a SSE-trending fracture extended ~ 1.3 km from the base of the crater (at ~3,000 m asl) to 2,700 m altitude.

Lava fountaining up to 300 m high from the uppermost section of the SSE fracture continued until about 0600, producing scoria ramparts 10 m high. Two thin (~ 1 m thick) lava flows from the fracture moved E. The N flow, from the highest part of the fracture, stopped at 2,750 m altitude, while the other, starting at 2,850 m elevation, reached the rim of the Valle del Bove (in the Belvedere area), pouring downvalley to ~ 2,500 m asl. At noon, the lava flows stopped, while the W vent of the central crater (Bocca Nuova) was the source of intense Strombolian activity.

The SSE fracture system continued to propagate downslope, crossing the rim of the Valle del Bove in the late evening. During the night of 14-15 December, lava emerged from the lowest segment of the fracture cutting the W flank of the Valle del Bove, reaching 2,400 m altitude (E of Cisternazza). Degassing and Strombolian activity built small scoria cones. Two lava flows advanced downslope from the base of the lower scoria cone at an estimated initial velocity of 15 m/s, which dramatically decreased when they reached the floor of the Valle del Bove.

The SSE fractures formed a system 3 km long and 350-500 m wide that has not propagated since 15 December. Between Southeast Crater and Cisternazza, the fracture field includes the 1989 fractures, which were reactivated with 30-50-cm offsets. The most evident offsets were down to the E, with right-lateral extensional movements. Numerous pit craters, <1 m in diameter, formed along the fractures.

Lava flows have been spreading down the Valle del Bove into the Piano del Trifoglietto, advancing a few hundred meters/day since 15 December. The high initial outflow rates peaked during the last week of 1991 and the first few days of 1992, and decreased after the second week in January. Strombolian activity at the vent in the upper part of the fracture has gradually diminished.

Lava flows were confined to the Valle del Bove until 24 December, when the most advanced front extended beyond the steep slope of the Salto della Giumenta (1,300-1,400 m altitude), accumulating on the floor of Val Calanna. Since then, many ephemeral vents and lava tubes have formed in the area N of Monte Zoccolaro, probably because of variations in the eruption rate. These widened the lava field in the area, and decreased feeding for flows moving into Val Calanna. However, by the end of December, lava flows expanded further in Val Calanna, moving E and threatening the village of Zafferana Etnea, ~2 km E of the most advanced flow front. This front stopped on 3 January, on the same day that a flow from the Valle del Bove moved N of Monte Calanna, later turning back southward and rejoining lava that had already stopped in Val Calanna. Since 9 January, lava flows in Val Calanna have not extended farther downslope, but have piled up a thick sequence of lobes.

Lava outflow from the vent continued at a more or less constant rate, producing a lava field in the Valle del Bove that consisted of a complex network of tubes and braiding, superposing flows, with a continuously changing system of overflows and ephemeral vents.

3. Lava flow measurements. An estimate of lava channel dimensions, flow velocity, and related rheological parameters was carried out where the flow enters the Valle del Bove. Flow velocities ranging from 0.4-1 m/s were observed 3-7 January in a single flow channel (10 m wide, ~ 2.5 m deep) at 1,800 m altitude, ~ 600 m from the vent. From these values, a flow rate of 8-25 m³/s and viscosities ranging from 70-180 Pas were calculated. Direct temperature measurements at several points on the flow surface with an Al/Ni thermocouple and a 2-color pyrometer (HOTSHOT) yielded values of 850-1,080°C.

4. Petrography and chemistry. Systematic lava sampling was carried out at the flow fronts and near the vents. All of the samples were porphyritic (P.I.»25-35%) and of hawaiitic composition, differing from the 1989 lavas, which fall within the alkali basalt field. Paragenesis is typical of Etna's lavas, with phenocrysts (maximum dimension, 3 mm) of plagioclase, clinopyroxene, and olivine, with Ti-magnitite microphenocrysts. The interstitial to hyalopitic groundmass showed microlites of the same minerals.

5. Seismicity. On 14 December at 0245, a seismic swarm occurred in the summit area (figure 44), related to the opening of upper SE-flank eruptive fractures. About 270 earthquakes were recorded, with a maximum local magnitude of 3. A drastic reduction in the seismic rate was observed from 0046 on 15 December, with only four events recorded until the main shock (Md 3.6) of a new sequence occurred at 2100. The seismic rate remained quite high until 0029 on 17 December, declining gradually thereafter.

At least three different focal zones were recognized. On 14 December, one was located NE of the summit and a second in the Valle del Bove. The third, SW of the summit, was active on 15 December. All three focal zones were confined to <3 km depth. Three waveform types were recognized, ranging from low-to-high frequency.

As the seismic swarm began on 14 December, volcanic tremor amplitude increased sharply. Maximum amplitude was reached on 21 December, followed by a gradually decreasing trend. As the tremor amplitude increased, the frequency pattern of its dominant spectral peaks changed, increasing within a less-consistent frequency trend. Seismicity rapidly declined and remained at low levels despite the ongoing eruption.

6. Ground deformation. EDM measurements and continuously recording shallow-borehole tiltmeters have been used for several years to monitor ground deformation at Etna. The tilt network has recently grown to 9 flank stations. A new tilt station (CDV) established on the NE side of the fracture in early 1990 showed a steady radial-component increase in early March 1991 after a sharp deformation event at the end of 1990 (figure 45), suggesting that pressure was building into the main central conduit. Maximum inflation was reached by October 1991, followed by a partial decrease in radial tilt, tentatively related to magma intrusion into the already opened S branch of the 1989 fracture system, perhaps releasing pressure in the central conduit.

The eruption's onset was clearly detected by all flank tilt stations, despite their distance from the eruption site. The signals clearly record deformation events closely associated in time with seismic swarms on the W flank (before the eruption began) and on the summit and SW sector (after eruption onset). The second swarm heralded the opening of the most active vent on the W wall of the Valle del Bove.

S-flank EDM measurements detected only minor deformation, in the zone affected by the 1989 fracture. Lines crossing the fracture trend showed brief extensions in January 1992.

The levelling route established in 1989 across the SE fracture was reoccupied 18-19 December 1991. A minor general decline had occurred since the previous survey (October 1990), with a maximum (-10 mm) at a benchmark near the fracture.

7. Gravity changes. Microgravity measurements have been carried out on Etna since 1986, using a network covering a wide area between 1,000 and 1,900 m asl. A reference station is located ~ 20 km NE of the central crater. Five new surveys were made across the 1989 fissure zone during the eruption (15 & 18 December 1991, and 9, 13, and 18 January 1992). Between 21 November and 15 December, the minimum value of gravity variations was about -20 mGal, E of the fracture zone. On 9 January, the gravity variations inverted to a maximum of about +15 mGal. Amplitude increased and anomaly extension was reduced on 13 January, and on 18 January gravity variations were similar to those 9 days earlier. Assuming that height changes were negligible, a change in mass of ~2 x 10⁶ tons (~2 x 10⁷ m³ volume), for a density contrast of 0.1 g/cm³ was postulated. However, if gravity changes were attributed to magma movement, a density contrast of 0.6 g/cm³ between magma and country rock could be assumed and magma displacement would be ~ 3 x 10⁶ m³.

8. Magnetic observations. A 447-point magnetic surveillance array was spaced at 5-m intervals near the fracture that cut route SP92 in 1989. Measurements of total magnetic field intensity (B) have been carried out at least every 3 months since October 1989. Significant long-term magnetic variations were not observed between February 1991 and January 1992, although the amplitude of variations seems to have increased since the beginning of the eruption.

9. Self-potential. A program of self-potential measurements along an 1.32-km E-W profile crossing the SE fracture system (along route SP92 at ~ 1,600 m altitude) began on 25 October 1989. Two large positive anomalies were consistently present during measurements on 5 and 17 January, and 9, 18, and 19 February 1992. The strongest was centered above the fracture system, the second was displaced to the W. Only the 5 January profile hints at the presence of a third positive anomaly, on its extreme E end. The persistent post-1989 SP anomalies could be related to a magmatic intrusion, causing electrical charge polarizations inside the overlying water-saturated rocks. A recent additional intrusion was very likely to have caused the large increase in amplitude and width of the SP anomaly centered above the fracture system, detected on the E side of the profile on 5 January 1992.

10. COSPEC measurements of SO₂ flux. The SO₂ flux from Etna during the eruption has been characterized by fairly high values, averaging ~ 10,000 t/d, ~ 3 times the mean pre-eruptive rate. Individual measurements varied between ~6,000 and 15,000 t/d.

11. Soil gases. Lines perpendicular to the 1989 fracture, at ~ 1,600 m altitude, have been monitored for CO₂ flux. A sharp increase in CO₂ output was recorded in September 1991, about 3 months before the eruption began (figure 46). Measurements have been more frequent since 17 December, but no significant variation in CO₂ emission has been observed. Samples of soil gases collected at 50 cm depth showed a general decrease in He and CO₂ contents since the beginning of January. Soil degassing at two anomalous exhalation areas, on the lower SW and E flanks at ~ 600 m altitude, dropped just before (SW flank—Paternò) and immediately after (E flank—Zafferana) the beginning of the eruption, and remained at low levels. A significant radon anomaly was recorded 26-28 January along the 1989 fracture, but CO₂ and radon monitoring have been hampered by snow.

The following, from R. Romano, describes activity in February and early March.

The SE-flank fissure eruption was continuing in early March, but was less vigorous than in previous months. An area of ~ 7 km² has been covered by around 60 x 10⁶ m³ of lava, with an average effusion rate of 8 m³/s. The size of the lava field (figure 43) has not increased since it reached a maximum width of 1.7 km in mid-February.

Lava from fissure vents at ~ 2,100 m asl flowed in an open channel to 1,850 m altitude, then advanced through tubes. Flowing lava was visible in the upper few kilometers of the tubes through numerous skylights. Lava emerged from the tube system through as many as seven ephemeral vents on the edge of the Salto della Giumenta (at the head of the Val Calanna, ~ 4.5 km from the eruptive fissure). These fed a complex network of flows in the Salto della Giumenta that were generally short and not very vigorous. None extended beyond the eruption's longest flow, which had reached 6.5 km from the eruptive fissure (1,000 m asl) before stopping in early January. Ephemeral vent activity upslope (within the Valle del Bove) ceased by the end of February. Lava production from fissure vents at 2,150 m altitude has gradually declined and explosive activity has stopped. Degassing along the section of the fissure between 2,300 and 2,200 m altitude was also gradually decreasing.

Small vents were active at the bottom of both central craters. Activity at the west crater (Bocca Nuova) was generally limited to gas emission, but significant ash expulsions were observed during the first few days in March. High-temperature gases emerged from the E crater (La Voragine). Collapse within Northeast Crater, probably between 26 and 27 February, was associated with coarse ashfalls on the upper NE flank (at Piano Provenzana and Piano Pernicana). After the collapse, a new pit crater ~ 50 m in diameter occupied the site of Northeast Crater's former vent. Activity from Southeast Crater was limited to gas emission from a modest-sized vent.

Seismic activity was characterized by low-intensity swarms. A few shocks were felt in mid-February ~ 12 km SE of the summit (in the Zafferana area).

Reference: Barberi, F., Bertagnini, F., and Landi, P., eds., 1990, Mt. Etna: the 1989 eruption: CNR-Gruppo Nazionale per la Vulcanologia: Giardini, Pisa, 75 p. (11 papers).

Information Contacts: GNV report: F. Barberi, Univ di Pisa; L. Villari, IIV. February-early March activity: R. Romano and T. Caltabiano, IIV; P. Carveni, M. Grasso, and C. Monaco, Univ di Catania.

The following people provided information for the GNV report. Institutional affiliations (abbreviated, in parentheses) and their report sections [numbered, in brackets] follow names. F. Barberi (UPI) [1, 2], A. Armantia (IIV) [2], P. Armienti (UPI) [2, 4], R. Azzaro (IIV) [2], B. Badalamenti (IGF) [11], S. Bonaccorso (IIV) [6], N. Bruno (IIV) [10], G. Budetta (IIV) [7, 8], A. Buemi (IIV) [4], T. Caltabiano (IIV) [8, 10], S. Calvari (IIV) [2, 3], O. Campisi (IIV) [6], M. Carà (IIV) [10], M. Carapezza (IGF, UPA) [11], C. Cardaci (IIV) [5], O. Cocina (UGG) [5], D. Condarelli (IIV) [5], O. Consoli (IIV) [6], W. D'Alessandro (IGF) [11], M. D'Orazio (UPI) [2, 4], C. Del Negro (IIV) [7, 8], F. DiGangi (IGF) [11], I. Diliberto (IGF) [11], R. Di Maio (DGV) [9], S. DiPrima (IIV) [5], S. Falsaperla (IIV) [5], G. Falzone (IIV) [6], A. Ferro (IIV) [5], F. Ferruci (GNV) [5], G. Frazzetta (UPI) [2], H. Gaonac'h (UMO) [2, 3], S. Giammanco (IGF) [11], M. Grasso (IIV) [10], M. Grimaldi (DGV) [7], S. Gurrieri (IGF) [11], F. Innocenti (UPI) [4], G. Lanzafame (IIV) [2], G. Laudani (IIV) [6], G. Luongo (OV) [6], A. Montalto (IIV, UPI) [5], M. Neri (IIV) [2], P. Nuccio (IGF, UPA) [11], F. Obrizzo (OV) [6], F. Parello (IGF, UPA) [11], D. Patanè (IIV) [5], D. Patella (DGV) [9], A. Pellegrino (IIV) [5], M. Pompilio (IIV) [2, 3, 4], M. Porto (IIV) [10], E. Privitera (IIV) [5], G. Puglisi (IIV) [2, 6], R. Romano (IIV) [10], A. Rosselli (GNV) [5], V. Scribano (UCT) [2], S. Spampinato (IIV) [5], C. Tranne (IIV) [2], A. Tremacere (DGV) [9], M. Valenza (IGF, UPA) [11], R. Velardita (IIV) [6], L. Villari (IIV) [1, 2, 6].

Institutions: DGV: Dipto di Geofisica e Vulcanologia, Univ di Napoli; GNV: Gruppo Nazionale per la Vulcanologia, CNR, Roma; IGF: Istituto per la Geochimica dei Fluidi, CNR, Palermo; IIV: Istituto Internazionale di Vulcanologia, CNR, Catania; OV: Osservatorio Vesuviano, Napoli; UCT: Istituto di Scienze della Terra, Univ di Catania; UGG: Istituto di Geologia e Geofisica, Univ di Catania; UMO: Dept de Géologie, Univ de Montréal; UPA: Istituto di Mineralogia, Petrologia, e Geochimica, Univ di Palermo; UPI: Dipto di Scienze della Terra, Univ di Pisa.

Jump to Index of Monthly Reports

03/1992 (BGVN 17:03) Lava production continues from SE-flank vent; town threatened by lava flow

Most of the following is from R. Romano.

The fissure eruption ... was continuing in mid-April. Lava production from the main vent at 2,100 m altitude (in the W wall of the Valle del Bove) has remained almost constant, accompanied by degassing of varying intensity. By mid-April, 85 x 10⁶ m³ of lava that had emerged at an average rate of 8 m³/s was estimated to cover an area of >7 km².

From March through mid-April, lava from the main vent immediately entered a complex tube system, reappearing through ephemeral vents ~ 5 km downslope, below the Valle del Bove. The vents formed on the edge of the Salto della Giumenta, at the head of the Val Calanna a few kilometers from Zafferana Etnea, population ~ 7,000 (see figure 43). No ephemeral vents or lava overflows have been observed since the end of February in the wide lava field that had developed in the S part of the Valle del Bove.

On 14 March, lava reached the base of the barrier constructed in early January at the bottom of the Val Calanna. During the second half of March and the first few days of April, lava from the ephemeral vents gradually filled the area from the base of the Salto della Giumenta to the barrier. On 3 April, vents began to form within the Salto della Giumenta, feeding flows inside the Val Calanna. By the morning of 7 April, lava was only a few meters from the top of the barrier, with an active front along the barrier's entire length. That afternoon, lava flowed around the S side of the barrier and began to advance along the access road in the Val Calanna. The next afternoon, lava spilled over the central part of the barrier, and began to move down the gorge of the neighboring Portella Calanna valley. Lava advanced rapidly, aided by the steep slope, covering 1 km in 5 days. At least six earth barriers were built to contain the lava, but none were successful. By 14 April, lava was overflowing the last barrier, at ~ 780 m elevation, 1.5 km from the inhabited center of Zafferana Etnea and 7.5 km from the main vent.

Efforts were also made to slow or halt the advancing lava by disrupting the feeder tube system. Experiments with directed explosives, designed to blast holes in the lava field and encourage lava breakouts, began on 13 April in the upper Valle del Bove and Val Calanna. Lava destroyed two isolated houses above Zafferana on 14 April and covered nearby orchards, but the lobe threatening the town had virtually stopped by the next day and evacuation plans were postponed. New lava approached Zafferana over earlier flows in the succeeding days, and was again within a kilometer of the town by 20 April.

Degassing from the summit craters has gradually decreased following the collapse episode in Northeast Crater at the end of February (17:02). Additional Northeast Crater collapses 21-29 March triggered ash ejections accompanied by distinctive seismicity. Moderate gas emission from the summit vents observed by B. Behncke on 21 March was punctuated around 0900 by several low-energy ash emissions from Northeast Crater. At 1230 on 24 March, a dark-gray, convoluted ash plume rose to ~ 1 km above the summit within ~ 5 minutes, and also appeared to spread laterally at its base. The plume gradually dissipated during the following 30 minutes, depositing tephra to the E.

Information Contacts: R. Romano, T. Caltabiano, and M. Porto, IIV; P. Carveni and M. Grasso, Univ di Catania; B. Behncke, GEOMAR, Kiel; Il Mattino, Napoli; AP; UPI; Reuters.

Jump to Index of Monthly Reports

04/1992 (BGVN 17:04) SE-flank fissure eruption continues; lava diversion attempted

Lava has emerged from a SE-flank fissure in the W wall of the Valle del Bove since 15 December, covering an estimated 7.3 km² with ~ 100 x 10⁶ m³ of lava. A well-developed tube system carried lava downslope, threatening the town of Zafferana Etnea and prompting attempts at lava diversion (figure 47). The lava production rate, as observed through numerous skylights along the main lava tube, has remained relatively constant, but distal flow fronts advanced at varying rates. The apparent intensity of gas emission from the eruptive fissure changed with weather conditions. During the last 10 days of April, fumarolic activity was observed in the W wall of the Valle del Bove, extending upslope from the eruptive fissure along its NNW trend. This zone was active on 14 December during the initial phase of the eruption.

Lava overwhelmed a series of barriers in early April, and advanced 1 km down a gorge (within the Valle di Portella Calanna) toward Zafferana during the second week in April. This flow stopped on 15 April at 750 m elevation, roughly 1.5 km from the inhabited center of Zafferana. Numerous ephemeral vents began to form below 1,000 m elevation on 19 April (on the E edge of Val Calanna, in which a barrier had been built in early January). Flows from these vents covered lava from previous days along the gorge below Portella Calanna. The longest stopped during the evening of 25 April at 755 m altitude, ~ 7.5 km from the eruptive fissure and 1.5 km from the center of Zafferana. Lava flows originated from a large ephemeral vent at the head of Val Calanna in the beginning of May, passing Portella Calanna atop previous flows on 6 May and reaching 850 m asl that evening.

Ephemeral vents also developed upslope, within the wide lava field that had formed in the S part of the Valle del Bove during previous months. The first formed around 1,900 m altitude (at Monte del Rifugio Menza) on 22 April, and a second occurred near the center of the lava field, at around 1,550 m elevation (near Poggio Canfareddi) on 25 April. Flows from these vents were not very substantial and were no longer active a few days later. On 5 May, only a modest active vent at the N edge of the lava field (around 1,600 m elevation) was observed.

Experiments with the use of explosives, cement blocks, and, more recently, lava blocks continued at skylights in the main lava tube (in the upper Valle del Bove, at around 2,100 m altitude, on 17, 21, and 29 April, and 4 May) and at ephemeral vents (near Portella Calanna on 15 April and in Val Calanna on 6 May). These were designed to cause lava overflows and thus reduce the amount of lava carried in tubes toward inhabited areas. As of early May, it was difficult to evaluate whether these experiments had favorably affected the course of the eruption. On 4 May an overflow began from a skylight in the main lava tube at around 2,100 m altitude, where blocks of cement had been dropped and explosives detonated on previous days. The modest overflow moved over the lava field that had formed in the preceding months. However, during this time, numerous ephemeral vents, varying daily in number and location, remained active above Zafferana at the head of Val Calanna (in the Salto della Giumenta).

Slow, weak degassing continued through early May from the summit craters. Weak ash ejections, caused by internal collapse, were observed only from Northeast Crater, on 22 April. Early April-early May seismic activity was much reduced from previous months.

Information Contacts: R. Romano and T. Caltabiano, IIV; P. Carveni and M. Grasso, Univ di Catania.

Jump to Index of Monthly Reports

05/1992 (BGVN 17:05) Fissure eruption continues; lava diverted; lava field described

The following is from R. Romano. Lava production from the fissure ... was continuing without noticeable variation in mid-June. Gas emission, from four explosion vents between 2,335 and 2,215 m elevation, has diminished along the upper part of the fissure. The main lava channel has roofed over, but lava was visible through a skylight beginning at 2,205 m elevation, where the effusion rate was estimated at 6-8 m³/s and the flow velocity at ~ 1 m/s on 7 and 13 June. Three more skylights were open along the main channel to 2,020 m asl. An overflow occurred on 12 June from one of the skylights, at 2,075 m altitude, but lava advanced only a few meters before returning to the main channel. This overflow was still active the next day. Ephemeral vents from the main tube remained active through the end of May: in the Valle del Bove; below the Valle del Bove in Val Calanna; and near the distal end of the flow field, along a deep gully under Portella Calanna (figure 48). Lava flows emerged more or less continuously from the latter vents, but did not descend below 800 m altitude. The total volume of lava produced by the eruption is estimated at 150 x 10⁶ m³.

Lava diversion. An earthen barrier built in a valley above the town of Zafferana Etnea in early January was breached by lava on 7 April. Lava overran a series of additional barriers the following week but stopped before reaching the town. Subsequent hazards efforts focused on reducing the lava supply to the end of the flow, by obstructing the main lava tube near the vent and disrupting lava production at ephemeral vents (17:3-4).

F. Barberi and L. Villari report successful lava diversion from the main tube, at a site 500 m downslope from the primary eruptive vent. In this area, at ~ 2,000 m elevation on the W wall of the Valle del Bove, lava was carried through a single tube locally broken by skylights. On 27 May, about 2/3 of the tube's lava was diverted into an artificially excavated channel by blasting through the 2-3-m-thick wall of the right levee. Two days later, bulldozers obstructed the natural channel by pushing large blocks of lava into it. By 1815 that day, all of the lava output (~30 m³/s) was flowing into the artificial channel. In effect, the diversion returned the active flow front to its position a few days after the onset of the eruption. Lava was moving downslope along the same path as the earlier main flow, but was > 6 km upslope from its previously most advanced front.

Flows generated by lava diversion efforts. R. Romano reports that as of 13 June, a vent remained active at the site of the first lava diversion. Although the vent has been shrinking, it continued to feed a flow that has advanced over lava from previous months, forming tubes and various ephemeral vents, many of which were near the S wall of the Valle del Bove. The ephemeral vents produced two lava flows, one near the S wall of the Valle del Bove at around 1,700 m elevation, the other in a more central position, at ~ 1,800 m asl on the main lava field. The lava flows that formed after the first diversion advanced more than a kilometer over the center of the lava field. Flows that followed the second diversion remained predominantly near the S wall of the Valle del Bove, passing and encircling a site at 1,575 m asl (Poggio Canfareddi), 2 km from their point of origin, on 3 June. This lava front stopped advancing on 5 June and several superposing lobes began to develop.

Seismicity and summit activity. Weak seismic activity began on 29 May, followed by an increase in volcanic tremor on 31 May that continued until the next day. Ash emissions, sometimes voluminous, occurred from the central craters at irregular intervals on 31 May and 1 June, first from the W vent (Bocca Nuova) then from the E vent (La Voragine). Only weak degassing preceded the ash ejection, but gas emission became more consistent beginning 2 June. COSPEC measurements yielded SO₂ flux values of ~ 10,000 t/d. Flashes from the summit craters were observed during the evening of 7 June from the W flank. Fieldwork on 12 June revealed that Northeast Crater was obstructed, with only fumarolic activity along the walls.

EDM data. S. Saunders reports that four lines of an EDM network on the upper S flank were remeasured on 7 May, showing a 138-ppm contraction that was interpreted as deflation during the eruption. Between July and October 1991, total extensional strain along these lines was 88 ppm, indicating pre-eruption inflation. Strain along these lines has returned to near pre-eruption levels.

Landsat Thematic Mapper data. The following is from D. Rothery. "The 1991-92 sustained lava eruption of Etna provides an opportunity to study lava flow development by remote sensing. The first cloud-free Landsat Thematic Mapper (TM) image of the eruption was recorded on 2 January at approximately 1000 (figure 49). Landsat repeats its coverage on a 16-day cycle; the next cloud-free acquisition was on 22 March and we are still awaiting receipt of those data. By manipulating radiance measurements in two wavebands, we hope to be able to constrain the surface temperature distribution of this flow along its length. The most noteworthy aspects of the 2 January data are: 1) There is a narrow 700-m length near the source that is radiant in TM band 4 (0.76-0.90 mm wavelength). As far as we know, this is the first time that thermal radiance in TM band 4 has been reported over a volcano. Field observations (A. Borgia) on 2 and 3 January show that this feature corresponds to a 10-15-m-wide open channel at the source of the flow. 2) The entire 6.5-km-long active flow is radiant in TM band 7 (2.08-2.35 mm wavelength). At least some of the areas that are also radiant in band 5 (1.55-1.75 mm) occur when the flow spills down a steep slope, breaking apart the raft of blocks and crust that otherwise blanket the underlying lava at near-magmatic temperatures."

Lava field characteristics. The following is an excerpt from a preliminary report by Wyn Hughes and Mark Bulmer, describing the eruption as of 18 May.

Lava leaving the eruptive vent advanced through a tube system that extended downslope to the foot of the western backwall of the Valle del Bove at 1,850 m asl. Several skylights were spaced at intervals along it. At the break in slope, numerous active ephemeral vents issued new lava-flow units onto the surface of the flow field (figure 48). These did not travel far from their source. Surface activity was otherwise absent within the Valle del Bove; lava was being efficiently transported through tubes toward the flow front. One tube system (with skylights and fume) could be traced through the center of the flow field in the Valle del Bove, toward Val Calanna. At the distal end of the Valle del Bove, several pressure ridges were visible, oriented perpendicular to the underlying ground slope.

Most of the surface activity was occurring in Val Calanna, where intense ephemeral vent activity was issuing new lava-flow units onto the flow-field surface. Lava was being supplied to this area through a series of tubes that descended from the Valle del Bove. Most of the activity in Val Calanna appeared to be supplied by a major tube system that could be traced (by skylights and fume) descending the backwall along its S margin (Salto della Giumenta). A smaller tube system probably supplied some ephemeral vents on the N margin of Val Calanna (S foot of Mte. Calanna).

In Val Calanna, effusive activity was mainly concentrated along the S margin of the flow field, where lava had ponded along the S wall of Val Calanna, and behind the man-made earthen barrier. From there, ephemeral vents in the crust fed numerous new lava-flow units, supplying three regions. Where lava moved directly NE, these were progressively widening the flow field at 1,050 m altitude. Flows that initially moved NE, but then changed to a more easterly direction, were supplying units that flowed around the N margin of the buried man-made barrier. Near the barrier, although active aa-textured flow fronts and channel-fed flow units could be traced on the surface of the flow field, most of the activity that contributed to its widening was supplied from tubes in the previous days' flow units. Ephemeral vents at 1,000 m elevation on the N margin of the buried man-made barrier supplied new flow units that were widening the field to the NE. However, these flow units were abutting the distal levee of the 1852-53 flow field, which was largely hindering the widening. On 18 May, some of these slow-moving tube-fed lavas managed to flow out of Val Calanna, and began the steep descent towards Zafferana. This activity was occurring on the NE side of the flow field. Three ephemeral vents had opened just below the S margin of the man-made barrier. A short distance downslope, flows from these vents combined to feed a front that advanced quite rapidly down the SW side of the flow field on the night of 17 May. By the next morning, and after destroying an abandoned dwelling during the night, the rate of advance had decreased, with the front at ~ 870 m asl. All of these active regions were being channel/tube-fed by lava from along the S wall of Val Calanna, which in turn was being supplied by tubes that descended from the Valle del Bove.

Flow-field morphology. Although the flow field was widening somewhat towards the NE end of Val Calanna, the activity was dominated by ephemeral vents extruding new flow units onto the surface of the original field. This was mainly occurring at ~ 1,800 and 1,050 m altitude, where the backwalls of the Valle del Bove and Val Calanna give way to their respective floors (figures 48 and 50). The surface activity was rapidly burying aa channel-fed flow units from early in the eruption. They could only be seen among the flows that had gone around the N margin of Mte. Calanna, and as isolated inliers on the floor of Val Calanna.

New flow units from ephemeral vents generally emerged with pahoehoe surface textures, in contrast to the early activity whose products had entirely aa textures. The flow-field surface on the floor of Val Calanna, as already occurred in the Valle del Bove, was slowly becoming dominated by pahoehoe textures. Small-scale pahoehoe textures, similar to those described by Pinkerton and Sparks (1978) for the sub-terminal 1975 flow field, prevailed around the ephemeral vents in Val Calanna. However, among the more active vents, pahoehoe slab textures that characterized the near-vent surfaces of new channel-fed flow units progressively changed to aa with increasing distance from the vent area.

Comparison with historical flow fields on Etna. The current ephemeral vent activity within the 1991-92 flow field is consistent with the pattern of historical eruptions that lasted > 100 days (Hughes, 1992). By then, the early channel-fed aa activity that characterized the lengthening and widening phases in the flow field's growth had given way to a tumulus-building phase at the vent area — for example, 1865 (Fouque, 1865); or at a break in slope below the vent area — for example, 1950-51 (Cumin 1954) and 1983 (Frazzetta and Romano, 1984). Important in the emplacement of the 1983 flow field was the evolution of the main supply channel near the vent into a lava tube. By the eruption's 60th day, the tube formed a continuous link between the vent and the lava mound that had accumulated around the break in slope at 2,000 m altitude. The hydrostatic pressures generated within the lava tube were then sufficient to lift and fracture the roof of the lava mound, allowing the escape of lava through ephemeral vent activity. This sequence of events signified the early stages of tumulus development. The present activity occurring at 1,800 m altitude within the Valle del Bove is similar.

The second area of ephemeral vent activity away from the vent area and initial break in slope appears, however, to be unique to the 1991-92 flow field; a similar phenomenon has not been documented for Etna flow fields of the last 250 years. For most, the concave profile of the volcano's flanks (figure 51) meant that once the lava had descended from the steep upper slopes it only encountered progressively gentler gradients. However, the terrain over which the 1991-92 lavas have flowed is much more irregular, with a terraced appearance. The steep terrain around the vent in the upper Valle del Bove is duplicated downslope in the upper reaches of Val Calanna. The morphologic positions of the ephemeral vent activity within the Valle del Bove and Val Calanna are similar (figure 50); both occur at the foot of a steep slope down which lava is transported through tubes. It must be concluded that conditions favoring tumulus construction have also been duplicated within Val Calanna.

References: Cumin, G., 1954, L'eruzione laterale del Novembre 1950-Dicembre 1951: BV, v. 15, p. 3-70.

Fouque, F., 1865, Sur l'eruption de l'Etna du 1st Fevrier 1865: C. Rend. Acad. Sci. Paris; v. 60, p. 1331-1334; and v. 61, p. 210-212.

Frazzetta, G., and Romano, R., 1984, The 1983 Etna eruption: event chronology and morphological evolution of the flows: BV, v. 47, p. 1079-1096.

Hughes, J.W., 1992, The Influence of volcanic systems on the morphological evolution of lava flow fields: Ph.D. dissertation, University of London, 255 p.

Pinkerton, H., and Sparks, R.S.J., 1976, The subterminal lavas, Mount Etna: a case history of the formation of a compound lava flow field: JVGR, v. 1, p. 167-182.

Information Contacts: F. Barberi, Univ di Pisa; L. Villari, IIV; R. Romano and T. Caltabiano, IIV; P. Carveni, M. Grasso, and C. Monaco, Univ di Catania; W. McGuire and A. Morrell, Cheltenham and Gloucester College of Higher Education; S. Saunders, West London Institute; D. Rothery, A. Borgia, R. Carlton, and C. Oppenheimer, Open Univ; J. Wyn Hughes and M. Bulmer, Univ College London.

Jump to Index of Monthly Reports

06/1992 (BGVN 17:06) Continued flank lava production

Lava production continued from the fissure that opened in the W wall of the Valle del Bove on 15 December. Gas emission from 4 vents in the upper part of the fissure (2,215-2,235 m altitude; figure 52) fluctuated daily, probably with changes in weather conditions. However, gas emission has diminished since the eruption's initial months.

No variation was evident in the movement of lava visible through a skylight high in the main channel, at 2,205 m altitude. Lava was also seen flowing through a skylight in lava tubes that formed in June along the channel into which lava was artificially diverted on 27 May (~ 1,980 m elevation) (17:05). From there, lava advanced through a complex series of tubes past the field that had formed in recent months. Lava again reached the surface around 1,800 m altitude from a changing number (generally 3-4) of ephemeral vents at varying locations representing tube bases. Lava flows extruded from these vents have generally been modest, have remained in the center of the lava field, and have not advanced beyond 1,600 m asl. As of the morning of 9 July, only one flow was active within the Valle del Bove, near the center at around 1,670 m altitude, with a fairly well-fed front. The volume of lava produced during ~7 months of eruption is estimated to be around 165 x 10⁶ m³.

Seismic activity during the period was characterized by low energy release. Significant increases were observed 8-9 July, when events of 2-4 Hz were recorded. The most significant perturbations were detected on 8 July at 1554, for 180 seconds, and at 1601 for 130 seconds. Tremor was almost nonexistent, obscured by seismic noise that characterizes periods of low activity at the volcano.

More or less voluminous gas emissions occurred from two vents at the bottom (~100 m from the rim) of the two central craters (Bocca Nuova and La Voragine). Incandescence caused by superheated gases (>1,000°C) from the vent in La Voragine was sometimes visible. Gas also emerged from a vent that has opened in Southeast Crater. Northeast Crater appeared to have been completely obstructed by internal collapse. COSPEC measurements of SO₂ flux from the summit crater showed relatively high values of ~ 8,000 t/d.

Information Contacts: R. Romano and T. Caltabiano, IIV; P. Carveni, M. Grasso, and C. Monaco, Univ di Catania; G. Luongo, OV.

Jump to Index of Monthly Reports

07/1992 (BGVN 17:07) Continued lava production from SE-flank fissure; lava diversion summarized

The following, from R. Romano, describes activity from early July through early August.

Early July-early August activity. The eruption ... was continuing after ~ 8 months. Gas emission from the upper part of the fissure has greatly diminished lately, although abundant white vapor was often observed, probably because of weather conditions. Fieldwork on 5 August revealed no notable changes in effusive activity from previous months. The lava flow was visible through a skylight at the beginning of the main lava channel (at 2,205 m asl) and through two smaller skylights at 2,100 m altitude. From there to ~ 1,800 m, lava flowed through a complex system of tubes, resurfacing from numerous ephemeral vents that varied in number (generally about 10) and location (mainly in the center of the lava field). From these ephemeral vents (all between 1,800 and 1,700 m elevation) very modest lava flows emerged. These advanced a few hundred meters at most, never moved past 1,600 m altitude, and remained within the pre-existing lava field. The total volume of lava produced by 234 days of activity was estimated at 170 x 10⁶ m³.

No significant changes were observed at the central craters, where gas emission continued. The more active vent in early August was at the W crater (Bocca Nuova). Northeast Crater has remained obstructed for a few months, with only weak fumarolic activity on the inner walls. Internal collapses continued to occur. Gas emission from Southeast Crater was unchanged.

Seismic activity was low, with only 22 recorded events from early July through early August. The majority of the seismicity was characterized by swarm sequences in the summit area. The most significant, on 11 August, consisted of four shocks with a maximum magnitude of 2.5. Harmonic tremor was of very low energy and showed no variation over time.

The following is from a report by L. Villari.

Civil Protection problems and lava diversion. An earthen barrier was erected at the E end of Val Calanna by the beginning of January 1992, to prevent or delay the advance of lava into a narrow valley leading directly to the nearby (~ 2 km downslope) village of Zafferana Etnea (17:02). Lava expanded into the large Val Calanna basin in February and March, and began to accumulate against the inner wall of the barrier on 14 March. By the end of the month, lava almost completely filled the Val Calanna basin and rose slowly up the barrier's inner wall. Several lobes successively reached the barrier, and the lava field progressively grew and thickened, reaching the barrier rim by 7 April. Lava first overflowed the barrier, along its N sector, during the evening of 8 April, quickly followed by other lobes along the S and central part of the barrier's rim. Lava covered ~ 1 km during the first few hours, merging downslope into a single stream that advanced quickly toward the village. The flow's confinement in a narrow valley favored more rapid progress downslope. Three minor earthen barriers were rapidly constructed along the valley (10-11 April, 830 m asl, 110 m long, 12 m high; 11-12 April, 810 m asl, 90 m long, 6 m high; 13-14 April, 770 m asl, 160 m long, 12 m high) to slow the advancing flow. The barriers were built, like the major one at the E end of Val Calanna, by digging the valley bottom in front of the advancing flow and accumulating the loose material on a small natural scarp. Because the valley is narrow, the confined basins were only able to contain small volumes of lava, and the flow's advance was only briefly delayed (for hours to a day). The front reached <1 km from Zafferana (at Piano dell'Acqua) on 16 April, ~1.5 km from the major barrier and 8 km from the eruptive fissure (figure 53).

At that time, morphologic conditions prevented any other local intervention to slow the lava advance. The creation of any possible artificial obstacle to the advancing front would divert the flow toward inhabited areas not necessarily threatened by the natural flow path. Diversion efforts were therefore concentrated far upslope, near the eruptive vent.

Attention was primarily on a skylight in the main lava tube at ~ 2,000 m altitude on the W wall of the Valle del Bove, a few hundred meters from the active vent. The diversion's early focus was blockage of the main tube carrying lava to the active front, by sliding solid rocks and concrete blocks into the flowing lava. Access problems required transport of solid materials to the site by helicopter, to be directly unloaded into the lava stream, or accumulated around the skylight's rim for later use. Lava tube blockage was also assisted by blasting large volumes of solid lava and welded scoriae forming the flow levees. This was partially successful and contributed to slowing the advance of the active front by several days.

Despite these efforts, on 5 May, a major new flow emerged from Val Calanna atop the 10 April flow, reaching Piano dell'Acqua on 11 May, 120 m beyond the 16 April flow and ~ 500 m from the outskirts of Zafferana. On 22 May, a further attempt to divert lava from the main natural tube to an artificially excavated channel high in the Valle del Bove produced a vigorous lobe that traveled 1 km in a few hours. Only 1/3 of the lava was spilled into the artificial channel, and the new flow roofed over within two days, with a significant loss of supply from the main natural flow.

A four-phase intervention plan was then defined (figure 54): a) digging an artificial channel to drain the main natural tube; b) cutting the lateral tube wall to a minimum thickness (2-3 m) that could be blasted through with a single charge; c) blasting the lateral wall; d) blocking the natural tube to divert all of the lava into the artificial channel.

Phases a and b were accomplished in about a week. A 7-ton charge, set off in a single explosion on 27 May at 1636, opened a large breach in the natural tube and caused spillage of ~ 80% of the flowing lava. The natural tube was progressively blocked by sliding solid materials into it during the next two days, and the flow was totally diverted into the artificial channel by 29 May. The artificially channeled flow went down the W slope of the Valle del Bove and remained confined inside the valley. The diversion effort stopped the most advanced front that had been moving toward Zafferana, by removing its source of supply.

The artificially channeled lava flow had extended to 1,550 m asl in the S part of the Valle del Bove (at Piano del Trifoglietto) by 30 May. Lava output from the ephemeral vents in Val Calanna quickly decreased, and molten lava was not evident within a few days.

The effusion rate from the eruptive fissure decreased sharply 31 May-1 June, causing the active flow front to be confined within the Valle del Bove, as activity resumed in the central craters. Several hours of continuous ash emission occurred from the W crater (Bocca Nuova) on 31 May, and an incandescent blowhole formed in the E crater (La Voragine) following gas blasts on 1 June. Noisy gas emission continued from La Voragine in succeeding days.

During June, lava flowing in the artificial channel expanded within the Valle del Bove to ~ 1,650 m elevation, overlapping the lava field that had formed since January. The effusion rate was reduced ~ 50% by the end of June, and the upper part of the artificial channel became a tube. The longest flow did not extend more than 1.5 km from the diversion point at 2,000 m altitude. At the end of June, the newly generated lava field, overlapping the old one, covered ~ 0.8 km².

Northeast Crater. Repeated inner-wall collapses have been observed in Northeast Crater since February. They became quasi-continuous from 26 February through mid-March, associated with explosive activity that ejected blocks and caused a little fine reddish ashfall. From the end of March until 23 May, the collapses were limited to episodes lasting only several hours each, associated with only minor fine ashfall. The crater bottom dropped ~70 m, leaving a pit ~100 m across in place of the previous funnel-shaped depression.

Lava flow measurements. Lava-channel dimensions, flow velocity, and related rheological parameters were observed at a skylight along the lava tube at 2,000 m altitude, and at ephemeral vents in the Val Calanna area, 7 km downstream at 1,000 m elevation. Flow velocities at the exit of the lava tube (~ 4-5 m wide and 5 m deep) in May and the beginning of June were 0.5-1 m/s; flow rates and viscosities were 15-25 m³/s and 100-300 Pas. At the ephemeral vents and the single-channeled flows (1-4 m wide and 1-2.5 m deep), March-May flow velocities were 0.1-0.3 m/s. The calculated flow rate ranged from 0.1 to 4 m³/s, with a corresponding viscosity of 150-1,300 Pas. (See the report by Murray, below, for velocities and flow rates from late June through mid-July).

Direct measurements in June along the main channel (10-40 cm below the lava surface) at 2,000 m altitude, using an immersion thermocouple (Pt-PtRh) yielded temperatures of 1,053-1,068°C. Values were similar (1,030-1,068°C) at several ephemeral vents (10-60 cm inside the lava flow) in the Val Calanna area from March until the end of May.

Petrography and chemistry. Analysis of lava sampled near the vent and at the flow fronts showed no significant variations in chemical or petrologic composition (17:02). All are porphyritic hawaiites (Mg# 52-54), with phenocrysts of plagioclase (15-25 volume %), clinopyroxene (7-10%), olivine (2-3%) and minor (~ 1%) Ti-magnetite.

Seismicity. Low-level seismic activity characterized February-June, despite the continuing eruption. The daily rate was quite low, with only 24 fault-derived earthquakes of M >1 recorded during the period, a rather low value for Etna. No variations were evident in the daily rate or the cumulative strain release (figure 55). Most of the recorded shocks were centered on the SE flank. Maximum local magnitude was 2.8. There were no significant changes in the pattern of volcanic tremor amplitude. Two short episodes of increasing amplitude, on 31 May and 1 June, had maximum overall amplitudes slightly lower than during the December 1991 eruptive phase.

From 26 February until May, seismic stations on the upper flanks recorded many shocks characterized by an emergent onset and low frequency content. At least three waveform types were recognized. All of the shocks were located near the summit craters at <1 km depth. At the same time, morphologic changes were noted within Northeast Crater, associated with the emission of non-juvenile tephra. Most of these shocks were believed to be linked to rockfalls within Northeast Crater. Some explosion shocks were recorded during the same period. These phenomena were most common in February and March, then gradually decreased, disappearing entirely by 23 May.

Ground deformation. Continuous monitoring of ground tilt in a shallow borehole network showed only minor variations since the eruption began in December 1991. No sign of the expected deflation of the volcano was noted, despite the large volume of magma that has been erupted.

EDM networks on the S, SW, and NE flanks, previously surveyed in 1991, several months before the eruption began, were re-measured in late spring and early summer. Contraction was observed, mostly on the SW and NE flanks, while the S flank did not show any appreciable change in line length. The overall deformation pattern of the volcano appears consistent with shallow magma injection into the eruptive fissure, trending roughly NNW-SSE (figure 56). GPS surveys in April-May 1992 detected significant contraction of lines, mostly on the W flank, compared to previous surveys in June-July 1991 (figure 57).

The following, from J.B. Murray, describes eruptive activity and the results of deformation studies, 9 June-14 July.

Lava flows. The rate of lava production from the vent in the W wall of the Valle del Bove was much lower than in April. Active flows were visited on 28 June, and 7, 10, 12, and 13 July. Central flow speeds of 2-10 m/minute (depending on slope), widths of 1.5-6 m, and a rate estimated at around 0.3-0.4 m³/s were noted at a single flow on 28 June. A flow about twice as big was seen to the E, suggesting a total discharge of the order of 1 m³/s. Flow fronts were only advancing to ~ 1.2 km from the vent on 28 June, but discharge seemed slightly increased during July visits to the fronts, which were about 2.2 km from the vent on 7 July, and 2.6 km by 13 July.

Summit activity. Continued collapse was occurring around the edge of Northeast Crater, with rockfalls every few minutes or so. Particularly big collapses were seen on 8 July between 1556 and 1610. Southeast Crater had strong high-temperature fumaroles, but no Strombolian activity.

The floors of the two central craters both had single vents that continuously discharged hot gas without any explosions. The vent in La Voragine was ~3 x 10 m, glowed bright red in daylight, and beginning 10 June emitted gas in voluminous puffs from which radiant heat could be felt. There were no signs of fresh bombs or scoriae around the vent. The depth of Bocca Nuova was estimated at ~160 ± 20 m.

Vertical movement. A 25-km levelling traverse, and heights derived from trigonometric levelling during trilateration, yielded details of vertical displacement of 241 stations across the summit and upper flanks since September 1991. Subsidence occurred along a narrow strip extending SSE from the summit, with maximum movements reaching just over 1 m (at two stations between Cisternazza and Belvedere). This central strip is flanked by a swelling to the W of 3-7 cm, and a much larger swelling to the E that reaches 37 cm (at Serra Giannicola Piccola). Southeast Crater has dropped 87 cm and Northeast Crater 48 cm, and the NE rift has risen another 3.4 cm (near Monte Pizzillo). These movements are similar to displacements seen over eruptive dikes in 1989, 1986, 1985, and 1983, but the swelling to the E is higher and broader than any previously recorded.

Horizontal movement. The summit trilateration network shows E-W extensions of 1-1.5 m since September 1991 across the graben and fissures leading S to the eruption site. It is clear that the main feeder dike passes between the Torre del Filosofo and Belvedere, and probably crosses into the Valle del Bove just E of Cisternazza (figure 53). Movements of this magnitude are not unusual during Etna's flank eruptions, and are similar to those recorded during the four eruptions mentioned above.

After network adjustment, some individual station vectors showed unexpected movements. Many of the stations E of the summit also show large eastward displacements, with two (near the Serra Giannicola Piccola) showing 1.3 m of eastward movement, and much of the Valle del Leone having moved 0.5 m ENE. The region at the top of the valley's E wall is cut by new N-S fissures, and SE of Southeast Crater is a region of complex fissuring N of a new cinder cone.

Dry-tilt data. Results from the 30 dry-tilt stations confirm that this eruption is a major one among recent eruptions. In addition to the expected large tilts near the eruptive fissures (192 µrad near Cisternazza), unusually large post-September 1991 tilts of 115 and 92 µrad occurred ~ 4 and 5 km SW of the summit (at Monte Palestra and Monte Vituddi). Unexpectedly large tilts were also recorded ~ 7 km NW and 4.5 km WNW of the summit (at Monte Maletto and Monte Nunziata), and both the Punta Lucia and Pizzi Deneri stations have abruptly increased their tilt to the E, as after the 1981 eruption.

The observed dry tilts are exceptional and suggest that something fairly fundamental has occurred. Only the 1981 eruption had tilts of this size at distant stations. That eruption marked a major turning point in Etna's deformation. After 1981, five stations that had previously been stable, even during flank eruptions, tilted during the next few years by amounts that eventually totalled as much as 1,000 µrad.

Information Contacts: L. Villari, R. Romano, and T. Caltabiano, IIV; P. Carveni, M. Grasso, and C. Monaco, Univ di Catania; G. Luongo, OV; J. Murray, Open Univ.

Jump to Index of Monthly Reports

08/1992 (BGVN 17:08) Increased lava emission from break in main tube

The eruption ... appears to have become more vigorous in early September. Until 2 September, activity was similar to previous months, with lava flowing through a complex system of tubes and resurfacing from ephemeral vents of varying number (recently about 4) and location. Lava flows from the ephemeral vents were generally of modest size, advancing only a few hundred meters and remaining within the pre-existing 1991-92 lava field. Gas emission from the upper part of the fissure has remained similar to past months, with modest variations linked to weather conditions.

The roof of the main lava tube broke open late in the evening of 2 September, near a former skylight at ~2,150 m altitude and above the site of artificial lava diversion in May (at ~2,000 m elevation; 17:07). The flow from the broken tube first moved ENE above the lava field, then along its S side over terrain not previously covered by lava from this eruption. Lava advanced ~ 1 km to 1,700 m altitude by the next morning, then slowed to a stop during the succeeding days, reaching ~1,650 m elevation. The main lava tube, with two fuming skylights, remained active on 4 September below 2,000 m altitude. The only large ephemeral vent was at around 1,700 m asl, in the central part of the lava field. Another overflow occurred during the morning of 9 September at around 1,980 m altitude, below the lava diversion area. The flow advanced across the central part of the lava field, quickly reaching 1,650 m elevation. The total volume of lava produced by 272 days of activity was estimated at 190 x 10⁶ m³.

Activity from the central crater's two vents remained similar to previous months, with continuing gas emission, strongest from the W vent (Bocca Nuova). Gas, sometimes voluminous, also continued to emerge from two small vents in Southeast Crater. Northeast Crater remained obstructed by debris. Landsliding persisted from the walls, particularly in the N and S parts of the crater. Very weak fumarolic activity occurred from Northeast Crater's inner walls. SO₂ flux from the summit craters, measured by COSPEC, remained at relatively low levels (~ 2,000 t/d) during August, but measurements in early September yielded higher values, ~ 5,000 t/d.

From 15 August through 11 September, 176 seismic events were recorded, characterized by low energy release. The most significant activity was a sequence of 43 summit-area events 6-7 September, with a maximum magnitude of 3.2. Harmonic tremor has been nearly absent.

Information Contacts: R. Romano and T. Caltabiano, IIV; P. Carveni, M. Grasso, and C. Monaco, Univ di Catania; G. Luongo, OV.

Jump to Index of Monthly Reports

09/1992 (BGVN 17:09) Lava flows from tube system remain within 1991-92 lava field

The SE-flank fissure eruption ... continued relatively unchanged in September and early October 1992. Gas emission from the upper part of the fissure was similar to previous months, varying with weather conditions. Lava continued to flow through a complex tube system, emerging from ephemeral vents at frequently changing locations. The resulting lava flows were generally modest-sized, advancing only a few hundred meters over the pre-existing lava field. This pattern of activity changed only when a substantial increase in the amount of lava moving through the main tube caused an overflow through a skylight. On 3 October at about 1830, lava began to emerge from a skylight at 2,150 m altitude, preceded by vigorous emission of white vapor. The overflow remained active on 8 October, and lava had advanced about 1 km. A similar episode occurred from the same location in early September. During 8 October fieldwork, numerous ephemeral vents were also active. Three were in the area of May's artificial lava diversion around 2,000 m altitude, three at ~ 1,800 m elevation (around Serra Pirciata), and 3-4 others near 1,700 m asl. Flows from the ephemeral vents remained modest in size, did not advance beyond 1,650 m altitude, and stayed within the Valle del Bove. Total lava volume from 300 days of activity was estimated at around 210 x 10⁶ m³.

Gas continued to emerge from two small vents on the floor of the central craters, at ~ 100 m depth. Gas emission generally occurred under pressure from the W crater (Bocca Nuova). A small vent on the S edge of Southeast Crater continued to emit gas. Northeast Crater remained obstructed by debris, with landslides still occurring in its N and S parts.

SO₂ emission, measured by COSPEC, continued to increase. During the first 10 days of October, values exceeded 10,000 t/d, twice Etna's average SO₂ flux.

Seismicity remained at low energy between 11 September and 13 October. About 230 microearthquakes were recorded, centered mainly in the summit area. The largest (M 3.0) occurred on 16 September at 0650 and was felt in nearby towns. On 27 September, a brief sequence of 7 events occurred on the W flank. The strongest shock (M 3.7), at 1255, was felt to ~ 70 km away (in the Siracusa area). Tremor has been nearly absent.

Information Contacts: R. Romano and T. Caltabiano, IIV; P. Carveni, M. Grasso, and C. Monaco, Univ di Catania; G. Luongo, OV.

Jump to Index of Monthly Reports

10/1992 (BGVN 17:10) More vigorous lava production and gas emission

The eruption ... appears to have become slightly stronger in recent weeks. A small increase in the effusion rate was apparent during the report period (13 October-12 November) at the main vent (2,210 m asl) after lava production had remained relatively constant for the previous several months. Lava initially moved through a single tube, with a surface trace marked by four skylights from 2,210 to 2,150 m altitude. The lava resurfaced (beginning at ~1,780 m elevation) within the lava field formed in past months. Three large ephemeral vents fed wide, thick flows, some of which advanced more than a kilometer within the lava field. On 11 November, the front of one flow was at 1,600 m altitude, in the center of the lava field. Small flows also emerged from tens of minor ephemeral vents, with locations that changed daily. Characteristic cumulo-domes formed in areas with high concentrations of ephemeral vents. The total volume of lava produced by 334 days of eruption was estimated at ~ 240x10⁶ m³.

Gas emission from the upper part of the eruptive fissure was also a little stronger than in previous months. Fluctuations in the apparent gas emission rate remained linked to weather conditions. Vigorous degassing continued from Southeast Crater and from the central crater's two vents. Rare, modest ash ejections occurred from the W vent of the central crater (Bocca Nuova). Weak fumarolic activity continued from the walls of Northeast Crater, still obstructed by debris. SO₂ flux, measured by COSPEC, remained high, ranging from 5,000 to 10,000 t/d, typically around 8,000 t/d.

Seismicity remained at low levels 13 October-12 November. About 100 events were recorded, mainly in the summit area, with magnitudes of 1.1-3.4. A large proportion of these occurred during the first week in November. The 34 events detected 3-4 November included a swarm of 15 summit-area shocks between 0500 and 0537 on the 3rd; the strongest, at 0500, had M 3.0. Of the four summit earthquakes recorded between 1220 and 1249 on 9 November, three had magnitudes exceeding 2.5, including the strongest of the report period, M 3.4, at 1249. Harmonic tremor has been nearly absent.

Information Contacts: R. Romano and T. Caltabiano, IIV; P. Carveni, M. Grasso, and C. Monaco, Univ di Catania; G. Luongo, OV.

Jump to Index of Monthly Reports

11/1992 (BGVN 17:11) Lava emerges from tubes onto 1991-92 lava field; small summit ash ejections

Lava production became more vigorous during the first half of November, but seemed to be decreasing in early December, a year after the SE-flank eruption began. After emerging from the vent, lava initially flows through a single tube, with a surface trace (from ~2,210 to 1,980 m altitude) marked by at least five skylights. Lava then continues into a complex of tubes, emerging from numerous ephemeral vents (which varied daily in number and location) onto the extensive lava field that has developed in past months. On 9 December, the ephemeral vents formed a linear zone between 1,700 and 1,600 m altitude, feeding small flows that did not advance below 1,580 m. The larger flows advanced NNE on the N side of the lava field, while other flows moved mainly toward the E. After 361 days of activity, the eruption's total lava output was estimated at 255 x 10⁶ m³.

Gas emission from the upper part of the eruptive fissure was less vigorous than in early November, with fluctuations linked to weather conditions. Small ash ejections from the central crater's W vent were observed, particularly during the first few days of December. Degassing from the summit craters was otherwise unchanged, and Northeast Crater remained obstructed. SO₂ flux, measured by COSPEC, remained at high levels, ranging from 6,000 to 10,000 t/d and averaging ~8,000 t/d.

Between 13 November and 8 December, 140 microshocks were recorded at Etna, mainly in the summit area. Energy levels remained low and magnitudes did not exceed 2.9. Several small seismic swarms occurred. The most vigorous, on 28 November between 0624 and 0858, included 10 events of M 1.7-2.9 centered in the summit area. The number of shocks increased briefly 28-30 November, when 62 were recorded. No harmonic tremor was detected.

Information Contacts: R. Romano and T. Caltabiano, IIV; P. Carveni, M. Grasso, and M. Porto, Univ di Catania; G. Luongo, OV.

Jump to Index of Monthly Reports

12/1992 (BGVN 17:12) Continued lava production; summit degassing

The eruption ... continued without major changes through early January 1993. Lava frequently flowed NE and NNE, and by early January there had been a notable expansion of the upper part of the lava field toward the NE. A new lava overflow was observed at the end of 1992 and the beginning of 1993 along the main lava tube above 2,000 m elevation. The overflow fed three distinct lobes that advanced a few hundred meters, to ~ 1,900 m asl. Lava continued to flow through the main tube, and was visible in early January through three skylights between 2,210 and ~ 1,900 m elevation. From there, the main tube divided into a complex tube system, from which lava emerged onto the surface at ~1,700 m altitude through small ephemeral vents. On 8 January, about six ephemeral vents were visible, feeding small flows that advanced NNE and E over the lava field formed in previous months. The NNE flow reached 1,650 m elevation, the E flow 1,600 m. The volume of lava produced by 394 days of activity was estimated at ~ 270 x 10⁶ m³.

Gas emission from the upper part of the eruptive fissure was not very intense. Apparent fluctuations were linked to weather conditions. Summit-crater degassing was similar to the previous month. Northeast Crater remained obstructed, with only weak fumarolic activity on the inner walls. SO₂ flux, measured by COSPEC, was still relatively high at ~ 7,000 t/d.

Of the 83 seismic events recorded 9 December-11 January, 51 occurred in four swarms, all located in the summit-crater area, with magnitudes of 1.5-3.3. The most significant swarm, on 2 January, had 17 events, with the strongest (M 3.3) at 1342. This swarm was accompanied by a slight increase in the amplitude of tremor, otherwise nearly absent during the period.

Information Contacts: R. Romano and T. Caltabiano, IIV; P. Carveni, M. Grasso, and M. Porto, Univ di Catania; G. Luongo, OV.

Jump to Index of Monthly Reports

01/1993 (BGVN 18:01) Continued lava production extends lava field; summit degassing; low seismicity

The eruption ... is now Etna's longest flank eruption of the 20th century, surpassing the 372 days of E-flank activity in 1950-51. However, dominantly effusive eruptions from the summit area's Northeast Crater have persisted for many years (May 1957-February 1964; January 1966-April 1971; and September 1975-January 1977) and intermittent explosive activity from the central crater has continued since 1979.

The most active flows advanced NE and NNE, extending the upper part of the 1991-93 lava field toward the NE. On the morning of 4 February, lava flowing in the main tube was visible through two skylights, and emerged from small ephemeral vents on the N and S sides of the lava field. The approximately five northern ephemeral vents, between ~1,900 and 1,600 m elevation, were the most impressive, and fed the strongest flows, to the NNE. The small S vents, two of which were very close to the S wall of the Valle del Bove at 1,550 m asl, were the sources of very modest flows that moved E. Flows from both sets of vents advanced over the pre-existing lava field, and did not extend beyond elevations of 1,600 m (N vents) and 1,550 m (S vents). The volume of lava produced by 429 days of activity was estimated at 280 x 10⁶ m³.

Gas emission from the upper part of the eruptive fissure has declined notably, and as of mid-February only the former explosive vent at the fissure's lower end (2,215 m elevation) remained active. Degassing from the summit craters was similar to previous months. Modest ash emissions, caused by internal rockfalls, occurred rarely from the central crater's W vent. During the early morning of 3 February, phreatic explosions from Northeast Crater ejected old lava fragments to tens of meters W of the rim. A modest ashfall occurred on the E side of the crater, and ash was still visible on the snow during the following days. Northeast Crater was obstructed again after this activity, and the next day only vigorous fumarolic activity was noted on the crater floor. SO₂ flux, measured by COSPEC, declined from ~ 7,000 t/d in December to 5,000-6,000 t/d in January, about average at Etna.

Seismicity remained at low energy levels during the report period (12 January-15 February). All of the 125 seismic events (M 0.7-3.4) recorded during the period were centered in the summit-crater area. The seismicity included only one swarm (23 events, maximum M 3.4) on 3 February between 0527 and 0623. All were low-frequency events (1-5 Hz) and occurred as wave-trains that resembled spasmodic tremor. With that exception, volcanic tremor was absent.

Information Contacts: R. Romano and T. Caltabiano, IIV; P. Carveni, M. Grasso, and C. Monaco, Univ di Catania; G. Luongo, OV.

Jump to Index of Monthly Reports

02/1993 (BGVN 18:02) Lava flows continue; volume estimates reported

The following information, based on the report of the IIV, covers the period December 1992 through February 1993.

The eruption ... continued as lava gently flowed from the vent on the W wall of Valle del Bove, significantly expanding the flow field formed after the flow diversion of May 1992 (17:05). Lava moved to Piano del Trifoglietto through a forked lava tube, emptying through several ephemeral vents located mainly on the N and S sides of the flow field (figure 58). In the first half of December, lava escaped mainly through the S vents. Many small flows gradually covered Poggio Canfareddi Hill, previously isolated by flows moving E toward Mt. Zoccolaro. In the second half of December, activity shifted to the N vents, expanding the flow field over a flat area that had not been covered by lava from the current eruption. Using data from a GPS survey done in January, the total volume of lava erupted through 1992 was estimated to be 198 ± 40 x 10⁶ m³. The lava covers an estimated 6.7 x 10⁶ m² and the mean rate of lava production is 6m³/s.

By January 1993, lava flows from the S vents advanced to the Poggio Canfareddi area and a complex network of minor flows reached the foot of Mt. Zoccolaro at 1,530-m elevation. Lava continued to flow from the N vents, expanding the field 400 m to the N. On 27-29 January, a fast-moving lobe of lava flowed to the NE, reaching 1,500 m elevation, 4 km distant from the eruptive fissure.

Effusive activity declined in February, ceased at the S vents by 8 February. Flow from the N vents was less than in previous months and shifted to vents on the northern-most side of the flow field. The new flows did not expand the flow field.

The seismic network recorded five swarms of long-period events. Fourteen events with M >1 occurred on 1 December, 14 events on 23 December, five events on 25 December, 51 events on 30 December-2 January, and 26 events on 3 February. No event exceeded M 3. The swarms were located in a small focal volume between the summit craters and Pizzi Deneri (~2 km NE) at depths asl. Volcano-tectonic seismicity during the period remained low (only three events) comparable to that observed throughout 1992.

The 9-station bore-hole tiltmeter network recorded no significant deformation except for a sharp event 18-19 December. Steady degassing from the Etna summit craters was observed and a weak ash emission occurred on the morning of 3 December from the Bocca Nuovo vent. Minor landslides repeatedly affected the E inner wall of the NE crater until January. The crater floor had sunk by early morning on 3 February.

The following report from geologists at the IIV and the Univ di Catania with seismic information from G. Luongo, updates and complements the official IIV report above.

A lava flow, at least a few hundred meters wide, has formed on the NE side of the lava field that has been building since 27 May 1992 (figure 58). The flow, in the vicinity of Monti Centenari (2 km NE of the active fissure), is completely independent from the old field and is moving E in the middle of Valle del Bove. The lava of this flow is visible from between 2,205 and 1,700 m through a series of skylights on the main tube. Lava is surfacing through 4-5 ephemeral vents at ~1,500 m elevation; the vents active in the past on the N, S, and central parts of the old lava field have closed. On the morning of 12 March, the most advanced flows had reached 1,425 m elevation and were moving over lava of previous eruptions. By 1300 on 14 March, the lava front was at 1,400 m elevation, ~ 5 m wide, 1 m high, and moving at an estimated 1 m/h.

The estimated volume of lava produced after 458 days of activity is 295 x 10⁶ m³. This estimate was calculated using the same method as previous estimates reported in the Bulletin, but is ~ 50% higher than the GPS value reported above. No significant changes in degassing of the summit craters were noticed. Northeast crater is still obstructed, with very active fumaroles along the inside walls. COSPEC measurements of SO₂ flux remained normal (5-6 x 10³ t/d), except in early March when measured values were 12.5 x 10³ t/d.

Between 12 February and 15 March, 169 events of M 1.2-2.9 were recorded, mainly in the summit crater area. The majority of events appeared to be related to active degassing at the surface, with characteristic frequencies of 1-6 Hz. Volcanic tremor was completely absent.

Information Contacts: IIV. The last three paragraphs are from R. Romano, T. Caltabiano, M. Grasso, and M. Porto, IIV; P. Carveni and C. Monaco, Univ di Catania; G. Luongo, OV.

Jump to Index of Monthly Reports

03/1993 (BGVN 18:03) 1991-93 eruption ends

The following, based on the report of the IIV, describes activity in March.

The 1991-93 eruption ended on March 30 after 473 days of continuous lava flows. Lava stopped flowing to the S side of the flow field in mid-February, but continued to flow from several vents at 1,700-1,650 m elevation on the N side of the field, covering previous flows from the current eruption. Shortly after 8 March, an overflight revealed a thin flow that had traveled 0.5 km from an ephemeral vent at 2,020 m elevation. On 11 March a large lava flow moved toward the Valle del Bove over an area not yet covered during this eruption. Flowing 1.5 km from a large ephemeral vent at the end of a tube at 1,550 m elevation, lava spread down some gullies, stopping after 3 days at 1,390 m elevation, 5 km from the eruptive fissure (figure 59).

Lava flows declined in the second half of March. On 21 March a vigorous flow emerged from a vent at 1,850 m elevation and traveled several hundred meters NE in a few hours before slowing and finally stopping within two days. The remaining ephemeral vents gradually disappeared and the last small lava flow was observed on the morning of 30 March. In the following days, fieldwork at the eruptive fissure and along the upper lava tube revealed that no molten lava remained in the tube and that the delivery system was cooling.

Steady degassing continued through March at the summit craters. The floor of Northeast crater dropped another several meters. Seismicity remained low, especially from 1-10 March. For the month, 65 long-period events and 8 volcano-tectonic events (maximum M 2.4) were recorded. The only notable swarm occurred on 28 March when 10 events were recorded in two minutes. There were no significant variations in the volcanic tremor amplitude. Four of the 9 bore-hole tiltmeters recorded a sharp deformation event of moderate amplitude at the beginning of March.

The 1991-93 eruption began on 15 December 1991 and lasted 473 days. It was probably the largest eruption at Etna in the last 300 years, covering ~ 7 km² with >250 million m³ of lava.

The following information compiled by volcanologists at the IIV, Univ di Catania, and OV complements the official IIV report above.

The lava flow that had reached 1,400 m elevation on 14 March (18:02) stopped on 17 March. At about 1700 on 21 March a modest lava flow escaped through a skylight on the main lava tube just below 2,000 m elevation. It was accompanied by intense degassing from the upper part of the eruptive fissure. Through 25 March lava was observed flowing inside the main vent at 2,205 m and small, short-lived flows issued from ephemeral vents in the N part of the lava field at ~ 1,900 m elevation. Poor weather prevented detailed observation of the last days of the eruption.

Degassing (vapor and gas) from the upper part of the eruptive fissure declined. By 20 March it was difficult to observe from a distance. Degassing increased at the summit craters (especially from the central crater) during the final phase of the eruption. Through 9 April, the NE crater, where recent rockfalls had occurred, continued to be obstructed and weak fumarolic activity was present along the walls. COSPEC measurements of SO₂ flux revealed a sharp increase during the last half of March (>16 x 10³ t/d on 23 March). Measurements in April indicated the flux was returning to a normal level of 6-8 x 10³ t/d.

From 16 March to 19 April, 337 seismic events were recorded. They ranged from M 1.0-3.0 and showed characteristic frequencies of 1-6 Hz. All were located in the summit crater region except a M 2.7 at 0649 on 14 April that was located low on the E flank. Volcanic tremor was totally absent.

During the 1991-93 eruption an estimated 300 x 10⁶ m³ of lava flowed from the fissure on the W wall of Valle del Bove at an average rate of 7.3 m³/s.

Information Contacts: The first section is from the official report of the IIV. The second section is from R. Romano, T. Caltabiano, M. Grasso, and M. Porto, IIV; P. Carveni and C. Monaco, Univ di Catania; and G. Luongo, OV.

Jump to Index of Monthly Reports

04/1993 (BGVN 18:04) Steady degassing; seismicity low

Steady degassing from the summit craters followed the end of the 1991-93 eruption on 30 March (18:03). Increased gas emissions were noted at the central (Voragine) and SE craters (see figure 59) in April, but no morphological changes were detected. The floor of Northeast Crater sank a few meters in early April and remained obstructed by fallen material.

Seismic activity was low with only two volcano-tectonic events recorded. The highest magnitude event (M 2.7) occurred 14 April on the SE flank of the volcano at ~ 10 km depth. Long-period events were similar to those recorded in March, but fewer in number. There was also a decreasing trend in volcanic tremor spectral amplitude. No major changes were recorded by shallow bore-hole tilt stations on the slopes of the volcano.

Information Contact: IIV.

Jump to Index of Monthly Reports

05/1993 (BGVN 18:05) Steady degassing continues; seismic swarm

Following the recent eruption's end in March, steady degassing was observed in May from all of the summit craters except Northeast Crater, which remained obstructed by debris in the bottom. Seismicity increased from two volcano-tectonic events in April (18:04) to 23 in May (M 1-3.2). Most of the events occurred between 1206 and 2039 on 24 May. At the same time, an earthquake swarm with 21 discrete events occurred below the NNW flank of the volcano at 13-26 km depth. The number of long-period events also increased compared to the last two months, but tremor amplitude and frequency were unchanged. Inflation was detected at one shallow bore-hole tilt station, but no other tilt variations were recorded.

Information Contact: IIV.

Jump to Index of Monthly Reports

03/1994 (BGVN 19:03) Summary of activity since the end of the 1991-1993 eruption

Only steady degassing has been observed at Bocca Nuova, Voragine, and Southeast summit craters following the December 1991-30 March 1993 eruption. Northeast Crater, obstructed by debris that fell from the inner wall, has not shown appreciable degassing.

On 3 August 1993 the Bocca Nuova bottom sank ~30 m during one hour of strong degassing and ash emission that produced an ash column hundreds of meters high; small blocks and a few fresh bombs fell close to the vent. Unusually strong noise was heard and ground vibration was felt at the summit area during this explosive activity. These phenomena also enlarged the unstable crater rim, causing rockfalls for several weeks. Activity did not change significantly through the end of 1993; continuous degassing activity was observed at all craters except Northeast Crater, where reddish ash emissions in early October were probably related to release of overpressurized gas.

A slight renewal of seismicity was observed after the end of the eruption. Fracturing was the probable cause of 83 events (M >1); 14 of them were M 2.5. The cumulative strain-release trend was almost flat throughout the entire period, the only significant episode was a seismic swarm on 24 May 1993 (twenty-one M 1 shocks; Mmax = 3.2). The seismic activity was mainly located on the N and SE sides of the volcano; the N events had hypocentral depths of 12-26 km, whereas the SE events were <10 km. Volcanic tremor amplitude remained low during 1993; a moderate increase was recorded in July. Also, 27 long-period earthquake swarms were recorded in 1993. The best constrained hypocentral locations revealed a source volume below the summit area at a depth of <=3 km.

Tilt recorded at most of Etna's bore-hole stations showed a continuous small deflation of the radial component that started during the 1991-93 eruption. This tilt was confirmed by general contraction measured by the three EDM networks.

The following report is from S. Saunders and W.l McGuire. An EDM network high on the S and E flanks has been reoccupied 13 times between 1981 and 1993. Measurements have revealed >5 m of lateral displacement associated with four rifting events. The network was at least partly re-occupied in April, July, and November 1993. All three surveys came after the cessation of effusive activity in March 1993 (18:03). Compared to the immediately preceding measurements, 1993 data showed that N-S trending lines, broadly parallel to the eruptive fracture and the W rim of the Valle del Bove, lengthened by small amounts (30-60 ppm). Lines trending E-W, perpendicular to the fracture zone, showed no significant length changes between November 1992 and November 1993. These data confirm that the rifting process is contemporaneous with the initial propagation of the feeder dike for the 1991-93 eruption, with little additional dilation-related lateral displacement during the later stages of activity or following the end of lava effusion.

Information Contacts: IIV; S. Saunders, West London Institute; W. McGuire, Cheltenham & Gloucester College of Higher Education.

Jump to Index of Monthly Reports

07/1994 (BGVN 19:07) Explosive degassing from La Voragine; fumarole temperatures reported

The following describes [fieldwork] on 1-27 June and 10-18 July 1994.

"As during visits in June-July and September-October 1993, Northeast Crater was blocked and inactive, but collapse was continuing around the edge with minor rockfalls every few minutes or so. Southeast Crater was also little changed from 1993, with a quietly degassing vent under the SE rim, but no indication of gas coming out under pressure. There was strong high-temperature fumarolic activity around the crater rim, temperatures being generally highest in the cracks.

"The Chasm (La Voragine) had a single vent in its floor measuring ~ 8 x 10 m, discharging gas continuously under pressure in rhythmic puffs at a rate of ~ 30 puffs/min. On 17 June and 12 July only, distinct explosions could be heard at the rate of 1-8/min. These were the first signs of explosive activity since the end of the 1991-93 eruption, and an indication that the Strombolian degassing that has characterized the summit over the past few hundred years is resuming.

"Bocca Nuova vent was degassing almost totally silently from two vents, one to the SE and one to the W; however, on 27 June when the weather was calm, 13 very faint gas puffs/min could be heard. The SE vent seemed similar to last year, measuring ~ 10 m in diameter, but the W vent had collapsed and enlarged considerably, now measuring perhaps as much as 50 m in diameter. On the early morning of 16 June a reddish tinge to the plume above Bocca Nuova was first noticed. Upon closer inspection on 17 June, the SE vent was seen to be pouring out thick clouds of red dust, apparently a result of internal collapse within the vent, while the W vent continued to emit white fume only. Dust emission intensified in the following days, causing the downwind side (S through W) of the summit to become a striking red color. The activity was continuing in mid-July.

"The levelling traverse showed comparatively small vertical movements since September 1993. The area near Belvedere, and other areas over the dyke intruded during the 1991-93 eruption, had subsided by up to 2 cm, as had the NE rift zone near Monte Pizzillo. During the same period, a small area ~1 km SW of the summit inflated by just over 1 cm. Horizontal movements measured since October 1993 showed generally small or insignificant changes, with nearly all lines recording changes of >1 cm. Only two stations appear to have moved by more than this; a station on the E edge of Southeast Crater had shifted 3 cm E relative to nearby stations, and a station close to the NW edge of the Bocca Nuova had moved 2 cm W. These movements are consistent with expansion of the central magma column as it refills.

"Surface temperatures were measured between 1 and 27 June at four active fumarole areas with a Minolta/Land Cyclops Compac 3 hand-held radiometer (8-14 mm). Temperatures were not corrected for spectral emissivity, so all radiant temperatures are given here as brightness temperatures. On the NE rift zone, nine areas of fumaroles were observed near the N edge of the 1966-67 lavas (between 2,450 and 2,500 m altitude). Temperatures for fumaroles at the two lowest of these areas ranged between 33 and 50°C. Another area of fumaroles observed at the upper rim of the W wall of the Valle del Bove around Belvedere, above the 1991-93 dyke, had temperatures in the 57.5-84.7°C range. Temperatures measured at fumaroles and cracks in the still-cooling 1991-93 lava-flow field in the Valle del Bove were between 85 and 221°C. The locations and temperatures of fumarole areas measured in the vicinity of the summit craters are given in table 5. Temperatures of the vents within the central craters were also measured from the crater rim: 342°C for the Chasm vent, and 159 and 81.5°C, respectively, for the SE and W vents of Bocca Nuova. Active fumaroles were observed, but not measured, along the 1991-93 fissure zone and 14 December 1991 cones and flows between Southeast Crater and Belvedere, along the October 1986 fissure zone, and in the Valle del Bove below Monte Simone."

Table 5. Fumarole temperatures in the vicinity of Etna's summit craters, 18 and 27 June and 14 October 1994. Courtesy of Andrew Harris, Open University.

    1994             FUMAROLE/RIFT                   TEMP (°C)
    DATE               LOCATIONS

    27 Jun       NE Crater - at N rim                50.4-65.0
    27 Jun       NE Crater - rifts at NW rim         56.0-141
    27 Jun       NE Crater - at dip in NW rim        45.5-97.4
    27 Jun       NE Crater - at E rim                51.4-85.6
    18 Jun       Bocca Nuova - on N slope            40.5-75.6
    18 & 27 Jun  Bocca Nuova - inside N rim          42.2-54.3
    27 Jun       Bocca Nuova - rifts at N rim        52.0-74.4
    18 Jun       Bocca Nuova - at SW rim             52.0-65.7
    18 & 27 Jun  Central Craters - at S rim          40.6-82.6
    27 Jun       Between central & SE Craters        59.1-81.3
    18 & 27 Jun  SE Crater - rifts & at N rim        51.2-312
    27 Jun       SE Crater - rifts & at W rim        60.0-208

    14 Oct       NE Crater - fum at N rim            39.2-77.4
    14 Oct       NE Crater - rifts at NW rim          153-246
    14 Oct       NE Crater - fum at W flank          50.4-74.2
    14 Oct       NE Crater - fum at W rim            41.0-210
    14 Oct       NE Crater - fum at S rim            50.5-221
    14 Oct       Bocca Nuova - fum at N flank        50.1-75.5
    14 Oct       Bocca Nuova - fum & rifts at N rim  47.3-74.5
    14 Oct       Bocca Nuova - fum at SW rim         50.0-72.4
    14 Oct       Central Craters - fum at S rim      49.2-82.4
    14 Oct       fum between central & SE craters    50.2-82.8
    14 Oct       SE Crater - rifts & fum at N rim    57.5-482
    14 Oct       SE Crater - rifts & fum at NW rim   56.4-218
    14 Oct       SE Crater - rifts & fum at W rim    46.8-99.5
    14 Oct       SE Crater - rifts & fum at S rim    49.9-88.0
    14 Oct       SE Crater - rifts & fum at E rim    68.5-180
    14 Oct       SE Crater - rifts & fum at NE rim   52.2-121

Information Contacts: J. Murray and A. Harris, Open Univ; L. Platt, Sheffield Univ; D. Renouf, UK.

Jump to Index of Monthly Reports

10/1994 (BGVN 19:10) Minor explosive degassing and higher fumarole temperatures

The following describes [fieldwork] between 23 September and 14 October 1994.

"There are continuing signs that activity is increasing. At the Chasm (La Voragine), 1-4 very low rumbles/min were heard, but on 14 October six explosions much louder than those heard in June/July (19:07) were heard in 10 minutes. The Bocca Nuova was also producing around one distinct long explosive blast per minute, as opposed to the faint gas puffs heard in the summer. However, no audible explosions were heard when the Chasm was active on 14 October. Northeast and Southeast craters were quiet as in June/July, but temperatures more than 100°C higher were measured at the fumaroles on their outer slopes. Another sign of increasing activity was that during the five days of levelling (25-30 September), 22 earth tremors were detected by the shaking of the instrument. This is > 10 times higher than 1993, and the largest total of tremors noted in this way since September 1991, before the 1991-93 eruption.

"The levelling traverse showed a slight subsidence of the summit since June 1994, the maximum value being just under 3 cm compared to the Piano Provenzana, 6.5 km NNE of the summit. The subsidence is more or less concentric around the summit, with the exception of some stations on the upper E flank and over the 1991-93 dyke, which have subsided nearly a centimetre more than those nearby.

"On 14 October the areas of active fumaroles measured during June were visited. These were measured again using a Minolta/Land 330 hand-held radiometer (8.5-14.5 mm). Temperatures were not corrected for spectral emissivity, so all radiant temperatures are given as brightness temperatures (table 5). At the N, W, and S rim of Northeast Crater, maximum fumarole and rift temperatures were 105-135°C higher than those measured in June. H₂S was also smelled in the vicinity of these high-temperature fumaroles. Higher maximum temperatures were also measured from rifts at the N rim of Southeast Crater, these being up to 170°C higher than those measured in June. It is stressed that these rises in temperature may be the result of different fumaroles being measured on the two dates, though in view of the thorough coverage in June this seems unlikely. Elsewhere, fumarole temperatures were similar to those measured in June. Fumarolic activity only was observed on the floor of Northeast Crater, which was measured from the rim at 40.1°C. The bocca on the floor of the Chasm was measured from the crater rim at 339°C. At the Bocca Nuova, a temperature of 173°C was measured for the SE bocca and of 40.7°C for the NW floor; these were measured from the crater rim. At Southeast Crater, fumaroles decreased in temperature and number around the W and E rims, such that fumaroles were few and cool on the S rim."

Information Contacts: J. Murray and A. Harris, Open Univ.

Jump to Index of Monthly Reports

06/1995 (BGVN 20:06) Small explosions in May followed by larger ash plumes in June

The following report from the Istituto Internacionale di Vulcanogia (IIV) describes activity from December 1994 to June 1995. Additional information came from Open University geologists, from Henry Gaudru (SVE), and fromaviation notices. Fumarole temperatures measured by Open University geologists in the vicinity of the summit craters increased at Northeast Crater (NEC) between June and October 1994 (table 6). Temperature increases were greatest at the fumarole field on the S rim of the crater, and decreased towards the N rim.

Table 6. Changes in maximum fumarole temperatures measured at Etna's summit craters between June and October 1994. Courtesy of Open University.

    Location         Maximum Temperature (C)        Temperature
                         June 94    October 94      increase (C)

    NE CRATER
    Fumaroles at N rim        65      77              12
    Rifts at NW rim          141     246             105
    Fumaroles at W rim        97     210             113
    Fumaroles at S rim        86     221             135

    BOCCA NUOVA
    Fumaroles on N flank      76      76               0
    Fumaroles & rifts (N rim) 74      74               0
    Fumaroles at SW rim       66      72               6

    CENTRAL CRATERS
    Fumaroles at S rim        83      82              -1
    Between S rim & SE crater 81      83               2

    SE CRATER
    Fumaroles & rifts-N rim  312     482             170
    Fumaroles & rifts-W rim  208     218              10

After several months of steady degassing from the summit craters, Bocca Nuova produced a short sequence of mild explosive events on 10-12 December 1994, characterized by brownish columns of non-juvenile ash rising <1 km and fallout of small lithic blocks close to the crater rim. The most intense episodes took place at 0830, 0900, and 1310 on 10 December, and were recorded by the IIV video surveillance system at La Montagnola (2,600 m elevation), 3 km S of the summit craters. In the same period a few small explosive events with lithic ash and block fallout occurred into NEC, and on its bottom a new degassing vent gradually formed by the end of 1994.

In January 1995 several ash puffs from NEC were observed. They were more frequent between 31 January and 3 February, but continued all month, forming a thin ash layer around the crater rim. The most significant activity from NEC in the following two months was strong steam degassing, sometimes with ash.

An intense episode of ash emission from NEC occurred at 1000 on 9 May. Red-brown ash and accretionary lapilli fell on Milo, a village on the middle slope of the volcano. No block fallout was observed near the crater rim, and steam emission continued unchanged.

On 23 May at 1605 a new NEC explosion ejected lithic blocks; most of them were affected by fumarolic alteration that changed hard lavas and scoriae into very brittle materials with vivid white, yellow, purple, and reddish colors that were very easy to recognize on the discontinuous snow mantle. The area of fallout was ~0.2 km² and the maximum block volume reached 0.2 m³, however, most of the blocks were only a few centimeters in size. No juvenile material was found among the fall products and the event resembled to a pure phreatic explosion that ejected very altered material picked up from the walls of the December 1994 degassing vent and the NEC crater bottom. On the morning of 26 May an explosion visible (by SVE members) from the N flank at 1,800 m elevation generated a gray ash-and-vapor plume above NEC. When the SVE group reached the summit area, small blocks were visible around NEC and near the lower slope of Bocca Nuova.

On 30 May a weak, ash-bearing plume was observed from an airplane by J.B. Murray. Stronger activity from the vicinity of Bronte was noted on 8 June, when thick ash clouds up to 70 m high were reported late in the morning. On a 12 June summit visit, scattered wall rock (lying <1 m apart in some places) was seen between NEC and Bocca Nuova. These rocks were also found ~500 m away on the W flanks of NEC. Only the faint steady sound of gas emanating from the SSE part of Bocca Nuova could be heard. The fume was too thick there to see the floor clearly, but two fuming vents were suspected, one beneath the N rim, and the other, ~100 m SSE of it. Huge white billows of vapor were seen coming from the S side of NEC. Voragine crater exhibited silent emissions from a central ~10-m-wide vent. Guides reported quiet emissions at Southeast Crater, but it was not visited.

The IIV reported gas explosions and inner-crater wall collapses from Bocca Nuova in June. Gas emission came from two vents on the crater bottom, the northernmost of which produced some small phreatic explosions that threw several centimeter-size lithic-lava blocks up to 50 m NE beyond the crater rim. Some ash emission from NEC was observed during June. Murray reported that as of mid-June guides had stopped taking tourists to the crater edge because of the danger from explosions. The situation reminded Murray of the activity following the 1983 eruption (SEAN 08:04), when a series of sudden, large non-magmatic explosions occurred from the NE crater.

Aviation notices (SIGMETs) were issued for Etna on 21 June when an ash cloud reportedly rose 4,200 m. Ano