Erta Ale

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  • 13.6°N
  • 40.67°E

  • 613 m
    2011 ft

  • 221080
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Most Recent Weekly Report: 24 November-30 November 2010


Scientists from the Afar Consortium Project observed the lava lake at Erta Ale during 21-23 November. They noted Strombolian activity from the lava lake in the southern pit crater. The lava lake had filled the pit crater and breached the W rim, spilling two lava flows into the main crater. The lava lake was encompassed by a scoria ring that was about 4 m high on the S side. By 23 November, the lake was above the scientist's eye level when they stood W of the southern pit in the main crater.

Source: Afar Rift Consortium


Most Recent Bulletin Report: June 2011 (BGVN 36:06)


Observers watch dynamic lava lake during November 2010

Erta Ale contains two lava lakes within its caldera. During the last three years, several expeditions have visited the volcano to examine changes (BGVN 33:06, 34:07, and 35:01). This report synthesizes the reports of two teams that visited Erta Ale during November 2010. Both teams noted that the lava lake within the southern crater has risen, nearly filling the entire crater and overflowing onto the caldera floor.

Southern Crater activity. Afar Rift Consortium (ARC) scientists visited Erta Ale during 21-23 November 2010 (figures 28 and 29). Tom Pfeiffer (Volcano Discovery) and Micheal Dalton-Smith visited Erta Ale during 25-28 November 2010. The lava lake had risen above previously formed terraces (see BGVN 35:01 for information on terraces). Both teams noted that the lava lake had risen ~40 m, nearly filling the S crater and breaching its W rim, spilling lava flows onto the larger caldera floor. The still-hot overflows traveled distances of 50-100 m on the caldera floor, and one recent long flow (estimated to be from November 24th given its temperature) had almost reached the W caldera walls.

Figure 28. Satellite image of the Erte Ale caldera showing the two crater pits. Courtesy of Google Earth, with labels by Afar Rift Consortium in reference to their 21-23 November 2010 visit (Field and Keir, 2010).
Figure 29. Photograph of the Erte Ale showing the lava lake with an elevated rim, taken 22 November 2010. Person in bottom left of photo for scale. Photo by L. Field (Afar Rift Consortium). Taken from Field and Keir (2010).

The ARC team noted Strombolian activity from the lava lake in the southern pit crater (figure 30).Throughout their visit, the ARC team saw extensive amounts of Pele's Hair and clouds rich in hydrogen-sulfide gas. Fountaining was reported by Pfeiffer to reach heights of 30-70 m. Degassing fountains kept the whole lava-lake surface violently boiling for a large portion of the latter team's visit.

Figure 30. Photograph of the first lava to breach the rim of Erta Ale's S crater and then to enter the main caldera. Taken 21 November 2010 by L. Field (from Field and Keir, 2010).

The still-active lake was circular, ~40 m in diameter (about half to two-thirds its size in 2008 and 2009). The lava lake was reported to be encompassed by a bounding ring of chilled material that was ~ 4 m high on the S side. The morphology of the ring wall constantly changed as more lava overflowed, with parts collapsing and rebuilding.

From the night of the 22 November 2010 until the ARC team left on 23 November, the team observed a periodic rise and decline of the lava lake level.

According to Pfeiffer the lava level rose and fell by about 2-4 m about every 30 minutes. During the 25-28 November observations intense eruptive phases were observed. Lava overflowed about 12 times and fed new flows that topped older flows. During 25-28 November, the overall average level of the lake's surface rose an estimated 3-5 m.

Northern Crater activity. The ARC noted that during 21-23 November the northern crater pit was relatively quiet. They observed a small amount of incandescence during the night of 21 November (figure 31). During the day, they noted a new cone about 1 m high and lava flows of limited extent.

Figure 31. Photograph taken in January 2011 of an Erta Ale hornito with an incandescent vent in the N crater. Photo taken by M. Fulle.

According to the Volcano Discovery team, the deeper N crater had not changed much since their previous visit in February 2008 (BGVN 33:06). During their 2010 visit they saw a 7-10 m high hornito, in the N crater's center, with a glowing vent that sometimes spattered lava. According to Dalton-Smith, flaming gas was seen during the day and on 25 November, an extremely bright glow was seen at night. Upon the team's arrival at the volcano, a large fresh flow had recently surged from the hornito and covered most of the N crater floor.

Location and tectonics. Erta Ale is located in the Afar rift, a region that shows signs of undergoing a continent to ocean transition. The Afar rift is located between the Nubian and the Somalian plates. There is reason to believe that the mantle below the Afar rift region has an above average temperature (Bastow and Keir, 2011). The Afar Rift Consortium also noted that recent fissure eruptions occurred on Erta Ale's N flank.

References. Field, L, and Keir, D. 2010, Observations from the Erta Ale eruption 21st Nov-23rd Nov 2010. Afar Rift Consortium (ARC) (URL: http://www.see.leeds.ac.uk/afar/new-afar/home-page-assets/Observations_from_Erta_Ale.pdf). Additional information about the work of the ARC can be found at URL: http://www.see.leeds.ac.uk/afar/.

Fulle, M, 2011, Stromboli Online (URL: http://www.swisseduc.ch/stromboli/perm/erta/lake-2011-en.html).

Bastow, ID, and Keir, D, 2011, The protracted development of the continent-ocean transition in Afar, Letters, Nature Geoscience, DOI: 10.1038/NGEO1095 published online on March 11, 2011.

Keir, D, Pagli, C, Bastow, ID, Ayele, A., 2011, The magma-assisted removal of Arabia in Afar: Evidence from dike injection in the Ethiopian rift captured using InSAR and seismicity, Tectonics, v. 30, TC2008, DOI: 10.1029/2010TC002785, published 22 March 2011.

Information Contacts: Afar Rift Consortium (URL: http://www.see.leeds.ac.uk/afar/); Tom Pfeiffer, Volcano Discovery (URL: http://www.VolcanoDiscovery.com/); Michael-Dalton-Smith, Digital Crossing Productions (URL: http://www.digitalcrossing.ca/); Marco Fulle, Osservatorio Astronomico, Trieste, Italy (URL: http://www.ts.astro.it/) and at Stromboli Online (URL: http://www.swisseduc.ch/stromboli/perm/erta/lake-2011-en.html).

Index of Weekly Reports


2010: November
2005: January | September | October
2004: December
2003: January

Weekly Reports


24 November-30 November 2010

Scientists from the Afar Consortium Project observed the lava lake at Erta Ale during 21-23 November. They noted Strombolian activity from the lava lake in the southern pit crater. The lava lake had filled the pit crater and breached the W rim, spilling two lava flows into the main crater. The lava lake was encompassed by a scoria ring that was about 4 m high on the S side. By 23 November, the lake was above the scientist's eye level when they stood W of the southern pit in the main crater.

Source: Afar Rift Consortium


5 October-11 October 2005

According to a news report, after a M 4.3 earthquake on 4 October an eruption occurred at Erta Ale. The earthquake occurred in the remote region of Afar and was the 11th earthquake in the region since September.

The following activity was incorrectly reported as occurring at Erta Ale when it actually occurred at Dabbahu. See the 12-18 October 2005 Weekly Volcanic Activity Report for the full report. A team of scientists visited the Da'Ure locality of Erta Ale on 4 and 5 October after there were reports of volcanic activity there on 26 September. They determined that a minor explosive eruption occurred from two semi-circular vents, producing ashfall that was ~5 cm thick near the vent and extended more than 500 m from the vent. Boulders ejected during the eruption were as large as 3 m and were deposited as far as 20 m away. The scientists noted intense degassing from the vents, the scent of sulfur dioxide, and the sound of boiling water in the vents.

Sources: Gezahegn Yirgu, Department of Earth Sciences, Addis Ababa University; Agence France-Presse (AFP)


28 September-4 October 2005

A group of scientists assessed the visible changes at Erta Ale on 26 September after activity began around 24 September. In comparison to observations made in November 2004, they found that the southern main crater/pit had widened significantly, with portions of the previous crater walls having collapsed into the lava lake. A new cone-shaped construct had grown within the southern main crater where there had been a platform. A lava lake occupied the entire width of the inner crater/pit. In the northern crater/pit, there was a solidified lava bulge and abundant "smoking" along the crater walls. No incandescent lava was visible in the pit.

Based on descriptions by local residents of seeing "red and glowing light shooting and rising into the air above the volcano," the scientists believe that a Strombolian eruption probably occurred, emitting a significant volume of fresh magma within, and possibly out of, the pit. According to news reports, about 50,000 nomads in Ethiopia's Afar region were displaced after the eruption.

Sources: Gezahegn Yirgu, Department of Earth Sciences, Addis Ababa University; Agence France-Presse (AFP)


21 September-27 September 2005

According to unconfirmed reports from local authorities, Erta Ale began erupting on 24 September after a series of earthquakes occurred along the Afar western margin on the previous day. The earthquakes, with a maximum magnitude of 5.5, were recorded at the Geophysical Observatory of Addis Ababa University. A group of geologists and geophysicists were planning to travel to the field to make observations.

Source: Gezahegn Yirgu, Department of Earth Sciences, Addis Ababa University


26 January-1 February 2005

An international team led by SVE, visited Erta Ale during 22-23 January. They observed no significant changes at the volcano since last observed in November 2004. Degassing continued from three of the four coalescent hornitos in the SW part of South Crater, but decreased slightly in comparison with observations made in December 2004. One hornito contained glowing molten lava. Degassing from North Crater also slightly decreased. Near the NW wall of the crater two small red glowing areas were visible at the summit of two hornitos in the crater.

Source: European Volcanological Society (SVE)


8 December-14 December 2004

During a trip to Erta Ale on 4 December, a group of scientists from SVE-SVG observed no activity in the lava lake in the volcano's South Pit crater. A solidified lava crust covered the crater floor about 15 m below the crater rim. The group also saw that new activity within North crater had produced a solidified lava bulge filling about 4/5 of the crater floor. Degassing from several small hornitos occurred in the central part of the lava bulge. During the evening, ten small incandescent vents were visible at the periphery of the lava bulge. In the morning, two plumes rose above the volcano.

Source: European Volcanological Society (SVE)


22 January-28 January 2003

A team of French scientists who visited the summit of Erta Ale on 4, and 13-14 January noted significant changes in morphology and activity at the volcano in comparison to several months previous. As has been the case for decades, a lava lake was present in the W part of the S pit crater. It was 120 x 80 m in size and its surface was ~100 m below the crater rim. Observers saw lava fountains spraying above the lake, as well as convection within it. The lava lake and resulting platform were higher than when observed in April 2002. Abundant SO2-rich gases were released that were not noted during earlier visits.

Source: Jacques-Marie Bardintzeff from Université Paris-Sud and Franck Pothé from Terra Incognita


Index of Bulletin Reports


Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

02/1971 (CSLP 71-22) Incandescent lava lakes clearly visible in both craters

05/1971 (CSLP 71-22) Fountaining seen from both active lava lakes

11/1971 (CSLP 71-22) Overflights during April-October reveal continued lava lake activity

03/1972 (CSLP 72-16) Increased activity seen; lava lakes higher

05/1972 (CSLP 72-16) Lava overflows from central pit

12/1973 (CSLP 73-156) Both craters still contain active crater lakes; recent N-flank eruption

01/1974 (CSLP 73-156) Review of 1973 activity

06/1987 (SEAN 12:08) Landsat data show two crusted lava lakes

12/1987 (SEAN 12:12) S lava lake remains larger and hotter than N lake

09/1988 (NASA STS 26) Space Shuttle photograph of the Rift Valley in Ethiopia

08/1992 (BGVN 17:08) Small lava fountains observed during overflight

09/1992 (BGVN 17:09) Lava lake in one of two summit-caldera craters; recent lava overflows of caldera rim

11/1992 (BGVN 17:11) Lava lake active in S crater during first fieldwork in many years

01/1993 (BGVN 18:01) Additions to previous report

07/1993 (BGVN 18:07) Review of satellite data reveals lava lake activity in June 1992

12/1995 (BGVN 20:11) Lava lake still active with fountains as high as 15 m

12/2001 (BGVN 26:12) Dynamic, molten lava lake in S crater during November 2000-February 2001

04/2003 (BGVN 28:04) Frequent changes in the active crater morphology and lava lake level

02/2004 (BGVN 29:02) February 2004 expedition finds molten-surfaced lava lake nearly gone

08/2004 (BGVN 29:08) Declining thermal output from small lava lake since early 2003

11/2004 (BGVN 29:11) On 4-5 December 2004 visitors noted active hornitos but solidified lava lake

01/2005 (BGVN 30:01) Hornitos on chilled lava lake surface in January 2005; December 2004 glass analyses

07/2005 (BGVN 30:07) Additional observations of the shrinking lava lake in January 2004

09/2005 (BGVN 30:09) Agitated lava lake during time of September 2005 earthquake swarm ~ 100 km S

03/2006 (BGVN 31:03) Molten lava lake observations as late as 3 January 2006

06/2008 (BGVN 33:06) Active lava lake visited in February 2008

07/2009 (BGVN 34:07) Changes at NW and S pit craters between 2002 and 2009

01/2010 (BGVN 35:01) February 2010 visit reveals little change in South pit crater's lava lake since 2002

06/2011 (BGVN 36:06) Observers watch dynamic lava lake during November 2010




Bulletin Reports

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


02/1971 (CSLP 71-22) Incandescent lava lakes clearly visible in both craters

Card 1132-1133 (18 February 1971) Incandescent lava lakes clearly visible in both craters

"Recent observations from the air (26 December 1970 by M. Reinart, and 4 February 1971 by the team of the Dept. of Geology HS-Univ) revealed important increase of activity at Erta'Ale volcano. Incandescent lava-lakes are now clearly visible in both craters even in the sunlight, meaning their temperatures are above 1,020°C. Fountaining was quite active. The most important fact is the change in shape of the northern pit-crater which has been modified by the sinking of a new pit 80 m across, at its northern edge. The crater has now a somewhat irregular outline (figure 1). The lava-lake, which previously was about 200 m below the upper rim has been lifted about 30 m up. The activity is presently concentrated in the central part of the lake about 100 m across. The edge of the molten lava-lake is surrounded by an embryonic cone, built by fountaining activity.

Figure 1. Sketch map of Erta 'Ale showing the active lava lakes and new pit crater within the summit caldera, February 1971. Courtesy of Jacques Varet.

"Erta'Ale volcano, the most active centre of Ethiopia is known for its permanent lava-lake activity since 1967, and most probably since 1906. Annual observations since 1967 by the CNRS-CNR research team in the Danakil depression show a quiet lava-lake activity, with no modification of the shape of the crater, nor new lava flow, since 1963, the date of the aerophotographic survey of the area.

"Erta'Ale is a basaltic shield volcano, 500 m high, with a base 50 km across. On its top an ellipse-shaped sinkhole opens, elongated NNW-SSE, which is the main tectonic direction of the Danakil depression. Two pit-craters, one small, one big, both with a molten lava-lake each, are gaping in the sink's northern half. In 1968 and 1969, the incandescence of the lava was hardly discernable by daylight; it was very conspicuous by night."

Information Contacts: Jacques Varet, Geology Department, Haile Selassie I University, Addis Ababa, Ethiopia; Haroun Tazieff, Paris, France.

05/1971 (CSLP 71-22) Fountaining seen from both active lava lakes

Card 1192-1193 (03 May 1971) Fountaining seen from both active lava lakes

"Erta'ale . . . was inspected by UNDP Geothermal Investigations Project Teams, D. Levitte and E.F. Lloyd on 27 March 1971, and Getahun Demisse and C. James on 30 March 1971. Both teams spent a night at the crater.

"Erta 'Ale crater, a NNW elongated subsidence of the shield's summit, contains two collapse pit craters in its northern half. The northern-most, and largest pit, is floored with pahoehoe lava, black by day but glowing red in some cracks by night. Displaced north of the pit centre is a 3-4 m high spatter cone encircling a lava lake 80 m in diameter. The lava surface fluctuates but is always above the surrounding lava field which may have flowed from the base of the cone or from fissures in the pit floor; one of us (C.J.) reported having observed such a fissure open and a small lava tongue flow from it, and E.F. Lloyd observed a temporary bright red glow SSW of the lava lake on 27 March 1971, probably due to the same cause. This suggests that magma underlies most of the floor of North Pit. High pressure gases escape from chimney-like spatter cones immediately south-east of the lake and on 27 March small lava clots were being erupted from one chimney. Fumaroles on the bench on the south side of the pit discharge gases of high SO2 content. The southern pit, approximately 70 m in diameter, has vertical to overhanging walls and contains a lava lake about 30 m below the lip. Pelee's hair has accumulated around the edge of the pit.

"Activity within both pits is similar. Rarely fountains erupt from the centre of the lakes, but almost continuously from their edge. Lava commonly fountains 10 m high and very occasionally 40 m. Violent fountains, marking the commencement of a cycle of activity, usually erupt at the lake edge when lake level is high and induce movement on the lake surface from the centre of the lake towards the locus of fountaining, and a 1-3 m drop of lake level. They slowly migrate around the lake edge anticlockwise; during 1.5 hours of continuous activity a fountain migrated through 120°. As the fountains decline lake level rises again accompanied by cracking of the cooled lake-crust, extrusion of lava tongues of the cracks and tilting and engulfment of large plates of the crust. Freshly extruded lava is bright orange suggesting temperatures approaching 1,050° C.

"Fountains are actively building, at a rate of tens of cms per day, the spatter cone surrounding North Pit lake and a bench edging South Pit lake. In spite of this, peak lake levels approach close to the lip of the cone and bench, suggesting that either the lava column is rising or that the cone and bench are sinking into the liquid lava as ejecta accumulates. It is probable that the lava column has continuedf to rise slowly since December 1970 when increased activity of Erta'ale was first noticed by Reinart."

Information Contacts: E.F. Lloyd, Addis Ababa, Ethiopia

11/1971 (CSLP 71-22) Overflights during April-October reveal continued lava lake activity

Card 1308 (02 November 1971) Overflights during April-October reveal continued lava lake activity

"Since March 1971, activity has been continuous in both lakes of Erta 'Ale volcano, but no extra-crateric eruption occurred. The level of the lakes remained unchanged.

"Flights over the volcano and photographs taken on 23 April, 28 May, 15 June, 19 September, and 4 October show no change in activity since the last reports. Incandescent lava lakes and fountaining activity are still visible in daylight in both craters.

"The main surface of the northern lava lake formed in December 1970 is unchanged, and its solidification is certainly going on, while the northern lava pool is still very active and surrounded by a double spatter rampart. Detailed photographs provide the following data: Total dimensions of the sink (oval), 1,600 x 700 m; Central pit horizontal dimensions (oval), 65 x 78 m; Central pit depth (edges to molten surface), 15 +/- 4 m; Northern pit dimensions of the December 1970 surface, 200 x 300 m; Northern pit height of the walls, 15 m (1st store) and 25 m (2nd store); Northern pit dimensions of the active pool, 48 x 52 m (internal diameter) and 75 m (external diameter)."

Information Contacts: Jacques Varet, Haile Sellassie I University, Addis Ababa, Ethiopia.

03/1972 (CSLP 72-16) Increased activity seen; lava lakes higher

Card 1363 (06 March 1972) Increased activity seen; lava lakes higher

"Captain Lebouteiller reported that Erta 'Ale lava lakes rose substantially in the last few days. In the northern pit, a new fissure, 5 m long, opened in the western part of the recently solidified surface, and a lava stream issued from this fissure covering the whole surface of the pit on 21 February. The whole northern pit is therefore occupied by a molten lava lake, the level of which is still rising. Fissures affecting the northern flank opened to a width of 1.5 m, but no observation was made at the northern extremity of these fissures to check if any lateral emission was occurring. Increase of activity within the northern pit was noticed by other observers last week. The most spectacular activity is observed around the central pit. The lava overflowed this pit at least twice last week. A flow on the southeastern side was still hot on the 21st, while another flow appeared on the southern side of the pit on the 23rd. This is the first overflowing observed in Erta 'Ale. Lava level was very high in that pit (nearly 1 m below the rim), and a new circular open fissure in which red lava was observed suggests possible future enlargment of the pit. Fountaining activity was intense, and projections were thrown to a height of up to ten metres.

"Samples of pelees hair were collected near the central pit, and the flow was sampled. Scoriae from this emission have been petrographically examined. They are made of plagioclase porphyritic basalt. Phenocrysts of plagioclase (an 80-70), olivine, and colourless clinopyroxene float in a yellow glass groundmass. The rock is similar to the basalt recently sampled in the northern pit by H. Tazieff's team. Although lava of apparently similar composition is rising in both craters, the fact that the level of the lava in the central pit is much higher than in the northern one (at least 35 m) is significant. It indicates that no direct high-level communication exists between both lake-feeders."

Information Contacts: Jacques Varet, Haile Sellassie I University, Addis Ababa, Ethiopia.

05/1972 (CSLP 72-16) Lava overflows from central pit

Card 1390 (10 May 1972) Lava overflows from central pit

Observations from the air of Erta 'Ale volcano, and study of numerous detailed photographs taken 13 April 1972 at 1000. lead to the following conclusions:

1. The central pit has overflowed with new lava since the last observation in February 1972 and three important new flows were observed, reaching 500 m long (figure 2).

Figure 2. Sketch maps of the Erta 'Ale summit region showing lava flows and crater morphology in February and April 1972. Courtesy of Jacques Varet.

2. Red molten lava in the central pit is still at the level of the rims, surrounded by a low double-rimmed spatter rampart under formation through fountain activity.

3. The lava level in the northern pit has risen since February 1972 and now coveres the upper platform. The active pool is slightly wider.

4. No lava flow has occurred outside the main sink and no change is observed along the open fissures affecting the northern flank of the volcano. This allows the following conclusions: (a) The lava has been continuously rising since February 1972. (b) The lava rose faster in the central pit than in the northern but both levels now appear equal (although no precise geodesy has been done). Both feeders are therefore probably connected at depth although lava is not rising at the same speed. The difference might be attributed to different degassing or different size or shape of the feeders. (c) A continuous process of overflowing is to be expected in the near future, if no lateral eruption or other sudden change happens as the lava has apparently been regularly rising up since 1968 (with 15 m uprising in one year, February 1971-February 1972, equal in both craters).

Information Contacts: Jacques Varet, Haile Sellassie I University, Addis Ababa, Ethiopia.

12/1973 (CSLP 73-156) Both craters still contain active crater lakes; recent N-flank eruption

Card 1759 (20 December 1973) Both craters still contain active crater lakes; recent N-flank eruption

"We are presently observing Erta 'Ale from both air and land. A new track has been built by H.H. Ras Mengesha Seyoum, Governor Tigre Province, reaching the crater. I was personally at the crater for the last two nights, and both craters are still active with permanent lava-lake activity and fountaining. Eruptions are frequently observed from both craters, filling the main elliptic sink and even overflowing the sink towards the south. An eruption also recently occurred on the northern flank, some 100 m long, in a northerly direction. The center of eruption of this flow is located on the northern edge of the crater and is still active (fumaroles). I intend to return to Erta 'Ale within a few days and also during the first days of January."

Information Contacts: Jacques Varet, Laboratoire de Petrographie-Volcanologie, University Paris-Sud, France.

01/1974 (CSLP 73-156) Review of 1973 activity

Card 1775 (14 January 1974) Review of 1973 activity

Erta 'Ale volcano was active throughout 1973, with continuous upwelling of the lava in continuation of the process noticed over the past two years. For two years now basaltic lava (plagioclase porphyritic transitional basalt) has been continuously overflowing the central pit, flowing in a southerly direction. Lava flows, several kilometres long, have completely filled Erta 'Ale sink during 1973 and have covered the southern flank of the shield volcano. This continuous activity built around the central pit a small shield partly covering the three hornitos. The lava lake surface is at the top of this shield, nearly 30 m higher than the 1972 level.

The northern pit is still active, but the level of the lava is estimated to be 35 m lower than in the northern pit. The lava level was, however, higher in the most recent months; lava flows emitted in 1973 have completely covered the surroundings of the northern pit, reaching the level of the main sink rim on the northern side where the lava did overflow. Three important red-glowing hornitos (one needle-shaped) surround the northern pit along a circular fissure. The main sink rim is now, particularly on the north side, intensely altered by fumaroles. It no longer represents a rampart to the lava, and merely constitutes an elongated graben with a NNW direction.

Information Contacts: Jacques Varet, Laboratoire de Petrographie-Volcanologie, University Paris-Sud, France.

06/1987 (SEAN 12:08) Landsat data show two crusted lava lakes

The following is abstracted from Rothery and others (1988). Landsat TM data acquired 5 January 1986 show both lakes. The northern one had shrunk to no more than 60 m across and the S lake was ~150 m in diameter. Temperatures derived from the data suggest that the lakes were quiescent with cool (< 400°C) crust. Incandescent cracks at ~1,150°C occupied < 0.4% of the surface area.

Reference. Rothery, D.A., Francis, P.W., and Wood, C.A., 1988, Volcano monitoring using short wavelength infrared data from satellites: JGR, v. 93, no. B7, p. 7993-8008.

Information Contacts: D. Rothery, Open Univ.
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12/1987 (SEAN 12:12) S lava lake remains larger and hotter than N lake

Landsat TM (band 7) data acquired 9 February 1987 suggest that . . . the lava lakes remained similar to . . . January 1986. The S lake was larger and hotter than its N companion, but temperature could not be constrained since the 1987 observation was based only on photographic format data.

Information Contacts: D. Rothery, Open Univ.
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09/1988 (NASA STS 26) Space Shuttle photograph of the Rift Valley in Ethiopia

Astronauts aboard the Space Shuttle in September 1988 photographed the Rift Valley of northern Ethiopia, including Erta Ale volcano.

Figure 3. Erta Ale is visible (dark area of lower right quadrant N of turquoise Afrera Ye Ch'ew Lake) in this near-vertical photograph taken in September 1988. North is towards the bottom right corner. The volcano has an active lava lake (barely discernible in the photograph) approximately 46 m wide. The region is hot, dry, below sea level, and mostly uninhabited. Other dark lava flows are visible from a number of smaller volcanoes S and SW of the lake. NASA Photograph STS026-033-080.

Information Contacts: NASA JSC Digital Image Collection (URL: http://images.jsc.nasa.gov/).

08/1992 (BGVN 17:08) Small lava fountains observed during overflight

A lava fountain estimated at 1-2 m high was observed in one vent during a 45-minute overflight on 21 September by the Geophysical Observatory's director, a volcanologist, and a geologist. Gas emission was seen at a second vent.

Information Contacts: L. Asfaw, Addis Abeba Univ, Ethiopia.
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09/1992 (BGVN 17:09) Lava lake in one of two summit-caldera craters; recent lava overflows of caldera rim

The [September] flight covered the Afar region from the Alebbagu and Hayli Gubbi volcanoes, to lakes Ba Kili and Karum. The N half of Erta Ale's elliptical caldera included two craters. The larger, ~300 m in diameter, was in the northernmost part of the caldera. Two strong fumaroles were active near its S rim, but no lava lake was evident. Two dark fresh-looking lava flows had originated from this crater; one had flowed over the caldera rim to the NNE, the other, to the SW, was confined by the caldera's W wall. A lava lake was observed in the second of the two craters, near the middle of the caldera. The crater was ~100 m in diameter and 80 m deep. The lava lake occupied ~1/3 of the crater's SW bottom. Fountaining and bright-red incandescence were clearly visible. Lava from the second crater had flowed over the S part of the caldera rim.

Information Contacts: P. Vetsch, SVG, Switzerland; L. Cantamessa, Géo-découverte, Switzerland; G. Assefa and L. Asfaw, Addis Abeba Univ.
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11/1992 (BGVN 17:11) Lava lake active in S crater during first fieldwork in many years

Geologists climbed to the summit . . . on 10-11 November, for the first time in many years. Members of the group made the first known descent into the active S crater . . . (figure 4). The active pit-crater was >100 m in diameter, with vertical walls and a lava lake at 100 m depth (figure 5). A winch and ropes were used to descend the E wall on the morning of 11 November for a 2-hour visit. The 40 x 70 m lava lake occupied the W part of the crater. Air temperature at the bottom of the crater was 35°C, ~5°C cooler than the ambient temperature at the rim. Wearing gas masks, geologists approached to within 2 m of the lava lake. The lake was continuously active with 4-5-m-high lava fountains in four locations and rapid motion of the lake surface outward from the center. The N crater was confirmed to be inactive, with the bottom full of fallen rock, although there were two strong fumaroles on the S rim.

Figure 4. Summit caldera of Erta Ale, April 1972, showing the N and S craters. Lava spillways over the caldera rim are shown diagrammatically. Sketch by Jacques Varet.
Figure 5. Diagrammatic plan view (top) and cross-section (bottom) of the active S crater at Erta Ale, November 1992. Courtesy of P. Vetsch.

Information Contacts: P. Vetsch, M. Vigny, and A. Schussele, SVG, Switzerland; L. Cantamessa, Géo-découverte, Switzerland; G. Pareau, Assoc of Alpine Guides of Chamonix, France; P. Villemin and A. Curvelier, Gaumont Television, Paris, France.
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01/1993 (BGVN 18:01) Additions to previous report

The November expedition . . . was organized by Haroun Tazieff in connection with a film about his volcanological work, produced by Gaumont Television. Climbers who descended into the active crater were Luigi Cantamessa (Géo-découverte), Gilbert Pareau (Association of Alpine Guides of Chamonix) Marc Vigny (SVG), Pierre Villemin (cameraman), Alain Curvelier (sound engineer), and Andre Schussele (medical doctor).

Information Contacts: P. Vetsch, SVG, Switzerland; L. Cantamessa, Géo-découverte, Switzerland.
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07/1993 (BGVN 18:07) Review of satellite data reveals lava lake activity in June 1992

"The visit . . . on 10-11 November 1992 showed that since the last recorded observation, made using Landsat TM data from 9 February 1987, the lava lake in the N crater had disappeared (presumably frozen over and collapsed), but that the lava lake in the S crater . . . was still active. This interpretation is consistent with visual observations made during an aircraft overflight on 21 September 1992 (17:8-9).

"New satellite data further narrow the window of uncertainty about when the N lava lake became inactive, and provide evidence of the continuity of activity at the S lava lake. Data from the Japanese Earth Resources Satellite-1 (JERS-1, also known as Fuyo-1) recorded on 9 June 1992 show the S lava lake to be a strong source of short-wavelength infrared radiation, which is convincing evidence that it was active. However, there is no trace of any short-wavelength infrared thermal radiance from the N lava lake, indicating that the lake had already ceased to exist.

"JERS-1 was launched on 11 February 1992. Its optical sensors record images in three visible channels, and (more importantly for thermal remote sensing of volcanoes) in four short-wavelength infrared channels: 1.55-1.77, 2.01-2.12, 2.13-2.25, and 2.27-2.40 µm. The image pixels are 18 m across. This contrasts with Landsat TM which has 30 m pixels in two short-wavelength infrared channels (1.55-1.75 and 2.08-2.35 µm). This is believed to be the first demonstration that JERS-1 data can play a useful role in volcano monitoring. The thermal anomaly covers an approximately equidimensional area 4-5 pixels across in all four short-wavelength infrared channels, which is roughly consistent with the size of the lava lake seen during fieldwork five months later."

Information Contacts: D. Rothery, Open Univ.
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12/1995 (BGVN 20:11) Lava lake still active with fountains as high as 15 m

Lava lakes have been present since 1967, and possibly 1906, although the N lava lake became inactive between 1988 and 1992. Recent ground observations were reported in September and November 1992. Observations have also been made using satellite imagery. New observations were made during 6-11 December 1995 by a team from Spele-Film and the Societe de Volcanologie Geneve while working for a French television network.

Only fumarolic activity was observed from the large crater (~300 m diameter) in the N part of the caldera. Fumaroles were concentrated SW of the pit within the crater, with some emissions coming from the inside wall and the slope of talus covering the pit floor. Almost all of the visible fumes came from the main pit, and seemed more abundant than in November 1992. A secondary pit crater with a diameter of ~15 m was seen in the SE part of the main pit.

Within the central part of the caldera, the S lava lake is located at the top of a small lava shield. The N and E flanks of this shield are partially covered by abundant lava flows originating from the N crater. The S flank of the shield is dominated by a large inactive cone. No fumes were visible, but the air near the pit-crater rim was very hot, frequently making it difficult to breathe without a mask. The diameter of the S pit-crater was ~140 m (based on a measured circumference of 446 +- 2 m), and the lake was 90 m below the W rim. The lava lake was similar in size and location to one observed in 1992, covering an area of ~60 x 100 m in the WSW part of the pit (figure 6). However, the level of the lake was believed to have risen ~5-6 m. Two slope breaks on the generally flat pit floor, not present in 1992, suggest that the entire floor may have subsided.

Figure 6. Sketch showing a cross-sectional view of the central pit-crater (S lava lake) at Erta Ale, December 1995. Courtesy of P. Vetsch.

Lava lake activity was characterized by intermittent fountaining from as many as four locations at a time. No regular pattern was noted, but fountaining was more frequent near the SW border of the lake, and the more intense fountains (5-15 m high), started near the center of the lake and migrated to the border. During the stronger fountaining phases, a large raft of cooled surface lava moved towards the lake center. The lava lake was generally more active than in 1992. Pele's hair was frequently seen above the fountains, and some rose on the hot air out of the pit.

Information Contacts: P. Vetsch, Societe de Volcanologie Geneve, B.P. 298, CH-1225 Chene-bourg, Switzerland (Email: pvetsch@iprolink.ch); L. Cantamessa, Geo-Decouverte, 65 rue de Lausanne, CH-1202 Geneva, Switzerland; G. Farve and C. Rufi, Spele-Film, Borex, Switzerland; C. Peter, 14 Haupstrasse, D-82547 Eurasburg, Germany.
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12/2001 (BGVN 26:12) Dynamic, molten lava lake in S crater during November 2000-February 2001

The Afar National Regional State has approved a program to grant access to Erta Ale volcano by either land or air transportation. The program, which will precede the formation of a "National Park of Volcanoes," enables visitation by natural science field workers. It also allows for traditional mining and salt transportation by caravans and seeks to protect the traditional life of the region's inhabitants.

Observations during 14 November 2000. Luigi Cantamessa (Geó-Découverte), accompanied by government representatives, visited the N part of the elliptical summit caldera (figure 7) on 14 November 2000. Little had changed since last described in December 1995 (BGVN 20:11/12), but continued collapse of the N crater wall was noted. Dense smoke came from the S rim of the crater, with a very strong smell of sulfur, as in the past. GPS measurements of elevation indicated that the E wall of the N crater was ~600 m high and the N rim, the highest point of the volcano, was ~15 m higher.

Figure 7. Aerial photograph showing the N part of the Erta Ale caldera. In this view looking generally W, the inactive northern crater (with fumarolic emissions) is on the right and the southern crater with an active lava lake is on the left. Courtesy of L. Cantamessa, Geó-Découverte.

The S crater (figure 8), in the central part of the caldera, contained a molten lava lake and had undergone some changes since the 1995 visit. A portion (1-2 m thick) of the NE wall had collapsed. The level of the lava lake, still in the W part of the crater, showed significant variations. The terraces on the E side of the crater appear to have been swamped by lava, after which the lake level apparently receded. The present level appeared to be lower than in 1995. A terrace of 2-3 m width now surrounds the lake at the foot of the crater walls. Intense activity was observed at the lake's surface. There were rapid movements of the surface from S to N. Many lava fountains reached ~10-15 m high.

Figure 8. Aerial photograph looking down into the southern crater of Erta Ale. The crater is about 145 m in diameter, with an active lava lake. Courtesy of L. Cantamessa, Geó-Découverte.

Observations during 29-30 January 2001. An expedition sponsored by Aventure et Volcansmade crater observations for 48 hours during 29-30 January 2001. Because of the extremely dry and hot climate that prevails in this region, smoke or vapor rarely obscured visual observations. The N crater exhibited only fumarolic activity, but due to thick fumes from its southern portion, gas masks were necessary for those who climbed into the crater.

The S crater was determined to be ~170 x 130 m, with the active lava lake (figure 9) on the W side having a diameter of ~121 m. The lava lake was located, based on GPS measurements, at 13° 36' 11" N, 40° 39' 49" E. Cyclic activity, approximately every 4 hours, consisted of the thin, dark crust on the lake surface splitting and causing a "fantastic" bubbling of the liquid lava across the entire ~12,000 m2 of the lake surface. Vigorous degassing created lava fountains 10-20 m high. Several times local collapses were seen which mainly affected the vertical walls in the SE part of the crater. The level of the lava lake remained stable.

Figure 9. Evening photograph showing the active lava lake in the southern crater of Erta Ale during 29-30 January 2001. Molten lava can be seen around the edges and through fractures in the cooled surface of the lake. Courtesy of Guy de Saint-Cyr, Aventure et Volcans.

Observations during 13-18 February 2001. Between 13 and 18 February 2001 two groups from the Société de Volcanologie (SVG), in an expedition organized by Géo-Découverte, reached the volcano by land and by helicopter (3 days later). The principal topographic elements in the N part of the caldera were the subject of GPS and telemetric measurements. The active S crater contained an elliptical lake (80 x 100 m) with a surface level 80 m below the rim and lava fountains rising 5-10 m high.

The relative absence of gas in the active crater allowed excellent observations. Over a period of 14 hours, Yves Bessard and Alain de Chambrier recorded details of the activity occurring at the lava lake, including lake movements and lava fountains. The surface of the lake was renewed approximately every 10 minutes. A continuous video recording over a period of 77 minutes was also taken from the edge of the lava lake at the bottom of the crater.

Systematic measurements of fumarole temperatures were made, primarily on the edge of the N crater and the external N edge of the caldera; values ranged from 60°C to more than 260°C at the strongly active N-crater fumaroles.

The last previous thermal measurements at Erta Ale were carried out in the 1970s by a team led by Haroun Tazieff; the most recent temperatures reported in the literature were obtained from infra-red satellite data (work mainly carried out by Oppenheimer, Francis, and Rothery). The thermal measurements collected by Marc Caillet, Steven Haefeli, and Pierre-Yves Burgi during 13-15 February 2001 are summarized below; more details on this fieldwork will be published in a journal paper.

The SVG team used a pyrometer, which works by remotely measuring the infrared radiations emitted by the lava, for the temperature measurements. Temperature calculations need an emissivity factor, the determination of which required an approach to the lava lake. For the temperature measurement of the crust, the only accessible part of the lake, the following protocol was followed. Using a steel wire, a steel sheet of 18 x 18 cm (8 mm thickness) containing a hole in which the thermocouple was inserted was deposited on the crust of the lake. Because of the distance separating the terrace from the lake (estimated at 15 m), this required the coordination of three people (Marc Caillet, Steven Haefeli, and Pierre-Yves Burgi). Caillet, standing where the ambient temperature reached 300°C, was equipped with a reflective cloth and used a large 8-m steel pole to move the thermocouple away from the wall.

Once the steel sheet was in contact with the lake's crust, temperature measurements were carried out every 30 seconds for 10 minutes, then each minute during the next 20 minutes, until the temperature stabilized. The temperature recorded at this time was 350°C. A pyrometric measurement in the same area of the thermocouple indicated a temperature of 342°C (with an emissivity index set to 0.9 on the pyrometer). By combining the temperatures obtained with the thermocouple and the pyrometer, and knowing the wavelength used by the pyrometer, an emissivity factor of 0.74 was determined. By collecting a sample of basalt, it was possible to confirm this value by the use of a furnace.

Acquisition of temperatures at various lake locations was carried out by pyrometry. Continuous pyrometric measurements were taken over periods of several tens of minutes (with a measurement each second) and were collected on a portable computer. The crust, many faults, and lava fountains were the three types of areas considered. These measurements were made from the edge of the pit and from the lower terrace. The measurements made near the lake were of primary importance because both the absorption of radiation by magmatic gases between the source and the observer and the enlarging of the pyrometer field of view with distance are two factors which tend to distort measurements. A difference of about 25°C was observed between the maxima measured from the edge and the bottom of the pit. In addition, the temperature measurements were taken at night in order to avoid any pollution due to the solar radiation (which can distort values up to 90%). The highest recorded temperature, 1,217°C, was found in a lava fountain. The temperature of the crust of the lake was very variable, 290°C near the cliffs to 520°C in the center of the lake, with an average of 474°C.

Information Contacts: Luigi Cantamessa, Geó-Découverte, 12-14 rue de Cendrier, CH-1201 Geneva, Switzerland (URL: http://www.erta-ale.org/, Email: info@geo-decouverte.ch); Annie Buard, Christophe Toussaint, Jean Claude Boissonnet, Philippe Roy, and Guy de Saint-Cyr, Aventure et Volcans, 73 cours de la Liberté, 69003 Lyon, France; P. Vetsch, Marc Caillet, Steven Haefeli, and Pierre-Yves Burgi, Société de Volcanologie (SVG), PO Box 6423, CH-1211 Geneva 6, Switzerland (URL: http://www.club-association.ch/svg/, Email: svg@worldcom.ch).
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04/2003 (BGVN 28:04) Frequent changes in the active crater morphology and lava lake level

Over the last few years the Afar National Regional State has allowed a program of visitation to Erta Ale volcano by natural science field workers. As a result, numerous expeditions have visited the volcano since November 2000 and January-February 2001 (BGVN 26:12). The following brief reports are a result of some of these visits during January, February, and April 2002, November-December 2002, and January 2003. Typical lava lake activity was commonly reported, but some changes, such as a significant changes of the lake level, were also noted.

Activity during January 2002. Members of the Société de Volcanologie Genève (SVG) visited Erta Ale at the end January 2002. The lava lake remained elliptical with a N-S axis of ~130-133 m and an E-W axis of ~104-111 m; the width had increased ~10 m as a result of crumbling of the terrace along the lake edge. The size of the pit-crater was the same, with an E-W diameter of ~170 m, while the height of the vertical E wall was 46 m. Attempts to measure CO2 and SO2 concentrations inside the crater on 27 January 2002 were unsuccessful because the gas concentrations were below the detection limits of the Dräger tubes (10 ppm SO2 and 0.5% CO2).

Activity during February 2002. During a 14-19 February 2002 stay on Erta Ale by a team that included Roberto Carniel and Jürg Alean (Stromboli Online), the lava lake was active and produced spectacular fountains of lava. The lake level oscillated by several meters during their observation period. Seismic measurements were conducted along with thermal and video recordings of the lake.

Activity during April 2002. During 12-21 April 2002 a group from SVG led by Franck Pothé and Evelyne Pradal visited the volcano and reported significant changes in the morphology and activity of the lava lake since January 2002. The level of the lake had risen ~15 m and its surface area had decreased by ~33%. Over a 36-hour period the level varied intermittently by 1-2 m, the variation sometimes occurring within several minutes. Activity on the lake was intense, with continuous degassing and small lava fountains ~15 m high.

Activity during November-December 2002. A German group from Volcano Expeditions International visited the volcano during November-December 2002. They reported that the S crater was ellipsoidal with dimensions of ~130 m N-S and ~160 m E-W (figure 10). The lava lake occupied about half of the crater, and the lake surface was ~90 m below the W rim of the S pit. The remaining area in the E was covered by basalt that had a terrace ~45 m below the crater rim (figure 10). Previous observations had located the terrace at ~70 m below the rim. It was widely covered with talus; hence, the lava lake must had risen up to the present terrace level between spring 2002 and this visit. Almost no talus was found on the terrace, indicating that the lava cover was not old. Lava fountaining up to 20 m high occurred mainly in the W, S, and center areas of the crater lake. GPS measurements were used to accurately map part of the caldera rim and locate some key points (figure 11).

Figure 10. A sketch map (top) and E-W cross-section (bottom) of the active S crater at Erta Ale on 4 December 2002.Courtesy of C. Weber.
Figure 11. Partial survey of the Erta Ale caldera measured using a 12-channel GPS receiver. GPS reception was excellent due to the exposed nature of Erta Ale, where signals are shaded only when the receiver is close to the caldera wall inside the caldera. The GPS point HAK is the climbing location at 13.60402°N, 40.66401°E, and elevation 563.0 m. The highest point was a hornito on the N caldera rim, location HNN, at 13.60829°N, 40.66222°E, elevation 594.9 m. Courtesy of Lothar Fritsch.

Several earthquakes were felt during the visit. No seismic equipment was present, but five events were felt on 4 and 5 December 2002. No significant change in the lava lake was noticed during these events. Strong fumarolic activity was observed inside and outside the NW crater as well as on the outside of the caldera rim. The surface near the crater rim was broken by cracks in concentric circles, and the crater walls were formed of very unstable material. On 6 December three large rockfalls from crater wall collapses occurred along ~50 m of the crater wall circumference within a few minutes. About 40 m of the wall height collapsed with an estimated average thickness of 10 m, thus ~20,000 m3 of material slid into the lake, creating a large cloud of orange-brown dust that filled the pit and generated large amounts of Pélé's Hair.

Activity during January 2003. French teams from Terra Incognita visited the summit on 4 and 13-14 January 2003. The ~120 m long by 80 m wide lava lake was still in the W portion of the S pit crater; its surface was ~100 m below the crater rim (figure 12). The new platform, located ~50 m below the rim, was in the E part of the crater and covered ~25% of the crater floor. Gas emissions were abundant, and were assumed to be rich in SO2 based on their blue color and strong odor. The lava lake exhibited convection and lava fountains.

Figure 12. Sketch map and cross-section of the Erta Ale lava lake, January 2003. Courtesy of Jacques-Marie Bardintzeff and Franck Pothé.

Information Contacts: P. Vetsch, Marc Caillet, Steven Haefeli, and Pierre-Yves Burgi, Société de Volcanologie Genève (SVG), PO Box 6423, CH-1211 Geneva 6, Switzerland (URL: http://www.volcan.ch/, Email: svg@worldcom.ch); Jürg Alean, Stromboli Online, Rheinstrasse 6, CH-8193 Eglisau, Switzerland (URL: http://stromboli.net/, Email: alean@stromboli.net); Christoph Weber and Lothar Fritsch, Volcano Expeditions International (VEI), Muehlweg 11, 74199 Untergruppenbach, Germany; Jacques-Marie Bardintzeff, Université Paris-Sud, F-91405 Orsay, France (Email: bardizef@geol.u-psud.fr); Franck Pothé, Terra Incognita, CP 701, 36 quai Arloing 69256 Lyon Cédex, France (Email: ti@terra-incognita.fr).
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02/2004 (BGVN 29:02) February 2004 expedition finds molten-surfaced lava lake nearly gone

In February 2004 an expedition led by German scientists visited Erta Ale. Afterwards, an overflight completed the survey of volcanic activity. Of significance was the discovery that an earlier lava lake had largely disappeared. Information from their report follows.

German scientists were at Erta Ale during 9-13 February 2004. They explored areas around the S crater of the volcano, which for the past several years has contained an active lava lake (see BGVN 28:04 and 26:12). The S crater retained only a very small fraction of the former lava lake. When visited it stood ~ 15 m in diameter, located roughly in the center of the old lake. Around the small lake were many active gas vents, and there was a hornito, about 2 m tall, on the SE side. Behind its ~ 1.5-m-high walls, the lake's lava changed levels and occasional lava fountains rose to ~ 10 m high.

On 12 February the expedition team descended to the second terrace (~90 m below the rim) of the S crater, to the surface of the former lake, and approached the small elevated lake. Samples of newly ejected lava were collected, and some were given to Gezahegn Yirgu at the University of Addis Ababa for analysis. Samples retained by the expedition team showed white crystals, approximately 1-2 mm in size, embedded in black material. On the evening of 12 February the team witnessed an overflow of the little lake, flooding the NW half of the second terrace. Parts of the western lake wall eventually collapsed, causing a lava flood wave as well as more violent fountaining (up to 20 m). This event lasted approximately 2 hours.

The entire crater was fogged by fumaroles, which were mainly active in the SE corner of the first terrace (~ 50 m below the rim). Gas masks were necessary inside the crater. From the smell and (blueish) color, these gases contained a high quantity of SO2.

No earthquakes were felt during the visit.

On 21 February a low overflight was made across the volcano. There were no more signs of a lava lake, and only three hornitos were active. Although the flight was made during the day, the glow allowed the hornitos to be visible. Upon return, Chris Heinlein noted that he found photos on the web by Luigi Cantamessa showing that during 15-17 November 2003 the lava lake was also largely gone.

Information Contacts: Carsten Peter, Meilenbergerstr. 1, D-82057 Icking-Dorfen, Germany; Chris Heinlein, Kreuzelbergstr. 62, 76189 Karlsruhe, Germany (Email: chrisheinlein@web.de); Arne Kaiser, Institute of Geophysics, University of Hamburg, Bundesstraβe 55, 20146 Hamburg, Germany (Email: arne.kaiser@dkrz.de); Luigi Cantamessa, Geó-Découverte, 12-14 rue de Cendrier, CH-1201 Geneva, Switzerland (URL: http://www.erta-ale.org/, Email: info@geo-decouverte.ch), Gezahegn Yirgu, Department of Geology and Geophysics, Faculty of Science, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia (URL: http://www.aau.edu.et/faculties/sc/geology/Geology.htm).
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08/2004 (BGVN 29:08) Declining thermal output from small lava lake since early 2003

Field expeditions during November 2003 and February 2004 found that the molten-surfaced lave lake at Erta Ale had almost disappeared (BGVN 29:02). HIGP MODIS Thermal Alerts satellite observations of infrared emissions from the volcano during January 2001-March 2004 confirmed the declining activity levels. MODIS acquires an image of subaerially active volcanoes such as Erta Ale an average of four times in each 48-hour period, twice by day and twice by night. Elevated levels of thermal emission (e.g. active lava flows) are detected by the MODVOLC algorithm, and collated (at http://modis.higp.hawaii.edu).

The level of radiative power output from the summit of Erta Ale (figure 13) averaged 75 MW during 2001 and 2002, dropped significantly during the first five months of 2003, and even further between June and November 2003 to a level beneath the detection limit of the algorithm (~ 10 MW). With the exception of one isolated thermal spike in December 2003, this decline in thermal output continued up to the time of the MODIS report (March 2004). Between December 2002 and March 2004, the average rate of power loss fell to approximately 30 MW. The field-expedition reports corroborated the MODIS observations that a substantial decline in the level of lava-lake activity at Erta Ale occurred since January 2003.

Figure 13. Level of radiative power output from the summit of Erta Ale, January 2001-March 2004. Data courtesy HIGP MODIS thermal alert system.

Observations during November-December 2003. Between 22 November and 6 December 2003, Joshua Jones and Roberto Carniel recorded continuous seismic, thermal, and acoustic data during fieldwork at the volcano. During this time they took several digital photographs showing a small but active lava lake in the southern crater of the summit caldera, and overflows were observed into the southern crater floor. The lava lake was approximately 20 m across.

References. Wright, R., and Flynn, L.P., 2004, Space-based estimate of the volcanic heat flux into the atmosphere during 2001 and 2002: Geology, v. 32, p. 189-192.

Information Contacts: Rob Wright and the HIGP MODIS Thermal Alerts Team, Hawaii Institute of Geophysics and Planetology, University of Hawaii, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.hgip.hawaii.edu/, Email: wright@higp.hawaii.edu); Joshua Jones, Department of Earth & Space Sciences, Box 351310, Seattle, WA 98195-1310, USA (Email: josh@ess.washington.edu); Roberto Carniel, Dipartimento di Georisorse e Territorio, University of Udine - via Cotonificio, 114 - 33100 Udine, Italy (Email: rcarniel@dgt.uniud.it).
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11/2004 (BGVN 29:11) On 4-5 December 2004 visitors noted active hornitos but solidified lava lake

Two teams sent reports on Erta Ale's behavior in December 2004. On 1-5 December the visiting team included Jacques-Marie Bardintzeff and a group from Ushuaia Nature, and on 4-5 December the team consisted of the volcanology travel group SVE-SVG. Both groups submitted similar reports and commented on substantial changes they observed compared to conditions described in past reports (most recently, BGVN 29:08). Although Erta Ale frequently contains a lava lake with an open surface of molten lava, that was not the case this time.

The lava lake's surface had chilled within the small (~ 200-m-diameter) S pit crater (figure 14). A solidified lava crust covered the crater floor. The crust's surface sat ~ 15 m below the W crater rim, and ~ 30 m below the E crater rim. On top of this crust stood four coalesced hornitos in the SE part of the S crater (figure 10). They were ~ 10 m high and represented the only portion of the crust where molten material was in evidence. Two hornitos emitted high temperature (more than 500°C) SO2-rich gas. Another hornito contained glowing molten lava. During the night of 4 December the SVE-SVG group saw degassing and incandescent lava at the summit of two of these hornitos. Bardintzeff described sampling molten material from 12 m depth, in one of the hornitos using a cable and an iron mass (figure 15).

Figure 14. The small S pit crater at Erta Ale as viewed from the E on 5 December 2004. Hornitos had grown on the W part of the crater floor; except for these windows into the molten material at depth, the rest of the lava lake surface had completely solidified. Photo provided by J. M. Bardintzeff.
Figure 15. The S pit crater at Erta Ale as seen from the W on 5 December 2004, with the four hornitos in the center of the photo. Two hornitos on the left emitted high temperature SO2. The hornito in the right foreground contained molten lava (which was sampled). Photo provided by J. M. Bardintzeff.

The SVE-SVG team noted recent activity within the North crater, where an uplifted area termed a 'lava bulge' had solidified. It covered ~80% of the crater floor and rose to about 20-25 m below the crater rim. In the lava bulge's central area, strong and noisy degassing of SO2 spouted from several small hornitos. At the bulge's periphery the observers saw ten small incandescent vents. Subsequently, two plumes rose above the volcano.

Information Contacts: Jacques-Marie Bardintzeff, Laboratoire de Pétrographie-Volcanologie, Bât. 504, Université Paris-Sud, F-91405, Orsay, France (Email: bardizef@geol.u-psud.fr, URL: http://www.lave-volcans.com/bardintzeff.html); Henry Gaudru, Société Volcanologique Européenne (SVE), C.P.1-1211 Geneva 17- Switzerland (Email: HgaudruSVE@compuserve.com, URL: http://www.sveurop.org/).
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01/2005 (BGVN 30:01) Hornitos on chilled lava lake surface in January 2005; December 2004 glass analyses

An expedition led by the volcanology travel group SVE-SVG visited Erta Ale during 22-23 January 2005. The observed eruptive activity was generally unchanged since November 2004 (BGVN 29:11). Degassing was still occurring from three of the four hornitos in the SW part of the South crater, but had decreased slightly in comparison with their December 2004 observations. The hornitos stood ~ 10 m high and represented the only portion of the lava crust covering the crater floor where gas emissions were seen. A window in the upper part of one of the hornitos permitted observation of glowing molten lava.

On 23 January 2005 members of the group descended into the crater and collected recent lava that had poured out from the hornitos during partial collapse. Degassing activity (mainly SO2) from the North crater had also slightly decreased in comparison with early December 2004 observations.

From a small terrace in the NW part of the crater it was possible to observe degassing from several hornitos (some several meters high in the central part of the 'lava bulge'). Near the NW wall of the crater two small, red glowing areas were visible at the summit of two other hornitos.

Chemical analyses. The following complements a previous Erta Ale report by Jacques-Marie Bardintzeff from November-December 2004 (BGVN 29:11). He sampled molten lava at 12 m depth in one of the hornitos of the crater on 5 December 2004 using a cable and an iron mass, and subsequently analyzed the chilled glass sample using an electron microprobe (table 1).

Table 1. Major-element chemistry of Erta Ale lava resulting from 18 representative glass analyses. Courtesy of Jacques-Marie Bardintzeff.

    Oxide    Weight percent

    SiO2      48.61-49.64
    Al2O3     12.99-13.60
    TiO2       2.37- 2.66
    MgO        6.13- 6.39
    FeO       11.25-12.20
    Cr2O          0- 0.11
    MnO        0.03- 0.34
    CaO       10.63-11.41
    Na2O       2.81- 3.08
    K2O        0.54- 0.69
    Total     97.44-98.71

Analysis also revealed some plagioclase phenocrysts (An = 80.9-70.4) as well as scarce clinopyroxene microcrysts (Wo = 43.5-44.0, En = 45.8-45.9, Fs = 10.2-10.6). Compared to the matrix glasses shown in table 1, glass inclusions trapped in plagioclase were richer in SiO2 (50.07-50.41 wt%) and poorer in TiO2 (1.84-1.95 wt %).

Correction. French scientists led by Jacques-Marie Bardintzeff and Franck Pothé visited the summit of Erta Ale on 13-14 January 2003 (BGVN 28:04). At that time the lava lake in the S pit crater was 180 m long, not 120 m as previously reported.

Information Contacts: Jacques-Marie Bardintzeff, Laboratoire de Pétrographie-Volcanologie, Bât. 504, Université Paris-Sud, F-91405, Orsay, France (Email: bardizef@geol.u-psud.fr, URL: http://www.lave-volcans.com/bardintzeff.html); Franck Pothé, Terra Incognita, CP 701, 36 quai Arloing 69256 Lyon Cédex, France (Email: ti@terra-incognita.fr); Henry Gaudru, Georges Kourounis, Derek Tessier, Brian Fletcher, Alexander Gerst, and Motomaro Shirao, Société Volcanologique Européenne (SVE)-Societe Volcanologique (SVG), Geneva, C.P.1, 1211 Geneva 17, Switzerland (URL: http://www.sveurop.org/, Email: HgaudruSVE@compuserve.com).
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07/2005 (BGVN 30:07) Additional observations of the shrinking lava lake in January 2004

The most recent reported observations of Erta Ale made during 22-23 January 2005 (BGVN 30:01) described hornitos on a chilled lava lake surface. The following report is courtesy of Tony Waltham, who recently authored an article discussing the Afar Triangle (Waltham, 2005). These observations from January 2004 further illustrate the shrinking of the lava lake previously noted by a February 2004 expedition (BGVN 29:02).

A group of English geologists who visited on 15-16 January 2004 observed an active lava lake estimated at about 25 m across almost in the center of the lower lava floor within the S crater (figure 16) with a turbulent lava surface ~ 3 m below its rim. Crusting was minimal, and there was no development of substantial lava rafts. Modest fountaining occurred mainly over the zone of rising lava under the southern margin, and none was observed to rise more than 3 m to rim level. A hornito just a few meters high was active on the SE side (figure 17), a few meters from the lake, and night viewing revealed incandescence from a few other fissures across the old lava floor. Minimal fumarolic activity within the crater generated some periods of thin blue haze, though there were major emissions of sulphurous fumes from many fumaroles and fissures around the remains of the old northern crater.

Figure 16. Erta Ale's remaining lava lake in the lower floor of the South crater, 15-16 January 2004. Courtesy of Tony Waltham.
Figure 17. Telephoto view of Erta Ale's lava lake, with a hornito barely visible on the left side, 15-16 January 2004. Courtesy of Tony Waltham.

Reference. Waltham, T., 2005, Extension tectonics in the Afar Triangle: Geology Today, v. 21, no. 3, p. 101-107.

Information Contacts: Tony Waltham, 11 Selby Road, Nottingham NG2 7BP, United Kingdom (Email: tony@geophotos.co.uk).
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09/2005 (BGVN 30:09) Agitated lava lake during time of September 2005 earthquake swarm ~ 100 km S

In conjunction with their investigation of eruptive activity related to a swarm of earthquakes at Dabbahu/Boina, a team of geologists from Addis Ababa University (AAU) also undertook field observations at Erta Ale, with the aid of a military helicopter (see map in this issue of BGVN, the report on Dabbahu/Boina). What follows is their report combined with other information they gathered.

Between 21 and 24 September 2005, the local people saw, from a distance, red and glowing light shooting and rising into the air above Erta Ale. This was an indication that a Strombolian eruption probably occurred, emitting a significant volume of fresh magma within and possibly out of the pit.

The AAU team surveyed Erta Ale's craters at about 0930 on 26 September from the helicopter, as landing was not possible. Within the small southern pit crater of the main crater, they observed a new cone-shaped construct and the presence of an actively convecting lava lake in the center of the new cone. The lava lake occupied the entire lower/inner pit with hot red lava visibly overturning at the edges of the pit. Molten lava was breaking through the lake's solidified black crust. In the northern pit crater, there was a conspicuous solidified lava bulge with dark emissions along the crater walls. No incandescent lava was visible in this pit.

In addition to their direct observations, the AAU team studied videos taken by Walta Information Center of the southern pit on November 2004 and 26 September 2005. The comparison revealed significant changes, particularly in the morphology and activity of the southern pit crater. In the later videos the main crater/pit had widened significantly, with portions of the earlier crater walls having collapsed into the lava lake. There was a new cone-shaped construct within the crater in place of the previous platform that existed between the rim of the outer crater/pit and the lower pit. The new cone was estimated to be some 20 to 30 m from the top of the crater rim. The new cone apparently contained layers of basaltic scoria covered by fresh lava flows. The combined thickness of tephra and lava was estimated to be 20 to 30 m. The lava lake occupied the entire width of the inner crater/pit and was then bounded by steep sides. The lake's surface stood 20 to 30 m below the cone's top.

Anthony Philpotts accompanied Gezahegn Yirgu and colleagues from Addis Ababa University faculty on a helicopter visit to Erta Ale on 15 October. They found the lava lake incredibly active, much more so than when filmed by earlier visitors in March 2005.

A brief review of satellite thermal anomaly data from MODIS/MODVOLC revealed an absence of thermal activity between 12 October 2004 and 31 March 2005, with a renewal beginning on 31 March 2005, increasing substantially in mid-2005 and continuing vigorously through at least 2 November 2005.

Information Contacts: Gezahegn Yirgu, Department of Earth Sciences, Addis Ababa University, P.O. Box: 1176, Addis Ababa, Ethiopia (Email: yirgu.g@geol.aau.edu.et); Walta Information Centre, Woreda Kirkos, Kebele 05, House No. 095, PO Box 12918, Addis Ababa, Ethiopia (Email: wic@telecom.net.et, URL: http://www.waltainfo.com); Anthony Philpotts, University of Connecticut, U-45, Beach Hall, Storrs, CT 06269, USA (Email: philpotts@charter.net); MODIS/MODVOLC Thermal Alerts Team, Hawaii Institute of Geophysics and Planetology (HIGP), University of Hawaii, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://www.modis.higp.hawaii.edu/).
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03/2006 (BGVN 31:03) Molten lava lake observations as late as 3 January 2006

Viviane Grandjean wrote of her observations at Erta Ale during 24 December 2005-3 January 2006 in Bulletin No. 57 of the Société de Volcanologie Genève. On 26 December she saw the lava lake through clouds of gas; its surface was calm, with incandescent lava visible through the broken chilled surface. The S pit crater had an estimated diameter of 170 m and vertical walls, and the lava lake was about 80 m in diameter. It seemed to shrink during the next days, one part appearing hardened and forming almost a second terrace. The plates of cooled surface lava were seen moving and converging amidst degassing lava. Lava fountains were periodically visible and generally outlined the borders of the lava lake under the rim.

On 27 December, the walls of the crater were estimated at about 50 m high, with a crater diameter of about 300 m. Members of the group descended into the crater to inspect a series of active hornitos near the N vents. At one end of the line a vent lined with sulfur opened. In the interior cavity of a smaller vent temperatures of about 800°C were measured. Degassing occurred generally in the area. Lava fountaining continued.

The lava lake appeared lower and calmer to observers on 28 December, with a potential second terrace still forming. Some group members descended into the crater again and observed rockfall and continued lava fountaining.

Information Contacts: Viviane Grandjean, c/o Société Volcanologique Européenne (SVE)-Société Volcanologique de Genève (SVG), Geneva, C.P.1, 1211 Geneva 17, Switzerland (URL: http://www.sveurop.org/).
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06/2008 (BGVN 33:06) Active lava lake visited in February 2008

Around 2-3 February 2008, a Volcano Discovery tour visited Erta Ale (figures 18-21). Tom Pfeiffer reported that the northern pit crater contained a lake of molten lava ~ 75 m across. Strong spattering and bursting bubbles were seen. At times, the lava lake rose and flooded the lower terrace. During this phase the usual fountains ceased. Richard Roscoe, who also visited during February 2008, presents animations of the flooding on his Photovolcanica website. He also shows photos of strong fountaining associated with falling lava lake levels.

Figure 18. Wide-angle photo showing the lava lake at Erta Ale, February 2008. Taken with fisheye-lens and a digital reflex camera. Courtesy Marco Fulle.
Figure 19. Folds developed in the crust of the lava lake at Erta Ale, February 2008. Courtesy of Tom Pfeiffer (Volcano Discovery).
Figure 20. Rising magmatic gases drove fountains like this one emerging above the surface of the lava lake at Erta Ale, February 2008. Courtesy of Tom Pfeiffer (Volcano Discovery).
Figure 21. Unusual egg-like sulfate structures at Erta Ale in February 2008. The delicate-looking incrustations cover an area of wet fumaroles on the rim of the North crater. Courtesy of Tom Pfeiffer (Volcano Discovery).

Occasionally, magmatic gas released in the middle of the lake created a zone a few meters in diameter where fountains typically lasted ~ 1 minute (figure 20). Thin threads of lava (Pelee's hair) are visible in some lava-fountain photographs. Richard Roscoe also features similar photos. Marco Fulle noted strong spattering when lava was drawn down (subducted) into the lake.

A Volcanologique de Genève (SVG) trip on 8-9 February 2008 noted extensions of ropy lava in the N crater. The lake was little changed from the group's last visit in 2005. The group visited the N Crater, and, given its constant degassing, was able to take gas samples. They also measured the lake's surface temperature (700°C). The descent into this crater, seemingly easy, was made difficult by a mantle of very unstable lava scoria. An elevated level of the lava lake halted a subsequent descent.

References. Rivallin, P., and Mougin, D., 2008, Trip report of Pierrette Rivallin and Dédé Mougin: LAVE Bulletin, no. 79, May 2008.

Information Contacts: Tom Pfeiffer, Volcano Discovery (Email: tpfeiffer@decadevolcano.net, URL: http://www.decadevolcano.net/; http://www.VolcanoDiscovery.com/); Marco Fulle, Osservatorio Astronomico, Trieste, Italy; Richard Roscoe, PhotoVolcanica.com (URL: http://www.photovolcanica.com/).
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07/2009 (BGVN 34:07) Changes at NW and S pit craters between 2002 and 2009

From 7-10 February 2009, an expedition team with Chris Weber visited Erta Ale (figure 22) and observed the long-active lava lake in the S pit crater. Although there have been intervening visits and reports (most recently from February 2008, BGVN 33:06), a comparison of observations from 2002 with 2008-2009 gives a sense of the changes to the craters (table 2).

Figure 22. Aerial photograph of the summit of Erta Ale volcano, viewed from the S in February 2002. The summit contained a 0.7 x 1.6 km elliptical caldera housing two steep-sided craters. Steam rose from the NW pit crater (left), and a lava lake resided in the S pit crater (right). A hornito is just S of the S pit crater. Courtesy of Jürg Alean.

Table 2. Summary of observations made during 2002, 2008,and 2009 of Erta Ale S and NW pits and lava lakes. The numbered terraces (former lake surfaces that chilled sufficiently to leave a conspicuous ledge) are shown on the sketch maps (figure 23). The undated 2008 observations came from the local guide, Meles Matwose. Courtesy of C. Weber.

    Date                Observations (South Crater, South Lava Lake, NW Crater, NW Lava Flows)

    04 Dec 2002         South Crater: Elliptical (terraces #1 and #2) ~ 160 m EW, ~ 130 m NS.
                          Two levels (terraces #1 & 2). About half the area (terrace #1) covered
                          by basalt on terrace ~ 45 m below pit rim.
                        South Lava Lake: About half the area (terrace #2) ~ 100 m EW. Lake
                          surface ~ 90 m below W rim of pit.
                        NW Crater: One level (terrace #3).

    2008                NW Crater: Massive collapse early in year caused new, deeper level
                          (terrace #4).
                        NW Lava Flows: Lava flows covered part of terraces #3 & 4. Latest flow
                          in Nov 2008.

    07-10 Feb 2009      South Crater: Elliptical shape (terraces #1, #2, and the lava lake)
                          ~ 190 m EW, ~ 150 m NS. Three levels (terraces #1, 2, lava lake).
                          Terrace (terrace #1) and 2002 lava lake edge (terrace #2) ~ 35 m
                          below W side of pit rim.
                        South Lava Lake: Lava lake ~ 60 m wide in W half of pit. Lake surface
                          higher than in 2002 and it oscillated ~ 5 m vertically and at times
                          came close to overflowing terraces #1 & 2.
                        NW Crater: Three levels (terraces #3, #4, and #5).

South pit crater. The active S pit expanded due to crater collapse on its W side between 2002 and 2009 (figure 23). The shape of the ellipsoidal crater increased by ~ 30 m EW and ~ 20 m NS.

Figure 23. Sketch maps for part of Erta Ale comparing GPS surveys from December 2002 and February 2009. Data from 2002 courtesy of L. Fitsch (BGVN 28:04). Courtesy of C. Weber.

The former lava-lake stand from 2002 left a remnant surface still visible in 2009 (terrace #2), an area marked as well by fractures and fumaroles. In both 2002 and 2009 terraces #1 and #2 still remained, separated by an elevation difference of ~ 40 m (BGVN 28:04).

During 2009, the W half of the S pit contained a 60 m wide active lava lake (figure 24). Fountaining there took place a few times per day, occasionally throwing spatter above the top of the crater walls. Some recent spatter was seen at the pit's W edge.

Figure 24. The active S crater lava lake in February 2009, with the molten lake surface at a much higher level than during November 2002, sometimes rising close to the terraces #1 and #2. The surface is approximately 35 m below the crater rim. Courtesy of C. Weber.

NW pit crater. In February 2009 the NW crater had preserved ledges at three levels (terraces #3, #4, and #5). This represented a substantive change in comparison to 2002 where only level #3 was observed (figure 11). According to Weber, a local guide (Meles Matwose) reported that the NW crater had a massive collapse in early 2008, establishing the deeper level #4. Lava flows covering the crater floor occurred at that time, as well as new lava flows at level #4. One of the latest lava flows, observed by Matwose in November 2008, covered a part of a new interior plateau at level #4. When the lava lake stood at the lowest level, #5, very little lava entered the NW crater.

During the February 2009 expedition, some hornitos on level #4 degassed vigorously inside the pit crater, and, on 9 February 2009, lava spattered ~ 15 m high associated with Strombolian emissions ejected at one hornito during 1800 to 2200 hours. Many photos taken inside the Erta Ale craters in January-February 2009 are shown on the Volcano Discovery website.

Films of Erta Ale. Marc Szeglat's Streaming Planet website provides some spectacular film taken December 2002 inside the S pit showing eruptive activity and researchers collecting data. Cameraman and author of the film was Szeglat, and the film narration is in German. Another short film by Szeglat taken in February 2008 is shown on his YouTube channel.

Recent research publication. Spampinato and others (2008) noted that active lava lakes represent the exposed, uppermost part of convecting magma systems and provide windows into the dynamics of magma transport and degassing. They reported on the main features of the lava lake surface in the S pit of Erta Ale based on observations from an infrared thermal camera made on 11 November 2006. Efficient magma circulation was reflected in the sustained transport of the surface, which was composed of pronounced incandescent cracks that separated wide plates of cooler crust. These crossed the lake from the upwelling to the down-welling margin with mean speeds ranging between 0.01 and 0.15 m/s. Hot spots eventually opened in the middle of crust plates and/or along cracks. These produced mild explosive activity lasting commonly between ~ 10 and 200 s. Apparent temperatures of cracks ranged between ~ 700 and 1070°C, and those of crust between ~ 300 and 500°C.

Reference. Spampinato, L., Oppenheimer, C., Calvari, S., Cannata, A., and Montalto, P., 2008, Lava lake surface characterization by thermal imaging: Erta 'Ale volcano (Ethiopia), Geochemistry Geophysics Geosystems, v. 9, issue Q12008, doi:10.1029/2008GC002164.

Information Contacts: Christoph Weber, Volcano Expeditions International (VEI), Muehlweg 11, 74199, Entergruppenbach, Germany (Email: mail@v-e-i.de, URL: http://www.v-e-i.de and http://www.volcanic-hazards.de); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://hotspot.higp.hawaii.edu/); Streaming Planet (URL: http://www.streaming-planet.de/); Marc Szeglat (Email: szeglat@arcor.de, URL: http://www.youtube.com/marcszeglat and http://www.vulkane.net/); Volcano Discovery (URL: http://www.volcanodiscovery.com/); Jürg Alean, Kantonsschule Zürcher Unterland, Bülach, Switzerland.
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01/2010 (BGVN 35:01) February 2010 visit reveals little change in South pit crater's lava lake since 2002

Christoph Weber sent a report about his 8-11 February 2010 visit to Erta Ale. We last reported on Erta Ale after a visit by Weber in February 2009 (BGVN 34:07). The volcano is famous for molten lava lakes.

Activity at the S pit crater was comparable to that noted in December 2002 (figure 25, also see BGVN 28:04). The elliptical pit crater measured ~ 180 m E-W and ~ 140 m N-S. The upper platform (terrace T) inside the crater was, on 10 February 2010, covered by a lava flow, and the lava lake surface was ~ 20 m below the W rim (figure 26). On 9 February the 65-m-wide active lake in the W half of the crater rose and overflowed the lower ring terraces. Fountaining at the lava lake took place most of the time during the observations (figure 27), occasionally higher than the pit crater walls. Fresh lava spatters were found at the S pit crater's W edge. A sample was taken out of the lava lake.

Figure 25. Sketch maps of the southern Erta Ale pit crater on 7 December 2002 and 9 February 2010. In 2002 the elliptical pit crater was ~ 160 m E-W and 130 m N-S. The lava lake (taking up ~ 50% of the crater) from E to W was ~ 100 m in diameter. In 2010 the crater was ~ 180 x 140 m. Courtesy of C. Weber.
Figure 26. Photo looking W towards the southern Erta Ale pit crater taken 10 February 2010. Courtesy of C. Weber.
Figure 27. Fountaining of the Erte Ale lava lake in the southern pit crater on 9 February 2010. Courtesy of C. Weber.

Information Contacts: Christoph Weber, Volcano Expeditions International (VEI), Muehlweg 11, 74199 Untergruppenbach, Germany (URL: http://www.v-e-i.de/).
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06/2011 (BGVN 36:06) Observers watch dynamic lava lake during November 2010

Erta Ale contains two lava lakes within its caldera. During the last three years, several expeditions have visited the volcano to examine changes (BGVN 33:06, 34:07, and 35:01). This report synthesizes the reports of two teams that visited Erta Ale during November 2010. Both teams noted that the lava lake within the southern crater has risen, nearly filling the entire crater and overflowing onto the caldera floor.

Southern Crater activity. Afar Rift Consortium (ARC) scientists visited Erta Ale during 21-23 November 2010 (figures 28 and 29). Tom Pfeiffer (Volcano Discovery) and Micheal Dalton-Smith visited Erta Ale during 25-28 November 2010. The lava lake had risen above previously formed terraces (see BGVN 35:01 for information on terraces). Both teams noted that the lava lake had risen ~40 m, nearly filling the S crater and breaching its W rim, spilling lava flows onto the larger caldera floor. The still-hot overflows traveled distances of 50-100 m on the caldera floor, and one recent long flow (estimated to be from November 24th given its temperature) had almost reached the W caldera walls.

Figure 28. Satellite image of the Erte Ale caldera showing the two crater pits. Courtesy of Google Earth, with labels by Afar Rift Consortium in reference to their 21-23 November 2010 visit (Field and Keir, 2010).
Figure 29. Photograph of the Erte Ale showing the lava lake with an elevated rim, taken 22 November 2010. Person in bottom left of photo for scale. Photo by L. Field (Afar Rift Consortium). Taken from Field and Keir (2010).

The ARC team noted Strombolian activity from the lava lake in the southern pit crater (figure 30).Throughout their visit, the ARC team saw extensive amounts of Pele's Hair and clouds rich in hydrogen-sulfide gas. Fountaining was reported by Pfeiffer to reach heights of 30-70 m. Degassing fountains kept the whole lava-lake surface violently boiling for a large portion of the latter team's visit.

Figure 30. Photograph of the first lava to breach the rim of Erta Ale's S crater and then to enter the main caldera. Taken 21 November 2010 by L. Field (from Field and Keir, 2010).

The still-active lake was circular, ~40 m in diameter (about half to two-thirds its size in 2008 and 2009). The lava lake was reported to be encompassed by a bounding ring of chilled material that was ~ 4 m high on the S side. The morphology of the ring wall constantly changed as more lava overflowed, with parts collapsing and rebuilding.

From the night of the 22 November 2010 until the ARC team left on 23 November, the team observed a periodic rise and decline of the lava lake level.

According to Pfeiffer the lava level rose and fell by about 2-4 m about every 30 minutes. During the 25-28 November observations intense eruptive phases were observed. Lava overflowed about 12 times and fed new flows that topped older flows. During 25-28 November, the overall average level of the lake's surface rose an estimated 3-5 m.

Northern Crater activity. The ARC noted that during 21-23 November the northern crater pit was relatively quiet. They observed a small amount of incandescence during the night of 21 November (figure 31). During the day, they noted a new cone about 1 m high and lava flows of limited extent.

Figure 31. Photograph taken in January 2011 of an Erta Ale hornito with an incandescent vent in the N crater. Photo taken by M. Fulle.

According to the Volcano Discovery team, the deeper N crater had not changed much since their previous visit in February 2008 (BGVN 33:06). During their 2010 visit they saw a 7-10 m high hornito, in the N crater's center, with a glowing vent that sometimes spattered lava. According to Dalton-Smith, flaming gas was seen during the day and on 25 November, an extremely bright glow was seen at night. Upon the team's arrival at the volcano, a large fresh flow had recently surged from the hornito and covered most of the N crater floor.

Location and tectonics. Erta Ale is located in the Afar rift, a region that shows signs of undergoing a continent to ocean transition. The Afar rift is located between the Nubian and the Somalian plates. There is reason to believe that the mantle below the Afar rift region has an above average temperature (Bastow and Keir, 2011). The Afar Rift Consortium also noted that recent fissure eruptions occurred on Erta Ale's N flank.

References. Field, L, and Keir, D. 2010, Observations from the Erta Ale eruption 21st Nov-23rd Nov 2010. Afar Rift Consortium (ARC) (URL: http://www.see.leeds.ac.uk/afar/new-afar/home-page-assets/Observations_from_Erta_Ale.pdf). Additional information about the work of the ARC can be found at URL: http://www.see.leeds.ac.uk/afar/.

Fulle, M, 2011, Stromboli Online (URL: http://www.swisseduc.ch/stromboli/perm/erta/lake-2011-en.html).

Bastow, ID, and Keir, D, 2011, The protracted development of the continent-ocean transition in Afar, Letters, Nature Geoscience, DOI: 10.1038/NGEO1095 published online on March 11, 2011.

Keir, D, Pagli, C, Bastow, ID, Ayele, A., 2011, The magma-assisted removal of Arabia in Afar: Evidence from dike injection in the Ethiopian rift captured using InSAR and seismicity, Tectonics, v. 30, TC2008, DOI: 10.1029/2010TC002785, published 22 March 2011.

Information Contacts: Afar Rift Consortium (URL: http://www.see.leeds.ac.uk/afar/); Tom Pfeiffer, Volcano Discovery (URL: http://www.VolcanoDiscovery.com/); Michael-Dalton-Smith, Digital Crossing Productions (URL: http://www.digitalcrossing.ca/); Marco Fulle, Osservatorio Astronomico, Trieste, Italy (URL: http://www.ts.astro.it/) and at Stromboli Online (URL: http://www.swisseduc.ch/stromboli/perm/erta/lake-2011-en.html).
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Erta Ale is an isolated basaltic shield volcano that is the most active volcano in Ethiopia. The broad, 50-km-wide volcano rises more than 600 m from below sea level in the barren Danakil depression. Erta Ale is the namesake and most prominent feature of the Erta Ale Range. The 613-m-high volcano contains a 0.7 x 1.6 km, elliptical summit crater housing steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located to the SE of the summit and is bounded by curvilinear fault scarps on the SE side. Fresh-looking basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera is renowned for one, or sometimes two long-term lava lakes that have been active since at least 1967, or possibly since 1906. Recent fissure eruptions have occurred on the northern flank of Erta Ale.

Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
1967 (in or before) 2014 (continuing) Confirmed 0 Historical Observations
1960 Jan Unknown Confirmed 0 Historical Observations
1940 Unknown Confirmed 0 Historical Observations
1906 May Unknown Confirmed 0 Historical Observations
[ 1904 Nov 1 ± 60 days ] [ Unknown ] Uncertain 2  
[ 1903 ] [ Unknown ] Uncertain 2  
[ 1873 ] [ Unknown ] Uncertain 2  

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.


Synonyms

Erta Ali | Artali | Oerteale | Hertale | Ginna Ale | Irta Ale | Sat Agomara | Ali Bogo | Erto Ale | Ertahale
Erta Ale is an isolated basaltic shield volcano that is the most active volcano in Ethiopia. The broad, 50-km-wide volcano rises 500 m from below sea level in the barren Danakil depression. It contains a 0.7 x 1.6 km, elliptical summit crater, seen here from the SE. The crater houses steep-sided pit craters that contain one or more lava lakes that have been active since at least 1967. Fresh black lava flows from the southern pit crater fill much of the floor of the larger crater and spill over its rim down the south flank.

Photo by Luigi Cantamessa, 1992 (courtesy of Pierre Vetsch).
This 1992 view looks south over the summit crater of Erta Ale volcano. A pit crater at the center, whose floor is not visible in this photo, contains an active lava lake. Overflows of lava from this crater during 1971-73 diverged around an older cone and covered much of the broad crater floor.

Photo by Luigi Cantamessa, 1992 (courtesy of Pierre Vetsch).
The steep-walled southern pit crater cuts the floor of the summit crater of Ethiopia's Erta Ale volcano. This November 1992 photo shows an active lava lake on the floor of the 100-m-deep crater. Fresh lava flows radiate away from the crater rim. They were produced by lava overflows from the crater, particularly during 1971-73. The southern pit crater has had an active lava lake since at least 1967, and possibly since 1906. Few observations are made of this remote volcano, located in the extremely hot and arid Afar region.

Photo by Luigi Cantamessa, 1992 (courtesy of Pierre Vetsch).
A permanent lava lake has been present at the isolated Erta Ale volcano in Ethiopia since at least 1967, and possibly since 1906. This November 1992 photo shows a lava lake in a 100-m deep crater in the southern part of the large summit crater. For many years two lava lakes were active simultaneously. During 1971-73 continuous overflows from the southern lava lake filled the entire crater floor and sent lava flows down the southern flank. The northern lava lake ceased activity sometime between satellite observations in February 1987 and June 1992.

Photo by Luigi Cantamessa, 1992 (courtesy of Pierre Vetsch).
The summit of Erta Ale volcano contains a dramatic 0.7 x 1.6 km, elliptical caldera housing steep-sided pit craters. Steam rises from the North pit at the left, and a lava lake was active in the center pit crater at the time of this February 2002 view from the south. Erta Ale is an isolated basaltic shield volcano that is the most active volcano in Ethiopia. Fresh-looking basaltic lava flows fill much of the caldera and have overflowed its rim on the southern side. One, or sometimes two, long-term lava lakes have been active since at least 1967.

Photo by Jürg Alean, 2002 (Kantonsschule Zürcher Unterland, Bülach, Switzerland).
Ale Bagu, also known as Ummuna, is an elongated, 1031-m-high stratovolcano (left center) located SW of Erta Ale, the volcano at the top-center showing a small orange-colored lava lake. In contrast to other volcanoes of the Erta Ale Range, Ale Bagu is mantled by basaltic pyroclastic rocks. The main crater is a steep-walled, 750 x 450 m depression; trachytic lava flows occupy the crater floor, and silicic lavas from the axial regional fissure extend to the NW and SE. Lake Giulietti (also known as Lake Afrera) is at the lower right.

NASA Landsat image, 1999 (courtesy of Hawaii Synergy Project, Univ. of Hawaii Institute of Geophysics & Planetology).

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

Barberi F, Varet J, 1970. The Erta Ale volcanic range (Danakill depression, Northern Afar, Ethiopia). Bull Volc, 34: 848-917.

Burgi P-Y, Caillet M, Haefeli S, 2002. Field measurements at Erta'Ale lava lake, Ethiopia. Bull Volc, 64: 472-485.

Francis P W, Rothery D A, 1987. Using the Landsat Thematic Mapper to detect and monitor active volcanoes: an example from Lascar volcano, northern Chile. Geology, 15: 614-617.

Harris A J L, Carniel R, Jones J, 2005. Identification of variable convective regimes at Erta Ale lava lake. J Volc Geotherm Res, 142: 207-223.

IAVCEI, 1973-80. Post-Miocene Volcanoes of the World. IAVCEI Data Sheets, Rome: Internatl Assoc Volc Chemistry Earth's Interior..

Oppenheimer C, Francis P, 1998. Implications of longeval lava lakes for geomorphological and plutonic processes at Erta 'Ale volcano, Afar. J Volc Geotherm Res, 80: 101-111.

Richard J J, Neumann van Padang M, 1957. Africa and the Red Sea. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI 4: 1-118.

Varet M J, 1971. Sur l'activite recente de l'Erta Ale (Dankalie, Ethiopie). CR Acad Sci Paris, Ser-D, 272: 1964-1967.

Wiart P, Oppenheimer C, 2005. Large magnitude silicic volcanism in north Afar: the Nabro volcanic range and Ma'alalta volcano. Bull Volc, 67: 99-115.

Wood C A, 1978. . (pers. comm.).

Volcano Types

Shield
Caldera
Pyroclastic cone(s)

Tectonic Setting

Rift zone
Intermediate crust (15-25 km)

Rock Types

Major
Basalt / Picro-Basalt
Andesite / Basaltic Andesite

Population

Within 5 km
Within 10 km
Within 30 km
Within 100 km
2,685
2,796
8,857
235,083

Affiliated Databases

Large Eruptions of Erta Ale Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).
WOVOdat WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.
EarthChem EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).
Smithsonian Collections Search the Smithsonian's NMNH Department of Mineral Sciences collections database. Go to the "Search Rocks and Ores" tab and use the Volcano Name drop-down to find samples.