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The Global Volcanism Program has no activity reports for Fogo.
The Global Volcanism Program has no Weekly Reports available for Fogo.
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.
03/1995 (BGVN 20:03) New eruption on 2 April generates lava flows within the caldera
04/1995 (BGVN 20:04) Fire fountains continue but lava extrusion rate declines
05/1995 (BGVN 20:05) Increased explosive activity; intense fumarolic emissions
12/1995 (BGVN 20:11/12) Eruption of 2 April through 28 May covered over 6 square kilometers of land
03/1995 (BGVN 20:03) New eruption on 2 April generates lava flows within the caldera
A fissure eruption that began the night of 2-3 April produced lava flows from the base of the Pico cone, located within the 8-km-diameter Cha Caldera (figure 1). This cone, also called Fogo Peak, has a crater ~500 m in diameter and 180 m deep. Caldera residents felt weak intermittent earthquakes as early as 25 March. After 0100 on 2 April the earthquakes increased in frequency, and felt events occurred at 0700 and 1500. At about 2015 residents felt a stronger earthquake that caused dishes to fall from cupboard shelves and may have opened a 200-m-long crack on the flanks of the cone.
|Figure 1. Topographic map of Fogo Island showing historical lava flows (shaded), current lava flows through 11 April (solid), and selected towns (hatched). Modified from Neumann van Padang and others (1967).|
Residents in Sao Filipe, ~15 km WSW of the vent, noticed a red glow around 2300 on the night of 2 April, probably the beginning of the eruption. Other residents reported that eruptive vents on the flank of Pico opened at 0006 on 3 April. Initially there was a burst or jetting of gas followed by ejection of large blocks. This Strombolian activity was followed by a "curtain of fire" that fed a lava flow, which cut off the main road to Portela village by 0200 (figure 2). By 0500 on 3 April, fine dark ash had begun to fall in areas close to the volcano. Around the same time, an eruption cloud to a height of 2,500 m was formed. Witnesses told reporters that the volcano was "spewing out smoke and flames." The head of the Cape Verde Red Cross stated that high flames could be seen and that "a pall of black smoke was hanging over the island."
|Figure 2. Map of Fogo caldera showing lava flows from the current eruption. Courtesy of João Gaspar, Universidade dos Açores.|
During the night of 2-3 April, several residents evacuated to the N coast. Once ashfall began, more caldera residents and some people in the eastern villages of Corvo, Achada Grande, Relva, Tintiera, Cova Matinho, Cova Figueira, and Estância Roque also evacuated to the coastal towns of Mosteiros (~9 km N of the summit) or Sao Filipe. Police officials reported that all of the ~1,300 people living within the caldera had managed to get out on foot and had been accounted for by noon on 3 April.
Under the supervision of the National Defense Minister, a Crisis Cabinet was created by the Cape Verde Government. About 60 Cape Verde Army soldiers were sent to the island and an emergency communications system was installed. Food and medicine were provided, and evacuation centers (schools, private institutions, and tent camps) were established to hold up to 5,600 people. Official reports indicated that almost 1,000 persons were sheltered in the Army camps at Sao Filipe, Patim, Achada Furna, and Mosteiros. During the first days of the eruption local authorities, Cape Verde soldiers, and volunteers, helped caldera residents save their belongings. Nobody was killed, and only 20 people needed medical assistance during the evacuation, including children with respiratory problems. Although numbers are uncertain, as many as 5,000 people may have been displaced during this eruption. As of 16 April, Portela residents continued to remove belongings by foot.
Around noon on 3 April some teachers who had driven from Sao Filipe to Mosteiros told geologist Veronica Carvalho Martins (U.S. Embassy in Cape Verde) of sandy ashfall along the road on the E side of the island just below the caldera; they also reported sounds "like an old stove." During a flight W of the caldera soon afterwards, Martins observed a high mushroom-shaped ash column rising from the caldera. Martins later saw a long fissure vent with lava fountains feeding an already well-developed flow that was moving W across a road towards the caldera wall and curving N. A vent SE of the fissure exhibited continuous strong ejection of brownish pyroclastic material, while to the NW a smaller vent was intermittently ejecting similar material.
João Gaspar (Universidade dos Açores) and colleagues from Cape Verde (ISE and IICT) reported that on 3 April a thick cloud of dark ash and vapor 2,500-5,000 m high could be seen from Santiago Island, ~60 km ENE. Early that morning three small vents were observed inside the caldera along the SW part of a N30°E fissure that crossed the main road within the caldera (figure 2). Fine dark ash and small pahoehoe lavas were produced, and large plastic bombs (1-4 m in diameter) were projected distances of 500 m. That afternoon the fissure reached 2 km in length, and four new vents opened in its NE section. Activity increased during the night of 3-4 April with the emission of more lava flows, but decreased the following morning. One Cape Verde official said that the lava was moving at a speed of 60 m/hour. Gaspar reported that explosive activity was centered at the NE vents, but strong fumarolic activity continued along the main fissure. Lava fountains reached ~ 400 m high and a cloud of dark ash and gases rose 2,000 m. A scoria cone with a crater open to the SW formed and produced aa lava flows with thicknesses of 3-10 m measured at different fronts.
Effusive activity remained intense on 4 April, but ejection of pyroclastic fragments had decreased significantly. Television pictures showed a lava "stream" coming from the fissure and, in the morning, a mantle of aa lava covering the central part of the caldera. Portuguese television and other press coverage on the evening of 5 April indicated that activity had decreased.
In the following days the lava flow reached the settlement of Boca de Fonte near the caldera wall ~2 km W of the eruption center, and by 9 April it had destroyed at least 5 houses (possibly 10), the main water reservoir, and several square kilometers of fertile land used to grow coffee, wine grapes, fruits, maize, tapioca, and beans. Reluctant farmers with cattle in the caldera were ordered to leave their homes or face arrest on 8 April. A TSF Radio correspondent reported on 9 April that the lava flow moving into Boca de Fonte was advancing at a rate of 10-14 m/hour, twice as fast as the day before. However, the flow slowed to 4-5 m/hour on the 10th. Weak tremor had been felt on the caldera floor since the start of the eruption. On 10 April the seismicity increased, and earthquakes with Mercalli intensities of III-IV occurred, probably due to obstruction of the main vent, where lava fountaining stopped briefly.
Richard Moore and Frank Trusdell (U.S. Geological Survey) arrived on 10 April to assess the volcanic hazards and advise the Government of Cape Verde. With the help of Martins, they installed a seismograph ~1 km S of the erupting vent. The seismograph recorded continuous tremor, indicative of the ongoing eruption, as well as microearthquakes (M <1) at 0759 and 1213 on 12 April. Volcanic tremor amplitude remained moderate to strong through 13-16 April. Lava temperature measured using a thermocouple on 11 April was 1,026°C; this temperature seems low, but the aa was highly viscous and sluggish, in contrast to the more fluid lava of Kilauea in Hawaii. Lava flows and spatter contain ~5% black pyroxene and 1% olivine phenocrysts, often together in clots.
Gaspar noted that on 11 April two main lava rivers had velocities of 5-6 m/s near the vent. One lobe moved towards the W and fed the flow-front moving towards Portela and Bangaeira villages. The other more active lobe was directed SW into the Cova Tina depression. The USGS team observed relatively low-volume eruptions of gas-rich spatter slowly building a cone, and lava cascading rapidly down the W flank of Pico being directed W and SW by high levees. The N flow-front, near Portela, stagnated during 10-11 April. At 1830 on 11 April, advancing flows were confined to the S part of the caldera, where two small lobes were moving W at a rate of ~15-20 m/hour, travelling S of the flows erupted the previous week.
During the morning of 12 April eruptive activity consisted of Strombolian gas-rich spatter ejection; volumetric output remained relatively low. At 1549 activity changed to Hawaiian-type fire fountains that typically rose 100-120 m above the vent, slowly building a scoria cone 100 m high. A new lava flow that started on 12 April overrode the first flow, which had stagnated ~1 km SW of Portela. This flow quickly traveled 3 km from the vent in the general direction of Portela, but remained entirely on top of the first flow. All other lava flows were inactive at 1900 on 12 April. Preliminary estimates of erupted volume through 12 April ranged from 50 to 75 x 106 m3 of lava.
Although volumetric output remained low, Hawaiian-type fire fountains continued on 13 April and a flow confined to a 3-m-wide channel cascaded down the W flank of the new cone. That channel continued to feed a sluggish aa flow moving W then N. The cinder and spatter cone reached a height of 120 m. The overriding lava flow only moved N another 46 m; most of the additional lava was expended covering the first flow. The added mass on top of the first flow also caused it to spread laterally.
Activity on 14 April continued unabated, increasing the height of the new cone to 130 m. The E lobe of the second flow reactivated and moved 470 m N during 13-14 April. At 1900 on 14 April the second flow was within 235 m of the distal end of the first flow, and lateral spreading was occurring at the flow margins. At this time the distal portion of the first lobe showed signs of renewed movement, induced by pressure from the overriding aa flow. The thick aa flow continued to spread slowly W the next day; maximum lateral spreading S of Boca de Fonte was ~3 m. The new E lobe of the second flow advanced an additional 6 m and stopped. At 1700 on 15 April the most active part of the overriding flow was on its NW side. Much of the lava production apparently went towards thickening the central part of the flow, estimated to be 16 m thick. At 1800 on 15 April spatter fountains were ~100 m high and cinder was falling as far as 2 km S of the vent.
Activity remained generally constant on 16 April, with fire fountains typically rising 100-120 m; the scoria cone stood 140 m tall. Estimates of lava-channel dimensions and speeds through 16 April yielded an erupted lava volume of 2.5-8 x 106 m3/day. The flow-front became remobilized at 1535 on 16 April, and by 1700 had moved 38 m beyond and NE of the distal end of the first flow. At that time the lava front was ~534 m from the nearest house in Portela. A lava temperature of 1,056°C was measured with a thermocouple in a spiny aa breakout near the terminus of the flow. From a few hundred meters away, USGS geologists watched the roof of a small house burn; it was buried soon thereafter. There was also considerable lateral spreading of the flow S of Boca de Fonte on 16 April. In this area, the flow-front monitor lines showed westward movement of 19-26.5 m. At 1800 the flow was still active and 41-72 m E of the Portela access road. Thickness at the margins of the active flows ranged from 1 to 20 m. The greater thicknesses are a strong indication that a breakout of spiny pahoehoe or aa can be expected, advancing the flow.
Fogo Island (476 km2), with a population of ~33,000, consists of a single massive volcano with an 8-km-wide caldera breached to the E; the W rim rises 700 m above the caldera floor. The central cone in the caldera, the highest point in the Cape Verde Islands, was apparently almost continuously active from the time of Portuguese settlement in 1500 A.D. until around 1760. Later historical lava flows reached the E coast. The last eruption was during June-August 1951 from caldera vents S and NW of the central cone. That eruption, also preceded by earthquakes, began with ejection of pyroclastic material that formed Mt. Rendall and Mt. Orlando (figure 2).
Reference. Neumann van Padang, M., Richards, A.F., Machado, F., Bravo, T., Baker, P.E., and LeMaitre, R.W., 1967, Catalogue of active volcanoes of the world including solfatara fields, part XXI, Atlantic Ocean: Rome, IAVCEI, 128 p.
Information Contacts: J. Gaspar and N. Wallenstein, Universidad dos Açores; A. Mota Gomes, Instituto Superior de Educação de Cabo Verde (ISE), Cape Verde; F. Costa and E. Correia, Centro de Geografia do Instituto de Investigação Cientifica de Tropical (IICT), [Portugal]; R. Moore, USGS; F. Trusdell, USGS Hawaiian Volcano Observatory; V. Carvalho Martins, U.S. Embassy, Cape Verde; UNDHA; Reuters; UPI; LUSA News Agency, RTP Internacional Television, Channel 1 Television, and TSF Radio, Lisbon.
04/98 (BGVN 20:04) Fire fountains continue but lava extrusion rate declines
On 2-3 April a fissure eruption began on Fogo Island from the SW flank of Pico cone (Fogo Peak) within the 8-km-diameter Cha Caldera (BGVN 20:03). During the initial stage of the eruption there was a burst or jetting of gas, followed by ejection of large blocks and fire fountaining. A lava flow cut off the main road to local villages by the morning of 3 April, and ash fell on the island. Approximately 1,300 residents in the caldera were evacuated.
Volcanologists from the United States, Portugal, and France were requested by the Cape Verdean government to help monitor and evaluate the activity. João Gaspar (Universidade dos Açores) and colleagues observed the activity until 11 April. U.S. Geological Survey (USGS) volcanologists, assisted by Cape Verdean geologists, installed a seismic station and monitored the eruption during 10-25 April. Additional information about the vent activity during 14-19 April was provided by Henry Gaudru and members of the Société Volcanologique Européenne who visited the volcano. François Le Guern (CNRS France) monitored the volcano on 25-27 April.
Summary of activity, 3-16 April. Detailed activity reports through 16 April have already been published (BGVN 20:03). Seven vents were active on the first day of the eruption, with fire-fountains feeding pahoehoe lava flows, ejection of volcanic bombs, and a gas-and-ash plume 2,000 m high. A scoria cone was soon built, from which lava flows were directed SW before turning NW towards the caldera wall. As the main aa flow approached the caldera scarp it turned N, covering the settlement of Boca de Fonte by 9 April and approaching Portela and Bangaeira (see map in BGVN 20:03). Less vigorous fire fountaining continued on 12-16 April, and fed new lava flows on top of the previous aa flow. There were occasional periods of Strombolian spatter ejections. By late on 16 April the remobilized flow-front was ~4 km from the source vent and only a little more than 500 m from the nearest house in Portela.
Activity during 17-25 April. Except where noted otherwise, the following observations are from the USGS team and their Cape Verdean colleagues. Activity continued on 17 April with little change at the vent. Spatter fountains rose 100-150 m, and the cone was ~150 m high. Volcanic tremor amplitude remained moderate to strong. The N end of the aa flow advanced ~150 m during 16-17 April, to ~420 m SW of the nearest house in Portela, and the E side of the flow moved 20-50 m ENE. The W side of the flow advanced >100 m and by 1430 had crushed half of the winery at Boca de Fonte. After these breakouts blocked the access road a new road was created through agricultural fields, forcing residents rescuing belongings to walk an additional 500 m. Flow movement was barely perceptible after 1430 and largely restricted to short spiny pahoehoe and aa oozes at flow margins, although lava output at the vent was unchanged.
Between 1630 and 2030 on 17 April, Gaudru noted that Strombolian explosions were less vigorous and that the main lava channel had widened from 2-3 m to 5-6 m because of lava-block obstructions. The W flank of the cone was also covered by cinders. Explosive activity increased at 1900, sending incandescent ejecta 150-200 m above the rim of the cone. A flame visible behind the E part of the cone was apparently coming from a small vent on the upper E flank. At 2000 explosions began ejecting material >300 m W instead of vertically.
Tremor amplitude began to increase around 0650 on 18 April, and at 0740 became continuous at about twice the previous amplitude. Eruptive style changed from fire fountaining to Strombolian activity, with spatter discharged by loud gas bursts every 3-8 seconds. Lava production increased during the morning; by noon the lava was largely pahoehoe in the upper 300 m of the channel. Estimated channel dimensions and the speed of lava in it yielded production rates of 4-8.5 x 106 m3/day. Microearthquakes were intermittent, with three larger events (all M <1) at 1314 and 1803 on 18 April, and at 0426 on 19 April.
Seismograph records showed that activity during 0110-0320 and 0426-0610 on 19 April was characterized by strong explosive bursts, which were interpreted to be vent clearing episodes after pieces of the cone and newly erupted spatter closed the conduit. After 0610 the seismicity indicated a return to fire-fountaining. A favorable wind direction permitted a close approach to the vent and lava channel to verify the volume estimate, but the lava appeared somewhat more viscous/sluggish. There was no measureable movement at the edges of the aa flow on 19 April after <3 m of movement the day before, however, lava continued ponding in its channel near the middle of the flow.
Observations made by Gaudru from 1230 on 18 April until 1230 on 19 April indicated that activity remained strong with incandescent fragments rising >200 m and loud detonations. Explosions every 1-2 seconds, accompanied by earthquakes, ejected particles ranging in size up to >1 m3. Gas outbursts were more intense, and black plumes hovered over the active cone. Partial obstruction of the crater caused a larger explosion at 1745 on 18 April that sent gas and cinders 500-600 m high. After several seconds of quiet, stronger explosive activity began again with sounds that shook the ground. The upper E flank crater sent an intermittent orange-red flame 10-15 m high for several hours during this period, higher than previous days. Eruptive activity observed by the Gaudru group became more regular at 0100 on 19 April, when an intense episode began that sent lava fountains >300 m high for several hours. Explosive activity began again at dawn that lasted throughout the morning of 19 April.
Tremor amplitude on 19 April changed from moderate-strong to moderate around 1500, when Strombolian activity reverted back to fire fountains. Fire fountain heights diminished somewhat on 20 April, rising generally 20-50 m above the vent. Intermittent Strombolian activity continued with more energetic bursts that sent viscous lava clots >160 m high. A full lava channel 200 m W of the vent appeared much like it did the day before. A new aa lobe was moving sluggishly on top of the earlier flow, and by 1700 its distal end was ~600 m from the N end of the flow, nearest to Portela.
Strong Strombolian activity on 21 April produced loud bursts of viscous spatter 50-150 m high. A levee formed on top of the spillway adjacent to the vent behind which fountains rose 10-20 m, often interrupted by explosions. Lava exited through a hole in the bottom of the levee into a W-flank channel roofed over in two places. At the bottom of the spillway the lava entered a sinuous channel, moving W and NW on top of the previously emplaced flow; this channel remained full all day. The volume of lava erupted was similar to values for the past several days, 4-8 x 106 m3/day. The 160-m-high cinder cone was no longer increasing significantly in height, but impact craters as large as 5 m wide and 1 m deep, created by fall of spatter bombs 0.5-2 m across, littered its flanks and parts of the cinder-mantled caldera floor up to 200 from the vent. As is common during eruptions of viscous mafic lava, the inner walls of the cone collapsed into the conduit, resulting in explosive vent-clearing episodes. The overriding aa flow on the E side of the N flow moved another 6 m N during 21 April.
Volcanic tremor on 21-22 April continued at moderate to strong levels, punctuated by frequent sonic bursts. Noisy Strombolian bursts sent clots of spatter over the top of the cone and onto its flanks. The volume of lava flowing into the channel was similar to that of 21 April. At noon, lava from a new crack on the N flank of the cone flowed 150 m N and soon stagnated. The aa flow advanced 2 m W near the new end of the road (150 m S of Boca de Fonte), and ~3 m NE on the E side of the N flow. Most of the volume of lava was concentrated in an aa lobe that was very slowly overriding the earlier flow. This lobe locally was at least 15 m thick and covered an estimated 75% of the existing flow field.
Activity on 23 April was spectacular. Deafening explosions from four discrete vents rocked the caldera all day; at times the ground was in continuous motion from concussion waves. The overriding aa lobe only moved ~4 m N on the E side of the main aa flow. However, early in the afternoon a new vent opened at the NW base of the cone. By 1700 lava was flowing W from this vent, and by 1807 spatter ejected to heights of 10-15 m was visible. Pahoehoe lava flowed on top of older aa and soon joined the large stagnating aa channel 500-700 m from the main cone. For the preceding 4 days the seismograph had recorded sonic bursts and microseisms. It was believed that shock waves associated with the bursts caused several fractures on the cone. One of these cracks provided a new pathway for lava to exit the cone, thus robbing the main channel of most of its lava. Strong volcanic tremor was interrupted by frequent sonic bursts.
Moderate to strong tremor continued on 24 April. At the main cone in the morning, Strombolian bursts every few seconds sent spatter fragments onto the cone's flanks. In the afternoon, the intense sonic bursts and Strombolian activity that had characterized the past few days were absent. A gray-black plume, laden with fine-grained (<1 mm) juvenile particles and volcanic gases, rose to heights approaching 1.5 km above the caldera floor. Lava in relatively low volumes continued to erupt from the NW base of the cone, moving horizontally from the cone into a tear-shaped cavity. Once the lava reached the surface, degassing occurred, at times intensely enough to drive low-level Strombolian activity. The amount of visible degassing rivaled the plume from the main vent. The depression and lava chute were 25-35 m long and 1-2 m wide. Lava moving at 1 m/s then spilled out of the chute and entered a channel, which was 3-5 m wide, with a speed of 6 m/minute. The flow in the chute and lava channel was initially pahoehoe, changing to aa with increasing distance. The new lava channel joined the former channel, now stagnant in its upper part, 500-700 m below the cone. This new channel caused the hydraulic head within the main cone to be lowered, resulting in decreased Strombolian activity.
By 25 April the lava extrusion rate slowed to ~250,000 m3/day, and tremor amplitude was somewhat diminished. Spatter generally was not visible within the cone and only rarely did isolated fragments clear its top. However, lava that had ponded in the aa channel advanced on the S side of the earlier large flow. This advance, which probably began late on 24 April, moved as much as 0.5 m/minute during the afternoon. Most of the new lobe was aa, with minor pahoehoe. The thermocouple temperature was 1,065°C (steady for several minutes) in the pahoehoe. At about 1500-1700 loud explosions at vents within the main cone increased in frequency, although spatter output did not change.
Activity in late April-early May. At the request of the Cape Verde government, the French Embassy in Praia and the Ministere de l' Environnement in Paris arranged for François Le Guern (CNRS) to observe the activity during 25-27 April. Incandescent scoria fountains rose 50 m over the crater 5-10 times/day followed by quiet periods. Sometimes explosions with black ash or transparent brown or blue haze lasted a few tens of minutes. Lava output was estimated to be 1 x 106 m3/day on 26 April with a lava front 300 m long, decreasing by 10-15% on the following days. On 27 April lava advanced <0.5 m/hour.
From late April through 2 May a team from the International Federation of Red Cross and Red Crescent Societies reported that lava continued to flow from the crater, though at a much reduced rate, and had already covered 5 km2 of cultivated land including five houses and a winery that was a major source of income for the displaced. At that time the flow was contained inside the existing banks of lava. News reports indicated that after a period of non-explosive emissions and weak lava flow production, the eruption strengthened slightly on 7 May with greater lava output. On 8 May the United Nations coordinator in Praia reported decreased activity with some explosions and moderate to strong tremor. The lava emission rate was relatively low, coming from vents at the NW base of the cone.
Displaced persons and future plans. Apart from the destruction to outlying buildings, the villages themselves remained intact but largely deserted in early May. During the day there was regular foot traffic as people removed items of use to the camps, including livestock. The Red Cross of Cape Verde has volunteers in four camps containing 157 families. The camps are: Sao Filipe, population 534 (including 313 children); Patim, population 88 (53 children); Achada Furna, population 156 (90 children); and Mosteiros, population 90 (55 children). Adding the ~150 people living with friends and relatives, the total number of displaced person comes to 1,014. These numbers fluctuate as people return to the area and re-evacuate following felt earthquakes.
With emergency needs met, government officials believe that the focus should be on the resettlement of displaced persons. The United Nations DHA-Disaster Mitigation Branch was focusing on civil protection preparedness planning for future volcanic eruptions and other natural disasters.
On 10 May, at the request of the Cape Verde government, a team of four geologists and two students from the Universidade dos Açores went to Fogo to study the eruption. Their objectives are to monitor the progress of the eruption and to begin research related to gas release and the risks of contamination of public water supplies.
Information Contacts: R. Moore, U.S. Geological Survey, Mail Stop 903, Federal Center Box 25046, Denver, CO 80225 USA (Email: email@example.com); Frank Trusdell, U.S. Geological Survey, Hawaiian Volcano Observatory, Hawaii National Park, HI 96718, USA; Veronica Carvalho Martins, U.S. Embassy, Rua Hoji Ya Henda 81, C.P. 201, Praia, Cape Verde; Arrigo Querido and Helena Tatiana Osorio, INGRH Servicos Estudos Hidrologicos, C.P. 367, Praia, Cape Verde; François LeGuern, CNRS Centre des Faibles Radioactivités, 91190 Gif-sur-Yvette, France; João Gaspar and Nicolau Wallenstein, Departamento Geociências, Universidad dos Açores, rue da Mae de Deus 58, 9500 Ponta Delgada, Açores, Portugal (Email: firstname.lastname@example.org); Henry Gaudru, Christine Pittet, Patrick Barois, and Marc Sagot, Société Volcanologique Européenne (SVE), C.P. 1, 1211 Geneva 17, Switzerland; United Nations Department of Humanitarian Affairs, Palais des Nations, 1211 Geneva 10, Switzerland; International Federation of Red Cross and Red Crescent Societies, C.P. 372, 1211 Geneva 19, Switzerland.
05/1995 (BGVN 20:05) Increased explosive activity; intense fumarolic emissions
Eruptive activity that began at Fogo on 2 April generated lava flows throughout the month (BGVN 20:03 and 20:04). Approximately 1,300 people evacuated from the Cha Caldera following fire fountaining from a fissure on the SW flank of the Pico cone. Lava flows covered the small settlement of Boca de Fonte (figure 3) by 9 April, and were ~500 m from Portela village a week later.
|Figure 3. Map of Fogo (Cha Caldera) showing lava flows from the current eruption as of 18 May 1995. Courtesy of João Gaspar, Universidade dos Açores.|
Cape Verde scientists reported on 19 April that all of the flow-fronts had stopped, explosive activity had decreased, and emission of pyroclastic material was intermittent. By that time a small pit formed near the W flank of the scoria cone and sent pahoehoe lava W on top of the first aa flows. West of Monte Saia these new lava flows spread laterally and overrode the N and S margins of the earlier aa flows. On 10 May three more houses were covered by flows S of Boca de Fonte. Fumarolic activity from late April through early May remained intense along the main NE-SW fault. Inhalation of volcanic gases caused throat and eye irritations, headaches, and other complaints.
Following a request by the Cape Verde government, volcanologists from Azores University arrived at Fogo on 11 May to assess public health problems related to the eruption. Until 14 May pahoehoe and toothpaste lava flows continued advancing S of Boca de Fonte and towards Portela village, while gases rose continuously from the main vents. On 14 May at 1600 the activity increased and an ash cloud rose 500 m. Measurements made the next day at the end of a lava tube 2 km W of the main vent showed lava velocities of 2 m/minute. Ropy pahoehoe lavas formed at this stage. The lava flow-front 10 m away from the lava tube had a velocity of 2 m/hour. Starting at 1900, and continuing for at least 5 hours, explosions in the scoria cone crater ejected blocks to heights of 30 m; most fell near the crater rim.
Several profiles were made of the caldera on 16 May to evaluate CO2 soil degassing using colorimetric tubes fixed in a 1-m-long probe. Values obtained 70 cm below the ground surface were always <2%. Ground temperatures changed from 67 to 115°C inside the SW craters where some explosions took place in the beginning of the eruption. Sulfur deposits could be observed in this section of the main fissure, but fumarolic activity was already very weak.
On the morning of 17 May dense clouds of gas and dust were released from the scoria cone while all the lava fronts appeared to be stationary. Through the afternoon explosive activity increased and strong explosions gave rise to discontinuous projections of spatter that reached 50 m high. Due to the explosions some large blocks of the crater wall collapsed and clouds of orange and red dust rose ~100 m. Streams of gases flowed down the SW slope of the scoria cone and reached the caldera wall on 18 May. People in the caldera felt nose and throat irritations >2 km from the main vents, making it impossible to approach without a gas mask. A strong sulfur smell was reported as far as Patim village, 8 km SW. On this day atmospheric samples were collected near the scoria cone. Chemical analysis of water from springs at Mosteiros (~9 km N) and wells in Sao Filipe (~15 km WSW) showed no contamination of the reservoirs by magmatic components.
Since the beginning of the eruption, lava flows have covered ~4.3 km2 of productive land, and preliminary data indicate an erupted volume of 22-35 x 106 m3. Boca de Fonte (population 56) was completely destroyed, and flow-fronts were 300 m from Portela as of 18 May. About 1,000 persons remain in shelters at Army camps in Sao Filipe, Patim, Achada Furna, and Mosteiros. During this eruption nobody was killed, but several needed medical assistance, mainly for respiratory problems due to inhalation of volcanic gas and dust.
Information Contacts: J.L. Gaspar, T. Ferreira, R. Coutinho, and G. Queiroz, Departamento Geociências, Universidad dos Açores, rue da Mae de Deus 58, 9500 Ponta Delgada, Açores, Portugal (Email: email@example.com); A. Mota Gomes, Instituto Superior de Educação de Cabo Verde (ISE), Cape Verde.
12/1995 (BGVN 20:11/12) Eruption of 2 April through 28 May covered over 6 square kilometers of land
The eruption that began on 2 April (BGVN 20:04 and 20:05) ended on or about 28 May, according to V. Martins. New lava flows covered ~6.3 km2 of land. The total volume of lava extruded was ~60-100 x 106 m3, assuming lava flow thicknesses of ~9-15 m; the known range was from 1 to >20 m. Based on six major-element XRF analyses, the lava flow erupted during the first night (3 April) was determined to be a differentiated kaersutite-bearing phonotephrite (IUGS system), whereas later lava flows and spatter were more primitive tephrite basanite.
Fogo Island consists of a single massive volcano with an 8-km-wide caldera breached to the E. The central cone was apparently almost continuously active from the time of Portuguese settlement in 1500 A.D. until around 1760. The June-August 1951 eruption from caldera vents S and NW of the central cone began with ejection of pyroclastic material.
Information Contacts: Richard Moore, U.S. Geological Survey, Mail Stop 903, Federal Center Box 25046, Denver, CO 80225 USA (Email: firstname.lastname@example.org); Frank Trusdell, U.S. Geological Survey, Hawaiian Volcano Observatory, Hawaii National Park, HI 96718, USA; Veronica Carvalho Martins, U.S. Embassy, Rua Hoji Ya Henda 81, C.P. 201, Praia, Cape Verde; Arrigo Querido, INGRH Servicos Estudos Hidrologicos, C.P. 367, Praia, Cape Verde.
The island of Fogo consists of a single massive stratovolcano that is the most prominent of the Cape Verde Islands. The roughly circular 25-km-wide island is truncated by a large 9-km-wide caldera that is breached to the east and has a headwall 1 km high. The caldera is located asymmetrically NE of the center of the island and was formed as a result of massive lateral collapse of the ancestral Monte Armarelo edifice. A very youthful steep-sided central cone, Pico, rises more than 1 km above the caldera floor to about 100 m above the caldera rim, forming the 2829 m high point of the island. Pico, which is capped by a 500-m-wide, 150-m-deep summit crater, was apparently in almost continuous activity from the time of Portuguese settlement in 1500 CE until around 1760. Later historical lava flows, some from vents on the caldera floor, reached the eastern coast below the breached caldera.
Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).
|Start Date||Stop Date||Eruption Certainty||VEI||Evidence||Activity Area or Unit|
|1995 Apr 2||1995 May 26||Confirmed||2||Historical Observations||WSW flank of Pico|
|1951 Jun 12||1951 Aug 21||Confirmed||2||Historical Observations||Northwest and south caldera floor|
|1857 Jun 27||1857 Dec 15||Confirmed||2||Historical Observations||SSE caldera floor|
|1852 Feb 19||1852 Mar 30 (?)||Confirmed||2||Historical Observations||NNW caldera floor|
|1847 Apr 9||1847 May 2 (?)||Confirmed||2||Historical Observations||North caldera floor|
|1816 Dec 31 ± 365 days||Unknown||Confirmed||Historical Observations|
|1799 Jun 2||1799 Jun 28||Confirmed||2||Historical Observations||North caldera floor|
|1785 Jan 24||1785 Feb 25||Confirmed||2||Historical Observations||North caldera floor|
|1769 Apr (in or after)||Unknown||Confirmed||Historical Observations||SW side|
|1500||1761 (?)||Confirmed||1||Historical Observations||Pico|
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.
|Vulcao | Grande, Pico|
|Feature Name||Feature Type||Elevation||Latitude||Longitude|
|Pico||Cone||2829 m||14° 57' 0" N||24° 21' 0" W|
|Feature Name||Feature Type||Elevation||Latitude||Longitude|
|A steep-sided central cone, Pico, rises more than 1 km above the floor of the caldera of Fogo volcano, forming the 2829 m high point of the island of Fogo. This massive stratovolcano is the most prominent of the Cape Verde Islands and is truncated by a large 9-km-wide caldera that is breached to the east. Pico was apparently in almost continuous activity from the time of Portuguese settlement in 1500 AD until around 1760. It is seen here in 1995 during an explosive and effusive eruption from a vent on its lower western flank.
Photo by Nicolau Wallenstein, 1995 (Center of Volcanology, Azores University).
|The massive 9-km-wide, horseshoe-shaped Cha caldera truncates the summit of Fogo stratovolcano, the most prominent in the Cape Verde islands. An ash plume (center) rises from the western flank of a steep-sided central cone, Pico, that rises more than 1 km above the caldera floor to form the 2829 m high point of the island. Pico, which is capped by a 500-m-wide, 150-m-deep summit crater, was apparently in almost continuous activity from the time of Portuguese settlement in 1500 AD until about 1760.
Photo by Dick Moore, 1995 (U.S. Geological Survey).
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.
Day S J, Heleno da Silva S I N, Fonseca J F B D, 1999. A past giant lateral collapse and present-day flank instability of Fogo, Cape Verde Islands. J Volc Geotherm Res, 94: 191-218.
Heleno S I N, Fonseca J F B D, 1999. A seismological investigation of the Fogo volcano, Cape Verde Islands: preliminary results. Volc Seism, 20: 199-217 (English translation).
Helono da Silva S I N, Day S J, Fonseca J F B D, 1999. Fogo volcano, Cape Verde Islands: seismicity-derived constraints on the mechanism of the 1995 eruption. J Volc Geotherm Res, 94: 219-231.
Mitchell-Thome R C, 1976. Geology of the Middle Atlantic Islands. Berlin: Gebruder Borntraeger, 382 p.
Neumann van Padang M, Richards A F, Machado F, Bravo T, Baker P E, Le Maitre R W, 1967. Atlantic Ocean. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI, 21: 1-128.