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Bulletin of the Global Volcanism Network

All reports of volcanic activity published by the Smithsonian since 1968 are available through a monthly table of contents or by searching for a specific volcano. Until 1975, reports were issued for individual volcanoes as information became available; these have been organized by month for convenience. Later publications were done in a monthly newsletter format. Links go to the profile page for each volcano with the Bulletin tab open.

Information is preliminary at time of publication and subject to change.


Recently Published Bulletin Reports

Suwanosejima (Japan) Small ash plumes continued during January through June 2019

Great Sitkin (United States) Small steam explosions in early June 2019

Ibu (Indonesia) Frequent ash plumes and small lava flows active in the crater through June 2019

Ebeko (Russia) Continuing frequent moderate explosions though May 2019; ashfall in Severo-Kurilsk

Klyuchevskoy (Russia) Weak thermal anomalies and moderate Strombolian-type eruptions in September 2018-June 2019

Yasur (Vanuatu) Strong thermal activity with incandescent ejecta continues, February-May 2019

Bagana (Papua New Guinea) Infrequent thermal anomalies, no ash emissions, February-May 2019

Ambae (Vanuatu) Declining thermal activity and no explosions during February-May 2019

Sangay (Ecuador) Explosion on 26 March 2019; activity from 10 May through June produced ash plumes, lava flows, and pyroclastic flows

Kadovar (Papua New Guinea) Ash emissions and thermal anomalies during October 2018-April 2019; lava emissions at the E flank coast and summit area

Sarychev Peak (Russia) Brief ash emission reported on 16 May 2019

Nyiragongo (DR Congo) Lava lake remains active through May 2019; three new vents around the secondary cone



Suwanosejima (Japan) — July 2019 Citation iconCite this Report

Suwanosejima

Japan

29.638°N, 129.714°E; summit elev. 796 m

All times are local (unless otherwise noted)


Small ash plumes continued during January through June 2019

Suwanosejima is an active volcanic island south of Japan in the Ryuku islands with recent activity centered at Otake crater. The current eruption began in October 2004 and activity has mostly consisted of small ash plumes, ballistic ejecta, and visible incandescence at night. This report summarizes activity during January through June 2019 and is based on reports by the Japan Meteorological Agency (JMA), and various satellite data.

Thermal activity recorded by the MIROVA system was low through January and February after a decline in November (figure 36), shown in Sentined-2 thermal infrared imagery as originating at a vent in the Otake crater (figure 37). During January an explosive event was observed at 1727 on the 3rd, producing a gray plume that rose 600 m above the crater. A white gas-and-steam plume rose to 1.5 km above the crater and nighttime incandescence was observed throughout the month. Reduced activity continued through February with no reported explosive eruptions and light gray plumes up to 900 m above the crater. Incandescence continued to be recorded at night using a sensitive surveillance camera.

Figure (see Caption) Figure 36. MIROVA log radiative power plot of MODIS thermal infrared data at Suwanosejima during September 2018 through June 2019. There was reduced activity in 2019 with periods of more frequent anomalies during March and June. Courtesy of MIROVA.
Figure (see Caption) Figure 37. A Sentinel-2 thermal satellite image shows Suwanosejima with the active Otake crater in the center with elevated temperatures shown as bright orange/yellow. There is a light area next to the vent that may be a gas plume. False color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

There was an increase in thermal energy detected by the MIROVA system in mid-March and there was a MODVOLC thermal alert on the 15th. Occasional small explosions occurred but no larger explosive events were recorded. A white plume was noted on the 27th rising to 900 m above the crater and an event at 1048 on the 30th produced a light-gray plume that rose to 800 m. Incandescence was only observed using a sensitive camera at night (figure 38).

Figure (see Caption) Figure 38. Incandescence from the Suwanosejima Otake crater reflecting in clouds above the volcano. Courtesy of JMA (Volcanic activity of Suwanosejima March 2019).

No explosive events were observed through April. A white gas-and-steam plume rose to 1,200 m above the crater on the 19th and incandescence continued intermittently. Minor explosions were recorded on 5, 30, and 31 May, but no larger explosive events were observed during the month. The event on the 30th produced ash plume that reached 1.1 km above the crater. Similar activity continued through June with one explosive event occurring on the 2nd. Overall, there was a reduction in the number of ash plumes erupted during this period compared to previous months (figure 39).

Figure (see Caption) Figure 39. Observed activity at Suwanosejima for the year ending in July 2019. The black vertical bars represent steam, gas, or ash plume heights (scale in meters on the left axis), yellow diamonds represent incandescence observed in webcams, gray volcano symbols along the top are explosions accompanied by ash plumes, red volcano symbols represent large explosions with ash plumes. Courtesy of JMA (Volcanic activity of Suwanosejima June 2019).

Geologic Background. The 8-km-long, spindle-shaped island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit of the volcano is truncated by a large breached crater extending to the sea on the east flank that was formed by edifice collapse. Suwanosejima, one of Japan's most frequently active volcanoes, was in a state of intermittent strombolian activity from Otake, the NE summit crater, that began in 1949 and lasted until 1996, after which periods of inactivity lengthened. The largest historical eruption took place in 1813-14, when thick scoria deposits blanketed residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed forming a large debris avalanche and creating the horseshoe-shaped Sakuchi caldera, which extends to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC 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://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Great Sitkin (United States) — July 2019 Citation iconCite this Report

Great Sitkin

United States

52.076°N, 176.13°W; summit elev. 1740 m

All times are local (unless otherwise noted)


Small steam explosions in early June 2019

The Great Sitkin volcano is located about 40 km NE of Adak Island in the Aleutian Islands and has had a few short-lived eruptions over the past 100 years. Prior to the latest activity in early June 2019 described below, small phreatic explosions occurred in June and August 2018 (BGVN 43:09). An eruption in 1974 produced a lava dome in the center of the crater. The Alaska Volcano Observatory (AVO) is the primary source of information for this September 2018-June 2019 reporting period.

Low-level unrest occurred from September 2018 through February 2019 with slightly elevated seismic activity (figure 6). Small explosions were seismically detected by AVO on 30 October, 5 and 16 November, and 11 December 2018, but they were not seen in regional infrasound data and satellite data did not show an ash cloud.

On 1, 7, and 9 June 2019, AVO reported small steam explosions as well as slightly elevated seismic activity. Steam plumes and surficial evidence of an explosion were not observed during these events. On 18 June 2019 weakly elevated surface temperatures were recorded, field crews working on Adak observed some steam emissions, and a gas flight was conducted. Elevated concentrations of carbon dioxide detected above the lava dome were likely associated with the steam explosions earlier in the month (figures 7 and 8). From 23 June through the end of the month seismicity began to decline back to background levels.

Figure (see Caption) Figure 6. A steam plume was seen at the summit of Great Sitkin on 7 December 2018. Photo by Andy Lewis and Bob Boyd; courtesy of AVO/USGS.
Figure (see Caption) Figure 7. Some degassing was observed on the southern flank of the Great Sitkin during an overflight on 18 June 2019. Photo by Laura Clor; image courtesy of AVO/USGS.
Figure (see Caption) Figure 8. View of Great Sitkin with white plumes rising from the summit on 20 June 2019. Photo by Laura Clor, courtesy of AVO/USGS.

Geologic Background. The Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger parasitic volcano capped by a small, 0.8 x 1.2 km ice-filled summit caldera was constructed within a large late-Pleistocene or early Holocene scarp formed by massive edifice failure that truncated an ancestral volcano and produced a submarine debris avalanche. Deposits from this and an older debris avalanche from a source to the south cover a broad area of the ocean floor north of the volcano. The summit lies along the eastern rim of the younger collapse scarp. Deposits from an earlier caldera-forming eruption of unknown age cover the flanks of the island to a depth up to 6 m. The small younger caldera was partially filled by lava domes emplaced in 1945 and 1974, and five small older flank lava domes, two of which lie on the coastline, were constructed along northwest- and NNW-trending lines. Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano. Historical eruptions have been recorded since the late-19th century.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/).


Ibu (Indonesia) — July 2019 Citation iconCite this Report

Ibu

Indonesia

1.488°N, 127.63°E; summit elev. 1325 m

All times are local (unless otherwise noted)


Frequent ash plumes and small lava flows active in the crater through June 2019

Ibu volcano on Halmahera island in Indonesia began the current eruption episode on 5 April 2008. Since then, activity has largely consisted of small ash plumes with less frequent lava flows, lava dome growth, avalanches, and larger ash plumes up to 5.5 km above the crater. This report summarizes activity during December 2018 through June 2019 and is based on Volcano Observatory Notice for Aviation (VONA) reports by MAGMA Indonesia, reports by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) and Badan Nasional Penanggulangan Bencana (BNPB), and various satellite data.

During December PVMBG reported ash plumes ranging from 200 to 800 m above the crater. There were 11 MODVOLC thermal alerts that registered during 1-12 December. An explosion on 12 January 2019 produced an ash plume that reached 800 m above the crater and dispersed to the S (figure 15). A report released for this event by Sutopo at BNPB said that Ibu had erupted almost every day over the past three months; an example given was of activity on 10 January consisting of 80 explosions. There were four MODVOLC thermal alerts through the month.

Figure (see Caption) Figure 15. An eruption at Ibu at 1712 on 21 January 2019 produced an ash plume that rose to 800 m above the crater. Courtesy of BNPB (color adjusted).

Throughout February explosions frequently produced ash plumes as high as 800 m above the crater, and nine MODVOLC thermal alerts were issued. Daily reports showed variable plume heights of 200-800 m most days throughout the month. Wind directions varied and dispersed the plumes in all directions. A VONA released at 1850 on 6 February reported an ash plume that rose to 1,925 m altitude (around 600 m above the summit) and dispersed S. Activity continued through March with the Darwin VAAC and PVMBG reporting explosions producing ash plumes to heights of 200-800 m above the crater and dispersing in various directions. There were ten MODVOLC alerts through the month.

Similar activity continued through April, May, and June, with ash plumes reaching 200-800 m above the crater. There were 12, 6, and 15 MODVOLC Alerts in April, May, and June, respectively.

Planet Scope satellite images show activity at a two vents near the center of the crater that were producing small lava flows from February through June (figure 16). Thermal anomalies were frequent during December 2018 through June 2019 across MODVOLC, MIROVA, and Sentinel-2 infrared data (figures 17 and 18). Sentinel-2 data showed minor variation in the location of thermal anomalies within the crater, possibly indicating lava flow activity, and MIROVA data showed relatively constant activity with a few reductions in thermal activity during January and February.

Figure (see Caption) Figure 16. Planet Scope natural color satellite images showing activity in the Ibu crater during January through June 2019, with white arrows indicating sites of activity. One vent is visible in the 21 February image, and a 330-m-long (from the far side of the vent) lava flow with flow ridges had developed by 24 March. A second vent was active by 12 May with a new lava flow reaching a maximum length of 520 m. Activity was centered back at the previous vent by 23-27 June. Natural color Planet Scope Imagery, copyright 2019 Planet Labs, Inc.
Figure (see Caption) Figure 17. Examples of thermal activity in the Ibu crater during January through May 2019. These Sentinel-2 satellite images show variations in hot areas in the crater due to a vent producing a small lava flow. Sentinel-2 false color (urban) images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 18. MIROVA log radiative power plot of MODIS thermal infrared at Ibu from September 2018 through June 2019. The registered energy was relatively stable through December, with breaks in January and February. Regular thermal anomalies continued with slight variation through to the end of June. Courtesy of MIROVA.

Geologic Background. The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, contained several small crater lakes through much of historical time. The outer crater, 1.2 km wide, is breached on the north side, creating a steep-walled valley. A large parasitic cone is located ENE of the summit. A smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. Only a few eruptions have been recorded in historical time, the first a small explosive eruption from the summit crater in 1911. An eruption producing a lava dome that eventually covered much of the floor of the inner summit crater began in December 1998.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC 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://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/).


Ebeko (Russia) — July 2019 Citation iconCite this Report

Ebeko

Russia

50.686°N, 156.014°E; summit elev. 1103 m

All times are local (unless otherwise noted)


Continuing frequent moderate explosions though May 2019; ashfall in Severo-Kurilsk

The Ebeko volcano, located on the northern end of the Paramushir Island in the Kuril Islands, consists of many craters, lakes, and thermal features and has been frequently erupting since late February 2017. Typical activity includes ash plumes, explosive eruptions, and gas-and-steam activity. The previous report through November 2018 (BGVN 43:12) described frequent ash explosions that sometimes caused ashfall in Severo-Kurilsk (7 km E). The primary source of information is the Kamchatka Volcanic Eruptions Response Team (KVERT). This report updates the volcanic activity at Ebeko for December 2018 through May 2019.

Frequent moderate explosive activity continued after November 2018. Volcanologists in Severo-Kurilsk observed explosions sending up ash, which drifted N, NE, and E, resulting in ash falls on Severo-Kurilsk on 28 different days between December 2018 and March 2019. On 25 December 2018 an explosion sent ash up to a maximum altitude of 4.5 km and then drifted N for about 5 km. Explosions occurring on 8-10 March 2019 sent ash up to an altitude of 4 km, resulting in ashfall on Severo-Kurilsk on 9-10 March 2019. An ash plume from these explosions rose to a height of 2.5 km and drifted to a maximum distance of 30 km ENE.

Satellite data analyzed by KVERT registered 12 thermal anomalies from December 2018 through May 2019. According to satellite data analyzed by MIROVA (Middle InfraRed Observation of Volcanic Activity), only one thermal anomaly was recorded from December 2018-May 2019, and no hotspot pixels were recognized using satellite thermal data from the MODVOLC algorithm.

Geologic Background. The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC 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://modis.higp.hawaii.edu/).


Klyuchevskoy (Russia) — July 2019 Citation iconCite this Report

Klyuchevskoy

Russia

56.056°N, 160.642°E; summit elev. 4754 m

All times are local (unless otherwise noted)


Weak thermal anomalies and moderate Strombolian-type eruptions in September 2018-June 2019

Klyuchevskoy has had alternating eruptive and less active periods since August 2015. Activity has included lava flows, a growing cinder cone, thermal anomalies, gas-and-steam plumes, and ash explosions. Though some eruptions occur near the summit crater, major explosive and effusive eruptions have also occurred from flank craters (BGVN 42:04 and 43:05). Intermittent moderate gas-and-steam and ash emissions were previously reported from mid-February to mid-August 2018. The Kamchatka Volcanic Eruptions Response Team (KVERT) is the primary source of information for this September 2018-June 2019 reporting period.

KVERT reported that moderate gas-and-steam activity, some of which contained a small amount of ash, and weak thermal anomalies occurred intermittently from the beginning of September 2018 through mid-April 2019. On 21-22 April 2019 webcam data showed a gas-and-steam plume extending about 160 km SE (figure 31). Moderate Strombolian-type volcanism began late April 2019 and continued intermittently through June 2019. On 11-12 June webcam data showed explosions that sent ash up to a maximum altitude of 6 km, with the resulting ash plume extending about 200 km WNW.

Figure (see Caption) Figure 31. Gas-and-steam plume containing some amount of ash rising from the summit of Klyuchevskoy on 22 April 2019. Photo by A. Klimova, courtesy of Institute of Volcanology and Seismology (IVS FEB RAS).

Thermal anomalies were noted by KVERT during two days in September 2018, six days in April 2019, eleven days in May 2019, and six days in June 2019. MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed infrequent weak thermal anomalies December 2018 through early May 2019.

Geologic Background. Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).


Yasur (Vanuatu) — June 2019 Citation iconCite this Report

Yasur

Vanuatu

19.532°S, 169.447°E; summit elev. 361 m

All times are local (unless otherwise noted)


Strong thermal activity with incandescent ejecta continues, February-May 2019

Yasur volcano on Tanna Island has been characterized by Strombolian activity with large incandescent bombs, frequent explosions, lava fountaining, and ash emissions for much of its known eruptive history. Melanesians from nearby islands are believed to have settled Tanna in about 400 BCE; it is now part of the nation of Vanuatu, independent since 1980. The Kwamera language (or Tannese) spoken on the SE coast of the island is thought to be the source of the name of the island. No known oral history describes volcanic activity; the first written English-language documentation of activity dates to 5 August 1774, when Captain James Cook saw "a great fire" on Tanna Island. Cook realized that it "was a Volcano which threw up vast quantities of fire and smoak and made a rumbling noise which was heard at a good distance" (The Captain Cook Society) (figure 51).

Figure (see Caption) Figure 51. Incandescence, steam, and dark ash from Yasur fill the sky in this sketch representing Captain James Cook's landing in the 'Resolution' at Tanna Island on 5 August 1774. The form of the volcano is behind the ship, the incandescence is in the upper right next to the ship's masts. "Landing at Tanna" by William Hodges, 1775-1776, National Maritime Museum, Greenwich, London. The Maritime Museum noted that this is one of a group of panel paintings produced by Hodges of encounters with islanders during the voyage, in which the European perception of each society at the time is portrayed. Image taken from Wikimedia Commons.

Based on numerous accounts from ships logs and other sources, volcanic activity has been continuous since that time. During periods of higher activity, multiple vents within the summit crater send ejecta 100 m or more above the crater rim, with large bombs occasionally landing hundreds of meters away. Continued activity during February-May 2019 is covered in this report with information provided by the Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD) which monitors the volcano and satellite data; photographs from tourists also provide valuable information about this remote location.

VMGD has maintained Alert Level 2 at Yasur since October 2016, indicating that it is in a major state of unrest. There is a permanent exclusion zone within 395 m of the eruptive vents where access is prohibited due to multiple hazards, primarily from large incandescent bombs up to 4 m in diameter which have been ejected from the vents onto the crater rim in the past, resulting in fatalities (BGVN 20:08).

Satellite and ground based information all support high levels of thermal activity during February -May 2019. MODVOLC thermal alerts were issued 11 times in February, 27 times in March, and 20 times each in April and May. The MIROVA graph also indicated the ongoing consistently high levels of thermal energy throughout the period (figure 52). Plumes of SO2 emissions are common from Vanuatu's volcanoes; newer higher resolution data available beginning in 2019 reveal a persistent stream of SO2 from Yasur on a near-daily basis (figure 53).

Figure (see Caption) Figure 52. The MIROVA graph of thermal energy at Yasur from 3 September 2018 through May 2019 indicates the ongoing activity at the volcano. Courtesy of MIROVA.
Figure (see Caption) Figure 53. The SO2 plumes from Yasur were persistent during January-May 2019 when they were visible many days of each week throughout the period. Top left: On 12 January plumes were visible drifting E from both Ambrym (top) and Yasur (bottom). Top right: Plumes drifted W from three Vanuatu volcanoes on 7 February, Gaua (top), Ambrym (middle) and Yasur (bottom). Bottom left: On 12 March N drifting plumes could be seen from Ambae (top) and Yasur (bottom). On 27 April, only Yasur had an SO2 plume drifting W. Courtesy of Goddard Space Flight Center.

Satellite imagery confirmed that the heat sources from Yasur were vents within the summit crater of the pyroclastic cone. Both northern and southern vent areas were active. On 7 March 2019 the N vent area had a strong thermal signal. Ten days later, on 17 March, similar intensity thermal anomalies were present in both the N and S vent areas (figure 54). On 6 April the S vent area had a stronger signal, and gas emissions from both vents were drifting N (figure 55). Satellite imagery from 21 May 2019 indicated a strong thermal signal inside the crater in the area of the vents, and included a weaker signal clearly visible on the inside E crater rim. Strong Strombolian activity or spatter sending large incandescent bombs as far as the crater rim are a likely explanation for the signal (figure 56), underscoring the hazardous nature of approaching the crater rim.

Figure (see Caption) Figure 54. Strong thermal anomalies from the crater of Yasur's pyroclastic cone seen in satellite images confirmed the ongoing high level of activity. Left: 7 March 2019, a strong thermal anomaly from the N vent area, shown with "Geology" rendering (bands 12, 4, 2). Right: 17 March 2019, thermal anomalies at both the N and S vent areas, shown with "Atmospheric Penetration" rendering (bands 12, 11, 8A). The crater is about 500 m in diameter. Sentinel-2 satellite imagery courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 55. Strong thermal anomalies (left) and gas emissions (right) at Yasur were captured with different bands in the same Sentinel-2 satellite image on 6 April 2019. Left: The thermal anomaly in the S vent area was stronger than in the N vent area, "Atmospheric Penetration" rendering (bands 12, 11, 8A). Right: Gas plumes drifted N from both vent areas, "Natural color" rendering (bands 4, 3, 2). The crater is about 500 m in diameter. Sentinel-2 satellite imagery courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 56. Thermal activity from the crater of Yasur on 21 May 2019 produced a strong thermal signal from the center of the crater and a weaker signal on the inside E crater rim, likely the result of hazardous incandescent bombs and ejecta, frequent products of the activity at Yasur. Left: "Atmospheric Penetration" rendering (bands 12, 11, 8A). Right: "Geology" rendering (bands 12, 4, 2). The crater is about 0.5 km in diameter. Sentinel-2 satellite imagery courtesy of Sentinel Hub Playground.

Tourists visit Yasur on a regular basis. A former lake on the N side of Yasur has left ripples in the sand deposits over older volcanic rocks on the N side of the volcano (figure 57) since it drained in 2000 (BGVN 28:01). Visitors are allowed to approach the S rim of the crater where incandescence from both the N and S vents is usually visible (figure 58). Incandescent spatter from the convecting lava in the vents is highly dangerous and unpredictable and often covers the inner slopes of the rim as well as sending bombs outside the crater (figure 59).

Figure (see Caption) Figure 57. The pyroclastic cone of Yasur viewed from the north on 6 May 2019. Ripples in volcaniclastic sand in the foreground are remnants of a lake that was present on the N side of the volcano until a natural dam breached in 2000. Copyrighted photo by Nick Page, used with permission.
Figure (see Caption) Figure 58. Two glowing vents were visible from the south rim of Yasur on 6 May 2019. The S vent area is in the foreground, the N vent area is in the upper left. Copyrighted by Nick Page, used with permission.
Figure (see Caption) Figure 59. Incandescent spatter at Yasur on 6 May 2019 sent fragments of lava against the inside crater wall and onto the rim. The convecting lava in the vent can be seen in the lower foreground. Copyrighted photo by Nick Page, used with permission.

Geologic Background. Yasur, the best-known and most frequently visited of the Vanuatu volcanoes, has been in more-or-less continuous Strombolian and Vulcanian activity since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island, this mostly unvegetated pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide, horseshoe-shaped caldera associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD), Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC 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://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); The Captain Cook Society (URL: https://www.captaincooksociety.com/home/detail/225-years-ago-july-september-1774); Royal Museums Greenwich (URL: https://collections.rmg.co.uk/collections/objects/13383.html); Wikimedia Commons, (URL: https://commons.wikimedia.org/wiki/File:The_Landing_at_Tana_one_of_the_New_Hebrides,_by_William_Hodges.jpg); Nick Page, Australia,Flickr: (URL: https://www.flickr.com/photos/152585166@N08/).


Bagana (Papua New Guinea) — June 2019 Citation iconCite this Report

Bagana

Papua New Guinea

6.137°S, 155.196°E; summit elev. 1855 m

All times are local (unless otherwise noted)


Infrequent thermal anomalies, no ash emissions, February-May 2019

With historical eruptions reported back to 1842, Papua New Guinea's Bagana volcano on the island of Bougainville has been characterized by viscous andesitic lava flows down the steep flanks of its cone, along with intermittent ash plumes and pyroclastic flows. Ongoing thermal anomalies and frequent ash plumes have been typical of activity during the current eruption since it began in early 2000. Activity declined significantly in December 2018 and remained low through May 2019, the period covered in this report (figure 33). Information for this report comes primarily from satellite images and thermal data.

Figure (see Caption) Figure 33. The MIROVA plot of radiative power at Bagana from 1 September 2018 through May 2019 shows a marked decline in thermal activity during December 2018 after ash explosions and satellite observations of flows during the previous months. Courtesy of MIROVA.

The last ash emission at Bagana was reported on 1 December 2018 by the Darwin Volcanic Ash Advisory Center (VAAC). A Sentinel-2 satellite image showed a linear thermal anomaly trending NW from the summit on 14 December (BGVN 50:01). On 8 January 2019, an image contained a dense steam plume drifting E and a very faint thermal anomaly on the N flank a few hundred meters from the summit. A more distinct thermal anomaly at the summit appeared on 22 February 2019 (figure 34). A visitor to the region photographed incandescence on the flank, likely from the volcano, at dawn around 19 February 2019 (figure 35).

Figure (see Caption) Figure 34. Sentinel-2 satellite imagery revealed thermal anomalies at Bagana in January and February 2019. Left: a very faint thermal anomaly was N of the summit at the edge of the E-drifting steam plume on 8 January 2019. Right: A thermal anomaly was located at the summit, at the base of the NE-drifting steam plume on 22 February 2019. Sentinel-2 satellite images with "Atmospheric Penetration" rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 35. A visitor near Bagana spotted incandescence on the flank at dawn, possibly from a lava flow. Posted online 19 February 2019. Courtesy of Emily Stanford.

Two faint thermal anomalies were visible at the summit in satellite imagery on 19 March; a single one appeared on 29 March 2019 (figure 36). No thermal anomalies were recorded in Sentinel-2 images during April or May, but steam plumes and gas emissions were visible through cloud cover on multiple occasions (figure 37).

Figure (see Caption) Figure 36. Faint thermal anomalies at Bagana were recorded in satellite imagery twice during March 2019. Left: 19 March, two anomalies appear right of the date label. Right: 29 March, a small anomaly appears right of the date label. Sentinel-2 image rendered with "Atmospheric Penetration" (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 37. Steam and gas emissions at Bagana were recorded in satellite imagery during April and May 2019. Left: A steam plume drifted NW from the summit on 23 April, visible through dense cloud cover. Right: A gas plume drifted SW from the summit on 18 May. Sentinel-2 image with "Geology" rendering (bands 12, 4, 2). Courtesy of Sentinel Hub Playground.

Geologic Background. Bagana volcano, occupying a remote portion of central Bougainville Island, is one of Melanesia's youngest and most active volcanoes. This massive symmetrical cone was largely constructed by an accumulation of viscous andesitic lava flows. The entire edifice could have been constructed in about 300 years at its present rate of lava production. Eruptive activity is frequent and characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although explosive activity occasionally producing pyroclastic flows also occurs. Lava flows form dramatic, freshly preserved tongue-shaped lobes up to 50 m thick with prominent levees that descend the flanks on all sides.

Information Contacts: MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Emily Stanford (Twitter: https://twitter.com/NerdyBatLady, image posted at https://twitter.com/NerdyBatLady/status/1098052063009792001/photo/1).


Ambae (Vanuatu) — June 2019 Citation iconCite this Report

Ambae

Vanuatu

15.389°S, 167.835°E; summit elev. 1496 m

All times are local (unless otherwise noted)


Declining thermal activity and no explosions during February-May 2019

Ambae (Aoba) is a large basaltic shield volcano in the New Hebrides arc, part of the multi-island country of Vanuatu. Its periodic phreatic and pyroclastic explosions originating in the summit crater lakes have been recorded since the 16th century. A pyroclastic cone appeared in Lake Voui during November 2005-February 2006 (BGVN 31:12, figure 30); an explosive eruption from a new pyroclastic cone in the lake began in mid-September 2017 (BGVN 43:02). Activity included high-altitude ash emissions (9.1 km), lava flows, and Strombolian activity. Intermittent pulses of ash emissions during the following months resulted in extensive ashfall and evacuations; multiple communities were affected by lahars. The most recent episode of the eruption from July to September 2018 (BGVN 44:02) resulted in 11-km-altitude ash plumes and the evacuation of the entire island due to heavy ashfall and lahars. This report covers activity from February to May 2019, with information provided by the Vanuatu Geohazards Observatory of the Vanuatu Meteorology and Geo-Hazards Department (VMGD) and satellite data from multiple sources.

Activity diminished after the extensive eruptive phase of July-September 2018 when substantial ash plumes and ashfall resulted in evacuations. An explosion with an ash plume on 30 October 2018 was the last activity reported for 2018. Thermal alerts were reported by the Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC thermal alerts system through January 2019, and the Log Radiative Power graph prepared by the MIROVA project showed decreasing thermal anomalies into June 2019 (figure 92). Satellite images recorded in April and May 2019 (figure 93) showed the configuration of the summit lakes to be little changed from the previous November except for the color (BGVN 44:02, figure 89). No ash emissions or SO2 plumes were reported during the period. VMGD noted that the volcano remained at Alert Level 2 through May 2019 with a 2-km-radius exclusion zone around the summit.

Figure (see Caption) Figure 92. The MIROVA log radiative power plot for Ambae showed ongoing intermittent thermal anomalies from early September 2018 through May 2019. Courtesy of MIROVA.
Figure (see Caption) Figure 93. Satellite imagery in April and May 2019 showed little change in the configuration of lakes at the summit of Ambae since November 2018 (see BGVN 44:02, figure 89). Left: 24 April 2019. Right: 29 May 2019. Sentinel-2 satellite imagery with "Natural Color" rendering (bands 4, 3, 2); courtesy of Sentinel Hub Playground.

Geologic Background. The island of Ambae, also known as Aoba, is a massive 2500 km3 basaltic shield that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW-trending rift zone dotted with scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. That large central edifice is also called Manaro Voui or Lombenben volcano. Post-caldera explosive eruptions formed the summit craters about 360 years ago. A tuff cone was constructed within Lake Voui (or Vui) about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast.

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD), Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC 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://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Sangay (Ecuador) — July 2019 Citation iconCite this Report

Sangay

Ecuador

2.005°S, 78.341°W; summit elev. 5286 m

All times are local (unless otherwise noted)


Explosion on 26 March 2019; activity from 10 May through June produced ash plumes, lava flows, and pyroclastic flows

Sangay is the southernmost active volcano in Ecuador, with confirmed historical eruptions going back to 1628. The previous eruption occurred during August and December and was characterized by ash plumes reaching 2,500 m above the crater. Lava flows and pyroclastic flows descended the eastern and southern flanks. This report summarizes activity during January through July 2019 and is based on reports by Instituto Geofísico (IG-EPN), Washington Volcanic Ash Advisory Center (VAAC), and various satellite data.

After the December 2018 eruption there was a larger reduction in seismicity, down to one event per day. During January, February, and most of March there was no recorded activity and low seismicity until the Washington VAAC reported an ash plume at 0615 on 26 March. The ash plume rose to a height of around 1 km and dispersed to the SW as seen in GOES 16 satellite imagery as a dark plume within white meteorological clouds. There was no seismic data available due to technical problems with the station.

More persistent eruptive activity began on 10 May with thermal alerts (figure 30) and an ash plume at 0700 that dispersed to the W. An explosion was recorded at 1938 on 11 May, producing an ash plume and incandescent material down the flank (figure 31). Two M 2 earthquakes were detected between 3.5 and 9 km below the crater on 10 May, possibly corresponding to explosive activity. By 17 May there were two active eruptive centers, the central crater and the Ñuñurcu dome (figure 32).

Figure (see Caption) Figure 30. MIROVA log radiative power plot of MODIS thermal infrared at Sangay for the year ending June 2019. The plot shows the August to December 2018 eruption, a break in activity, and resumed activity in May 2019. Courtesy of MIROVA.
Figure (see Caption) Figure 31. An explosion at Sangay on 10 May 2019 sent ballistic projectiles up to 650 m above the crater at a velocity of over 400 km/hour, an ash plume that rose to over 600 m, and incandescent blocks that traveled over 1.5 km from the crater at velocities of around 150 km/hour. Screenshots are from video by IG-EPN.
Figure (see Caption) Figure 32. A photograph of the southern flank of Sangay on 17 May 2019 with the corresponding thermal infrared image in the top right corner. The letters correspond to: a) a fissure to the W of the lava flow; b) an active lava flow from the Ñuñurcu dome; c) the central crater producing a volcanic gas plume; d) a pyroclastic flow deposit produced by collapsing material from the front of the lava flow. Prepared by M. Almeida; courtesy of IG-EPN (special report No. 3 – 2019).

Activity at the central crater by 21 May was characterized by sporadic explosive eruptions that ejected hot ballistic ejecta (blocks) with velocities over 400 km/hour; after landing on the flanks the blocks travelled out to 2.5 km from the crater. Ash plumes reached heights between 0.9-2.3 km above the crater and dispersed mainly to the W and NW; gas plumes also dispersed to the W. The Ñuñurcu dome is located around 190 m SSE of the central crater and by 21 May had produced a lava flow over 470 m long with a maximum width of 175 m and an estimated minimum volume of 300,000 to 600,000 m3. Small pyroclastic flows and rockfalls resulted from collapse of the lava flow front, depositing material over a broad area on the E-SE flanks (figure 33). One pyroclastic flow reached 340 m and covered an area of 14,300 m2. During the 17 May observation flight the lava flow surface reached 277°C.

Figure (see Caption) Figure 33. A view of the ESE flanks of Sangay on 17 May 2019. The area within the black dotted line is the main area of pyroclastic flow deposition from the Ñuñurco Dome. Photo by M. Almeida; courtesy of IG-EPN (special report No. 4 – 2019).

At the end of June activity was continuing at the central crater and Ñuñurco Dome. At least three lava flows had been generated from the dome down the SE flank and pyroclastic flows continued to form from the flow fronts (figure 34). Pyroclastic material had been washed into the Upano river and steam was observed in the Volcán River possibly due to the presence of hot rocks. Ash plumes continued through June reaching heights of 800 m above the crater (figure 35), but no ashfall had been reported in nearby communities.

Figure (see Caption) Figure 34. Sentinel-2 natural color (left) and thermal (center) images (bands 12, 11, 4), and 1:50 000 scale maps (right) of Sangay with interpretation on the background of a 30 m numerical terrain model (WGS84; Zone 17S) (Prepared by B. Bernard). The dates from top to bottom are 17 May, 22 May, 27 May, 16 June, and 26 June 2019. Prepared by B. Bernard; courtesy IG-EPN (special report No. 4 – 2019).
Figure (see Caption) Figure 35. Plots giving the heights and dispersal direction of ash plumes at Sangay during May and June 2019. Top: Ash plume heights measures in meters above the crater. Bottom: A plot showing that the dominant dispersal direction of ash plumes is to the W during this time. Courtesy of IG-EPN (special report No. 4 – 2019).

Geologic Background. The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador's volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within horseshoe-shaped calderas of two previous edifices, which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been sculpted by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of a historical eruption was in 1628. More or less continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

Information Contacts: Instituto Geofísico (IG-EPN), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC 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://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Kadovar (Papua New Guinea) — May 2019 Citation iconCite this Report

Kadovar

Papua New Guinea

3.608°S, 144.588°E; summit elev. 365 m

All times are local (unless otherwise noted)


Ash emissions and thermal anomalies during October 2018-April 2019; lava emissions at the E flank coast and summit area

Steeply-sloped Kadovar Island is located about 25 km NNE from the mouth of the Sepik River on the mainland of Papua New Guinea. The first confirmed historical eruption with ash plumes and lava extrusion began in early January 2018, resulting in the evacuation of around 600 residents from the N side of the approximately 1.4-km-diameter island (BGVN 43:03); continuing activity from October 2018 through April 2019 is covered in this report. Information was provided by the Rabaul Volcano Observatory (RVO), the Darwin Volcanic Ash Advisory Center (VAAC), satellite sources, and photos from visiting tourists.

Activity during March-September 2018. After the first recorded explosions with ash plumes in early January 2018, intermittent ash plumes continued through March 2018. A lava flow on the E flank extended outward from the island, extruding from a vent low on the E flank and forming a dome just offshore. The dome collapsed and regrew twice during February 2018; the growth rate slowed somewhat during March. A satellite image from 21 March 2018 was one of the first showing the new dome growing off the E flank with a thermal anomaly and sediment plumes in the water drifting N and E from the area. Thermal anomalies were visible at both the summit vent and the E-flank coastal dome in in April and May 2018, along with steam and gas rising from both locations (figure 19).

Figure (see Caption) Figure 19. Sentinel-2 satellite imagery of Kadovar provided clear evidence of thermal activity at the new E-flank coastal dome during March-May 2018. Sediment plumes were visible drifting N and E in the water adjacent to the coastal dome. The summit crater also had a persistent steam plume and thermal anomaly in April and May 2018. Left: 21 March 2018. Middle 10 April 2018. Right: 15 May 2018. Images all shown with "Geology" rendering using bands 12, 4, and 2. Courtesy of Sentinel Hub Playground.

A trip to Kadovar by tourists in mid-May 2018 provided close-up views of the dense steam plumes at the summit and the growing E-flank coastal dome (figures 20 and 21). The thermal anomaly was still strong at the E-flank coastal dome in a mid-June satellite image, but appeared diminished in late July. Intermittent puffs of steam rose from both the summit and the coastal dome in mid-June; the summit plume was much denser on 29 July (figure 22). Ash emissions were reported by the Darwin VAAC and photographed by tourists during June (figure 23) and September 2018 (BGVN 43:10), but thermal activity appeared to decline during that period (figure 24).

Figure (see Caption) Figure 20. A tourist photographed Kadovar and posted it online on 19 May 2018. Steam plumes rose from both the summit and the E-flank coastal dome in this view taken from the SE. Courtesy of Tico Liu.
Figure (see Caption) Figure 21. A closeup view of the E-flank coastal dome at Kadovar posted online on 19 May 2018 showed steam rising from several places on the dome, and dead trees on the flank of the volcano from recent eruptive activity. Courtesy of Tico Liu.
Figure (see Caption) Figure 22. The thermal anomaly was still strong at the E-flank coastal dome of Kadovar in a 14 June 2018 satellite image (left), but appeared diminished on 29 July 2018 (right). Intermittent puffs of steam rose from both the summit and the coastal dome on 14 June; the summit plume was much denser on 29 July. Sentinel-2 images both show "Geology" rendering using bands 12, 4, and 2. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 23. An ash plume rose from the summit of Kadovar and drifted W while steam and gas rose from the E-flank coastal dome, posted online 27 June 2018. Courtesy of Shari Kalt.
Figure (see Caption) Figure 24. Thermal activity at Kadovar for the year ending on 26 April 2019 was consistent from late April 2018 through mid-June 2018; a quiet period afterwards through late September ended with renewed and increased thermal activity beginning in October 2018. All distances are actually within 1 km of the summit of Kadovar, a DEM georeferencing error makes some locations appear further away. Courtesy of MIROVA.

Multiple satellite images during August and early September 2018 showed little or no sign of thermal activity at the E-flank coastal dome, with only intermittent steam plumes from the summit. A new steam plume on the eastern slope appeared in a 22 September 2018 image (figure 25). The Rabaul Volcano Observatory (RVO) reported explosive activity on the afternoon of 21 September. Noises of explosions were accompanied by dark gray and brown ash clouds that rose several hundred meters above the summit crater and drifted NW. Local reports indicated that the activity continued through 26 September and ashfall was reported on Blupblup island during the period. Ground observers noted incandescence visible from both the summit and the E-flank coastal dome.

Figure (see Caption) Figure 25. Steam plumes were seen in satellite images of Kadovar during August and early September 2018, but no thermal anomalies. Intermittent steam plumes rose from the summit vent on 28 August (left). A new dense steam plume originating mid-way down the E flank appeared on 22 September 2018 (right). Sentinel-2 images both show "Geology" rendering using bands 12, 4, and 2. Courtesy of Sentinel Hub Playground.

Activity during October-December 2018. Evidence of both thermal and explosive activity reappeared in October 2018 (figure 24). The Darwin VAAC reported intermittent ash plumes rising to 2.7 km altitude and drifting W on 1 October 2018. Low-level continuous ash emissions rising less than a kilometer and drifting W were reported early on 3 October. A higher plume drifted WNW at 2.4 km altitude on 7 October. Intermittent discrete emissions of ash continued daily at that altitude through 16 October, drifting NW or W. Ash emissions drifting NW and thermal anomalies at the summit were visible in satellite imagery on 2 and 12 October (figure 26). A brief ash emission was reported on 21 October 2018 at 2.4 km altitude drifting NE for a few hours. Intermittent ash emissions also appeared on 29 October moving SE at 1.8 km altitude. For the following three days ash drifted SW, W, then NW at 2.1 km altitude, finally dissipating on 1 November; the thermal anomaly at the summit was large and intense in satellite images on 27 October and 1 November compared with previous images (figure 27).

Figure (see Caption) Figure 26. Ash emissions drifting NW and thermal anomalies at the summit of Kadovar were visible in satellite imagery on 2 and 12 October 2018; no thermal activity was noted at the E-flank coastal dome. Sentinel-2 images both show "Geology" rendering using bands 12, 4, and 2. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 27. Strong thermal anomalies at the summit of Kadovar on 27 October and 1 November 2018 were not concealed by the steam plumes drifting SW and NW from the summit. Sentinel-2 images both show "Geology" rendering using bands 12, 4, and 2. Courtesy of Sentinel Hub Playground.

An ash explosion was photographed by tourists on a cruise ship on the afternoon of 6 November 2018 (figure 28). After the explosion, a dense steam plume rose from a large dome of lava near the summit at the top of the E flank (figure 29). Continuous ash emissions rising to 1.8 km altitude were reported by the Darwin VAAC beginning on 9 November 2018 moving WNW and lasting about 24 hours. A new ash plume clearly identifiable on satellite imagery appeared on 13 November at 2.4 km altitude moving E, again visible for about 24 hours. Another shipboard tourist photographed an ash plume on 18 November rising a few hundred meters above the summit (figure 30).

Figure (see Caption) Figure 28. An explosion at Kadovar photographed on the afternoon of 6 November 2018 sent a dense gray ash plume hundreds of meters above the summit drifting W; blocks of volcanic debris descended the flanks as well. View is from the S. Courtesy of Coral Expeditions, used with permission.
Figure (see Caption) Figure 29. Tourists on a cruise ship passed by Kadovar on 6 November 2018 and witnessed a steam plume drifting W from a large dome of lava near the summit at the top of the E flank after an ash explosion. Smaller steam plumes were visible in the middle and at the base of the E flank, but no activity was visible at the coastal dome off the E flank (lower right). View is from the SE. Courtesy of Coral Expeditions, used with permission.
Figure (see Caption) Figure 30. An ash plume rose at dusk from the summit of Kadovar and was witnessed by a cruise ship tourist on 18 November 2018. View is from the E; the E-flank coastal dome is a lighter area in the lower foreground. Courtesy of Philip Stern.

Low-level ash emissions were reported briefly on 28 November at about 1 km altitude moving SE. Intermittent puffs of ash were seen drifting WSW on 2 and 3 December at about 1.2 km altitude. They were the last VAAC reports for 2018. Two thermal anomalies were visible at the summit in satellite imagery on 26 November, they grew larger and more intense through 16 December when multiple anomalies appeared at the summit and on the E flank (figure 31).

Figure (see Caption) Figure 31. Multiple thermal anomalies near the summit of Kadovar grew larger and more intense between 26 November and 16 December 2018. Sentinel-2 images show "Geology" rendering using bands 12, 4, and 2. Courtesy of Sentinel Hub Playground.

Activity during January-April 2019. Multiple thermal anomalies were still visible at the summit in satellite imagery on 5 January 2019 as regular puffs of steam drifted SE from the summit, leaving a long trail in the atmosphere (figure 32). Additional imagery on 10 and 30 January showed a single anomaly at the summit, even through dense meteorologic clouds. A short-lived ash emission rose to 2.4 km altitude on 11 January 2019 and drifted E; it dissipated the next day. Multiple minor intermittent discrete ash plumes extended WNW at 3.0 km altitude on 18 January; they dissipated within six hours.

Figure (see Caption) Figure 32. Multiple thermal anomalies were visible in satellite imagery of Kadovar on 5 January 2019 as regular puffs of steam drifted SE from the summit. Sentinel-2 image shows "Geology" rendering using bands 12, 4, and 2. Courtesy of Sentinel Hub Playground.

The Royal New Zealand Air Force released images of eruptive activity on 10 February 2019 (figure 33). Satellite imagery in February was largely obscured by weather; two thermal anomalies were barely visible through clouds at the summit on 14 February. The Darwin VAAC reported an ash emission at 1.8 km altitude drifting ESE on 16 February; a similar plume appeared on 21 February that also dissipated in just a few hours.

Figure (see Caption) Figure 33. The Royal New Zealand Air Force released images of an ash plume at Kadovar on 10 February 2019. Courtesy of Brad Scott.

Satellite imagery on 1 March 2019 confirmed a strong thermal anomaly from the summit and down the E flank almost to the coast. A month later on 5 April the anomaly was nearly as strong and a dense ash and steam plume drifted N from the summit (figure 34). A tourist witnessed a dense steam plume rising from the summit on 4 April (figure 35). Multiple discrete eruptions were observed in satellite imagery by the Darwin VAAC on 9 April at 1.2-1.5 km altitude drifting SE. The thermal anomaly at the summit persisted in satellite imagery taken on 15 April 2019.

Figure (see Caption) Figure 34. A strong thermal anomaly appeared from the summit down the E flank of Kadovar on 1 March 2019 (left). A month later on 5 April the strong anomaly was still present beneath a dense plume of ash and steam (right). Sentinel-2 imagery shows "Geology" rendering with bands 12, 4, and 2. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 35. A dense steam plume is shown here rising from the summit area of Kadovar, posted online on 4 April 2019. View is from the N. Courtesy of Chaiyasit Saengsirirak.

Geologic Background. The 2-km-wide island of Kadovar is the emergent summit of a Bismarck Sea stratovolcano of Holocene age. Kadovar is part of the Schouten Islands, and lies off the coast of New Guinea, about 25 km N of the mouth of the Sepik River. The village of Gewai is perched on the crater rim. A 365-m-high lava dome forming the high point of the andesitic volcano fills an arcuate landslide scarp that is open to the south, and submarine debris-avalanche deposits occur in that direction. Thick lava flows with columnar jointing forms low cliffs along the coast. The youthful island lacks fringing or offshore reefs. No certain historical eruptions are known; the latest activity was a period of heightened thermal phenomena in 1976.

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Tico Liu, Hong Kong (Facebook: https://www.facebook.com/tico.liu. https://www.facebook.com/photo.php?fbid=10155389178192793&set=pcb.10155389178372793&type=3&theater); Shari Kalt (Instagram user LuxuryTravelAdvisor: https://www.instagram.com/luxurytraveladviser/, https://www.instagram.com/p/BkhalnuHu2j/); Coral Expeditions, Australia (URL: https://www.coralexpeditions.com/, Facebook: https://www.facebook.com/coralexpeditions); Philip Stern (Facebook: https://www.facebook.com/sternph, https://www.facebook.com/sternph/posts/2167501866616908); Brad Scott, GNS Science Volcanologist at GNS Science, New Zealand (Twitter: https://twitter.com/Eruptn); Chaiyasit Saengsirirak, Bangkok, Thailand (Facebook: https://www.facebook.com/chaiyasit.saengsirirak, https://www.facebook.com/photo.php?fbid=2197513186969355).


Sarychev Peak (Russia) — June 2019 Citation iconCite this Report

Sarychev Peak

Russia

48.092°N, 153.2°E; summit elev. 1496 m

All times are local (unless otherwise noted)


Brief ash emission reported on 16 May 2019

Located on Matua Island in the central Kurile Islands of Russia, Sarychev Peak has historical observations of eruptions dating back to 1765. Thermal activity in October 2017 (BGVN 43:11) was the first sign of renewed activity since a major eruption with ash plumes and pyroclastic flows in June 2009 (BGVN 34:06). The following month (November 2017) there was fresh dark material on the NW flank that appeared to be from a flow of some kind. After that, intermittent thermal anomalies were the only activity reported until explosions with ash plumes took place that lasted for about a week in mid-September 2018 (figure 24). Additional explosions in mid-October were the last reported for 2018. A single ash explosion in May 2019 was the only reported activity from November 2018 to May 2019, the period covered in this report. Information is provided by the Sakhalin Volcanic Eruption Response Team (SVERT) and the Kamchatka Volcanic Eruptions Response Team (KVERT), members of the Far Eastern Branch, Russian Academy of Sciences (FEB RAS), and from satellite data.

Figure (see Caption) Figure 24. Multiple ash plumes were observed at Sarychev Peak during September 2018. Left: 13 September. Right: 18 September. Photos by S. A. Tatarenkov, courtesy of IMGG FEB RAS.

Satellite imagery in mid-September and early October 2018 showed gas emissions from the summit vent, and a weak thermal anomaly in October (figure 25). KVERT lowered the Aviation Color Code from Orange to Yellow on 1 November 2018, and SVERT released a VONA on 12 November 2018 lowering the Aviation Color Code from Yellow to Green after the ash emissions in October.

Figure (see Caption) Figure 25. Minor gas emissions were visible at Sarychev Peak in satellite imagery in mid-September and early October 2018; a possible weak thermal anomaly appeared in the summit vent in October. Top left: 13 September. Top right: 18 September. Bottom left: 8 October. Bottom right: 11 October. The 13 September image uses "Natural Color" rendering (bands 4, 3, 2) and the other images use "Geology" rendering (bands 12, 4, 2). Sentinel-2 satellite imagery courtesy of Sentinel Hub Playground.

Sentinel-2 satellite instruments in March, April, and May 2019 acquired images that showed dark streaks in the snow-covered peak radiating out from the summit vent in various directions. As the spring snows melted, more dark streaks appeared. It is unclear whether the streaks represent fresh ash, particulates from gas emissions in the snow, or concentrated material from earlier emissions that were exposed during the spring melting (figure 26). No further activity was reported until the Tokyo VAAC noted an eruption on 16 May 2019 that produced an ash plume which rose to 2.4 km altitude and drifted S. It was visible in satellite imagery for 3 or 4 hours before dissipating. SVERT reported the ash plume visible up to 50 km SE of the island. They also noted that weak thermal anomalies had been seen in satellite data on 10, 12, and 17 May 2019.

Figure (see Caption) Figure 26. Streaks of brown radiate outward from the summit vent at Sarychev Peak in Sentinel-2 satellite imagery taken during March-May 2019. The exact material and timing of deposition is unknown. Top left: 17 March. Top middle: 14 April. Top right: 19 April. Bottom left: 29 April, Bottom middle: 6 May. Bottom right: 26 May 2019. Sentinel-2 images with "Natural Color" rendering using bands 4,3, and 2. Courtesy of Sentinel Hub Playground.

Geologic Background. Sarychev Peak, one of the most active volcanoes of the Kuril Islands, occupies the NW end of Matua Island in the central Kuriles. The andesitic central cone was constructed within a 3-3.5-km-wide caldera, whose rim is exposed only on the SW side. A dramatic 250-m-wide, very steep-walled crater with a jagged rim caps the volcano. The substantially higher SE rim forms the 1496 m high point of the island. Fresh-looking lava flows, prior to activity in 2009, had descended in all directions, often forming capes along the coast. Much of the lower-angle outer flanks of the volcano are overlain by pyroclastic-flow deposits. Eruptions have been recorded since the 1760s and include both quiet lava effusion and violent explosions. Large eruptions in 1946 and 2009 produced pyroclastic flows that reached the sea.

Information Contacts: Institute of Marine Geology and Geophysics, Far Eastern Branch of the Russian Academy of Sciences, (FEB RAS IMGG), 693 022 Russia, Yuzhno-Sakhalinsk, ul. Science 1B (URL: http://imgg.ru/ru); Sakhalin Volcanic Eruption Response Team (SVERT), Institute of Marine Geology and Geophysics, Far Eastern Branch, Russian Academy of Science, Nauki st., 1B, Yuzhno-Sakhalinsk, Russia, 693022 (URL: http://www.imgg.ru/en/, http://www.imgg.ru/ru/svert/reports); Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Nyiragongo (DR Congo) — May 2019 Citation iconCite this Report

Nyiragongo

DR Congo

1.52°S, 29.25°E; summit elev. 3470 m

All times are local (unless otherwise noted)


Lava lake remains active through May 2019; three new vents around the secondary cone

Since at least 1971 scientists and tourists have observed a lava lake within the Nyiragongo summit crater. Lava flows have been a hazard in the past for the nearby city of Goma (15 km S). The previous report (BGVN 43:06) of activity between November 2017 and May 2018 described nearly daily record of thermal anomalies due to the active lava lake and lava fountaining, gas-and-steam plumes, and the opening of a new vent within the crater in February 2016. Monthly reports from the Observatoire Volcanologique de Goma (OVG) disseminate information regarding the volcano's activity. This report updates the activity during June 2018-May 2019.

OVG noted that the level of the lava lake changes frequently, and was lower when observed on October 2018, 12 April 2019, and 12 May 2019. According to data from the OVG, on 15 April 2019 the secondary cone that formed in February 2016 produced lava flows and ejecta. In addition, at least three other vents formed surrounding this secondary cone. During most of April 2019 the lava lake was still active; however, beginning on 12 April 2019, seismic and lava lake activity both declined.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data continues to show almost daily, strong thermal anomalies every month from June 2018 through 24 May 2019 (figure 66). Similarly, the MODVOLC algorithm reports a majority of the hotspot pixels (2,406) occurring within the lava lake at the summit crater (figure 67).

Figure (see Caption) Figure 66. Thermal anomalies at Nyiragongo for June 2018 through 24 May 2019 as recorded by the MIROVA system (Log Radiative Power) were frequent and strong. Courtesy of MIROVA.
Figure (see Caption) Figure 67. Map showing the number of MODVOLC hotspot pixels at Nyiragongo from 1 June 2018 to 31 May 2019. Nyiragongo (2,423 pixels) is at the bottom center; Nyamuragira volcano (342 pixels) is about 13 km NW. Courtesy of HIGP-MODVOLC Thermal Alerts System.

Geologic Background. One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes of a stratovolcano contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

Information Contacts: Observatoire Volcanologique de Goma (OVG), Goma, North Kivu, DR Congo (URL: https://www.facebook.com/Observatoire-Volcanologique-de-Goma-OVG-180016145663568/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC 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://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

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Bulletin of the Global Volcanism Network - Volume 24, Number 02 (February 1999)

Managing Editor: Richard Wunderman

Ambrym (Vanuatu)

Benbow lava lake disappears in avalanche

Bezymianny (Russia)

Explosions on 25 February send gas-and-ash plume 5 km above the summit

Colima (Mexico)

Details of the 10 February explosion and fires lit by volcanic bombs

Etna (Italy)

Extensive lava flows discharging from a 4 February fissure on the SE flank

Galeras (Colombia)

Low seismicity; fumarole and tilt measurements

Guagua Pichincha (Ecuador)

Moderate seismicity and phreatic eruptions during January-February

Ibu (Indonesia)

Eruptions that began on 18 December 1998 continued in January 1999

Izalco (El Salvador)

Strong fumarolic activity around the summit crater

Krakatau (Indonesia)

Sporadic ash eruptions in February and March 1999

Lengai, Ol Doinyo (Tanzania)

Lava flows spilling over the crater rim in November 1998

Lopevi (Vanuatu)

Strombolian explosions beginning November 1998

Pacaya (Guatemala)

Explosive activity resumes; summary of activity 1987-98

Sheveluch (Russia)

Low-level seismicity and fumarolic plumes

Shishaldin (United States)

Steam plumes and thermal activity seen at summit

Soufriere Hills (United Kingdom)

Ash venting and numerous pyroclastic flows in December 1998 and January 1999

Tolbachik (Russia)

Gas-and-steam explosion; minor seismicity

White Island (New Zealand)

Minor ash-and-steam emissions continue



Ambrym (Vanuatu) — February 1999 Citation iconCite this Report

Ambrym

Vanuatu

16.25°S, 168.12°E; summit elev. 1334 m

All times are local (unless otherwise noted)


Benbow lava lake disappears in avalanche

Ambrym Island was investigated by John Seach and Perry Judd during a climb into the caldera 1-8 January 1999. A lava lake in Benbow cone was present during 1-3 January but was covered by deposits from an avalanche that occurred overnight 4-5 January. Fumarolic and Strombolian activity was observed at other craters.

Activity at Benbow. Benbow crater was climbed from the S, after which observers lowered themselves using ropes 200 m down from the crater rim to a point where they could observe the crater interior. In the center of the crater, an active lava lake was seen 220 m below the observation point. The lava lake was ~40 m in diameter and constantly in motion. Large explosions caused lava fountains that reached 100 m high. Bombs glowed for up to one minute in daylight and radiated great heat. Bombs could be heard landing on the side of the pit where they caused glowing avalanches. At night a strong glow from the lava lake was visible in the sky over Benbow.

Elsewhere inside Benbow crater, Pele's hair covered the ground and fumaroles were active on the NE crater wall. Acid rain burned eyes and skin. Heavy rainfall caused many waterfalls to form inside the crater rim and a shallow brown pond formed on the floor of the first level.

During 4-5 January violent Strombolian explosions could be heard almost hourly. Each series of explosions lasted 5-10 minutes and produced dark ash columns above the crater. At some time during these explosions an avalanche on the W side of the lava lake crater completely covered the lava lake. No night glow was visible above the crater after the night of 5 January.

On 6 January Benbow crater was entered again. The wall collapse that covered the lava lake was confirmed visually. In the location of the former lava lake was a depression of rubble with two small, glowing vents nearby. The entire crater was clear of magmatic gases. Three violent Strombolian eruptions were viewed from the crater rim in the afternoon. Bombs were thrown 300 m into the air and dark ash clouds were emitted.

Activity at Niri Mbwelesu Taten. This small collapse pit continuously emitted white, brown, and blue vapors. Red deposits covered the crater walls. A small amount of yellow deposits covered the S wall. Fumarole temperatures were 66 to 69°C at a point 40 m SE of the pit. On 6-7 January numerous deep, loud degassings were heard from a distance of 4 km.

Activity at Niri Mbwelesu. Pungent, sulfurous-smelling white vapor was emitted from this crater. Periods of good visibility enabled views 200 m down from the crater rim, but the bottom could not be seen. Rockfalls were heard inside the crater.

Activity at Mbwelesu. Excellent visibility to the bottom of this crater enabled detailed observations of the lava lake. Night observations were also obtained. The lava lake was in constant motion and splashing lava out over the sides of the pit. The lake was at a lower level than during observations made three months earlier (BGVN 23:09). Large explosions sent lava fountains up to 100 m in height and threw lava onto the sides of the pit causing glowing avalanches. During one night observation a 20 x 5 m section of the crater wall broke off and fell into the lava lake. The 60-m-wide lake radiated heat that could be felt from the viewing area 380 m away. North of the lava lake was a circular vent 20 m in diameter that glowed brilliantly from magma inside and huffed out burning gasses every 20 seconds. Foul gas, smelling of rotten fish, was emitted from the crater. South of the lava lake was an elongated vent (40 x 10 m) that spattered lava every 5-10 seconds and sent showers of glowing orange lava spray 150 m high.

On the S side of Mbwelesu, fumarole temperatures averaged 43°C at 10 m from the crater edge. On the SE side, 40 m from the crater edge, fumaroles measured 57°C. On 4 January ashfall occurred on the S side of the caldera.

Geologic Background. Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides arc. A thick, almost exclusively pyroclastic sequence, initially dacitic, then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major plinian eruption with dacitic pyroclastic flows about 1900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the caldera floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.

Information Contacts: John Seach, P.O. Box 16, Chatsworth Island, NSW, 2469, Australia.


Bezymianny (Russia) — February 1999 Citation iconCite this Report

Bezymianny

Russia

55.972°N, 160.595°E; summit elev. 2882 m

All times are local (unless otherwise noted)


Explosions on 25 February send gas-and-ash plume 5 km above the summit

During February, seismic and volcanic activity at Bezymianny increased in intensity, causing the hazard status to be raised from Green to Yellow on 16 February and then to Orange on 25 February. The activity decreased on the 26th and the "Level of Concern Color Code" was reduced to Yellow. In the first two weeks of the month, numerous weak earthquakes were registered under the volcano, and fumarolic plumes rising up to a few hundred meters above the summit occurred frequently.

Starting on 15 February and continuing the following week, seismicity rose above background levels and 20-40 shallow earthquakes were registered every day. The hazard status was raised to Yellow. Fumarolic plumes continued to rise to a few hundred meters above the summit, and could be seen when not obscured by clouds. Satellite images during the week indicated a persistent thermal anomaly possibly caused by rock avalanches from the summit dome.

The hazard status was raised to Orange on 25 February after volcanic tremor began under the volcano and continued for ~6 hours. Two large explosions during that period each lasted several minutes and a gas-and-ash plume rose 5 km above the summit. Satellite images that morning showed an ash-rich plume heading SE. Over the next few days, using satellite imagery, the ash cloud was tracked for 1,500 km to the SE, but by early on the 27th the cloud had dissipated. Activity declined after the 25th and the hazard status was reduced to Yellow.

On 27-28 February the seismicity was above background levels. Low-level spasmodic tremor continued to be recorded. On the morning of 28 February a steam-and-gas plume rose 300 m. The volcano was obscured by clouds after 28 February.

Geologic Background. Prior to its noted 1955-56 eruption, Bezymianny had been considered extinct. The modern volcano, much smaller in size than its massive neighbors Kamen and Kliuchevskoi, was formed about 4700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7000 years ago. Three periods of intensified activity have occurred during the past 3000 years. The latest period, which was preceded by a 1000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large horseshoe-shaped crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Information Contacts: Olga Chubarova, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Tom Miller, Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.


Colima (Mexico) — February 1999 Citation iconCite this Report

Colima

Mexico

19.514°N, 103.62°W; summit elev. 3850 m

All times are local (unless otherwise noted)


Details of the 10 February explosion and fires lit by volcanic bombs

The unusually large 10 February explosion was followed by collateral reports by (a) F. Núñez-Cornú, G. Réyes-Davila, and C. Suárez-Plascenia and (b) John B. Murray. In addition, this summary of the interval 26 February to 16 March benefitted from press releases from the Colima Volcano Observatory. These three sources are discussed in separate sections below.

Geophysical signature of the 10 February explosion. F. Núñez-Cornú, G. Réyes-Davila, and C. Suárez-Plascencia provided the following report.

"On 10 February at 0145 an explosive event occurred at Colima's summit dome; this generated a shock wave that broke windows and opened gates in the small town of Juan Barragan, 8.75 km SE of the summit. The sonic wave was also heard in the towns of Tonila, Quesería, San Marcos, Atenquique, El Fresnito, Ejido de Atenquique, and up to 28 km NE of the volcano at Ciudad Guzman.

"This was the biggest explosion reported for the volcano in the last 80 years; the resulting exhalation emitted both ash and lava blocks (bombs made up of both fresh and altered components). A substantial amount of incandescent tephra fell and started fires on both the volcano's upper slopes and on Nevado de Colima's S slopes; most of the fires were extinguished by snow and rain storms during the subsequent 48 hours.

"As summarized in table 8, a seismic event took place hours before the explosion, at 2231 of 9 February; it was followed by other volcanic and tremor signals at about 0100; some of these precursory events saturated the amplitude response of analog instruments at stations EZV4 (Somma) and EZV7 (Volcancito). Four additional large, post-eruptive seismic events also occurred. These strong events were observed clearly at farther stations EZV3 (Nevado, 5.8 km from the summit), and EZV2 (Cerro Grande, 25 km from the summit)."

Table 8. Noteworthy seismic events around the time of the 10 February 1999 explosion at two Colima seismic stations (EZV3 and EZV2); the earliest reading (on the top line) took place the night before the explosion. See text for station locations. Courtesy of F. Nunez-Cornu, G. Reyes-Davila, and C. Suarez-Plascencia.

Date Time EZV3 coda (sec) EZV3 amp max (mm) EZV2 coda (sec) EZV2 amp max (mm)
10 Feb 1999 2231 175 saturated 120 8
10 Feb 1999 0157 -- saturated 300 saturated
10 Feb 1999 0359 160 16 65 3
10 Feb 1999 0552 110 saturated 25 2
10 Feb 1999 0730 140 30 70 3
10 Feb 1999 1318 140 34 75 3

"Currently the Jalisco civil defense operates an observational base called Nevado located 900 m NW from the summit of Nevado de Colima.

"Since the end of November 1998, three seismic instruments (MarsLite with LE3d (1 Hz) sensors) were deployed to complement the RESCO network at the volcano. To improve spatial resolution the authors moved one of these instruments to El Playon on 11 February. On the way to El Playon we observed fires on the southern slopes of Nevado out to a maximum distance of 4.5 km from the volcano's summit.

"On the road at a spot 2.9 km NE of the summit and at 3,120 m elevation we found several impact craters. The first one contained an andesite block with dimensions of 0.37 x 0.44 x 0.43 m. Several small impacts occurred nearby. We found another impact pit near the road, 100 m away from the first site but at similar distance and direction from the summit. This pit measured 1.94 x 0.70 m on the surface and had a depth of 0.60 m. It contained a partially buried andesite block (identified as R3) that measured 0.60 x 0.41 x 0.70 m. The block's temperature was 40°C. The pit sat in a spot surrounded by 10- to 15-m-tall trees; their lack of visible damage suggested a near vertical angle of impact, which we estimated as 80-85°.

"At 70 m away from block R3 we found a volcanic bomb that struck the middle of the road. The bomb consisted of hydrothermally altered volcanic breccia (identified as R4, figure 34), which had shattered on the road over an area 1.73 x 1.64 m; the bomb failed to excavate a crater.

Figure (see Caption) Figure 34. Impact crater R4, created by Colima's 10 February 1999 explosion. Courtesy of F. Nunez-Cornu, G. Reyes-Davila, and C. Suarez-Plascencia.

"In traveling across El Playon we observed dozens of impacts, but elected to stay the minimum time possible in order to reduce exposure to hazards. Most of the bombs seen and sampled consisted of either andesite resembling the new dome or hydrothermally altered andesite, perhaps from the 1987 crater wall. When visiting the same area on 26 February, we found the small and medium impact craters difficult to identify; most of the impacts below trees were covered by newly fallen leaves."

Leveling survey and field examination of the 10 February bombs. On 28 February, John B. Murray, assisted by members of the Colima fire department (Mitchell Ventura, Filiberto de la Mora, and Juan Carlos Martinez) measured two branches of a N-flank leveling traverse last surveyed in January 1997. The first branch, which was 740 m long, left the Playon vehicle track and followed the path up Volcancito passing through stations Porte de Colima (1.3 km from the volcano's summit) and Albergue (1.9 km from the summit). The movement measured since 1997 showed subsidence at stations nearest the volcano totaling 13 mm for the entire section. This was nearly double the subsidence measured during 1995-97, an interval without any lava emission. There was also 13 mm of subsidence seen during 1990-92, an interval which included lava emission (in 1991).

The second branch of the leveling traverse began at Albergue station and ended at Voltaire station, a spot 2.3 km from the summit. Compared to 1997, the Albergue station had subsided just over 8 mm relative to the Voltaire station. Little significant change occurred here during 1995-97 (1 mm rise) and 1990-92 (0.4 mm rise). During a 15-year interval (1982-97) these two stations subsided a total of only 6 mm, and thus looks like a small though significant change in movement. Most of the change (5.6 mm) was measured between two stations 160 m apart at a distance of 2 km from the summit. The possibility of a small error cannot be ruled out, although the movement does follow the same sense throughout this section of the leveling traverse.

The total subsidence between the farthest (2.3 km) and the nearest (1.3 km) station to the summit was 22 mm. This is rather larger than during the 1991 crisis, when the subsidence between the same two stations was 13 mm. Viewing this movement as deflation of a magma chamber (Murray, 1993), this may simply be a reflection of the rather larger output of the volcano in 1998-99 compared to 1991. However, equally tenable is the hypothesis that the movement is due to volcano spreading, or even to Colima's slow slipping down the southern flanks of the larger Nevado volcano, on whose southern slopes Colima is situated. Increases in the rate of subsidence were also observed following the Mexican earthquake of 1985, as well as during the 1991 crisis described above. Although the subsidence during 1997-99 is greater than previously measured, there is nothing in the measurements to suggest that the volcano is building up to a bigger eruption, or to distinguish between the Mogi deflation or downslope slipping models.

The distribution of volcanic bombs from the 10 February explosion was noted at sites along the leveling traverse. Table 9 lists the estimated average distance between impact craters at the various sites where measurements were made. Murray and co-worker identified fragments that varied in size between 10 and 70 cm in diameter, there being no noticeable trend in size between bombs found in the region 1.3 to 2.8 km from the summit. The largest bomb crater found had taken away one third of the road on the north edge of the 1869 lava flow near station Hector, a spot 2.1 km from the summit. This crater was at least 2 m in diameter. However, the numbers of impacts per unit area decreased as distance from the volcano increased.

There is also some evidence of directed blast in table 9, there being distinctly higher concentrations of bombs NNE of the volcano (station Esteban) than at similar distances NE (station C15). Bombs appeared to be of two distinct types: 1) solid, dark, fresh-looking andesitic rocks with high density and no sign of vesiculation, and 2) crumbly, light-colored, altered, vesicular, pumice-like ejecta with low density (guessed at around 1,000 kg/m3) There did not appear to be any predominance of one type or the other with distance from the volcano.

Table 9. Average spacing of N-flank bomb strikes that were found after Colima's 10 February 1999 explosion. Courtesy of John B. Murray.

Site Distance from summit Distance between impacts
Volcancito foot 1.4 km 3 m
Playon (Campsite) 1.7 km 5 m
Playon (Esteban station) 2.0 km 45 m
1869 flow edge (Fire Station) 2.1 km 20 m
Caldera Wall (C15 station) 2.1 km 45 m

A bomb found near the campsite, 1.75 km from the summit, left evidence of its trajectory as it had smashed a 10 cm branch of a tree just before landing. The bomb itself was of solid andesite, and had fractured into several pieces on landing, but it appeared to have had an original diameter of about 40 cm. It had made an impact crater ~1 m in diameter and 50 cm deep. Using the level as a horizontal marker, three measurements of the angle between the broken branch and the crater bottom gave 44 ± 3° from the horizontal.

Six fire sites were inspected and described; usually these were associated with a bomb, but not always. At first, these fire sites went unnoticed because they chiefly consumed low-growing vegetation, and in no case was a completely burned tree to be found. The view towards the volcano from the Playon was unaffected, as green bushes and trees were seen as usual.

For example, at fire site 3, located 2 km NNE of the summit (N side of road, just past bend near station Esteban) we found an isolated pumice bomb 20 cm across, but without burnt vegetation in contact. However, the bomb ignited grass clumps 2 and 3.5 m away; none of the grass between the bomb and the clumps had been affected.

Most fire sites were close to bombs, usually burning on the side away from the volcano. However, most were not in direct contact with the bomb in question, but centered around dry vegetation, particularly tall grass clumps, succulents, small bushes, and (occasionally) trees. The grass and succulents were not dead, but had fresh green shoots sprouting from the top. Presumably because of the high water content, only the dry, dead leaves at the base of the succulents were burned, but there were large areas where succulents were affected in this way, the adjacent vegetation being quite unaffected. There was often no obvious associated bomb in the vicinity. Similarly with grass clumps, there would be gaps of 2 or 3 m between burned clumps, from which the fire had apparently spread radially for a short distance before going out, with no sign of burning of the dry, low grass cover in between. However, not all bombs in the same area had the same effect. In some cases, the only sign of burning was directly beneath the bomb itself, where the grass was singed black but still fairly intact. Yet in places nearby, the landscape had clearly been very slowly burned over an extensive area 10 to 30 m wide, and in one case discussed below, it was still burning.

Murray goes on to comment: "The odd characteristics of these fire sites suggests the possibility of an abnormal ignition mechanism. It seems that ignition depended in many cases not on the proximity to the source of heat (bombs) but rather on the characteristics of the ignited vegetation. It was as if in certain (sometimes quite extensive) areas those low-growing plants below a certain water content, or containing appropriate oils would ignite, and the rest would not. This implies a very high air temperature close to the ground over areas in some cases tens of meters across. The most obvious source of these high temperatures would seem to be hot gas, usually emanating from bombs but not always so. Where associated with bombs, the isolated fire sites would always be on the side facing away from the summit. In other words, there is evidence that extensive degassing took place from bombs upon impact; and that there might also have been some local associated ground-hugging nuees of a weak and intermittent type."

Explosion on 28 February 1999. Murray also noted that "At 1715 on 28 February, while examining the distant bombs and impact craters 2.8 km NE of the summit on the forest road outside the caldera, we heard a distant, faint rushing sound coming from the summit, resembling a large rockfall or an aircraft. On looking up, a large whitish-grey convective cloud, like a cumulus cloud, could be seen rising from the summit and blowing in our direction. It had clearly started some time previously and was already stretching some distance towards us. A heavy rain of ash began nine minutes later, at 1724, ceasing at ~1731. The ashfall, which was sampled, sounded like large raindrops hitting the leaves in the nearby forest but on spreading out a sheet of paper on the ground, only sand-sized ash particles could be seen accumulating on it. At the end of the shower, there was one particle every centimeter approximately, the largest particle being ~ 2 mm across, and the smallest just under 0.5 mm. From the sound of the particles falling in the trees round about, it sounded as if much larger particles were involved in the shower, but none of these fell on the spread-out paper."

Official press releases. A 26 February update by the Colima Volcano Observatory stated that chemical analysis of Colima's water and ash had indicated insignificant risk to human health. At this time the established security limit was set at 10-10.5 km from the summit. Evacuated settlements included Yerbabuena, Causenta, Atenguillo, El Fresnal, La Cofradía, Juan Barragán, El Agostadero, Los Machos, El Alpizahue, El Saucillo, and El Borbollón. The local populations were advised to avoid a long list of drainages, as well as to hand-carry important documents, and to advise authorities of those requiring help in order to secure transport in case of more extensive evacuations. Meanwhile, during the previous 24 hours the monitored parameters indicated relative quiet, suggesting possible voluntary return to evacuated areas at noon on 2 March if these conditions persisted. The 5 March update noted degassing events during the previous 24 hours, the majority of these around 1400 on 5 March. The 16 March update mentioned the recent occurrence of both degassing and minor ash emissions.

Reference. Murray, J.B., 1993, Ground deformation at Colima Volcano, Mexico, 1982 to 1991: Geofisica Internacional, v. 32, no. 4, p. 659-669.

Geologic Background. The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the 4320 m high point of the complex) on the north and the 3850-m-high historically active Volcán de Colima at the south. A group of cinder cones of late-Pleistocene age is located on the floor of the Colima graben west and east of the Colima complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, and have produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions (most recently in 1913) have destroyed the summit and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.

Information Contacts: F. Nunez-Cornu1,4, G. Reyes-Davila2, and C. Suarez-Plascencia3,4; 1) Laboratoria Sismologia, University of Guadelajara, Guadelajara, Mexico; 2) RESCO, University of Colima, Colima, Mexico; 3) Department of Geology, University of Guadelajara, Guadelajara, Mexico; 4) U. Est. Proteccion Civil Jalisco; Colima Volcano Observatory, Universidad de Colima, Av. Gonzalo de Sandoval 444, Colima, Colima 28045, Mexico (URL: https://portal.ucol.mx/cueiv/); J.B. Murray, Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, England.


Etna (Italy) — February 1999 Citation iconCite this Report

Etna

Italy

37.748°N, 14.999°E; summit elev. 3295 m

All times are local (unless otherwise noted)


Extensive lava flows discharging from a 4 February fissure on the SE flank

The following report summarizes activity observed at Etna from January through February 1999. Bocca Nuova exhibited minor explosive activity through early February, but Northeast Crater and Voragine were quiet. Southeast Crater had seven distinct eruptive episodes between 5 January and 4 February; the latest was accompanied by the opening of a new eruptive fissure at its southeastern base. The information for this report was compiled by Boris Behncke at the Istituto di Geologia e Geofisica, University of Catania (IGGUC), and posted on his internet web site. The compilation was based on personal summit visits, observations from Catania, and other sources cited in the text.

Activity at Southeast Crater (SEC) until 23 January. After one week of relative quiet, the sixteenth eruptive episode of SEC since 15 September occurred shortly before noon on 5 January; this was preceded by weak Strombolian activity that started around midnight. The paroxysmal phase was characterized by vigorous fountaining, and lava flowed towards the northeast while tephra was driven southwest by the strong wind. Loud detonations were audible in towns on the flanks of Etna.

Episode 17, during the night of 9-10 January, was preceded by mild Strombolian activity; the paroxysmal phase occurred shortly after midnight. Lava presumably flowed NE again and tephra fell NE; Fiumefreddo, ~8 km SW of Taormina, received a light showering of ash. Loud detonations during the final phase were audible over a wide area, and clear weather conditions permitted many in the Catania area to watch the spectacular display.

After the shortest repose interval observed since early in the current eruptive sequence in September, episode 18 took place on the morning of 13 January, between about 0630 and 0930. Visibiliby was hampered by clouds, but loud detonations were audible in a wide area around the volcano. Ash fell as far as Giarre, ~15 km E.

The next eruptive episode occurred on 18 January, shortly after 0800, and lasted ~ 45 minutes. Minor Strombolian and effusive activity had occurred earlier during the night. As in preceding episodes, the culminating phase was characterized by initial strong lava fountaining which gradually became more ash-rich, generating a dense eruption column. Due to calm conditions, the column rose several kilometers above the summit (3 km as estimated from Catania) and attained a spectacular mushroom shape visible in the morning sky from all around the volcano. At the SEC cone itself, the heavy fallout and rapid accumulation of pyroclastics led to frequent avalanches, especially on the steep eastern side. After 0830, dull explosion sounds were audible to as far as Catania, accompanying the rhythmic uprush of dark ash. The activity declined rapidly at 0845, but ash emissions became again more forceful after 0900 and continued sporadically for several hours, accompanied by sliding of hot pyroclastics from the steep E side of the cone. No information was available about lava flows although it is likely that they occurred, possibly on the NE side of SEC.

SEC erupted again after only two days and four hours of inactivity, shortly after noon on 20 January. Increased gas emission began at ~ 1215, and by 1240 a lava fountain appeared at the vent of the SE Crater cone. This fountain rapidly rose to a height of several hundred meters, and the column which rose above it became more and more ash-rich. Less than 15 minutes after the onset of the eruption there occurred the first slides of hot pyroclastics from the upper part of the cone, and five minutes later the whole cone and part of Etna's main summit cone were veiled by a black curtain of falling bombs and scoriae. By 1300, the vertical eruption column had risen several kilometers above Etna's summit. Ten minutes later the activity began to decline rapidly, and by 1315 the eruptive episode was essentially over, with only a few ash puffs being emitted during the following 30 minutes.

During a summit visit by Boris Behncke and Giovanni Sturiale (IGGUC) on 21 January, the crater was completely quiet, and only a few weak fumaroles played on the SW and E crater rims. The cone at SEC had grown higher than 3,250 m, about as high as the rim of the former Central Crater (filled by lavas and pyroclastics in the 1950's and 60's). While its flanks were steep and regular on most sides, obliterating any trace of the pre-1998 crater rim, a deep V-shaped notch was present in the northern crater rim through which lava had spilled onto the cone's flanks during recent eruptive episodes. These lavas had formed a fan-shaped lava field on the northeastern base of the cone, extending to the rim of Valle del Bove.

Behncke and Sturiale also investigated the pyroclastic deposits of the recent eruptive episodes which extended in relatively narrow fans from SEC in various directions. During the 18 and 20 January epidsodes, most fallout had occurred in a radius of <1 km from the cone, mainly on the SE side of the former Central Crater where 0.5-1 m of pyroclastics had accumulated since late 1998. Meter-sized bombs had fallen up to 500 m from SEC, creating spectacular impact craters. Among the most peculiar features of the recent eruptive products was a small lahar on the southwestern side of SEC which extended ~300 m from the base of its cone; this was probably produced during the 5 January episode. Records of lahars are relatively rare in the recent history of Etna, the most notable occurring in 1755.

On the morning of 23 January, SEC was the site of yet another eruptive episode that began at about 0630 and probably lasted less than one hour. Due to the absence of wind, an eruption column rose several kilometers above the summit then drifted slowly SE. In Catania, the ashfall was not dense, but people in the streets felt particles entering in the eyes; these particles were less than 1 mm in diameter and left a thin, discontinuous film on the ground. More serious effects were caused by the fallout in the upper southern parts of the mountain where skiing was rendered impossible by scoria on the snow. The repose period between this and the previous eruptive episode was two days and 18 hours.

There appears to have been no significant seismic or eruptive activity between 23 January and 4 February; the few clear views during that period revealed no morphological changes.

The January eruptive episodes continued to build the SEC cone, which has changed beyond recognition from its mid-1998 appearance. The large crater formed in 1990 at the summit of the SEC cone was completely filled, and a new, tall summit grew over it, burying any trace of the 1990 crater and much of the lava flows erupted from mid-1997 to late July 1998. After the 23 January episode the cone's new summit was at ~ 3,270 m elevation, almost 90 m higher than the highest point of the 1990 crater rim in 1997.

New eruptive fissure opens on 4 February. A new eruptive episode from SEC began at 1600, producing a spectacular eruption column visible from Catania and all around the mountain. Like previous episodes, this event was characterized by vigorous fire-fountaining, tephra emission, and lava, and was preceded by a gradual increase in gas emissions and then mild Strombolian activity. The activity began to culminate at around 1600 when a tall fountain jetted from the summit crater of the cone, and lava spilled through the breach in the N crater rim.

Sometime around 1630, the SE side of the cone fractured, and a new vent opened about halfway down the cone's flank, producing a tall lava fountain 250-350 m high and feeding a dense, ash-laden eruption column. An eruption column rose ~ 2-3 km above the summit before being driven SE, dropping fine ash on the flanks. Lava soon began to flow SE from this vent (figure 75). At about 1640, a row of incandescent spots appeared below the newly formed vent, indicating that a fissure had begun to propagate downslope from the base of the SEC cone. Vigorous lava fountaining and tephra emission from the new vent on the SE flank of SEC diminished rapidly shortly after 1700, but activity continued at the smaller vents on the fissure below that vent, at ~ 2,950 m elevation, and lava advanced rapidly towards the rim of Valle del Bove. At nightfall, both this lava flow and the lava erupted at the beginning of the episode onto the northern side of SEC were brightly incandescent and well visible from towns on the eastern side of the volcano, causing rumors of the opening of fractures on both sides of the cone. However, the northern flow soon stagnated and cooled, and no further lava emission occurred on that side for the remainder of February.

Figure (see Caption) Figure 75. Sketch map showing Etna's summit craters SEC, Voragine (V), and Bocca Nuova (BN). The approximate extent of lava flows emitted during the 4 February eruption are in medium gray and those following the 4 February eruption are in black. Flows erupted from 1971 to 1993 are shown in light gray. Courtesy of Boris Behncke.

On 5 February, lava had begun to spill into Valle del Bove, forming a cascade on its steep western wall. The flow advanced very slowly, and had not yet reached the valley floor (at ~2,000 m elevation) on the next day when the new eruptive fissure was visited by Behncke and Giuseppe Scarpinati (L'Association Volcanologique Européenne, LAVE). Mild explosive activity was building several hornitos in the upper part of the ~100-m-long, SE-trending fissure at the base of the SEC cone while lava was issuing from numerous vents along the whole length of the fissure, feeding several channellized flows and some minor a`a flows. The effusion rate was estimated at 5 m3/s or more, significantly higher than during previous mainly effusive eruptions near Etna's summit craters (mainly at NE Crater in the 1970's) and similar to the effusion rates of some of Etna's flank eruptions. Pahoehoe lava was abundant around the effusive vents. The cone of SEC was found to be fractured from its summit down to its base, but only the main 4 February vent appeared to have produced significant eruptive activity while only minor spatter and scoriae were found in the part of the fracture between that vent and the still-active fissure.

On 15 February, Behncke and Scarpinati again visited the eruptive fissure and observed its activity for about 4 hours. By that day the lava spilling into the Valle del Bove had reached ~ 2,000 m elevation. There was no sign that the activity was diminishing, and the effusion rate remained perhaps as high as 5 m3/s.

Lava continued to issue from a number of effusive vents on the active fissure, forming at least two main rivers and several smaller and short-lived flows. In the course of a few hours Behncke and Scarpinati saw some of the lesser flows cease and others reactivate, forming blocky a`a while the more vigorous and long-lived flows moved in well-defined channels and showed no significant flux variations. Numerous short lava tubes, well-developed flow channels, and secondary vents had formed. Most effusive activity occurred ~50-100 m downslope from the upper end of the fissure, but several vents were also higher upslope. In the uppermost part of the fissure, numerous hornitos had formed, most of them concentrated in three clusters, and this area had countless incandescent vents producing high-pressure gas emission accompanied by a persistent hissing noise. The largest hornitos formed thin, vertical spires up to 3 m high while others were small humps a few tens of centimeters high. There was little explosive activity; only one vent in the uppermost hornito cluster rarely ejected incandescent pyroclastics.

Similar activity continued through the end of February. Lava flowed into the Valle del Bove, forming numerous lobes that moved on top or adjacent to earlier flows, and the farthest flow fronts did not extend much beyond 2,000 m elevation, remaining above the Monti Centenari, a cluster of cones formed during the 1852-53 eruption on the floor of Valle del Bove. The flow field gradually widened to ~500 m on the rim, and flows were issuing from numerous ephemeral vents on the W slope of the Valle.

Activity at Bocca Nuova (BN), Voragine, and Northeast Crater (NEC). Little significant activity occurred at these craters during January-February 1999 except for a brief resurgence of activity at BN during the week preceding the 4 February SEC events. During the 21 January visit by Behncke and Sturiale, spattering and Strombolian activity occurred deep within the large crater in the southeastern part of BN, accompanied by dense gas emission.

The cone in the northwestern part of BN produced violent noisy explosions every few minutes which ejected fountains of bombs high above the crater rim; ejecta frequently fell outside the crater, mostly to the W but in a few cases also SW and S. Between the explosions, deep-seated minor activity occurred within the 50-80-m-wide crater of the cone. No effusive activity had taken place in BN since it was invaded by lava from Voragine on 22 July 1998.

Bright crater glow was visible above BN in the first nights of February, the first time in about five months. This glow persisted during the night of 3-4 February but was much weaker on the evening of 4 February, indicating a drop of the magma level, probably related to the opening of the eruptive fissure on the SE base of SEC earlier that day. During the following week, only infrequent weak glows were visible above BN and then vanished altogether.

Very little activity except profuse steaming was observed within the Voragine during the 21 January visit by Behncke and Sturiale, who were able to descend into this crater and arrived at the "diaframma," the septum that separates the Voragine from Bocca Nuova. The floor of the crater was very flat in its eastern part, while a cluster of four craters with low cones occupied its central-western portion. The central crater, ~50 m wide and 30 m deep, was completely quiet; on its W side a much shallower, ~20-m-wide crater contained a 2-m-wide degassing hole with overhanging walls on whose floor numerous incandescent spots could be seen. A small crater with a diameter of less than 20 m, and ~ 10 m deep, lay on the SE side of the central crater. The largest crater in the Voragine was in the SW part of the Voragine and was between 70 and 100 m wide and more than 50 m deep with very steep and unstable walls, so that its floor could not be seen. Eruptive activity occurred at depth; as could be judged from the noises this was similar to the activity observed in the southeastern BN vents on the same day. A fifth vent that was active in August and early September 1998 on the crest of the "diaframma" appeared to have collapsed into the large SW vent, and only a part of its cone remained standing.

Geologic Background. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Information Contacts: Boris Behncke, Istituto di Geologia e Geofisica (IGGUC), Palazzo delle Scienze, Università di Catania, Corso Italia 55, 95129 Catania, Italy.


Galeras (Colombia) — February 1999 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


Low seismicity; fumarole and tilt measurements

Seismicity remained low during January and February 1999. Volcano-tectonic (VT) earthquakes were common from two sources at depths of 0.2-18.8 km and had a coda magnitude range between -0.6 and 3. The first area was below the active cone, and the second was NNE of Galeras. The most significant VT event registered on 3 January at 0714 with a coda magnitude of 3, an epicenter ~14 km NNE of the volcano, and felt earthquakes in Pasto. Other types of VT events located toward the E flank have been called "trenes" (trains) because they are recorded consecutively, to make up packets of 2-5 events. They were small events, recorded at only four of the nine stations in the Galeras network. Those events had a depth range of 3.3-7.3 km and a coda magnitude range between -0.6 and 0.9.

Previous VT events at times have preceded seismic sequences, such as those during November-December 1993 and March 1995, as well as a small seismic sequence in July 1997. However, events have also been recorded in periods of no seismic sequences.

Quasi-monochromatic volcanic tremor episodes were recorded during 4-6 January. The maximum amplitudes were obtained on the E-W components of the broadband stations whereas the minimal amplitudes were recorded on the vertical components of those stations. The spectral frequencies show stable values with small variations of 0.5 Hz. Analysis of the tremor episodes suggested that the source directions of these events were toward the active cone of the volcano.

The electronic tiltmeter Peladitos, on the E flank of Galeras, showed stable behavior with small variations (<1 µrad) in both radial and tangential components. The Chorrillo and Huairatola portable tiltmeters showed stable behavior in the tangential components whereas the radial components continued a descending trend that began at the end of September 1998. Through 26 January, the cumulative decline in the Chorrillo radial component was ~35 µrad, and the Huairatola radial component decline was ~600 µrad.

Most of the radon stations showed stable behavior of the Rn-222 gas emission with changes <200 pCi/l. In contrast, the Meneses-1 station showed variations of ~ 3,300 pCi/l on an ascending trend; the Meneses-3 stations, ~2,700 pCi/l on a descending trend.

When the Alfa Deformes fumarole was measured in December 1998, it had a pH of 0.6. The next measurement, in May 1998, revealed a pH of 2.3, followed by a gradual decline to a value of 0.3 on 25 February. Measured fumarole temperatures generally remained stable, although the La Joya fumarole had increased to 181°C on 6 March from 148°C on 25 February. Scientists observed numerous fissures emitting gas during a summit visit, as well as cracks that could generate small landslides on the main cone.

Geologic Background. Galeras, a stratovolcano with a large breached caldera located immediately west of the city of Pasto, is one of Colombia's most frequently active volcanoes. The dominantly andesitic complex has been active for more than 1 million years, and two major caldera collapse eruptions took place during the late Pleistocene. Long-term extensive hydrothermal alteration has contributed to large-scale edifice collapse on at least three occasions, producing debris avalanches that swept to the west and left a large horseshoe-shaped caldera inside which the modern cone has been constructed. Major explosive eruptions since the mid-Holocene have produced widespread tephra deposits and pyroclastic flows that swept all but the southern flanks. A central cone slightly lower than the caldera rim has been the site of numerous small-to-moderate historical eruptions since the time of the Spanish conquistadors.

Information Contacts: Observatorio Vulcanológico y Sismológico de Pasto (OVSP), Carrera 31, 18-07 Parque Infantil, PO Box 1795, Pasto, Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html).


Guagua Pichincha (Ecuador) — February 1999 Citation iconCite this Report

Guagua Pichincha

Ecuador

0.171°S, 78.598°W; summit elev. 4784 m

All times are local (unless otherwise noted)


Moderate seismicity and phreatic eruptions during January-February

The Instituto Geofísico (IG-EPN) monitors seismic events, crustal deformation, geochemistry, and records visual observations at Guagua Pichincha. This volcano consists of a 2-km-wide caldera, breached to the west, on whose floor lies a dome complex and the present explosion craters. The following report summarizes their daily observations from 1 January to 31 March 1999. During this period, a Yellow alert status persisted.

Bad weather often prevented or hindered visual observations. Guards at the refuge station and visiting scientists frequently reported noises and the strong smell of sulfur from the fumaroles. COSPEC data from 16 January and 13 March showed only background concentrations of SO2 from the fumaroles, following the maximum concentrations yet recorded (170 t/day) on 10 December. Ash-and-steam plumes from dome fumaroles, when visible, ranged from 100 to 800 m in height, while explosion plumes reached 3 km. The 1981 explosion crater had increased in diameter and almost absorbed the September 1998 crater.

People living along the Cristal river (W flank) confirmed the seismic detection of small debris flows and floods that were generated on 7 and 27 January, 2, 16, and 21 February, and 1 March, all related to intense rainfalls; these traveled down the Rio Cristal at least 10-15 km. Estimated volumes are between 0.3 and 1 x 10-6 m3 with estimated peak discharges of 100-250 m3/s.

Phreatic explosions covered the dome and the interior of the caldera with ash and rocks. A guard at the refuge station and Civil Defense personnel found 2-5 mm of new ash and new impact craters in the Terraza area following the explosions of 21 and 23 January. Analysis of the ash showed no juvenile material, suggesting that magma had not ascended. Ballistically ejected rock fragments up to 30 cm in diameter were found 1-1.5 km S and SE of the dome, the result of phreatic explosions in this time period.

Volcano-tectonic (VT), long-period (LP), and hybrid earthquakes, sometimes in multiples, occurred almost daily throughout January, February, and March. Phreatic explosions were frequent during that period, occurring on average once per day in February and March. Daily LP event counts varied between 1 and 40, but many days had few VT or LP events. Still, 24 VT events occurred on 28 February and 1 March. .High-frequency tremor episodes of a few minutes to as much as four hours (9 February) duration were recorded, but possible associated effects in at the caldera summit could not be confirmed due to bad weather. Some rockfalls in the caldera were heard by the refuge guards while tremor episodes were occurring.

On 9 February and 14 March instruments detected 16 and 70 tectonic earthquakes along the N part of the Quito fault. The largest events had magnitudes of 3.7 and 4.0, respectively. It had been speculated that these events represented sympathetic responses to stresses produced by the volcano's magma chamber. This idea came from an earlier observation of an "on-off scenario" where the presence earthquakes in the N Quito area correlated with little seismicity registering under the caldera, and vice versa.

Reduced displacement measurements (RDs) of phreatic explosions ranged from those too small to measure to several that were 20 cm2 or greater. Some of these larger RDs, such as those on 18 and 28 January, and 13, 19, and 28 February, were the largest since October 1998. The one on 28 February was the largest yet recorded. A summary of seismic events since August 1998 is presented in table 2.

Table 2. Monthly summaries of explosions and seismic events at Guagua Pichincha, August 1998-March 1999. Courtesy IG-EPN.

Month Phreatic Explosions Volcano-tectonic Long-period Hybrid
Aug 1998 8 23 18 29
Sep 1998 24 73 165 1,626
Oct 1998 25 49 191 1,448
Nov 1998 18 52 234 419
Dec 1998 7 59 94 166
Jan 1999 18 41 218 1,163
Feb 1999 28 60 190 2,099
Mar 1999 21 115 73 940

Geologic Background. Guagua Pichincha and the older Pleistocene Rucu Pichincha stratovolcanoes form a broad volcanic massif that rises immediately to the W of Ecuador's capital city, Quito. A lava dome is located at the head of a 6-km-wide breached caldera that formed during a late-Pleistocene slope failure ~50,000 years ago. Subsequent late-Pleistocene and Holocene eruptions from the central vent in the breached caldera consisted of explosive activity with pyroclastic flows accompanied by periodic growth and destruction of the central lava dome. One of Ecuador's most active volcanoes, it is the site of many minor eruptions since the beginning of the Spanish era. The largest historical eruption took place in 1660, when ash fell over a 1000 km radius, accumulating to 30 cm depth in Quito. Pyroclastic flows and surges also occurred, primarily to then W, and affected agricultural activity, causing great economic losses.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador.


Ibu (Indonesia) — February 1999 Citation iconCite this Report

Ibu

Indonesia

1.488°N, 127.63°E; summit elev. 1325 m

All times are local (unless otherwise noted)


Eruptions that began on 18 December 1998 continued in January 1999

Local residents first noticed thick gray ash emissions from the summit on 18 December 1998 (corrected from BGVN 24:01); this information reached the Volcanological Survey of Indonesia (VSI) Gamkonora volcano observatory on the 31st. On 2 January personnel from VSI who went to the island to take COSPEC measurements of the SO2 release observed a loud eruption that caused up to 3 mm of ashfall in and around Tugure Batu Village. The eruption lasted 35 minutes and generated a plume 1,000 m high. Another eruption observed on 5 January 1999 lasted for 60 minutes. Thunderclaps from the summit were heard on 16 January and a night glow from ejecta was evident above the summit area. Residents also reportedly saw lava at the crater rim. The seismometer from Gamkonora (an RTS PS-2) was installed ~2 km from the summit of Ibu on 3 February along with an ARGOS satellite system tiltmeter.

Field observations on 11 March revealed continuing eruptions and rumbling noises, but the larger eruptions (accompanied by booming and thick ash ejection) had decreased to a rate of one every 15-20 minutes. When observed on 2 February larger eruptions occurred every 5 minutes. Seismograph records are still dominated by explosion events; during 9-15 March there were 779 events, increased from 673 events the previous week.

Geologic Background. The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, contained several small crater lakes through much of historical time. The outer crater, 1.2 km wide, is breached on the north side, creating a steep-walled valley. A large parasitic cone is located ENE of the summit. A smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. Only a few eruptions have been recorded in historical time, the first a small explosive eruption from the summit crater in 1911. An eruption producing a lava dome that eventually covered much of the floor of the inner summit crater began in December 1998.

Information Contacts: R. Sukhyar and Dali Ahmad, Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).


Izalco (El Salvador) — February 1999 Citation iconCite this Report

Izalco

El Salvador

13.813°N, 89.633°W; summit elev. 1950 m

All times are local (unless otherwise noted)


Strong fumarolic activity around the summit crater

During fieldwork on Santa Ana volcano in February, increased steaming was observed at the summit of Izalco relative to levels of previous years. Strong fumarolic activity occurred along the entire circumference of the 250-m-wide summit crater, with the exception of the NE side facing Cerro Verde. Activity was most vigorous at a vent on the N side of the crater floor, but was also strong along much of the inner rim of the crater and along its outer flanks. Steaming was observed over broad areas on the outer southern flanks to ~50 m below the rim, and on the W flank immediately N of a shoulder of the cone at ~1,800 m elevation, roughly 150 m below the summit. Activity had earlier been noticed to have increased in November 1998 following Hurricane Mitch. Most of the steaming was water vapor, and the increased activity was attributed to saturation of the still-warm cone by heavy rains accompanying the hurricane.

Geologic Background. Volcán de Izalco, El Salvador's youngest volcano, was born in in 1770 CE on the southern flank of Santa Ana volcano. Frequent strombolian eruptions from Izalco provided a night-time beacon for ships, causing the volcano to be known as El Faro, the "Lighthouse of the Pacific." During the two centuries prior to the cessation of activity in 1966, Izalco built a steep-sided, 650-m-high stratovolcano truncated by a 250-m-wide summit crater. Izalco has been one of the most frequently active volcanoes in North America, and its sparsely vegetated slopes contrast dramatically with neighboring forested volcanoes. Izalco's dominantly basaltic-andesite pyroclasts and lava flows are geochemically distinct from those of both Santa Ana and its fissure-controlled flank vents. Lava flows were mostly erupted from flank vents and deflected southward by the slopes of Santa Ana, traveling as far as about 7 km from the summit of Izalco.

Information Contacts: Carlos Pullinger, Calle Padres Aguilar 448, Colonia Escalon, San Salvador, El Salvador; Demetrio Escobar, Centro de Investigaciones Geotecnicas (CIG), Final Blvd. Venezuela y calle a La Chacra, Apdo. Postal 109, San Salvador, El Salvador; Lee Siebert and Paul Kimberly, Global Volcanism Program, Smithsonian Institution.


Krakatau (Indonesia) — February 1999 Citation iconCite this Report

Krakatau

Indonesia

6.102°S, 105.423°E; summit elev. 813 m

All times are local (unless otherwise noted)


Sporadic ash eruptions in February and March 1999

Krakatau erupted on 5 February 1999 accompanied by thunderclaps and an ash plume that reached a height of ~1,000 m above the summit. The activity continued until 10 February with ash plumes reaching ~100-300 m above the summit. The continuing sporadic eruptions deposited small amounts of ash over most of the island; a deposit of ~0.3 mm was measured near the observatory. On 11 February, the glow of ejecta was observed reaching ~25 m above the summit and continued during the night.

Activity decreased early during the week of 9-15 March. Weak booming noises were heard twice on 9 and 10 March, but plumes were not observed. At the end of the week booming noises were rare, and a white-gray ash plume was seen on 14 March that rose 100-300 m above the summit. The current activity is a continuation of eruptions that began in 1992.

Geologic Background. The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

Information Contacts: R. Sukhyar and Dali Ahmad, Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).


Ol Doinyo Lengai (Tanzania) — February 1999 Citation iconCite this Report

Ol Doinyo Lengai

Tanzania

2.764°S, 35.914°E; summit elev. 2962 m

All times are local (unless otherwise noted)


Lava flows spilling over the crater rim in November 1998

The following report is based on photos taken between September and November 1998. Most of the photos were taken by local mountain guide Burra Ami Gadiye. Sketches and descriptions of the photos were provided by Celia Nyamweru of St. Lawrence University.

Lava from within the crater breached the rim, causing small lava flows down the outer crater wall; the breach on the NW probably occurred in late October, and the breach on the E began in early November. Small, narrow tongues of pahoehoe lava erupted continuously from vents around the upper slopes of cones T37S, T37N, and T40 (figure 55). Most of these flows moved E or NE, although a few moved W. The tops of T37S and T37N were built up into broad cones with jagged crowns. Some growth also occurred at T40. Little change was apparent on any of the other cones that were in existence in August (BGVN 23:10). In mid-November a new cone, which has been numbered T50, formed at the base of the SE wall.

Figure (see Caption) Figure 55. View of Ol Doinyo Lengai looking N from the summit on 29 September 1998. Traced by Celia Nyamweru from a photo by B.A. Gadiye.

Activity during September and October. Narrow flows of pahoehoe lava emerged in late September from vents close to the summit of T37S and flowed E and W. The westward-flowing lava reached the center of the crater; the eastward-flowing lava reached the rim of T24 and the base of the crater wall. These flows were very dark in color suggesting they were still fluid or only very recently formed. The summit of T37S had a jagged profile (figure 56), replacing the broad dome seen in August.

Figure (see Caption) Figure 56. View of Ol Doinyo Lengai looking NW from SE crater rim as seen on 29 September 1998. Traced by C. Nyamweru from photographs by B. A. Gadiye.

Small, narrow, very dark colored pahoehoe flows emerged in early October from vents close to the summits of T37S and T40 (figure 57). Behind T40 and to the right of T45, the T37 cluster showed some dark lava extending westwards from its summit past T47, the very tall narrow cone in front of the south wall. Cone T40 had fresh lava extending from the summit onto its lower slopes.

Figure (see Caption) Figure 57. Photograph of Ol Doinyo Lengai taken on 3 October 1998 of the view S from the N crater rim. Courtesy B.A. Gadiye.

In another photo on 7 October (figure 58), the top of T37S was dark brown, in striking contrast with the very pale brown lower slopes. Surrounding cones were pale brown. A large dark brown flow from a source between T45 and T37 extended around the eastern slope of T45. The flow showed no sign of whitening along the edges of the slabs, unlike the flow in front of it, and, therefore, might have been only a few hours old. The E crater wall was estimated to be 5 m high based on the appearance of a person in one photo. This was not an estimate of the lowest point on the crater wall.

Figure (see Caption) Figure 58. Photograph of Ol Doinyo Lengai taken on 7 October 1998 of the view SW from the E crater rim. Courtesy B.A. Gadiye.

Activity during November. In early November fresh, black, shiny, pahoehoe lava flowed from a vent between T45 and T37S. Gadiye noted the source of the flow as the cone T5T9. Only the very top of T5T9 remained visible, since the remainder was covered by 20 m of lava. Another lava flow originated from a vent on the S slope of T40 and flowed around the E side of this cone. According to Gadiye the crater had filled and lava was pouring over the NW rim. A few weeks later he took two photographs, noting that the lava was spilling over the crater rim on the E and had burned the grass on the slope. The lava in one of these photos (taken just outside the rim) consisted of brown and gray smooth pahoehoe flows that did not seem to be more than 10 to 20 cm thick. Judging from the pale color, it had probably undergone weathering during the weeks since it flowed.

Aerial photographs taken late in November showed several narrow tongues of very dark lava over an older surface of white and pale brown lava. These dark flows originated from the slopes of T37S and from the cluster of cones around T37N1. A narrow white streak that overflowed the rim on the NW side was probably recent lava. A few days later fresh pahoehoe flows effused from T37S and T37N and flowed E toward the crater wall and the remains of the rim of T24 (figure 59). In this area was a new cone near the base of the S wall: a low circular feature, just out of view in figure 59, which Gadiye described as "a new cone near the SE rim that is boiling and giving out a lot of steam." This has been designated T50. Lava was seen to be overflowing the NW rim. T37S had a very jagged appearance and there also seemed to have been considerable growth at T37N1, between T37S and T45. Some fresh pahoehoe, very dark over the white older flows, was also visible farther west on the crater floor, near the T44/T48/T49 cone cluster.

Figure (see Caption) Figure 59. Photograph of Ol Doinyo Lengai taken on 24 November 1998 looking SW from the crater floor. Courtesy of B.A. Gadiye.

Geologic Background. The symmetrical Ol Doinyo Lengai is the only volcano known to have erupted carbonatite tephras and lavas in historical time. The prominent stratovolcano, known to the Maasai as "The Mountain of God," rises abruptly above the broad plain south of Lake Natron in the Gregory Rift Valley. The cone-building stage ended about 15,000 years ago and was followed by periodic ejection of natrocarbonatitic and nephelinite tephra during the Holocene. Historical eruptions have consisted of smaller tephra ejections and emission of numerous natrocarbonatitic lava flows on the floor of the summit crater and occasionally down the upper flanks. The depth and morphology of the northern crater have changed dramatically during the course of historical eruptions, ranging from steep crater walls about 200 m deep in the mid-20th century to shallow platforms mostly filling the crater. Long-term lava effusion in the summit crater beginning in 1983 had by the turn of the century mostly filled the northern crater; by late 1998 lava had begun overflowing the crater rim.

Information Contacts: Celia Nyamweru, Department of Anthropology, St. Lawrence University, Canton, NY 13617 USA (URL: http://blogs.stlawu.edu/lengai/).


Lopevi (Vanuatu) — February 1999 Citation iconCite this Report

Lopevi

Vanuatu

16.507°S, 168.346°E; summit elev. 1413 m

All times are local (unless otherwise noted)


Strombolian explosions beginning November 1998

During 1963-82 ash emissions, lava flows, lava fountains, and Strombolian explosions occurred intermittently at Lopevi. In 1968-69 activity mainly affected the SE flank (figure 1), where two lava flows from the summit reached the sea. The twenty-year pattern of activity ended with emission of a major plume that rose to 6,000 m on 24 October 1982 (SEAN 07:010).

Figure (see Caption) Figure 1. View of the SE flank of Lopevi volcano, looking toward the NW in May 1995. Paama Island, from which recent observations were made, and Ambrym Island, a currently active volcano, are in the background (to the N). Courtesy IRD; photo by P. Evin, IRD.

Since then, activity had been generally fumarolic. Eruptive activity resumed in July 1998. A series of Strombolian explosions in the main 1963 crater (just NW of the central crater) was observed during November 1998. On 29, 30, and 31 December 1998, Strombolian explosions and Vulcanian emissions were observed from the island of Paama every 4-5 minutes.

Sporadic eruptive activity observed between the end of December 1998 and March 1999 was confined to the 1963 crater on the NW flank (figure 2). The appearance of this large crater, at ~900 m elevation, ruined the perfect conic profile of Lopevi, a rare volcano of the archipelago without a caldera.

Figure (see Caption) Figure 2. View of the active crater on Lopevi's NW flank as seen in January 1999. Courtesy IRD; photo by J-M. Bore, IRD.

Lopevi, an island ~6 km in diameter, 1,450 m high, and 3,500 m above the seafloor, is one of the most active of the Vanuatu archipelago. The first written description came from Captain Cook, who in 1774 entered in his ship's log that the volcano was "seemingly without activity." Volcanic crises reported since 1863 appear to have occurred in cycles of ~15-20 years. In 1960, following a significant Plinian eruption from the NW flank, a series of pyroclastic flows, lava flows, Strombolian activity, and fumarolic emissions were observed during one month. In 1963, over a period of several months, large quantities of flowing lava and ash spread through ~ 1,000 ha in the NW part of the island.

Geologic Background. The small 7-km-wide conical island of Lopevi, known locally as Vanei Vollohulu, is one of Vanuatu's most active volcanoes. A small summit crater containing a cinder cone is breached to the NW and tops an older cone that is rimmed by the remnant of a larger crater. The basaltic-to-andesitic volcano has been active during historical time at both summit and flank vents, primarily along a NW-SE-trending fissure that cuts across the island, producing moderate explosive eruptions and lava flows that reached the coast. Historical eruptions at the 1413-m-high volcano date back to the mid-19th century. The island was evacuated following major eruptions in 1939 and 1960. The latter eruption, from a NW-flank fissure vent, produced a pyroclastic flow that swept to the sea and a lava flow that formed a new peninsula on the western coast.

Information Contacts: Michel Lardy, Institut de recherche pour le développement (IRD), B.P. 76, Port Vila, Vanuatu; Douglas Charley and Roland Priam, Department of Geology, Mines and Water Resources, PMB 01, Port Vila, Vanuatu.


Pacaya (Guatemala) — February 1999 Citation iconCite this Report

Pacaya

Guatemala

14.382°N, 90.601°W; summit elev. 2569 m

All times are local (unless otherwise noted)


Explosive activity resumes; summary of activity 1987-98

Explosive activity resumed on 2 January 1999 at Pacaya for the first time since the end of a major eruptive episode on 19 September 1998. Current activity has consisted of small explosions that ejected ash without incandescent material. Beginning on 8 January, the number of explosions increased from 100-200/day to more than 400/day, reaching a peak of ~ 550 on 21 January (figure 19). Explosion counts declined to ~200/day by the end of the month. Volcanologists from INSIVUMEH and the Smithsonian Institution observed frequent small ash eruptions during a 1 February visit. The explosions were not accompanied by detonations, and produced billowing gray-to-brown ash columns that rose ~100 m above the vent. They observed that two vents produced explosions; the largest explosions originated from the westernmost and lower of two vents in the breached crater. Intense fumarolic activity occurred from the inclined floor of the summit crater, its rim, and the outer flanks.

Figure (see Caption) Figure 19. Daily explosion counts at Pacaya during January 1999. Courtesy of INSIVUMEH.

Significant changes to the morphology of MacKenney cone had occurred since a strong explosive eruption on 18-19 September 1998. That eruption left a major breach 20-25 m wide that extended SW. By the time of the 1 February visit, erosion had widened the breach to 70-80 m. At its head, the breach had nearly vertical walls more than 50 m deep, and formed a gully that extended more than 1 km down to ~1,800 m elevation. The NE side of the crater was also notched, but not nearly as deeply. Fractures and down-dropped blocks of summit agglutinate material along the crater rim also showed this SW-NE orientation in line with the location of two flank vents active during September 1998. The breach gives MacKenney cone a twin-peaked appearance when viewed from the W flank (figure 20). The present form of the crater increases the possibility of future eruptive or collapse events being directed toward the W-flank village of El Patrocinio (figure 21).

Figure (see Caption) Figure 20. A prominent gully extends more than 1 km down the SW flank of Pacaya from the twin-peaked summit of MacKenney cone, 1 February 1999. The dark lava flow at the lower right was one of two emplaced from flank vents at the end of the 18-19 September 1998 eruption. Photograph courtesy of Lee Siebert.
Figure (see Caption) Figure 21. Sketch map of Pacaya and nearby towns. Hachured arcuate line indicates the caldera rim. Contour interval 100 m; contour intervals around MacKenney crater are approximate. Courtesy of INSIVUMEH.

The accumulation of spatter and ejecta from the September 1998 explosions had built MacKenney cone to a height about 30-35 m above an older cone immediately SE of MacKenney crater. The older cone, the previous vantage point for observing explosive activity from Pacaya, had itself grown about 10 m in the past decade from the accumulation of ejecta from MacKenney crater. The height of MacKenney cone now exceeds that of Cerro Grande, a vegetated ~2,560-m-high prehistorical cone of Pacaya located 2 km NE of MacKenney.

September 1998 eruption. A major explosive and effusive eruption took place on 18-19 September (table 3). During the first 17 hours of the eruption, a 1.2-km-long lava flow descended WNW into the caldera moat and down the flank of the volcano to the Montanas las Granadillas area SW of Cerro Chino. From 1700-2200 an explosive eruption ejected ash columns to 5 km above the crater, producing ashfall to the SW and NNW. Fine ashfall caused the closing of the international airport in Guatemala City for 35 hours. About 1 m of volcanic bombs were deposited on the caldera rim. Pyroclastic avalanches of incandescent ejecta mantled the upper half of the cone. One 3-m-wide impact crater was formed at the base of the lava flow near El Patrocinio, and 1-m-wide impact craters were found as far as 5 km from the vent. During the final explosive phase, the SW rim of MacKenney crater collapsed, forming a debris avalanche that traveled 2 km down the SW flank to ~1,500 m elevation. Coarse blocks littered the surface of the deposit, whose light color contrasted with that of adjacent dark-colored lava flows.

Table 3. Summary of major eruptive events at Pacaya volcano from January 1987 to September 1998.

Date Description of Volcanic Activity
21 Jan 1987 Ash fell over areas of the villages of Amatitlan and Santa Elena Barillas. The villages of El Caracol and El Patrocinio were evacuated.
25 Jan 1987 10-15 cm of ash fell over El Caracol, El Rodeo, and in part over El Patrocinio.
14 Jun 1987 Lava flow reached 2.5 km SW; 600 people evacuated.
7-11 Mar 1989 Two lava flows threatened to reach El Patrocinio and El Rodeo. A third lava flow traveled 3 km on the W flank.
02 Apr 1990 A 4-hour-long eruption deposited 10 cm of ash in El Patrocinio and El Caracol.
15 Sep 1990 Moderate intensity eruption caused a moderate ash fall over El Patrocinio.
05 Mar 1991 Minor ashfall in El Caracol and El Patrocinio.
06, 14, 16 Jun 1991 Continuing eruptive activity destroyed the active crater (MacKenney).
08, 12, 14, 15 Jul 1991 Moderate intensity eruption; minor ashfall over El Caracol (3 km from the crater).
27 Jul 1991 An eruption caused a 26-cm-thick ash layer to be deposited over El Caracol and El Patrocinio, 1.5 cm in Escuintla, and a thin layer in Santa Lucia Cotzumalguapa.
01 Aug 1991 A 3,000-m-high column caused ashfall over Barbarena and Cuilapa.
10 Jan 1993 Collapse in the active crater sent a glowing avalanche to the side of El Caracol. The post-collapse eruption column drifted toward Santa Lucia Barillas. The acidity of the ash damaged vegetation in the region.
21 Sep 1993 4-hour eruption caused a minor ashfall over El Caracol.
16 Mar 1994 Eruption lasted until midnight and had an incandescent lava fountain 300 m high. Most of the ash fell on the volcano's flanks.
15 Oct 1994 Phreatomagmatic explosion; acid ashfall damaged vegetation in Santa Elena Barillas and Los Llanos. Population was affected by pulmonary and respiratory problems.
07 Apr 1995 A lahar completely covered a house and killed a little girl in Los Rios. The inhabitants were evacuated as 25-35-cm-thick volcanic sand was deposited over the village. As a result of a hazard study, many villagers had been previously evacuated.
01-07 Jun 1995 A debris avalanche caused by collapse of the W crater rim destroyed a radio station and partially burned the vegetation of Cerro Chino in a 4-km2 area.
07 Jun 1995 Lahars moving as a dense, dough-like mass, cut roads and wiped away a bridge. Consequently many families in El Patrocinio and Los Rios were evacuated and later part of the population was relocated in La Colima.
17 Sep 1995 A 1-km-high column from a phreatomagmatic explosion deposited 3 cm of fine ash in Santa Elena Barillas and a fine veil of volcanic dust in Barbarena and near Cuilapa.
11 Oct 1996 At dawn the eruption produced a sustained lava fountain 500-700 m high and lava flows as long as 1.5 km on the SE flank. The 35 km/h wind with blasts at 45 km/h caused a fine ash fall as far as Puerto San Jose, 60 km to the S on the Pacific Ocean.
11 Nov 1996 A 9-hour-long eruption produced a 2-km long lava flow and deposited 7-12 cm of ash near El Caracol and Finca El Rabon. El Rodeo received a 2-3 cm thick blanket of ash. It was necessary to evacuate the population of El Caracol, El Rodeo, and some women and children of El Patrocinio.
20 May 1998 A 5-hour eruption produced a 4-km-high ash column. S wind caused ashfall in the capital City, Ciudad de Guatemala (2 mm in the N and 4 mm in the S areas of the city). La Aurora International airport was closed for three days. Incandescent bombs and hot blocks ignited trees in the mountainous areas of Cerro Grande, 2 km NNE of MacKenney crater. 254 people were evacuated from San Francisco de Sales, El Cedro, and El Pepinal. Two people were injured by falling scoriaceous bombs in S.F. de Sales.
14 Jun 1998 A moderate eruption began at 0600 and lasted until 1900. An incandescent lava fountain was oscillating between 150 and 400 m high. A large ash column (600-800 m high) was blown to the S and produced scoriaceous ashfall in El Caracol. There was no need to evacuate. Condensation of atmospheric humidity due to the heat fed a cloud that reached 1,500-1,700 m in height. The Unidad Coordinadora Deptal de Escuintla del Ministerio de Agricoltura, Ganaderia y Alimentacion reported the loss of Q70,000 (US $10,000) from partial destruction of coffee, corn, and bean crops, and for purchase of food for livestock. Aircraft reported ash at 5,500 m.
18 Jun 1998 A 10-minute explosion at 1045 caused the ejection of semi-incandescent blocks (>= 35 cm) over all the volcano flanks. Then, 20 minutes later, fine ash lightly fell over the city of San Vincente Pacaya.
18 Sep 1998 The main eruption had one effusive and one explosive phase. The first lasted 17 hours, producing a 1,200-m-long tongue of lava that emerged from the WNW rim of the active crater and then deviated to the Montanas las Granadillas area SW of Cerro Chino. The second phase occurred from 1700 to 2200 hours. It expelled an ash column that reached 5,000 m altitude and produced ash and lapilli fall to the SW and NNW.A very thin film of fine ash (~ 1 mm) caused the La Aurora International airport to be closed again for 35 hours, after which it reopened with restrictions. Three lava flows accompanied the explosive phase; the first one, 400 m long, went WNW and reached the base of the cone. There it joined the second flow (from the N flank). The third lava flow departed from the second flow and went to the S toward El Caracol. During the proximal explosive phase the SW rim of the MacKenney crater collapsed, causing a debris avalanche 2 km long, and a cloud of hot ash and gases that burned vegetation in the distal reaches.

Several lava flows accompanied the explosive activity (figure 22). The longest of these traveled ~4 km from a notch in the NE crater rim. The flow initially descended northward into the caldera moat where it was deflected by the caldera wall, flowed across the moat, and then down the SW flank to 1,760 m elevation before diverging around a small kipuka and scorching trees at its northern margin below Cerro Chino. Much of the caldera moat was covered by lava flows of the September eruption, and the prominent 1984 spatter cone low on the N flank was nearly buried.

Figure (see Caption) Figure 22. Photograph of the lava flow (foreground) that descended from Pacaya's caldera moat down the W flank. This flow and the two dark lobes above it originated from MacKenney cone during the 18-19 September 1998 eruption. Light-colored tephra deposits between the flows mantle previous lava flows. Photograph taken on 1 February 1999. Courtesy of Paul Kimberly, SI.

At the end of the eruption, two small lava flows took place from flank vents on opposite sides of the cone. A vent on the upper NE flank at ~2,450 m elevation produced a short lava flow that reached the caldera moat. A vent on the lower SW flank at ~1,800 m elevation (figure 22) produced a short lava flow that divided into two lobes, one traveling to the SW and the other to the south.

Summary of 1987-1998 activity. Routine explosive activity characteristic of Pacaya occurred through much of the period from 1987 to the present but is not listed in table 3. Strong explosive eruptions in January 1987 and June 1991 destroyed the upper part of MacKenney cone, deepening and widening the crater, after which renewed eruptions reconstructed the cone. Major eruptions on 7 and 14 June 1995 destroyed the WNW side of the crater, leaving two notches at the summit. Debris from the 7 June collapse slammed into the caldera wall at Cerro Chino, 1 km NW of the summit, and produced a secondary hot cloud that swept over Cerro Chino, destroyed a radio antenna, and affected houses within 2 km of the active vent. The shockwave threw INSIVUMEH observer Pastor Alfaro down a slope, fracturing his leg. The 7 June event produced a 2.5-km-high plume. The second collapse on 14 June produced an avalanche that traveled SW toward El Rodeo and was accompanied by a 4-km-high plume. Lava flows subsequently traveled 2 km. Figure 23 shows RSAM plots for 1995-98.

Figure (see Caption) Figure 23. Plot of seismic activity at Pacaya as represented by Real-time Seismic Amplitude Measurement (RSAM) counts during January 1995-December 1998. Courtesy of INSIVUMEH.

A strong explosive eruption on 20 May 1998 produced a 4-km-high ash column. Incandescent bombs burned trees on the SSW flank of Cerro Grande, 2 km N of the crater, and scoria fall damaged vegetation and crops. Two persons in the settlement of San Francisco de Sales, 2.5 km NE of the crater, were injured by falling scoria blocks. The ash plume was primarily blown to the NE, with a lesser plume to the SW (figure 24). Ash fell from 1300-1600 in the villages and towns within 5 km of the volcano. During 1400-1830 ash fell in the capital city of Guatemala, causing closure of the international airport. Ashfall covered an area of 800 km2, and had an estimated volume of ~2.3 x 106 m3. The eruption caused the evacuation of 254 residents from surrounding villages to the town of San Vicente de Pacaya. Lava flows during the 20 May eruption traveled down the N, W, and SW flanks and had a volume of 6.3 x 105 m3.

Figure (see Caption) Figure 24. Isopachs of the 20 May 1998 explosive eruption from Pacaya volcano. Courtesy of Otoniel Matias, INSIVUMEH.

Geologic Background. Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.

Information Contacts: Otoniel Matias, Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Ministerio de Communicaciones, Transporte y Obras Publicas, 7A Avenida 14-57, Zona 13, Guatemala City, Guatemala; Lee Siebert and Paul Kimberly, Global Volcanism Program, National Museum of Natural History, Room E-442, Smithsonian Institution, Washington DC 20560-0119.


Sheveluch (Russia) — February 1999 Citation iconCite this Report

Sheveluch

Russia

56.653°N, 161.36°E; summit elev. 3283 m

All times are local (unless otherwise noted)


Low-level seismicity and fumarolic plumes

Seismicity under the volcano was about at background levels from December 1998 through February 1999. On 2 February a M 2 earthquake was located at 23 km depth. Weak volcanic tremor and small earthquakes were registered during the first half of February, and on 21 February a 6-minutes series of shallow earthquakes was detected. The Level of Concern Color Code remained Green.

The volcano was frequently obscured by clouds, making observations only intermittently possible. Fumarolic plumes rising 50-400 m were noted on 10 December, 8, 13-14, and 20 January, 6-7, 13, 16-18, and 22 February. Higher plumes, in the range of 700-800 m above the summit, were observed on 21 and 23 January, and 5 February. On 10 and 15 February fumarolic plumes rose 1,000 m.

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: Olga Chubarova, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Tom Miller, Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.


Shishaldin (United States) — February 1999 Citation iconCite this Report

Shishaldin

United States

54.756°N, 163.97°W; summit elev. 2857 m

All times are local (unless otherwise noted)


Steam plumes and thermal activity seen at summit

During the first week of February, National Weather Service personnel in Cold Bay, 93 km ENE of Shishaldin, observed anomalous steaming. On 9 February a vigorous steam plume rose as high as 1,830 m above the vent and a long plume drifted downwind. Satellite imagery taken that day showed a thermal anomaly at the vent in addition to the steam plume. The steam activity decreased during the week, becoming only light puffs rising a few meters above the vent; however, the thermal anomaly at the vent persisted. A newly installed seismic net recorded slightly elevated seismicity beginning at the end of January.

The hazard status was raised to Yellow on 18 February due to the persistence of the thermal anomaly and the identification of low-level seismic tremor. Pilots and ground observers reported a large steam plume rising to 5,800 m on 18 February. No ash was detected on satellite imagery. Cloudy weather precluded ground observations for most of the following week.

Shishaldin volcano, located near the center of Unimak Island in the eastern Aleutian Islands, is a spectacular symmetrical cone with a basal diameter of approximately 16 km. A small summit crater typically emits a noticeable steam plume with occasional small amounts of ash. Shishaldin is one of the most active volcanoes in the Aleutian volcanic arc, situated near that part of the arc where the maximum rate of subduction occurs. It has erupted at least 27 times since 1775. Major explosive eruptions occurred in 1830 and 1932, and eight historical eruptions have produced lava flows. Steam and minor ash emission began in March 1986 and continued intermittently through mid-February, 1987. A poorly documented short-lived eruption of steam and ash, perhaps as high as 10 km, occurred in December 1995 (BGVN 21:01). Fresh ash was noted on the upper flanks and crater rim but no specific eruptive event was identified for the deposits.

Geologic Background. The beautifully symmetrical volcano of Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The 2857-m-high, glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steady steam plume rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is Holocene in age and largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the west and NE sides at 1500-1800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century.

Information Contacts: Alaska Volcano Observatory, a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.


Soufriere Hills (United Kingdom) — February 1999 Citation iconCite this Report

Soufriere Hills

United Kingdom

16.72°N, 62.18°W; summit elev. 915 m

All times are local (unless otherwise noted)


Ash venting and numerous pyroclastic flows in December 1998 and January 1999

Several small dome collapses, some that were initially explosive, generated pyroclastic flows in December. Episodes of ash venting occurred almost daily and seismicity was dominated by volcano-tectonic earthquakes and rockfalls. The number of volcano-tectonic earthquakes declined toward the end of December but the number of long-period signals, corresponding to ash venting, increased slightly. Some explosive eruptions during early- to mid-January generated substantial ash clouds. Brief episodes of ash venting, correlating with seismic tremor, became shorter and weaker toward the end of January. Small-volume pyroclastic flows were generated by dome collapse, but some flows may have been generated by fountain collapse during small explosive eruptions. The average SO2 flux was elevated throughout December and January. Eastward movement of the Long Ground and Tar River GPS sites continued.

Visual observations.Daily periods of volcanic tremor during December coincided with steam-and-ash venting. On 8 December mudflows occurred all around the volcano.

A pyroclastic flow generated by dome collapse on 14 December reached the sea at the Tar River delta. Deposits were fluidized, fine-grained material with very few blocks. A large ash cloud was generated that rose rapidly to ~6,100 m. Ash fell W and NW of the volcano, attaining a thickness of 2 mm in Salem and containing accretionary lapilli up to 2 mm in diameter. On 19 December a pyroclastic flow reached the Tar River delta in less than five minutes. Powerful black jets of ash and rock burst from the dome at the onset of the event but it is unclear if this explosive activity preceded or followed the dome collapse. The small deposit was almost entirely confined to the incised channel in the Tar River valley on top of the 14 December deposits. On 21 December, at the onset of a sudden large seismic signal, dense black jets of ash and vigorously convecting ash clouds escaped from the main vent in the 3 July scar. Ballistic blocks rose 80 m above the vent. Very vigorous ash venting continued for more than 30 minutes after the initial explosion. A minor dome collapse on 27 December resulted in a small-volume pyroclastic flow reaching the Tar River delta. Poor visibility hampered observations, but a significant ash cloud was generated.

Minor ash venting took place on 1 and 5 January. At 0358 on 7 January, a large long-period seismic signal immediately preceded a 30-minute episode of tremor (usually associated with vigorous ash venting). Later the same day, a small dome collapse generated a pyroclastic flow that traveled half-way down the Tar River valley and a low-level ash cloud that moved W over Plymouth. On 13 January an explosive event generated an ash cloud to 6,100 m and a pyroclastic flow. The onset of the seismic signal had a long-period component, and a pressure wave was recorded at Long Ground. A booming sound was reported by many. The pyroclastic-flow deposit in the Tar River valley was small in volume but its extent suggested that the flow had been very mobile. Narrow small-volume pyroclastic-flow deposits were observed S of the dome as far as the former position of Galway's Soufriere. Two small dome-collapse pyroclastic flows occurred on 14 January. At 0827 on 15 January a small explosive event generated an ash cloud that rose to 4,600 m. The cloud moved NW and light ashfall affected Salem and Old Towne. Ash venting continued in pulses for 15 minutes. Another small explosion on 16 January generated an ash cloud to 3,000 m. Rockfalls were triggered on the inner walls of the 3 July scar and on the outer SE and NE flanks of the dome. A minor dome-collapse pyroclastic flow on 20 January almost reached the sea at the Tar River delta. The resulting steam-rich plume dissipated rapidly. Several brief (20 minute) episodes of tremor preceded by a rockfall corresponded to weak ash venting on 24 January. Further short episodes of ash venting occurred on 25 and 27 January.

Clear conditions on 26 and 27 January enabled MVO staff to survey the dome (figure 44). The canyon, which had been incised through the dome, was clearly visible. It bisected the dome in a NW-SE direction from the top of Tar River Valley to the top of Gages Valley. The inner walls of the canyon were vertical and surfaces looked fresh because of repeated small rockfalls.

Figure (see Caption) Figure 44. Photograph of the dome area at Soufriere Hills taken in late January 1999. This was used to calculate the dome volume and shows an exceptionally clear view of the gully running through the dome. Courtesy MVO; photograph by Richard Herd and Chloe Harford.

Seismicity. Seismicity in December consisted chiefly of volcano-tectonic earthquakes and rockfall signals. Many of the latter were associated with small pyroclastic flows or venting. Small clusters of earthquakes were located under George's Hill to the NW of the dome, under Roaches Yard to the SE, and under Hermitage Estate to the NE.

Overall, January was quiet seismically. Pyroclastic-flow signals had low-frequency precursors. These events were associated with booming noises and were followed by periods of vigorous ash venting, suggesting the collapses were caused by violent degassing of the dome.

Ground deformation. The only area where significant deformation took place in December was on the E flank. The vectors for Long Ground showed eastward movement of these two sites amounting to 5 cm since lava stopped erupting. Most of this movement occurred during the last three months (a time of increased surface activity). The differential movement between Whites and Long Ground since June 1996 is more than 10 cm. The two sites are 733 m apart and the movement between them cannot be fit elastically. A ground inspection on 30 December revealed a possible fault between the two sites. The only surface expression is a linear break in the road and it is not currently known whether this is related to volcanic deformation or to surficial movements. The Tar River GPS pin has followed a similar movement to Long Ground throughout the eruption. The Perches site, until it was destroyed in July, followed a similar path. One possible interpretation is that a sector of the volcano including Long Ground, Perches, and Tar River is moving as a block along faults in a NE direction.

Eastward movement of Long Ground and Tar River continued in January but at a reduced rate. A local EDM network of five pins was set up on 27 January to learn whether the surface feature is a fault.

Environmental monitoring. The miniCOSPEC was used several times in December. The SO2 flux was elevated and on 22 December and reached a peak average flux of 1,700 metric tons per day (figure 45). Sulfur-dioxide flux decreased throughout January, but generally remained elevated. Concentrations were also measured at ground level by using diffusion tubes around the island.

Figure (see Caption) Figure 45. Average daily SO2 fluxes at Soufriere Hills measured by miniCOSPEC, December 1998-January 1999. The lines connecting measured points are guidelines only; the actual measured levels varied. The measurements made on 19 January showed a very low flux: observations suggested that at least part of the plume was at a very low altitude and may have been found partly below the elevation of the traversing helicopter. Data courtesy of MVO.

Ash and rainwater collection continued throughout January. Ash samples from the small explosive events tended to very coarse, with lithic and crystal fragments up to 6 mm in size in the Richmond Hill-St. Georges area. In contrast, ash generated by dome-collapse pyroclastic flows was very fine-grained.

Volume measurements. A detailed photographic and theodolite survey was conducted from twelve sites around the volcano at the end of January. A photographic survey was also conducted from the helicopter with the GPS onboard. The information has been processed to produce a detailed dome map and volume measurement. The dome had a volume of 76.8 x 106 m3 and its highest point was 977 m at the top of the White River Valley. The dome was split deeply by the collapse on 3 July 1998 and by subsequent events. The N part of the dome, which comprises three main buttresses above Gages, the N flank, and Tar River, contains two-thirds of the total dome volume. The scar cuts up to 100 m into the pre-1995 crater floor and has removed a minimum of 5.4 x 106 m3 of old rock from this area.

Geologic Background. The complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. The volcano is flanked by Pleistocene complexes to the north and south. English's Crater, a 1-km-wide crater breached widely to the east by edifice collapse, was formed about 2000 years ago as a result of the youngest of several collapse events producing submarine debris-avalanche deposits. Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits, including those from an eruption that likely preceded the 1632 CE settlement of the island, allowing cultivation on recently devegetated land to near the summit. Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but no historical eruptions were recorded until 1995. Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth and pyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption.

Information Contacts: Montserrat Volcano Observatory (MVO), Mongo Hill, Montserrat, West Indies (URL: http://www.mvo.ms/).


Tolbachik (Russia) — February 1999 Citation iconCite this Report

Tolbachik

Russia

55.832°N, 160.326°E; summit elev. 3611 m

All times are local (unless otherwise noted)


Gas-and-steam explosion; minor seismicity

On 18 February, a gas-and-steam explosion generated a plume to 600 m above the volcano. Small (magnitudes near zero) shallow earthquakes were registered under the volcano and continued through the month, coincident with M 1.5 events at 15-30 km depth. No further unusual seismicity was reported as of mid-March.

The massive Tolbachik basaltic volcano is located at the southern end of the dominantly andesitic Kliuchevskaya volcano group. The Tolbachik massif is composed of two overlapping, but morphologically dissimilar volcanoes. The flat-topped Plosky Tolbachik shield volcano with its nested Holocene Hawaiian-type calderas up to 3 km in diameter is located east of the older and higher sharp-topped Ostry Tolbachik stratovolcano. Lengthy rift zones extending NE and SSW of the volcano have erupted voluminous basaltic lava flows during the Holocene, with activity during the past two thousand years being confined to the narrow axial zone of the rifts. The last eruptive activity, in 1975-76, vented from both the summit and SSW-flank fissures; it was the largest historical basaltic eruption in Kamchatka.

Geologic Background. The massive Tolbachik basaltic volcano is located at the southern end of the dominantly andesitic Kliuchevskaya volcano group. The massif is composed of two overlapping, but morphologically dissimilar volcanoes. The flat-topped Plosky Tolbachik shield volcano with its nested Holocene Hawaiian-type calderas up to 3 km in diameter is located east of the older and higher sharp-topped Ostry Tolbachik stratovolcano. The summit caldera at Plosky Tolbachik was formed in association with major lava effusion about 6500 years ago and simultaneously with a major southward-directed sector collapse of Ostry Tolbachik volcano. Lengthy rift zones extending NE and SSW of the volcano have erupted voluminous basaltic lava flows during the Holocene, with activity during the past two thousand years being confined to the narrow axial zone of the rifts. The 1975-76 eruption originating from the SSW-flank fissure system and the summit was the largest historical basaltic eruption in Kamchatka.

Information Contacts: Olga Chubarova, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Tom Miller, Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.


White Island (New Zealand) — February 1999 Citation iconCite this Report

White Island

New Zealand

37.52°S, 177.18°E; summit elev. 321 m

All times are local (unless otherwise noted)


Minor ash-and-steam emissions continue

Volcanic-tremor levels on White Island (BGVN 23:10-23:12 and 24:01) have remained low since 22 January and low-level eruptive activity continued through mid-March. On 12 February, the low-energy hydrothermal activity within Metra Crater was dominated by gas-and-steam emissions from small fumaroles on the N and W sides of the crater. Four small ponds had formed on the crater floor. A weak gas (SO2) and steam plume from PeeJay Vent rose 400-500 m, forming haze visible 40-50 km away.

During a visit by C.P. Wood on 13 March activity was generally constant with the ash-and-steam column rising to ~ 1,060 m and drifting many kilometers downwind, with sea discoloration from fall-out evident to 1 km from the island. PeeJay Vent was continuously emitting ash-charged gray-brown steam, but with varying intensity. During peak discharges, observers standing on the 1978/90 Crater Complex edge noted a rumbling noise from PeeJay, but no block ejection was seen. The vent diameter appeared to have increased and was an obvious funnel shape lined with whitish sublimate deposits. Ash could not be collected because of the wind direction. Metra Crater was occupied by a lurid lime-green lake, which largely filled the original crater and peripheral scallops to ~ 1 m below the rim (the old lake floor). There was no sign of thermal disturbance in the Metra lakelet. The ash surface throughout Main Crater was rain-washed and smooth (except for the route used by tourist operators), with no sign of recent impact craters near the 1978/90 Crater Complex edge.

Geologic Background. Uninhabited 2 x 2.4 km White Island, one of New Zealand's most active volcanoes, is the emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes; the summit crater appears to be breached to the SE, because the shoreline corresponds to the level of several notches in the SE crater wall. Volckner Rocks, four sea stacks that are remnants of a lava dome, lie 5 km NNE. Intermittent moderate phreatomagmatic and strombolian eruptions have occurred throughout the short historical period beginning in 1826, but its activity also forms a prominent part of Maori legends. Formation of many new vents during the 19th and 20th centuries has produced rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project.

Information Contacts: Brad Scott, Wairakei Research Centre, Institute of Geological and Nuclear Sciences (IGNS) Limited, Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

Atmospheric Effects

The enormous aerosol cloud from the March-April 1982 eruption of Mexico's El Chichón persisted for years in the stratosphere, and led to the Atmospheric Effects section becoming a regular feature of the Bulletin. Descriptions of the initial dispersal of major eruption clouds remain with the individual eruption reports, but observations of long-term stratospheric aerosol loading will be found in this section.

Atmospheric Effects (1980-1989)  Atmospheric Effects (1995-2001)

Special Announcements

Special announcements of various kinds and obituaries.

Special Announcements

Additional Reports

Reports are sometimes published that are not related to a Holocene volcano. These might include observations of a Pleistocene volcano, earthquake swarms, or floating pumice. Reports are also sometimes published in which the source of the activity is unknown or the report is determined to be false. All of these types of additional reports are listed below by subregion and subject.

Kermadec Islands


Floating Pumice (Kermadec Islands)

1986 Submarine Explosion


Tonga Islands


Floating Pumice (Tonga)


Fiji Islands


Floating Pumice (Fiji)


Andaman Islands


False Report of Andaman Islands Eruptions


Sangihe Islands


1968 Northern Celebes Earthquake


Southeast Asia


Pumice Raft (South China Sea)

Land Subsidence near Ham Rong


Ryukyu Islands and Kyushu


Pumice Rafts (Ryukyu Islands)


Izu, Volcano, and Mariana Islands


Acoustic Signals in 1996 from Unknown Source

Acoustic Signals in 1999-2000 from Unknown Source


Kuril Islands


Possible 1988 Eruption Plume


Aleutian Islands


Possible 1986 Eruption Plume


Mexico


False Report of New Volcano


Nicaragua


Apoyo


Colombia


La Lorenza Mud Volcano


Pacific Ocean (Chilean Islands)


False Report of Submarine Volcanism


Central Chile and Argentina


Estero de Parraguirre


West Indies


Mid-Cayman Spreading Center


Atlantic Ocean (northern)


Northern Reykjanes Ridge


Azores


Azores-Gibraltar Fracture Zone


Antarctica and South Sandwich Islands


Jun Jaegyu

East Scotia Ridge


Additional Reports (database)

08/1997 (BGVN 22:08) False Report of Mount Pinokis Eruption

False report of volcanism intended to exclude would-be gold miners

12/1997 (BGVN 22:12) False Report of Somalia Eruption

Press reports of Somalia's first historical eruption were likely in error

11/1999 (BGVN 24:11) False Report of Sea of Marmara Eruption

UFO adherent claims new volcano in Sea of Marmara

05/2003 (BGVN 28:05) Har-Togoo

Fumaroles and minor seismicity since October 2002

12/2005 (BGVN 30:12) Elgon

False report of activity; confusion caused by burning dung in a lava tube



False Report of Mount Pinokis Eruption (Philippines) — August 1997

False Report of Mount Pinokis Eruption

Philippines

7.975°N, 123.23°E; summit elev. 1510 m

All times are local (unless otherwise noted)


False report of volcanism intended to exclude would-be gold miners

In discussing the week ending on 12 September, "Earthweek" (Newman, 1997) incorrectly claimed that a volcano named "Mount Pinukis" had erupted. Widely read in the US, the dramatic Earthweek report described terrified farmers and a black mushroom cloud that resembled a nuclear explosion. The mountain's location was given as "200 km E of Zamboanga City," a spot well into the sea. The purported eruption had received mention in a Manila Bulletin newspaper report nine days earlier, on 4 September. Their comparatively understated report said that a local police director had disclosed that residents had seen a dormant volcano showing signs of activity.

In response to these news reports Emmanuel Ramos of the Philippine Institute of Volcanology and Seismology (PHIVOLCS) sent a reply on 17 September. PHIVOLCS staff had initially heard that there were some 12 alleged families who fled the mountain and sought shelter in the lowlands. A PHIVOLCS investigation team later found that the reported "families" were actually individuals seeking respite from some politically motivated harassment. The story seems to have stemmed from a local gold rush and an influential politician who wanted to use volcanism as a ploy to exclude residents. PHIVOLCS concluded that no volcanic activity had occurred. They also added that this finding disappointed local politicians but was much welcomed by the residents.

PHIVOLCS spelled the mountain's name as "Pinokis" and from their report it seems that it might be an inactive volcano. There is no known Holocene volcano with a similar name (Simkin and Siebert, 1994). No similar names (Pinokis, Pinukis, Pinakis, etc.) were found listed in the National Imagery and Mapping Agency GEOnet Names Server (http://geonames.nga.mil/gns/html/index.html), a searchable database of 3.3 million non-US geographic-feature names.

The Manila Bulletin report suggested that Pinokis resides on the Zamboanga Peninsula. The Peninsula lies on Mindanao Island's extreme W side where it bounds the Moro Gulf, an arm of the Celebes Sea. The mountainous Peninsula trends NNE-SSW and contains peaks with summit elevations near 1,300 m. Zamboanga City sits at the extreme end of the Peninsula and operates both a major seaport and an international airport.

[Later investigation found that Mt. Pinokis is located in the Lison Valley on the Zamboanga Peninsula, about 170 km NE of Zamboanga City and 30 km NW of Pagadian City. It is adjacent to the two peaks of the Susong Dalaga (Maiden's Breast) and near Mt. Sugarloaf.]

References. Newman, S., 1997, Earthweek, a diary of the planet (week ending 12 September): syndicated newspaper column (URL: http://www.earthweek.com/).

Manila Bulletin, 4 Sept. 1997, Dante's Peak (URL: http://www.mb.com.ph/).

Simkin, T., and Siebert, L., 1994, Volcanoes of the world, 2nd edition: Geoscience Press in association with the Smithsonian Institution Global Volcanism Program, Tucson AZ, 368 p.

Information Contacts: Emmanuel G. Ramos, Deputy Director, Philippine Institute of Volcanology and Seismology, Department of Science and Technology, PHIVOLCS Building, C. P. Garcia Ave., University of the Philippines, Diliman campus, Quezon City, Philippines.


False Report of Somalia Eruption (Somalia) — December 1997

False Report of Somalia Eruption

Somalia

3.25°N, 41.667°E; summit elev. 500 m

All times are local (unless otherwise noted)


Press reports of Somalia's first historical eruption were likely in error

Xinhua News Agency filed a news report on 27 February under the headline "Volcano erupts in Somalia" but the veracity of the story now appears doubtful. The report disclosed the volcano's location as on the W side of the Gedo region, an area along the Ethiopian border just NE of Kenya. The report had relied on the commissioner of the town of Bohol Garas (a settlement described as 40 km NE of the main Al-Itihad headquarters of Luq town) and some or all of the information was relayed by journalists through VHF radio. The report claimed the disaster "wounded six herdsmen" and "claimed the lives of 290 goats grazing near the mountain when the incident took place." Further descriptions included such statements as "the volcano which erupted two days ago [25 February] has melted down the rocks and sand and spread . . . ."

Giday WoldeGabriel returned from three weeks of geological fieldwork in SW Ethiopia, near the Kenyan border, on 25 August. During his time there he inquired of many people, including geologists, if they had heard of a Somalian eruption in the Gedo area; no one had heard of the event. WoldeGabriel stated that he felt the news report could have described an old mine or bomb exploding. Heavy fighting took place in the Gedo region during the Ethio-Somalian war of 1977. Somalia lacks an embassy in Washington DC; when asked during late August, Ayalaw Yiman, an Ethiopian embassy staff member in Washington DC also lacked any knowledge of a Somalian eruption.

A Somalian eruption would be significant since the closest known Holocene volcanoes occur in the central Ethiopian segment of the East African rift system S of Addis Ababa, ~500 km NW of the Gedo area. These Ethiopian rift volcanoes include volcanic fields, shield volcanoes, cinder cones, and stratovolcanoes.

Information Contacts: Xinhua News Agency, 5 Sharp Street West, Wanchai, Hong Kong; Giday WoldeGabriel, EES-1/MS D462, Geology-Geochemistry Group, Los Alamos National Laboratory, Los Alamos, NM 87545; Ayalaw Yiman, Ethiopian Embassy, 2134 Kalorama Rd. NW, Washington DC 20008.


False Report of Sea of Marmara Eruption (Turkey) — November 1999

False Report of Sea of Marmara Eruption

Turkey

40.683°N, 29.1°E; summit elev. 0 m

All times are local (unless otherwise noted)


UFO adherent claims new volcano in Sea of Marmara

Following the Ms 7.8 earthquake in Turkey on 17 August (BGVN 24:08) an Email message originating in Turkey was circulated, claiming that volcanic activity was observed coincident with the earthquake and suggesting a new (magmatic) volcano in the Sea of Marmara. For reasons outlined below, and in the absence of further evidence, editors of the Bulletin consider this a false report.

The report stated that fishermen near the village of Cinarcik, at the E end of the Sea of Marmara "saw the sea turned red with fireballs" shortly after the onset of the earthquake. They later found dead fish that appeared "fried." Their nets were "burned" while under water and contained samples of rocks alleged to look "magmatic."

No samples of the fish were preserved. A tectonic scientist in Istanbul speculated that hot water released by the earthquake from the many hot springs along the coast in that area may have killed some fish (although they would be boiled rather than fried).

The phenomenon called earthquake lights could explain the "fireballs" reportedly seen by the fishermen. Such effects have been reasonably established associated with large earthquakes, although their origin remains poorly understood. In addition to deformation-triggered piezoelectric effects, earthquake lights have sometimes been explained as due to the release of methane gas in areas of mass wasting (even under water). Omlin and others (1999), for example, found gas hydrate and methane releases associated with mud volcanoes in coastal submarine environments.

The astronomer and author Thomas Gold (Gold, 1998) has a website (Gold, 2000) where he presents a series of alleged quotes from witnesses of earthquakes. We include three such quotes here (along with Gold's dates, attributions, and other comments):

(A) Lima, 30 March 1828. "Water in the bay 'hissed as if hot iron was immersed in it,' bubbles and dead fish rose to the surface, and the anchor chain of HMS Volage was partially fused while lying in the mud on the bottom." (Attributed to Bagnold, 1829; the anchor chain is reported to be on display in the London Navy Museum.)

(B) Romania, 10 November 1940. ". . . a thick layer like a translucid gas above the surface of the soil . . . irregular gas fires . . . flames in rhythm with the movements of the soil . . . flashes like lightning from the floor to the summit of Mt Tampa . . . flames issuing from rocks, which crumbled, with flashes also issuing from non-wooded mountainsides." (Phrases used in eyewitness accounts collected by Demetrescu and Petrescu, 1941).

(C) Sungpan-Pingwu (China), 16, 22, and 23 August 1976. "From March of 1976, various large anomalies were observed over a broad region. . . . At the Wanchia commune of Chungching County, outbursts of natural gas from rock fissures ignited and were difficult to extinguish even by dumping dirt over the fissures. . . . Chu Chieh Cho, of the Provincial Seismological Bureau, related personally seeing a fireball 75 km from the epicenter on the night of 21 July while in the company of three professional seismologists."

Yalciner and others (1999) made a study of coastal areas along the Sea of Marmara after the Izmet earthquake. They found evidence for one or more tsunamis with maximum runups of 2.0-2.5 m. Preliminary modeling of the earthquake's response failed to reproduce the observed runups; the areas of maximum runup instead appeared to correspond most closely with several local mass-failure events. This observation together with the magnitude of the earthquake, and bottom soundings from marine geophysical teams, suggested mass wasting may have been fairly common on the floor of the Sea of Marmara.

Despite a wide range of poorly understood, dramatic processes associated with earthquakes (Izmet 1999 apparently included), there remains little evidence for volcanism around the time of the earthquake. The nearest Holocene volcano lies ~200 km SW of the report location. Neither Turkish geologists nor scientists from other countries in Turkey to study the 17 August earthquake reported any volcanism. The report said the fisherman found "magmatic" rocks; it is unlikely they would be familiar with this term.

The motivation and credibility of the report's originator, Erol Erkmen, are unknown. Certainly, the difficulty in translating from Turkish to English may have caused some problems in understanding. Erkmen is associated with a website devoted to reporting UFO activity in Turkey. Photographs of a "magmatic rock" sample were sent to the Bulletin, but they only showed dark rocks photographed devoid of a scale on a featureless background. The rocks shown did not appear to be vesicular or glassy. What was most significant to Bulletin editors was the report author's progressive reluctance to provide samples or encourage follow-up investigation with local scientists. Without the collaboration of trained scientists on the scene this report cannot be validated.

References. Omlin, A, Damm, E., Mienert, J., and Lukas, D., 1999, In-situ detection of methane releases adjacent to gas hydrate fields on the Norwegian margin: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Yalciner, A.C., Borrero, J., Kukano, U., Watts, P., Synolakis, C. E., and Imamura, F., 1999, Field survey of 1999 Izmit tsunami and modeling effort of new tsunami generation mechanism: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Gold, T., 1998, The deep hot biosphere: Springer Verlag, 256 p., ISBN: 0387985468.

Gold, T., 2000, Eye-witness accounts of several major earthquakes (URL: http://www.people.cornell.edu/ pages/tg21/eyewit.html).

Information Contacts: Erol Erkmen, Tuvpo Project Alp.


Har-Togoo (Mongolia) — May 2003

Har-Togoo

Mongolia

48.831°N, 101.626°E; summit elev. 1675 m

All times are local (unless otherwise noted)


Fumaroles and minor seismicity since October 2002

In December 2002 information appeared in Mongolian and Russian newspapers and on national TV that a volcano in Central Mongolia, the Har-Togoo volcano, was producing white vapors and constant acoustic noise. Because of the potential hazard posed to two nearby settlements, mainly with regard to potential blocking of rivers, the Director of the Research Center of Astronomy and Geophysics of the Mongolian Academy of Sciences, Dr. Bekhtur, organized a scientific expedition to the volcano on 19-20 March 2003. The scientific team also included M. Ulziibat, seismologist from the same Research Center, M. Ganzorig, the Director of the Institute of Informatics, and A. Ivanov from the Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences.

Geological setting. The Miocene Har-Togoo shield volcano is situated on top of a vast volcanic plateau (figure 1). The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Pliocene and Quaternary volcanic rocks are also abundant in the vicinity of the Holocene volcanoes (Devyatkin and Smelov, 1979; Logatchev and others, 1982). Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Figure (see Caption) Figure 1. Photograph of the Har-Togoo volcano viewed from west, March 2003. Courtesy of Alexei Ivanov.

Observations during March 2003. The name of the volcano in the Mongolian language means "black-pot" and through questioning of the local inhabitants, it was learned that there is a local myth that a dragon lived in the volcano. The local inhabitants also mentioned that marmots, previously abundant in the area, began to migrate westwards five years ago; they are now practically absent from the area.

Acoustic noise and venting of colorless warm gas from a small hole near the summit were noticed in October 2002 by local residents. In December 2002, while snow lay on the ground, the hole was clearly visible to local visitors, and a second hole could be seen a few meters away; it is unclear whether or not white vapors were noticed on this occasion. During the inspection in March 2003 a third hole was seen. The second hole is located within a 3 x 3 m outcrop of cinder and pumice (figure 2) whereas the first and the third holes are located within massive basalts. When close to the holes, constant noise resembled a rapid river heard from afar. The second hole was covered with plastic sheeting fixed at the margins, but the plastic was blown off within 2-3 seconds. Gas from the second hole was sampled in a mechanically pumped glass sampler. Analysis by gas chromatography, performed a week later at the Institute of the Earth's Crust, showed that nitrogen and atmospheric air were the major constituents.

Figure (see Caption) Figure 2. Photograph of the second hole sampled at Har-Togoo, with hammer for scale, March 2003. Courtesy of Alexei Ivanov.

The temperature of the gas at the first, second, and third holes was +1.1, +1.4, and +2.7°C, respectively, while air temperature was -4.6 to -4.7°C (measured on 19 March 2003). Repeated measurements of the temperatures on the next day gave values of +1.1, +0.8, and -6.0°C at the first, second, and third holes, respectively. Air temperature was -9.4°C. To avoid bias due to direct heating from sunlight the measurements were performed under shadow. All measurements were done with Chechtemp2 digital thermometer with precision of ± 0.1°C and accuracy ± 0.3°C.

Inside the mouth of the first hole was 4-10-cm-thick ice with suspended gas bubbles (figure 5). The ice and snow were sampled in plastic bottles, melted, and tested for pH and Eh with digital meters. The pH-meter was calibrated by Horiba Ltd (Kyoto, Japan) standard solutions 4 and 7. Water from melted ice appeared to be slightly acidic (pH 6.52) in comparison to water of melted snow (pH 7.04). Both pH values were within neutral solution values. No prominent difference in Eh (108 and 117 for ice and snow, respectively) was revealed.

Two digital short-period three-component stations were installed on top of Har-Togoo, one 50 m from the degassing holes and one in a remote area on basement rocks, for monitoring during 19-20 March 2003. Every hour 1-3 microseismic events with magnitude <2 were recorded. All seismic events were virtually identical and resembled A-type volcano-tectonic earthquakes (figure 6). Arrival difference between S and P waves were around 0.06-0.3 seconds for the Har-Togoo station and 0.1-1.5 seconds for the remote station. Assuming that the Har-Togoo station was located in the epicentral zone, the events were located at ~1-3 km depth. Seismic episodes similar to volcanic tremors were also recorded (figure 3).

Figure (see Caption) Figure 3. Examples of an A-type volcano-tectonic earthquake and volcanic tremor episodes recorded at the Har-Togoo station on 19 March 2003. Courtesy of Alexei Ivanov.

Conclusions. The abnormal thermal and seismic activities could be the result of either hydrothermal or volcanic processes. This activity could have started in the fall of 2002 when they were directly observed for the first time, or possibly up to five years earlier when marmots started migrating from the area. Further studies are planned to investigate the cause of the fumarolic and seismic activities.

At the end of a second visit in early July, gas venting had stopped, but seismicity was continuing. In August there will be a workshop on Russian-Mongolian cooperation between Institutions of the Russian and Mongolian Academies of Sciences (held in Ulan-Bator, Mongolia), where the work being done on this volcano will be presented.

References. Devyatkin, E.V. and Smelov, S.B., 1979, Position of basalts in sequence of Cenozoic sediments of Mongolia: Izvestiya USSR Academy of Sciences, geological series, no. 1, p. 16-29. (In Russian).

Logatchev, N.A., Devyatkin, E.V., Malaeva, E.M., and others, 1982, Cenozoic deposits of Taryat basin and Chulutu river valley (Central Hangai): Izvestiya USSR Academy of Sciences, geological series, no. 8, p. 76-86. (In Russian).

Geologic Background. The Miocene Har-Togoo shield volcano, also known as Togoo Tologoy, is situated on top of a vast volcanic plateau. The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Information Contacts: Alexei V. Ivanov, Institute of the Earth Crust SB, Russian Academy of Sciences, Irkutsk, Russia; Bekhtur andM. Ulziibat, Research Center of Astronomy and Geophysics, Mongolian Academy of Sciences, Ulan-Bator, Mongolia; M. Ganzorig, Institute of Informatics MAS, Ulan-Bator, Mongolia.


Elgon (Uganda) — December 2005

Elgon

Uganda

1.136°N, 34.559°E; summit elev. 3885 m

All times are local (unless otherwise noted)


False report of activity; confusion caused by burning dung in a lava tube

An eruption at Mount Elgon was mistakenly inferred when fumes escaped from this otherwise quiet volcano. The fumes were eventually traced to dung burning in a lava-tube cave. The cave is home to, or visited by, wildlife ranging from bats to elephants. Mt. Elgon (Ol Doinyo Ilgoon) is a stratovolcano on the SW margin of a 13 x 16 km caldera that straddles the Uganda-Kenya border 140 km NE of the N shore of Lake Victoria. No eruptions are known in the historical record or in the Holocene.

On 7 September 2004 the web site of the Kenyan newspaper The Daily Nation reported that villagers sighted and smelled noxious fumes from a cave on the flank of Mt. Elgon during August 2005. The villagers' concerns were taken quite seriously by both nations, to the extent that evacuation of nearby villages was considered.

The Daily Nation article added that shortly after the villagers' reports, Moses Masibo, Kenya's Western Province geology officer visited the cave, confirmed the villagers observations, and added that the temperature in the cave was 170°C. He recommended that nearby villagers move to safer locations. Masibo and Silas Simiyu of KenGens geothermal department collected ashes from the cave for testing.

Gerald Ernst reported on 19 September 2004 that he spoke with two local geologists involved with the Elgon crisis from the Geology Department of the University of Nairobi (Jiromo campus): Professor Nyambok and Zacharia Kuria (the former is a senior scientist who was unable to go in the field; the latter is a junior scientist who visited the site). According to Ernst their interpretation is that somebody set fire to bat guano in one of the caves. The fire was intense and probably explains the vigorous fuming, high temperatures, and suffocated animals. The event was also accompanied by emissions of gases with an ammonia odor. Ernst noted that this was not surprising considering the high nitrogen content of guano—ammonia is highly toxic and can also explain the animal deaths. The intense fumes initially caused substantial panic in the area.

It was Ernst's understanding that the authorities ordered evacuations while awaiting a report from local scientists, but that people returned before the report reached the authorities. The fire presumably prompted the response of local authorities who then urged the University geologists to analyze the situation. By the time geologists arrived, the fuming had ceased, or nearly so. The residue left by the fire and other observations led them to conclude that nothing remotely related to a volcanic eruption had occurred.

However, the incident emphasized the problem due to lack of a seismic station to monitor tectonic activity related to a local triple junction associated with the rift valley or volcanic seismicity. In response, one seismic station was moved from S Kenya to the area of Mt. Elgon so that local seismicity can be monitored in the future.

Information Contacts: Gerald Ernst, Univ. of Ghent, Krijgslaan 281/S8, B-9000, Belgium; Chris Newhall, USGS, Univ. of Washington, Dept. of Earth & Space Sciences, Box 351310, Seattle, WA 98195-1310, USA; The Daily Nation (URL: http://www.nationmedia.com/dailynation/); Uganda Tourist Board (URL: http://www.visituganda.com/).