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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 22, Number 11 (November 1997)

Managing Editor: Richard Wunderman

Ambrym (Vanuatu)

August visit reveals lava fountains, Strombolian explosions

Arenal (Costa Rica)

January-November tremor and earthquakes

Asosan (Japan)

Two tourists killed by volcanic gas on 23 November

Atmospheric Effects (1995-2001) (Unknown)

Volcanic aerosol optical thicknesses since 1960

Avachinsky (Russia)

Fumarolic plume on 22 December

Bezymianny (Russia)

Explosive eruption on 5 December

Campi Flegrei (Italy)

Increase in sulfate concentrations and fumarole temperatures

Chiginagak (United States)

Increased fumarolic activity in late October

Karymsky (Russia)

Low-level Strombolian activity continues

Kilauea (United States)

Bench collapse and pit formation; lava flows continue to reach the coast

Klyuchevskoy (Russia)

Elevated seismicity during 13 October-1 December; gas-and-steam plumes

Koryaksky (Russia)

Above-background seismicity in late December

Langila (Papua New Guinea)

Increased eruptive activity at Crater 2

Long Valley (United States)

Summary of 1996 activity

Manam (Papua New Guinea)

Moderate explosions in late November

Monowai (New Zealand)

Inferred eruption during 15-18 December

Poas (Costa Rica)

June-November earthquakes; thermally stable fumaroles

Popocatepetl (Mexico)

Low activity through November; lava extrusion and explosion in December

Rabaul (Papua New Guinea)

Slow ongoing inflation

Sheveluch (Russia)

Normal seismicity and fumarolic activity

Soufriere Hills (United Kingdom)

Explosions and dome growth

Vulcano (Italy)

Trends in fumarolic gas composition during 1996-97

Yasur (Vanuatu)

Strombolian eruptions; decreasing seismic activity since March 1997



Ambrym (Vanuatu) — November 1997 Citation iconCite this Report

Ambrym

Vanuatu

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

All times are local (unless otherwise noted)


August visit reveals lava fountains, Strombolian explosions

During 5-13 August 1997, a team from the Société de Volcanologie Genève (SVG) observed Ambrym caldera and deployed an infrared (1.55 µm wavelength) optical pyrometer (Optix-G, Keller GMBH., Ibbenburen-Lagenbeck). Temperatures of lavas were estimated from the pyrometer by measuring emissivity factors of lavas heated to known temperatures in an oven. In some cases comparisons were also made with a thermocouple on the floor of Marum crater (contact the authors regarding procedures and results).

At Benbow cone, most activity, including lava fountaining, occurred inside the S part of the crater. A deep crater in the cone's N flank emitted a large amount of hot, very concentrated gas. The crater bottom was not visible; however, strong night glow revealed the proximity of magma.

At Marum cone, three different craters were active during the SVG visit. At Mbwelesu, the main crater, two closely spaced openings full of lava were visible from the rim. The lava surface was continuously overturned by fountains that were tens of meters high. The maximum temperature of the chimney opening was estimated with the optical pyrometer at 910°C. The pyrometer measurement was taken on the NNE side of the crater rim under conditions of good visibility and strong degassing.

At Niri Mbwelesu, a secondary crater close to Mbwelesu's rim, strong degassing was observed. Although the crater was often full of vapor, occasionally the bottom was visible. A small, elongated lake surrounded by fumaroles was seen in the crater near a glowing opening that was emitting pulses of hot gas; however, magma was not directly observed.

Inside Niri Mbwelesu Taten, a small collapse pit (169 x 185 m; 140 m deep) to the S of Niri Mbwelesu, Strombolian explosions were observed until 7 August. The explosions lasted a few hours, stopped, then resumed a few hours later. The explosions were caused by the bursting of magma bubbles 2-3 m in diameter as they reached the surface. The noise from the explosions could be heard a few kilometers away. Shock waves were sometimes observed in the cloud above the pit. The maximum temperature of liquid lava inside the pit was estimated with the optical pyrometer at 964°C. Pyrometer measurements were taken standing on the S border of the crater rim under conditions of good visibility. Maximum temperature estimates on liquid lava varied between ~935°C and 965°C.

In addition, the team measured rain acidity at different sites inside the caldera. A clear gradient was found: the rain had a pH of 2 on the Benbow crater rim and a pH of 4 close to the caldera's border.

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: P. Vetch and S. Haefeli, Société de Volcanologie Genève (SVG), C.P. 298, CH-1225, Chene-bourg, Switzerland.


Arenal (Costa Rica) — November 1997 Citation iconCite this Report

Arenal

Costa Rica

10.463°N, 84.703°W; summit elev. 1670 m

All times are local (unless otherwise noted)


January-November tremor and earthquakes

Seismicity for Arenal during January through November 1997 is shown on figure 83. The monthly earthquake count peaked in July at around 1,600 events, but many months had fewer than 600. Tremor reached durations of 250-300 hours during January, March, and June.

Figure (see Caption) Figure 83. Arenal's monthly earthquake count and tremor duration for the interval January-October 1997. Data were registered at station "VACR," 2.7 km NE of the main crater. Courtesy of OVSICORI-UNA

Arenal's first historical eruption, in mid-1968, began an unbroken sequence of Strombolian explosions and lava effusion from multiple vents. Since then the volcano has erupted material of basaltic-andesite composition.

Geologic Background. Conical Volcán Arenal is the youngest stratovolcano in Costa Rica and one of its most active. The 1670-m-high andesitic volcano towers above the eastern shores of Lake Arenal, which has been enlarged by a hydroelectric project. Arenal lies along a volcanic chain that has migrated to the NW from the late-Pleistocene Los Perdidos lava domes through the Pleistocene-to-Holocene Chato volcano, which contains a 500-m-wide, lake-filled summit crater. The earliest known eruptions of Arenal took place about 7000 years ago, and it was active concurrently with Cerro Chato until the activity of Chato ended about 3500 years ago. Growth of Arenal has been characterized by periodic major explosive eruptions at several-hundred-year intervals and periods of lava effusion that armor the cone. An eruptive period that began with a major explosive eruption in 1968 ended in December 2010; continuous explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows characterized the eruption from vents at the summit and on the upper western flank.

Information Contacts: E. Fernandez, R. Van der Laat, F. de Obaldia, T. Marino, V. Barboza, W. Jimenez, R. Saenz, E. Duarte, M. Martinez, E. Hernandez, and F. Vega, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.


Asosan (Japan) — November 1997 Citation iconCite this Report

Asosan

Japan

32.884°N, 131.104°E; summit elev. 1592 m

All times are local (unless otherwise noted)


Two tourists killed by volcanic gas on 23 November

Tomoki Tsutsui (Aso Volcanological Laboratory, Kyoto University) reported that a new fumarolic vent ~10 m in diameter formed on the S wall of Crater 1 in early November; later, small mounds of mud formed around the vent. Although Crater 1 had been quiet since 1993, hot greenish-gray water remained in the crater. Videos of Crater 1 taken by the Aso Volcano Museum recorded emissions of mud fragments and white fumes from the new vent, as well as a bubbling noise; other instruments detected low-level volcanic tremors.

According to news reports, inhalation of volcanic gas killed two men, aged 62 and 51 years, after they collapsed ~100 m S of Crater 1's rim at 0945 and 1040 on 23 November. Volcanic gas concentration around the crater is monitored using a sensor installed by the Japan Meteorological Agency in April 1997. Due to high levels of SO2 (~5 ppm), the Crater 1 overlook was closed on the morning of 23 November, but re-opened at 0900 when the SO2 level dropped to2 levels rose to ~8 ppm. The weather station at Aso had recorded no abnormal volcanic conditions.

Seventy-one people have been hospitalized due to inhalation of volcanic gases at Aso since 1980; of those, seven were killed. In June 1994, five junior high school students on a field trip collapsed near Crater 1.

Aso, a 24-km wide caldera, produced Pleistocene pyroclastic-flow deposits that cover much of Kyushu. Fifteen central cones form an E-W line on the caldera floor. Naka-dake, one of the intra-caldera cones, has erupted more than 165 times since 553 AD. Naka-dake has a group of craters (1.1 km long) including Crater 1 at the summit. Strombolian, phreatic, and phreatomagmatic eruptions are common in Crater 1. The 4 km2 100-m-deep Crater 1 is accessible by cable car, automobile, and on foot.

Geologic Background. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Information Contacts: Tomoki Tsutsui, Aso Volcanological Laboratory, Kyoto University, Choyo, Aso, Kumamoto, 869-1404, Japan; Volcano Research Center, Earthquake Research Institute (ERI), University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html).


Atmospheric Effects (1995-2001) (Unknown) — November 1997 Citation iconCite this Report

Atmospheric Effects (1995-2001)

Unknown

Unknown, Unknown; summit elev. m

All times are local (unless otherwise noted)


Volcanic aerosol optical thicknesses since 1960

Richard A. Keen submitted the following report. About once per year, on average, the moon is eclipsed as it passes into the earth's shadow; at these times it can be used a remote sensor of the globally averaged optical depth of stratospheric aerosols of volcanic origin. Conceptually, the linkage between volcanic aerosols and lunar eclipses is as follows: 1) The moon is visible during total lunar eclipses due to sunlight refracted into the shadow (umbra) by the earth's atmosphere (primarily the stratosphere); 2) Stratospheric aerosols reduce the transmission of sunlight into the umbra; and 3) The path length of sunlight through a stratospheric aerosol layer is ~40x the vertical thickness of the layer. Therefore, the brightness of the eclipsed moon is extremely sensitive to the amount of aerosols in the stratosphere.

Methodology and data reduction. Aerosol optical thicknesses can be calculated for the date of an eclipse from the difference between the observed brightness of the eclipse and a modeled brightness computed for an aerosol-free standard atmosphere, modified by assumed distributions of ozone and cloud. A report on this technique, applied to observations during 1960 through 1982, appeared in Keen (1983); an update following the eruption of Pinatubo was reported in February 1993 (Bulletin v. 18, no. 2).

This report updates the time series from 1960 through the lunar eclipse of 16 September 1997 (figure 4), the last total lunar eclipse until January 2001. Plotted values are actual derived optical depths, modified as described below. Due to the higher concentration of Agung and El Chichón aerosols in the southern and northern hemispheres, respectively, a sampling bias due to the moon's passing though the southern or northern portion of the umbra was removed by using an empirical adjustment factor of 0.8 (thus, if the moon passed south of the earth's shadow axis during an eclipse following Agung, the derived optical thickness was multiplied by 0.8, while the derived value was divided by 0.8 if the moon passed north of the axis).

Figure with caption Figure 4. Volcanic aerosol optical thicknesses derived from 35 total or near-total lunar eclipses during 1960-97. Courtesy of Richard Keen.

No lunar eclipses occurred until 18 months after the June 1991 Pinatubo eruption, while results from Agung and El Chichón indicate that peak optical depths occurred about 9 months after those eruptions. Therefore, for plotting purposes, the time series of optical thicknesses following Pinatubo was extrapolated backwards to a date 9 months after the eruption using a composite decay curve derived from the Agung and El Chichón data. Finally, the global optical depths were set to zero on the dates of the eruptions of Agung, Fuego, and Pinatubo; observed values were near zero for eclipses close to the eruption dates of Fernandina and El Chichón.

Time series. The volcanic eruptions probably responsible for the major peaks in the time series are identified, although the correlation of Fernandina with the 1968 peak is highly uncertain. Comparative maximum global optical thicknesses are: Pinatubo (1991), 0.15; Agung (1963), 0.10; El Chichón (1982), 0.09; Fernandina (1968), 0.06; Fuego (1974), 0.04. The results indicate that the volcanic aerosol veil from Pinatubo disappeared between the eclipses of November 1993 and April 1996, with optical depth probably reaching zero sometime in 1995. A slight increase to an observed value of 0.01 for the September 1997 eclipse is close to the noise level due to the uncertainty in the brightness observations; if real, it could indicate aerosols from the eruption of Soufriere Hills. Interestingly, a similarly slight increase in optical depth in 1979 may have been due to the eruption of Soufriere of St. Vincent.

Acknowledgments. Thanks are due to the following who supplied observations of the four eclipses in 1996-97: K. Hornoch and M. Plsek (Czech Republic), G. Glitscher (Germany), K. Yoshimoto (Japan), K. Al-Tell, N. Abanda, M. Odeh, S. Abdo (Jordan), R. Bouma, G. Comello, H. Feijth, and E. van Dijk (Netherlands), B. Granslo and O. Skilbrei (Norway), C. Vitorino and A. Pereira (Portugal), P. Schlyter (Sweden), R. Pickard, A. Moss, J. Shanklin, and W. Worraker (UK), and D. Green (USA).

Reference. Keen, R., 1983, Volcanic aerosols and lunar eclipses: Science, v. 222, p. 1011- 1013.

Information Contacts: Richard A. Keen, 34296 Gap Road, Golden, CO 80403 USA.


Avachinsky (Russia) — November 1997 Citation iconCite this Report

Avachinsky

Russia

53.256°N, 158.836°E; summit elev. 2717 m

All times are local (unless otherwise noted)


Fumarolic plume on 22 December

Seismicity continued at normal background levels during November 1996-December 1997. On 22 December, a fumarolic plume rose ~200 m above the crater.

Geologic Background. Avachinsky, one of Kamchatka's most active volcanoes, rises above Petropavlovsk, Kamchatka's largest city. It began to form during the middle or late Pleistocene, and is flanked to the SE by the parasitic volcano Kozelsky, which has a large crater breached to the NE. A large horseshoe-shaped caldera, breached to the SW, was created when a major debris avalanche about 30,000-40,000 years ago buried an area of about 500 km2 to the south underlying the city of Petropavlovsk. Reconstruction of the volcano took place in two stages, the first of which began about 18,000 years before present (BP), and the second 7000 years BP. Most eruptive products have been explosive, with pyroclastic flows and hot lahars being directed primarily to the SW by the breached caldera, although relatively short lava flows have been emitted. The frequent historical eruptions have been similar in style and magnitude to previous Holocene eruptions.

Information Contacts: Vladimir Kirianov, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Russia; Tom Miller, Alaska Volcano Observatory (AVO).


Bezymianny (Russia) — November 1997 Citation iconCite this Report

Bezymianny

Russia

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

All times are local (unless otherwise noted)


Explosive eruption on 5 December

An explosive eruption began on 5 December. Seismic and fumarolic activity had mainly been normal since May 1997 (BGVN 22:09). Seismicity was at background level during 13 October-2 November with normal fumarolic activity (plumes 50-100 m tall) observed during 21-26 October. During 3-9 November seismicity increased and plumes up to 1 km high were seen; the plume extended 10-15 km SSE on 8-9 November. Normal low plumes were again seen on 12, 14-15, 18, 27, and 30 November.

A growing hot spot was monitored on satellite images by Alaska Volcano Observatory (AVO) remote sensing specialists during 3-4 December. The hot spot was not accompanied by unusual activity; it was assumed to be related to small debris avalanches at the dome. Visual observations during that period indicated that a fumarolic plume rose 500 m above the volcano and extended 15-20 km SW.

An explosive eruption began at about 0630 on 5 December. No preliminary seismicity was detected; however, the eruption's onset was indicated by an abrupt increase in seismicity. By 0830, the eruption plume reached a height of 6 km and had traveled ~20 km NE. By 1200 observers in the towns of Kozyrevsky and Klyuchi reported an increase in the eruption's intensity; at 1215, the Kamchatka Volcanic Eruption Response Team (KVERT) estimated the plume height at ~9 km dispersing >50 km NE . . . . Seismicity remained elevated until 1400, but eruptive activity declined.

Several volcanic ash advisories were issued to warn aviators about the ash plume during 5-7 December. For example, an advisory at 1015 on 5 December reported an ash plume extending 15 km NE at an altitude of ~6 km. Another advisory cited a GMS infrared image taken at [0932] showing a plume 55 km wide extending NE (figure 4). [Satellite imagery at 1332 showed the plume rising to ~9-10 km; it was 63 km wide and extended 211 km E. Pilot reports later in the day estimated the ash plume at altitudes of ~12-13 km.] . . . .

Figure (see Caption) Figure 4. [Sketches showing Bezymianny's ash plume on 5 December 1997 at 0932 (2132 GMT on 4 December) and 1332 (0132 GMT) based on GMS infrared satellite imagery. Courtesy of SAB.]

. . . [Judging from] satellite imagery, activity declined during the night of 5-6 December. At 0800 on 6 December, a small steam plume with little to no ash rose ~3.5-4 km and moved ~20 km NE. By 1030 decreased eruptive activity led KVERT to downgrade the hazard status to yellow (during the eruption it was red). Local seismicity was masked by intense aftershocks following a M 7.8 earthquake off the E coast of Kamchatka during the night of 5-6 December.

On 7 December, a gas-and-steam plume rose 500 m above the volcano and extended as far as 1 km SE. A fumarolic plume on 8-9 December rose 50-100 m and extended SE. By 9 December, the hazard status had returned to green and seismicity was at background. During 15-21 December, the volcano was obscured by clouds but seismicity remained normal. A fumarolic plume on 24 December rose 50-100 m above the volcano.

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: Vladimir Kirianov, Kamchatka Volcanic Eruptions Response Team, IVGG, Piip Blvd, 9 Petropavlovsk-Kamchatskiy, 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; NOAA/NESDIS Satellite Analysis Branch (SAB), Room 401, 5200 Auth Road, Camp Spring, MD 20746, USA.


Campi Flegrei (Italy) — November 1997 Citation iconCite this Report

Campi Flegrei

Italy

40.827°N, 14.139°E; summit elev. 458 m

All times are local (unless otherwise noted)


Increase in sulfate concentrations and fumarole temperatures

Since the ground upheaval events of 1982-84, systematic geochemical surveillance has been performed at Campi Flegrei. Fumarolic gases, crater lakes, and thermal springs have been monitored; since 1984, no significant physical or chemical changes have occurred.

However, two characteristics showed a statistically significant change; the temperature in the Bocca Grande fumarole increased (figure 19) and the sulfate concentration in crater lakes and thermal springs increased sharply during 1995-97 (figure 20). These increases may have resulted from a perturbation in the area caused by increased permeability; thus the interaction of confined, hot, sulfate-rich aquifers may have increased.

Figure (see Caption) Figure 19. Temperature of Bocca Grande fumarole at Campi Flegrei during 1988-97. Courtesy of M. Martini.
Figure (see Caption) Figure 20. Sulfate concentration in crater lakes and thermal springs at Campi Flegrei, 1988-97. Courtesy of M. Martini.

Geologic Background. Campi Flegrei is a large 13-km-wide caldera on the outskirts of Naples that contains numerous phreatic tuff rings and pyroclastic cones. The caldera margins are poorly defined, and on the south lie beneath the Gulf of Pozzuoli. Episodes of dramatic uplift and subsidence within the dominantly trachytic caldera have occurred since Roman times. The earliest known eruptive products are dated 47,000 yrs BP. The caldera formed following two large explosive eruptions, the massive Campanian ignimbrite about 36,000 BP, and the over 40 km3 Neapolitan Yellow Tuff (NYT) about 15,000 BP. Following eruption of the NYT a large number of eruptions have taken place from widely scattered subaerial and submarine vents. Most activity occurred during three intervals: 15,000-9500, 8600-8200, and 4800-3800 BP. Two eruptions have occurred in historical time, one in 1158 at Solfatara and the other in 1538 that formed the Monte Nuovo cinder cone.

Information Contacts: Marino Martini, Dipartimento di Scienze della Terra, Università di Firenze, Via La Pira 4, 50125, Firenze, Italy.


Chiginagak (United States) — November 1997 Citation iconCite this Report

Chiginagak

United States

57.135°N, 156.99°W; summit elev. 2221 m

All times are local (unless otherwise noted)


Increased fumarolic activity in late October

Beginning 22 October, the Alaska Volcano Observatory (AVO) received several reports of increased steaming, snowmelt, and sulfur smells at Chiginagak volcano. Residents of the area, including the community of Pilot Point (60 km NW), noticed increased steam emissions as early as mid-summer 1997. Possible new thermal anomalies were detected on AVHRR satellite imagery in late October. According to AVO, this change in fumarolic activity may have reflected increased heat flux at the volcano.

On 30 October, observers on an AVO flight reported an enlarged area of fumarolic activity directly above previously known sites, including new fumaroles at approximately 1,920 m. However, there were no signs of recently erupted ash, large-scale melting, or mud flows. Observers at Pilot Point reported vigorous steam emissions over the following weeks. During the first week of December, persistent poor weather conditions obscured observations; however, steam was observed on 2 and 3 December. No thermal anomalies were observed on satellite images during the first week of December.

Chiginagak is not monitored by scientific instrumentation; however, satellite imagery and observers in Pilot Point provide information. In addition, Chiginagak is located in a National Wildlife Refuge; the U.S. Fish and Wildlife Service frequently overflies the area, especially when activity persists or intensifies.

Geologic Background. The symmetrical, calc-alkaline Chiginagak stratovolcano located about 15 km NW of Chiginagak Bay contains a small summit crater, which is breached to the south, and one or more summit lava domes. Satellitic lava domes occur high on the NW and SE flanks of the glacier-mantled volcano. An unglaciated lava flow and an overlying pyroclastic-flow deposit extending east from the summit are the most recent products of Chiginagak. They most likely originated from a lava dome at 1687 m on the SE flank, 1 km from the summit of the volcano, which has variably been estimated to be from 2075 to 2221 m high. Brief ash eruptions were reported in July 1971 and August 1998. Fumarolic activity occurs at 1600 m elevation on the NE flank of the volcano, and two areas of hot-spring travertine deposition are located at the NW base of the volcano near Volcano Creek.

Information Contacts: 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.


Karymsky (Russia) — November 1997 Citation iconCite this Report

Karymsky

Russia

54.049°N, 159.443°E; summit elev. 1513 m

All times are local (unless otherwise noted)


Low-level Strombolian activity continues

During 13 October-24 November seismicity remained above background level; low-level Strombolian eruptive activity that has continued since January 1996 (BGVN 21:01) consisted of gas and ash explosions occurring every 20 minutes, sending ash and steam 200-400 m above the crater. During 24 November- 29 December there was elevated seismicity and explosions every 20-30 minutes that sent ash and steam 300-400 m above the crater. On 14 December, the level of concern was downgraded to yellow from orange, indicating that the volcano's activity was less indicative of a major eruption.

Geologic Background. Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Information Contacts: Vladimir Kirianov, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry; Tom Miller, Alaska Volcano Observatory.


Kilauea (United States) — November 1997 Citation iconCite this Report

Kilauea

United States

19.421°N, 155.287°W; summit elev. 1222 m

All times are local (unless otherwise noted)


Bench collapse and pit formation; lava flows continue to reach the coast

Activity within the Pu`u `O`o crater was at a diminished level during late October-23 November 1997. Lava in the crater was visible only from the crater walls. The Pu`u `O`o vent rarely effused lava onto the crater floor during November; the magma column remained 10-20 m below the rim. Magma in the vent circulated below the crusted lava surface, where it was not visible except from the air.

Lava from the S shield continued to travel ~10 km to the coast in tubes; travel time was estimated at ~3 hours from the vent to the ocean. The eruption rate was 500,000-600,000 m3/day. Although lava continued to flow into the ocean at East Kamokuna and Waha'ula, no breakouts of lava from the tubes onto the coastal plain occurred after the 18-19 October event (BGVN 22:09).

At East Kamokuna, a bench collapse in the first week of November removed 1.9 hectares of recent deposits and created a new cliff a few meters high and ~50 m long; after the collapse, lava began building a shelf at the foot of the new cliff. Curtain-like steam plumes rose continuously from the 500-m-long edge of the lava flow. A smaller lava bench collapse (0.26 hectares) occurred on 24 November.

Sulfur dioxide emissions from Pu`u `O`o remained high during November. Although during late October the emission rate had been 1,500-2,000 metric tons/day (t/d), during November it increased to 2,800 t/d and occasionally reached 5,000 t/d. On 16 November, eastern Hawaii, especially Hawaii Volcanoes National Park, was engulfed in one of 1997's worst volcanic-smog episodes. Elevated levels of volcanic smog were detected as far away as Oahu (~330 km NW). Gentle winds from the SE pushed SO2 emissions from Kilauea's E rift zone inland, resulting in levels of airborne SO2 that exceeded Environmental Protection Agency standards; the National Park Service thus closed headquarters at the Kilauea summit for the day. On 7 December, SO2 emissions were 4,300 t/d.

Although visible activity within Pu`u `O`o crater remained diminished, visitors and nearby residents heard roaring sounds during 24 November-5 December. Tephra fell up to 10 km from the vents and included "Pele's hair" (thin strings of solidified lava ~2.5 cm in length). During 28-30 November, a particularly active period of tephra deposition occurred; the associated emission events were detected on seismic instruments near the Pu`u `O`o vent.

On 7 December the SW flank of Pu`u `O`o cone collapsed, creating a funnel-shaped pit ~50 m in diameter at the surface midway between the S base and rim. A small glowing hole on the floor of the pit revealed that the pit intersected the magma supply system underlying the cone and flank vents. The new collapse pit resembled the Great Pit that formed on the cone's W slope in early 1993 (BGVN 18:02 and 18:03); the Great Pit later enlarged, causing the cone's W wall to collapse in January 1997 (BGVN 22:01). Pits of this type form when Pu`u `O`o is undermined by magma feeding the on-going eruption.

Lava output inside Pu`u `O`o crater visibly increased during 7-8 December; flows from the crater vent filled the crater's E side. The increased activity may have been related to the formation of the new collapse pit.

Kilauea is one of five coalescing volcanoes that comprise the island of Hawaii. Historically its eruptions originated primarily from the summit caldera or along one of the lengthy E and SW rift zones that extend from the summit caldera to the sea. This latest Kilauea eruption began in January 1983 along the E rift zone. The eruption's early phases, or episodes, occurred along a portion of the rift zone that extends from Napau Crater on the uprift end to ~8 km E on the downrift end. Activity eventually centered on what was later named Pu`u `O`o. Between January 1983 and December 1996 the volume of erupted lava totaled ~1.45 km3.

Geologic Background. Kilauea, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 km2, destroying nearly 200 houses and adding new coastline to the island.

Information Contacts: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawaii Volcanoes National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/observatories/hvo/); Ken Rubin and Mike Garcia, Hawaii Center for Volcanology, University of Hawaii, Dept. of Geology & Geophysics, 2525 Correa Rd., Honolulu, HI 96822 USA (URL: http://www.soest.hawaii.edu/GG/hcv.html).


Klyuchevskoy (Russia) — November 1997 Citation iconCite this Report

Klyuchevskoy

Russia

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

All times are local (unless otherwise noted)


Elevated seismicity during 13 October-1 December; gas-and-steam plumes

During 13 October-29 December, seismicity under Kliuchevskoi was above background level. During 13 October- 2 November the activity occurred at depths of 20-30 km, but during 3-16 November, hypocenters were concentrated both near the summit crater and at depths of 25-30 km. Volcanic tremor recorded on 10-16 November was followed by tremor under the volcano and earthquake hypocenters 25-30 km deep during 17 November-14 December.

Gas-and-steam plumes rose 100 m above the crater on 18, 25, and 30 October, and on 1-2, 17-18, 23, and 28 November. A gas-and-steam plume rose 70 m above the summit crater on 6-7 November; by 8 November the plume rose 1 km above the crater and extended 5 km NW. By 9 November, the plume returned to a more typical height of 50-100 m. On 11-12 and 14-16 November, gas-and-steam plumes rose 100-200 m. During 2-6 December a gas-and- steam plume rose 300-1,000 m and extended 5-10 km SE to SW. On 7 December, a fumarolic plume rose less than 300 m above the summit crater. A gas-and-steam plume rose 300-700 m above the summit crater and extended 3-10 km NE and SW on 8-9 and 12 December. On 23, 24, and 28 December, a gas- and-steam plume rose 100-300 m and extended 3-5 km SE to SW. A fumarolic plume rose 2 km above the volcano on 25 December.

The level of concern was upgraded to yellow from green during 3-16 November, indicating that normal activity could possibly change into an eruption. During 17-23 November, although seismicity continued above background, the level of concern returned to green. On 1 December, the level of concern was again upgraded to yellow but returned to green as of 15 December.

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: Vladimir Kirianov, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk- Kamchatskiy 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.


Koryaksky (Russia) — November 1997 Citation iconCite this Report

Koryaksky

Russia

53.321°N, 158.712°E; summit elev. 3430 m

All times are local (unless otherwise noted)


Above-background seismicity in late December

Seismicity was at normal background levels from September 1996 through mid-December 1997; the period of normal activity began in July 1996 (BGVN 21:09). However, during 22-29 December, seismicity was reported above background level.

Geologic Background. The large symmetrical Koryaksky stratovolcano is the most prominent landmark of the NW-trending Avachinskaya volcano group, which towers above Kamchatka's largest city, Petropavlovsk. Erosion has produced a ribbed surface on the eastern flanks of the 3430-m-high volcano; the youngest lava flows are found on the upper W flank and below SE-flank cinder cones. Extensive Holocene lava fields on the western flank were primarily fed by summit vents; those on the SW flank originated from flank vents. Lahars associated with a period of lava effusion from south- and SW-flank fissure vents about 3900-3500 years ago reached Avacha Bay. Only a few moderate explosive eruptions have occurred during historical time, but no strong explosive eruptions have been documented during the Holocene. Koryaksky's first historical eruption, in 1895, also produced a lava flow.

Information Contacts: Vladimir Kirianov, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk- Kamchatskiy 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.


Langila (Papua New Guinea) — November 1997 Citation iconCite this Report

Langila

Papua New Guinea

5.525°S, 148.42°E; summit elev. 1330 m

All times are local (unless otherwise noted)


Increased eruptive activity at Crater 2

Since 20 October, increased activity was noticeable at Crater 2; emissions were thicker, occasional roaring or rumbling sounds were heard, and Vulcanian explosions produced dark black clouds that rose ~2 km above the crater. Occasional loud Vulcanian activity occurred throughout November. A bright fluctuating glow and occasional incandescent projections were visible during 15-25 November. Weak fumarolic vapor was released from Crater 3. Seismic levels remained moderate.

Geologic Background. Langila, one of the most active volcanoes of New Britain, consists of a group of four small overlapping composite basaltic-andesitic cones on the lower eastern flank of the extinct Talawe volcano. Talawe is the highest volcano in the Cape Gloucester area of NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE; Langila volcano was constructed NE of the breached crater of Talawe. An extensive lava field reaches the coast on the north and NE sides of Langila. Frequent mild-to-moderate explosive eruptions, sometimes accompanied by lava flows, have been recorded since the 19th century from three active craters at the summit of Langila. The youngest and smallest crater (no. 3 crater) was formed in 1960 and has a diameter of 150 m.

Information Contacts: Patrice de Saint-Ours, RVO.


Long Valley (United States) — November 1997 Citation iconCite this Report

Long Valley

United States

37.7°N, 118.87°W; summit elev. 3390 m

All times are local (unless otherwise noted)


Summary of 1996 activity

This report summarizes 1996 activity (Hill, 1996). More recent activity will be presented in subsequent reports.

During early 1996, a series of small earthquake swarms occurred in the S moat of the caldera between Convict Lake moraine and the SE margin of the resurgent dome. Swarm activity in the area gradually increased in intensity during February-March 1996, culminating with an earthquake swarm during 29 March-10 April, the most energetic in the caldera since January 1983 (SEAN 07:12); the swarm included 24 earthquakes of M 3 or greater. On 30 March two M 4.0 events occurred; on 1 April there was a M 4.1 event, the largest in the sequence. Altogether the swarm included over 1,600 locatable earthquakes (M >0.5) and had a cumulative seismic moment of ~5 x 1022 dyne-cm, the equivalent of a single M 4.8 earthquake. Instruments showed no unusual ground deformation associated with the swarm.

Earthquake activity within the caldera gradually slowed following the 29 March-10 April swarm through the remainder of April and May. Activity increased again in June with four bursts of seismicity at 5-day intervals during 9-25 June. Swarms on 9, 14, and 25 June were located near the SW margin of the resurgent dome (figure 19), near the junction of Highways 203 and 395; the swarm on 19-20 June was located at the SE margin of the resurgent dome (~2 km N of the airport). The largest earthquakes in these swarms were a M 2.6 event on 9 June, M 3.2 and M 3.5 events on 14 June, and a M 3.3 event on 19 June. The long-base tiltmeter, centered 1 km SE of the 19-20 June swarm, showed a 0.3 µrad tilt down to the NW coincident with that swarm.

Figure (see Caption) Figure 19. Earthquake epicenters in the Long Valley region during 1996. Courtesy of USGS.

Small earthquake swarms on 30 July, and 7 and 9 August, were the last to occur within the caldera for the remainder of 1996; all were located near the SW margin of the resurgent dome. The caldera was relatively quiet during the last half of 1996 (figure 20), producing only occasional small earthquakes, all less than M 3.

Figure (see Caption) Figure 20. Daily number of earthquakes (M > 1.0) measured in 1996 at Long Valley Caldera. Courtesy of the USGS.

Occasional long-period volcanic earthquakes continued to occur during 1996 at depths of 10-20 km beneath the Devils Postpile area SW of Mammoth Mountain. These events have become more frequent since their 1989 onset during a swarm beneath Mammoth Mountain (SEAN14:06).  Minor volcano- tectonic earthquake activity in the shallow crust (<10 km depth) beneath Mammoth Mountain showed no significant change in rate or spatial distribution since 1989.

Long-term uplift and extensional deformation of the resurgent dome gradually slowed through the last half of 1996; this was defined by 2-color geodimeter measurements. The decrease in the resurgent dome's deformation rate and intra-caldera earthquake activity during the last half of 1996 was similar to the relative seismic quiescence and low deformation rates during 1984 to mid-1989. Continuous deformation monitoring showed no significant changes during 1996, with the exception of the 0.3 µrad tilt accompanying the 19-20 June earthquake swarm.

Dominant variations in carbon dioxide soil-gas concentrations in the tree-kill areas around Mammoth Mountain reflected the blanketing effect of snow during the winter months. Continuous CO2 monitors at Horseshoe Lake showed increased concentrations from early February through the end of April. Concentrations gradually returned to minimum values by mid-summer. The areas showing evidence of high CO2 soil-gas concentrations around the flank of Mammoth Mountain changed relatively slowly since 1991. In the late summer of 1995, there were seven areas of CO2-induced tree-kill scattered around the S, W, and N flanks of the mountain covering ~150 acres. A series of small collapse pits extending from the S-most tree-kill area at Horseshoe Lake merged with a crack in the bottom of Horseshoe Lake that was first detected in late September. Whether this system of shallow fractures is related to the anomalously high CO2 soil-gas concentration in the adjacent Horseshoe Lake tree-kill area has not been determined; however, the fracture system explained Horseshoe Lake's tendency to drain internally. A survey around Horseshoe Lake was planned in order to determine if the fracture system was associated with local deformation.

The 17 x 32 km Long Valley caldera lies E of the central Sierra Nevada, ~320 km E of San Francisco. The caldera formed ~730,000 years ago as a result of the Bishop Tuff eruption. Resurgent doming was followed by eruptions of rhyolite from the caldera moat and rhyodacite from the outer ring-fracture vents until ~50,000 years ago. Since then the caldera has remained thermally active, and in recent years has undergone significant deformation. Although distinct from Long Valley Caldera, both Inyo Craters and Mammoth Mountain are adjacent to it.

Reference. Hill, David P., 1996, Long Valley Caldera monitoring report (October- December 1996): U.S. Geological Survey, Volcano Hazards Program.

Geologic Background. The large 17 x 32 km Long Valley caldera east of the central Sierra Nevada Range formed as a result of the voluminous Bishop Tuff eruption about 760,000 years ago. Resurgent doming in the central part of the caldera occurred shortly afterwards, followed by rhyolitic eruptions from the caldera moat and the eruption of rhyodacite from outer ring fracture vents, ending about 50,000 years ago. During early resurgent doming the caldera was filled with a large lake that left strandlines on the caldera walls and the resurgent dome island; the lake eventually drained through the Owens River Gorge. The caldera remains thermally active, with many hot springs and fumaroles, and has had significant deformation, seismicity, and other unrest in recent years. The late-Pleistocene to Holocene Inyo Craters cut the NW topographic rim of the caldera, and along with Mammoth Mountain on the SW topographic rim, are west of the structural caldera and are chemically and tectonically distinct from the Long Valley magmatic system.

Information Contacts: David Hill, U.S. Geological Survey, MS 977, 345 Middlefield Rd., Menlo Park, CA 94025 USA (URL: https://volcanoes.usgs.gov/observatories/calvo/).


Manam (Papua New Guinea) — November 1997 Citation iconCite this Report

Manam

Papua New Guinea

4.08°S, 145.037°E; summit elev. 1807 m

All times are local (unless otherwise noted)


Moderate explosions in late November

Moderate activity dominated during November except for the last week, when Vulcanian explosions occurred at Main Crater. The mild level of activity at Main Crater that began in late August continued until mid- November. Beginning on 23 November, the crater released thicker white and gray emissions. Moderate Vulcanian explosions (~700 m above the crater) started on 27 November and produced fine ashfalls. South Crater noiselessly and gently released thin to thick white vapor; a weak steady glow was visible on most nights during November.

Instrumental observation revealed no significant change in seismicity (~1,200 to 1,400 low-frequency events/day of small amplitude). Steady radial inflation of 1 µrad was detected at the Tabele observatory (4 km SW).

Geologic Background. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical 1807-m-high basaltic-andesitic stratovolcano to its lower flanks. These "avalanche valleys" channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island's shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most historical eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent historical eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Information Contacts: Patrice de Saint-Ours, RVO.


Monowai (New Zealand) — November 1997 Citation iconCite this Report

Monowai

New Zealand

25.887°S, 177.188°W; summit elev. -132 m

All times are local (unless otherwise noted)


Inferred eruption during 15-18 December

A cluster of high-amplitude acoustic signals from Monowai was recorded during 15-17 December (figure 4). During the activity, 171 acoustic waves of varying duration were recorded. Of the waves, nine were interpreted as explosive, determined according to seismic signal characteristics. The explosive waves occurred during the first episode of heightened activity on 15 December. The signals indicated that an eruptive event stronger than those of September 1996 (BGVN 21:11) and April 1997 (BGVN 22:05) was occurring. However, infrared and visible GOES-9 imagery showed no evidence of near-surface activity.

Figure (see Caption) Figure 4. Acoustic signals from Monowai Seamount during 13-18 December. Courtesy of O. Hyvernaud.

Three small acoustic waves on 12 and 14 December preceded the heightened activity. The first high- amplitude acoustic wave was generated at 2330 GMT on 14 December; the last was generated at 2021 GMT on 17 December. The acoustic activity stopped suddenly after a sequence of weak, very long acoustic waves. The strongest wave, generated at 0021 GMT on 16 December, had a peak-to-peak amplitude of 0.46 mm/s but was not explosive.

Monowai Seamount lies midway between the Kermadec and Tonga Islands, ~1,400 km NE of New Zealand. The adjacent trench is significantly shallower (~4 km) than the Tonga and Kermadec trenches (9-11 km deep). A T-wave swarm was detected in November 1995 (BGVN 20:11/12). Other noteworthy recent activity at Monowai included a possible eruption in 1944, and about seven documented eruptions during 1977-90 (BGVN 16:03).

Geologic Background. Monowai, also known as Orion seamount, rises to within 100 m of the sea surface about halfway between the Kermadec and Tonga island groups. The volcano lies at the southern end of the Tonga Ridge and is slightly offset from the Kermadec volcanoes. Small parasitic cones occur on the N and W flanks of the basaltic submarine volcano, which rises from a depth of about 1500 m and was named for one of the New Zealand Navy bathymetric survey ships that documented its morphology. A large 8.5 x 11 km wide submarine caldera with a depth of more than 1500 m lies to the NNE. Numerous eruptions from Monowai have been detected from submarine acoustic signals since it was first recognized as a volcano in 1977. A shoal that had been reported in 1944 may have been a pumice raft or water disturbance due to degassing. Surface observations have included water discoloration, vigorous gas bubbling, and areas of upwelling water, sometimes accompanied by rumbling noises.

Information Contacts: Olivier Hyvernaud, BP 640, Laboratoire de Geophysique, Papeete, Tahiti, French Polynesia.


Poas (Costa Rica) — November 1997 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


June-November earthquakes; thermally stable fumaroles

This report focuses on June-November 1997 but includes histograms of monthly earthquake counts for the period January-November (figures 65 and 66). On these plots, earthquakes are grouped into three frequencies. ... Tremor was absent at Poás during November 1996 through October 1997; during November 1997 tremor prevailed for 22 hours. The previous high was in October 1996 (28 hours).

Figure (see Caption) Figure 65. Monthly count of low-frequency earthquakes (
Figure (see Caption) Figure 66. Monthly counts of medium- and high-frequency earthquakes detected at Poás during January-November 1997. Courtesy of OVSICORI-UNA.

Compared to its level in May, the lake surface in the northernmost crater rose during June-November. The greenish-turquoise lake's temperatures were as follows: June, 32°C; July, 31°C; September, 35°C; October, 34°C; November, 35°C. Deformation measurements in June disclosed no significant change.

During June-November a fumarole on the N terrace had a temperature of 91-92°C; sulfur was deposited at this fumarole even though gas emissions appeared low. During June-July, and again in October, colorless gas columns were conspicuous above the pyroclastic cone in the crater's center; the columns rose 300 m above the crater floor. Later, during September and November, these columns rose ~400 m. During June-September, escaping steam made a loud noise that was audible from the crater rim; during June-November, at a point where scientists could gain access, the steam's temperature remained at 92-93°C.

Geologic Background. The broad, well-vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Information Contacts: E. Fernandez, R. Van der Laat, F. de Obaldia, T. Marino, V. Barboza, W. Jimenez, R. Saenz, E. Duarte, M. Martinez, E. Hernandez, and F. Vega, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA).


Popocatepetl (Mexico) — November 1997 Citation iconCite this Report

Popocatepetl

Mexico

19.023°N, 98.622°W; summit elev. 5393 m

All times are local (unless otherwise noted)


Low activity through November; lava extrusion and explosion in December

Low levels of eruptive and seismic activity characterized Popocatépetl through most of November. Typically, a few events occurred each day, including short episodes of low-amplitude harmonic tremor and gas- and-steam venting in plumes that drifted to the NE or SE. Tiltmeters showed little variation in November but indicated a slight increasing trend. Bad weather and poor visibility occurred frequently.

Table 9 lists type-A seismic events recorded during November. Two episodes of harmonic tremor were recorded on 1 November. A 2 November lightning strike disabled video monitoring until the 5th. Poor weather impeded observation on 11-12 November during a slight increase in activity. On 15 November, a slight increase in the number of events was accompanied by minor ash emission. Some ash was also emitted in conjunction with seismic events on 21 November.

Table 9. Type-A seismic events recorded at Popocatépetl in November 1997. Courtesy of CENAPRED.

Date Time Magnitude Depth (km) Flank
01 Nov 1997 0250 2.0 4.0 --
01 Nov 1997 0311 2.1 10.2 NE
01 Nov 1997 1849 2.8 6.1 SE
02 Nov 1997 1600 2.1 2.8 S
04 Nov 1997 0019 2.1 5.4 SE
04 Nov 1997 0036 2.2 5.5 --
05 Nov 1997 1538 1.9 6.0 NE
06 Nov 1997 0001 2.5 5.5 --
08 Nov 1997 1255 1.7 6.6 --
10 Nov 1997 1420 2.2 6.6 NE
22 Nov 1997 2204 2.3 2.1 SE
25 Nov 1997 0457 2.4 4.9 --
25 Nov 1997 0826 2.6 5.0 --
25 Nov 1997 0837 2.4 2.4 SE
26 Nov 1997 1517 2.9 3.6 N

On 24 November, seismic and associated eruptive activity began to increase. Thirty-six low- to moderate- intensity seismic events were recorded, including significant exhalations at 0823, 0829, 0857, and 0953; during these events, ash plumes rose to 1 km and drifted NE. Low-amplitude harmonic tremor 3-5 minutes in duration occurred in the afternoon. On 25 November, 42 seismic events were recorded; some were accompanied by ash emissions and periods of tremor lasting 2-8 minutes. No significant deformation was observed. During a 25 November helicopter flight, increased gas and steam from fumaroles obstructed views of the crater and dome. By 27 November, activity was subsiding; 29 seismic events and tremor 2-3 minutes long were recorded. Levels of seismic activity continued to decline until the end of the month.

The last of several flow-detection monitoring stations (BGVN 22:10) was installed on 7 November; also, a temporary high-gain broad-band seismograph was installed at the Canario station to study the N flank in more detail. The Canario station's instrumentation included a triaxial short-period seismograph, a triaxial broad-band seismograph, a digital inclinometer, a flow detector, and a rain gage. To reinforce the seismic and geodetic monitoring system, a new station was installed on 28 November on the W flank just under Ventorrillo peak near the Nexpayantla ravine at 4,452 m elevation. The instrumentation includes a triaxial short- period seismograph and a biaxial tiltmeter.

Two important eruption episodes highlighted activity in December. Both eruptions involved extrusion of lava into the crater, creating a dome that sealed fumaroles.

Small- and moderate-intensity emissions of gas and steam characterized activity at the volcano for most of December. Small type-A tectonic events occurred regularly along with incidents of tremor. The first increase in activity began 5 December with 15 small gas-and-steam emissions, tremor of 90 minutes duration beginning at 1335, and two type-A seismic events in the late afternoon. At 0315 on 6 December activity increased considerably and continued throughout the day. A moderately large high-frequency tremor accompanied by continuous gas, steam, and ash exhalations lasted until 1700. Early in the morning of the 6th a faint glow at the fumarole was observed through the video monitor, indicating the presence of incandescent material in the crater interior. In the late afternoon the gas emission abruptly stopped, possibly due to obstructions of the vents. Observers speculated that these phenomena indicated the extrusion of new lava in the bottom of the crater. No significant changes of the other measured parameters could be observed.

The following day saw a considerable decrease in activity: only six moderate emissions including some short ash puffs. Continuing very low emissions over several days indicated the vents were partially closed. On the morning of 9 December personnel from CENAPRED and the Instituto de Geof¡sica, UNAM, made a helicopter overflight during which the presence of a large lava dome, spread across almost over the entire crater floor, was seen. This observation confirmed the assumption of a new lava extrusion on 5-6 December. No important changes on the volcano flanks or the glacier could be observed. SO2 measurements made the afternoon of 9 December gave preliminary values of 6,100 tons/day. The other parameters that are continuously monitored showed little variation. Popocatépetl returned to characteristic low levels of activity, although some earthquakes of M 2.2 occurred at a depth of ~4.7 km during 14-15 December. On 13 December strong winds and low temperatures caused damage to monitoring equipment, including the video transmission link.

After several weeks of very low activity an eruption clearly observed from neighboring towns started at 1930 on 24 December. The activity began with a 2-minute explosion followed by 15 smaller volcano-tectonic events and several moderate emissions. According to reports from the nearby towns of San Nicolas de los Ranchos and Amecameca, during the first event observed brightness around the summit was produced by the expulsion of incandescent materials, and an associated shock wave was felt. From Puebla grass fires were reported on the E flank of the volcano. Ashfalls were reported starting at 2045 in towns E of the volcano (Atlixco, Calpan, and San Nicolas de los Ranchos). The whole episode lasted a total of 30 minutes. All monitored parameters except for seismicity then returned to normal levels. This eruption was probably associated with the reopening of conduits inside the crater, obstructed since 6 December by lava extrusion. This obstruction was carefully monitored because pressurization of the system raised the possibility of explosive events. Following the eruption of 24 December activity returned to very low, stable levels for the remainder of the month. The volcanic- alert system remained on "yellow" (caution) through all of December.

Geologic Background. Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Information Contacts: Roberto Meli, Roberto Quaas Weppen, Alejandro Mirano, Bertha López Najera, Alicia Martinez Bringas, A. Montalvo, G. Fregoso, and F. Galicia, Centro Nacional de Prevencion de Desastres (CENAPRED); J.L. Macias, Instituto de Geofisica, UNAM, Circuito Cientifico.


Rabaul (Papua New Guinea) — November 1997 Citation iconCite this Report

Rabaul

Papua New Guinea

4.271°S, 152.203°E; summit elev. 688 m

All times are local (unless otherwise noted)


Slow ongoing inflation

Slow caldera inflation continued throughout November. Weak emissions of white vapor were produced by Tavurvur cone. The volume of emissions increased at the end of the month in response to rainfall. On 26 November, weak night glow was visible and a brief rumbling sound was heard.

Slow, ongoing inflation has occurred since the last significant lava-producing eruption at Tavurvur on 14 March (BGVN 22:03), despite subsequent minor Strombolian and Vulcanian eruptions on 12 April, 1 June, 11 July, and 17 August (BGVN 22:04, 22:05, 22:07, and 22:08). The inflation mainly affected areas within ~3 km of Tavurvur and the Greet Harbour shallow magma reservoir. Maximum rates of tilt were no more than 4 µrad /month; maximum monthly uplift was no more than 1 cm.

One high-frequency event from the NW was recorded on 14 November; no low-frequency events occurred during the month. SO2 output measured by COSPEC decreased in mid-November from ~800 to ~300 tons/day. Soil CO2 flux, monitored at 14 locations around the bay, was relatively low (<=200 mg/(m2 day)).

Geologic Background. The low-lying Rabaul caldera on the tip of the Gazelle Peninsula at the NE end of New Britain forms a broad sheltered harbor utilized by what was the island's largest city prior to a major eruption in 1994. The outer flanks of the 688-m-high asymmetrical pyroclastic shield volcano are formed by thick pyroclastic-flow deposits. The 8 x 14 km caldera is widely breached on the east, where its floor is flooded by Blanche Bay and was formed about 1400 years ago. An earlier caldera-forming eruption about 7100 years ago is now considered to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the northern and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and western caldera walls. Several of these, including Vulcan cone, which was formed during a large eruption in 1878, have produced major explosive activity during historical time. A powerful explosive eruption in 1994 occurred simultaneously from Vulcan and Tavurvur volcanoes and forced the temporary abandonment of Rabaul city.

Information Contacts: Patrice de Saint-Ours, Rabaul Volcano Observatory, P.O. Box 386, Rabaul, Papua New Guinea.


Sheveluch (Russia) — November 1997 Citation iconCite this Report

Sheveluch

Russia

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

All times are local (unless otherwise noted)


Normal seismicity and fumarolic activity

Background seismicity prevailed during 13 October-29 December. Normal fumarolic activity was seen during 30 October-2 November and 6-7 November. No fumarolic activity was observed during 10 November-14 December. For the period 15-29 December, Shiveluch was usually obscured by clouds; however, on 22 December, a gas-and-steam plume rising 100 m above the volcano was seen.

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: Vladimir Kirianov, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk- Kamchatskiy 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.


Soufriere Hills (United Kingdom) — November 1997 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)


Explosions and dome growth

The following summarizes Scientific Reports of the Montserrat Volcano Observatory (MVO) during 12 October-23 November 1997.

General. During September, activity was dominated by collapses with simultaneous pyroclastic flows down ghauts (BGVN 22:10). Particular events differed in magnitude, column height, or pyroclastic runout, possibly due to time elapsed between events. During 12-21 October, 29 explosions were recorded for a total of 61 since the latest episode began on 28 September. After the last explosion on 21 October, a new dome was seen in the crater, extruding at a rate of up to 8 m3/s. The new dome grew during the following week on the S side, weakening the crater wall on the Galway's side (figure 33) and creating two large vertical cracks on the outside of the wall by 2 November. Further growth in the weakened area led to a 4 November collapse, which removed much of the pre-explosion dome complex material. A subsequent collapse on the 6th removed a significant portion of the new dome and old material. Pyroclastic flows from these collapses reached the sea and a fan deposit at the mouth of White River was significantly extended. Dome growth coincided with large swarms of hybrid earthquakes. After the 6 November collapse, the swarms subsided yet seismicity remained relatively high. Low levels of eruptive activity prevailed for the rest of November. Although bad weather limited observation of the dome, the lobe in the Galway's area was seen as the focus of growth during 9-23 November but at a slower rate. Seismicity included rockfall signals and small-amplitude hybrid earthquakes.

Figure (see Caption) Figure 33. Map of Montserrat showing selected towns and features around the Soufriere Hills volcano.

Visual observations. Vulcanian explosions up to 21 October resulted in pyroclastic flows into surrounding ghauts. Intervals between explosions averaged 8.5 hours with a range of 2.75 to 20.5 hours. During 14-16 October, 12 explosions occurred; intervals between single events lengthened towards the end of the period. Three vigorous explosions on 20-21 October sent plumes to 9,100 m, pumice to Salem and Olveston, and ash to the N. Pumice from Cork's Hill measured up to 10 cm in diameter and ballistics fell 2 km N from the vent. Pyroclastic flows were generally radial for larger explosions; however, the N ghauts were preferred routes because the crater is open to the N. Some flows had relatively small runouts (<1 km) in only one or two ghauts. Pyroclastic flows over the past month have left thin (0.3-1 m) deposits on all flanks, accumulating and infilling the topography. Fort Ghaut in Plymouth and Mosquito Ghaut were completely filled, and Tuitt's and White's Ghauts were partially filled, resulting in fans advancing into towns. Gage's Soufriere was significantly filled with material stacked in front of St. George's hill.

A new dome was first recorded as an incandescence inside the scar during the evening of 22 October. The next day, fresh lava overspilled the tephra rampart between the scar and crater and, by 25 October, occupied a substantial portion of the scar. The lava appeared to be blocky, coarse material, which, due to oxidation at the top of the conduit, is darker than normal (similar to last October; BGVN 21:10). By 25 October the dome's peak had risen to 910 m, 40 m below the crater rim. Growth to the N and vertical infilling of the scar caused rockfalls that traveled a few hundred meters down Tuitt's Ghaut; however, rockfalls were few in number considering the rate and blockiness of the extrusion as well as the steepness of the ghaut. Dome growth continued over the next few weeks with vigorous ash-and-steam venting. Rockfalls from the new dome and old crater coincided with hybrid earthquake swarms.

An overflight on 2 November revealed two large vertical cracks on the Galway's side of the crater; by the next day, these had evolved to deep gullies. Rockfalls on the dome's S side occurred on the morning of 4 November. At 1206 on 4 November, a wide section of the crater in the Galway's area collapsed and caused an hour of pyroclastic flows. Some of the flows reached the sea at O'Garra's and formed a delta. Ash clouds rose to 3000 m. The collapse removed a large part of the old dome but left the 22 October dome mostly intact. Observations on 6 November included two distinct lobes of the new dome separated by a small crater venting ash; the N lobe remained at its 2 November height of 937 m while the S lobe grew. Following 18 hours of high- amplitude tremor a second collapse in the Galway's area began at 1430 on 6 November and lasted 35 minutes. More material was removed than in the previous collapse, rockfalls occurred in Tar River valley and Gage's areas, and an ash plume reaching 4,500 m drifted W.

After a few days of poor visibility, growth of the new dome in the collapse area was revealed. A fin-shaped lobe had grown almost vertically in the old crater wall position; it had a coarse, blocky outer face but a smooth appearance on the inner surface where it extruded out of a cleft in the dome center that exhibited vigorous degassing and venting of ash. The distinct N and S lobes divided by a central cleft or vent were similar to earlier structures (BGVN 21:08 and 22:05), although in this case the N lobe extruded first to reach a certain size then relaxed while growth shifted to the S lobe; this in turn lead to a catastrophic collapse of the old crater wall. Overflight observation on 11 November showed that the S lobe had doubled in size in 3 days to fill the collapse scar of 4-6 November; however, it was extruding at a slower rate. Ash and steam continued to vent from the central cleft. Ash clouds rose to 1800 m drifting W and fell out over Plymouth. Rockfall spalling off the S lobe eroded chutes S of the dome and accumulated in thick deposits in Galway's Soufriere.

Seismicity. Figures 34, 35, and 36 show seismicity during 12 October-23 November. The sequence that began on 22 September (BGVN 22:10) continued until 21 October. Seventy-six explosions at intervals of 3-34 hours were recorded. The explosions appeared as 1-Hz signals of varying relative amplitude and were followed by pyroclastic-flow signals; long-period energy continued through the flow duration and persisted as lower-amplitude tremor of 0.5 to 3 hours duration. Signals coincided with ash venting but there was little or no precursor activity.

Figure (see Caption) Figure 34. Daily events at Soufriere Hills triggering the broadband network system, 12 October-23 November 1997. Event counts are from 1600 on the previous day to 1600 on the date indicated. Data courtesy of MVO.
Figure (see Caption) Figure 35. Seismic swarms at Soufriere Hills during 20 October-13 November 1997. Data courtesy of MVO.
Figure (see Caption) Figure 36. Explosions from Soufriere Hills measured at the Windy Hill broadband station during 12-23 October 1997. Amplitudes are peak-to-peak in counts. Data courtesy of MVO.

The second explosion of 20 October and the first of 21 October were accompanied by swarms of hybrid and volcano-tectonic earthquakes. The second explosion of 21 October initiated 24 hours of hybrid and volcano- tectonic earthquakes and rockfalls down Tuitt's ghaut before ending in a long, sparse swarm on 23 October, although a high level of long-period earthquakes lingered thereafter. Volcano-tectonic earthquakes typically occurred 2-4 km from the top of the dome.

During late October and early November, intense swarms sometimes merged with tremor having frequencies similar to individual hybrids. Hybrid swarms during 1-2 November produced the highest amplitudes since 24 June, reported from stations in Antigua, Dominica, and Nevis. Large pyroclastic-flow signals were recorded on 4 and 6 November. During 6-8 November, particularly high levels of tremor occurred. Individual hybrids were detected on paper but not on the networks due to high background noise; thus low numbers of events did not reflect low activity. Tremor and hybrids were associated with ash venting at the dome. Small pyroclastic flows were recorded on 9 November, but otherwise hybrid earthquakes did not generate external activity. Amplitudes became progressively smaller later in November; from 14 November to the end of the month, rockfall signals dominated, although a significant number of low-amplitude hybrids not grouped in swarms occurred but were not detected by the network.

Ground deformation. On 20 October, a GPS survey was taken; however, the only sites accessible were White's, Harris, and Windy Hill due to thick ash cover. Measurement from Harris to White's showed a 2-cm increase since 20 September, closer to the pre-June 1997 level. Although less than two standard deviations below the mean, this single measurement did not indicate an acceleration in deformation. The line from Harris to Windy Hill showed slight shortening since 12 August. EDM measurements to Lee's Yard from MVO on 14 October revealed an increase of 1 cm since July.

Volume measurements. Gross morphology of the pre-21 September dome was unchanged since the collapse on that day (BGVN 22:10) until 22 October with some exceptions (see Visual observations). The volume of the 22 October dome was measured by geometric calculation until a survey was taken. Assuming the dome completely filled the explosion crater by 23 October (when overspilling was observed), the volume was approximately 1.7 x 106 m3 resulting in an extrusion rate of 8-10 m3/s, depending on the time of first appearance. A detailed survey was made on 6 November, before the collapse, from several points; theodolite points from Jackboy Hill, Center Hills, and Flemings, a GPS point at Center Hills (to be used in future surveys as an additional static photo point), and helicopter survey photographs of most areas around the dome except the Galway's side. Good coverage of the N lobe of the 22 October dome was obtained. Since this area had not changed since 3 November, the volume was calculated at 5 x 106 m3. Collapse volumes were calculated separately for an average extrusion rate of 5 m3/s over the first 11 days of the "22 October" dome growth. Visual observation revealed that the 4 November collapse involved less material than the 6 November collapse. The latest estimates of collapse volumes were 1.8 x 106 m3 from 4 November and 3.4 x 106 m3 from 6 November. The bulk of the collapse material was deposited in fans at the end of valleys that will be surveyed when the ash subsides. A 17 November survey of the White River valley fan revealed total deposits of 13.6 x 106 m3, an increase of 5.5 x 106 m3 since 15 May, resulting mostly from the 4 and 6 November collapses. The survey did not include recent deposits in the upper valley still covered in ash.

Environmental monitoring. Dust Trak sampling to measure airborne particulates was carried out at four fixed sites. The values at the fixed sites were low (<0.05 mg/m3) during 12 October-23 November, except for the Catholic school site, which sometimes recorded elevated levels (0.05-0.1 mg/m3). This effect is caused by the large amount of human activity at this site and its location near a main road. Towards the end of this reporting period the three sites (not including the school) all had remarkably similar average concentrations each day. A new Dust Trak site was established at Mango Drive in Woodlands on 16 November to replace the Runaway site.

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), c/o Chief Minister's Office, PO Box 292, Plymouth, Montserrat (URL: http://www.mvo.ms/).


Vulcano (Italy) — November 1997 Citation iconCite this Report

Vulcano

Italy

38.404°N, 14.962°E; summit elev. 500 m

All times are local (unless otherwise noted)


Trends in fumarolic gas composition during 1996-97

Periodic observations of the chemical composition of fumarolic gases have been made at Vulcano since 1977. Several fumaroles with different temperatures but similar chemical compositions were observed. Differing trends in fumarolic gas composition at different locations on Vulcano have been observed during 1996-97.

Table 5 shows the trend in chemical composition of gases emitted by fumaroles on the rim and inside the crater during 1996-97. For fumaroles on the rim, percentages of typical magmatic species such as SO2, H2, and CO increased during 1996-97; percentages decreased for fumaroles inside the crater. Scientists estimated that the magmatic system was opening on the rim and closing inside the crater. This evolution pattern revealed that the stability of the system was affected by deformation of the Fossa cone produced by increased vapor pressures at depth.

Table 5. Fumarolic gas composition (percentages) on the rim (A) and inside the crater (B) of Vulcano, 1996-97. Courtesy of M. Martini.

Component A (rim) 1996 A (rim) 1997 B (crater) 1996 B (crater) 1997
Temperature 348°C 328°C 399°C 426°C
H2O (vol.) 84.41 88.86 81.50 85.38
CO2 (dry) 93.90 92.37 97.40 97.13
H2S 2.66 3.10 0.41 0.40
SO2 1.46 2.11 1.11 0.99
HCl 0.97 1.26 0.54 0.78
HF 0.52 0.46 0.077 0.029
B 0.017 0.023 0.014 0.017
NH4 0.010 0.010 0.006 0.017
H2 0.041 0.121 0.081 0.048
N2 0.525 0.547 0.580 0.513
CO 0.00047 0.00072 0.0038 0.0024

Correction: Boris Behncke (Istituto di Geologia e Geofisica at Università di Catania) noted that during a visit in late April 1997 (BGVN 22:07) steam emissions from the Fossa Grande crater appeared slightly more voluminous than during visits in 1995 and 1996. This statement may have created a false impression of renewed increase in fumarolic activity when it was actually due to the relative humidity of the air. Fieldwork by other scientists during spring 1997 revealed low fumarole temperatures and less abundant emissions. This was confirmed by Behncke during June-July and 10-12 October when fumarolic emissions were the lowest since 1989.

Geologic Background. The word volcano is derived from Vulcano stratovolcano in Italy's Aeolian Islands. Vulcano was constructed during six stages during the past 136,000 years. Two overlapping calderas, the 2.5-km-wide Caldera del Piano on the SE and the 4-km-wide Caldera della Fossa on the NW, were formed at about 100,000 and 24,000-15,000 years ago, respectively, and volcanism has migrated to the north over time. La Fossa cone, active throughout the Holocene and the location of most of the historical eruptions, occupies the 3-km-wide Caldera della Fossa at the NW end of the elongated 3 x 7 km island. The Vulcanello lava platform forms a low, roughly circular peninsula on the northern tip of Vulcano that was formed as an island beginning in 183 BCE and was connected to Vulcano in about 1550 CE. Vulcanello is capped by three pyroclastic cones and was active intermittently until the 16th century. The latest eruption from Vulcano consisted of explosive activity from the Fossa cone from 1898 to 1900.

Information Contacts: Marino Martini, Dipartimento di Scienze della Terra, Università di Firenze, Via La Pira 4, 50125, Firenze, Italy; Boris Behncke, Istituto di Geologia e Geofisica, Universitá di Catania, Corso Italia 55, 95129 Catania, Italy.


Yasur (Vanuatu) — November 1997 Citation iconCite this Report

Yasur

Vanuatu

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

All times are local (unless otherwise noted)


Strombolian eruptions; decreasing seismic activity since March 1997

ORSTOM reported in late November that there has been little change in the appearance of Yasur's crater since February 1997. During this interval only craters B and C (figure 11) were active; crater A was quiet. Crater B produced a few explosions and small ash plumes; occasionally small lava bombs (a few tens of centimeter in diameter) reached the lip of the crater.

Figure (see Caption) Figure 11. Sketch of the summit crater area at Yasur. Labels A, B, and C correspond to named craters. The sketch was based on photographs taken on 28 February 1997. Drawn by Alfreda Mabonlala; provided courtesy of P. Gineste, ORSTOM.

Seismic signals in 1997 (figure 12), with frequencies of 1-7 Hz, were related to Strombolian explosions and correlated with surface phenomena (Nabyl and others, 1997). All signals were recorded 2 km from the crater (figure 13), relayed to an ARGOS satellite, and then to the receiving station. Regional seismicity accounted for a small percentage of signals and thus had negligible effect on event counts.

Figure (see Caption) Figure 12. Daily seismicity and smoothed average seismicity recorded at Yasur during January through early November 1997. The solid line depicts smoothed averages of 25 recording periods; the averages were made to the number of events with vertical displacements reaching over 12 µm. The histogram shows the number of events with vertical displacements over 60 µm; these stronger events were absent during October and early November 1997. Such quiet intervals were common during early 1996 and much of 1995. Courtesy of ORSTOM.
Figure (see Caption) Figure 13. The ARGOS-linked monitoring station with Yasur to the N in the background, 2 November 1997. Courtesy of Pascal Gineste, ORSTOM.

Continuous seismic monitoring since March 1997 (figure 12) revealed a general decrease in Strombolian activity over time. Still, some powerful explosions were recorded during August 1997 (BGVN 22:08). These powerful events occurred only a few times per day and had vertical displacements greater than 60 µm; their scarcity was taken as a further indication of decreased activity. Since October 1993, seismic monitors recorded periods of high activity during December 1993-March 1995 and during May 1996-April 1997; slightly elevated activity occurred during August-October 1995. It was also reported by ORSTOM that an undisclosed radiometric technique suggested that fresh magma entered the system in May 1996.

During 29 July-4 August 1997 a team from the Soci't' de Volcanologie GenŠve (SVG) visited Yasur and made visual and other observations, including some temperature estimates of lavas using an optical pyrometer. The team saw small but almost continuous Strombolian activity in the N vents area. The continuous activity was interrupted by stronger explosions every 1-1.5 hours; the explosions threw lava fragments in all directions. The fragments fell mainly inside the crater but sometimes fell on the NE part of the outside rim; in one instance, a bomb ~1 m in diameter was found still hot on the rim. The stronger phases of the eruption were accompanied by ground vibrations. Small convulsing ash clouds sometimes issued from another part of the vent area, indicating that at least two separate vents were active.

At the S vents area, the SVG team observed gas, ash, and old material suddenly and noisily emitting from different vents during the beginning of their visit; a few to no red lava fragments were projected during these emissions. The activity sounded like a jet engine and caused gases to ignite. Towards the end of their visit, the team observed that the quantity of ash emitted had increased; the eruptions created ash clouds that were easily seen from the volcano's foot.

The SVG team measured temperatures with an infrared (1.55 µm wavelength) optical pyrometer (Optix-G, Keller GMBH., Ibbenburen-Lagenbeck). At an opening in the N vents area, a maximum temperature of 581°C was obtained on a weakly incandescent area. Strong degassing was present around the target at the time of the measurement (2 August).

Figure (see Caption) Figure 14. Photograph of Yasur looking N on 2 November 1997. Courtesy of Pascal Gineste, ORSTOM.
Figure (see Caption) Figure 15. Photograph looking N towards Yasur with a dry lake bed in the foreground, 2 November 1997. In 1975 there was a landslide of 50,000 m3 of material, leaving a detachment scar 100 m wide that can be seen in this photo. Courtesy of Pascal Gineste, ORSTOM.
Figure (see Caption) Figure 16. Photograph looking S at the crater rim of Yasur during a period of quiet activity, 2 November 1997. Courtesy of Pascal Gineste, ORSTOM.

Reference. Nabyl, A., J. Dorel, and M. Lardy, 1997, A comparative study of low frequency seismic signals recorded at Stromboli (Italy) and Yasur (Vanuatu), New Zealand Journal of Geol. and Geophys. (December issue).

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: M. Lardy, D. Charley, and P. Gineste, Centre ORSTOM, BP 76, Port Vila, Vanuatu, and Départment des Mines et de la Géologie et des Resources en Eaux; J. Tabbagh, Centre de Téléobservation Informatisé des Volcans, CNRS-CRG, Garchy, France; A. Nabyl and J. Dorel, OPG, Centre de recherches volcaniques (CRV), Clermont Ferrand, France; Mf. le Cloarec, Centre des faibles radioactivités CFR, Gif sur Yvette, France; P. Vetch and S. Haefeli, Société de Volcanologie Genève (SVG), C.P. 298, CH-1225, Chene-bourg, Switzerland.

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/).