Logo link to homepage

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

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

Bezymianny (Russia) Ongoing thermal anomalies, gas-and-steam plumes, and lava dome growth during February-May 2019; strong explosion in mid-March

Nevados de Chillan (Chile) Small ash explosions and dome growth during December 2018-May 2019; ballistic ejecta deposited around the crater, with a pyroclastic flow in May



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/).


Bezymianny (Russia) — June 2019 Citation iconCite this Report

Bezymianny

Russia

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

All times are local (unless otherwise noted)


Ongoing thermal anomalies, gas-and-steam plumes, and lava dome growth during February-May 2019; strong explosion in mid-March

Volcanism at Bezymianny has been frequent since 1955. During the last reporting period, observations primarily consisted of moderate gas-and-steam emissions and thermal anomalies. Lava dome growth has been reported, as well as the effusion of several lava flows onto the dome flanks. Monitoring is the responsibility of the Kamchatka Volcano Eruptions Response Team (KVERT). Activity during February to mid-March 2019 consisted of predominantly moderate gas-and-steam emissions. Incandescent, hot avalanches from the lava dome, strong fumarolic activity, and a thermal anomaly began to occur in mid-March 2019. This reporting period includes activity from February-May 2019.

One explosion occurred during this reporting period. According to video data from KVERT and seismic data from the Kamchatka Branch of the Geophysical Service, on 15 March 2019 an explosion sent ash up to an altitude of 15 km. According to the KVERT Weekly Reports, satellite data showed large ash clouds from this eruption drifting several thousands of kilometers east from the volcano. The Volcano Observatory Notice for Aviation (VONA) issued by KVERT for this event described ash clouds to a distance of about 870 km. Ashfall was reported in Ust'-Kamchatsk (115 km E) on 15 March and Nikolskoe (350 km E) on 15-16 March 2019.

Beginning 15 March and continuing through May 2019, the number of hot avalanches from the lava dome top significantly increased, as well as the temperature of the thermal anomalies as reported by KVERT based on satellite data. Incandescent lava dome growth with extruding, viscous lava flows accompanying strong fumarolic activity and thermal anomalies continued in late April-May 2019 (figure 30).

Figure (see Caption) Figure 30. Fumarolic plume rising above at Bezymianny on 14 April 2019. Photo by A. Klimova, courtesy of the Institute of Volcanology and Seismology FEB RAS, KVERT.

MODIS infrared data processed by MIROVA showed stronger and more frequent thermal anomalies in mid-March 2019 compared to the typical thermal activity since late January and afterwards through May (figure 31). According to the MODVOLC algorithm, 11 hotspot pixels were recorded between February and May 2019.

Figure (see Caption) Figure 31. Thermal anomalies at Bezymianny for September 2018 through May 2019 as recorded by the MIROVA system (Log Radiative Power). Courtesy of MIROVA.

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: 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/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Kamchatka Branch of the Geophysical Service, Russian Academy of Sciences (KB GS RAS) (URL: http://www.emsd.ru/); 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/).


Nevados de Chillan (Chile) — June 2019 Citation iconCite this Report

Nevados de Chillan

Chile

36.868°S, 71.378°W; summit elev. 3180 m

All times are local (unless otherwise noted)


Small ash explosions and dome growth during December 2018-May 2019; ballistic ejecta deposited around the crater, with a pyroclastic flow in May

The current Nevados de Chillán eruption period began on 8 January 2018 with a phreatic explosion from the new Nicanor crater, within the Nuevo crater; a new dome was observed within this crater the next day. Dome growth continues with explosions that eject ash plumes and incandescent ejecta. This bulletin summarizes activity from December 2018 through May 2019 and is based on reports by Chile's Servicio Nacional de Geología y Minería (SERNAGEOMIN)-Observatorio Volcanológico de Los Andes del Sur (OVDAS) and satellite imagery.

Throughout December 2018 pulsating emissions from the Nicanor crater produced white plumes predominantly composed of water vapor, with occasional ash ejections giving the plume a gray appearance. Incandescence was frequently observed during the night due to the ejection of hot ballistic ejecta emplaced around the crater during explosions. After 11 months of observations, the dacite dome in the crater maintained a semi-stable extrusion rate of around 345 m3/day. Explosions were reported on 7, 17, 28, and 29 December.

Similar background activity continued through January with pulsating gas-and-steam plumes occasionally including ash, and incandescence observed during the nights due to hot ejecta around the crater. Explosions were recorded at 0500 and 1545 on 11 January, and on 13, 21, and 31 January (figures 33 and 34). During the night explosions and incandescent ejecta were observed impacting the area around the crater.

Figure (see Caption) Figure 33. An explosion at Nevados de Chillán on 11 January 2019. The explosion ejected incandescent blocks that impacted the flanks. The timestamp is at the top left of each image; screenshots are of footage courtesy of SERNAGEOMIN.
Figure (see Caption) Figure 34. An explosion at Nevados de Chillán on 31 January 2019 produced an ash plume from the Nicanor crater. Courtesy of SERNAGEOMIN.

Activity continued through February similar to previous months. The dome in the crater maintained a low extrusion, and activity alternated between dome growth and partial destruction during explosions. Steam-and-gas plumes with occasional ash content continued, with plumes reaching 1 km and drifting in multiple directions. Incandescence was observed during the night. Explosions were reported on 15 February.

During March through May, typical activity consisting of pulsating emission of steam plumes with occasional ash content, and incandescence at night, continued. Intermittent explosions associated with the partial destruction of the dome continued, with events reported on 1 March at 2323, and on 4, 7, and 8 March. Several explosions were reported during 8-9 and 23-30 April. Three explosions were reported on 3 May with one of them producing a 2-km-high ash plume and a pyroclastic flow on 10 May (figure 35). Additional explosions occurred on the 12 and 18 May.

Figure (see Caption) Figure 35. An explosion at Nevados de Chillán on 10 May 2019 produced an ash plume that rose to 2 km above the crater and a pyroclastic flow. The white plume in the bottom two images is steam from the interaction of the hot pyroclastic material and the snow. Screenshots are of a video courtesy of SERNAGEOMIN with timestamps indicated in the top left of each image.

Satellite data from December 2018 through May 2019 recorded intermittent thermal energy, with an increase after February 2019 (figure 36). Thermal anomalies from MODIS instruments were detected by the MODVOLC system on 29 March and 17 May 2019 (two anomalies). A thermal anomaly in the Nicanor crater was persistent in Sentinel-2 data throughout this period.

Figure (see Caption) Figure 36. Thermal anomalies at the active Nicanor crater of the Nevados de Chillán complex. Top: Sentinel-2 thermal image of showing the location of the thermal anomaly (orange). Bottom: MIROVA log radiative power plot of MODIS thermal infrared data from September 2018 through May 2019. Thermal signatures are intermittent and increase after February 2019. Note that the black lines are not from the crater and are unlikely to be related to volcanic activity. Courtesy of Sentinel Hub Playground and MIROVA.

Geologic Background. The compound volcano of Nevados de Chillán is one of the most active of the Central Andes. Three late-Pleistocene to Holocene stratovolcanoes were constructed along a NNW-SSE line within three nested Pleistocene calderas, which produced ignimbrite sheets extending more than 100 km into the Central Depression of Chile. The largest stratovolcano, dominantly andesitic, Cerro Blanco (Volcán Nevado), is located at the NW end of the group. Volcán Viejo (Volcán Chillán), which was the main active vent during the 17th-19th centuries, occupies the SE end. The new Volcán Nuevo lava-dome complex formed between 1906 and 1945 between the two volcanoes and grew to exceed Volcán Viejo in elevation. The Volcán Arrau dome complex was constructed SE of Volcán Nuevo between 1973 and 1986 and eventually exceeded its height.

Information Contacts: Servicio Nacional de Geología y Minería (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Search Bulletin Archive by Publication Date

Select a month and year from the drop-downs and click "Show Issue" to have that issue displayed in this tab.

   

The default month and year is the latest issue available.

Bulletin of the Global Volcanism Network - Volume 21, Number 12 (December 1996)

Managing Editor: Richard Wunderman

Alaid (Russia)

Eruption sends a plume 5-6 km high on 3 December

Arenal (Costa Rica)

Ongoing vigorous eruptions the subject of visits, reports, and concerns

Atmospheric Effects (1995-2001) (Unknown)

Lidar data from Germany may suggest an aerosol layer centered at about 19 km

Bezymianny (Russia)

Fumarolic plumes seen

Fournaise, Piton de la (France)

November intrusion signaled by radon and geophysical measurements

Fuego (Guatemala)

A white-to-gray smoke column seen rising over the crater

Iliamna (United States)

Seismic swarm from 1 August continues into 1997

Karymsky (Russia)

Elevated seismicity persists; up to 300 explosions daily

Klyuchevskoy (Russia)

Above-background seismicity; ash-and-steam plumes up to 3 km tall

Langila (Papua New Guinea)

Eruptions continue during October-December

Manam (Papua New Guinea)

Paroxysmal eruptions on 3 December cause 13 deaths

Mutnovsky (Russia)

Fumarolic plume up to 1 km above the crater

Negro, Cerro (Nicaragua)

Fumarole temperatures decrease further

Pacaya (Guatemala)

Strombolian eruptions and lava flows from MacKenney crater

Pavlof (United States)

Intermittent eruptions from 15 September through [3] January

Poas (Costa Rica)

Fumarolic columns rise 500 m above the crater floor

Popocatepetl (Mexico)

Eruption on 25 December seen by airline pilots in satellite imagery

Rabaul (Papua New Guinea)

Tavurvur's 4-5 October eruptions yield the largest lava flow in over 200 years

San Cristobal (Nicaragua)

December vapor plumes appear smaller than previous ones

Santa Maria (Guatemala)

Ash emissions and small collapses at Santiaguito dome

Sheveluch (Russia)

Typical fumarolic plumes

Soufriere Hills (United Kingdom)

Dramatic fracturing on SW wall as dome growth continues

Turrialba (Costa Rica)

Number of microseismic events continues to increase

Villarrica (Chile)

Crater observations for the interval 11 September 1996-13 January 1997



Alaid (Russia) — December 1996 Citation iconCite this Report

Alaid

Russia

50.861°N, 155.565°E; summit elev. 2285 m

All times are local (unless otherwise noted)


Eruption sends a plume 5-6 km high on 3 December

On 3 December, satellite imagery indicated a plume rising to a height of 5-6 km from Alaid. The nearest seismic station, located in the town of Severo-Kurilsk (Paramushir Island), 25 km E of Alaid, recorded the beginning of local seismic activity at about the same time as the satellite report. A large snow storm obscured the volcano, and no visual reports of eruptive activity were received from the coast guard, ships, or aircraft in the area.

Geologic Background. The highest and northernmost volcano of the Kuril Islands, 2285-m-high Alaid is a symmetrical stratovolcano when viewed from the north, but has a 1.5-km-wide summit crater that is breached widely to the south. Alaid is the northernmost of a chain of volcanoes constructed west of the main Kuril archipelago. Numerous pyroclastic cones dot the lower flanks of this basaltic to basaltic-andesite volcano, particularly on the NW and SE sides, including an offshore cone formed during the 1933-34 eruption. Strong explosive eruptions have occurred from the summit crater beginning in the 18th century. Reports of eruptions in 1770, 1789, 1821, 1829, 1843, 1848, and 1858 were considered incorrect by Gorshkov (1970). Explosive eruptions in 1790 and 1981 were among the largest in the Kuril Islands during historical time.

Information Contacts: 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; Vladimir Kirianov, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; NOAA/NESDIS Satellite Analysis Branch; Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA.


Arenal (Costa Rica) — December 1996 Citation iconCite this Report

Arenal

Costa Rica

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

All times are local (unless otherwise noted)


Ongoing vigorous eruptions the subject of visits, reports, and concerns

During late 1996, Arenal's ongoing Strombolian eruptions continued. OVSICORI-UNA noted that late-1996 avalanches had traveled down the N and SW flanks. For example, one at 1109 on 11 December traveled down the N flank to ~1,300 m elevation. Acidic rainfall also continued to damage vegetation.

Some noteworthy September eruptions and their associated pyroclastic flows were mentioned in BGVN 21:09. Others also occurred late in 1996; one at 0926 on 11 December reached a point on the SW flank at 1,230 m elevation. Another pyroclastic flow occurred at 1630 on 30 December reaching 1,000 m elevation.

Observations during 19-24 November. Multiple pyroclastic flows with distinct pulses were reported by Steve O'Meara, Tippy D'Auria, and Robert Benward who watched Arenal for much of five days (19-24 November 1996) from 3.8 km due N of the summit (location determined by GPS); they found it very active with eruptions occurring intermittently from five distinct vents. The group noted long-duration fountaining and jetting; on 20 November these processes were continuous for over 30 minutes. The group saw multiple eruptions discharging plumes to heights >1 km, observed ashfall, and heard window-rattling explosion noises. They watched an advancing incandescent summit lava flow lobe whose front frequently calved off and produced spectacular incandescent rockfalls and avalanches. Also, they witnessed tumbling boulders and noted periodically strong snorting and huffing noises at the summit vents associated with the escape of incandescent gas.

Sheared from the lava flow front, some of the boulders were easily the size of small cars. As the boulders fell they made audible impact bursts and broke into smaller pieces as they rolled and bounced down the mountain (sometimes reaching the 700-m elevation). The scene of the falling and breaking boulders looked similar to a fireworks display.

The source of the lava lobe appeared to be the new spatter cone on the N side of Crater C, which the flow all but encompassed. The main lobe branched into three separate ones, each a source of rock falls. A lava lobe also appeared to be moving E into the saddle between craters C and D. A new lobe was moving down Crater C's NW side.

The source of the pyroclastic flows was unclear to the group, though they thought it might be the new spatter cone. On video footage some of the pyroclastic flows were very distinct. Many of the flows were also accompanied by a sluggish, reddish, small ash eruption from what appears to be one of the five vents, though these eruptions could also have issued from the spatter cone. Pyroclastic flows traveled 100-1000 m from the summit, but stayed within well-defined channels on the W side of the latest 1996 lava flow. O'Meara was somewhat concerned to encounter an active campsite at Laguna Cedeño--right in the path of some of the pyroclastic flows--and only 2 km from the summit.

Table 19 shows a sample of some of the kinds of observations recorded during the O'Meara group's stay. During their visit they also considered the positions of the sun and moon. The group suggested that the largest eruptions may have had a possible correlation to moon phase and tidal pulls as well as moon rise and set times. It appeared that the more violent eruptions of Vent 1 occurred at intervals of 6.5 hours. Using that hypothesis, the group claimed to have successfully and confidently estimated vent 1's major blasts to within 2 minutes of the events.

Table 19. A sample of the field notes, from 20 November 1996, describing Arenal activity during the O'Meara group's 5-day visit (complete observations available upon request). Courtesy of Steven O'Meara, Tippy D'Auria, and Robert Benward.

Time Observations
1206 Eruption; vent 2.
1258 Vents degassing.
0108 Vent 5 eruption with possible pyroclastic flow.
0113-0118 Small eruptions with sustained jetting combined with summit glow; jetting episodes appear to trigger lava flow surges.
0149 More degassing and summit glow.
0215-0245 Large eruption with continuous fountaining-jetting activity for 30 minutes; several bursts of intense activity (particularly vents 1 and 4, with a single blast from vent 2).
0255 A medium eruption from twin vents; 30 seconds later a small emission at vent 4.
0252 Degassing.
0328 Small explosion.
0333 Huffing noise at vent 2; D'Aurria likens it to the snorting of a bull getting ready to charge.
0338 Large discharge of blocks from vent 2 accompanied by snorting noises.
0339 Vents 3 and 4 spitting.
0345 Medium eruption from the center vent; heavy huffing; lots of gas escaping and boulders rolling from northerly flow.
0416 Explosion followed by degassing.
0442 Vent 4 spattering.
0448 Vent 2, small amounts of spattering.
0450 Vent 1, small silent eruption.
0451 Vent 1, larger and louder eruption.
0454 Medium-to-strong eruption noted from three different vents creating a large pyroclastic flow and discharging several large lava fragments. Saw the new lava flow area in the vicinity of vent 1, W of the large block lava flow.
0509 Medium eruption from center vent.
1000 Big explosions and noise.
1036 Big explosion and noise.
1045 Small eruption and big noise.
1110 Small eruption of reddish color observed from the settlement of Tabacón.

Behavior at the five vents during the group's visit were as follows. Vents 1 and 3 were twin summit vents that appeared to be centered in Crater C. Vent 1 was the stronger of the two when they erupted separately. Both sent plumes vertically and produced prolonged roars and blasts.

Vent 2, located on the E side of Crater C, was the strongest and loudest, producing most of the house- and window-shaking eruptions. Many times the ejecta would blow out of this vent at a 45° angle toward Crater D. Sometimes, E- and N-arcing ejecta fell about a quarter of the way down the volcano's slope. This vent may have been the eastern lava lobe's source.

Vent 4 was centered on the new summit spatter cone N of Crater C. The vent ejected occasional spatter, though some long-enduring fountaining-degassing episodes also took place. Whereas vent 4 had been active when the group arrived, it was almost inactive by 22 November, though the lava flow around it continued to advance.

Vent 5, on the W side of the summit, produced very strong ash eruptions, but these events were mostly associated with muffled blasts at the observation site. Variously directed eruptions sometimes sent ejecta E, at a 45° angle toward the W, and at other times vertically.

Seismic data, recent reports, and a hazards caution. During September and November OVSICORI-UNA noted that both tremor and earthquakes were common, though not in unusual abundance (tremor duration, 300 and 237 hours; number of earthquakes, 875 and 471; respectively). Earthquakes were more abundant during October, a month when 1,094 registered, more than at any time during 1996. At the OVSICORI-UNA station, tremor duration in the previous months of 1996 had ranged between 261 and 434 hours; during October it was also moderately high (381 hours).

Some Arenal reports and abstracts that may not appear in typical European and North American literature indexes have come out recently. Five technical reports on Arenal appeared in a volume in November 1996 (ICE, 1996). The reports include discussions of 1) the volcano's behavior during the year 1993, 2) the spectral character of seismic signals and the P-wave velocity in the upper part of the edifice, 3) possible eruptions in 1915 and 1922, 4) the hazards, costs, and hazard perceptions associated with a moderate eruption, and 5) how meta-igneous, granulite facies xenoliths in Arenal lavas could provide evidence for a mafic basement. In addition, at least one of about 50 papers at a recent conference in Perú discussed hazards from Arenal (Laurent, 1996).

As a caution to people visiting or acting as guides at the popular volcano it should be noted that Melson and others (1997) have looked at the frequency of eruptions in a sample of over 196 days between 1987 and 1994. They found that hazardous pyroclastic eruptions occurred at wide-ranging intervals, from as little as a minute to over a day apart. However, 96% had a recurrence interval of <100 minutes. During these eruptions, ballistic blocks and bombs and infrequent pyroclastic flows posed the greatest hazards.

References. ICE Boletín, 1996, año 6, no. 11-12, Dirección de Ingeniería Civil, Departamento de Ingeniería Geológica, 78 p.

Laurent, K., 1996, Impacto de los desastres ocasionados por los volcanes Arenal e Irazú sobre la infraestructura energética de Costa Rica y medidas actuales para mitigar sus efectos: El Segundo Seminario Latinamericano "Volcanes, Sismos Y Prevencion" en Lima-Arequipa, Perú, del 4 al 9 de noviembre de 1996, J-C Thouret (coodinator), 178 p.

Melson, W.G., O'Hearn, T., Funk, V., Barquero, J., Barboza, V., Saenz, R., Fernandez, E., McNutt, S., and Benoit, J., 1997, Probabilistic volcanic hazard assessment, Arenal volcano, Costa Rica, 1987-95: unpublished report, Smithsonian Institution, Washington DC, U.S.A., 10 p.

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. Fernández, E. Duarte, V. Barboza, R. Van der Laat, E. Hernandez, M. Martinez, and R. Sáenz, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; G.J. Soto and J.F. Arias, Oficina de Sismología y Vulcanología del Arenal y Miravalles (OSIVAM), Instituto Costarricense de Electricidad (ICE), Apartado 10032-1000, San José, Costa Rica; Steven O'Meara, PO Box 218, Volcano, HI 96785, USA.


Atmospheric Effects (1995-2001) (Unknown) — December 1996 Citation iconCite this Report

Atmospheric Effects (1995-2001)

Unknown

Unknown, Unknown; summit elev. m

All times are local (unless otherwise noted)


Lidar data from Germany may suggest an aerosol layer centered at about 19 km

Lidar data for part of 1996 (mid-May through the month of September) over Germany (table 8) indicated a possible aerosol layer centered between 14.7 and 21.6 km altitude. The possible layer's center often resided at ~19 km. The "ci" in Table 9 stands for cirrus. Cirrus in the tropopause region usually obscures the lower boundary of the aerosol layer.

Table 8. Backscattering ratios from German lidar data for the Nd-YAG wavelength of 0.53 µm, 16 May-30 September 1996. The equivalent backscattering ratios for ruby are in parentheses (ruby wavelength, 0.69 µm). Courtesy of Horst Jäger.

DATE LAYER ALTITUDE (km) (peak) BACKSCATTERING RATIO BACKSCATTERING INTEGRATED
Garmisch-Partenkirchen, Germany (47.5°N, 11.0°E)
16 May 1996 11-30 (19.8) 1.11 (1.20) --
22 May 1996 ci-29 (14.7) 1.09 (1.20) --
24 May 1996 12-31 (17.9) 1.11 (1.20) --
31 May 1996 14-38 (20.1) 1.09 (1.20) --
08 Jun 1996 14-27 (19.6) 1.09 (1.20) --
19 Jun 1996 9-27 (18.8) 1.10 (1.20) --
03 Jul 1996 13-28 (19.7) 1.07 (1.20) --
31 Jul 1996 11-30 (19.4) 1.09 (1.20) --
06 Aug 1996 ci-26 (19.5) 1.07 (1.20) --
08 Aug 1996 ci-27 (18.5) 1.06 (1.10) --
18 Aug 1996 12-27 (21.6) 1.06 (1.10) --
23 Aug 1996 11-26 (16.4) 1.06 (1.10) --
26 Sep 1996 12-26 (19.1) 1.06 (1.10) --
30 Sep 1996 12-25 (15.6) 1.07 (1.20) --

Information Contacts: Horst Jäger, Fraunhofer -- Institut für Atmosphärische Umweltforschung, Kreuzeckbahnstrasse 19, D-8100 Garmisch-Partenkirchen, Germany.


Bezymianny (Russia) — December 1996 Citation iconCite this Report

Bezymianny

Russia

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

All times are local (unless otherwise noted)


Fumarolic plumes seen

On 5-6 and 17 December and on 4, 9, and 14-15 January, fumarolic plumes were observed reaching as high as 100 m above the crater. The plumes extended 10 km downwind.

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: 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; Vladimir Kirianov, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia.


Piton de la Fournaise (France) — December 1996 Citation iconCite this Report

Piton de la Fournaise

France

21.244°S, 55.708°E; summit elev. 2632 m

All times are local (unless otherwise noted)


November intrusion signaled by radon and geophysical measurements

During the last four years, quiet prevailed at Piton de la Fournaise (figure 35), with unusually low seismic activity and no eruptions. During late November, however, scientists at the Observatoire Volcanologique du Piton de la Fournaise noted an increase in radon flux followed a day later by an increase in seismicity. This also accompanied changes in tilt, local extension, and larger-scale distance movements. These observations led the scientists to infer that there had been a magma intrusion.

Figure (see Caption) Figure 35. Sketch map of Piton de la Fournaise and vicinity showing the locations of observation stations. Notice that the topographic contour intervals on this map are uneven. Courtesy of OVPDLF.

Seismicity. In September a 16-km-deep swarm of earthquakes was recorded ~5 km NW of the summit. Seismicity continued to increase under the summit, and a M 2.3 event was registered on 18 October. A short but intense seismic crisis (figure 36), which began at 2126 on 26 November, consisted of 134 registered events. Among them, there were 37 earthquakes larger than M 1 and two in the range of M 2-2.4. The strongest one took place at 2149, an event nearly coincident with changes recorded by inclinometers and extensometers and inferred to correspond to the beginning of the principal magma movement. The seismic activity decreased at 2220 and ended with a final event of M 1.9 at 2310. After that, seismicity remained low. All events during this seismic crisis originated at about sea level ( ~2.5 km below the summit) at the Soufrière region, slightly N of the summit.

Figure (see Caption) Figure 36. Cumulative seismic moment during January-November 1996 at Piton de la Fournaise. Thin dotted line shows cumulative seismic moment under the summit; heavier line represents volcano-wide cumulative seismic moment minus the cumulative seismic moment under the summit. Courtesy of OVPDLF.

Tilt and extension.Although not shown in figure 37, a small amount of ground movement might have taken place prior to the prominent tilt event at about 2149 on 26 November. The tilt accompanied inflation of the summit region, and tilts of 16, 8, and 4 µrad were recorded at stations Soufrière, Dolomieu, and Bory, respectively. Stations Chapelle and Chateau Fort at the base of the cone tilted <1 µrad. Displacements of <0.1 mm were also recorded by extensometers at stations Magne, Chateau Fort, Soufrière, and Dolomieu.

Figure (see Caption) Figure 37. Tilts at stations Bory, Soufriére, and Dolomieu at Piton de la Fournaise. "Rad" and "tgt" refer to radial and tangential components, respectively. Courtesy of OVPDLF.

Distance change. Distances between station Piton Partage and different prisms on the cone were measured automatically by a TM3000 instrument (figure 38). During 25-26 November, a decrease up to 10 mm occurred for prisms on the profile between Soufrière and Puy Mi-Cote (prisms 1M20, 2M54, 2M53, 2M52, 2M42, and 1M40). In addition, the distance decreased slightly for one prism at Magne (2M26); no distance change was observed for the prisms between Chapelle and Bory and for one prism at the E side of the cone (2M31).

Figure (see Caption) Figure 39. Radon flux at stations Chateau Fort and Cratere Catherine at Piton de la Fournaise. Courtesy of OVPDLF.

Geologic Background. The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.

Information Contacts: Thomas Staudacher; Patrick Bachèlery; Valéry Ferrazzini, and Kei Aki, Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France.


Fuego (Guatemala) — December 1996 Citation iconCite this Report

Fuego

Guatemala

14.473°N, 90.88°W; summit elev. 3763 m

All times are local (unless otherwise noted)


A white-to-gray smoke column seen rising over the crater

During 12-19 November a white-to-gray column was observed rising 70-200 m above the crater; winds then dispersed it to the S over the volcano's flanks. On 20 November the column rose to 500 m and drifted E; the following day the column's height was 200 m and oriented SW. From 25 November to 12 December the column was again at 50-200 m height and blown toward the S and SW. During this observation period the Fuego-Acatenango seismic network recorded a few earthquakes up to M 1.

Geologic Background. Volcán Fuego, one of Central America's most active volcanoes, is one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between 3763-m-high Fuego and its twin volcano to the north, Acatenango. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at Acatenango. In contrast to the mostly andesitic Acatenango, eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

Information Contacts: Otoniel Matías, Seccion Vulcanologia, INSIVUMEH (Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia of the Ministerio de Communicaciones, Transporte y Obras Publicas), 7A Avenida 14-57, Zona 13, Guatemala City, Guatemala.


Iliamna (United States) — December 1996 Citation iconCite this Report

Iliamna

United States

60.032°N, 153.09°W; summit elev. 3053 m

All times are local (unless otherwise noted)


Seismic swarm from 1 August continues into 1997

The seismic swarm that began on 1 August (BGVN 21:08-21:10) continued during December and the first half of January. There were 2-16 earthquakes recorded each day.

Geologic Background. Iliamna is a prominent, 3053-m-high glacier-covered stratovolcano in Lake Clark National Park on the western side of Cook Inlet, about 225 km SW of Anchorage. Its flat-topped summit is flanked on the south, along a 5-km-long ridge, by the prominent North and South Twin Peaks, satellitic lava dome complexes. The Johnson Glacier dome complex lies on the NE flank. Steep headwalls on the southern and eastern flanks expose an inaccessible cross-section of the volcano. Major glaciers radiate from the summit, and valleys below the summit contain debris-avalanche and lahar deposits. Only a few major Holocene explosive eruptions have occurred from the deeply dissected volcano, which lacks a distinct crater. Most of the reports of historical eruptions may represent plumes from vigorous fumaroles east and SE of the summit, which are often mistaken for eruption columns (Miller et al., 1998). Eruptions producing pyroclastic flows have been dated at as recent as about 300 and 140 years ago (into the historical period), and elevated seismicity accompanying dike emplacement beneath the volcano was recorded in 1996.

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) — December 1996 Citation iconCite this Report

Karymsky

Russia

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

All times are local (unless otherwise noted)


Elevated seismicity persists; up to 300 explosions daily

Although no visual observations were made, during December and 1-20 January seismicity remained above background in a manner that suggested continued low-level Strombolian eruptions. Seismic data indicated that up to 300 explosions occurred each day.

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


Klyuchevskoy (Russia) — December 1996 Citation iconCite this Report

Klyuchevskoy

Russia

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

All times are local (unless otherwise noted)


Above-background seismicity; ash-and-steam plumes up to 3 km tall

The seismicity at Kliuchevskoi remained above background levels during December and 1-20 January. Fumarolic plumes were observed during December rising 100-1,200 m above the volcano and extending 5-15 km downwind. On 28 December and 4 January, gas-and-steam explosions rose to 200-300 m above the crater, and plumes extended 10-20 km to the NW.

An increase in eruptive activity was first noticed at 1740 on 7 January 1997 from the town of Kliuchi, ~30 km NE of the volcano. An ash-and-steam plume was observed rising 2,500-3,000 m above the crater and extending 20 km SE. Seismic activity, while still elevated, did not show an increase. An AVO analysis of a satellite image taken early on the morning of 8 January indicated that the plume had subsided. On 9 and 11 January, gas-and-steam explosions, possibly with minor ash, rose to 300-700 m above the crater, and the plumes traveled 10-15 km to the W or SW. On 13-14 and 16 January gas-and-steam plumes reached a height of 300-600 m and extended 10 km E. On 15 January, a gas-and-steam explosion rose 1,200 m above the crater, and its plume moved 15 km SE.

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: 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; Vladimir Kirianov, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia.


Langila (Papua New Guinea) — December 1996 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)


Eruptions continue during October-December

Eruptive activity at Crater 2 continued during October-December. The activity pattern of 7-26 October was similar to that during January-September. Emissions included thin, white to thick, gray vapor-and-ash clouds. The ash clouds rose ~1-2 km above the crater. Ashfall was observed on 8-22 October on the N, NW, and SE sides of the volcano. Weak, steady, red glows were seen on the nights of 7, 12-13, 20-21, and 26 October. Projections of red incandescent lava fragments occurred on the nights of 8-10 and 17 October. After 26 October eruptive activity declined to emissions of thin, weak, white vapor. During November and December, activity at Crater 2 consisted of emissions of thin, weak, white vapor, and, occasionally, moderate ash clouds. Light ashfall was observed on 5 and 11-12 November on the N, NW, and SE sides of the volcano.

Crater 3 remained quiet during October-December. Thin, weak, white vapor began to emit on 1 December. Seismic monitoring was conducted only between 11 November and 4 December. Seismicity was low during this period.

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: B. Talai, I. Itikarai, and P. de Saint Ours, RVO.


Manam (Papua New Guinea) — December 1996 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)


Paroxysmal eruptions on 3 December cause 13 deaths

A series of large eruptions took place during October and November, and culminated with a paroxysmal phase on 3 December. The paroxysm accounted for 13 deaths in a coastal village called Budua Old near SW Valley (figure 7).

Figure (see Caption) Figure 7. Sketch map of Manam Island, showing the distribution of the four valleys. After Palfreyman and Cooke, 1976.

After the last large eruption in 1992 (BGVN 17:09-17:11), Main Crater remained inactive with weak vapor emissions, while South Crater showed intermittent phases of weak to moderate, mainly Strombolian, activity. Mild Vulcanian explosions resumed at both craters in mid-September 1996 (BGVN 21:09), and Strombolian eruptions returned to both craters in October. During October and November, five strong phases of activity occurred at Main Crater at intervals of 7-12 days; four of them were preceded or accompanied by moderate activity at South Crater (figure 8). From early October to 10 November, the first four phases progressively increased in strength, and were accompanied by a large buildup in seismic amplitude (figure 9). Like the strongest phase of the 1992 eruption (BGVN 17:09-17:11), the first four phases of eruptions at Main Crater produced pyroclastic flows and lava flows in NE Valley.

Figure (see Caption) Figure 8. A rough (qualitative) estimate of the level of October-December volcanic activity at Manam. Activity is shown as a relative scale that is arbitrary, with the highest intensity artificially set at "100". Courtesy of RVO.
Figure (see Caption) Figure 9. Relative seismic amplitude during October-December at Manam. Courtesy of RVO.

At South Crater, ash-laden emissions, roaring sounds, and fluctuating glows occurred on 19 November, and moderate Strombolian projections (200 m high) and ash-laden emissions (~700 m high) were observed on 20-21 November. The fifth phase of eruptions at Main Crater took place on 20-22 November. On 20 November, Main Crater produced frequent roaring sounds, bright fluctuating night glows, and up to ~800-m-high brown emissions, indicating deep-seated Strombolian activity. Strombolian eruptions were sub-continuous until 1800 on 21 November, with a 3-km high, dark, convoluting column. Several lava tongues traveled down the upper part of NE Valley, and reached an altitude of 600-700 m. On 22 November two lava flows moved down to an altitude of ~200 m in the central and N parts of the valley. On the afternoon of 22 November, the fifth eruptive phase declined, and the Strombolian activity changed to 2-3 km high, thick, gray emissions, which were accompanied by jet sounds. Frequency, volume, and height of the emissions progressively decreased during the next two days.

On 28 November, eruptive activity at South Crater increased with the emissions of weak to moderate, gray-brown plumes (up to 500 m high) and occasional Strombolian projections (~50 m high). On 29 November, emissions became sub-continuous. In the next two days Strombolian projections progressively rose as high as 100-200 m above the crater. At Main Crater, white to gray ash clouds were occasionally released, and glow was seen at night from two locations on the NE rim of the crater. On 30 November, emissions at Main Crater were thick and continuous, but no strong activity was observed.

Strombolian explosions at South Crater increased in strength (occasionally up to heights of 400 m) and frequency (at 1-2 minute intervals) on the morning of 2 December, died out in the afternoon, then resumed in the night. On the morning of 3 December, Strombolian explosions occurred at ~1 minute intervals with ~200-m-high projections, and light gray plumes rose ~500 m high. Seismicity increased but was still in the normal range. Strombolian projections were sub-continuous until 1300, and reached as high as 300 m above the crater. At 1430 explosions took place every a few seconds with heavy scoria falls on the upper cone, similar to the situations in the strongest phases of the 1984, 1987, and 1992 eruptions (SEAN 09:02, 09:03, 12:06, and BGVN 17:09-17:11), which sent pyroclastic flows and lava flows into the SE and SW Valleys.

Large pyroclastic flows started to move into SE Valley at about 1500, and into SW Valley around 1505. The central eruption column became thicker as it incorporated the ash cloud elutriated above the pyroclastic flows. At 1510 ash clouds that were generated by the pyroclastic flows moved down SE Valley and extended over the ground at 400-600 m above sea level. At 1515 the dark central billowing pillar reached an altitude of ~5 km, and spread W of the island. Dense ash and scoria falls caused darkness in the W part of the island for 90 minutes. Pyroclastic flows continuously moved into both SE and SW Valleys at short intervals. At 1520 one large pyroclastic flow in SW Valley reached the sea and was followed by many others. Approximately at that time, pyroclastic flows overran the village of Budua Old, resulting in 13 deaths. The devastated area extended ~1.5 km on either side of the central channel of SW Valley. In SE Valley, pyroclastic flows started to reach the sea around 1530. The overriding ash clouds progressed <100 m offshore. However, within ~10 minutes bubbles were seen piercing the water surface as far as 500 m offshore, indicating that underwater propagation of the hot pyroclastic flows reached quite a distance from the shoreline.

The central column was very dense. Eruption sounds were muffled to a continuous deep roar. Although emitted at South Crater, some pyroclastic flows moved into NE Valley and descended to mid-slope, but none was able to override the 100-m vertical valley walls that protect the cultivated and inhabited flanks of the island. At 1605 the pitch of the roaring sound slightly decreased, indicating the beginning of decline in eruptive activity. By 1615 pyroclastic flows no longer reached the sea, and at 1630 all pyroclastic flows stopped. At 1645-1700 ash began to fall again on the downwind (W-NW) side of the island. At night Strombolian activity continued at South Crater, with ~3 loud explosions every hour. At 0925 on 4 December, a large hot avalanche moved down SW Valley to an altitude of ~20 m. Explosions occurred at South Crater with decreasing strength and frequency until 7 December.

At Main Crater, two vents were active with intermittent, thick, dark, convoluting clouds on the morning of 3 December. Moderately thick, gray clouds were observed rising 500-1,000 m above the crater, with weak night glows until 15 December.

The paroxysmal eruption on 3 December changed the configuration of South Crater by sculpting a 100-m-deep, V-shaped crack NW-SE across the summit. There was an absence of high-frequency earthquakes during and after the paroxysm. This suggested that the crack, which had a similar alignment to one pair of valleys, may have pre-dated the eruption, having been covered by earlier eruption debris. Blocks up to 4 m in size from the crater wall were found in pyroclastic-flow deposits in the lower part of SW Valley.

Neither the start of the 1996 eruption nor its strong phases were anticipated by monitoring results. Ground deformation, monitored by the water tube tiltmeters at Tabele Observatory (figure 7), showed steady conditions between April and mid-September. Resumption of activity at both craters in mid-September accompanied a hardly discernible radial deflation (~0.5 µrad). From then to 8-12 November, the tiltmeters accumulated a barely significant ~1 µrad radial inflation, and thereafter a slight deflation (~1 µrad). However, a remarkable deflation of ~1.5 µrad was recorded during the paroxysm at South Crater.

Reference. Palfreyman, W.D., and Cooke, R.J.S., 1976, Eruptive history of Manam volcano, Papua New Guinea in Johnson R.W. (ed.), Volcanism in Australasia, Elsevier, Amsterdam, p. 117-131.

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: B. Talai, I. Itikarai, and P. de Saint Ours, RVO; NOAA/NESDIS Satellite Analysis Branch; Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA.


Mutnovsky (Russia) — December 1996 Citation iconCite this Report

Mutnovsky

Russia

52.449°N, 158.196°E; summit elev. 2288 m

All times are local (unless otherwise noted)


Fumarolic plume up to 1 km above the crater

On 25 November, a fumarolic plume was observed rising to a height of 1 km above the crater.

Geologic Background. Massive Mutnovsky, one of the most active volcanoes of southern Kamchatka, is formed of four coalescing stratovolcanoes of predominately basaltic composition. Multiple summit craters cap the volcanic complex. Growth of Mutnovsky IV, the youngest cone, began during the early Holocene. An intracrater cone was constructed along the northern wall of the 1.3-km-wide summit crater. Abundant flank cinder cones were concentrated on the SW side. Holocene activity was characterized by mild-to-moderate phreatic and phreatomagmatic eruptions from the summit crater. Historical eruptions have been explosive, with lava flows produced only during the 1904 eruption. Geothermal development is planned at Mutnovsky, which has the highest heat capacity of any volcano in the Kuril-Kamchatka arc.

Information Contacts: 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; Vladimir Kirianov, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia.


Cerro Negro (Nicaragua) — December 1996 Citation iconCite this Report

Cerro Negro

Nicaragua

12.506°N, 86.702°W; summit elev. 728 m

All times are local (unless otherwise noted)


Fumarole temperatures decrease further

On 23 December a visit to the crater found that the maximum fumarole temperature was only 606°C, indicating a decrease by another 30°C since the previous measurements on 27 November (BGVN 21:11).

Geologic Background. Nicaragua's youngest volcano, Cerro Negro, was created following an eruption that began in April 1850 about 2 km NW of the summit of Las Pilas volcano. It is the largest, southernmost, and most recent of a group of four youthful cinder cones constructed along a NNW-SSE-trending line in the central Marrabios Range. Strombolian-to-subplinian eruptions at intervals of a few years to several decades have constructed a roughly 250-m-high basaltic cone and an associated lava field constrained by topography to extend primarily NE and SW. Cone and crater morphology have varied significantly during its short eruptive history. Although it lies in a relatively unpopulated area, occasional heavy ashfalls have damaged crops and buildings.

Information Contacts: Alain Creusot, Instituto Nicaraguense de Energía, Managua, Nicaragua.


Pacaya (Guatemala) — December 1996 Citation iconCite this Report

Pacaya

Guatemala

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

All times are local (unless otherwise noted)


Strombolian eruptions and lava flows from MacKenney crater

Reports by Otoniel Matías of INSIVUMEH described volcanic activity after the 11 November eruption (BGVN 21:11) until 12 December. Seismic data were registered at a local one-component station (exact location undisclosed).

Activity during 11-30 November 1996. Heightened explosive Strombolian activity from MacKenney crater on 11 November was accompanied by abundant lava flows that covered most of the SW flank and traveled as far as 2 km from the volcano. The ash column reached 2 km, and deposited a 7-cm-thick layer of coarse tephra (1-3 cm in size) over the village of El Caracol (~4 km SW of the summit). Ash transported SW by strong winds fell in Escuintla and, as some local newspapers reported, in the Mexican city of Tapachula (300 km NW). At 2010 of the same day the eruption started dying down.

For the remainder of the month there was continuous emission of white-blue "smoke" at variable heights (50-300 m) above the crater. After the 11 November eruption seismicity was dominated by type-A volcano-tectonic swarms. During the next few days the swarm's foci deepened from 0.2-1 km to 5-10 km and then to 15-20 km and finally on 18 November, to 25-35 km. On 12 November a lava tongue ~2.5 km long was flowing S toward Cerro Buena Vista. On 13 November another small lava flow ~450 m long was observed on the SW flank.

During 15-18 November there were explosions of variable intensity every 1-3 minutes; the strongest explosions lasted 25-50 seconds and had amplitudes of 35-40 mm (peak-to-peak) and frequencies of 3-5 Hz. These explosions expelled pyroclastic material 75-150 m above the crater, depositing most material inside the crater.

On 20 November the seismic activity became characterized by harmonic tremor and type-B earthquakes, indicating magma movement toward the crater. The same day an eyewitness reported a red glow inside the main crater. Early on 21 November the white-blue column rose >500 m above MacKenney crater, but later that day decreased to ~300 m.

During 26-28 November the seismicity became characterized by alternating periods of activity followed by quiet for about 12 hours. The seismic activity shifted between seismo-tectonic swarms (one event every 2-10 minutes) and continuous tremor, suggesting that magma was ascending from depth and the confining rock was adjusting to the new stress field. After 28 November the activity was again dominated by seismo-tectonic events. Originating at depths of 0.2-1 km and up to M 1, there were 467 such events during a 24-hour observation period.

Activity during 1-12 December 1996. The white-blue column observed during November was also reported throughout this period at heights of 70-250 m. On 2, 3, and 4 December small explosions every 1-8 minutes were accompanied by ejection of incandescent material up to 100 m above MacKenney crater. This Strombolian activity was associated with harmonic tremor, although such tremors had appeared since the night of 1 December.

On 5 December puffs of steam lasting 5-7 minutes built up a column that rose 400 m. On 6 December, steam-and-ash expulsions of variable intensity turned brown in color and were observed at intervals of 2-10 minutes.

During 7-10 December the seismicity was characterized by tremor (mean amplitude, 2-5 mm; frequency, 3-4 Hz; and duration, 2-15 minutes) and type-A seismic events at 0.3-1 km depth. On 10-11 December steaming was observed on the N, W, and SW flanks of the MacKenney cone.

On 12 December white-blue emissions reached 300 m above the crater and drifted slowly SW for 5 km. That day, low-amplitude, low-frequency (0.5-1 Hz) harmonic tremor alternated with pulses of disharmonious tremor with amplitude 3-10 mm and 4-6 Hz frequency. During these pulses, steam-and-ash emissions occurred in association with considerable mass wasting inside the crater.

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

Information Contacts: Otoniel Matías, Seccion Vulcanologia, INSIVUMEH (Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia of the Ministerio de Communicaciones, Transporte y Obras Publicas), 7A Avenida 14-57, Zona 13, Guatemala City, Guatemala.


Pavlof (United States) — December 1996 Citation iconCite this Report

Pavlof

United States

55.417°N, 161.894°W; summit elev. 2493 m

All times are local (unless otherwise noted)


Intermittent eruptions from 15 September through [3] January

The current episode of eruptive activity, which began on 15 September (BGVN 21:08-21:10), persisted [through 3 January]. On 2 December, infrared video taken by the Alaska State Troopers confirmed that the E summit vent was more active than the W vent. The source of intense steaming low on the N flank, which had been intermittently visible to aerial and ground observers for several weeks, was not a new flank vent, but simply a site where lava was in contact with ice or meltwater. Meltwater channels extended down to the low pass between Pavlof and Pavlof Sister, then to the NW into the Cathedral River drainage. On the early morning of 4 December, seismic activity abruptly declined to about background, the lowest level after the onset of the eruption. The substantial decrease in seismicity implied that eruptive activity probably abated.

After a few days of quiescence, seismicity sharply increased on 10 December, accompanying intense long eruption pulses. Steam plumes reached an altitude of 8,500 m, and ash plumes rose to 7,700 m. On 11 December, pilots reported a steam plume at 8,700 m altitude and an ash cloud at 5,200 m. Satellite imagery indicated that a thick 20-km-wide plume extended as far as 160 km SE and a thinner, more diffuse part of the plume then turned E, extending 105 km. Seismicity declined on 12 December. However, lava fountaining from the summit vents and intermittent bursts of steam and ash to below 6,100 m continued; two lava flows were still active on the N flank. Seismicity decreased to about background levels on the evening of 13 December, but observers in Cold Bay, 60 km SW, reported lava fountaining prior to the seismic decrease. There was no steam or ash visible on the morning of 15 December.

Seismic activity began to build again around midnight on 25 December. In the early morning of 27 December seismicity quickly and steadily increased, reaching the highest level to date in this eruption episode. Early morning satellite images and pilot observations showed a summit hot spot, an active lava flow, and an ash plume extending tens of kilometers downwind (NW). That afternoon observers reported discontinuous bursts of ash and steam rising several hundred meters above the summit. Ground observers in Nelson Lagoon, 80 km NE, reported vigorous fire fountaining and a lava flow visible at night. On 28 December, visual reports in the afternoon from pilots and ground observers in Cold Bay indicated plumes reaching altitudes of 3,700-4,900 m and extending for up to 32 km WNW.

Seismicity started to decline in the afternoon, and the volcano was quiet during the night. On the morning of 29 December, pilots and ground observers in Cold Bay reported no eruptive activity. On 2 January, a pilot report indicated steam and ash drifting S from the summit. On the morning of 3 January, an observer in Cold Bay spotted a small burst of ash rising just above the summit. The eruptive pause continued during the week of 11-17 January with very low levels of seismicity.

Geologic Background. The most active volcano of the Aleutian arc, Pavlof is a 2519-m-high Holocene stratovolcano that was constructed along a line of vents extending NE from the Emmons Lake caldera. Pavlof and its twin volcano to the NE, 2142-m-high Pavlof Sister, form a dramatic pair of symmetrical, glacier-covered stratovolcanoes that tower above Pavlof and Volcano bays. A third cone, Little Pavlof, is a smaller volcano on the SW flank of Pavlof volcano, near the rim of Emmons Lake caldera. Unlike Pavlof Sister, Pavlof has been frequently active in historical time, typically producing Strombolian to Vulcanian explosive eruptions from the summit vents and occasional lava flows. The active vents lie near the summit on the north and east sides. The largest historical eruption took place in 1911, at the end of a 5-year-long eruptive episode, when a fissure opened on the N flank, ejecting large blocks and issuing lava flows.

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.


Poas (Costa Rica) — December 1996 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Fumarolic columns rise 500 m above the crater floor

During the four-month interval of September-December 1996 OVSCICORI-UNA reported the following N crater lake temperatures: 40, 35, 31, and 29°C, respectively. There were also fluctuations in the N crater lake's surface height. Defining a lake surface height increase with respect to the height in August as positive (+), during the four-month interval the progressive shifts were as follows: +13 cm, -54 cm, -31 cm, and +144 cm. Figures 62 and 63 show temperature and pH for the N crater lake and some chemical data for rainfall during the first eleven months of 1996.

Figure (see Caption) Figure 62. The pH and temperature of the N crater lake at Poás. Data points show discrete values taken at the date shown. Courtesy of OVSICORI-UNA.
Figure (see Caption) Figure 63. The chemistry of rainwater falling on Cerro Pelon at Poás. The ion concentration (for SO2+4 and Cl- in mg/liter) and pH (± 0.5 units) during the interval 26 January-28 November. Bars and points show discrete values taken at the date shown. Courtesy of OVSICORI-UNA.

Also during September-October, the accessible fumaroles on the pyroclastic cone maintained a maximum temperature of 93-94°C. Gas columns in the interval rose 500 m above the crater floor.

The number of low-frequency Poás earthquakes registered as follows: 2,351 (September), 2,043 (October), 1,704 (November, adjusted because of 14 days without data). December earthquakes have not yet been reported.

September contained the largest number of earthquakes recorded in any month in 1996. Low-frequency tremor, not seen since May, appeared for ~8 hours in September, also the most seen up to that point in 1996. Continuing the trend, tremor occurred for 28 hours during October. No tremor was recorded in November. For comparison, tremor had reached over 300 hours in December 1995.

Deformation during August and September 1996 was very low. Two lines in the sector S of the crater contracted by an average of ~5 mm (2-3 ppm), a shift considered insignificant. Although electronic tilt measurements were absent for August-September, two leveling lines along the crater's S border have lacked significant tilt since 1995.

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. Fernández, E. Duarte, V. Barboza, R. Van der Laat, E. Hernandez, M. Martinez, and R. Sáenz, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA).


Popocatepetl (Mexico) — December 1996 Citation iconCite this Report

Popocatepetl

Mexico

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

All times are local (unless otherwise noted)


Eruption on 25 December seen by airline pilots in satellite imagery

Popocatépetl erupted on 25 December 1996 beginning around 1145 as seen in satellite imagery and discussed in pilot reports from American Airlines. Comparison of satellite imagery at 1145 and 1215 suggested that the eruption was not continuous.

About 1145 on 25 December the ash cloud was bounded by the following points: 19.0°N, 98.6°W; 19.2°N, 98.8°W; 19.3°N, 98.6°W; and 19.1°N, 98.4°W. At around that time GOES-8 data indicated that the eruption's ash plume moved N and E while dispersing rather quickly in both infrared and visible imagery. At 1645 that day the ash plume appeared nearly linear. It formed a band ~50 km wide trending WNW-ESE (from 20.2°N, 99.2°W to 19.6°N, 97.1°W) and covering a distance of ~230 km.

The plume from the prior day's eruption was indistinguishable by 26 December, based on GOES-8 infrared imagery. A SIGMET valid during 2300-2400 on 25 December indicated only near-source ash, suggesting that by this time conditions had return to normal. No additional eruptions were seen around that time.

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: NOAA/NESDIS Synoptic Analysis Branch, USA.


Rabaul (Papua New Guinea) — December 1996 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)


Tavurvur's 4-5 October eruptions yield the largest lava flow in over 200 years

Strong Strombolian eruptions occurred at Tavurvur on 4-5 October, but activity was generally low during November and December. Before the eruptions in October, activity consisted of weak to moderate emissions of white vapor and occasional ash clouds that rose ~600 m above the crater. Some of the ash emissions were accompanied by roaring noises. Light ashfall was observed to the N and NW. Three moderate explosions occurred at 1209 on 3 October, and at 0017 and 0219 on 4 October, producing dark gray ash clouds 3-4 km high.

Strombolian eruptions started with emissions of dark gray ash clouds at 1200 on 4 October. At that time, real-time seismic amplitude measurement (RSAM) values were 30-50. Eruptive activity gradually increased, with more frequent emissions of thick, dark gray ash clouds. The activity rapidly increased at 1430, and peaked at 1450 with an RSAM value of ~680. Activity quickly declined after only 20 minutes, to an RSAM value of 300 by about 1700. Activity soon increased again, and reached another peak at about 2000 with an RSAM value of 800. Frequent loud explosions rattled windows and doors 7-8 km from the crater, and were heard as far as 40 km away. Red incandescent lava fragments were frequently projected ~1 km above the crater. Some of the ejecta were 1-2 m in diameter during the peak eruptions. The hot and plastic ejecta were deformed during flight.

Beginning at 2000, the eruptive activity slightly decreased and RSAM values dropped to ~710 in two hours, then the activity increased again and peaked at about 2320. According to the RSAM data, activity remained almost unchanged from then until 0820 the next morning with a constant RSAM value of ~860. From 0820 on 5 October, the activity began to decline, accompanied by frequent explosions. The frequency of explosions peaked at 1700 on 5 October (~150 explosions/hour), and decreased exponentially, with only ~20 explosions/hour at 0700 on 6 October. The last relatively large explosion occurred on 25 October.

During the strong phase of Strombolian eruptions, a significant amount of lava was erupted. Effusive activity began around 0130 on 5 October. Lava flowed to the S of the vent, covering a large area of coconut plantation and burying two houses. Three lobes of the lava flow moved into the sea, ~1.6 km from the vent. The volume of lava was estimated at 4-5 x 106 m3, the largest amount produced at Tavurvur in more than 200 years. Effusive activity occurred at Tavurvur during the 1994 eruption (BGVN 19:08-19:10), with a lava flow of ~0.4 x 106 m3.

Ash clouds produced by the Strombolian eruptions and the subsequent large explosions rose 3-4 km above the crater. Light ash fell on the N, NW, W, SW, and SE areas of the caldera. Moderate, damp ashfall was observed on Matupit Island 1.5 km W of the vent.

A low level of eruptive activity occurred at Tavurvur during November and December, with very weak to moderate emissions of white vapor. However, emissions of small volumes of pale gray ash took place twice in December, the first on 6-7 December. Pale gray emissions with a very low ash content began on the morning of 6 December, then gradually changed to weak, white vapor the next day. The ash clouds rose ~3 km above the crater before being blown to the NE, NW, and W. Very light ashfall was observed on 7 December in Rabaul Town, ~5 km NW of the crater. The second ash emission began on 27 December and was continuing at the end of the month.

During October-December, 27 high-frequency earthquakes were recorded. Two events on 24 December were felt with an intensity of III. During November and December, seismicity was generally low; the only seismic increases were associated with the two ash-emission episodes.

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: B. Talai, I. Itikarai, and P. de Saint Ours, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.


San Cristobal (Nicaragua) — December 1996 Citation iconCite this Report

San Cristobal

Nicaragua

12.702°N, 87.004°W; summit elev. 1745 m

All times are local (unless otherwise noted)


December vapor plumes appear smaller than previous ones

Since the end of the last rainy season, the vapor plume continuously present over the volcano has reduced in size compared to recent years. Late in 1996, fumaroles outside the crater decreased significantly. Fumaroles inside the crater concentrated in the lower part of the S and SE walls and had temperatures estimated to be in the 650-700°C range.

During the night and early morning on 24 December several incandescent areas were observed in the crater. These areas were similar to those reported over the past 15 years. Incandescence was visible from the top of the volcano at 500 m distance, and from the rim of the 1976 crater, a feature 400 m in diameter and 100-150 m deep. During 1996 small local earthquakes were detected monthly.

Geologic Background. The San Cristóbal volcanic complex, consisting of five principal volcanic edifices, forms the NW end of the Marrabios Range. The symmetrical 1745-m-high youngest cone, named San Cristóbal (also known as El Viejo), is Nicaragua's highest volcano and is capped by a 500 x 600 m wide crater. El Chonco, with several flank lava domes, is located 4 km W of San Cristóbal; it and the eroded Moyotepe volcano, 4 km NE of San Cristóbal, are of Pleistocene age. Volcán Casita, containing an elongated summit crater, lies immediately east of San Cristóbal and was the site of a catastrophic landslide and lahar in 1998. The Plio-Pleistocene La Pelona caldera is located at the eastern end of the complex. Historical eruptions from San Cristóbal, consisting of small-to-moderate explosive activity, have been reported since the 16th century. Some other 16th-century eruptions attributed to Casita volcano are uncertain and may pertain to other Marrabios Range volcanoes.

Information Contacts: Alain Creusot, Instituto Nicaraguense de Energía, Managua, Nicaragua.


Santa Maria (Guatemala) — December 1996 Citation iconCite this Report

Santa Maria

Guatemala

14.757°N, 91.552°W; summit elev. 3745 m

All times are local (unless otherwise noted)


Ash emissions and small collapses at Santiaguito dome

Santa María's large SW-flank crater that formed in a major eruption in 1902 contains Santiaguito, a dacite dome active almost continuously since 1922. In accord with this pattern, a small explosion was observed on 14 October. During 19 November-12 December 1996 several explosions of moderate-to-high intensity occurred almost daily. These explosions, three per hour, expelled ash in columns that rose variably 300-1,000 m above the active Caliente cone. The ash plumes, white-to-dark-gray in color, remained 8-15 minutes above the volcano before being blown W or SW or both directions. Light ashfalls were reported in the Rosario Palajunoi Estate (15 km from the volcano), La Finca Estate (~7 km SSW of the cone), over the woods in Siete Orejos area, but mostly in the proximity of Caliente cone.

Some of the explosions triggered small collapses and avalanches of blocks and ash down the Nimà Segundo river (SE flank) and along a channel opened by lava flows on the E flank of the volcano.

Geologic Background. Symmetrical, forest-covered Santa María volcano is part of a chain of large stratovolcanoes that rise above the Pacific coastal plain of Guatemala. The sharp-topped, conical profile is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank, and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four vents, with activity progressing W towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

Information Contacts: Otoniel Matías, INSIVUMEH.


Sheveluch (Russia) — December 1996 Citation iconCite this Report

Sheveluch

Russia

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

All times are local (unless otherwise noted)


Typical fumarolic plumes

On 5-6 December, and on 7 and 14-15 January, the usual fumarolic emissions were observed above the volcano.

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: 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; Vladimir Kirianov, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia.


Soufriere Hills (United Kingdom) — December 1996 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)


Dramatic fracturing on SW wall as dome growth continues

The following condenses the daily Scientific Reports of the Montserrat Volcano Observatory (MVO) for the period 9 December 1996-10 January 1997.

Visual observations during 9-31 December On 9 December it was noted that a crack on Galway's wall had opened 33 cm in five days. One side of the crack had moved by 7 cm, consistent with the wall being pushed outwards. Helicopter inspections on 10 December detected 20-m-deep cracks along and on top of this wall, making it very unstable. On 11 December a new dome appeared to the S of the 1 October dome, between Castle Peak and Galway's Wall (see map in BGVN 21:11). New fractures 100 m long and 1 m wide were seen at the E end of Galway's Wall.

On 14 December the new dome volume was estimated at 500,000 m3 ; having grown over a period of 2-3 days, its extrusion was comparable to the initial rates for the 1 October dome. On 15 December the new dome's top was at 910 m, higher than the October 1 dome at that time; growth had occurred along a linear structure oriented ESE. By 16 December the top of the dome was estimated at 920 m. Observations that day showed that the dome had nearly filled the scar left by the explosion in September and that a new spine had grown from its top.

On 17 December the new dome started to overflow the September explosion scar; this caused several moderate-sized rockfalls and small pyroclastic flows into the Tar River that traveled ~250 m from the dome. That day the new dome was 909 m high, its surface rubbly with coarse blocks, and its shape conical with a flat top and two spines. Comparison of recent dome surveys with previous results showed that older material near the new dome rose 80 m, a volume change of perhaps 7 x 106 m3 since the beginning of December. On 17 December several large steam clouds ascended above the volcano, probably caused by steam venting from the new dome.

On 19 December the new dome's E face was near-vertical and appeared very unstable. Discrete pulses of rockfalls and small pyroclastic flows from the dome occurred only a few minutes apart; these descended as far as 1 km along the gully on the S side of Castle Peak creating many small ash clouds that rose 300 m above the crater and drifted slowly W. A dome survey carried out using laser-ranging binoculars estimated the new dome's volume at approximately 800,000 m3, yielding an extrusion rate of 0.5 m3/s. That evening both the E side of the new dome and part of the pre-September dome failed, causing moderately large pyroclastic flows. These flows traveled down the Tar River and over its fan reaching to within 40 m of the sea; ash clouds rose 3 km and were carried SW. As the flows were generated observations from the airport suggested that fresh lava emerged into the dome nearly as quickly as it was lost in the flows. The next day, ground and helicopter observations indicated a reactivation of the 1 October dome growth. Many small rockfalls descended the 1 October dome's N side, fewer from its S side. Small pyroclastic flows generated ash clouds characterized by little convection, possibly suggesting that colder material was involved. This was confirmed by observations during the night using an infrared imaging system. This imaging system also showed that the entire 1 October dome was active.

During the following days, rockfalls and pyroclastic flows caused many more ash clouds which deposited ash in Plymouth; associated clouds displayed robust convection, suggesting that hot, fresh material was involved. A helicopter inspection on 22 December confirmed that the activity was restricted to the 1 October dome and that there was no sign of activity on the 11 December dome.

On 23 December heavy rain caused mudflows in Fort Ghaut that carried half-meter diameter boulders into the sea. On 25 December some uplift was observed on the N flank of the October 1 dome, perhaps due to an injection of fresh lava. On 26 December satellite imagery showed ash ~100 km WSW at a height of 1-2 km.

Ground and helicopter observations on 26 December showed a significant amount of new material on the top of the dome, darker in color and smoother than the older material. On 29 December, glowing all over the NE flank and avalanching of incandescent blocks were observed. Incandescence in daylight suggested that this dome lava may have been hotter than previous dome lavas. A considerable amount of material was observed on 31 December falling down the N flank of the pre-September dome towards Farrell's Wall. The new material at the top of the dome had changed texture, and looked more slabby than before.

Visual observations during 1-10 January 1997. The first seven days of January were characterized by numerous rockfalls and small pyroclastic flows from the 1 October dome, mainly down its NE and E sides. Much of this activity was channeled into the Tar River valley by way of either an erosion chute cutting across the top of Castle Peak or one to its N. At times of peak activity the pyroclastic flows occurred every few minutes and the largest traveled ~300 m past the Tar River Soufriere. Many of the rockfalls and flows generated ash clouds that drifted W and SW, forming a semi-continuous ash plume observed at altitudes of 1.3-1.6 km. On 3 January the plume was reported at 2 km altitude, and on 4 January satellite observations detected the plume 360 km W of Montserrat.

Theodolite measurements of the dome on 5 January showed that although the height had remained relatively constant at ~900 m since 1 January, a new lobe of lava at the top of the dome was ~50 m thick. It was calculated that 4.6 x 106 m3 of material was added between 25 December and 5 January, an extrusion rate of 4.4 m3/s. This was the highest sustained extrusion rate yet measured during this eruption. A helicopter inspection on 5 January revealed material slowly accumulating against the N crater wall; only 7 m of ridge remained above the divide to Tuitt's Ghaut. On 6 January the glowing dome appeared less steep in its upper part.

On 8 January several pyroclastic flows originating from behind Castle Peak moved down the Tar River Valley to reach beyond the Tar River Estate House; at least one pyroclastic flow reached the sea. Further growth was observed on the NW side of the 1 October dome, but was still contained inside the 17-18 September scar. Several new glowing channels eroded by the pyroclastic flows on the E side of the dome were visible. On 10 January a new, unstable-looking extrusion was observed in the middle of the heavily eroded chute crossing Castle Peak. This new extrusion was butterfly shaped and composed of slabs of fresh lava.

Seismicity and seismically detected mass wasting. Seismic activity during 9-11 December was characterized by swarms of shallow volcano-tectonic earthquakes, at times large enough to be felt close to the volcano. A few rockfalls from the dome and some landslides from the Galway's Wall were also detected by the seismic network, indicating that the wall became increasingly unstable during intense earthquake activity. However, a lack of seismicity on 12 December was accompanied by more landslides on Galway's Wall. During the following days rockfalls occurred sporadically, but their number slightly increased after 16 December, as the 11 December dome kept growing. Also, a few landslides from Galway's Wall suggested continued slow deformation. Seismicity increased on 20 December with a shallow volcano-tectonic earthquake swarm that reached the level of intensity of the early December swarms, although maximum magnitudes were not as large as before. Several rockfalls were also detected, mostly from the 1 October dome.

On 22 December the volcano-tectonic seismicity died out, rockfall signals continued, and hybrid seismicity reached April levels. This and increases in the quantity of ash and pyroclastic flows were taken as an indication that the dome growth rate had increased, but poor visibility prevented dome observations. By 24 December hybrid events and continuous tremor dominated the records, but by 27 December banded tremor reached a maximum. Banded tremor, which was last seen between late July and mid-September, had taken place associated with large pyroclastic flows and the 17-18 September explosion.

On 28 December large hybrid events and rockfall signals dominated, but regularly spaced bands of continuous seismic tremor returned on 30 December. Lower in amplitude than before, the banded tremor occurred at ~10-hour intervals. By 31 December the activity was again dominated by banded tremor episodes ~5 hours apart, and by hybrid earthquakes and rockfall signals. This pattern of seismicity continued during the first seven days of January. Volcano-tectonic earthquakes returned on 4 January with signals similar to the November and December events, but possibly from slightly greater depths (2-3 km). From 8 to 10 January, in correspondence with increased dome activity, the seismicity became dominated by rockfall and pyroclastic-flow signals.

COSPEC, EDM, and other measurements. COSPEC measurements were made on 27 and 28 December. The data from 27 December averaged 350 metric tons/day (t/d) but reached ~400 t/d shortly after one of the peaks in seismic tremor. The average fluxes on 28 December, and on 1, 4, 9, and 10 January were 325, 300, 400, 1,130, and 390 t/d, respectively. The increase in emission of SO2 measured on 9 January was probably due to a partial collapse of the dome.

EDM measurements carried out on the E triangle on 10 and 13 December suggested a continuation of the shortening trend started several weeks earlier. On 16 December, the S triangle had been unchanged since 4 December; on 18 December the lines N of the volcano had also not changed significantly since 5 November. The average shortening on the lines to Castle Peak during 20-22 December was 6 cm; such high rates of deformation had occasionally been seen in the past. In contrast, the shortening seen there during 26-28 December was small (2.4 mm). This drop in the deformation rate roughly coincided with the appearance of new material at the surface on the 1 October dome.

Gravity measurements on the E flank on 22 December showed no significant changes since July 1996. Changes at stations on the upper slope were consistent with the mass added to the dome.

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/).


Turrialba (Costa Rica) — December 1996 Citation iconCite this Report

Turrialba

Costa Rica

10.025°N, 83.767°W; summit elev. 3340 m

All times are local (unless otherwise noted)


Number of microseismic events continues to increase

Microseismic events, which were only detected locally, appeared 540 times during September, leading to the largest monthly total yet seen in 1996. The totals for October and November were 308 and 220 (the latter was extrapolated from 17 days of recording). Monthly microearthquake totals were essentially zero for the first four months of 1996 and generally grew steadily through September. The seismic station (VTU) lies 0.5 km SW of the active crater. The cumulative dry-tilt for the first 10 months of 1996 measured 10 µrad. The temperature and pH, however, remained relatively stable for the two available measurements during 1996 (BGVN 21:08).

Geologic Background. Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive edifice covers an area of 500 km2. Three well-defined craters occur at the upper SW end of a broad 800 x 2200 m summit depression that is breached to the NE. Most activity originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred during the past 3500 years. A series of explosive eruptions during the 19th century were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters.

Information Contacts: E. Fernández, E. Duarte, V. Barboza, R. Van der Laat, E. Hernandez, M. Martinez, and R. Sáenz, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.


Villarrica (Chile) — December 1996 Citation iconCite this Report

Villarrica

Chile

39.42°S, 71.93°W; summit elev. 2847 m

All times are local (unless otherwise noted)


Crater observations for the interval 11 September 1996-13 January 1997

The following summarizes observations of eruptive activity during 11 September 1996-13 January 1997, based on descriptions by volcano guides and a visit to the volcano by Werner Keller in January 1997.

On 11 September 1996 a group of mountain climbers observed intense degassing of water vapor and reported that the small lava pond on the crater floor was not visible. On 14 September (BGVN 21:09) there was emission of ash accompanied by a dull rumbling noise. Guide Claudio Marticorena of Pucon was close to the summit with a group of tourists at the time of the ash emissions and reported that lava blocks tens of centimeters in diameter were ejected above the rim of the summit crater.

October and November were characterized by a notable rise of the magma column within the central crater pit, which was almost completely filled to its rim. Mountain guides Victor Sepulveda and Claudio Marticorena reported a vigorously convecting lava lake 50 m in diameter with fountaining from several areas of the lake. Frequent bursts ejected spatter and incandescent bombs beyond the summit crater, onto the upper flanks of the cone every few seconds. This activity lasted until mid-November 1996, followed by a rapid subsidence of the magmatic column and accompanied by strong vapor emission later that month. In December, the characteristic nocturnal crater glow observed at Villarrica during the past years disappeared.

Fumarolic emissions from the summit crater diminished in early January 1997, and on 4 January Sepulveda noted that the inner crater pit was again completely visible, for the first time since late November 1996. At that date, the central pit was ~100 m deep, with two small degassing vents at the bottom. No incandescent lava was visible in either of the vents, but gas emissions produced a distinct noise. The S part of the intracrater platform left after the 1984-85 eruption had collapsed into the central pit. On 13 January, mountain guides noted incandescent lava within the central pit: this suggested a new rise of the magma column.

Geologic Background. Glacier-clad Villarrica, one of Chile's most active volcanoes, rises above the lake and town of the same name. It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. A 6-km-wide caldera formed during the late Pleistocene. A 2-km-wide caldera that formed about 3500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesitic cone at the NW margin of the Pleistocene caldera. More than 30 scoria cones and fissure vents dot the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Historical eruptions, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

Information Contacts: Boris Behncke, Geomar Research Center for Marine Geosciences, Wischhofstrasse 1-3, 24148 Kiel, Germany; Werner Keller, Wiesenstrasse 8, 86438 Kissing, Germany.

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/).