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Bulletin of the Global Volcanism Network

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

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


Recently Published Bulletin Reports

Aira (Japan) Ash plumes continue at the Minamidake crater from July through December 2018

Ibu (Indonesia) Thermal anomalies and ash explosions from the crater continue during May-November 2018

Masaya (Nicaragua) Lava lake activity continued from May through October 2018; lava lake lower than recent months

Sarychev Peak (Russia) Thermal anomalies, surface activity, and ash explosions during October-November 2017 and September-October 2018

Suwanosejima (Japan) Multiple explosive events with incandescence and ash plumes during November 2018

Etna (Italy) Lava flows emerge from NSEC in late August and late November 2018; Strombolian activity continues from multiple vents

Dukono (Indonesia) Regular ash explosions continuing as of September 2018

Ulawun (Papua New Guinea) Ash plumes on 8 June, 21 September, and 5 October 2018

Langila (Papua New Guinea) Several weak ash plumes during June, September, and October 2018

Sangeang Api (Indonesia) Ongoing crater activity and thermal anomalies during September 2017-October 2018

Sheveluch (Russia) Thermal anomalies along with minor gas and steam emissions continue through October 2018

Gamalama (Indonesia) Weak explosion on 4 October 2018



Aira (Japan) — January 2019 Citation iconCite this Report

Aira

Japan

31.593°N, 130.657°E; summit elev. 1117 m

All times are local (unless otherwise noted)


Ash plumes continue at the Minamidake crater from July through December 2018

Sakurajima is one of the most active volcanoes in Japan and is situated in the Aira caldera in southern Kyushu. It regularly produces ash plumes and scatters blocks onto the flanks during explosions. This report covers July through December 2018 and describes activity at the Minamidake crater, which has continued with the activity typically observed at Sakurajima volcano. In late 2017 the eruptive activity has migrated from being centered at the Showa crater, to being focused at the Minamidake crater. This change has continued into the later half of 2018. The following activity summarizes information issued by the Japan Meteorological Agency (JMA), the Japan Volcanic Ash Advisory Center (VAAC), and satellite data.

Activity from July through December 2018 was focused at the summit Minamidake crater with 8 to 64 ash emission events per month, with 50-60% being explosive in nature during four of the six months reported (table 20, figure 67). The maximum explosions per day was 64 on 31 August (figure 68). No pyroclastic flows were recorded during this time. Recent activity at the Showa crater has been declining and no activity was observed during the reporting period. Sakurajima has remained on Alert Level 3 on a 5-level scale during this time, reflecting the regular ash plumes and volcanic blocks that erupt out onto the slopes of the volcano during explosive events.

Table 20. Monthly summary of eruptive events recorded at Sakurajima's Minamidake crater in Aira caldera, July-December 2018. The number of events that were explosive in nature are in parentheses. No events were recorded at the Showa crater during this time. Data courtesy of JMA (July to December 2018 monthly reports).

Month Ash emissions (explosive) Max. plume height above the crater Max. ejecta distance from crater
Jul 2018 29 (16) 4.6 km 1.7 km
Aug 2018 64 (37) 2.8 km 1.3 km
Sep 2018 44 (22) 2.3 km 1.1 km
Oct 2018 8 (0) 1.6 km --
Nov 2018 14 (2) 4 km 1.7 km
Dec 2018 56 (34) 3 km 1.3 km
Figure (see Caption) Figure 67. Satellite images showing ash plumes from Sakurajima's Minamidake summit crater (Aira caldera) in August, September, and November 2018. Natural color satellite images (bands 4, 3, 2) courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 68. Explosions per day at Sakurajima's Minamidake summit crater (Aira caldera) for July through December 2018. Data courtesy of JMA.

Activity through July consisted of 29 ash emission events (16 of which were explosive) producing ash plumes up to a maximum height of 4.6 km above the crater and ballistic ejecta (blocks) out to 1.7 km from the crater, but ash plumes were more commonly 1.2 to 2.5 km high. The largest explosive event occurred on 16 July, producing an ash plume up to 4.6 km from the vent and ejecting ballistic rocks out to 1.3-1.7 km from the crater (figure 69). On 17 July, sulfur dioxide emissions were measured at 1,300 tons per day, and on 26 July emissions were measured to be 2,100 tons per day.

Figure (see Caption) Figure 69. Ash plumes erupting from the Sakurajima Minamidake crater (Aira caldera) on 16 July 2018 at 1538 (upper) and 1500 (lower) local time. The ash plumes reached 4.6 km above the crater rim and ejected rocks out to 1.3-1.7 km from the crater. Higashikorimoto webcam images courtesy of JMA (July 2018 monthly report).

During August the Minamidake crater produced 64 ash emission events (37 explosive in nature) with a maximum ash plume height of 2.8 km above the crater, and a maximum ballistic ejecta distance of 1.3 km from the crater on 31 August (figure 70). Ash plumes were more commonly up to 1 to 2.1 km above the crater. Sulfur dioxide emissions were very high on 2 August, measured as high as 3,200 tons per day, and was measured at 1,500 tons per day on 27 August.

Figure (see Caption) Figure 70. Activity at Sakurajima volcano (Aira Caldera) in August 2018. Top: A gas-and-ash plume that reached 2.8 km above the crater at 1409 on 29 August. Bottom: Scattered incandescent blocks out to 1-1.3 km from the crater on the flanks of Sakurajima after an explosion on 31 August. Higashikorimoto and Kaigata webcam images courtesy of JMA (August 2018 monthly report).

Throughout September 44 ash emission events occurred, with 22 of those being explosive in nature. The Maximum ash plume height reached 2.3 km above the crater, and the maximum ejecta landed out to 1.1 km from the crater. An explosive event on 9 September ejected material out to 700 m away from the crater and on 22 September an event scattered blocks out to 1.1 km from the crater (figure 71).

Figure (see Caption) Figure 71. Incandescent blocks on the flanks of Sakurajima volcano (Aira caldera) after an explosion on 22 September 2018 at 2025. The event scattered blocks out to 1.1 km from the Minamidake crater. Kaigata webcam image courtesy of JMA (September 2018 monthly report).

October and November were relatively quiet with regards to the number of ash emission events with only 22 events over the two months. The maximum ash plume heights reached 1.6 and 4 km, respectively. An observation flight on 22 October showed the currently inactive Showa crater restricted to minor fumarolic degassing, and steam-and-gas and dilute ash plume activity in the Minamidake crater (figure 72). An eruption on 14 November at 0043 local time produced an ash plume to over 4 km above the crater and scattered incandescent blocks out to over 1 km from the crater (figure 73). This was the first ash plume to exceed a height of 4 km since 16 July 2018. Two events occurred during 16-19 November that produced ash plumes up to 1.6 km. Sulfur dioxide measurements were 3,400 tons on 4 October, 400 tons on 17 October, 1,000 tons on 23 October, 1,100 tons on 6 November, and 1,400 tons on 20 November.

Figure (see Caption) Figure 72. Minor fumarolic degassing has occurred in Sakurajima's Showa crater (Aira caldera) and the vent has been blocked by ash and rock. The active Minamidake crater is producing a blue-white plume to 400 m above the crater and a dilute brown plume that remained within the crater. Images taken by the Japan Maritime Self-Defense Force 1st Air Group P-3C on 22 October 2018, courtesy of JMA (October 2018 monthly report).
Figure (see Caption) Figure 73. Eruption of Sakurajima (Aira caldera) on 14 November at 0043 local time ejecting incandescent blocks more than 1 km from the crater and an ash plume up to 4 km above the crater. Photos courtesy of The Asahi Shimbun.

Small ash plumes continued through December with 56 ash emission events, 34 of which were explosive in nature. The maximum ash plume height above the crater reached 3 km, and the maximum distance that ejecta traveled from the vent was 1.3 km, both during an event on 24 December (figure 74). An explosive event produced an ash plume that reached a height of 2.5 km above the crater and scattered ejecta out to 1.1 km from the crater.

Figure (see Caption) Figure 74. An explosive event at 1127 on 24 December 2018 at Sakurajima's Minamidake crater (Aira caldera). The ash plume reached 3 km above the crater rim. Higashikorimoto webcam image courtesy of JMA (December 2018 monthly report).

Intermittent incandescence was observed at the summit at nighttime throughout the entire reporting period. Areas of elevated thermal energy within the Minamidake crater were visible in cloud-free Sentinel-2 satellite images (figure 75) and elevated temperatures were detected in MIROVA on a few days.

Figure (see Caption) Figure 75. Sentinel-2 thermal satellite images showing the summit area of Sakurajima volcano, Aira caldera, in October 2018. The areas of elevated thermal activity (bright orange-red) are visible within the Minamidake crater. No thermal anomalies are visible within the Showa crater. Thermal (Urban) satellite images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Geologic Background. The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan's most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the Aira caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim of Aira caldera and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4850 years ago, after which eruptions took place at Minamidake. Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu's largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); 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); 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/); The Asahi Shimbun (URL: http://www.asahi.com/ajw/articles/AJ201811140035.html accessed on 12 March 2018).


Ibu (Indonesia) — December 2018 Citation iconCite this Report

Ibu

Indonesia

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

All times are local (unless otherwise noted)


Thermal anomalies and ash explosions from the crater continue during May-November 2018

Continuing activity at Ibu has consisted of numerous thermal anomalies and, except apparently for the period from September 2017 through early March 2018, intermittent ash explosions (BGVN 43:05). This activity continued through November 2018. The Alert Level has remained at 2 (on a scale of 1-4), and the public was warned to stay at least 2 km away from the active crater, and 3.5 km away on the N side.

Ash plumes were seen frequently during May-November 2018 (table 4). Plume heights above the crater were generally 400-80 m. However, ash plumes on 28 and 29 July rose 5.5 and 4.8 km, respectively. Seismicity associated with ash plumes were characterized by explosion and avalanche signals.

Table 4. Ash explosions reported at Ibu, May-November 2018. Data courtesy of PVMBG and Darwin VAAC.

Date Time Ash plume (height above crater rim) Plume Drift
05 May 2018 0622 600 m N, NE
06 Jun 2018 1206 500 m N
12 Jun 2018 1750 600 m N
14-19 Jun 2018 -- 200-600 m N
21 Jun 2018 0857 600 m N
22-26 Jun 2018 -- 850 m WNW, W
27 Jun 2018 -- 500 m W
06 Jul 2018 -- 800 m N
10-15 Jul 2018 -- 200-800 m --
28 Jul 2018 1852 5.5 km SE
29 Jul 2018 1612 4.8 km N, SE
13 Aug 2018 0259 600 m --
20 Aug 2018 1742 1.2 km --
24 Aug 2018 0838 800 m S
28, 30 Sep 2018 -- 500 m N, NE
06 Oct 2018 -- 500 m WSW
19 Oct 2018 1223 400 m N
26 Nov 2018 -- 500 m SE

The number of thermal anomalies during this time, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, ranged from 2 days/month (July) to 9 days/month (September); some events were two pixels. Days with anomalies and ash explosions were not well correlated. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, also based on analysis of MODIS data, detected numerous hotspots every month of the reporting period, almost all of which were within 5 km of the volcano and of low-to-moderate power. Infrared satellite imagery showed that the volcano had at least two, and sometimes three, active dome or vent locations (figure 14).

Figure (see Caption) Figure 14. Sentinel-2 satellite images of Ibu on 19 August 2018. Top image (infrared, bands 12, 11, 8A) shows a large central hotspot and a smaller thermal area immediately to the west. Bottom image (natural color, bands 8, 4, 3) shows both an ash plume (gray) and steam plume (white), along with fresh and older lava in the crater. Courtesy of Sentinel Hub Playground.

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/); 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).


Masaya (Nicaragua) — November 2018 Citation iconCite this Report

Masaya

Nicaragua

11.984°N, 86.161°W; summit elev. 635 m

All times are local (unless otherwise noted)


Lava lake activity continued from May through October 2018; lava lake lower than recent months

Masaya is one of the most active volcanoes in Nicaragua and one of the few volcanoes on Earth to contain an active lava lake. The edifice has a caldera that contains the Masaya (also known as San Fernando), Nindirí, San Pedro, San Juan, and Santiago (currently active) craters. In recent years, activity has largely consisted of lava lake activity along with dilute plumes of gas with little ash. In 2012 an explosive event ejected ash and blocks. This report summarizes activity during May through October 2018 and is based on Instituto Nicaragüense de Estudios Territoriales (INETER) reports and satellite data.

Reports issued from May through July 2018 noted that Masaya remained relatively calm. Sentinel-2 thermal satellite images show consistently high temperatures in the Santiago crater with the active lava lake present (figure 65).

Figure (see Caption) Figure 65. Sentinel-2 thermal satellite images showing the detected heat signature from the active lava lake at Masaya during May-July 2018. The lava lake is visible (bright yellow-orange) and a gas-and-steam plume is visible traveling towards the W to SW. Thermal (urban) satellite images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Reports from August through October 2018 indicated relatively low levels of activity. On 28 September the lava lake within the Santiago crater was observed with a lower surface than previous months. Fumarole temperatures up to 340°C were recorded (figure 66). Sentinel-2 thermal images show the large amount of heat consistently emanating from the active lava lake (figure 67). Sulfur dioxide was measured on 28 and 30 August with an average of 1,462 tons per day, a higher value than the average of 858 tons per day detected in February. Sulfur dioxide levels ranged from 967 to 1,708 tons per day on 11 September.

Figure (see Caption) Figure 66. FLIR (forward-looking infrared) and visible images of the Santiago crater at Masaya showing fumarole temperatures. The scale in the center shows the range of temperatures in the FLIR images. Courtesy of INETER (September 2018 report).
Figure (see Caption) Figure 67. Sentinel-2 thermal satellite images showing the heat signature from the active lava lake at Masaya during August-October 2018. The lava lake is visible (bright yellow-orange) and a gas-and-steam plume is visible traveling towards the SW. Thermal (urban) satellite images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Overall, activity from May through October 2018 was relatively quiet with continued lava lake activity. The thermal energy detected by the MIROVA algorithm showed fluctuations but were consistent (figure 68). The MODVOLC algorithm for near-real-time thermal monitoring of global hotspots detected 4-8 anomalies per month for this period, which is lower than previous years (figure 69).

Figure (see Caption) Figure 68. Middle infrared MODIS thermal anomalies at Masaya for April through October 2018. The data show relatively constant thermal activity related to the persistent lava lake. Courtesy of MIROVA.
Figure (see Caption) Figure 69. Thermal alerts for Masaya in May through October 2018. Courtesy of HIGP - MODVOLC Thermal Alerts System.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras pyroclastic shield volcano and is a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The twin volcanoes of Nindirí and Masaya, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6500 years ago. Historical lava flows cover much of the caldera floor and have confined a lake to the far eastern end of the caldera. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals cause health hazards and crop damage.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://webserver2.ineter.gob.ni/vol/dep-vol.html); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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/).


Sarychev Peak (Russia) — November 2018 Citation iconCite this Report

Sarychev Peak

Russia

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

All times are local (unless otherwise noted)


Thermal anomalies, surface activity, and ash explosions during October-November 2017 and September-October 2018

Located on Matua Island in the central Kurile Islands, Russia, Sarychev Peak (figures 19 and 20) had a significant eruption in June-July 2009 (BGVN 34:06, 35:09). Prior to this, a 1946 eruption resulted in the crater with a diameter and depth of approximately 250 m, with steep, sometimes overhanging crater walls. The N crater wall may have collapsed after a 1960 eruption, based on eyewitness accounts. A 1976 eruption included strong emissions and lava flows which resulted in a crater diameter of approximately 200 m and a floor 50-70 m below the rim. The eruption on 11-16 June 2009 encompassed more than ten large explosions, resulting in pyroclastic flows and ash plumes. The area of island covered by the June 2009 pyroclastic flows was more than 8 km2 (BGVN 34:06). Monitoring reports come from the Kamchatkan Volcanic Eruption Response Team (KVERT) and the Sakhalin Island Volcanic Eruption Response Team (SVERT).

Figure (see Caption) Figure 19. Photo looking into the crater of Sarychev Peak from the crater rim on 27 June 2017. Courtesy of V. Gurianov, Institute of Volcanology and Seismology FEB, RAS, KVERT.
Figure (see Caption) Figure 20. Sentinel-2 satellite image (natural color, bands 4, 3, 2) of Sarychev Peak on 8 September 2017. Courtesy of Sentinel Hub Playground.

Thermal anomalies were noted by the NOAA Cooperative Institute for Meteorological Satellite Studies over a period of five hours on 14 October 2017 in satellite data from Terra MODIS, S-NPP VIIRS, and Himawari-8; a plume of unknown composition accompanied the anomaly. A smaller thermal anomaly was present on 12 October, but not seen the following day during favorable viewing conditions. Another thermal anomaly was reported by SVERT on 21 October; views on other days that week of 17-23 October were obscured by clouds. On 7 November gas emissions and an elongated area of snow melt and potential thermal signature was visible on the N flank of the volcano (figure 21). On 8 and 13 November steam emissions were reported by SVERT and cloud cover prevented additional observations.

Figure (see Caption) Figure 21. Sentinel-2 satellite images of Sarychev Peak on 7 November 2017. Top image (natural color, bands 4, 3, 2) shows a white plume rising from the summit crater and a dark area extending about 1.25 km NW on the snow-covered slopes. Bottom image (atmospheric penetration, bands 12, 11, 8A) shows hot areas (in orange) of volcano material near the summit within the dark area seen in visible imagery. Courtesy of Sentinel Hub Playground.

The volcano was usually cloud-covered after mid-November 2017 through mid-February 2018. A small white plume seen in Sentinel-2 imagery on 20 February 2018 was not accompanied by a noticeable thermal anomaly, and the island appeared completely snow-covered. No activity of any kind was seen on the next cloud-free images taken on 4 and 11 May 2018, when the summit crater was filled with snow.

KVERT noted in a September report that there had been a thermal anomaly periodically observed after 7 May 2018. Fumarolic plumes were visible on 5 and 18 June 2018 (figure 22). Thermal anomalies were present on 8 and 11-12 September. Moderate explosions were reported during 11-15 September 2018, with ash emissions rising 3-4 km. On 14 September ash plumes drifted as far as 120 km NNE and the Aviation Color Code was raised to Orange. Explosions on 17 September generated ash plumes that rose as high as 4.5 km and drifted 21 km NE. Additional ash plumes identified in satellite images drifted 265 km E during 17-18 September. The eruption continued through 21 September, and a thermal anomaly was again visible on 22 September.

Figure (see Caption) Figure 22. Fumarolic activity at Sarychev Peak on 18 June 2018. Courtesy of FEC SRC Planeta, Institute of Volcanology and Seismology FEB RAS, KVERT.

Based on Tokyo VAAC data and satellite images, KVERT reported that at 1330 on 10 October 2018 an ash plume reached 1.7-2 km altitude and drifted 95 km E. SVERT reported that on 15 October an ash plume rose to 2.1 km altitude and drifted 65-70 km E. KVERT reported that a thermal anomaly was also identified in satellite images on 15 October. No further activity was seen through the end of October.

Thermal anomalies identified in MODIS data by the MIROVA system during October 2016-October 2018 occurred intermittently during the summer months each year (figure 23). However, most of those events were low-power and located several kilometers from the crater, so the heat source is unclear.

Figure (see Caption) Figure 23. Thermal anomalies detected by the MIROVA system using MODIS data at Sarychev Peak for the year ending 18 October 2017 (top) and ending 24 October 2018 (bottom), plotted as log radiative power. Most of the events shown were located several kilometers from the summit crater. Courtesy of MIROVA.

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: Sakhalin Volcanic Eruptions Response Team (SVERT), Institute of Marine Geology and Geophysics (IMG&G) Far East Division Russian Academy of Sciences (FED RAS), 1B Science St., Yuzhno-Sakhalinsk, 693022, Russia (URL: http://www.imgg.ru/); 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/); NOAA, Cooperative Institute for Meteorological Satellite Studies (CIMSS), Space Science and Engineering Center (SSEC), University of Wisconsin-Madison, 1225 W. Dayton St. Madison, WI 53706, (URL: http://cimss.ssec.wisc.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).


Suwanosejima (Japan) — January 2019 Citation iconCite this Report

Suwanosejima

Japan

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

All times are local (unless otherwise noted)


Multiple explosive events with incandescence and ash plumes during November 2018

Suwanosejima, an andesitic stratovolcano in Japan's northern Ryukyu Islands, was intermittently active for much of the 20th century, producing ash plumes, Strombolian explosions, and ash deposits. Continuous activity since October 2004 has produced intermittent explosions, generating ash plumes in most months that rise hundreds of meters above the summit to altitudes between 1 and 3 km. Ongoing activity for the second half of 2018 is covered in this report with information provided by the Japan Meteorological Agency (JMA) and the Tokyo Volcanic Ash Advisory Center (VAAC).

Activity during July-December 2018 was intermittent with explosions reported twice in September and 21 times during November. Incandescent activity was observed a few times each month, increasing significantly during November. Thermal data support a similar pattern of activity; the MIROVA thermal anomaly graph indicated intermittent activity through the period that was most frequent during October and November (figure 33). MODVOLC thermal alerts were issued once in September (9), three times in October (7, 21), and four times on 14 and 15 November.

Figure (see Caption) Figure 33. MIROVA thermal data for Suwanosejima from 7 February through December 2018 indicated intermittent activity at the summit that increased to more significant activity during October and November before declining by the end of the year. Courtesy of MIROVA.

There were no explosions at Suwanosejima during July or August 2018; steam plumes rose 900-1,000 m above the crater rim and incandescence was intermittently observed on clear nights. During September incandescence was also observed at night; in addition, explosions were reported on 12 and 13 September, with ash plumes rising 1,100 m above the crater rim. October was again quiet with no explosions, only steam plumes rising 800 m, and occasional incandescence at night, although thermal activity increased (figure 33).

More intense activity resumed during November 2018 with 21 explosions reported. On 9 and 14 November tephra was ejected up to 700 m from the Mitake crater. The Tokyo VAAC reported an ash plume visible in satellite imagery at 2.4 km altitude moving E on 14 November. The next day, a plume was reported at 2.7 km altitude drifting NW but it was not visible in satellite imagery. JMA reported gray ash plumes that rose up to 2,000 m above the crater rim on 16 and 23 November (figure 34). The ash plume on 23 November was visible in satellite imagery drifting N at 2.7 km altitude. On 30 November the Tokyo VAAC reported an ash plume visible in satellite data drifting SE at 2.4 km altitude. Incandescence was often observed at night from the webcams throughout the month. Ashfall was confirmed in the village 4 km SSW on 14, 17, and 23 November, and sounds were reported on 20 November.

Figure (see Caption) Figure 34. Ash plumes rose 2,000 m above the crater rim at Suwanosejima on 23 November 2018 as seen with the 'campsite' webcam. Courtesy of JMA (Volcanic activity commentary (November, 2018) of Suwanose Island).

During December 2018, no explosive eruptions were reported, but an ash plume rose 1,800 m above the summit on 26 December. Incandescence was observed on clear nights in the webcam. Throughout 2018, a total of 42 explosive events were reported; 21 of them occurred during November (figure 35).

Figure (see Caption) Figure 35. Eruptive activity at Suwanosejima during 2018. Black bars represent heights of steam, gas, or ash plumes in meters above crater rim (left axis), gray volcanoes along the top represent explosions, usually accompanied by ash plumes, red volcanoes represent large explosions with ash plumes, orange diamonds indicate incandescence observed in webcams. Courtesy of JMA (Volcanic activity of Suwanose Island in 2018).

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

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/).


Etna (Italy) — December 2018 Citation iconCite this Report

Etna

Italy

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

All times are local (unless otherwise noted)


Lava flows emerge from NSEC in late August and late November 2018; Strombolian activity continues from multiple vents

Italy's Mount Etna on the island of Sicily has had historically recorded eruptions for the past 3,500 years and has been erupting continuously since September 2013 through at least November 2018. Lava flows, explosive eruptions with ash plumes, and Strombolian lava fountains commonly occur from its summit areas that include the Northeast Crater (NEC), the Voragine-Bocca Nuova (or Central) complex (VOR-BN), the Southeast Crater (SEC) (formed in 1978), and the New Southeast Crater (NSEC) (formed in 2011). A new crater, referred to as the "cono della sella" (saddle cone), emerged during early 2017 in the area between SEC and NSEC and has become the highest part of the SEC-NSEC complex. Activity during late 2017 and early 2018 consisted mostly of sporadic Strombolian activity with infrequent minor ash emissions from multiple vents at various summit craters. Lava flow activity resumed in late August 2018 and again in late November and is covered in this report with information provided primarily by the Osservatorio Etneo (OE), part of the Catania Branch of Italy's Istituo Nazionale di Geofisica e Vulcanologica (INGV).

After several months of low-level activity in early 2018, increases in Strombolian activity at several vents began in mid-July (BGVN 43:08). This was followed by new lava flows emerging from the saddle cone and the E vent of the NSEC complex in late August. Discontinuous low-intensity Strombolian activity and intermittent ash emissions were reported from multiple vents at various summit craters during September through November. In late November, renewed Strombolian activity and a new, small flow emerged from a small scoria cone inside the E vent of the NSEC crater and persisted through the end of the month. The MIROVA thermal anomaly correspond to ground observations of increased thermal activity at Etna beginning in mid-July, peaking in late August, and increasing again at the end of November 2018 (figure 222).

Figure (see Caption) Figure 222. MIROVA thermal anomaly graph for Etna from April through early December 2018 shows the increases in thermal activity from lava flows and increased Strombolian activity in late August and late November. Courtesy of MIROVA.

Low-energy Strombolian activity resumed at both of the Bocca Nuova BN-1 vents as well as the vents in the Northeast Crater (NEC) during the second week of July 2018 and continued throughout the month. The activity from BN-1 was nearly continuous, but not always visible; occasionally, lava fragments rose 100 m and could be seen outside of the crater rim. Intermittent ash emissions accompanied the Strombolian activity. Activity at NEC was characterized by strong and prolonged explosions (up to several tens of seconds), sometimes with reddish-brown ash emissions (figure 223). Three vents on the floor of NEC continued to widen due to collapse of the inner walls. A seismic swarm on 18-19 July was located between 4 and 9 km depth.

Figure (see Caption) Figure 223. Ash emissions from the Northeast Crater of Etna on a) 27 July and b) 28 July 2018 rose a few tens of meters and quickly dispersed. Left image by INGV personnel, right image by volcanology guide Francesco Ciancitto. Courtesy of INGV (Rep. 31/2018, ETNA, Bollettino Settimanale, 23/07/2018 - 29/07/2018, data emissione 31/07/2018).

During a field inspection on 30 July INGV personnel noted activity at the three vents at the bottom of Northeast Crater; the farthest west produced ash emissions, the center produced steam, and the vent under the NE crater wall produced Strombolian activity that sent ejecta as high as the crater rim. Frequent ash emissions from NEC were observed on 3, 4, and 5 August. During the first week of August 2018 Strombolian activity also continued at BN-1 (figure 224). The webcam at Montagnola (EMOH) recorded incandescence at night from Bocca Nuova.

Figure (see Caption) Figure 224. Activity during the first half of August 2018 at Etna was concentrated at BN-1, the Northeast Crater (NEC), and the E vent of the New Southeast Crater (NSEC), shown in red. Courtesy of INGV (Rep. 33/2018, ETNA, Weekly Bulletin, 08/06/2018 - 12/08/2018, issue date 08/14/2018).

After several months of calm, explosive activity also resumed at the E vent of the of the New Southeast Crater, high on the E flank, in early August. An explosion in the early morning of 1 August 2018 generated a gray-brown ash plume that rose several hundred meters above the summit (figure 225). Smaller emissions occurred throughout the day, and the EMOH camera recorded sporadic Strombolian explosions at night, which continued through the first week of August.

Figure (see Caption) Figure 225. After several months of calm, a resurgence of explosive activity was observed at the E vent (formed 25 November 2015) on the high E flank of the New Southeast Crater. The activity started with an explosion at 0408 UTC (= local time -2 hours), and generated a gray-brown ash plume that rose several hundred meters above the top of the volcano (a, b). In the following hours other smaller ash emissions occurred, and in the evening, the EMOH camera recorded sporadic Strombolian explosions (c). This activity continued, with fluctuations in the frequency and magnitude of the explosions, for the rest of the month (d, e, f). Courtesy of INGV (Rep. 32/2018, ETNA, Bollettino Settimanale, 30/07/2018 - 05/08/2018, data emissione 07/08/2018).

Similar activity at BN-1, NEC, and the reactivated vent at NSEC continued through the second and third weeks of August. On 16 August 2018 a new vent opened in the BN-2 area on the E side of the Voragine (inactive since December 2015) and exhibited both degassing and Strombolian activity (figure 226). During that week Strombolian activity also continued at the NEC, but activity became more sporadic at the E vent of NSEC. During the last week of August, Strombolian activity and intense degassing continued in the western sector of Bocca Nuova (BN-1). Occasionally, lapilli fragments a few centimeters in diameter were ejected onto the S rim of the crater. Strombolian activity also continued from multiple vents at the bottom of NEC. The frequency and intensity of explosions was variable and increased significantly during 22 August, ejecting coarse pyroclastic material outside the crater rim.

Figure (see Caption) Figure 226. The crater floor of Bocca Nuova at Etna on 16 and 17 August 2018 with thermal (a) and visible (b) images. The incandescent areas are highlighted with colors ranging from yellow to red and white in the thermal image. BN-1 (reactivated in November 2016) is in the foreground, and vent BN-2, which re-opened on 16 August in the south-eastern sector of the Bocca Nuova, is in the back (upper right). Thermal image by Francesco Ciancitto, photograph by Marco Neri. Courtesy of INGV (L'Etna non va in vacanza: aumenta di intensità l'attività eruttiva sommitale, 23 Agosto 2018, INGV Blog).

Beginning on 23 August 2018 about 1800 UTC, activity resumed at the saddle cone located between the old cone of the Southeast Crater (SEC) and the new cone (NSEC). Strombolian activity, initially modest, quickly became more intense, producing almost continuous explosions with the launch of coarse ejecta up to a height of 100-150 m. At 1830 UTC, while Strombolian explosions of modest intensity were also taking place at the E vent of NSEC, a small lava flow emerged from the E vent and traveled a few hundred meters E towards the Valle del Bove. Shortly after 1830 UTC another lava overflow was also observed moving N from the saddle cone (figures 227 and 228).

Figure (see Caption) Figure 227. Strombolian ejecta rose 100 m from the cono della sella (saddle cone) at the New Southeast Crater of Etna and lava flowed from both the E vent (left) and N from the saddle cone (right), shortly before midnight on 23 August 2018. Photo by Boris Behncke, courtesy of INGV blog 25 August 2018 (L'Etna fa gli straordinari: attività eruttiva al Nuovo Cratere di Sud-Est).
Figure (see Caption) Figure 228. Map of the summit crater area (DEM 2014, Aerogeophysics Laboratory - Rome Section 2, modified). BN = Bocca Nuova; VOR = Voragine; NEC = Northeast Crater; SEC = Southeast Crater; NSEC = New Southeast Crater. The yellow dots indicate the position of the degassing vents and those in red are the vents with Strombolian activity. The map also shows the flows produced by the saddle cone and the E vent of NSEC through 27 August 2018. Courtesy of INGV (Rep. N° 35/2018, ETNA, Bollettino Settimanale, 20/08/2018 - 26/08/2018, data emissione 28/08/2018).

Strombolian explosions of moderate intensity continued throughout the night from the saddle cone. The following morning (24 August) a small lava overflow emerged from the vent and stopped after traveling a few tens of meters towards the S flank of the NSEC cone (figure 228, small orange flow within saddle, and figure 229b). The Strombolian activity was accompanied by an abundant and continuous emission of ash, whichformed a small plume that rose a few hundred meters from the vent (figure 229c). The Strombolian activity at the saddle cone decreased gradually on 25 August.

Figure (see Caption) Figure 229. Eruptive activity at Etna during 23-24 August 2018. a) 23 August shortly before midnight; Strombolian activity from the saddle cone and lava flows from the E vent of the NSEC (white arrow) and from the cone of the saddle northwards (red arrow). Photo by B. Behncke taken from Fornazzo. b) 24 August, Strombolian activity and small lava overflow southward taken by the thermal camera of La Montagnola. c) 24 August, ash emitted during the Strombolian activity from the cone of the saddle, taken by the visible camera of La Montagnola. Courtesy of INGV (Rep. 35/2018, ETNA, Bollettino Settimanale, 20/08/2018 - 26/08/2018, data emissione 28/08/2018).

Strombolian activity was continuing on 27 August 2018 at NSEC, and the flow to the N into the Valle del Leone began cooling after lava stopped feeding it that evening. The same day, a new lava overflow emerged from the E vent of NSEC (figure 230) and flowed E towards the Valle del Bove for about 24 hours (figure 231).

Figure (see Caption) Figure 230. Map of the summit crater area of Etna (DEM 2014, Aerogeophysics Laboratory - Rome Section 2, modified). BN = Bocca Nuova; VOR = Voragine; NEC = Northeast Crater; SEC = Southeast Crater; NSEC = New Southeast Crater. The yellow dots are degassing vents and those in red have Strombolian activity. The map also shows the flows produced by NSEC during the last two weeks of August 2018. The yellow flow was cooling by 27 August when the new red flow emerged from the E vent of NSEC and lasted for about 24 hours. Courtesy of INGV (Rep. 36/2018, ETNA, Bollettino Settimanale, 27/08/2018 - 02/09/2018, data emissione 04/09/2018).
Figure (see Caption) Figure 231. A thermal image taken by Pizzi Deneri on 27 August 2018 at Etna shows the two flows on the flanks of NSEC. View is from the N. The flow labelled in red flows E from the E vent, and the other flow travels N from the Cono della sella (saddle cone) into the Valle del Leone and then moves east. Courtesy of INGV (Rep. 36/2018, ETNA, Bollettino Settimanale, 27/08/2018 - 02/09/2018, data emissione 04/09/2018).

Discontinuous Strombolian activity continued from NSEC after the effusive activity ended in late August. Several loud explosions from NSEC were reported by people living near the E flank of Etna during the first week of September. Strombolian activity, modest ash emissions, and significant gas emissions were also produced by BN-1; BN-2 exhibited only continuous degassing activity. Explosive activity declined during the second week of September. Discontinuous low-intensity Strombolian activity and intermittent ash emissions from Bocca Nuova, New Southeast Crater, and Northeast Crater characterized activity for the remainder of September. During the last week of the month, NEC produced frequent gray-brown ash emissions from a vent located in the western part of the crater floor, and included jets of ash, blocks, and volcanic bombs (figure 232).

Figure (see Caption) Figure 232. Ash emissions from Etna's Northeast Crater in late September 2018. The four top images are explosions from a vent at the bottom of NEC on 24 September 2018; the bottom image is one of the many ash emissions observed on 30 September. Courtesy of INGV (Rep. N° 40/2018, ETNA, Bollettino Settimanale, 24/09/2018 - 30/09/2018, data emissione 02/10/2018).

Discontinuous low-intensity Strombolian activity and intermittent ash emissions from the Bocca Nuova, the New Southeast Crater, and Northeast Crater characterized activity during all of October 2018. Two vents remained active at the bottom of Bocca Nuova (BN-1). During a visit on 16 October, INGV-OE geologists noted that the northernmost vent produced nearly continuous Strombolian activity with frequent explosions; occasionally fragments exceeded the crater rim in height but still fell within the crater. The southernmost vent, on the crater floor about 130 m from the edge, was characterized by explosive activity that produced mainly spattering which covered both the crater floor and walls (figure 233). On 25 October the webcam at Bronte recorded an ash emission from Bocca Nuova that resulted from three closely-spaced explosions. The ash was red and dispersed rapidly to the S causing ashfall near Torre del Filosofo and Rifugio Sapienza.

Figure (see Caption) Figure 233. Inside the Bocca Nuova BN-1 crater at Etna on 16 October 2018, two vents were active. The northernmost vent (yellow arrow) had Strombolian activity; the southernmost vent, visible on the right, produced mostly "spattering". Photo by M. Coltelli, courtesy of INGV (Rep. N° 43/2018, ETNA, Bollettino Settimanale, 15/10/2018 - 21/10/2018, data emissione 23/10/2018).

Strombolian activity at NSEC gradually intensified during the first week of November 2018 and was sometimes accompanied by ash emissions that rapidly dispersed, falling mainly near the vent and in the Valle del Bove to the E. Audible explosions from the activity were heard in Zafferana Etnea on the E flank. Several clear views of the summit and details of the active vents were well exposed during an overflight on a clear 9 November day (figure 234).

Figure (see Caption) Figure 234. An aerial view of the Etna summit craters taken on a clear 9 November 2018 day with the assistance of the 2nd Coast Guard Core of Catania. View is to the NW. BN = Bocca Nuova; VOR = Voragine; NEC = Northeast Crater; SEC = Southeast Crater; NSEC = New Southeast Crater. Courtesy of INGV (Rep. N° 46/2018, ETNA, Bollettino Settimanale, 05/11/2018 - 11/11/2018, data emissione 13/11/2018).

Three vents were visible at BN-1 during the 9 November 2018 overflight (figure 235); continuous Strombolian activity occurred at vent 1, whose fallout of pyroclastic debris remained within the crater; discontinuous Strombolian activity was observed at vent 2 associated with weak, pulsing ash emissions; only degassing activities were observed at vent 3. At BN-2, intense degassing accompanied discontinuous Strombolian activity that was associated with weak pulsating ash emissions, and several high temperature gas emission points. Scientists also observed a collapse on a portion of the northern inner wall of BN-1 from the explosion on 25 October.

Figure (see Caption) Figure 235. Aerial view of Bocca Nuova (BN) and Voragine (VOR) at Etna on 9 November 2018 taken with helicopter support of the 2nd Coast Guard Core of Catania. The yellow hatched line indicates the wall of the area that collapsed on 25 October 2018. Inset a) thermal image of Bocca Nuova showing the structure of the three eruptive vents within BN-1 and the eruptive vent within the BN-2. Courtesy of INGV (Rep. N° 46/2018, ETNA, Bollettino Settimanale, 05/11/2018 - 11/11/2018, data emissione 13/11/2018).

Modest outgassing continued at Voragine (VOR) from the 7 August 2016 vent near the rim during November. At NEC, continuous and intense Strombolian activity from the crater floor caused pyroclastic ejecta to land outside the crater rim (figure 236). At the NSEC complex, high-temperature anomalies were visible at the NW crater edge, and the E vent of NSEC had a small scoria cone that produced discontinuous Strombolian explosions and minor ash emissions (figure 237).

Figure (see Caption) Figure 236. Aerial view of Voragine (VOR) and the Northeast Crater (NEC) at Etna taken on 9 November 2018 with helicopter support of the 2nd Coast Guard Core of Catania. The 7 August 2016 vent at VOR had a vigorous steam emission (yellow arrow). Inset a) thermal image showed the Strombolian activity in the bottom of NEC. Courtesy of INGV (Rep. N° 46/2018, ETNA, Bollettino Settimanale, 05/11/2018 - 11/11/2018, data emissione 13/11/2018).
Figure (see Caption) Figure 237. Thermal activity was evident in several places at the SEC-NSEC complex at Etna during the 9 November 2018 overflight with the helicopter of the 2nd Coast Guard Core of Catania (inset a, upper image). The small scoria cone (conetto di scorie) was visible inside the E vent (Bocca orientale) of the New Southeast Crater, seen from the East on 9 November (lower image). Upper image from INGV weekly (Rep. N° 46/2018, ETNA, Bollettino Settimanale, 05/11/2018 - 11/11/2018, data emissione 13/11/2018), lower image by Stefano Branca (INGV-Osservatorio Etneo) from INGV blog (Piccoli coni crescono: aggiornamento sullo stato di attività dell'Etna al 7 dicembre 2018).

A seismic swarm with over 40 events affected the W flank of Etna on 20 November 2018; the hypocenters were located between 15 and 27 km depth. A small lava flow also emerged on 20 November from the scoria cone inside the E vent at NSEC. The flow lasted for a few hours and remained inside the E vent. A new flow from the same scoria cone at the NSEC east vent appeared on 26 November accompanied by continued Strombolian activity. The flow remained high on the E flank at an elevation of about 3,200 m. Flow activity continued into the first days of December with frequent incandescent blocks moving down the NSEC E flank (figure 238). Elsewhere at Etna, Strombolian activity continued accompanied by sporadic and modest ash emissions from Bocca Nuova, the New Southeast Crater and the Northeast Crater through the end of November (figure 239).

Figure (see Caption) Figure 238. Strombolian activity and emission of a small lava flow from the E vent of the New Southeast Crater was seen from the E at dawn on 29 November 2018. The lava flow was very short, but the detachment and rolling of numerous incandescent blocks from the front and sides of the flow created the impression that the flow reached the base of the New Southeast Crater cone. The scoria cone inside the E vent grew considerably compared to its size observed on 9 November (figure 237). Photo by Giò Giusa. Courtesy of INGV, INGV Blog (Piccoli coni crescono: aggiornamento sullo stato di attività dell'Etna al 7 dicembre 2018).
Figure (see Caption) Figure 239. Incandescence from Strombolian activity was visible inside the NSEC (right) and BN (left) craters at Etna on 22 November 2018 as viewed from Tremestieri Etneo. Photo by B. Behncke, courtesy of INGV (Rep. N° 48/2018, ETNA, Bollettino Settimanale, 19/11/2018 - 25/11/2018, data emissione 27/11/2018).

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

Information Contacts: Sezione di Catania - Osservatorio Etneo, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/it/ ); 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/).


Dukono (Indonesia) — December 2018 Citation iconCite this Report

Dukono

Indonesia

1.693°N, 127.894°E; summit elev. 1229 m

All times are local (unless otherwise noted)


Regular ash explosions continuing as of September 2018

The long-term eruption at Dukono has been characterized by frequent ash explosions through at least March 2018 (BGVN 43:04). The current report shows that this pattern continued through at least September 2018. The data below were provided by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Center for Volcanology and Geological Hazard Mitigation (CVGHM), and the Darwin Volcanic Ash Advisory Centre (VAAC).

Between April and September 2018 there were about five reports per month about ash plumes. Altitudes generally ranged from 1.4-2.1 km, although 3 km was reported during 2-8 May and 3.4 km was reported during 25-31 July (table 18).

Table 18. Monthly summary of reported ash plumes from Dukono for April-September 2018. The direction of drift for the ash plume through each month was highly variable. Data courtesy of the Darwin VAAC and PVMBG.

Month Plume Altitude (km) Notable Plume Drift
Apr 2018 1.5-2.1 --
May 2018 1.5-3 Ash plumes drifted as far as 225 km NW on 28 May
Jun 2018 1.4-2.1 --
Jul 2018 1.8-3.4 --
Aug 2018 1.8-2.4 --
Sep 2018 1.8-2.1 --

No thermal anomalies at Dukono, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, were detected during the reporting period. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, also based on analysis of MODIS data, detected a low-power hotspot in early April (about 2.5 km from the volcano) and a possible low-power hotspot in late August 2018 (about 5 km from the volcano).

Geologic Background. Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

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/); 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/).


Ulawun (Papua New Guinea) — November 2018 Citation iconCite this Report

Ulawun

Papua New Guinea

5.05°S, 151.33°E; summit elev. 2334 m

All times are local (unless otherwise noted)


Ash plumes on 8 June, 21 September, and 5 October 2018

Typical activity at Ulawun consists of sporadic explosions with weak ash plumes. During 2017, sporadic explosions occurred between late June through early November with ash plumes rising no more than 3 km in altitude (BGVN 42:12). This report describes activity between January and September 2018.

According to the Darwin Volcanic Ash Advisory Centre (VAAC), a NOTAM (Notice to Airmen) stated that on 8 June 2018 an ash plume rose to an altitude of 2.1 km and drifted W. The Darwin VAAC also reported that a pilot observed an ash plume on 21 September 2018 rising to an altitude of 3.7 km and drifting W. Ash was not confirmed in satellite images, though weather clouds obscured views.

On 5 October 2018 the Darwin VAAC identified a steam-and-ash emission in satellite images rising to an altitude of 4.6 km and drifting WSW. It was also reported by ground observers. The Rabaul Volcano Observatory reported that during 1-12 October white, and sometimes light gray, emissions rose from the summit crater; seismicity was low.

Geologic Background. The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the north coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Information Contacts: 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/); 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.


Langila (Papua New Guinea) — November 2018 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)


Several weak ash plumes during June, September, and October 2018

After Vulcanian activity in the latter part of 2009, activity at Langila subsided, with infrequent activity until 2016, when activity increased somewhat through May 2018 (BGVN 34:11, 35:02, 42:01, and 42:09). This pattern of intermittent activity continued through October 2018. No reports were available from the Rabaul Volcano Observatory during the current reporting period (June-October 2018), but volcanic ash warnings were issued by the Darwin Volcanic Ash Advisory Centre (VAAC).

Four explosions were reported by the Darwin VAAC in June 2018, generating ash plumes that rose 2.1-3.4 km (table 6). There were no reports of an explosion in July or August 2018. Additional ash plumes were detected on 29 September and 30 October 2018

Table 6. Reports of ash plumes from Langila during 1 June-30 October 2018 based on analyses of satellite imagery and wind model data. Courtesy of the Darwin VAAC.

Date Ash plume altitude (km) Ash plume drift Observations
07 Jun 2018 3.4 SW Detached from the summit.
10 Jun 2018 2.1 -- Dissipated.
17 Jun 2018 2.4 W --
20-21 Jun 2018 2.4 W, NW --
29 Sep 2018 2.4 NE --
30 Oct 2018 2.7 SE --

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: 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/).


Sangeang Api (Indonesia) — November 2018 Citation iconCite this Report

Sangeang Api

Indonesia

8.2°S, 119.07°E; summit elev. 1949 m

All times are local (unless otherwise noted)


Ongoing crater activity and thermal anomalies during September 2017-October 2018

A significant increase in the number of thermal anomalies at Sangeang Api was recorded during February and June through mid-August 2017, along with a small Strombolian eruption in mid-July that generated an ash plume (BGVN 42:09). The high number of thermal anomalies continued through at least 20 October 2018. The current report summarizes activity between 1 September 2017 and 20 October 2018. The volcano is monitored by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) and Darwin Volcanic Ash Advisory Centre (VAAC).

Based on a Volcano Observatory Notice for Aviation (VONA) from PVMBG, on 9 May 2018 a gas emission was observed at 1807 that rose to an altitude of 4,150 m and drifted W. Consequently, the Aviation Color Code was raised from unassigned to Yellow. Clear thermal satellite imagery the next day showed hot material traveling about 500 m SE out of the summit crater and continuing another 500 m down the E flank (figure 18).

Figure (see Caption) Figure 18. Sentinel-2 satellite image of Sangeang Api on 10 May 2018. This "Atmospheric penetration" view (bands 12, 11, and 8A) highlights hot material extending more than a kilometer from the vent in the summit crater to the SE and onto the E flank. Courtesy of Sentinel Hub.

Based on another VONA from PVMBG, an ash emission at 1338 on 15 October 2018 rose 250 m above the summit and drifted SW, W, and NW. The VONA noted that the ash emission possibly rose higher than what a ground observer had estimated. Seismic data was dominated by signals indicating emissions as well as local tectonic earthquakes. The Aviation Color Code was raised from Yellow to Orange.

During the reporting period, MODIS satellite instruments using the MODVOLC algorithm recorded thermal anomalies between 3 and 12 days per month, many of which had multiple pixels. October 2017 had the greatest number of days with hotspots (12), while the lowest number was recorded during December 2017 through February 2018 (3-4 days per month). The vast majority of anomalies issued from the summit; a few were along the E flanks. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, also based on analysis of MODIS data, recorded numerous hotspots during the previous 12 months through mid-October 2018, except for the second half of January 2018 (figure 19). Almost all recorded MIROVA anomalies were within 5 km of the volcano and of low to moderate radiative power.

Figure (see Caption) Figure 19. Thermal anomalies identified by the MIROVA system (Log Radiative Power) at Sangeang Api for the year ending 19 October 2018. Courtesy of MIROVA.

Geologic Background. Sangeang Api volcano, one of the most active in the Lesser Sunda Islands, forms a small 13-km-wide island off the NE coast of Sumbawa Island. Two large trachybasaltic-to-tranchyandesitic volcanic cones, 1949-m-high Doro Api and 1795-m-high Doro Mantoi, were constructed in the center and on the eastern rim, respectively, of an older, largely obscured caldera. Flank vents occur on the south side of Doro Mantoi and near the northern coast. Intermittent historical eruptions have been recorded since 1512, most of them during in the 20th century.

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/); 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).


Sheveluch (Russia) — November 2018 Citation iconCite this Report

Sheveluch

Russia

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

All times are local (unless otherwise noted)


Thermal anomalies along with minor gas and steam emissions continue through October 2018

Volcanic activity at Sheveluch declined during the period of May through October 2018. This decline followed a lengthy cycle of eruptive activities which began in 1999, including pyroclastic flows, explosions, and lava dome growth, as previously reported through April 2018 (BGVN 43:05). According to the Kamchatka Volcanic Eruption Response Team (KVERT), during this time a thermal anomaly was detected in satellite imagery and two gas-and-steam events were reported in July and October 2018. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

KVERT reported that satellite data showed a plume of re-suspended ash up to 62 km to the SE of the volcano on 18 July 2018. Moderate gas and steam emissions rose from the volcano on 19-26 October 2018. Thermal anomalies were frequently reported by KVERT during May through October 2018. The MIROVA system detected intermittent low-power thermal anomalies during this time.

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: Kamchatka Volcanic Eruptions Response Team (KVERT), Far East Division, 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/).


Gamalama (Indonesia) — November 2018 Citation iconCite this Report

Gamalama

Indonesia

0.8°N, 127.33°E; summit elev. 1715 m

All times are local (unless otherwise noted)


Weak explosion on 4 October 2018

The most recent of the previous intermittent weak explosions on Gamalama was on 3 August 2016, which produced an ash plume and ashfall that closed a nearby airport for a day (BGVN 42:03). This report discusses eruptive activity in October 2018. The volcano is monitored by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM).

PVMBG reported that an explosion at 1152 on 4 October 2018, likely phreatic, generated an ash plume that rose about 250 m above the summit and drifted NW. Eight volcanic earthquakes were recorded about an hour before the event. Based on satellite data and information from PVMBG, the Darwin Volcanic Ash Advisory Centre (VAAC) reported that during 5-6 October ash plumes rose to an altitude of 2.1 km and drifted W and NW. The Alert Level remained at 2 (on a scale of 1-4); visitors and residents were warned not to approach the crater within a 1.5-km radius. On 10 October PVMBG reported only gas emissions (mostly water vapor), and the Aviation Color Code was lowered from Orange to Yellow.

No significant SO2 levels near the volcano were recorded by NASA's satellite-borne ozone instruments (Suomi NPP/OMPS and Aura/OMI) during early October. However, Simon Carn reported that the newer TropOMI instrument aboard the Copernicus Sentinel-5P satellite showed significant SO2 levels as high as 12 TRM/DU (levels in middle troposphere layer, as measured in Dobson Units) on 4 October 2018 (figure 7).

Figure (see Caption) Figure 7. Weak SO2 emissions from Gamalama on 4 October 2018 were detected by the Sentinel-5P TROPOMI instrument. Courtesy of Simon Carn.

Geologic Background. Gamalama is a near-conical stratovolcano that comprises the entire island of Ternate off the western coast of Halmahera, and is one of Indonesia's most active volcanoes. The island was a major regional center in the Portuguese and Dutch spice trade for several centuries, which contributed to the thorough documentation of Gamalama's historical activity. Three cones, progressively younger to the north, form the summit. Several maars and vents define a rift zone, parallel to the Halmahera island arc, that cuts the volcano. Eruptions, recorded frequently since the 16th century, typically originated from the summit craters, although flank eruptions have occurred in 1763, 1770, 1775, and 1962-63.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 5+7, Bandung 40122, Indonesia (URL: http://www.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/); Simon Carn, Geological and Mining Engineering and Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA (URL: http://www.volcarno.com/, Twitter: @simoncarn).

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Bulletin of the Global Volcanism Network - Volume 29, Number 08 (August 2004)

Managing Editor: Richard Wunderman

Anatahan (United States)

Explosions and ash plumes end in early August

Arenal (Costa Rica)

Pyroclastic flows on 6 July generated by detached lavas

Asamayama (Japan)

Eruption on 1 September causes an elongate ashfall deposit

Egon (Indonesia)

Explosive ash eruptions in July and August; ashfall and evacuations

Erta Ale (Ethiopia)

Declining thermal output from small lava lake since early 2003

Kerinci (Indonesia)

Dark ash plumes in late July-early August 2004

Krakatau (Indonesia)

Brief period of increased activity in early July

Nightingale Island (United Kingdom)

Earthquake swarm on 29-30 July followed by floating pumice

Papandayan (Indonesia)

Increased seismicity and elevated crater temperatures in July



Anatahan (United States) — August 2004 Citation iconCite this Report

Anatahan

United States

16.35°N, 145.67°E; summit elev. 790 m

All times are local (unless otherwise noted)


Explosions and ash plumes end in early August

The current eruption began after increased seismicity on 31 March 2004 (BGVN 29:04 and 29:05). Lava was noted in the crater on [12] April and may have extruded for a few weeks thereafter. The most energetic phase occurred during 24-28 April, when a ash clouds rose ~ 1,000 m. This report summarizes activity from mid-June through September 2004.

During June, seismicity was higher as a result of more frequent small explosions every few tens of seconds, and a 100-km-long, light-colored plume of steam and ash was occasionally visible. A cone active since at least 10 June produced continuous Strombolian explosions that ejected material as high as 100 m every few tens of seconds to minutes, filling the inner crater by about 10 July. The seismicity level was generally significantly lower during 14-16 June, after which it returned to earlier levels. On 27 June a tropical storm knocked out the last seismic station on the island.

The last time the weather was clear enough to see well, on 3 July, the Washington VAAC reported a 31-km-long ash plume well below 3 km altitude. During a few days in mid-July, prolonged periods, 10-15 minutes long, of continuous ash emission began to occur and became more frequent. A plume of light ash and steam trailed tens of kilometers WSW at altitudes less than 3 km.

Seismicity increased on 23 July to approximately double the level of the previous day, approaching the previous high of late April. The seismic signals indicated somewhat larger and longer periods of ash emission. Strombolian explosions continued to occur very frequently. The explosions threw mostly coarse material upward a hundred meters or so at intervals of tens of seconds to a few minutes. A plume of light ash and steam trailed a few tens of kilometers downwind, generally W, at altitudes below 1.8 km. An Air Force Weather Advisory on 24 July reported that their satellite could see the source as a hot spot. The Commonwealth of the Northern Mariana Islands Emergency Management Office (CNMI/EMO) reported a plume of light ash trailing a few tens of kilometers WSW at altitudes below ~ 3 km.

Joe Kaipat (EMO) visited the island on 25 July with personnel from Fish and Wildlife and reported observing an ash plume probably a few tens of kilometers long moving NE. This plume persisted until 3 August, less than a few kilometers long and below 600 m. After 26 July seismicity decreased to a very low level, with the signals indicating that the frequent individual explosions of several days before had decreased significantly in size and number and finally ceased by 31 July. Instead, ash and gas were being ejected almost continuously. Seismicity remained very low and frequent individual explosions ceased through August and September 2004.

Geologic Background. The elongate, 9-km-long island of Anatahan in the central Mariana Islands consists of a large stratovolcano with a 2.3 x 5 km compound summit caldera. The larger western portion of the caldera is 2.3 x 3 km wide, and its western rim forms the island's high point. Ponded lava flows overlain by pyroclastic deposits fill the floor of the western caldera, whose SW side is cut by a fresh-looking smaller crater. The 2-km-wide eastern portion of the caldera contained a steep-walled inner crater whose floor prior to the 2003 eruption was only 68 m above sea level. A submarine cone, named NE Anatahan, rises to within 460 m of the sea surface on the NE flank, and numerous other submarine vents are found on the NE-to-SE flanks. Sparseness of vegetation on the most recent lava flows had indicated that they were of Holocene age, but the first historical eruption did not occur until May 2003, when a large explosive eruption took place forming a new crater inside the eastern caldera.

Information Contacts: Juan Takai Camacho and Ramon Chong, CNMI/EMO, Saipan, MP 96950, USA (URL: http://www.cnmihsem.gov.mp/); Frank Trusdell, U.S. Geological Survey, Hawaiian Volcano Observatory (HVO), PO Box 51, Hawaii National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/nmi/activity/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch, NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ssd.noaa.gov/).


Arenal (Costa Rica) — August 2004 Citation iconCite this Report

Arenal

Costa Rica

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

All times are local (unless otherwise noted)


Pyroclastic flows on 6 July generated by detached lavas

A sequence of pyroclastic flows moved down the N and NE flanks in September 2003 (BGVN 28:09). In general, Arenal's behavior during October 2003-March 2004 was similar to past years, with Crater C exhibiting ongoing gas emissions, lava flows, and sporadic Strombolian eruptions, and Crater D emitting fumarolic gases. The month with the highest number of inferred eruption earthquakes and the longest duration of tremor was March 2004 (table 23); long-period earthquakes spiked in May 2004.

Table 23. Seismic activity registered at Arenal's station VACR, October 2003-June 2004. From 24 June onward, the seismic station was out of service. Courtesy of OVSICORI-UNA.

Month Eruption earthquakes Tremor (hours) Long-period earthquakes
Oct 2003 997 521 16
Nov 2003 724 468 --
Dec 2003 -- -- --
Jan 2004 910 610 10
Feb 2004 896 639 8
Mar 2004 1169 661 18
Apr 2004 957 604 4
May 2004 901 405 53
Jun 2004 974 401 --

Typical NE-flank lava flows persisted on 11 October 2003; in addition, some lava flows began to descend the SE flank, but they ceased by month's end. November 2003 reports noted NE-flank lava flows reaching 8 km NE of the edifice. There were a few October eruptions that produced columns of ash more than 500 m above Crater C's rim. During November lava flows persisted on the NE; some extended 8 km. During December 2003, tephra fell on both Crater C's NE and SE sides; acid rain was also noted.

On 12 March 2004 a hot avalanche occurred at the lava front progressing toward Arenal's NE side; the avalanche cascaded downslope and stopped at 850 m elevation. Near the crater's N edge some blocks fell and portions of that mass-wasting event reached vegetation. Eruptive activity declined but crevasses continue to widen. Small cold avalanches were also seen.

Pyroclastic flows on 6 July 2004. At 1319 on 6 July a series of pyroclastic flows descended the NE flank; other pyroclastic flows may have occurred later. Several medium-size pulses affected some patches of vegetation in the lower areas of the cone, ~ 900 m below the summit. The hot avalanches and airborne materials formed a plume of ash and dust blown SW. The pyroclastic flows resulted from the collapse of the upper areas of a lava flow, and impacted an area affected by flows during 1999-2003, but also invaded other areas. This type of phenomena has been common, particularly in recent years, to the N and NE. Figure 99 shows the distal portion of the area of pyroclastic-flow. Deposits included both abundant fine-grained materials and substantial blocks. Direct observations were hampered by the pyroclastic flows as well as cloud cover. Authorities temporarily closed routes around the volcano, but the area was within the National Park in a zone excluding visitors.

Figure (see Caption) Figure 99. The lower portions of Arenal's 6 July 2004 pyroclastic-flow deposit, as outlined by OVSICORI-UNA scientists. Eliecer Duarte provided a rough estimate of distance from the middle left to the lower right side of the area (the 'heel to the tip of the toe') as 250 m. Locations of some of the burned and singed vegetation are indicated. Loose mass-wasted materials (labeled as deposits from rockslides) also accompanied the pyroclastic flows. Courtesy of OVSICORI-UNA.

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: Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica. (URL: http://www.ovsicori.una.ac.cr).


Asamayama (Japan) — August 2004 Citation iconCite this Report

Asamayama

Japan

36.406°N, 138.523°E; summit elev. 2568 m

All times are local (unless otherwise noted)


Eruption on 1 September causes an elongate ashfall deposit

An explosive eruption occurred from the summit crater of Asama at 2002 on 1 September 2004. Most of the initial reporting was in Japanese, although many of those reports had segments in English. Setsuya Nakada and Yukio Hayakawa provided links to initially available reports. According to the Geological Survey of Japan's website (managed by N. Geshi) and an article there summarizing contributions from many organizations and authors, the 1 September eruption was a single Vulcanian explosion.

According to the preliminary report of JMA, red-hot blocks spread several kilometers from the summit and caused many wildfires. Video images showed an extraordinary amount of incandescence at height, as well as bright zones on the ground surface. Some of the burns remained limited to the area of contact between the hot bombs and alpine vegetation.

On 3 September Yukio Hayakawa (Gunma University) visited parts of Asama's upland areas where wildfires had occurred (figure 16). There he found bombs up to a meter in diameter. Because of their greater size, the larger bombs cooled more slowly and had the greatest thermal impact. At least one large bomb had cracked and fragmented on impact, delivering relatively hot material over a wide area. This process accounted for the largest burned area he inspected. Hayakawa photographed an impressive impact crater associated with a large volcanic bomb from the 1 September eruption (figure 17). Along the impact crater's rim, the network of low-lying alpine vegetation was torn loose and lay folded back and upside-down.

Figure (see Caption) Figure 16. An image depicting Asama's topography with the route hiked (yellow) to investigate the eruption-induced wildfires (orange dot is the fire site investigated, at ~2,000 m elevation). Two urban areas indicated in Japanese on the map are Miyota town and Komoro city (white circles on left and right, respectively); the two sit ~7 km apart. Courtesy of Yukio Hayakawa, Gunma University.
Figure (see Caption) Figure 17. A fresh impact crater formed by a large bomb from the 1 September 2004 Asama eruption. Crater diameter at the plane of the undisturbed land surface was ~6 m, crater depth was ~1 m, and the rim of disturbed material stood up to ~0.5 m high. The impactor is visible at the NW wall of the crater (~0.8 m). Courtesy of Yukio Hayakawa, Gunma University.

After the eruption, a helicopter flight around the volcano also confirmed that many ballistic blocks had landed on the volcano's upper flanks (figure 18). Asia Air Survey (Ltd.) also compiled a comprehensive set of post-eruption aerial stereophotos of Asama and surroundings. Ones taken of the crater on 3 September showed the principal crater immersed in a circular bank of dense white volcanic gases. A thin white plume blew NE. Impact scars were also visible on these photos, scattered over the upper flanks.

Figure (see Caption) Figure 18. The Asama summit crater as seen in a series of shots taken from a helicopter two days after the 1 September 2004 eruption: (top) The main crater engulfed in white fumes with a thin plume blowing NE; (center) a closer view of the outer W flank and adjacent moat area, ~1 km from the crater; (bottom) a still closer view depicting a conspicuously cratered surface on the summit's NW flank. The center photo also shows two big craters in the center right; a trail following the outer crater rim is largely tephra covered but segments remain recognizable. Courtesy of the Geological Survey of Japan (captions and photos by H. Hoshizumi, GSJ).

Tephra sampling and distribution. Strong winds blew the eruption cloud NE. Ashfall occurred ~250 km from the volcano and reached to the Pacific Ocean (with ash reported at the coastal locations of Soma and Haranomachi cities in Fukushima Prefecture). The ash-fall deposit covered a narrow and elongated area, forming a classic cigar-shaped pattern. Field work was begun to establish the mass and distribution of the tephra blanket (figure 19). The Earthquake Research Institute (ERI) noted that 5-cm-diameter cinders appeared up to ~5 km from the crater. In some cases rainfall occurred during or after the ashfall; in some cases it washed away fine-grained portions of the ash-fall deposit. In preliminary ERI and Geological Survey of Japan (GSJ) reports and personal communication, workers calculated tentative estimates of eruptive products on the order of 40,000-230,000 metric tons. The initial estimate by Hayakawa was 200,000 metric tons.

Figure (see Caption) Figure 19. One preliminary (working) map of Asama's 1 September 2004 tephra mass (out to ~70 km from the source) showing data points used to constrain the isomass contours (in units of grams per meter squared). For comparison, one S- to SE-directed isomass contour (141 g/m2) was also included from a 1982 eruption. The base map is in Japanese but English names have been added to selected urban areas. Courtesy of Yukio Hayakawa, Gunma University.

Geophysical and geochemical observations. Investigators at ERI Tokyo plotted the time-series of deformation recorded by four 3-component GPS stations within a few kilometers of the summit over January to early September 2004. Of these, only one station, ASM4, ~4 km S of the summit, showed any clear and consistent variation. Its changes were only clear in one component: it moved to the S on the order of 5-10 mm, motion that became most apparent after June 2004 (figure 20). Other groups also maintained GPS (and tilt?) stations on Asama and may have seen more diagnostic ground displacement associated with the eruption.

Figure (see Caption) Figure 20. Time-series deformation of Asama recorded at GPS station ASM4, January-September 2004. The three orthogonal components are shown as follows: Upper row is in the E-W direction, middle row is in the N-S direction, and bottom row is in the up-down direction. The GPS reference frame was ITRF2000. These data were posted on the web on 6 September 2004 by the Volcano Research Center, University of Tokyo.

ERI briefly discussed seismic signals received at the station for Asama, which arrived at about 2002 on 1 September 2004. The first extensive seismic signal was of elevated amplitude and persisted for about a minute. Another plot suggested that the entire set of 1 September eruptive signals spanned about 30 minutes. SO2 measurements used the differential optical absorption spectrometer (DOAS) technique. Ground-based traverses on 3 September measured an average of 1,475 metric tons/day, with respective measured lows and highs of 1,168 and 1,738 tons/day.

Satellite data. The TOMS Volcanic Emissions Group used the Atmospheric Infrared Sounder (AIRS) to detect emissions from Asama's 1 September eruption. AIRS is a hyperspectral imager on the EOS/Aqua satellite. It provides higher spatial resolution than TOMS, and as an infrared sensor it produces nighttime images of volcanic clouds. AIRS volcanic cloud studies are a collaborative effort between the TOMS group and the Atmospheric Spectroscopy Laboratory in the Department of Physics at UMBC.

A sub-circular cloud was associated with the eruption on 1 September (figure 21). When detected at 1554 UTC the cloud was well out over the Pacific Ocean, ~640 km from Asama. Travel time for the cloud was 4 hours and 52 minutes, which implies a (straight line) mean velocity for the cloud's center of ~130 km/hour. Even though there was no quantitative estimate of aerosol and gas, there was a strong volcanic signal. The AIRS image is presented as a bias difference (in Kelvin, K; the scale at the right). The larger the bias difference, the stronger the volcanic signal. In this case, a significant area reached a difference of over 10 K.

Figure (see Caption) Figure 21. Asama's 1 September 2004 eruption generated a cloud that persisted and was imaged ~640 km ENE. The local time of this image was 0054 on 2 September (1554 UTC 1 September). Courtesy of Simon Carn and L. Larrabee Strow, UMBC.

Geologic Background. Asamayama, Honshu's most active volcano, overlooks the resort town of Karuizawa, 140 km NW of Tokyo. The volcano is located at the junction of the Izu-Marianas and NE Japan volcanic arcs. The modern Maekake cone forms the summit and is situated east of the horseshoe-shaped remnant of an older andesitic volcano, Kurofuyama, which was destroyed by a late-Pleistocene landslide about 20,000 years before present (BP). Growth of a dacitic shield volcano was accompanied by pumiceous pyroclastic flows, the largest of which occurred about 14,000-11,000 BP, and by growth of the Ko-Asama-yama lava dome on the east flank. Maekake, capped by the Kamayama pyroclastic cone that forms the present summit, is probably only a few thousand years old and has an historical record dating back at least to the 11th century CE. Maekake has had several major plinian eruptions, the last two of which occurred in 1108 (Asamayama's largest Holocene eruption) and 1783 CE.

Information Contacts: Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (GSJ AIST) (URL: http://www.aist.go.jp/); Yukio Hayakawa, Faculty of Education, Gunma University, Aramaki 4-2, Maebashi Gunma 371-8510, Japan (URL: http://www.hayakawayukio.jp/English.html); Setsuya Nakada, Volcano Research Center, Earthquake Research Institute (ERI), University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html); Simon Carn, TOMS Volcanic Emissions Group, University of Maryland, 1000 Hilltop Circle, Baltimore, MD 21250, USA (URL: https://so2.gsfc.nasa.gov/); L. Larrabee Strow, Atmospheric Spectroscopy Laboratory, Physics Department, 1000 Hilltop Circle, Baltimore, MD 21250, USA (URL: http://asl.umbc.edu/).


Egon (Indonesia) — August 2004 Citation iconCite this Report

Egon

Indonesia

8.676°S, 122.455°E; summit elev. 1661 m

All times are local (unless otherwise noted)


Explosive ash eruptions in July and August; ashfall and evacuations

Volcanic activity began at Egon in late January when ash explosions caused local ashfall (BGVN 29:03). Activity subsequently decreased, and evacuated residents returned home. Reports from the Directorate of Volcanology and Geological Hazard Mitigation (DVGHM) indicated that in May 2004 only ten A-type volcanic earthquakes were detected. These types of events increased to 19 during June, when three shallow B-type volcanic earthquakes were also registered (table 1).

Table 1. Seismicity at Egon during 20 June-29 August 2004. Courtesy of DVGHM.

Date Volcanic A Volcanic B Tremor Tectonic
20 Jun-27 Jun 2004 7 2 -- 23
28 Jun-04 Jul 2004 9 3 -- 24
05 Jul-11 Jul 2004 9 2 continuous 2
12 Jul-18 Jul 2004 22 139 2 35
19 Jul-25 Jul 2004 17 109 -- 54
26 Jul-01 Aug 2004 5 37 -- 28
02 Aug-08 Aug 2004 3 38 34 28
09 Aug-15 Aug 2004 2 49 49 16
16 Aug-22 Aug 2004 1 70 51 16
23 Aug-29 Aug 2004 4 90 42 17

Volcanism resumed at 1930 on 3 July 2004 when small explosions along with rumbling sounds and a white- gray ash plume rose 100 m and caused ashfall to the SE. Ash from a second small explosion that began with increasing A-type volcanic earthquakes on 6 July at 0100 again drifted SE. Maximum amplitudes (peak-to-peak) of the explosion earthquakes were 1 mm and lasted 60 seconds. White plumes rising to ~ 75 m above the summit were then observed during 5-18 July. Continuous emission earthquakes were recorded during the week of 5-12 July with 2 mm amplitude. After 11 July a PS-2 telemetered seismograph was operational.

A significant ash explosion accompanied by rumbling sounds at 2240 on 25 July 2004 sent a plume ~ 1,000-1,500 m above the summit. A thick black ash column drifted NW and the smell of sulfur gas was very strong. Seismic data indicated that the eruptions lasted about 2 hours and 30 minutes; tremor amplitude was 30-35 mm. Ashfall affected the Egon (3 km NW) and Nangatobong (7.5 km NNW) villages, and 339 families evacuated to Waigete. Daily seismic events increased from 14 to 36 prior to the eruption. Ash explosions continued through 1600 the next day, sending plumes ~ 250 m above the summit at intervals of about a minute. Additional evacuations occurred from Egon, Nangatobong, and Itoper villages. Another explosion at 2200 on 28 July sent volcanic material to a height of 750 m; ash drifted WSW. Recorded tremor emission showed maximum amplitudes decreasing from 5 mm to 2 mm.

By the week of 9-15 August observers were only reporting a thin white plume to ~ 100 m above the summit, although tremor was still being recorded. Similar activity continued through 22 August. On 27 August two eruptions ejected ash plumes more than 250 m high. Shallow volcanic earthquakes increased significantly during the week of 23-29 August.

Geologic Background. Gunung Egon, also known as Namang, sits astride the narrow waist of eastern Flores Island. The barren, sparsely vegetated summit region has a 350-m-wide, 200-m-deep crater that sometimes contains a lake. Other small crater lakes occur on the flanks. A lava dome forms the southern summit. Solfataric activity occurs on the crater wall and rim and on the upper S flank. Reports of historical eruptive activity prior to explosive eruptions beginning in 2004 were inconclusive. A column of "smoke" was often observed above the summit during 1888-1891 and in 1892. Strong "smoke" emission in 1907 reported by Sapper (1917) was considered by the Catalog of Active Volcanoes of the World (Neumann van Padang, 1951) to be an historical eruption, but Kemmerling (1929) noted that this was likely confused with an eruption on the same date and time from Lewotobi Lakilaki.

Information Contacts: Dali Ahmad, Hetty Triastuty, Nia Haerani, Suswati, and Sri Kisyati, Directorate of Volcanology and Geological Hazard Mitigation, Jalan Diponegoro No. 57, Bandung 40122, Indonesia, URL: http://www.vsi.esdm.go.id/).


Erta Ale (Ethiopia) — August 2004 Citation iconCite this Report

Erta Ale

Ethiopia

13.6°N, 40.67°E; summit elev. 613 m

All times are local (unless otherwise noted)


Declining thermal output from small lava lake since early 2003

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

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

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

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

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

Geologic Background. Erta Ale is an isolated basaltic shield that is the most active volcano in Ethiopia. The broad, 50-km-wide edifice rises more than 600 m from below sea level in the barren Danakil depression. Erta Ale is the namesake and most prominent feature of the Erta Ale Range. The volcano contains a 0.7 x 1.6 km, elliptical summit crater housing steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located SE of the summit and is bounded by curvilinear fault scarps on the SE side. Fresh-looking basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera is renowned for one, or sometimes two long-term lava lakes that have been active since at least 1967, or possibly since 1906. Recent fissure eruptions have occurred on the N flank.

Information Contacts: Rob Wright and the HIGP MODIS Thermal Alerts Team, Hawaii Institute of Geophysics and Planetology, University of Hawaii, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.hgip.hawaii.edu/); Joshua Jones, Department of Earth & Space Sciences, Box 351310, Seattle, WA 98195-1310, USA; Roberto Carniel, Dipartimento di Georisorse e Territorio, University of Udine - via Cotonificio, 114 - 33100 Udine, Italy.


Kerinci (Indonesia) — August 2004 Citation iconCite this Report

Kerinci

Indonesia

1.697°S, 101.264°E; summit elev. 3800 m

All times are local (unless otherwise noted)


Dark ash plumes in late July-early August 2004

Although frequently active, the most recent eruptive period at Kerinci had ended by late 2002 (BGVN 27:08 and 27:12). A new eruptive episode was reported by the Directorate of Volcanology and Geological Hazard Mitigation (DVGHM) starting in late July. However, the Darwin Volcanic Ash Advisory Centre (VAAC) issued an advisory on 22 June after receiving a report of ash from Kerinci at ~ 3.8 km altitude (summit level) drifting W; no ash was visible on satellite imagery.

During 24-31 July 2004 observers reported seeing a "white, thick blackish" plume rising 100-600 m above the crater rim and drifting WSW. Ashfall deposits as thick as 1 cm were identified at distances of 3 km from the summit. The number of volcanic earthquakes recorded rose during this week and remained high through the week ending on 8 August (table 5). Another eruption on the morning of 6 August sent a gray ash plume 600 m above the summit. Based on the increased activity, DVGHM raised the hazard status to Alert Level II (yellow).

Table 5. Seismicity at Kerinci, 12 July-29 August 2004. Courtesy of DVGHM.

Date Volcanic A Volcanic B Local Tectonic Emission
12 Jul-18 Jul 2004 2 1 -- continuous
19 Jul-25 Jul 2004 5 3 2 continuous
26 Jul-01 Aug 2004 6 3 1 continuous
02 Aug-08 Aug 2004 5 2 2 continuous
09 Aug-15 Aug 2004 1 1 -- continuous
16 Aug-22 Aug 2004 2 2 -- continuous
23 Aug-29 Aug 2004 -- 1 -- continuous

Volcanic earthquakes decreased during 9-15 August, although continuous emission signals were still being recorded and thin white plumes were seen rising 50-300 m above the summit. Similar activity continued the following week. A thick gray plume rising 50 m was reported the week of 23-29 August, but there was no change in seismicity.

Geologic Background. Gunung Kerinci in central Sumatra forms Indonesia's highest volcano and is one of the most active in Sumatra. It is capped by an unvegetated young summit cone that was constructed NE of an older crater remnant. There is a deep 600-m-wide summit crater often partially filled by a small crater lake that lies on the NE crater floor, opposite the SW-rim summit. The massive 13 x 25 km wide volcano towers 2400-3300 m above surrounding plains and is elongated in a N-S direction. Frequently active, Kerinci has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838.

Information Contacts: Dali Ahmad, Hetty Triastuty, Nia Haerani, and Sri Kisyati, Directorate of Volcanology and Geological Hazard Mitigation, Jalan Diponegoro No. 57, Bandung 40122, Indonesia, URL: http://www.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/).


Krakatau (Indonesia) — August 2004 Citation iconCite this Report

Krakatau

Indonesia

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

All times are local (unless otherwise noted)


Brief period of increased activity in early July

Intense activity occurred at Anak Krakatau beginning on 4 July 2004, when gas and steam emissions increased. The number of volcanic earthquakes also increased on 5 July to between 1 and 4 events per day, then abruptly rose to as high as 58 events/days during the week of 12-18 July before dropping again to 2-17 daily events (table 5). Based on the increased activity, the hazard status was upgraded to Alert Level II (yellow) on 16 July; visitors were not allowed to approach the summit or crater. Seismicity recorded at the Kalianda station after 18 July through 15 August was variable, but did not exhibit the high numbers recorded in the first half of July.

Table 5. Seismicity at Krakatau, 4 July-15 August 2004. Courtesy of DVGHM.

Date Deep volcanic (A-type) Shallow volcanic (B-type) Local Tectonic
04 Jul-11 Jul 2004 77 56 3
12 Jul-18 Jul 2004 113 51 8
19 Jul-25 Jul 2004 22 5 4
26 Jul-01 Aug 2004 36 12 21
02 Aug-08 Aug 2004 45 42 65
09 Aug-15 Aug 2004 10 14 8

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

Information Contacts: Dali Ahmad, Hetty Triastuty, Nia Haerani, and Sri Kisyati, Directorate of Volcanology and Geological Hazard Mitigation, Jalan Diponegoro No. 57, Bandung 40122, Indonesia, URL: http://www.vsi.esdm.go.id/).


Nightingale Island (United Kingdom) — August 2004 Citation iconCite this Report

Nightingale Island

United Kingdom

37.42°S, 12.48°W; summit elev. 365 m

All times are local (unless otherwise noted)


Earthquake swarm on 29-30 July followed by floating pumice

[This event was originally assigned to Tristan da Cunha, but later work located the earthquake swarm on the SE submarine flank of Nightingale Island, about 40 km S.]

The Comprehensive Nuclear Test Ban Treaty Organisation (CTBTO) in Vienna operates a recently installed (July 2002) satellite-linked real-time hydroacoustic station on the island of Tristan da Cunha, with two elements (figure 1). These are designed to record T phases and use three-component short-period seismometers sampled at 100 samples per second. Roderick Stewart, a scientist with the CTBTO, reported that seismic activity, including several felt events, occurred in the vicinity of Tristan da Cunha in July and August 2004. This is the first time that seismicity near this volcano has been instrumentally recorded.

Figure (see Caption) Figure 1. Map of the island of Tristan da Cunha showing the locations of the two CTBTO hydroacoustic stations. Station locations courtesy of R. Stewart, CTBTO.

An intense swarm of seismic activity was recorded, and felt, on the night of 29-30 July. The activity lasted approximately six hours and peaked around 2100-2200 UTC on 29 July. There were a number of large earthquakes in the swarm; the largest, at approximately 2220 UTC on 29 July, had a body-wave magnitude of 4.2. The epicenter was in the vicinity of the island, but location uncertainties make it impossible to say whether the source was onshore or offshore. Seismic activity continued to be recorded, and occasionally felt, throughout August 2004, but was declining slowly (figure 2). No long-period earthquakes or tremor signals were positively identified although, according to Stewart, the temporal pattern of the swarm appeared to be volcanic. A pseudo-RSAM plot of the data from one of the stations showed that the activity grew gradually to a peak over a period of two or three hours and that the larger events occurred after this peak.

Figure (see Caption) Figure 2. Hourly count of earthquakes at Tristan da Cunha from 27 July to 31 August 2004. Events were counted manually on constant gain plots. The counts of earthquakes during the initial swarm were more than 100 per hour. Courtesy of R. Stewart, CTBTO.

Stewart described the earthquakes as follows. "All the earthquake signals were impulsive with well-developed P and S phases, typical of volcano-tectonic activity. With only two stations, it is not possible to determine individual hypocentres with any confidence and the locations of the earthquakes can only be inferred from general observations made on the data. First-motion analysis of the P waves was made difficult because the arrivals were very small on the horizontal components. However, it was possible to determine that the P wave was always arriving from the SE at both stations and that the angle of incidence of the arriving P wave was very steep, within 10 degrees of vertical. S-P times were between 4 and 5 seconds at both stations, with H09N1 typically a fraction of a second longer than H09W1. Depending on the velocities assumed, these S-P times indicate that the earthquakes were between 20 and 30 km from the stations. The simplest interpretation of both the above observations is that the earthquakes occurred at depth directly below the volcano. However, an offshore location to the SE cannot be ruled out. What is certain is that these events occurred close to the volcano."

Reports from the island of rocks floating in the water in the days following the seismic activity, along with an initial offshore estimate of the location of the largest earthquake (which had large uncertainties), led to speculation of an underwater eruption. One newspaper account from the Tristan Times on 6 August described "angular and not round" rocks seen by fishermen floating "all around the Island." In a 14 September BBC World Service interview, Island Administrator Mike Hentley stated that fishermen found "huge lumps of [pumice], up to 10 or 12 kg floating on the surface to the south/west of the Island." He further described the pumice as "a very crumbly, light grey stone." Samples of this pumice collected by James Glass (figure 3) are being sent to the Global Volcanism Program.

Figure (see Caption) Figure 3. Photographs of pumice collected near Tristan da Cunha, August 2004. No scale or size description was provided with the photos, but the top photo of the single sample appears to have been taken on a window ledge and the bottom photo of multiple samples on a bench `seat cushion. Courtesy of James Glass, Tristan Times.

The Tristan Times also reported on 30 September that volcanologist Victoria Hards from the British Geological Survey (BGS) arrived on the island on 10 September to assess the potential threat of the recent seismic activity. She reportedly determined that the 29-30 July event was caused by rising magma 25 km SE of the island. She also noted that there was no sign of activity at the 1961 eruption site, and no eruption was imminent so there was no threat to the settlement. The BGS planned to monitor the seismic data over the next four months to assess any longer-term implications.

Geologic Background. Nightingale Island and the adjacent smaller Middle (or Alex) and Stoltenhoff Islands and associated small islets are the southernmost of the Tristan da Cunha island group. The heavily eroded island consists of early and late stage ash and agglomerate units with intervening massive trachytic intrusions and lava flows. Volcanic rocks were K-Ar dated at between 0.4 and 0.15 million years, and a radiocarbon date of about 39,000 yrs BP was obtained from an ash layer overlain by a lava flow. An earthquake swarm lasting 6 hours beginning on 29 July 2004 was followed by observation of large blocks of floating phonolitic pumice that washed up on Tristan da Cunha. The event was considered to have originated from an eruption associated with an earthquake swarm 37-53 km SSE of Tristan da Cunha on the submarine SE flank of Nightingale Island.

Information Contacts: David Booth, British Geological Survey, Murchison House, Edinburgh EH9 3LA, UK; Roderick Stewart, Preparatory Commission for the Comprehensive Nuclear Test Ban Treaty Organisation (CTBTO), Vienna International Centre, PO Box 1200, A-1400 Vienna, Austria; Juanita Brock and James Glass, Tristan Times (URL: http://www.tristantimes.com); BBC World Service (URL: http://www.bbc.co.uk/worldservice/).


Papandayan (Indonesia) — August 2004 Citation iconCite this Report

Papandayan

Indonesia

7.32°S, 107.73°E; summit elev. 2665 m

All times are local (unless otherwise noted)


Increased seismicity and elevated crater temperatures in July

Volcanic activity increased at Papandayan beginning 17 July 2004. On 13 July, volcanic earthquakes increased from a range of between 1-3 events per day to 7-9 events per day and increased to 57 events on 16 July (table 3). The temperature on Baru Crater I increased from 84 to 88.5°C, and at Baru Crater II the temperature increased from 89 to 102°C. A visible thin white plume rose 25-100 m. This activity prompted a rise in the hazard status to Alert Level II. During the following week volcanic and local tectonic earthquakes increased, but there were no emissions. A white thin plume rose to 50-150 m above the summit. After 26 July seismicity declined and remained low through at least mid-August. The thin white plume was observed throughout this time, but its maximum height decreased each week until it was only 25-75 m above the summit during 9-15 August.

Table 3. Seismicity at Papandayan, 5 July-15 August 2004. Courtesy of DVGHM.

Date Volcanic A Volcanic B Local Tectonic Emission
05 Jul-11 Jul 2004 -- 21 -- --
12 Jul-18 Jul 2004 20 101 4 2
19 Jul-25 Jul 2004 65 129 10 --
26 Jul-01 Aug 2004 8 44 8 --
02 Aug-08 Aug 2004 4 32 3 --
09 Aug-15 Aug 2004 1 46 4 --

Geologic Background. Papandayan is a complex stratovolcano with four large summit craters, the youngest of which was breached to the NE by collapse during a brief eruption in 1772 and contains active fumarole fields. The broad 1.1-km-wide, flat-floored Alun-Alun crater truncates the summit of Papandayan, and Gunung Puntang to the north gives a twin-peaked appearance. Several episodes of collapse have created an irregular profile and produced debris avalanches that have impacted lowland areas. A sulfur-encrusted fumarole field occupies historically active Kawah Mas ("Golden Crater"). After its first historical eruption in 1772, in which collapse of the NE flank produced a catastrophic debris avalanche that destroyed 40 villages and killed nearly 3000 people, only small phreatic eruptions had occurred prior to an explosive eruption that began in November 2002.

Information Contacts: Dali Ahmad, Hetty Triastuty, Nia Haerani, Suswati, and Sri Kisyati, Directorate of Volcanology and Geological Hazard Mitigation, Jalan Diponegoro No. 57, Bandung 40122, Indonesia, URL: http://www.vsi.esdm.go.id/).

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.

View Atmospheric Effects Reports

Special Announcements

Special announcements of various kinds and obituaries.

View Special Announcements Reports

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/).