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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

Ebeko (Russia) Continued explosions, ash plumes, and ashfall; June-November 2020

Kuchinoerabujima (Japan) Intermittent thermal anomalies and small eruptions in May and August 2020

Nyamuragira (DR Congo) Numerous thermal anomalies and gas emissions from the lava lake through November 2020

Raung (Indonesia) Explosions with ash plumes and a thermal anomaly at the summit crater, July-October 2020

Sinabung (Indonesia) Explosions begin again on 8 August 2020; dome growth confirmed in late September

Heard (Australia) Persistent thermal anomalies in the summit crater from June through October 2020

Sabancaya (Peru) Daily explosions produced ash plumes, SO2 plumes, and thermal anomalies during June-September 2020

Rincon de la Vieja (Costa Rica) Frequent small phreatic explosions with intermittent ash plumes during April-September 2020

Fuego (Guatemala) Daily explosions, ash emissions, and block avalanches during August-November 2020

Kikai (Japan) Explosion on 6 October 2020 and thermal anomalies in the crater

Manam (Papua New Guinea) Intermittent ash plumes, thermal anomalies, and SO2 emissions in April-September 2020

Karymsky (Russia) New eruption during April-July 2020; ash explosions in October 2020



Ebeko (Russia) — December 2020 Citation iconCite this Report

Ebeko

Russia

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

All times are local (unless otherwise noted)


Continued explosions, ash plumes, and ashfall; June-November 2020

Volcanism at Ebeko, located on the N end of the Paramushir Island in the Kuril Islands, has been ongoing since October 2016, characterized by frequent moderate explosions, ash plumes, and ashfall in Severo-Kurilsk (7 km ESE) (BGVN 45:05). Similar activity during this reporting period of June through November 2020 continues, consisting of frequent explosions, dense ash plumes, and occasional ashfall. Information for this report primarily comes from the Kamchatka Volcanic Eruptions Response Team (KVERT) and satellite data.

Activity during June was characterized by frequent, almost daily explosions and ash plumes that rose to 1.6-4.6 km altitude and drifted in various directions, according to KVERT reports and information from the Tokyo VAAC advisories using HIMAWARI-8 satellite imagery and KBGS (Kamchatka Branch of the Geophysical Service) seismic data. Satellite imagery showed persistent thermal anomalies over the summit crater. On 1 June explosions generated an ash plume up to 4.5 km altitude drifting E and S, in addition to several smaller ash plumes that rose to 2.3-3 km altitude drifting E, NW, and NE, according to KVERT VONA notices. Explosions on 11 June generated an ash plume that rose 2.6 km altitude and drifted as far as 85 km N and NW. Explosions continued during 21-30 June, producing ash plumes that rose 2-4 km altitude, drifting up to 5 km in different directions (figure 26); many of these eruptive events were accompanied by thermal anomalies that were observed in satellite imagery.

Figure (see Caption) Figure 26. Photo of a dense gray ash plume rising from Ebeko on 22 June 2020. Photo by L. Kotenko (color corrected), courtesy of IVS FEB RAS, KVERT.

Explosions continued in July, producing ash plumes rising 2-5.2 km altitude and drifting for 3-30 km in different directions. On 3, 6, 15 July explosions generated an ash plume that rose 3-4 km altitude that drifted N, NE, and SE, resulting in ashfall in Severo-Kurilsk. According to a Tokyo VAAC advisory, an eruption on 4 July produced an ash plume that rose up to 5.2 km altitude drifting S. On 22 July explosions produced an ash cloud measuring 11 x 13 km in size and that rose to 3 km altitude drifting 30 km SE. Frequent thermal anomalies were identified in satellite imagery accompanying these explosions.

In August, explosions persisted with ash plumes rising 1.7-4 km altitude drifting for 3-10 km in multiple directions. Intermittent thermal anomalies were detected in satellite imagery, according to KVERT. On 9 and 22 August explosions sent ash up to 2.5-3 km altitude drifting W, S, E, and SE, resulting in ashfall in Severo-Kurilsk. Moderate gas-and-steam activity was reported occasionally during the month.

Almost daily explosions in September generated dense ash plumes that rose 1.5-4.3 km altitude and drifted 3-5 km in different directions. Moderate gas-and-steam emissions were often accompanied by thermal anomalies visible in satellite imagery. During 14-15 September explosions sent ash plumes up to 2.5-3 km altitude drifting SE and NE, resulting in ashfall in Severo-Kurilsk. On 22 September a dense gray ash plume rose to 3 km altitude and drifted S. The ash plume on 26 September was at 3.5 km altitude and drifted SE (figure 27).

Figure (see Caption) Figure 27. Photos of dense ash plumes rising from Ebeko on 22 (left) and 26 (right) September 2020. Photos by S. Lakomov (color corrected), IVS FEB RAS, KVERT.

During October, near-daily ash explosions continued, rising 1.7-4 km altitude drifting in many directions. Intermittent thermal anomalies were identified in satellite imagery. During 7-8, 9-10, and 20-22 October ashfall was reported in Severo-Kurilsk.

Explosions in November produced dense gray ash plumes that rose to 1.5-5.2 km altitude and drifted as far as 5-10 km, mainly NE, SE, E, SW, and ENE. According to KVERT, thermal anomalies were visible in satellite imagery throughout the month. On clear weather days on 8 and 11 November Sentinel-2 satellite imagery showed ashfall deposits SE of the summit crater from recent activity (figure 28). During 15-17 November explosions sent ash up to 3.5 km altitude drifting NE, E, and SE which resulted in ashfall in Severo-Kurilsk on 17 November. Similar ashfall was observed on 22-24 and 28 November due to ash rising to 1.8-3 km altitude (figure 29). Explosions on 29 November sent an ash plume up to 4.5 km altitude drifting E (figure 29). A Tokyo VAAC advisory reported that an ash plume drifting SSE on 30 November reached an altitude of 3-5.2 km.

Figure (see Caption) Figure 28. Sentinel-2 satellite imagery of a gray-white gas-and-ash plume at Ebeko on 8 (left) and 11 (right) November 2020, resulting in ashfall (dark gray) to the SE of the volcano. Images using “Natural Color” rendering (bands 4, 3, 2), courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 29. Photos of continued ash explosions from Ebeko on 28 October (left) and 29 November (right) 2020. Photos by S. Lakomov (left) and L. Kotenko (right), courtesy of IVS FEB RAS, KVERT.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows a pulse in low-power thermal activity beginning in early June through early August (figure 30). On clear weather days, the thermal anomalies in the summit crater are observed in Sentinel-2 thermal satellite imagery, accompanied by occasional white-gray ash plumes (figure 31). Additionally, the MODVOLC algorithm detected a single thermal anomaly on 26 June.

Figure (see Caption) Figure 30. A small pulse in thermal activity at Ebeko began in early June and continued through early August 2020, according to the MIROVA graph (Log Radiative Power). The detected thermal anomalies were of relatively low power but were persistent during this period. Courtesy of MIROVA.
Figure (see Caption) Figure 31. Sentinel-2 satellite imagery showed gray ash plumes rising from Ebeko on 11 June (top left) and 16 July (bottom left) 2020, accompanied by occasional thermal anomalies (yellow-orange) within the summit crater, as shown on 24 June (top right) and 25 August (bottom right). The ash plume on 11 June drifted N from the summit. Images using “Natural Color” rendering (bands 4, 3, 2) on 11 June (top left) and 16 July (bottom left) and the rest have “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

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

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Kamchatka Branch of the Geophysical Service, Russian Academy of Sciences (KB GS RAS) (URL: http://www.emsd.ru/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Kuchinoerabujima (Japan) — November 2020 Citation iconCite this Report

Kuchinoerabujima

Japan

30.443°N, 130.217°E; summit elev. 657 m

All times are local (unless otherwise noted)


Intermittent thermal anomalies and small eruptions in May and August 2020

Kuchinoerabujima encompasses a group of young stratovolcanoes located in the northern Ryukyu Islands. All historical eruptions have originated from the Shindake cone, with the exception of a lava flow that originated from the S flank of the Furudake cone. The current eruptive period began in January 2020 and has been characterized by small explosions, ash plumes, ashfall, a pyroclastic flow, and gas-and-steam emissions. This report covers activity from May to October 2020, which includes small explosions, ash plumes, crater incandescence, and gas-and-steam emissions. The primary source of information for this report comes from monthly and annual reports from the Japan Meteorological Agency (JMA) and advisories from the Tokyo Volcanic Ash Advisory Center (VAAC).

Volcanism at Kuchinoerabujima remained relatively low during May through October 2020, according to JMA. During this time, SO2 emissions ranged from 40 to 3,400 tons/day; occasional gas-and-steam emissions were reported, rising to a maximum of 900 m above the crater. Sentinel-2 satellite images showed a particularly strong thermal anomaly in the Shindake crater on 1 May (figure 10). The thermal anomaly decreased in power after 1 May and was only visible on clear weather days, which included 19 August and 3 and 13 October. Global Navigation Satellite System (GNSS) observations identified continued slight inflation at the base of the volcano during the entire reporting period.

Figure (see Caption) Figure 10. Sentinel-2 thermal satellite images showed a strong thermal anomaly (bright yellow-orange) in the Shindake crater at Kuchinoerabujima on 1 May 2020 (top left). Weaker thermal anomalies were also seen in the Shindake crater during 19 August (top right) and 3 (bottom left) and 13 (bottom right) October 2020. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images; courtesy of Sentinel Hub Playground.

Three small eruptions were detected by JMA on 5, 6, and 13 May, which produced an ash plume rising 500 m above the crater on each day, resulting in ashfall on the downwind flanks. Incandescence was observed at night using a high-sensitivity surveillance camera (figure 11). On 5 and 13 May the Tokyo VAAC released a notice that reported ash plumes rising 0.9-1.2 km altitude, drifting NE and S, respectively. On 20 May weak fumaroles were observed on the W side of the Shindake crater. The SO2 emissions ranged from 700-3,400 tons/day.

Figure (see Caption) Figure 11. Webcam images of an eruption at Kuchinoerabujima on 6 May 2020 (top), producing a gray ash plume that rose 500 m above the crater. Crater incandescence was observed from the summit crater at night on 25 May 2020 (bottom). Courtesy of JMA (Monthly bulletin report 509, May 2020).

Activity during June and July decreased compared to May, with gas-and-steam emissions occurring more prominently. On 22 June weak incandescence was observed, accompanied by white gas-and-steam emissions rising 700 m above the crater. Weak crater incandescence was also seen on 25 June. The SO2 emissions measured 400-1,400 tons/day. White gas-and-steam emissions were again observed on 31 July rising to 800 m above the crater. The SO2 emissions had decreased during this time to 300-700 tons/day.

According to JMA, the most recent eruptive event occurred on 29 August at 1746, which ejected bombs and was accompanied by some crater incandescence, though the eruptive column was not visible due to the cloud cover. However, white gas-and-steam emissions could be seen rising 1.3 km above the Shindake crater drifting SW. The SO2 emissions measured 200-500 tons/day. During August, the number of volcanic earthquakes increased significantly to 1,032, compared to the number in July (36).

The monthly bulletin for September reported white gas-and-steam emissions rising 900 m above the crater on 9 September and on 11 October the gas-and-steam emissions rose 600 m above the crater. Seismicity decreased between September and October from 1,920 to 866. The SO2 emissions continued to decrease compared to previous months, totaling 80-400 tons/day in September and 40-300 tons/day in October.

Geologic Background. A group of young stratovolcanoes forms the eastern end of the irregularly shaped island of Kuchinoerabujima in the northern Ryukyu Islands, 15 km W of Yakushima. The Furudake, Shindake, and Noikeyama cones were erupted from south to north, respectively, forming a composite cone with multiple craters. All historical eruptions have occurred from Shindake, although a lava flow from the S flank of Furudake that reached the coast has a very fresh morphology. Frequent explosive eruptions have taken place from Shindake since 1840; the largest of these was in December 1933. Several villages on the 4 x 12 km island are located within a few kilometers of the active crater and have suffered damage from eruptions.

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, 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 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Nyamuragira (DR Congo) — December 2020 Citation iconCite this Report

Nyamuragira

DR Congo

1.408°S, 29.2°E; summit elev. 3058 m

All times are local (unless otherwise noted)


Numerous thermal anomalies and gas emissions from the lava lake through November 2020

Nyamuragira (also known as Nyamulagira) is a shield volcano in the Democratic Republic of the Congo with a 2 x 2.3 km caldera at the summit. A summit crater lies in the NE part of the caldera. In the recent past, the volcano has been characterized by intra-caldera lava flows, lava emissions from its lava lake, thermal anomalies, gas-and-steam emissions, and moderate seismicity (BGVN 44:12, 45:06). This report reviews activity during June-November 2020, based on satellite data.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed numerous thermal anomalies associated with the volcano during June-November 2020, although some decrease was noted during the last half of August and between mid-October to mid-November (figure 91). Between six and seven thermal hotspots per month were identified by MODVOLC during June-November 2020, with as many as 4 pixels on 11 August. In the MODVOLC system, two main hotspot groupings are visible, the largest being at the summit crater, on the E side of the caldera.

Figure (see Caption) Figure 91. MIROVA graph of thermal activity (log radiative power) at Nyamuragira during March 2020-January 2021. During June-November 2020, most were in the low to moderate range, with a decrease in power during November. Courtesy of MIROVA.

Sentinel-2 satellite images showed several hotspots in the summit crater throughout the reporting period (figure 92). By 26 July and thereafter, hotspots were also visible in the SW portion of the caldera, and perhaps just outside the SW caldera rim. Gas-and-steam emissions from the lava lake were also visible throughout the period.

Figure (see Caption) Figure 92. Sentinel-2 satellite images of Nyamuragira on 26 July (left) and 28 November (right) 2020. Thermal activity is present at several locations within the summit crater (upper right of each image) and in the SW part of the caldera (lower left). SWIR rendering (bands 12, 8A, 4). Courtesy of Sentinel Hub Playground.

Geologic Background. Africa's most active volcano, Nyamuragira, is a massive high-potassium basaltic shield about 25 km N of Lake Kivu. Also known as Nyamulagira, it has generated extensive lava flows that cover 1500 km2 of the western branch of the East African Rift. The broad low-angle shield volcano contrasts dramatically with the adjacent steep-sided Nyiragongo to the SW. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Historical eruptions have occurred within the summit caldera, as well as from the numerous fissures and cinder cones on the flanks. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Historical lava flows extend down the flanks more than 30 km from the summit, reaching as far as Lake Kivu.

Information Contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/exp).


Raung (Indonesia) — December 2020 Citation iconCite this Report

Raung

Indonesia

8.119°S, 114.056°E; summit elev. 3260 m

All times are local (unless otherwise noted)


Explosions with ash plumes and a thermal anomaly at the summit crater, July-October 2020

A massive stratovolcano in easternmost Java, Raung has over sixty recorded eruptions dating back to the late 16th Century. Explosions with ash plumes, Strombolian activity, and lava flows from a cinder cone within the 2-km-wide summit crater have been the most common activity. Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) has installed webcams to monitor activity in recent years. An eruption from late 2014 through August 2015 produced a large volume of lava within the summit crater and formed a new pyroclastic cone in the same location as the previous one. The eruption that began in July 2020 is covered in this report with information provided by PVMBG, the Darwin Volcanic Ash Advisory Center (VAAC), and several sources of satellite data.

The 2015 eruption was the largest in several decades; Strombolian activity was reported for many months and fresh lava flows covered the crater floor (BGVN 45:09). Raung was quiet after the eruption ended in August of that year until July of 2020 when seismicity increased on 13 July and brown emissions were first reported on 16 July. Tens of explosions with ash emissions were reported daily during the remainder of July 2020. Explosive activity decreased during August, but thermal activity didn’t decrease until mid-September. The last ash emissions were reported on 3 October and the last thermal anomaly in satellite data was recorded on 7 October 2020.

Eruption during July-October 2020. No further reports of activity were issued after August 2015 until July 2020. Clear Google Earth imagery from October 2017 and April 2018 indicated the extent of the lava from the 2015 eruption, but no sign of further activity (figure 31). By August 2019, many features from the 2015 eruption were still clearly visible from the crater rim (figure 32).

Figure (see Caption) Figure 31. Little change can be seen at the summit of Raung in Google Earth images dated 19 October 2017 (left) and 28 April 2018 (right). The summit crater was full of black lava flows from the 2015 eruption. Courtesy of Google Earth.
Figure (see Caption) Figure 32. A Malaysian hiker celebrated his climbing to the summit of Raung on 30 August 2019. Weak fumarolic activity was visible from the base of the breached crater of the cone near the center of the summit crater, and many features of the lava flow that filled the crater in 2015 were still well preserved. Courtesy of MJ.

PVMBG reported that the number and type of seismic events around the summit of Raung increased beginning on 13 July 2020, and on 16 July the height of the emissions from the crater rose to 100 m and the emission color changed from white to brown. About three hours later the emissions changed to gray and white. The webcams captured emissions rising 50-200 m above the summit that included 60 explosions of gray and reddish ash plumes (figure 33). The Raung Volcano Observatory released a VONA reporting an explosion with an ash plume that drifted N at 1353 local time (0653 UTC). The best estimate of the ash cloud height was 3,432 m based on ground observation. They raised the Aviation Color Code from unassigned to Orange. About 90 minutes later they reported a second seismic event and ash cloud that rose to 3,532 m, again based on ground observation. The Darwin VAAC reported that neither ash plume was visible in satellite imagery. The following day, on 17 July, PVMBG reported 26 explosions between midnight and 0600 that produced brown ash plumes which rose 200 m above the crater. Based on these events, PVMBG raised the Alert Level of Raung from I (Normal) to II (Alert) on a I-II-III-IV scale. By the following day they reported 95 explosive seismic events had occurred. They continued to observe gray ash plumes rising 100-200 m above the summit on clear days and 10-30 daily explosive seismic events through the end of July; plume heights dropped to 50-100 m and the number of explosive events dropped below ten per day during the last few days of the month.

Figure (see Caption) Figure 33. An ash plume rose from the summit of Raung on 16 July 2020 at the beginning of a new eruption. The last previous eruption was in 2015. Courtesy of Volcano Discovery and PVMBG.

After a long period of no activity, MIROVA data showed an abrupt return to thermal activity on 16 July 2020; a strong pulse of heat lasted into early August before diminishing (figure 34). MODVOLC thermal alert data recorded two alerts each on 18 and 20 July, and one each on 21 and 30 July. Satellite images showed no evidence of thermal activity inside the summit crater from September 2015 through early July 2020. Sentinel-2 satellite imagery first indicated a strong thermal anomaly inside the pyroclastic cone within the crater on 19 July 2020; it remained on 24 and 29 July (figure 35). A small SO2 signature was measured by the TROPOMI instrument on the Sentinel-5P satellite on 25 July.

Figure (see Caption) Figure 34. MIROVA thermal anomaly data indicated renewed activity on 16 July 2020 at Raung as seen in this graph of activity from 13 October 2019 through September 2020. Satellite images indicated that the dark lines at the beginning of the graph are from a large area of fires that burned on the flank of Raung in October 2019. Heat flow remained high through July and began to diminish in mid-August 2020. Courtesy of MIROVA.
Figure (see Caption) Figure 35. Thermal anomalies were distinct inside the crater of the pyroclastic cone within the summit crater of Raung on 19, 24, and 29 July 2020. Data is from the Sentinel-2 satellite shown with Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

After an explosion on 1 August 2020 emissions from the crater were not observed again until steam plumes were seen rising 100 m on 7 August. They were reported rising 100-200 m above the summit intermittently until a dense gray ash plume was reported by PVMBG on 11 August rising 200 m. After that, diffuse steam plumes no more than 100 m high were reported for the rest of the month except for white to brown emissions to 100 m on 21 August. Thermal anomalies of a similar brightness to July from the same point within the summit crater were recorded in satellite imagery on 3, 8, 13, 18, and 23 August. Single MODVOLC thermal alerts were reported on 1, 8, 12, and 19 August.

In early September dense steam plumes rose 200 m above the crater a few times but were mostly 50 m high or less. White and gray emissions rose 50-300 m above the summit on 15, 20, 27, and 30 September. Thermal anomalies were still present in the same spot in Sentinel-2 satellite imagery on 2, 7, 12, 17, and 27 September, although the signal was weaker than during July and August (figure 36). PVMBG reported gray emissions rising 100-300 m above the summit on 1 October 2020 and two seismic explosion events. Gray emissions rose 50-200 m the next day and nine explosions were recorded. On 3 October, emissions were still gray but only rose 50 m above the crater and no explosions were reported. No emissions were observed from the summit crater for the remainder of the month. Sentinel-2 satellite imagery showed a hot spot within the summit crater on 2 and 7 October, but clear views of the crater on 12, 17, and 22 October showed no heat source within the crater (figure 37).

Figure (see Caption) Figure 36. The thermal anomaly at Raung recorded in Sentinel-2 satellite data decreased in intensity between August and October 2020. It was relatively strong on 13 August (left) but had decreased significantly by 12 September (middle) and remained at a lower level into early October (right). Data shown with Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground
Figure (see Caption) Figure 37. A small but distinct thermal anomaly was still present within the pyroclastic cone inside the summit crater of Raung on 7 October 2020 (left) but was gone by 12 October (middle) and did not reappear in subsequent clear views of the crater through the end of October. Satellite imagery of 7 and 12 October processed with Atmospheric penetration rendering (bands 12, 11, 8A). Natural color rendering (bands 4, 3, 2) from 17 October (right) shows no clear physical changes to the summit crater during the latest eruption. Courtesy of Sentinel Hub Playground.

Geologic Background. Raung, one of Java's most active volcanoes, is a massive stratovolcano in easternmost Java that was constructed SW of the rim of Ijen caldera. The unvegetated summit is truncated by a dramatic steep-walled, 2-km-wide caldera that has been the site of frequent historical eruptions. A prehistoric collapse of Gunung Gadung on the W flank produced a large debris avalanche that traveled 79 km, reaching nearly to the Indian Ocean. Raung contains several centers constructed along a NE-SW line, with Gunung Suket and Gunung Gadung stratovolcanoes being located to the NE and W, respectively.

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/); 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/); 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/); 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/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Google Earth (URL: https://www.google.com/earth/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); MJ (URL: https://twitter.com/MieJamaludin/status/1167613617191043072).


Sinabung (Indonesia) — November 2020 Citation iconCite this Report

Sinabung

Indonesia

3.17°N, 98.392°E; summit elev. 2460 m

All times are local (unless otherwise noted)


Explosions begin again on 8 August 2020; dome growth confirmed in late September

Indonesia’s Sinabung volcano in north Sumatra has been highly active since its first confirmed Holocene eruption during August and September 2010. It remained quiet after the initial eruption until September 2013, when a new eruptive phase began that continued through June 2018. A summit dome emerged in late 2013 and produced a large lava “tongue” during 2014. Multiple explosions produced ash plumes, block avalanches, and deadly pyroclastic flows during the eruptive period. A major explosion in February 2018 destroyed most of the summit dome. After a pause in eruptive activity from September 2018 through April 2019, explosions resumed during May and June 2019. The volcano was quiet again until an explosion on 8 August 2020 began another eruption that included a new dome. This report covers activity from July 2019 through October 2020 with information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), referred to by some agencies as CVGHM or the Indonesian Center of Volcanology and Geological Hazard Mitigation, the Darwin Volcanic Ash Advisory Centre (VAAC), and the Badan Nacional Penanggulangan Bencana (National Disaster Management Authority, BNPB). Additional information comes from satellite instruments and local news reports.

Only steam plumes and infrequent lahars were reported at Sinabung during July 2019-July 2020. A new eruption began on 8 August 2020 with a phreatic explosion and dense ash plumes. Repeated explosions were reported throughout August; ashfall was reported in many nearby communities several times. Explosions decreased significantly during September, but SO2 emissions persisted. Block avalanches from a new growing dome were first reported in early October; pyroclastic flows accompanied repeated ash emissions during the last week of the month. Thermal data suggested that the summit dome continued growing slowly during October.

Activity during July 2019-October 2020. After a large explosion on 9 June 2019, activity declined significantly, and no further emissions or incandescence was reported after 25 June (BGVN 44:08). For the remainder of 2019 steam plumes rose 50-400 m above the summit on most days, occasionally rising to 500-700 m above the crater. Lahars were recorded by seismic instruments in July, August, September, and December. During January-July 2020 steam plumes were reported usually 50-300 m above the summit, sometimes rising to 500 m. On 21 March 2020 steam plumes rose to 700 m, and a lahar was recorded by seismic instruments. Lahars were reported on 26 and 28 April, 3 and 5 June, and 11 July.

A swarm of deep volcanic earthquakes was reported by PVMBG on 7 August 2020. This was followed by a phreatic explosion with a dense gray to black ash plume on 8 August that rose 2,000 m above the summit and drifted E; a second explosion that day produced a plume that rose 1,000 m above the summit. According to the Jakarta Post, ash reached the community of Berastagi (15 km E) along with the districts of Naman Teran (5-10 km NE), Merdeka (15 km NE), and Dolat Rayat (20 km E). Continuous tremor events were first recorded on 8 August and continued daily until 26 August. Two explosions were recorded on 10 August; the largest produced a dense gray ash plume that rose 5,000 m above the summit and drifted NE and SE (figure 77). The Darwin VAAC reported the eruption clearly visible in satellite imagery at 9.7 km altitude and drifting W. Later they reported a second plume drifting ESE at 4.3 km altitude. After this large explosion the local National Disaster Management Authority (BNPB) reported significant ashfall in three districts: Naman Teran, Berastagi and Merdeka. Emissions on 11 and 12 August were white and gray and rose 100-200 m. Multiple explosions on 13 August produced white and gray ash plumes that rose 1,000-2,000 m above the summit. Explosions on 14 August produced gray and brown ash plumes that rose 1,000-4,200 m above the summit and drifted S and SW (figure 77). The Darwin VAAC reported that the ash plume was partly visible in satellite imagery at 7.6 km altitude moving W; additional plumes were moving SE at 3.7 km altitude and NE at 5.5 km altitude.

Figure (see Caption) Figure 77. Numerous explosions were recorded at Sinabung during August 2020. An ash plume rose to 5,000 m above the summit on 10 August (left) and drifted both NE and SE. On 14 August gray and brown ash plumes rose 1,000-4,200 m above the summit and drifted S, SW, SE and NE (right) while ashfall covered crops SE of the volcano. Courtesy of PVMBG (Sinabung Eruption Notices, 10 and 14 August 2020).

White, gray, and brown emissions rose 800-1,000 m above the summit on 15 and 17 August. The next day white and gray emissions rose 2,000 m above the summit. The Darwin VAAC reported an ash plume visible at 5.2 km altitude drifting SW. A large explosion on 19 August produced a dense gray ash plume that rose 4,000 above the summit and drifted S and SW. Gray and white emissions rose 500 m on 20 August. Two explosions were recorded seismically on 21 August, but rainy and cloudy weather prevented observations. White steam plumes rose 300 m on 22 August, and a lahar was recorded seismically. On 23 August, an explosion produced a gray ash plume that rose 1,500 m above the summit and pyroclastic flows that traveled 1,000 m down the E and SE flanks (figure 78). Continuous tremors were accompanied by ash emissions. White, gray, and brown emissions rose 600 m on 24 August. An explosion on 25 August produced an ash plume that rose 800 m above the peak and drifted W and NW (figure 79). During 26-30 August steam emissions rose 100-400 m above the summit and no explosions were recorded. Dense gray ash emissions rose 1,000 m and drifted E and NE after an explosion on 31 August. Significant SO2 emissions were associated with many of the explosions during August (figure 80).

Figure (see Caption) Figure 78. On 23 August 2020 an explosion at Sinabung produced a gray ash plume that rose 1,500 m above the summit and produced pyroclastic flows that traveled 1,000 m down the E and SE flanks. Courtesy of PVMBG (Sinabung Eruption Notice, 23 August 2020).
Figure (see Caption) Figure 79. An explosion on 25 August 2020 at Sinabung produced an ash plume that rose 800 m above the peak and drifted W and NW. Courtesy of PVMBG (Sinabung Eruption Notice, 25 August 2020).
Figure (see Caption) Figure 80. Significant sulfur dioxide emissions were measured at Sinabung during August 2020 when near-daily explosions produced abundant ash emissions. A small plume was also recorded from Kerinci on 19 August 2020. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Explosive activity decreased substantially during September 2020. A single explosion reported on 5 September produced a white and brown ash plume that rose 800 m above the summit and drifted NNE. During the rest of the month steam emissions rose 50-500 m above the summit before dissipating. Two lahars were reported on 7 September, and one each on 11 and 30 September. Although only a single explosion was reported, anomalous SO2 emissions were present in satellite data on several days.

The character of the activity changed during October 2020. Steam plumes rising 50-300 m above the summit were reported during the first week and a lahar was recorded by seismometers on 4 October. The first block avalanches from a new dome growing at the summit were reported on 8 October with material traveling 300 m ESE from the summit (figure 81). During 11-13 October block avalanches traveled 300-700 m E and SE from the summit. They traveled 100-150 m on 14 October. Steam plumes rising 50-500 m above the summit were reported during 15-22 October with two lahars recorded on 21 October. White and gray emissions rose 50-1,000 m on 23 October. The first of a series of pyroclastic flows was reported on 25 October; they were reported daily through the end of the month when the weather permitted, traveling 1,000-2,500 m from the summit (figure 82). In addition, block avalanches from the growing dome were observed moving down the E and SE flanks 500-1,500 m on 25 October and 200-1,000 m each day during 28-31 October (figure 83). Sentinel-2 satellite data indicated a very weak thermal anomaly at the summit in late September; it was slightly larger in late October, corroborating with images of the slow-growing dome (figure 84).

Figure (see Caption) Figure 81. A new lava dome appeared at the summit of Sinabung in late September 2020. Block avalanches from the dome were first reported on 8 October. Satellite imagery indicating a thermal anomaly at the summit was very faint at the end of September and slightly stronger by the end of October. The dome grew slowly between 30 September (top) and 22 October 2020 (bottom). Photos taken by Firdaus Surbakti, courtesy of Rizal.
Figure (see Caption) Figure 82. Pyroclastic flows at Sinabung were accompanied ash emissions multiple times during the last week of October, including the event seen here on 27 October 2020. Courtesy of PVMBG and CultureVolcan.
Figure (see Caption) Figure 83. Block avalanches from the growing summit dome at Sinabung descended the SE flank on 28 October 2020. The dome is visible at the summit. Courtesy of PVMBG and MAGMA.
Figure (see Caption) Figure 84. A very faint thermal anomaly appeared at the summit of Sinabung in Sentinel 2 satellite imagery on 28 September 2020 (left). One month later on 28 October the anomaly was bigger, corroborating photographic evidence of the growing dome. Atmospheric penetration rendering (bands 12, 11, 8A) courtesy of Sentinel Hub Playground.

Geologic Background. Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. The youngest deposit is a SE-flank pyroclastic flow 14C dated by Hendrasto et al. (2012) at 740-880 CE. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); The Jakarta Post, 3rd Floor, Gedung, Jl. Palmerah Barat 142-143 Jakarta 10270 (URL: https://www.thejakartapost.com/amp/news/2020/08/08/mount-sinabung-erupts-again-after-year-of-inactivity.html);Rizal (URL: https://twitter.com/Rizal06691023/status/1319452375887740930); CultureVolcan (URL: https://twitter.com/CultureVolcan/status/1321156861173923840).


Heard (Australia) — November 2020 Citation iconCite this Report

Heard

Australia

53.106°S, 73.513°E; summit elev. 2745 m

All times are local (unless otherwise noted)


Persistent thermal anomalies in the summit crater from June through October 2020

The remote Heard Island is located in the southern Indian Ocean and contains the Big Ben stratovolcano, which has had intermittent activity since 1910. The island’s activity, characterized by thermal anomalies and occasional lava flows (BGVN 45:05), is primarily monitored by satellite instruments. This report updates activity from May through October 2020 using information from satellite-based instruments.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed frequent thermal activity in early June that continued through July (figure 43). Intermittent, slightly higher-power thermal anomalies were detected in late August through mid-October, the strongest of which occurred in October. Two of these anomalies were also detected in the MODVOLC algorithm on 12 October.

Figure (see Caption) Figure 43. A small pulse in thermal activity at Heard was detected in early June and continued through July 2020, according to the MIROVA system (Log Radiative Power). Thermal anomalies appeared again starting in late August and continued intermittently through mid-October 2020. Courtesy of MIROVA.

Sentinel-2 thermal satellite imagery showed a single thermal anomaly on 3 May. In comparison to the MIROVA graph, satellite imagery showed a small pulse of strong thermal activity at the summit of Big Ben in June (figure 44). Some of these thermal anomalies were accompanied by gas-and-steam emissions. Persistent strong thermal activity continued through July. Starting on 2 July through at least 17 July two hotspots were visible in satellite imagery: one in the summit crater and one slightly to the NW of the summit (figure 45). Some gas-and-steam emissions were seen rising from the S hotspot in the summit crater. In August the thermal anomalies had decreased in strength and frequency but persisted at the summit through October (figure 45).

Figure (see Caption) Figure 44. Thermal satellite images of Heard Island’s Big Ben volcano showed strong thermal signatures (bright yellow-orange) sometimes accompanied by gas-and-steam emissions drifting SE (top left) and NE (bottom right) during June 2020. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 45. Thermal satellite images of Heard Island’s Big Ben volcano showed persistent thermal anomalies (bright yellow-orange) near the summit during July through October 2020. During 14 (top left) and 17 (top right) July a second hotspot was visible NW of the summit. By 22 October (bottom right) the thermal anomaly had significantly decreased in strength in comparison to previous months. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Geologic Background. Heard Island on the Kerguelen Plateau in the southern Indian Ocean consists primarily of the emergent portion of two volcanic structures. The large glacier-covered composite basaltic-to-trachytic cone of Big Ben comprises most of the island, and the smaller Mt. Dixon lies at the NW tip of the island across a narrow isthmus. Little is known about the structure of Big Ben because of its extensive ice cover. The historically active Mawson Peak forms the island's high point and lies within a 5-6 km wide caldera breached to the SW side of Big Ben. Small satellitic scoria cones are mostly located on the northern coast. Several subglacial eruptions have been reported at this isolated volcano, but observations are infrequent and additional activity may have occurred.

Information Contacts: MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Sabancaya (Peru) — October 2020 Citation iconCite this Report

Sabancaya

Peru

15.787°S, 71.857°W; summit elev. 5960 m

All times are local (unless otherwise noted)


Daily explosions produced ash plumes, SO2 plumes, and thermal anomalies during June-September 2020

Sabancaya, located in Peru, is a stratovolcano that has been very active since 1986. The current eruptive period began in November 2016 and has recently been characterized by lava dome growth, daily explosions, ash plumes, ashfall, SO2 plumes, and ongoing thermal anomalies (BGVN 45:06). Similar activity continues into this reporting period of June through September 2020 using information from weekly reports from the Observatorio Vulcanologico INGEMMET (OVI), the Instituto Geofisico del Peru (IGP), and various satellite data. The Buenos Aires Volcanic Ash Advisory Center (VAAC) issued a total of 520 reports of ongoing ash emissions during this time.

Volcanism during this reporting period consisted of daily explosions, nearly constant gas-and-ash plumes, SO2 plumes, and persistent thermal anomalies in the summit crater. Gas-and-ash plumes rose to 1.5-4 km above the summit crater, drifting up to 35 km from the crater in multiple directions; several communities reported ashfall every month except for August (table 7). Sulfur dioxide emissions were notably high and recorded almost daily with the TROPOMI satellite instrument (figure 83). The satellite measurements of the SO2 emissions exceeded 2 DU (Dobson Units) at least 20 days each month of the reporting period. These SO2 plumes sometimes persisted over multiple days and ranged between 1,900-10,700 tons/day. MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows frequent thermal activity through September within 5 km of the summit crater, though the power varied; by late August, the thermal anomalies were stronger compared to the previous months (figure 84). This increase in power is also reflected by the MODVOLC algorithm that detected 11 thermal anomalies over the days of 31 August and 4, 6, 13, 17, 18, 20, and 22 September 2020. Many of these thermal hotspots were visible in Sentinel-2 thermal satellite imagery, occasionally accompanied by gas-and-steam and ash plumes (figure 85).

Table 7. Persistent activity at Sabancaya during June through September included multiple daily explosions that produced ash plumes rising several kilometers above the summit and drifting in multiple directions; this resulted in ashfall in communities within 35 km of the volcano. Satellite instruments recorded daily SO2 emissions. Data courtesy of OVI-INGEMMET, IGP, and the NASA Global Sulfur Dioxide Monitoring Page.

Month Avg. daily explosions by week Max plume heights (km above the crater) Plume drift (km) and direction Communities reporting ashfall Minimum days with SO2 over 2 DU SO2 emissions per day (tons) by week
Jun 2020 20, 10, 9, 13 1.5-4 30 km, SE, S, SW, NE, W, E Chivay, Achoma, Ichupampa, Yanque, and Coporaque, Sallali, Madrigal, Lari, and Ichupampa 28 8,400, 2,200, 3,100, 7,600
Jul 2020 20, 15, 11, 12, 19 2-2.6 15-30 km E, NE, NW, SE, SW, S, W Achoma and Chivay 23 4,400, 6,000, 1,900, 2,100, 5,900
Aug 2020 18, 12, 9, 29 1.7-3.6 20-30 km W, SW, SE, S, E, NW - 20 2,300, 3,800, 5,300, 10,700
Sep 2020 39, 35, 33, 38, 40 1.8-3.5 25-35 km SE, S, SW, W, E, NE, N, NW, W Lari, Achoma, Maca, Chivay, Taya, Huambo, Huanca, and Lluta 28 9,700, 2,600, 8,800, 7,800, 4,100
Figure (see Caption) Figure 83. Sulfur dioxide plumes were captured almost daily from Sabancaya during June through September 2020 by the TROPOMI instrument on the Sentinel-5P satellite. Some of the largest SO2 plumes occurred on 19 June (top left), 5 July (top right), 30 August (bottom left), and 10 September (bottom right) 2020. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.
Figure (see Caption) Figure 84. Thermal activity at Sabancaya varied in power from 13 October 2019 through September 2020, but was consistent in frequency, according to the MIROVA graph (Log Radiative Power). A pulse in thermal activity is shown in late August 2020. Courtesy of MIROVA.
Figure (see Caption) Figure 85. Sentinel-2 thermal satellite imagery showed frequent gas-and-steam and ash plumes rising from Sabancaya, accompanied by ongoing thermal activity from the summit crater during June through September 2020. On 23 June (top left) a dense gray-white ash plume was visible drifting E from the summit. On 3 July (top right) and 27 August (bottom left) a strong thermal hotspot (bright yellow-orange) was accompanied by some degassing. On 1 September (bottom right) the thermal anomaly persisted with a dense gray-white ash plume drifting SE from the summit. Images using “Natural Color” rendering (bands 4, 3, 2) on 23 June 2020 (top left) and the rest have “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

OVI detected slight inflation on the N part of the volcano, which continued to be observed throughout the reporting period. Persistent thermal anomalies caused by the summit crater lava dome were observed in satellite data. The average number of daily explosions during June ranged from 18 during 1-7 June to 9 during 15-21 June, which generated gas-and-ash plumes that rose 1.5-4 km above the crater and drifted 30 km SE, S, SW, NE, W, and E (figure 86). The strongest sulfur dioxide emissions were recorded during 1-7 June measuring 8,400 tons/day. On 20 June drone video showed that the lava dome had been destroyed, leaving blocks on the crater floor, though the crater remained hot, as seen in thermal satellite imagery (figure 85). During 22-28 June there were an average of 13 daily explosions, which produced ash plumes rising to a maximum height of 4 km, drifting NE, E, and SE. As a result, ashfall was reported in the districts of Chivay, Achoma, Ichupampa, Yanque, and Coporaque, and in the area of Sallali. Then, on 27 June ashfall was reported in several areas NE of the volcano, which included the districts of Madrigal, Lari, Achoma, Ichupampa, Yanque, Chivay, and Coporaque.

Figure (see Caption) Figure 86. Multiple daily explosions at Sabancaya produced ash plumes that rose 1.5-4 km above the crater during June 2020. Images are showing 8 (left) and 27 (right) June 2020. Courtesy of OVI (Reporte Semanal de Monitorio de la Actividad de la Volcan Sabancaya, RSSAB-24-2020/INGEMMET Semana del 08 al 14 de junio del 2020 and RSSAB-26-2020/INGEMMET Semana del 22 al 28 de junio del 2020).

Slight inflation continued to be monitored in July, occurring about 4-6 km N of the crater, as well as on the SE flank. Daily explosions continued, producing gas-and-ash plumes that rose 2-2.6 km above the crater and drifting 15-30 km E, NE, NW, SE, SW, S, and W (figure 87). The number of daily explosions increased slightly compared to the previous month, ranging from 20 during 1-5 July to 11 during 13-19 July. SO2 emissions that were measured each week ranged from 1,900 to 6,000 tons/day, the latter of which occurred during 6-12 July. Thermal anomalies continued to be observed in thermal satellite data over the summit crater throughout the month. During 6-12 July gas-and-ash plumes rose 2.3-2.5 km above the crater, drifting 30 km SE, E, and NE, resulting in ashfall in Achoma and Chivay.

Figure (see Caption) Figure 87. Multiple daily explosions at Sabancaya produced ash plumes that rose 2-3.5 km above the crater during July 2020. Images are showing 7 (left) and 26 (right) July 2020. Courtesy of OVI (Reporte Semanal de Monitorio de la Actividad de la Volcan Sabancaya, RSSAB-28-2020/INGEMMET Semanal: del 06 al 12 de julio del 2020 and RSSAB-30-2020/INGEMMET Semanal: del 20 al 26 de julio del 2020).

OVI reported continued slight inflation on the N and SE flanks during August. Daily explosive activity had slightly declined in the first part of the month, ranging from 18 during the 3-9 August to 9 during 17-23 August. Dense gray gas-and-ash plumes rose 1.7-3.6 km above the crater, drifting 20-30 km in various directions (figure 88), though no ashfall was reported. Thermal anomalies were observed using satellite data throughout the month. During 24-30 August a pulse in activity increased the daily average of explosions to 29, as well as the amount of SO2 emissions (10,700 tons/day); nighttime incandescence accompanied this activity. During 28-29 August higher levels of seismicity and inflation were reported compared to the previous weeks. The daily average of explosions increased again during 31 August-6 September to 39; nighttime incandescence remained.

Figure (see Caption) Figure 88. Multiple daily explosions at Sabancaya produced ash plumes that rose 1.7-3.6 km above the crater during August 2020. Images are showing 1 (left) and 29 (right) August 2020. Courtesy of OVI (Reporte Semanal de Monitorio de la Actividad de la Volcan Sabancaya, RSSAB-31-2020/INGEMMET Semanal del 27 de julio al 02 de agosto del 2020 and RSSAB-35-2020/INGEMMET Semanal del 24 al 30 de agosto del 2020).

Increased volcanism was reported during September with the daily average of explosions ranging from 33 during 14-20 September to 40 during 28 September-4 October. The resulting gas-and-ash plumes rose 1.8-3.5 km above the crater drifting 25-35 km in various directions (figure 89). SO2 flux was measured by OVI ranging from 2,600 to 9,700 tons/day, the latter of which was recorded during 31 August to 6 September. During 7-13 September an average of 35 explosions were reported, accompanied by gas-and-ash plumes that rose 2.6-3.5 km above the crater and drifting 30 km SE, SW, W, E, and S. These events resulted in ashfall in Lari, Achoma, and Maca. The following week (14-20 September) ashfall was reported in Achoma and Chivay. During 21-27 September the daily average of explosions was 38, producing ash plumes that resulted in ashfall in Taya, Huambo, Huanca, and Lluta. Slight inflation on the N and SE flanks continued to be monitored by OVI. Strong activity, including SO2 emissions and thermal anomalies over the summit crater persisted into at least early October.

Figure (see Caption) Figure 89. Multiple daily explosions at Sabancaya produced ash plumes that rose 1.8-2.6 km above the crater during September 2020. Images are showing 4 (left) and 27 (right) September 2020. Courtesy of OVI (Reporte Semanal de Monitorio de la Actividad de la Volcan Sabancaya, RSSAB-36-2020/INGEMMET Semanal del 31 de agosto al 06 de septiembre del 2020 and RSSAB-39-2020/INGEMMET Semanal del 21 al 27 de septiembre del 2020).

Geologic Background. Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning "tongue of fire" in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions date back to 1750.

Information Contacts: Observatorio Volcanologico del INGEMMET (Instituto Geológical Minero y Metalúrgico), Barrio Magisterial Nro. 2 B-16 Umacollo - Yanahuara Arequipa, Peru (URL: http://ovi.ingemmet.gob.pe); Instituto Geofisico del Peru (IGP), Calle Badajoz N° 169 Urb. Mayorazgo IV Etapa, Ate, Lima 15012, Perú (URL: https://www.gob.pe/igp); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Rincon de la Vieja (Costa Rica) — October 2020 Citation iconCite this Report

Rincon de la Vieja

Costa Rica

10.83°N, 85.324°W; summit elev. 1916 m

All times are local (unless otherwise noted)


Frequent small phreatic explosions with intermittent ash plumes during April-September 2020

Rincón de la Vieja is a remote volcanic complex in Costa Rica that contains an acid lake. Frequent weak phreatic explosions have occurred since 2011 (BGVN 44:08). The most recent eruption period began in January 2020, which consisted of small phreatic explosions, gas-and-steam plumes, pyroclastic flows, and lahars (BGVN 45:04). This reporting period covers April through September 2020, with activity characterized by continued small phreatic explosions, three lahars, frequent gas-and-steam plumes, and ash plumes. The primary source of information for this report is the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA) using weekly bulletins and the Washington Volcanic Ash Advisory Center (VAAC).

Small, frequent, phreatic explosions were common at Rincón de la Vieja during this reporting period. One to several eruptions were reported on at least 16 days in April, 15 days in May, 8 days in June, 10 days in July, 18 days in August, and 13 days in September (table 5). Intermittent ash plumes accompanied these eruptions, rising 100-3,000 m above the crater and drifting W, NW, and SW during May and N during June. Occasional gas-and-steam plumes were also observed rising 50-2,000 m above the crater rim.

Table 5. Monthly summary of activity at Rincón de la Vieja during April through September 2020. Courtesy of OVSICORI-UNA.

Month Minimum total days of eruptions Ash plume height (m above the crater) Notable plume drift Gas-and-steam plume height (m above the crater)
Apr 2020 16 200-1,000 - 50-1,500
May 2020 15 200-3,000 W, NW, SW 200-2,000
Jun 2020 8 100-2,000 N -
Jul 2020 10 1,000 - -
Aug 2020 18 500-1,000 - 500
Sep 2020 13 700 - 50

During April small explosions were detected almost daily, some of which generated ash plumes that rose 200-1,000 m above the crater and gas-and-steam emissions that rose 50-1,500 m above the crater. On 4 April an eruption at 0824 produced an ash plume that rose 1 km above the crater rim. A small hydrothermal explosion at 0033 on 11 April, recorded by the webcam in Sensoria (4 km N), ejected water and sediment onto the upper flanks. On 15 April a phreatic eruption at 0306 resulted in lahars in the Pénjamo, Azufrada, and Azul rivers, according to local residents. Several small explosions were detected during the morning of 19 April; the largest phreatic eruption ejected water and sediment 300 m above the crater rim and onto the flanks at 1014, generated a lahar, and sent a gas-and-steam plume 1.5 km above the crater (figure 30). On 24 April five events were recorded by the seismic network during the morning, most of which produced gas-and-steam plumes that rose 300-500 m above the crater. The largest event on this day occurred at 1020, ejecting water and solid material 300 m above the crater accompanied by a gas-and-steam plume rising up to 1 km.

Figure (see Caption) Figure 30. Webcam image of small hydrothermal eruptions at Rincón de la Vieja on 19 April 2020. Image taken by the webcam in Dos Ríos de Upala; courtesy of OVSICORI-UNA.

Similar frequent phreatic activity continued in May, with ash plumes rising 200-1,500 m above the crater, drifting W, NW, and SW, and gas-and-steam plumes rising up to 2 km. On 5 May an eruption at 1317 produced a gas-and-steam plume 200 m above the crater and a Washington VAAC advisory reported that an ash plume rose to 2.1 km altitude, drifting W. An event at 1925 on 9 May generated a gas-and-steam plume that rose almost 2 km. An explosion at 1128 on 15 May resulted in a gas-and-steam plume that rose 1 km above the crater rim, accompanied by a gray, sediment-laden plume that rose 400 m. On 21 May a small ash eruption at 0537 sent a plume 1 km above the crater (figure 31). According to a Washington VAAC advisory, an ash plume rose 3 km altitude, drifting NW on 22 May. During the early evening on 25 May an hour-long sequence of more than 70 eruptions and emissions, according to OVSICORI-UNA, produced low gas-and-steam plumes and tephra; at 1738, some ejecta was observed above the crater rim. The next day, on 26 May, up to 52 eruptive events were observed. An eruption at 2005 was not visible due to weather conditions; however, it resulted in a minor amount of ashfall up to 17 km W and NW, which included Los Angeles of Quebrada Grande and Liberia. A phreatic explosion at 1521 produced a gray plume that rose 1.5 km above the crater (figure 31). An eruption at 1524 on 28 May sent an ash plume 3 km above the crater that drifted W, followed by at least three smaller eruptions at 1823, 1841, and 1843. OVSICORI-UNA reported that volcanism began to decrease in frequency on 28-29 May. Sulfur dioxide emissions ranged between 100 and 400 tons per day during 28 May to 15 June.

Figure (see Caption) Figure 31. Webcam images of gray gas-and-steam and ash emissions at Rincón de la Vieja on 21 (left), and 27 (right) May 2020. Both images taken by the webcam in Dos Ríos de Upala and Sensoria; courtesy of OVSICORI-UNA.

There were eight days with eruptions in June, though some days had multiple small events; phreatic eruptions reported on 1-2, 13, 16-17, 19-20, and 23 June generated plumes 1-2 km above the crater (figure 32). During 2-8 June SO2 emissions were 150-350 tons per day; more than 120 eruptions were recorded during the preceding weekend. Ashfall was observed N of the crater on 4 June. During 9-15 June the SO2 emissions increased slightly to 100-400 tons per day. During 16-17 June several small eruptive events were detected, the largest of which occurred at 1635 on 17 June, producing an ash plume that rose 1 km above the crater.

Figure (see Caption) Figure 32. Webcam images of gray gas-and-steam and ash plumes rising from Rincón de la Vieja on 1 (top left), 2 (top right), 7 (bottom left), and 13 (bottom right) June 2020. The ash plume on 1 June rose between 1.5 and 2 km above the crater. The ash plume on 13 June rose 1 km above the crater. Courtesy of OVSICORI-UNA.

Explosive hydrothermal activity was lower in June-September compared to January-May 2020, according to OVSICORI-UNA. Sporadic small phreatic explosions and earthquakes were registered during 22-25 and 29 July-3 August, though no lahars were reported. On 25 July an eruptive event at 0153 produced an ash plume that rose 1 km above the crater. Similar activity continued into August. On 5 and 6 August phreatic explosions were recorded at 0546 and 0035, respectively, the latter of which generated a plume that rose 500 m above the crater. These events continued to occur on 10, 16, 19-20, 22-25, 27-28, and 30-31 August, generating plumes that rose 500 m to 1 km above the crater.

On 3 September geologists observed that the acid lake in the main crater had a low water level and exhibited strong gas emissions; vigorous fumaroles were observed on the inner W wall of the crater, measuring 120°C. Gas-and-steam emissions continued to be detected during September, occasionally accompanied by phreatic eruptions. On 7 September an eruption at 0750 produced an ash plume that rose 50 m above the crater while the accompanying gas-and-steam plume rose 500 m. Several low-energy phreatic explosions occurred during 8-17, 20, and 22-28 September, characterized primarily by gas-and-steam emissions. An eruption on 16 September ejected material from the crater and generated a small lahar. Sulfur dioxide emissions were 100 tons per day during 16-21 September. On 17 September an eruption at 0632 produced an ash plume that rose 700 m above the crater (figure 33). A relatively large eruptive event at 1053 on 22 September ejected material out of the crater and into N-flank drainages.

Figure (see Caption) Figure 33. Webcam image of an eruption plume rising above Rincón de la Vieja on 17 September 2020. Courtesy of OVSICORI-UNA.

Geologic Background. Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A Plinian eruption producing the 0.25 km3 Río Blanca tephra about 3,500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/, https://www.facebook.com/OVSICORI/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html).


Fuego (Guatemala) — December 2020 Citation iconCite this Report

Fuego

Guatemala

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

All times are local (unless otherwise noted)


Daily explosions, ash emissions, and block avalanches during August-November 2020

Guatemala's Volcán de Fuego has been erupting vigorously since 2002 with reported eruptions dating back to 1531. These eruptions have resulted in major ashfalls, pyroclastic flows, lava flows, and damaging lahars, including a series of explosions and pyroclastic flows in early June 2018 that caused several hundred fatalities. Eruptive activity consisting of explosions with ash emissions, block avalanches, and lava flows began again after a short break and has continued; activity during August-November 2020 is covered in this report. Daily reports are provided by the Instituto Nacional de Sismologia, Vulcanología, Meteorología e Hidrologia (INSIVUMEH); aviation alerts of ash plumes are issued by the Washington Volcanic Ash Advisory Center (VAAC). Satellite data provide valuable information about heat flow and emissions.

Summary of activity during August-November 2020. Eruptive activity continued at Fuego during August-November 2020, very similar to that during the first part of the year (table 22). Ash emissions were reported daily by INSIVUMEH with explosions often in the 6-12 per hour range. Most of the ash plumes rose to 4.5-4.7 km altitude and generally drifted SW, W, or NW, although rarely the wind direction changed and sent ash to the S and SE. Multiple daily advisories were issued throughout the period by the Washington VAAC warning aviators about ash plumes, which were often visible on the observatory webcam (figure 136). Some of the communities located SW of the volcano received ashfall virtually every day during the period. Block avalanches descended the major drainages daily as well. Sounds were heard and vibrations felt from the explosions most days, usually 7-12 km away. The stronger explosions could be felt and heard 20 km or more from the volcano. During late August and early September a lava flow was active on the SW flank, reaching 700 m in length during the second week of September.

Table 22. Eruptive activity was consistently high at Fuego throughout August – November 2020 with multiple explosions every hour, ash plumes, block avalanches, and near-daily ashfall in the communities in certain directions within 10-20 km of the volcano. Courtesy of INSIVUMEH daily reports.

Month Explosions per hour Ash Plume Heights (km) Ash plume distance (km) and direction Drainages affected by block avalanches Communities reporting ashfall
Aug 2020 2-15 4.3-4.8 SW, W, NW, S, N, 8-20 km Seca, Taniluya, Ceniza, Trinidad, Las Lajas, Honda, Santa Teresa Panimaché I and II, Morelia, Rochela, Finca Palo Verde, Yepocapa, Santa Sofia, El Porvenir, Palo Verde, Sangre de Cristo, Santa Lucía Cotzumalguapa
Sep 2020 3-16 4.3-4.9 W, SW, NW, N, S, 8-20 km Seca, Taniluya, Ceniza, Trinidad, Las Lajas, Honda, Santa Teresa Panimaché I and II, Morelia, Santa Sofía, Finca Palo Verde, Sangre de Cristo, Yepocapa, Porvenir, Yucales, Ojo de Agua, Finca La Conchita
Oct 2020 3-19 4.1-4.8 SW, W, S, SE, N, E, 10-20 km Seca, Taniluya, Ceniza, Trinidad, Las Lajas, Honda, Santa Teresa Panimache I and II, Morelia, Sangre de Cristo, Yepocapa, La Rochela, El Porvenir, Ceilán, Santa Sofía, Yucales, Finca Palo Verde
Nov 2020 4-14 4.0-4.8 S, SW, SE, W, NW, 10-35 km Seca, Taniluya, Ceniza, Trinidad, Las Lajas, Honda, Santa Teresa El Jute Panimaché I and II, Sangre de Cristo, Morelia, Ceilan, La Rochela, El Zapote, Santa Sofía, Yucales, San Juan Alotenango, Ciudad Vieja, San Miguel Dueñas y Antigua Guatemala, Palo Verde, El Porvenir, San Pedro Yepocapa, Quisaché, Santa Emilia
Figure (see Caption) Figure 136. Consistent daily ash emissions produced similar looking ash plumes at Fuego during August-November 2020. Plumes usually rose to 4.5-4.8 km altitude and drifted SW. Courtesy of INSIVUMEH.

The frequent explosions, block avalanches, and lava flows produced a strong thermal signal throughout the period that was recorded in both the MIROVA project Log Radiative Power graph (figure 137) and in numerous Sentinel-2 satellite images (figure 138). MODVOLC data produced thermal alerts 4-6 days each month. At least one lahar was recorded each month; they were most frequent in September and October.

Figure (see Caption) Figure 137. The MIROVA graph of activity at Fuego for the period from 15 January through November 2020 suggested persistent moderate to high-level heat flow for much of the time. Courtesy of MIROVA.
Figure (see Caption) Figure 138. Atmospheric penetration rendering of Sentinel-2 satellite images (bands 12, 11, 8A) of Fuego during August-November 2020 showed continued thermal activity from block avalanches, explosions, and lava flows at the summit and down several different ravines. Courtesy of Sentinel Hub Playground.

Activity during August-November 2020. The number of explosions per hour at Fuego during August 2020 was most often 7-10, with a few days that were higher at 10-15. The ash plumes usually rose to 4.5-4.8 km altitude and drifted SW or W up to 15 km. Incandescence was visible 100-300 m above the summit crater on most nights. All of the major drainages including the Seca, Santa Teresa, Ceniza, Trinidad, Taniluyá, Las Lajas, and Honda were affected by block avalanches virtually every day. In addition, the communities of Panimaché I and II, Morelia, Santa Sofía, Finca Palo Verde, El Porvenir, San Pedro Yepocapa, and Sangre de Cristo reported ashfall almost every day. Sounds and vibrations were reported multiple days every week, often up to 12 km from the volcano, but occasionally as far as 20 km away. Lahars carrying blocks of rocks and debris 1-2 m in diameter descended the SE flank in the Las Lajas and Honda ravines on 6 August. On 27 August a lava flow 150 m long appeared in the Ceniza ravine. It increased in length over the subsequent few days, reaching 550 m long on 30 August, with frequent block avalanches falling off the front of the flow.

The lava flow in the Ceniza ravine was reported at 100 m long on 5 September. It grew to 200 m on 7 September and reached 700 m long on 12 September. It remained 200-350 m long through 19 September, although instruments monitored by INSIVUMEH indicated that effusive activity was decreasing after 16 September (figure 139). A second flow was 200 m long in the Seca ravine on 19 September. By 22 September, active flows were no longer observed. The explosion rate varied from a low of 3-5 on 1 September to a high of 12-16 on 4, 13, 18, and 22-23 September. Ash plumes rose to 4.5-4.9 km altitude nearly every day and drifted W, NW, and SW occasionally as far as 20 km before dissipating. In addition to the active flow in the Ceniza ravine, block avalanches persisted in the other ravines throughout the month. Ashfall continued in the same communities as in August, but was also reported in Yucales on 4 September along with Ojo de Agua and Finca La Conchita on 17 September. The Las Lajas, Honda, and El Jute ravines were the sites of lahars carrying blocks up to 1.5 m in diameter on 8 and 18 September. On 19 and 24 September lahars again descended Las Lajas and El Jute ravines; the Ceniza ravine had a lahar on 19 September.

Figure (see Caption) Figure 139. Avalanche blocks descended the Ceniza ravine (left) and the Las Lajas ravine (right) at Fuego on 17 September 2020. The webcam that captured this image is located at Finca La Reunión on the SE flank. Courtesy of INSIVUMEH (BOLETÍN VULCANOLÓGICO ESPECIAL BEVFGO # 76-2020, 18 de septiembre de 2020, 14:30 horas).

The same activity continued during October 2020 with regard to explosion rates, plume altitudes, distances, and directions of drift. All of the major ravines were affected by block avalanches and the same communities located W and SW of the summit reported ashfall. In addition, ashfall was reported in La Rochela on 2, 3, 7-9 and 30 October, in Ceilán on 3 and 7-9 October, and in Yucales on 5, 14, 18 and 19 October. Multiple strong explosions with abundant ash were reported in a special bulletin on 14 October; high levels of explosive activity were recorded during 16-23 October. Vibrations and sounds were often felt up to 15 km away and heard as far as 25 km from the volcano during that period. Particularly strong block avalanches were present in the Seca and Ceniza ravines on 20, 25, and 30 October. Abundant rain on 9 October resulted in lahars descending all of the major ravines. The lahar in the Las Lajas ravine overflowed and forced the closure of route RN-14 road affecting the community of San Miguel on the SE flank (figure 140). Heavy rains on 15 October produced lahars in the Ceniza, Las Lajas, and Hondas ravines with blocks up to 2 m in diameter. Multiple lahars on 27 October affected Las Lajas, El Jute, and Honda ravines.

Figure (see Caption) Figure 140. Heavy rains on 9 October 2020 at Fuego caused lahars in all the major ravines. Debris from Las Lajas ravine overflowed highway RN-14 near the community of San Miguel on the SE flank, the area devastated by the pyroclastic flow of June 2018. Courtesy of INSIVUMEH (BEFGO #96 VOLCAN DE FUEGO- ZONA CERO RN-14, SAN MIGUEL LOS LOTES y BARRANCA LAS LAJAS, 09 de octubre de 2020).

On 8 November 2020 a lahar descended the Seca ravine, carrying rocks and debris up to 1 meter in diameter. During the second week of November 2020, the wind direction changed towards the SE and E and brought ashfall to San Juan Alotenango, Ciudad Vieja, San Miguel Dueñas, and Antigua Guatemala on 8 November. Especially strong block avalanches were noted in the Seca and Ceniza ravines on 14, 19, 24, and 29 November. During a period of stronger activity in the fourth week of November, vibrations were felt and explosions heard more than 20 km away on 22 November and more than 25 km away on 27 November. In addition to the other communities affected by ashfall during August-November, Quisaché and Santa Emilia reported ashfall on 30 November.

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

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/ ); 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);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/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html).


Kikai (Japan) — November 2020 Citation iconCite this Report

Kikai

Japan

30.793°N, 130.305°E; summit elev. 704 m

All times are local (unless otherwise noted)


Explosion on 6 October 2020 and thermal anomalies in the crater

Kikai is a mostly submarine caldera, 19-km-wide, just S of the Ryukyu Islands of Japan. At the NW rim of the caldera lies the island of Satsuma Iwo Jima (also known as Satsuma-Iojima and Tokara Iojima), and the island’s highest peak, Iodake, a steep stratovolcano. Recent weak ash explosions at Iodake occurred on 2 November 2019 and 29 April 2020 (BGVN 45:02, 45:05). The volcano is monitored by the Japan Meteorological Agency (JMA) and satellite sensors. This report covers the period May-October 2020. During this time, the Alert Level remained at 2 (on a 5-level scale).

Activity at Kikai has been relatively low since the previous eruption on 29 April 2020. During May through October occasional white gas-and-steam emissions rose 0.8-1.3 km above the Iodake crater, the latter of which was recorded in September. Emissions were intermittently accompanied by weak nighttime incandescence, according to JMA (figure 17).

Figure (see Caption) Figure 17. White gas-and-steam emissions rose 1 km above the crater at Satsuma Iwo Jima (Kikai) on 25 May (top) 2020. At night, occasional incandescence could be seen in the Iodake crater, as seen on 29 May (bottom) 2020. Both images taken by the Iwanoue webcam. Courtesy of JMA (An explanation of volcanic activity at Satsuma Iwo Jima, May 2nd year of Reiwa [2020]).

A small eruption at 0757 on 6 October occurred in the NW part of the Iodake crater, which produced a grayish white plume rising 200 m above the crater (figure 18). Faint thermal anomalies were detected in Sentinel-2 thermal satellite imagery in the days just before this eruption (28 September and 3 October) and then after (13 and 23 October), accompanied by gas-and-steam emissions (figures 19 and 20). Nighttime crater incandescence continued to be observed. JMA reported that sulfur dioxide emissions measured 700 tons per day during October, compared to the previous eruption (400-2,000 tons per day in April 2020).

Figure (see Caption) Figure 18. Webcam images of the eruption at Satsuma Iwo Jima (Kikai) on 6 October 2020 that produced an ash plume rising 200 m above the crater (top). Nighttime summit crater incandescence was also observed (bottom). Images were taken by the Iwanoue webcam. Courtesy of JMA (An explanation of volcanic activity at Satsuma Iwo Jima, October 2nd year of Reiwa [2020]).
Figure (see Caption) Figure 19. Weak thermal hotspots (bright yellow-orange) were observed at Satsuma Iwo Jima (Kikai) during late September through October 2020. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 20. Webcam image of a white gas-and-steam plume rising 1.1 km above the crater at Satsuma Iwo Jima (Kikai) on 27 October 2020. Image was taken by the Iwanoue webcam. Courtesy of JMA (An explanation of volcanic activity at Satsuma Iwo Jima, October 2nd year of Reiwa [2020]).

Geologic Background. Kikai is a mostly submerged, 19-km-wide caldera near the northern end of the Ryukyu Islands south of Kyushu. It was the source of one of the world's largest Holocene eruptions about 6,300 years ago when rhyolitic pyroclastic flows traveled across the sea for a total distance of 100 km to southern Kyushu, and ashfall reached the northern Japanese island of Hokkaido. The eruption devastated southern and central Kyushu, which remained uninhabited for several centuries. Post-caldera eruptions formed Iodake lava dome and Inamuradake scoria cone, as well as submarine lava domes. Historical eruptions have occurred at or near Satsuma-Iojima (also known as Tokara-Iojima), a small 3 x 6 km island forming part of the NW caldera rim. Showa-Iojima lava dome (also known as Iojima-Shinto), a small island 2 km E of Tokara-Iojima, was formed during submarine eruptions in 1934 and 1935. Mild-to-moderate explosive eruptions have occurred during the past few decades from Iodake, a rhyolitic lava dome at the eastern end of Tokara-Iojima.

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); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Manam (Papua New Guinea) — October 2020 Citation iconCite this Report

Manam

Papua New Guinea

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

All times are local (unless otherwise noted)


Intermittent ash plumes, thermal anomalies, and SO2 emissions in April-September 2020

Manam, located 13 km off the N coast of Papua New Guinea, is a basaltic-andesitic stratovolcano with historical eruptions dating back 400 years. Volcanism has been characterized by low-level ash plumes, occasional Strombolian activity, lava flows, pyroclastic avalanches, and large ash plumes from Main and South, the two active summit craters. The current eruption period has been ongoing since 2014, typically with minor explosive activity, thermal activity, and SO2 emissions (BGVN 45:05). This reporting period updates information from April through September 2020, consisting of intermittent ash plumes from late July to mid-September, persistent thermal anomalies, and SO2 emissions. Information comes from Papua New Guinea's Rabaul Volcano Observatory (RVO), part of the Department of Mineral Policy and Geohazards Management (DMPGM), the Darwin Volcanic Ash Advisory Center (VAAC), and various satellite data.

Explosive activity was relatively low during April through late July; SO2 emissions and low power, but persistent, thermal anomalies were detected by satellite instruments each month. The TROPOMI instrument on the Sentinel-5P satellite recorded SO2 emissions, many of which exceeded two Dobson Units, that drifted generally W (figure 76). Distinct SO2 emissions were detected for 10 days in April, 4 days in May, 10 days in June, 4 days in July, 11 days in August, and 8 days in September.

Thermal anomalies recorded by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system were sparse from early January through June 2020, totaling 11 low-power anomalies within 5 km of the summit (figure 77). From late July through September a pulse in thermal activity produced slightly stronger and more frequent anomalies. Some of this activity could be observed in Sentinel-2 thermal satellite imagery (figure 78). Occasionally, these thermal anomalies were accompanied by gas-and-steam emissions or ash plumes, as shown on 28 July. On 17 August a particularly strong hotspot was detected in the S summit crater. According to the MODVOLC thermal alert data, a total of 10 thermal alerts were detected in the summit crater over four days: 29 July (5), 16 August (1), and 3 (1) and 8 (3) September.

Figure (see Caption) Figure 76. Distinct sulfur dioxide plumes rising from Manam and drifting generally W were detected using data from the TROPOMI instrument on the Sentinel-5P satellite on 28 April (top left), 24 May (top right), 16 July (bottom left), and 12 September (bottom right) 2020. Courtesy of the NASA Global Sulfur Dioxide Monitoring Page.
Figure (see Caption) Figure 77. Intermittent thermal activity at Manam increased in power and frequency beginning around late July and continuing through September 2020, as shown on the MIROVA Log Radiative Power graph. Courtesy of MIROVA.
Figure (see Caption) Figure 78. Sentinel-2 thermal satellite images showing a persistent thermal anomaly (yellow-orange) at Manam’s summit craters (Main and South) each month during April through August; sometimes they were seen in both summit craters, as shown on 8 June (top right), 28 July (bottom left), and 17 August (bottom right). A particularly strong anomaly was visible on 17 August (bottom right). Occasional gas-and-steam emissions accompanied the thermal activity. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Activity during mid-July slightly increased compared to the previous months. On 16 July seismicity increased, fluctuating between low and moderate RSAM values through the rest of the month. In Sentinel-2 satellite imagery a gray ash plume was visible rising from the S summit crater on 28 July (figure 78). RSAM values gradually increased from a low average of 200 to an average of 1200 on 30 July, accompanied by thermal hotspots around the summit crater; a ground observer reported incandescent material was ejected from the summit. On 31 July into 1 August ash plumes rose to 4.3 km altitude, accompanied by an incandescent lava flow visible at the summit, according to a Darwin VAAC advisory.

Intermittent ash plumes continued to be reported by the Darwin VAAC on 1, 6-7, 16, 20, and 31 August. They rose from 2.1 to 4.6 km altitude, the latter of which occurred on 31 August and drifted W. Typically, these ash plumes extended SW, W, NW, and WSW. On 11 September another ash plume was observed rising 2.4 km altitude and drifting W.

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

Information Contacts: 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; 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/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Karymsky (Russia) — October 2020 Citation iconCite this Report

Karymsky

Russia

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

All times are local (unless otherwise noted)


New eruption during April-July 2020; ash explosions in October 2020

Karymsky is an active volcano, part of Kamchatka’s eastern volcanic zone. Eruptive activity has been frequent since 1996 and has included ash explosions, gas-and-steam and ash emissions, and thermal anomalies. The most recent eruptive period ended in September 2019 (BGVN 44:11) with a new one beginning in April 2020. Both eruptions consisted of moderate explosive activity and ash plumes. This report updates information from November 2019 through October 2020, which describes a short-lived eruption from April to July and renewed activity in October. Information comes from daily, weekly, and special reports from the Kamchatka Volcanic Eruptions Response Team (KVERT), the Tokyo Volcanic Ash Advisory Center (VAAC), and satellite data.

Activity at Karymsky after November 2019 primarily consisted of moderate gas-and-steam emissions and rare weak thermal anomalies in the summit crater (on 2, 8, and 17 December 2019, according to KVERT). No thermal activity was reported during January through March 2020.

Over the weeks of late March to early April 2020, minor amounts of ash were present in gas-and-steam emissions that led to trace ashfall deposits on the snowy flanks and were visible in satellite imagery (figure 47). A weak thermal anomaly was observed in satellite imagery on 6 April. On 13 April the Tokyo VAAC reported an ash plume to 2.1 km altitude drifting SE. Gas-and-steam emissions containing some ash rose 2 km altitude on 17 April and drifted up to 80 km SE on both 17 and 21 April, accompanied by a weak thermal anomaly seen in satellite data. On 18 April the Tokyo VAAC released an advisory noting an ash plume at 1.5-2.1 km altitude drifting S.

Figure (see Caption) Figure 47. Sentinel-2 natural color satellite images showing ash deposits (dark gray) on the snowy flanks at Karymsky from just before the eruptive period began on 20 March 2020 (top left) through April 2020. Images with “Natural Color” (bands 4, 3, 2) rendering; courtesy of Sentinel Hub Playground.

KVERT reported intermittent thermal anomalies during May, along with moderate gas-and-steam emissions. On 10 May gas-and-steam plumes containing some ash drifted 77 km SE while ash plumes observed in HIMAWARI-8 satellite imagery rose to 2.7 km altitude. A dense plume drifting S resulted in large ash deposits covering all but the N flank of the volcano by 14 May, as observed in Sentinel-2 natural color satellite imagery (figure 48). KVERT reported that ash continued to be observed during 24-31 May, rising to a maximum altitude of 7 km on 27 May and extending in multiple directions. On 29 and 31 May explosions generated ash plumes that rose to 6 and 4 km altitude, respectively, and both extended up to 380 km SW, SE, and E. MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows a pulse in thermal activity within 5 km of the summit crater starting in late May, reflecting the renewed activity (figure 49). On 1 June another strong brown-gray ash plume was seen rising from Karymsky, drifting SE in satellite imagery, depositing large amounts of ash on all flanks (figure 48).

Figure (see Caption) Figure 48. Sentinel-2 natural color satellite images showing ash deposits (dark gray) on the all the snowy flanks at Karymsky on 14 May (left) and 1 June (right) 2020. Images with “Natural Color” (bands 4, 3, 2) rendering; courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 49. A pulse of thermal activity at Karymsky during late May through July 2020 was seen in the MIROVA graph (Log Radiative Power). Courtesy of MIROVA.

Intermittent ash emissions and moderate explosive activity continued in June. During 1-4 June continuous ash plumes rose to a high of 4.6 km altitude and drifted up to 400 km generally E, according to KVERT and the Tokyo VAAC advisories. By 19 June, KVERT stated that possible Strombolian activity was occurring, accompanied by moderate gas-and-steam emissions and frequent thermal anomalies; Sentinel-2 thermal satellite imagery also showed a thermal anomaly in the crater (figure 50). Ash plumes and gas-and-steam plumes containing some amount of ash were seen drifting SW and NW on 30 June (figure 51).

Figure (see Caption) Figure 50. Sentinel-2 thermal satellite images show a bright thermal hotspot (yellow-orange) in the summit crater of Karymsky during June 2020, sometimes accompanied by gas-and-steam emissions. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 51. Photos of an ash plume rising from Karymsky on 30 June drifting SW (top) and a fumarolic gas plume containing some amount of ash drifting NW (bottom). Both photos by A. Sokorenko; courtesy of IVS FEB RAS, KVERT.

Similar activity continued into July, which included possible Strombolian activity, moderate gas-and-steam emissions, and frequent thermal anomalies. On 14 July a gas-and-steam plume that contained some ash drifted 26 km SW (figure 52); the Tokyo VAAC advisory reported a continuous ash plume that rose 3 km altitude and drifted SW. During 27-30 July Strombolian and Vulcanian explosions generated ash plumes that rose 3-3.7 km altitude and extended 250 km SW and SE. The frequency of thermal anomalies seen in MIROVA decreased in July; the MODVOLC system detected one thermal hotspot on 28 July.

Figure (see Caption) Figure 52. Fumarolic activity at Karymsky on 14 July 2020. Photo has been color corrected. Photo by Ivan Nuzhdaev; courtesy of IVS FEB RAS, KVERT.

Activity decreased in August; thermal anomalies were reported on 5-7, 10, 18, and 21 August, the latter of which was last observed thermal anomaly, according to KVERT. Moderate gas-and-steam emissions continued to occur through the week of 3 September (figure 53). On 26 September, the Tokyo VAAC issued an advisory for a small ash plume that rose to 1.8 km altitude and extended SE.

Figure (see Caption) Figure 53. Minor gas-and-steam emissions rose from Karymsky on 2 September 2020. Photo by A. Gerasimov; courtesy of KVERT.

After a brief period of little to no activity, Tokyo VAAC advisories on 10 and 11 October both reported small ash plumes that rose 1.8 km altitude and drifted SE. An ash plume on 17 October rose to 3.9 km altitude drifting E; on 20 October an ash plume drifted up to 50 km SE. KVERT reported that a new eruption began on 21 October; pilots observed explosions at 1430 that generated ash plumes up to 4 km altitude and extended 40 km SE (figure 54). Multiple ash plumes during that day rose up to 6.4 km altitude and drifted as far as 530 km SE, accompanied by a thermal anomaly. Frequent ash explosions continued through the end of the month, with the highest plume rising to an altitude of 6 km on 30 October. In late October two thermal anomalies were detected in MIROVA.

Figure (see Caption) Figure 54. Frame from a video of the eruption at Karymsky on 21 October 2020. The ash plume is rising 6 km altitude. Video by Bel-Kam-Tour, courtesy of Russia Today.

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

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Bel-Kam-Tour, st. Elizova, 39 Paratunka Kamchatka Krai, 684000, Russia (URL: https://bel-kam-tour.business.site/); Russia Today (RT), Borovaya St., 3 bldg. 1, Moscow 111020 (URL: https://www.rt.com/).

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Bulletin of the Global Volcanism Network - Volume 30, Number 10 (October 2005)

Managing Editor: Richard Wunderman

Arenal (Costa Rica)

Frequent pyroclastic flows from crater C since August 2004

Endeavour Segment (Canada)

Intense earthquake swarm in February-March 2005

Lengai, Ol Doinyo (Tanzania)

Lava continues to spill over crater rim through much of 2005

Negra, Sierra (Ecuador)

Eruption ends 30 October; some lava on NE flank, more on E caldera floor

Northern EPR at 10.7°N (Undersea Features)

November 2003 visit finds evidence of very recent eruption

Pacaya (Guatemala)

Steam clouds and tremor in 2004; incandescence and lava flows in 2005

Santa Maria (Guatemala)

Partial dome collapses in 2004; explosions and ash columns in 2005



Arenal (Costa Rica) — October 2005 Citation iconCite this Report

Arenal

Costa Rica

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

All times are local (unless otherwise noted)


Frequent pyroclastic flows from crater C since August 2004

As described in the previous Arenal report (BGVN 29:08), on 6 July 2004 a series of pyroclastic flows descended the NE flank. These flows resulted from the collapse of the upper portions of a lava flow, and affected areas beyond those affected by pyroclastic flows during 1999-2003. Similar events have been common in recent years on the volcano's N and NE sides, as Crater C continued to emit gases, lava flows, and sporadic strombolian eruptions through 2004 and at least as late as November 2005. Throughout the period of this report (August 2004-September 2005) the lava flow that began to be emitted towards the NE flank in June 2004 remained active. Occasional blocks spalled off the N edge of the crater towards the NE. The NE and SE flanks continued to be affected by pyroclastic flows and acid rain. Crater D displayed fumarole activity from July 2004 through September 2005. The seismograph station VACR (2.9 km NE of the active Crater C) was out of service from 24 June 2004 until 20 August 2004. Table 24 summarizes the seismicity registered at VACR from August 2004 to September 2005.

Table 24. Seismic activity registered at Arenal's station VACR, August 2004 - September 2005. From 24 June to 20 August 2004 VACR was not operating. No data were reported for December 2004. Courtesy of OVSICORI-UNA.

Month Eruption earthquakes Daily average LP Events Tremor (hours) Comments
Aug 2004 414 35 -- 147 VACR not operating 24 Jun-20 Aug.
Sep 2004 1125 37 -- 330 --
Oct 2004 1155 37 32 293 --
Nov 2004 584 34 -- 153 --
Dec 2004 -- -- -- -- --
Jan 2005 540 22 5 357 VACR operated for 25 days.
Feb 2005 941 35 12 448 --
Mar 2005 903 29 15 458 --
Apr 2005 567 19 13 592 --
May 2005 618 20 3 600 --
Jun 2005 697 23 10 606 --
Jul 2005 827 27 23 560 --
Aug 2005 597 20 33 548 --
Sep 2005 548 18 16 576 --

During July 2004-January 2005, pyroclastic flows were produced by the collapse of the active lava flow front. In August 2004 some eruptions generated ash columns higher than 500 m above Crater C.

Through most of February 2005 Arenal was hidden by storm clouds, but late in the month it could be observed that the lava flow formerly active on the NE flank had stopped, and no other active flow was seen. The number of eruptions and the amount of ejected pyroclastic material were both reduced in February, and few eruptions produced plumes as high as 500 m. The dome in Crater C continued to grow.

At the beginning of March a SW-trending lava flow was observed, and blocks were ejected to the W. During April 2005 this flow continued, and ejected blocks caused small fires in the surrounding vegetation. A new lava flow began on the SE flank, and blocks ejected to the S and SE again caused fires. In May and June 2005 the SW flow continued. In July the SW lava flow deposited blocks towards the SW, the W and the NW. The SE lava flow released small avalanches off its front and sides. Occasional eruptions produced ash columns higher than 500 m above Crater C.

In August 2005 the SE lava flow stopped. Few eruptions produced ash columns higher than 500 m above Crater C. During September 2005 the SW lava flow was active and deposited blocks to the SW, the W and the NW. The NE and SE flanks continued to be affected by the fall of pyroclastic material and acid rain.

Observatorio Vulcanológico y Sismológico de Costa Rica -Universidad Nacional (OVSICORI-UNA) reported that around 1500 on 2 November a pyroclastic flow was observed on the SE flank of Arenal. On 3 November researchers from OVSICORI-UNA visited the affected area and, contrary to what witnesses had reported, determined that the 2 November event took place on the W flank of the volcano. The mid-size pyroclastic flow produced gas, dust, and ash that were carried by strong winds towards the SE.

Despite the rainy and hazy conditions during the fieldwork it was possible to confirm the affected area and deposits. The movement of lava flows on the SW flank had been observed for the last several months. Materials descending from the summit bifurcate, covering a wide fan that ranges from the W to the SW flank. The main pyroclastic flow affected an area from the summit down to ~ 1000 m altitude. A smooth alley was carved in the steep walls of upper W flank by the transport of incandescent material. Most of the material was deposited in a distal zone 75 m wide, at the break in the steep upper cone slope.

Samples were taken from hot loose blocks spalled from the lava flow; one block was still at 154°C, and was accompanied by several other massive blocks that were fractured by rapid cooling and rough transport. There is evidence that the fine fall material was only deposited in the upper and middle part of the edifice towards the SE.

Given the sustained deposition of material in the area, visitors were advised to follow instructions and safety measures and adhere to the advice of the Park Rangers and tour guides.

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


Endeavour Segment (Canada) — October 2005 Citation iconCite this Report

Endeavour Segment

Canada

47.95°N, 129.1°W; summit elev. -2050 m

All times are local (unless otherwise noted)


Intense earthquake swarm in February-March 2005

At 1631 on 26 February 2005 (0031 UTC on 27 February), a hydroacoustic network detected the start of what became an intense earthquake swarm (Ridge 2000 TCS (Time Critical Studies) Oversight Committee, 2005). The source of the swarm was on the Endeavour segment of the northern Juan de Fuca Ridge (JdFR) (figure 1).

Figure (see Caption) Figure 1. Location map of the February 2005 earthquake swarm on the Juan de Fuca ridge along the Endeavour Segment. Courtesy Ridge 2000 TCS Oversight Committee, 2005.

More than 3,740 earthquakes were detected over a 5.5-day period (figure 2). Event counts were as high as 50-70 per hour, which is similar in scale to event counts associated with sea-floor-spreading events on the ridge at both the Middle Valley segment in September 2001 and at the Endeavour segment in 1999. The hydroacoustic array is the Sound Surveillance System (SOSUS) of the National Oceanic and Atmospheric Administration (NOAA).

Figure (see Caption) Figure 2. Histogram showing the number of seismic events per hour on the Endeavour segment of the Juan de Fuca ridge. The x-axis extends over Julian days 56-64, 2005 (25 February-5 March 2005). Courtesy National Oceanic and Atmospheric Agency (NOAA) Vents web site, 2005.

The preliminary location of the swarm's epicenters was 48°14.5'N, 128°57.6'W (figure 2), ~ 36 km NNE of the Main Endeavour vent field and a few kilometers E of the intersection of the Heck Seamounts with the JdFR axis. The sequence also produced three large earthquakes (mb 4.5, 4.8, and 4.9) detected by instruments of the National Earthquake Information Center (NEIC), the University of Washington, and the Pacific Northwest Seismograph Network (PNSN). The February-March 2005 seismic swarm also maintained an elevated, nearly constant rate of similar-magnitude earthquakes for several days, behavior consistent with magma intrusion and in contrast to the "mainshock-aftershock" sequence characteristic of tectonic events.

Research response personnel were on station by 6 March, just six days after notification of the seismic swarm, a task that often requires a lead time of over a year. Results from the response cruise indicate that it is unlikely that the February-March 2005 earthquake swarm (figure 3) induced any corresponding expression at the sea floor (i.e., eruption of a lava flow) or in the water column (i.e., formation of new hydrothermal venting, either chronic or event plumes).

Figure (see Caption) Figure 3. Epicenters of the 305 larger earthquakes along the Endeavour Segment. Those indicated by the larger red dots were located using 4 or more hydrophones.The epicenters indicated by the smaller black dots were smaller events located using three hydrophones, and they may not be as well constrained. Epicenters are plotted through 1 March 2005 and comprise 305 events. Courtesy National Oceanic and Atmospheric Agency (NOAA) Vents web site, 2005.

In-situ and shipboard physical and chemical data from the three long tow-yo casts and seven vertical casts revealed no water-column signal that can be clearly associated with the recent earthquake swarm, whether magmatic or tectonic. Initial calculations of methane to hydrogen ratios from the Main Endeavour Field, and from Mothra, High Rise, or Salty Dawg vent fields along the Endeavour segment are comparable to historical (2003) values from vent fluids. No evidence of any temperature or optical anomalies was seen in the near-bottom camera tow data (CTD or MAPR) overlying an axial magma chamber reflector, close to the region of the February/March swarm. Camera images of the sea floor revealed no fresh basalt; rather, the entire camera tow track documented lavas with moderate to heavy sediment cover. Finally, no bathymetric anomalies were detected as the cruise scientists searched for evidence of new lava flows in the earthquake area by comparing before and after high-resolution multibeam bathymetry data. The earthquake swarm was thus thought to reflect a magmatic intrusion that failed to generate measurable changes in the sea floor or an intrusive magmatic event that did not reach sufficiently shallow crustal depths to lead to extrusion (eruptive flows) or stimulate venting at new or existing vent fields as discernable via surface-ship sampling.

References. Ridge 2000 TCS (Time Critical Studies) Oversight Committee, 2005, Recent detected events on the Juan de Fuca Ridge, Status report on time critical studies: Ridge 2000 Events, v. 3 (Spring 2005), p. 14-15.

Davis, E.E., and Currie, R.G., 1993, Geophysical observations of the northern Juan de Fuca Ridge system: Lessons in sea-floor spreading: Canadian Journal of Earth Sciences, v. 30 (2), p. 278-300.

Geologic Background. The Endeavour Segment (or Ridge) lies near the northern end of the Juan de Fuca Ridge, west of the coast of Washington and SW of Vancouver Island. The northern end is offset to the east with respect to the West Valley Segment, which extends north to the triple junction with the Sovanco Fracture Zone and the Nootka Fault. The 90-km-long, NNE-SSW-trending segment lies at a depth of more than 2000 m and is the site of vigorous high-temperature hydrothermal vent systems that were first discovered by scientists in 1981. Five major vent fields that include sulfide chimneys and black smoker vents, first seen from the submersible vehicle Alvin in 1984, are spaced at about 2-km intervals in a 1-km-wide axial valley at the center of the ridge. Preliminary uranium-series dates of Holocene age were obtained on basaltic lava flows, and other younger "zero-age" flows were sampled. Seismic swarms were detected in 1991 and 2005.

Information Contacts: Pacific Marine Environmental Laboratory (PMEL), National Oceanic and Atmospheric Agency (NOAA), 7600 Sand Point Way NE, Building 3, Seattle, WA 98115-6349, and Hatfield Marine Science Center, 2115 SE Oregon State University Drive, Newport, OR 97365 (URL: https://www.pmel.noaa.gov/eoi/); Robert Dziak, NOAA PMEL, Hatfield Marine Science Center, 2115 SE Oregon State University Drive, Newport, OR 97365.


Ol Doinyo Lengai (Tanzania) — October 2005 Citation iconCite this Report

Ol Doinyo Lengai

Tanzania

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

All times are local (unless otherwise noted)


Lava continues to spill over crater rim through much of 2005

Vigorous eruptive activity was observed in July 2004, and visitors in January 2005 noted that a new crater rim overflow area had developed along the N rim (see report and map in BGVN 30:04). The mountain guide for Martin Haigh reported on 15 May that last lava flows had occurred in March.

Activity during 3-5 July 2005. During 3-5 July 2005 Bernard Marty and others visited the crater to conduct gas sampling. His report follows.

At the time of arrival (0800 on 3 July), sporadic lava flows of the aa type were emitted from a vent at the base of T56B, which was itself disrupted by an explosion, leaving an open cavity about 15 m in diameter. The lava was flowing toward the E overflow, but never reached the crater rim. At about 1130, lava was spilling violently from T58B and flowing towards the E overflow.

Sampling had to be interrupted at T46 due to the risk of a sudden lava flood in the sampling area, a real possibility if the thin W wall of T58B fractured following thermal erosion of the wall by molten lava in the lava lake. One hundred meters S of T46, close to the base of T47, a deep hole ~ 1.5 m diameter and bordered by lava splashes emitted a piercing sound. A pahoehoe lava flow was emitting high temperature gases with no visible steam.

A lava pond, not directly observed but for which bubble explosions were clearly visible, was discharging surges of lava towards the E rim while the adjacent T58C cone, now higher than T58B, was discharging high-velocity gases that occasionally splashed lava. The eruption lasted all day and the following night, with variations from steady-state outpouring with lower degassing, to bursts of large bubbles with enhanced lava emission. By the afternoon of 4 July the lava, which was then overflowing the E slope of the volcano, ignited a bush fire. The lava emission rate was estimated at about 0.3 m3/s, with a speed of ~ 2 m/s in the flat area toward the volcano's flank.

At 0500 on 5 July lava flows suddenly invaded the mountain camp's kitchen area to a depth of one meter. Fortunately no one was hurt, but the episode illustrated that there was no safe area within the N crater.

Activity during 19 July-9 August 2005. During 19 July-9 August a team of observers led by Fred Belton camped in the inactive S crater. They submitted the following report of the active N crater as viewed from the SE crater rim.

Activity during the past year was confined to the crater's central portion. Since its initial violent eruption from a hole in the crater floor on 15 July 2004, T58C has grown to a height of ~ 12 m and is at the time of this report the second highest cone in the crater, tall and narrow with large blocks scattered about the crater floor below, indicating that it has undergone some flank collapses in the preceding months. T49B has grown significantly taller since July 2004 and is the tallest feature in the crater, rising at least 15 m above its base.

T56B, which has remained open to the SE since July 2004, has grown a small cone on its SE flank. The new cone, which has not been named because it is so high on the flank of T56B, is being undermined by a large tunnel. The tunnel begins at the SE base of the small unnamed cone and extends under it to the open vent of T56B. Clearly the tunnel was a recent active feature, and the tunnel entrance appears to be the result of collapse during or after an eruption.

T58B contained a large and deep (10-12 m) open pit, which clearly indicated the presence of past lava-lake activity at two levels. The solid crust of a former lava lake about 4 m below the rim contained a hole near its center that opened into a much deeper chamber. At some point during the night of 4 August this deeper pit was filled by lava so that only the upper level remained.

T57B appeared unchanged from July 2004 until its S half was covered by a thick layer of fused spherical lapilli from a short but powerful eruption of T58C on 20-21 July (figure 85).

Figure (see Caption) Figure 85. At 0100 on 21 July a short but powerful eruption from Ol Doinyo Lengai's T58C vent produced these fresh black lava flows and a lapilli field on the flank of T57B. This view is looking NW. Courtesy of Fred Belton.

Spatter cones T40, T46, T47, T51, T45, T37, T37B, and the ash cones have continued to be gradually covered by lava flows from the active cone group in the central crater. In particular, T40, which was the primary active cone during much of 1999, is now well on its way to disappearing under the lava. Lava flows from the central cone area have continued to build up the height of the mound in the central crater so that several cones are easily visible from Engare Sero village. T53 (~ 80 m NW of T40) no longer existed. A deep hole in the crater floor, just N of T47 and surrounded by recent pahoehoe flows from T58B, is possibly all that remains of the summit vent of T39. The hole was degassing at a high temperature but did not show any evidence of recent effusive activity. An area in the E part of the crater, which is sheltered by outcroppings and sometimes used by campers, had been covered by a thick flow of slabby pahoehoe lava from T58B. A large amount of vegetation on the E flank of Lengai had also been burned by lava flowing through the E-crater-rim overflow (figure 86). Several locations on the N crater rim had become crossed by small lava flows.

Figure (see Caption) Figure 86. The light-colored stripe represents the overflow of recent lavas from Ol Doinyo Lengai down the E flank, as photographed on 7 Aug 2005 from the S crater. The blackened area represents burned vegetation from the bush fire reported by Bernard Marty on 4 July 2005. The lavas, termed natrocarbonatites, turn light colored on the surfaces upon cooling and absorbing moisture. Courtesy of Fred Belton.

Table 10 shows a multi-year set of measurements of the width of crater rim overflows. The N rim overflow was first measured on 7 August 2005.

Table 10. Measurements of the widths of lava overflowing the crater rim at Ol Doinyo Lengai. The values represent the arc length of the crater rim covered by lava flows on the various dates. Measurements were made by pacing the distance several times and averaging the results. The dashes mean that the overflow had not yet come into existence on the date indicated. The lengths of the flows beyond the crater rim are not shown on this table. Courtesy of Fred Belton and Chris Weber.

Date NW overflow width E overflow width W overflow width N overflow width
Jul 2000 60 m 38 m -- --
23 Jul 2001 106 m 38 m -- --
05 Aug 2002 135 m 39 m 12 m --
02 Aug 2003 135 m 44 m 17 m --
07 Jul 2004 135 m 44 m 17 m --
16 Jul 2004 135 m 47 m 17 m --
07 Aug 2005 135 m 72 m 20 m ~1 m at each of three locations

Although there was no activity on 19 July, an unobserved eruption may have begun around 2300 on 20 July and probably ended by 0130 on 21 July, according to reports by a camping group in the W portion of the crater floor. The activity reached its peak between 0100 and 0130 and involved strong lava fountains from a vent about halfway up the E side of T58C. The fountains deposited a deep (at least 0.5 m) bed of lapilli around the base and on the S flank and top of cone T57B, and sent pahoehoe and aa flows to the E. One of the flows traveled tens of meters down Lengai's E slopes. The lapilli consisted mostly of hollow spheroids with diameters up to 1.2 cm. Many of the lapilli were fused, and sections of the field broke apart under their own weight, leaving a blocky, fissured surface.

On 21 July at 1511 lava flowed from T58B's active vent during a 12-minute eruption. At 2100 on the same day a third eruption sent strong surges of lava from the same vent and continued throughout the night. Atmospheric clouds prevented detailed observations, but clear conditions at 0500 on 22 July revealed that a large lava channel had formed just E of T58B and had been thermally eroded to a depth of more than one meter. Maximum flow rate during the eruption was estimated to be 0.5 m3/s. The eruption continued until about 1800 and deposited pahoehoe flows over a large part of the SE crater floor.

With the exception of a very minor lava flow from T58C at 1930 on 26 July and the brief (unobserved) appearance of a lava lake in T58B on the night of 4 August, no further activity occurred through 9 August. There were frequent sounds of lava at depth near the base of T58C and inside the open vent of T58B. The lava lake that briefly occupied T58B filled up its deep inner pit and then solidified, leaving a flat surface of new lava about 4 m below the lowest place on the cone's rim. During 4-9 August lava could be heard moving near the surface somewhere inside T58B's vent, but it never became visible. Observations ended at 0800 on 9 August 2005.

Activity during September and October 2005. Kees DeJong reported the following, which was posted on Belton's website: "We climbed Oldonyo Lengai 13 September 2005, arriving at the crater rim [at 0710]. Tourists that had camped in the crater said that eruptions began at midnight (and that there were no eruptions the previous days). Lava kept flowing until about [0846]; we left the crater at [1300] that day."

Photos that Kees made indicated that lava was flowing from about halfway up the side of T48B and across the crater floor toward the W, but that it was not a particularly large eruption. Earlier, probably on 11 September, a small amount of lava flowed down the N flank of T49B and a short distance across the crater floor. Other photos indicated (by comparing specific lava flows on the crater floor with the same lava flows in 7 August photos) a high probability that there were no lava flows at all between 9 August and 11 September. On 19 September Burra Gadiye reported to Roger Mitchell that he had seen no activity that day.

Anatoly Zaytsev climbed on 30 September and reported that they did not see eruptive activity during their visit (between 1100 and 1500). They did see some natrocarbonatite lavas with estimated ages of 2-3 weeks. These were probably the flows from 13 September described above.

Following a visit during 1-3 October, Jaco de Borst reported the following. "During the first of October there was also no activity, only 'smoke' from several cones and cracks. On the second of October there were several 'small' eruptions. In daylight and at night, the cone that was erupting was the biggest and close to the overflow where the trail reaches the crater. Lava only reached the foot of the cone [Belton noted that he was describing T49B]. We left in the morning of 3 October, I think at about 1000. When we left there was no activity... [other] than some noise and 'smoke.' The night eruptions we saw... I think [occurred] about 5 o'clock in the morning [on 3 October]."

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

Information Contacts: Christoph Weber, Volcano Expeditions International, Muehlweg 11, 74199 Untergruppenbach, Germany (URL: http://www.v-e-i.de/); Celia Nyamweru, Department of Anthropology, St. Lawrence University, Canton, NY 13617, USA (URL: http://blogs.stlawu.edu/lengai/); Frederick Belton, Developmental Studies Department, PO Box 16, Middle Tennessee State University, Murfreesboro, TN 37132, USA (URL: http://oldoinyolengai.pbworks.com/); Bernard Donth, Waldwiese 5, 66123 Saarbruecken, Germany.


Sierra Negra (Ecuador) — October 2005 Citation iconCite this Report

Sierra Negra

Ecuador

0.83°S, 91.17°W; summit elev. 1124 m

All times are local (unless otherwise noted)


Eruption ends 30 October; some lava on NE flank, more on E caldera floor

Our last report (BGVN 30:09) described the first five days of this eruption, and was taken largely from a valuable joint report of Ecuador's Instituto Geofísico and Parque Nacional Galápagos. Here we report information from several sources on these topics: (a) initial observations of the eruption, (b) caldera-floor deformation prior to the eruption, (c) observations of the eruption's progress during 26 to 30 October (when it ended), and (d) satellite infrared observations of thermal fluxes associated with the eruption.

Eruption's start and subsequent plumes. As noted previously (BGVN 30:09), the eruption began around 1730 on 22 October 2005, when an explosion was heard by many residents of the volcano's S flank. Satellite images showed no activity at 1715, but revealed a large eruption at 1745 local time (2345 UTC). The eruption cloud reached an estimated altitude of at least 15 km (50,000 ft) and was moving SW.

At about this time, passengers and crew on Lindblad Expeditions' 80 passenger vessel M/N Polaris had an excellent view of the eruptive plume (figure 5). Lucho Verdesoto, the expedition leader, reported that the ship was then at Cerro Dragon, Santa Cruz island. Sunset was at 1753. As night fell they sailed to a position ~ 18 km NE of the volcano, where they had clear views of flows descending the volcano's upper NE flank (figure 6).

Figure (see Caption) Figure 5. Early photo of the Sierra Negra plume from the cruise ship Polaris, anchored off NW Santa Cruz island around sunset on 22 October 2005. Courtesy of Lucho Verdesoto.
Figure (see Caption) Figure 6. Lava spews skyward from circumferential fissure vents near the N rim of Sierra Negra caldera as flows descend the upper N flank. The photos were taken on 22 October, during the first few hours of the eruption, from the Polaris. Courtesy of Lucho Verdesoto.

Naturalist Carman Guzman wrote, "After sunset the show was fascinating so we decided to move the Polaris to a much closer location. After dinner, we were only eleven miles from the eruption itself. What a thrill! The darkness of the night enhanced the beauty of the fiery reds and oranges that were seen at the top of the caldera. We spent several hours enjoying this rare and fantastic event. Rivers of lava were running down the slopes of the volcano and enormous flames were lighting up the sky."

According to NASA MODIS imagery and VAAC/NOAA reports, on 25 October 2005 a large plume of gases and steam was observed in GOES 12 imagery for 1545 local time (2145 UTC). The plume extended ~ 460 km W and SW of the summit at an altitude of ~ 4.6 km. Figure 7 shows the average concentration of SO2 over the Sierra Negra plume as imaged by NASA's Aura satellite for the period 23 October-1 November.

Figure (see Caption) Figure 7. The average concentration of sulfur dioxide (SO2) over Sierra Negra from 23 October-1 November measured by the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite. In agreement with reports from the ground, OMI stopped seeing measurable sulfur dioxide coming from the volcano on 31 October. The column abundances of SO2 appear on the associated key (in Dobson Units, DU, a product of concentration and pathlength that reflects the number of SO2 molecules in a unit area of the atmospheric column). Courtesy of NASA Earth Observatory/Natural Hazards website.

Deformation monitoring. In the early stages of this eruption, Bill Chadwick (NOAA) submitted a report on pre-eruption deformation (figure 8). The plot shows both Synthetic Aperture Radar (InSAR) and GPS data on vertical deformation of the caldera floor. Chadwick wrote that he, Dennis Geist (University of Idaho), and Dan Johnson (University of Puget Sound, recently deceased) installed a 27 station GPS network at Sierra Negra in 2000, that was reoccupied in 2001 and 2002 (Geist and others, in press). With help from UNAVCO (a consortium supporting high-precision deformation measurements), the group then added a 6-station, continuous GPS network in 2002. Since then, there occurred a change from caldera subsidence to caldera uplift in March 2003. During this uplift, an M 4.6 earthquake on 16 April 2005 marked trapdoor faulting. The continuous GPS network measured a surface displacement of 85 cm within 10 seconds. Both this event and the previous case of trapdoor faulting in 1997-8-documented by satellite measurements using Interferometric Synthetic Aperture Radar (InSAR) (Amelung and others, 2000)-were preceded by over a meter of inflation (Jónsson and others, 2005). Both the 1997-98 and 2005 trapdoor movements occurred along the caldera floor's S side.

Figure (see Caption) Figure 8. Recent history of uplift at the center of Sierra Negra's caldera. The data plotted are only through April 2005 when the trapdoor faulting event occurred. Although not plotted, GPS data since April has continued to indicate robust deformation. Courtesy Bill Chadwick, NOAA.

Aside from its immediate affects, the April 2005 earthquake left the later inflation rate unchanged. Caldera-centered uplift has continued since then without pause at about the same high rate. During the interval from March 2002 to April 2005 there was about ~ 1.2 m of uplift. Rates after the April 2005 earthquake are not plotted but were roughly the same as those during the interval March 2002-April 2005. The only other large earthquakes at Sierra Negra in the last year were an M 4.0 on 23 February 2005, which was associated with a small (2 cm) displacement near the trapdoor fault, an M 4.6 on 19 September 2005 that caused no obvious displacements, and an M 5.5, just 3 hours before the 22 October eruption started. The GPS data has not yet been processed.

Field descriptions of the eruption. The eruption began on 22 October with venting along a 2-km fissure near the caldera's N rim (figure 6). The fissure descended the caldera's inner wall at its E end. Flows were fed both northward down the outer N flank and southward onto the NE caldera floor. Although flows reached 5 km down the outer flank, flow into the caldera soon dominated, with strong channels descending inner caldera slopes before combining to form a wide aa flow banked against the caldera's E wall and moving steadily southward (see figures and discussion, BGVN 30:09).

Figure 9 is a photo taken by Greg Estes on 24 October. It highlights the vigorous venting and intracaldera flows at that point in the eruption. Figure 10, a post-eruption satellite photo, illustrates the broad pattern of still-cooling, erupted lavas (which appear as light colored areas on this 2 November thermal-infrared image). Although this may represent the best overview of the new lavas at this time, some of the thinnest flows or chilled flow features may not appear on this image.

Figure (see Caption) Figure 9. The Sierra Negra eruption setting as viewed from the E caldera rim. The fissure vent was vigorously emitting fountains, and there were several anastomosing lava flows pouring into the caldera. Photo was taken at night on 24 October 2005, day 3 of the eruption. The scattered glow in the foreground was due to ponded lava covering the caldera's E floor. Courtesy of Greg Estes (Galápagos resident and Park Guide).
Figure (see Caption) Figure 10. The Sierra Negra eruption setting as viewed from space in a false color ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) infrared image taken at night on 2 November, ~ 3 days after the eruption ended. N is towards the top. Caldera is 7 x 10.5 km across. Note the extra-caldera, N-flank lava flows, the lunate zone of ponded lavas along the E caldera. NASA image created by Jesse Allen, Earth Observatory, using data provided courtesy of Eric Fielding (NASA/JPL), the NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team.

By 26 October, fissure activity had narrowed to one major vent very near the N rim, but at 0830 on the 27th, eyewitness Godfrey Merlin reported that a second vent opened downslope and SE of the first. This new vent did not diminish the activity of the first, meaning that the total flux of erupting lava nearly doubled.

By about 1400 on the 27th, a team including Dennis Geist (University of Idaho), Terry Naumann (University of Alaska), and Karen Harpp (Colgate University) had arrived at the E caldera rim and began sending back a series of valuable reports. Their first report noted a major vent immediately below GPS station SN12 on the rim NE of the caldera's center. This vent emitted a large intracaldera aa flow.

Some active N-flank vents stood about 300-400 m NW of a station (GV01) on the caldera's N rim . There, two major vents fed lava fountains up to 50 m high. Most lava being erupted was flowing into the caldera, although some of the scoria from the fountains was falling outside the caldera and then forming a short, sluggish flow. Lava inside the caldera was cascading from the vents down the slope on the N edge of the caldera in 3 main channels, each 30-40 m across, with lava flowing at ~10 m/s (36 km/h) and in some cases over 10 m/s, and coalescing into a major aa flow to the S. On the caldera floor these channels merged into one big aa channel about 100 m wide that flowed more slowly both to the S, clockwise along the base of the E caldera wall, and into the moat along the S edge of the caldera floor. Pahoehoe outbreaks occurred along the margins of the major aa flow. New aa lava covered an estimated one-third of the caldera floor.

The report for 28 October noted that the eruption was still going strong. There were no significant new events on this day, but it appeared that the lava flux had increased because the vents looked wider and there seemed to be a lot more gas emitted. The lava continued to feed from the vents to the caldera floor in two large streams, each ~ 20 m across with lava traveling at 5-10 m/s, adding up to probably hundreds of millions of cubic meters of lava per day. The aa field continued to grow. The group reached the caldera floor and were able to sample both lava and tephra.

By 0700 on the 29th some of the vents had shut down and the two lava channels to the W (previously fed by the upper vent) stopped moving. The lower vent still emitted lava and fed one channel E of the others. The team estimated the channel to be ~10 m wide and moving ~5 m/s. Assuming a 2-m depth, the lava flux was 5 to 10 million cubic meters per day, about half that seen the morning of the 29th.

The emission rate continued to diminish throughout the 29th and by the evening it was only 10-20% of that seen on the 28th. In addition, the amount of gases emitted decreased such that the gas plume only rose ~1 km, whereas earlier plumes had risen to several kilometers. The lower vent was no longer fountaining continuously as it had on the 28th; instead the fountaining came in bursts at intervals of about 1-30 seconds. A lava lake sloshed around in the lower vent's crater; some lava escaped this crater along a breach in the crater rim. The upper vent (the one that shut off) was still incandescent with a lot of gas coming out, so it was possible that there was a lava lake there too.

The eruption appeared to end on the 30th. Glow was observed at 0200, but had ceased by 0400. The vents still emitted gas, but not fresh lava. However, it was possible that there was still N-flank activity. There were reports of lava flows there, and while it was certain that at least some of these flows were clastogenic (composed of spatter from fire fountains that accumulated and then began to flow), it was uncertain whether there were also actively erupting flank vents. The team remained separated from this area by hot lava, thwarting reconnaissance. Initial estimates of the coverage of the caldera floor were an area of ~14 km2. Assuming a 3-4 m average flow thickness, this was ~0.05 km3 (50,000,000 m3) of lava. There were obviously high error bars on this estimate, but it was clearly much less than the ~1 km3 extruded in the 1979 eruption.

MODVOLC Thermal Alerts. A large set of thermal hotspots in multispectral imagery was observed beginning late 22 October (local time and date) and continuing through 16 November 2005 (figure 11). Although MODVOLC data were missing for some days and reduced for others (presumably due to cloud cover screening the radiation from the satellite) these hot-spot pixels dramatically document the course of the eruption. Data on figure 11 appear consistent with in situ observations, in that by the second day, lava was at least 5 km down the outer N slope and covering much of the E caldera floor. By the 8th day (30 October), the outer slope flows had cooled significantly, but flows inside the caldera had continued their clockwise advance, filling all low points to the extreme SW corner of the caldera. Ten days later (9 November), the eruption had ended and only flows from the vents to the SE caldera floor were still emitting detectable heat. The last pixels observed, two above the original vent area on the N rim, were on 16 November.

Figure (see Caption) Figure 11. Selected images of MODVOLC thermal anomalies for Sierra Negra measured from satellite (MODIS) data at three days during and after the 2005 eruption. Part A presents an overview of the region (smaller scale than the other images) on 24 October. Parts B-D give a zoom-in on the 7 x 10.5 km caldera. Part B represents 24 October; Part C, 30 October; and part D, 9 November 2005. Since the eruption ended 30 October, the latter two images must thus portray the post-eruptive thermal inertial of the cooling lavas. Courtesy of Hawai`i Institute of Geophysics and Planetology, University of Hawai`i.

References. Amelung, F., Jónsson, S., Zebker, H., and Segall, P., 2000, Widespread uplift and 'trapdoor' faulting on Galápagos volcanoes observed with radar interferometry: Nature, v. 407, p. 993-996.

Geist, D.J., Chadwick, W.W., Jr., and Johnson, D.J., in press, Results from new GPS monitoring networks at Fernandina and Sierra Negra volcanoes, Galápagos, 2000-2002: Journal of Volcanology and Geothermal Research (in press).

Jónsson, S., H. Zebker, and F. Amelung, 2005, On trapdoor faulting at Sierra Negra volcano, Galápagos; Journal of Volcanology and Geothermal Research, v. 144, p. 59-71.

Geologic Background. The broad shield volcano of Sierra Negra at the southern end of Isabela Island contains a shallow 7 x 10.5 km caldera that is the largest in the Galápagos Islands. Flank vents abound, including cinder cones and spatter cones concentrated along an ENE-trending rift system and tuff cones along the coast and forming offshore islands. The 1124-m-high volcano is elongated in a NE direction. Although it is the largest of the five major Isabela volcanoes, it has the flattest slopes, averaging less than 5 degrees and diminishing to 2 degrees near the coast. A sinuous 14-km-long, N-S-trending ridge occupies the west part of the caldera floor, which lies only about 100 m below its rim. Volcán de Azufre, the largest fumarolic area in the Galápagos Islands, lies within a graben between this ridge and the west caldera wall. Lava flows from a major eruption in 1979 extend all the way to the north coast from circumferential fissure vents on the upper northern flank. Sierra Negra, along with Cerro Azul and Volcán Wolf, is one of the most active of Isabela Island volcanoes.

Information Contacts: Lucho Verdesoto and Carman Guzman, M/NPolaris, Galápagos Islands, Ecuador; Francisco Dousdebes, Galápagos Expedition Manager, Metropolitan Touring, Ecuador; Lindblad Expeditions (URL: http://www.expeditions.com/); U.S. National Aeronautical and Space Administration (NASA) (URL: http://earthobservatory.nasa.gov/); Bill Chadwick, Cooperative Institute for Marine Resources Studies (CIMRS), National Oceanic and Atmospheric Agency (NOAA) Pacific Marine Environmental Laboratory (PMEL), Oregon State University, 2115 SE OSU Drive, Newport, OR 97365, USA; Dennis Geist, Department of Geological Sciences, University of Idaho, Moscow, ID 83844-3022 USA; Terry Naumann, Department of Geology, University of Alaska at Anchorage, Anchorage, AK 99598, USA (URL: https://www.uaa.alaska.edu/academics/college-of-arts-and-sciences/departments/geology/); Karen Harpp, Department of Geology, Colgate University, 408 Lathrop Hall, Hamilton, NY 13346, USA (URL: http://www.colgate.edu/facultysearch/FacultyDirectory/karen-harpp); MODVOLC Alerts Team, Hawaii Institute of Geophysics and Planetology (HIGP), University of Hawaii at Manoa, 1680 East-West Road, Post 602, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).


Northern EPR at 10.7°N (Undersea Features) — October 2005 Citation iconCite this Report

Northern EPR at 10.7°N

Undersea Features

10.73°N, 103.58°W; summit elev. -2900 m

All times are local (unless otherwise noted)


November 2003 visit finds evidence of very recent eruption

In a recent publication, Rubin and van der Zander (2005) discuss radiometric methods for dating lavas as one means to establish eruption chronologies. Some of their techniques were applied to samples of fresh lava (erupted September-October 2003) found on the East Pacific Rise (EPR) at 10°44'N (Voight and others, 2004). This location lies ~ 1,900 km WNW of the Galápagos Islands. During a November 2003 biological sampling visit to the EPR at 10°44'N, divers in the submersible Alvin expected to be revisiting an established hydrothermal vent field. Instead, they found indicia all of which were consistent with a recent eruption, notably fresh lava, bacterial mats, and diffuse snow- blower vents issuing from lava collapses. The team acted immediately after the cruise by sending the lava samples to the University of Hawai`I for dating. Researchers there determined that an eruption had occurred within 1 to 2 months prior to the site visit. A hydrophone array (designated N-EPR) nominally monitored this part of the EPR since 1996, but not in real time. Unfortunately, the system failed to record data during the 2002-2004 interval due to a hardware problem.

Ages for lavas erupted within the past 1.5-2 years were determined with the 210Po-210Pb dating method (Rubin and others, 1994). To use this method, analyses should begin as soon as possible after samples are collected from suspected eruption locales. Radioactive disequilibrium is largest, and temporal resolution of the method is highest, immediately following eruption. According to Rubin and van der Zander (2005, p. 28) "Polonium is volatile at magmatic temperatures and degasses from magmas when they erupt. This creates an initial 210Po (half-life = 138.4 day) deficit relative to grand parental 210Pb in freshly erupted magmas. This deficit is subsequently erased with time via radioactive ingrowth toward secular equilibrium."

References. Rubin, K.H., Macdougall, J.D., and Perfit, M.R., 1994, 210Po-210Pb dating of recent volcanic eruptions on the seafloor: Nature, v. 368, p. 841-844.

Rubin, K., and van der Zander, I., 2005, Obtaining high-resolution chronologies of submarine lava eruptions: Better dating through radiochemistry: Ridge 2000 Events, v. 3 (Spring 2005), p. 28-30.

Voight, J. R., Zierenberg, R.A., McClain, J., and the Science Party: Batson, P., Beers, K., Daly, M., Dushman, B., Gollner, S., Govenar, B., Haney, T.A., Hourdez, S., Liow, L.H., Parker, C., Von Damm, K., Zekley, J., and Zelnio, K.A., 2004, FIELD cruise to the northern EPR: Discoveries made during biological investigations from 8°37'N to 12°48'N: Ridge 2000 Events, v. 2(1), p. 22-24.

Geologic Background. Divers in the submersible Alvin discovered an extremely fresh lava flow in an unexpected location at 10°44'N on the East Pacific Rise during an expedition in November 2003. The young flow was covered by bacterial mats, had large amounts of bacterial floc ("snow-blowers") issuing from diffuse vents, and was sparsely populated by small animals. Uranium-series dating indicated that the eruption had taken place within a time window only a few months to weeks prior to the observations. This segment of the East Pacific Rise, located just north of the Clipperton Transform Fault, is an area with an estimated low magma production rate.

Information Contacts: Ken Rubin, Department of Geology and Geophysics, SOEST, University of Hawai`I, 1680 East West Road, Honolulu, HI 96822, USA.


Pacaya (Guatemala) — October 2005 Citation iconCite this Report

Pacaya

Guatemala

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

All times are local (unless otherwise noted)


Steam clouds and tremor in 2004; incandescence and lava flows in 2005

Frequent steam plumes through 2002 and 2003 indicated that Pacaya was active, although incandescence from the long-term lava lake ended after June 2001. During the latter half of October 2003 constant steam and abundant emissions of water and gas were being blown to the NNW and W of the volcano (BGVN 28:10). All of the following information is derived from the reports of Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH).

Throughout November and December 2003 and the first half of 2004, abundant clouds and columns of white and off-white gases and steam were expelled from Pacaya, generally reaching less than 400 m above the volcano and dispersing mostly to the W and SW; these were occasionally visible from Guatemala City, 30 km to the NNE.

During June, July, and August 2004, near-continuous tremor and frequent long-period earthquakes were recorded at seismograph station PCG (~ 1.4 km to the W of Pacaya). On 14 June, weak incandescence was observed in the central crater of MacKenney Cone for the first time since August 2000. Pacaya continued to expel off-white smoke and/or steam which usually drifted to the S and SW and rose to 150-300 m above the volcano. On 19 July, ejection of small lava fragments began to form a cone in the bottom of the central crater of MacKenney Cone.

During September-November 2004, tremor increased somewhat (from ~ 2mm in June, July, and September to 4-7 mm in December), and white steam and/or gas plumes rose 300-500 m above MacKenney Cone. Incandescence was observed throughout this time and lava clasts were expelled from the MacKenney Cone on 7-9 December.

On 3 January 2005, small expulsions of incandescent lava clasts rose from the central crater, and a narrow lava flow from the S rim of the crater reached 75-100 m down the flank. Station PCG continued to register tremor, and incandescence and white plumes persisted. On 10 January, lava flowed ~ 30 m from the SW rim of the central crater of MacKenney Cone. On 12 January, two lava flows, one to the S ( ~ 125 m) and one to the SW (~ 50 m) left the central crater. Observers saw incandescent lava fragments rising <10 m above the mouth of the intra-crater cone, and "smoke" whiffs rising from the MacKenney Cone. During the last 5 days of January 2005, numerous small lava flows descended the S and SW flanks of the volcano.

During February, March, and April 2005, incandescence, tremor, and minor lava flows continued. On 2 February observers reported that avalanches from the lava flow fronts during the previous days formed a debris fan covering about 2/3 of the SW flank. On 28 February expulsion of incandescent lava fragments reached heights of 10-50 m for brief periods. On 1 March INSIVUMEH recommended that park officials prevent tourists from climbing Pacaya because of avalanches, lava expulsion, and gas emissions. In March and April explosions of lava reached 100 m in height, and smoke/gas emissions continued.

Lava emission continued during May. On 4 May, three flows were active, extending up to 100 m down the SW flank and 150 m W in the direction of Cerro Chino. On 9 May two active flows from the base of the intracrater cone reached 200 m down the W flank. Plumes from the MacKenney Cone rose as high as 800 m above the crater. Ejection of incandescent material continued throughout the month. Lava flows moving to the SW and W in the direction of Cerro Chino reached lengths of 150-250 m.

During early June, incandescent lava clasts were ejected as high as ~ 75 m above Pacaya's crater. An intra-crater lava flow extended ~ 300 m from the SW base of the central cone. On 6 June, a lava flow traveled ~ 200 m down the volcano's W flank. By 27 June a lava flow extended ~ 300 m down the SW flank. A white steam column rose ~ 150 m over the central crater and drifted SW. Incandescent lava expulsions reached heights of 15-50 m. On the night of 27 June two rivers of lava, 75 and 150 m long, were observed in front of Cerro Chino. Constant expulsions of pyroclastic material rose 20-30 m above the crater.

Lava flows in July traveled 200-300 m down the SW flank. Small plumes emitted from the volcano's central crater rose to low altitudes. Avalanches of incandescent volcanic blocks produced small ash clouds to low levels.

During 7-11 September, occasional Strombolian activity occurred. Volcanic bombs from two craters rose up to 30 m above their rims. Incandescence from lava flows on the SE flank was visible on several nights.

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

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/).


Santa Maria (Guatemala) — October 2005 Citation iconCite this Report

Santa Maria

Guatemala

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

All times are local (unless otherwise noted)


Partial dome collapses in 2004; explosions and ash columns in 2005

Prior to the period covered by this report, recent activity at Santa María was characterized by weak-to-moderate explosions producing ash, crater-rim collapses and avalanches of block lava and ash, pyroclastic flows, and an active lava flow (BGVN 28:10). Activity was similar from October 2003 to June 2004, consisting mostly of explosions from Santiaguito, a lava-dome complex that includes the Caliente vent. The explosions produced ash plumes, and there were numerous block-lava-and-ash avalanches from Caliente collapses (BGVN 29:06). From July 2004 until October 2005, these types of activity continued.

Activity during July-September 2004. During July to September 2004, weak-to-moderate explosions at Santiaguito produced plumes to a maximum height of ~ 1.5 km above the volcano. Frequent avalanches of volcanic material including blocks and ash traveled SE and SW down Caliente cone. In early September 2004, several weak-to-moderate explosions produced ash clouds to a maximum height of 2 km above the volcano. Partial collapses of the lava dome caused pyroclastic flows to travel down the volcano's NE and SW flanks. On 27 September, several avalanches of volcanic material from active lava-flow fronts traveled SW.

Activity during October 2004. During October 2004 moderate explosions produced ash-and-gas plumes that rose to a maximum altitude of 9 km. Explosions on 4 October produced small pyroclastic flows to the SW. On 11 October, a partial lava-dome collapse to the SW produced a pyroclastic flow that traveled toward the Nimá Segundo River. An ash cloud formed that rose to a height of ~ 500 m and covered most of the dome complex. The collapse was preceded by an explosion that produced an ash-and-gas cloud to ~ 1.5 km above the volcano. Small explosions on 12 October produced small lava-dome collapses to the SW that generated avalanches of lava blocks and ash.

Small lahars traveled down San Isidro ravine on 14 and 15 October. A small collapse of the SW edge of the lava dome in the Caliente crater produced a pyroclastic flow on 17 October. The flow traveled down the S flank and produced a steam-and-ash plume to a height of ~ 800 m upon contact with dammed water. Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH) reported that this collapse, like those that occurred on previous days and weeks, was associated with a new cycle of magmatic injection. The Washington VAAC reported that hot spots and plumes possibly containing ash were occasionally visible on satellite imagery on 21 October; imagery on 31 October showed a possible ash-bearing plume at ~ 4.5 km altitude.

Activity during November 2004. During November, weak-to-moderate explosions produced gas-and-ash plumes to ~ 1 km above the volcano. Many explosions were accompanied by block-and-ash avalanches from the NE and SW edges of Caliente dome. The Washington VAAC reported that satellite imagery on 3 November showed a possible ash-bearing plume at a height of ~ 5 km altitude. On 12 November, the collapse of a small sector of the SW edge of the Caliente dome produced a pyroclastic flow. On 14 November at 2012, a tectonic earthquake caused a lava-flow collapse SW of the Caliente dome, triggering a pyroclastic flow that descended to the head of San Isidro ravine, an area of abundant accumulation of pyroclastic material and a known area for lahar initiation. During December, weak-to-moderate explosions produced plumes to a maximum height of 1.3 km above the crater. Frequent block-lava avalanches traveled down the SW flank of Caliente dome. A moderate explosion on 4 December caused a partial lava-dome collapse and a pyroclastic flow that traveled SW. On 22 December small collapses occurred from lava-flow fronts on the SW side of Caliente dome. According to the Washington VAAC, ash plumes were visible on satellite imagery on several days during 22-27 December.

Activity during January-October 2005.During January 2005, frequent explosions (table 2) produced columns of gray and white ash up to 2 km in height, ash fall in towns near the volcano and frequent blocky avalanches. Early in the month, avalanches of incandescent blocks were released from lava flow fronts towards the NE and SE flanks of Santiaguito.

Table 2. Explosions recorded at the Santiaguito cone of Santa María in January 2005. Missing dates were not reported. Courtesy of INSIVUMEH.

Date Number of Explosions
04 Jan 2005 93
07 Jan 2005 62
10 Jan 2005 31
11 Jan 2005 20
12 Jan 2005 14
13 Jan 2005 13
14 Jan 2005 15
24 Jan 2005 16
25 Jan 2005 56
26 Jan 2005 16
27 Jan 2005 52
28 Jan 2005 65

During February 2005, frequent explosions and avalanches continued. On 10 February 2005 the Washington VAAC reported that satellite imagery showed a plume of ash and steam moving SW from the summit and ash extending 55 km after an eruption around 0645. A continuous plume of ash and steam was emitted after an eruption around 0745 and ash extended around 230 km from the summit moving at 2-50 km/hour.

During March 2005, several weak-to-moderate explosions produced ash plumes to a maximum height of ~ 1.3 km above the dome. Avalanches of volcanic blocks traveled down the E and SW flanks of Caliente dome. On 16 March, small amounts of fine ash fell in Xepax, Xecavioc, Llanos de Pinal, Las Majadas, and Quetzaltenango. During 19-20 March, ash fell to the E in the town of Zunil.

During 21-25 April several explosions at Santiaguito produced ash plumes that rose to ~ 1.2 km above the dome. Lava avalanches occurred down the SW flank of Caliente dome. Explosions on 25 April produced pyroclastic flows that traveled S down Caliente.

Continuing explosive activity from Santiaguito during 4-9 May sent ash columns as high as 1.3 km above the vent. Small collapses at the Caliente dome generated pyroclastic flows 500-3,000 m long. Constant avalanches were reported on 10 May from the lava-flow front and the Caliente dome, along with one small ash explosion. Minor explosions on 13 May sent gray ash plumes 400-600 m high. Avalanches from the SW-flank lava flow continued. Explosions during 17-20 May produced ash clouds to ~ 1 km above the volcano; ash fell 7-10 km from Caliente dome.

During the first week of June 2005, moderate explosions produced plumes that rose to ~ 1.2 km above the volcano. On 2 June, the partial collapse of the lava dome in the crater of Caliente dome generated a pyroclastic flow that traveled ~ 4 km SW. On 22-24 June explosion columns reached ~ 900 m above the crater and extended several kilometers to the SSW and W. On 27 June, in the region of Palajunoj on the SW flank, constant avalanches of lava blocks were observed. During 6-18 July, weak-to-moderate explosions continued , with plumes rising to ~ 1.3 km above the volcano. Throughout July avalanches of volcanic material were produced at the front of an active lava flow, and from the SW edge of Caliente dome.

August and early September reports were unavailable, but during 7-11 September, small-to-moderate explosions at Santiaguito produced plumes that rose to a maximum height of ~ 1.5 km above the volcano on 8 September. On 7 September, a moderate lahar traveled down the volcano's flank. About a dozen pyroclastic flows, and avalanches of volcanic material occurred from the SW edge of the lava dome, and from the front of lava deposits on the SW flank of Caliente dome.

On 26 October 2005 a small eruption produced an ash plume that drifted SW to the Pacific and was recorded on MODIS satellite imagery (figure 33). The Washington VAAC reported a hot spot that lasted for about 6 hours with an estimated plume height of 4.5 km. On 28 October a plume rose to an altitude of ~ 4.9 km.

Figure (see Caption) Figure 33. MODIS (Moderate Resolution Imaging Spectroradiometer) image showing a Santa María eruption plume on 26 October 2005. The volcano's summit is identifiable by a small red outline indicating an area hotter than its surroundings. Wafting away from the summit is a thin, faint ash plume that heads SW toward the Pacific. NASA image courtesy the MODIS Rapid Response Team at NASA GSFC.

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

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/).

Atmospheric Effects

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

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

Special Announcements

Special announcements of various kinds and obituaries.

Special Announcements  Obituaries

Misc 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 subject.

Additional Reports  False Reports