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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

Sangay (Ecuador) Ash plumes, lava flows, pyroclastic flows, and lahars during July-December 2020; larger explosions in September

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

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

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

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



Sangay (Ecuador) — January 2021 Citation iconCite this Report

Sangay

Ecuador

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

All times are local (unless otherwise noted)


Ash plumes, lava flows, pyroclastic flows, and lahars during July-December 2020; larger explosions in September

Sangay is one of the most active volcanoes in Ecuador with the current eruptive period continuing since 26 March 2019. Activity at the summit crater has been frequent since August 1934, with short quiet periods between events. Recent activity has included frequent ash plumes, lava flows, pyroclastic flows, and lahars. This report summarizes activity during July through December 2020, based on reports by Ecuador's Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), ash advisories issued by the Washington Volcanic Ash Advisory Center (VAAC), webcam images taken by Servicio Integrado de Seguridad ECU911, and various satellite data.

Overall activity remained elevated during the report period. Recorded explosions were variable during July through December, ranging from no explosions to 294 reported on 4 December (figure 80), and dispersing mostly to the W and SW. SO2 was frequently detected using satellite data (figure 81) and was reported several times to be emitting between about 770 and 2,850 tons/day. Elevated temperatures at the crater and down the SE flank were frequently observed in satellite data (figure 82), and less frequently by visual observation of incandescence. Seismic monitoring detected lahars associated with rainfall events remobilizing deposits emplaced on the flanks throughout this period.

Figure (see Caption) Figure 80. A graph showing the daily number of explosions at Sangay recorded during July through December 2020. Several dates had no recorded explosions due to lack of seismic data. Data courtesy of IG-EPN (daily reports).
Figure (see Caption) Figure 81. Examples of stronger SO2 plumes from Sangay detected by the Sentinel 5P/TROPOMI instrument, with plumes from Nevado del Ruiz detected to the north. The image dates from left to right are 31 August 2020, 17 September 2020, 1 October 2020 (top row), 22 November 2020, 3 December 2020, 14 December 2020 (bottom row). Courtesy of NASA Global Sulfur Dioxide Monitoring Page.
Figure (see Caption) Figure 82. This log radiative power MIROVA plot shows thermal output at Sangay during February through December 2020. Activity was relatively constant with increases and decreases in both energy output and the frequency of thermal anomalies detected. Courtesy of MIROVA.

Activity during July-August 2020. During July activity continued with frequent ash and gas emission recorded through observations when clouds weren’t obstructing the view of the summit, and Washington VAAC alerts. There were between one and five VAAC alerts issued most days, with ash plumes reaching 570 to 1,770 m above the crater and dispersing mostly W and SE, and NW on two days (figure 83). Lahar seismic signals were recorded on the 1st, 7th, three on the 13th, and one on the 19th.

Figure (see Caption) Figure 83. Gas and ash plumes at Sangay during July 2020, at 0717 on the 17th, at 1754 on the 18th, and at 0612 on the 25th. Bottom picture taken from the Macas ECU 911 webcam. All images courtesy of IG-EPN daily reports.

During August there were between one and five VAAC alerts issued most days, with ash plumes reaching 600 to 2,070 m above the crater and predominantly dispersing W, SW, and occasionally to the NE, S, and SE (figure 84). There were reports of ashfall in the Alausí sector on the 24th. Using seismic data analysis, lahar signals were identified after rainfall on 1, 7, 11-14, and 21 August. A lava flow was seen moving down the eastern flank on the night of the 15th, resulting in a high number of thermal alerts. A pyroclastic flow was reported descending the SE flank at 0631 on the 27th (figure 85).

Figure (see Caption) Figure 84. This 25 August 2020 PlanetScope satellite image of Sangay in Ecuador shows an example of a weak gas and ash plume dispersing to the SW. Courtesy of Planet Labs.
Figure (see Caption) Figure 85. A pyroclastic flow descends the Sangay SE flank at 0631 on 27 August 2020. Webcam by ECU911, courtesy of courtesy of IG-EPN (27 August 2020 report).

Activity during September-October 2020. Elevated activity continued through September with two significant increases on the 20th and 22nd (more information on these events below). Other than these two events, VAAC reports of ash plumes varied between 1 and 5 issued most days, with plume heights reaching between 600 and 1,500 m above the crater. Dominant ash dispersal directions were W, with some plumes traveling SE, S, SE, NE, and NW. Lahar seismic signals were recorded after rainfall on 1, 2, 5, 8-10, 21, 24, 25, 27, and 30 September. Pyroclastic flows were reported on the 19th (figure 86), and incandescent material was seen descending the SE ravine on the 29th. There was a significant increase in thermal alerts reported throughout the month compared to the July-August period, and Sentinel-2 thermal satellite images showed a lava flow down the SE flank (figure 87).

Figure (see Caption) Figure 86. Pyroclastic flows descended the flank of Sangay on 19 (top) and 20 (bottom) September 2020. Webcam images by ECU911 from the city of Macas, courtesy of IG-EPN (14 August 2018 report).
Figure (see Caption) Figure 87. The thermal signature of a lava flow is seen on SW flank of Sangay in this 8 September 2020 Sentinel-2 thermal satellite image, indicated by the white arrow. False color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Starting at 0420 on the morning of 20 September there was an increase in explosions and emissions recorded through seismicity, much more energetic than the activity of previous months. At 0440 satellite images show an ash plume with an estimated height of around 7 km above the crater. The top part of the plume dispersed to the E and the rest of the plume went W. Pyroclastic flows were observed descending the SE flank around 1822 (figure 88). Ash from remobilization of deposits was reported on the 21st in the Bolívar, Chimborazo, Los Ríos, Guayas and Santa Elena provinces. Ash and gas emission continued, with plumes reaching up to 1 km above the crater. There were seven VAAC reports as well as thermal alerts issued during the day.

Figure (see Caption) Figure 88. An eruption of Sangay on 22 September 2020 produced a pyroclastic flow down the SE flank and an ash plume that dispersed to the SW. PlanetScope satellite image courtesy of Planet Labs.

Ash plumes observed on 22 September reached around 1 km above the crater and dispersed W to NW. Pyroclastic flows were seen descending the SE flank (figure 89) also producing an ash plume. A BBC article reported the government saying 800 km2 of farmland had experienced ashfall, with Chimborazo and Bolívar being the worst affected areas (figure 90). Locals described the sky going dark, and the Guayaquil was temporarily closed. Ash plume heights during the 20-22 were the highest for the year so far (figure 91). Ash emission continued throughout the rest of the month with another increase in explosions on the 27th, producing observed ash plume heights reaching 1.5 km above the crater. Ashfall was reported in San Nicolas in the Chimborazo Province in the afternoon of the 30th.

Figure (see Caption) Figure 89. A pyroclastic flow descending the flank of Sangay on 22 September 2020. Webcam image by ECU911 from the city of Macas, courtesy of IG-EPN (Sangay Volcano Special Report - 2020 - No 5, 22 September 2020).
Figure (see Caption) Figure 90. Ashfall from an eruption at Sangay on 22 September 2020 affected 800 km2 of farmland and nearby communities. Images courtesy of EPA and the Police of Ecuador via Reuters (top-right), all via the BBC.
Figure (see Caption) Figure 91. Ash plume heights (left graph) at Sangay from January through to late September, with the larger ash plumes during 20-22 September indicated by the red arrow. The dominant ash dispersal direction is to the W (right plot) and the average speed is 10 m/s. Courtesy of IG-EPN (Sangay Volcano Special Report - 2020 - No 5, 22 September 2020).

Thermal alerts increased again through October, with a lava flow and/or incandescent material descending the SE flank sighted throughout the month (figure 92). Pyroclastic flows were seen traveling down the SE flank during an observation flight on the 6th (figure 93). Seismicity indicative of lahars was reported on 1, 12, 17, 19, 21, 23, 24, and 28 October associated with rainfall remobilizing deposits. The Washington VAAC released one to five ash advisories most days, noting plume heights of 570-3,000 m above the crater; prevailing winds dispersed most plumes to the W, with some plumes drifting NW, N, E to SE, and SW. Ashfall was reported in Alausí (Chimborazo Province) on the 1st and in Chunchi canton on the 10th. SO2 was recorded towards the end of the month using satellite data, varying between about 770 and 2,850 tons on the 24th, 27th, and 29th.

Figure (see Caption) Figure 92. A lava flow descends the SE flank of Sangay on 2 October 2020. Webcam images courtesy of ECU 911.
Figure (see Caption) Figure 93. A pyroclastic flow descends the Sangay SE flank was seen during an IG-EPN overflight on 6 October 2020. Photo courtesy of S. Vallejo, IG-EPN.

Activity during November-December 2020. Frequent ash emission continued through November with between one and five Washington VAAC advisories issued most days (figure 94). Reported ash and gas plume heights varied between 570 and 2,700 m above the crater, with winds dispersing plumes in all directions. Thermal anomalies were detected most days, and incandescent material from explosions was seen on the 26th. Seismicity indicating lahars was registered on nine days between 15 and 30 November, associated with rainfall events.

Figure (see Caption) Figure 94. Examples of gas and ash plumes at Sangay during November 2020. Webcam images were published in IG-EPN daily activity reports.

Lahar signals associated with rain events continued to be detected on ten out of the first 18 days of November. Ash emissions continued through December with one to five VAAC alerts issued most days. Ash plume heights varied from 600 to 1,400 m above the crater, with the prevailing wind direction dispersing most plumes W and SW (figure 95). Thermal anomalies were frequently detected and incandescent material was observed down the SE flank on the 3rd, 14th, and 30th, interpreted as a lava flow and hot material rolling down the flank. A webcam image showed a pyroclastic flow traveling down the SE flank on the 2nd (figure 96). Ashfall was reported on the 10th in Capzol, Palmira, and Cebadas parishes, and in the Chunchi and Guamote cantons.

Figure (see Caption) Figure 95. Examples of ash plumes at Sangay during ongoing persistent activity on 9, 10, and 23 December 2020. Webcam images courtesy of ECU 911.
Figure (see Caption) Figure 96. A nighttime webcam image shows a pyroclastic flow descending the SE flank of Sangay at 2308 on 2 December 2020. Image courtesy of ECU 911.

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

Information Contacts: Instituto Geofísico (IG-EPN), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec); ECU911, Servicio Integrado de Seguridad ECU911, Calle Julio Endara s / n. Itchimbía Park Sector Quito – Ecuador. (URL: https://www.ecu911.gob.ec/; Twitter URL: https://twitter.com/Ecu911Macas/); 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/); 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/); Planet Labs, Inc. (URL: https://www.planet.com/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); BBC News “In pictures: Ash covers Ecuador farming land” Published 22 September 2020 (URL: https://www.bbc.com/news/world-latin-america-54247797).


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).


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).


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).


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).

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Bulletin of the Global Volcanism Network - Volume 16, Number 05 (May 1991)

Managing Editor: Lindsay McClelland

Aira (Japan)

Frequent explosions continue

Arenal (Costa Rica)

Strombolian activity and seismicity increase, then decline; block lava flows on S and SW flanks

Barren Island (India)

Explosions and lava flows from NE flank vent

Colima (Mexico)

Continued lava dome growth; increased avalanching follows earthquakes and tremor episodes

Deception Island (Antarctica)

Stronger earthquakes; anomalous water temperature in caldera center

Etna (Italy)

Strong degassing

Galeras (Colombia)

More seismic events but lower energy release; thermal activity remains moderate

Gede-Pangrango (Indonesia)

Brief earthquake swarm

Guallatiri (Chile)

Strong fumarolic activity

Irazu (Costa Rica)

Tectonic earthquake swarm

Kavachi (Solomon Islands)

Continued explosions from new island

Kilauea (United States)

E rift lava continues to flow through tubes into the ocean

Langila (Papua New Guinea)

Ash emission resumes; steady glow

Lascar (Chile)

High crater temperatures detected by satellite

Lewotobi (Indonesia)

Ash emission follows increased seismicity

Lokon-Empung (Indonesia)

Increased gas emission, then ash eruption

Manam (Papua New Guinea)

Ash ejection declines to weak vapor emission

Merapi (Indonesia)

Continued seismicity but lava dome unchanged

Obituary Notices (Unknown)

Deaths of three volcanologists (Maurice and Katia Krafft, Harry Glicken) at Unzen

Ontakesan (Japan)

Earthquake swarms and tremor; renewed steam emission from 1979 vent

Pinatubo (Philippines)

Major stratospheric cloud, pyroclastic flows, and new summit caldera; >300 killed by eruption and typhoon

Poas (Costa Rica)

Strong gas emission; rain adds water to nearly dry crater lake

Rabaul (Papua New Guinea)

Continued low-level seismicity; slight uplift

Rincon de la Vieja (Costa Rica)

More details on 8 May eruption and deposits

Ruiz, Nevado del (Colombia)

Frequent lithic ash emissions; occasional vigorous earthquake swarms

Sabancaya (Peru)

Vigorous Vulcanian activity; mudflows force daily clearing of river channel

San Jose (Chile-Argentina)

New fumarole field on upper S flank

Soputan (Indonesia)

Explosion sounds and incandescence; frequent seismicity

Stromboli (Italy)

More frequent explosions

Ulawun (Papua New Guinea)

Large gas plume and numerous weak earthquakes

Unzendake (Japan)

41 killed by pyroclastic flow from lava dome

Whakaari/White Island (New Zealand)

Ash emission from new vent; continued deformation



Aira (Japan) — May 1991 Citation iconCite this Report

Aira

Japan

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

All times are local (unless otherwise noted)


Frequent explosions continue

Frequent explosions continued through mid-June, with 17 recorded in May and 20 as of 19 June, bringing the year's total to 142. The highest ash clouds rose 3,000 m on 3 May and 2300 m on 18 June. An air shock from a 10 May explosion broke a window, the first explosion damage since December 1990.

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

Information Contacts: JMA.


Arenal (Costa Rica) — May 1991 Citation iconCite this Report

Arenal

Costa Rica

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

All times are local (unless otherwise noted)


Strombolian activity and seismicity increase, then decline; block lava flows on S and SW flanks

On 20 April, seismic explosion signals became moderately more frequent, and seismicity increased to >40 recorded earthquakes/day (RSN network). Seismicity was similar in May, with a daily average of 20 recorded earthquakes and a maximum of 43 (Univ Nacional network). Strombolian explosive activity was stronger, more voluminous, and more frequent, especially on 19-26 May when explosions vibrated windows and were heard 34 km SE (in Quesada). Several explosions were recorded at a seismic station 98 km away (Juan Diaz). Plumes rose to 1 km height above Crater C, depositing ash to Chambacú (17.5 km NE) and La Palma (4 km N). After 26 May, seismic and eruptive activity returned to normal levels. Gas emission continued with periodic, smaller explosions; plumes were carried predominantly to the NE, W, and SW. Block lava flows continued down the SW and S flanks, reaching 700 m elevation by the end of April.

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

Information Contacts: E. Fernández, J. Brenes, V. Barboza, and T. Marino, OVSICORI; R. Barquero, ICE.


Barren Island (India) — May 1991 Citation iconCite this Report

Barren Island

India

12.278°N, 93.858°E; summit elev. 354 m

All times are local (unless otherwise noted)


Explosions and lava flows from NE flank vent

Reports of strong emissions of "thick smoke" on 30 April prompted a visit to the island on 16 May by geologists from the GSI [see additional information about the start of the eruption in 16:10]. Lava poured continuously from a subsidiary vent on the NE face of the central volcanic cone, travelling N into a valley, then W along the course of the 1803 lava flow (figure 1). An area of ~800 x 200 m had been covered by fresh lava, with an average thickness of 5-6 m. Explosions at the vent occurred at intervals of several seconds, ejecting bombs, lapilli, and ash to heights >50 m.

Figure (see Caption) Figure 1. Geologic sketch map of Barren Island, by D. Haldar, T. Laskar, and J.K. Biswas. Courtesy of the GSI.

On 7 June at 1602, John Deed, pilot of Thai Airways International flight 307, observed a gray to dark-gray plume rising ~3 km above the summit and extending roughly 90 km NE. No lava was visible.

Geologic Background. Barren Island, a possession of India in the Andaman Sea about 135 km NE of Port Blair in the Andaman Islands, is the only historically active volcano along the N-S volcanic arc extending between Sumatra and Burma (Myanmar). It is the emergent summit of a volcano that rises from a depth of about 2250 m. The small, uninhabited 3-km-wide island contains a roughly 2-km-wide caldera with walls 250-350 m high. The caldera, which is open to the sea on the west, was created during a major explosive eruption in the late Pleistocene that produced pyroclastic-flow and -surge deposits. Historical eruptions have changed the morphology of the pyroclastic cone in the center of the caldera, and lava flows that fill much of the caldera floor have reached the sea along the western coast.

Information Contacts: Director General, GSI; Deputy Director General, GSI Eastern Region; T. Fox, ICAO.


Colima (Mexico) — May 1991 Citation iconCite this Report

Colima

Mexico

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

All times are local (unless otherwise noted)


Continued lava dome growth; increased avalanching follows earthquakes and tremor episodes

During the weeks preceding 5 June, volcanic seismicity recorded by RESCO remained at low levels, showing only a few avalanches/day. Poor visibility prevented daily visual observations from the city of Colima, but sporadic observations from sites near the volcano (Yerbabuena and La Joya) have shown strong fumarolic activity (mainly vapor and a small grayish plume) and continued growth of the dome extrusion.

On 6 June between about 0000 and 0200, a tremor episode was clearly recorded by station EZV7 (at Volcancito, ~1 km NE of the summit), but was barely detectable at other stations. Activity then returned to previous levels. A second tremor episode, much stronger and clearly recorded by several stations, occurred between about 1800 and 2100, after which seismicity again returned to relative quiet. The activity was interpreted as probably being of phreatic origin, given recent rainfall in the region. Witnesses about 13 km from the volcano (in the Tonila area) reported conspicuous incandescence at the crater.

A third seismic episode, on 8 June between about 2000 and 2200, consisted of four large, complex shallow earthquakes followed by almost monochromatic harmonic tremor. The caretaker at nearby La Joya reported hearing four explosions followed by strong sustained whistling. On 9 June, a few small closely-spaced B-type earthquakes seemed to mark the onset of another tremor episode, but it did not materialize and no further tremor activity had been recorded as of 13 June.

During the evening of 9 June, there was an increase in both the number and duration of avalanche events, which remained of small magnitude. Long-duration avalanches continued as of 13 June, but their numbers had decreased. Geophysicists noted that the increased number and duration of avalanches on 9 June was similar to that observed before the 16 April dome collapse. No deep seismicity, indicating stress at depth, has been detected, but the tremor, not previously observed, suggested changes in activity requiring careful monitoring.

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

Information Contacts: F. Alejandro Nava, Francisco Núñez-Cornú, Gilberto Ornelas-Arciniega, Ariel Ramírez-Vázquez, G.A. Reyes-Dávila, Hector Tamez, and R. García, CICT, Universidad de Colima; Z. Jiménez, I. Yokoyama, and S. de la Cruz-Reyna, UNAM.


Deception Island (Antarctica) — May 1991 Citation iconCite this Report

Deception Island

Antarctica

63.001°S, 60.652°W; summit elev. 602 m

All times are local (unless otherwise noted)


Stronger earthquakes; anomalous water temperature in caldera center

"Spanish-Argentine volcanological, geophysical, and geodetic scientists visited Deception Island during the 1990-91 austral summer (28 November 1990-13 March 1991) to provide measurements of the background activity. The present activity generally has remained unchanged from previous years.

"A digital microseismic network was installed to record the local and regional seismic activity for 3 months (figure 3). On 14 January, a M 3.2 earthquake was recorded on the NE sector of the island. After this event the seismic activity changed dramatically compared to that recorded during the previous 4 summers, increasing in magnitude and decreasing in frequency. In general, the epicenters are related to the 1970 eruption vents and they are associated with the fissure system (figure 4). Episodes of volcanic tremors were also recorded in Fumarole Bay.

Figure (see Caption) Figure 3. Daily number of seismic events recorded by a temporary digital microseismic network at Deception Island, 14 December 1990-23 February 1991. Courtesy of Ramón Ortiz.
Figure (see Caption) Figure 4. Epicenters of earthquakes (mb >1.2) recorded at Deception Island, 1 December 1990-23 February 1991. Courtesy of Ramón Ortiz.

"During the 1990-91 fieldwork, more than 300 gravimetric measurements were carried out, the magnetic map of the island was completed, and temperatures in fumaroles and hot soils were monitored. A volcanologically oriented GPS network was established and four GPS benchmarks (Argentine Station, Pendulum Cove, Fumarole Bay, and Whalers Bay) were measured with double-frequency receivers. Finally, three dry-tilt stations were installed in Telefon Bay (1970 eruption area), Crater Lake (1842 eruption sector), and Fumarole Bay.

"The Spanish Oceanographic vessel Las Palmas recorded water temperature and salinity distribution in Port Foster. An area of anomalous temperature was detected in the central part of the caldera."

Geologic Background. Ring-shaped Deception Island, one of Antarctica's most well known volcanoes, contains a 7-km-wide caldera flooded by the sea. Deception Island is located at the SW end of the Shetland Islands, NE of Graham Land Peninsula, and was constructed along the axis of the Bransfield Rift spreading center. A narrow passageway named Neptunes Bellows provides entrance to a natural harbor that was utilized as an Antarctic whaling station. Numerous vents located along ring fractures circling the low, 14-km-wide island have been active during historical time. Maars line the shores of 190-m-deep Port Foster, the caldera bay. Among the largest of these maars is 1-km-wide Whalers Bay, at the entrance to the harbor. Eruptions from Deception Island during the past 8700 years have been dated from ash layers in lake sediments on the Antarctic Peninsula and neighboring islands.

Information Contacts: R. Ortiz, Museo Nacional de Ciencias Naturales, Spain; J. Viramonte, Univ Nacional de Salta, Argentina; R. Soto, Real Instituto y Observatorio de la Armada, Spain.


Etna (Italy) — May 1991 Citation iconCite this Report

Etna

Italy

37.748°N, 14.999°E; summit elev. 3320 m

All times are local (unless otherwise noted)


Strong degassing

Nearly continuous degassing was observed ... on 24 May. Northeast Crater's active vent was slightly incandescent and weakly emitting gas. Normal degassing, with sporadic rumbling, occurred at La Voragine, whose elliptical vent E of the central crater floor had reopened. The floors of Bocca Nuova and Southeast Crater were not visible due to their strong degassing.

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

Information Contacts: H. Gaudru, EVS, Switzerland; Franco Emmi, Etna guide.


Galeras (Colombia) — May 1991 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


More seismic events but lower energy release; thermal activity remains moderate

The number of seismic events (high-frequency, low-frequency, and long-period) increased during May, while seismic energy release and reduced displacement decreased from April values (figures 40 and 41). The high-frequency activity (M 0.5-1.9) was centered W of the crater at 2-8 km depth. Tremor episodes were less frequent and had lower reduced displacements than in April. The tiltmeter 0.9 km E of the crater (Crater Station) continued to show deformation, with 20 µrad inflation (tangential component) in May, for a total inflation since September of 102 µrad. Other stations showed oscillations or only very low cumulative inflation.

Figure (see Caption) Figure 40. Daily number of high-frequency events (bottom) and energy release (top) at Galeras, May 1991. Courtesy of INGEOMINAS.
Figure (see Caption) Figure 41. Daily number of long-period events (bottom) and reduced displacement (top) at Galeras, May 1991. Courtesy of INGEOMINAS.

SO2 flux, measured by COSPEC, varied between low and moderate levels. Fumarole temperatures in Besolima fissure continued to decrease (436°C in May compared to 468°C in April), while temperatures remained fairly constant at Deformes (254°C compared to 250-265°C since December 1990) and Calvache (89°C compared to 88-92°C since December 1989).

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

Information Contacts: INGEOMINAS-OVP.


Gede-Pangrango (Indonesia) — May 1991 Citation iconCite this Report

Gede-Pangrango

Indonesia

6.77°S, 106.965°E; summit elev. 3008 m

All times are local (unless otherwise noted)


Brief earthquake swarm

Three shocks were felt (intensities I-III) on 30 April. Seismicity later returned to normal levels (10-15 events/day) during the second week of May (table 1).

Table 1. Number of earthquakes at Gede, May 1991. Courtesy of VSI.

Dates Deep Volcanic (VT) Shallow Volcanic Tectonic
01-04 May 1991 22 51 47
05-11 May 1991 197 635 9
12-18 May 1991 8 16 20
19-25 May 1991 23 8 9
26-31 May 1991 9 8 13

Geologic Background. Gede volcano is one of the most prominent in western Java, forming a twin volcano with Pangrango volcano to the NW. The major cities of Cianjur, Sukabumi, and Bogor are situated below the volcanic complex to the E, S, and NW, respectively. Gunung Pangrango, constructed over the NE rim of a 3 x 5 km caldera, forms the high point of the complex at just over 3000 m elevation. Many lava flows are visible on the flanks of the younger Gunung Gede, including some that may have been erupted in historical time. The steep-walled summit crater has migrated about 1 km NNW over time. Two large debris-avalanche deposits on its flanks, one of which underlies the city of Cianjur, record previous large-scale collapses. Historical activity, recorded since the 16th century, typically consists of small explosive eruptions of short duration.

Information Contacts: W. Modjo, VSI.


Guallatiri (Chile) — May 1991 Citation iconCite this Report

Guallatiri

Chile

18.42°S, 69.092°W; summit elev. 6071 m

All times are local (unless otherwise noted)


Strong fumarolic activity

Two strongly active zones of fumaroles were observed during a summit visit on 2 November 1990. The more intense fumaroles, 80 m below the . . . summit, produced a plume 200 m high accompanied by a jet-engine noise. Some boiling mud pools were also seen. The second zone, on the S side of the volcano at ~3,000 m elev, contained about 10 fumaroles. The volcano was otherwise snow-covered.

Geologic Background. One of northern Chile's most active volcanoes, Volcán Guallatiri is a symmetrical ice-clad stratovolcano at the SW end of the Nevados de Quimsachata volcano group. It lies just W of the border with Bolivia and is capped by a central dacitic dome or lava complex, with the active vent situated on its S side. Thick lava flows are prominent on the lower N and W flanks of the andesitic-to-rhyolitic volcano. Minor explosive eruptions have been reported since the beginning of the 19th century. Intense fumarolic activity with "jet-like" noises continues, and numerous solfataras extend more than 300 m down the W flank.

Information Contacts: P. Vetsch and R. Haubrichs, SVG, Switzerland.


Irazu (Costa Rica) — May 1991 Citation iconCite this Report

Irazu

Costa Rica

9.979°N, 83.852°W; summit elev. 3432 m

All times are local (unless otherwise noted)


Tectonic earthquake swarm

A large swarm of tectonic earthquakes was recorded just S of the crater from 2 January through the end of February. On 25 May, a rapid increase in the number of tectonic earthquakes marked the start of a second swarm in the same zone. A shock located about 1 km E of the crater was felt on 28 May (M 3.5), and two others centered near the crater were felt on 5 June at 0534 (M 3.5) and 0540 (M 3.2). Scientists believe that the seismicity may represent reactivation of the fault zone involved in the M [7.6] earthquake that occurred about 90 km ESE on 22 April. No changes in surface activity at the volcano were reported.

Geologic Background. Irazú, one of Costa Rica's most active volcanoes, rises immediately E of the capital city of San José. The massive volcano covers an area of 500 km2 and is vegetated to within a few hundred meters of its broad flat-topped summit crater complex. At least 10 satellitic cones are located on its S flank. No lava flows have been identified since the eruption of the massive Cervantes lava flows from S-flank vents about 14,000 years ago, and all known Holocene eruptions have been explosive. The focus of eruptions at the summit crater complex has migrated to the W towards the historically active crater, which contains a small lake of variable size and color. Although eruptions may have occurred around the time of the Spanish conquest, the first well-documented historical eruption occurred in 1723, and frequent explosive eruptions have occurred since. Ashfall from the last major eruption during 1963-65 caused significant disruption to San José and surrounding areas.

Information Contacts: R. Barquero, ICE; Mario Fernández, Red Sismológica Nacional (RSN), Univ de Costa Rica; ACAN news service, Panamá City, Panamá.


Kavachi (Solomon Islands) — May 1991 Citation iconCite this Report

Kavachi

Solomon Islands

8.991°S, 157.979°E; summit elev. -20 m

All times are local (unless otherwise noted)


Continued explosions from new island

Pilots from Solomon Islands Airways reported that "the volcano is still active and increasing in size, though slowly" as of 14 June. Photographs taken on 12 May (by Rod Marsland, a Rabaul-based pilot) show the island to have been ~110 m in diameter, with a 15-m-diameter crater (assuming a height of 25 m based on an average of several visual estimates). Lava was being ejected to 30 m height in the photos. The new island's exact location remains uncertain.

Geologic Background. Named for a sea-god of the Gatokae and Vangunu peoples, Kavachi is one of the most active submarine volcanoes in the SW Pacific, located in the Solomon Islands south of Vangunu Island. Sometimes referred to as Rejo te Kvachi ("Kavachi's Oven"), this shallow submarine basaltic-to-andesitic volcano has produced ephemeral islands up to 1 km long many times since its first recorded eruption during 1939. Residents of the nearby islands of Vanguna and Nggatokae (Gatokae) reported "fire on the water" prior to 1939, a possible reference to earlier eruptions. The roughly conical edifice rises from water depths of 1.1-1.2 km on the north and greater depths to the SE. Frequent shallow submarine and occasional subaerial eruptions produce phreatomagmatic explosions that eject steam, ash, and incandescent bombs. On a number of occasions lava flows were observed on the ephemeral islands.

Information Contacts: P. de Saint-Ours, RVO.


Kilauea (United States) — May 1991 Citation iconCite this Report

Kilauea

United States

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

All times are local (unless otherwise noted)


E rift lava continues to flow through tubes into the ocean

Lava . . . continued to flow into the sea at two sites on the W side of the flow field (figure 79). More than 95% of the lava advanced through the Wahaula tube system, which divided a few hundred meters from the coast and fed the W and E entry points in the Poupou area. The W Poupou entry has been persistently explosive, continuing to throw tephra onto a large littoral cone on the old sea cliff. Growth of the littoral cone halted in May as erosional mechanisms (weather and cliff collapse) kept pace with explosive activity at the lava/sea interface. Below the old sea cliff, the W entry had built a small bench that extended <10-15 m into the ocean and was easily broken up by high surf. The E branch of the tube continued to feed the E Poupou entry points, which in previous months had built a sizeable 2-level bench below the old sea cliff. Throughout May, there were at least two major entry points off this bench. In early May, fluid lava flows broke out onto the E bench from its junction with the old sea cliff, covering the W side of the bench and entering the ocean. Successive overflows and inflation (perhaps caused by lava underplating) continued to build the lower bench, and by the end of the month it was within 1-2 m of the upper bench.

Figure (see Caption) Figure 79. Lava produced by Kilauea's Kupaianaha vent, 1983-91. Arrows indicate flow in tubes and crosses at the coast mark sites where lava was entering the ocean in May 1991. Surface flows are shown above the tube's E and W branches. Courtesy of HVO.

Small lava flows broke out during May from the Wahaula tube between ~180 m (600 ft) elevation and the flat area near the coast. Two large flows were active. One (Waiaka) moved downslope atop the Wahaula tube in April, turning E off the tube near the coast and entering the ocean 17 April-2 May. This flow's activity declined during the first 2 weeks in May, and the flow was stagnant by the 16th. In mid-May, a new (Paradise) flow broke away from the Wahaula tube between 150 and 180 m elevation (500-600 ft) and established a new tube to the E. By the end of May, this flow was entering the ocean at the same site as the Waiaka flow.

A lava pond remained in the bottom of Pu`u `O`o crater through May. Kupaianaha's lava pond remained completely crusted over. Fume from the pond area diminished significantly, and the primary area of degassing shifted from the Kupaianaha shield area to a skylight in the tube system near 620 m (2,050 ft) elevation. In early May, all of the skylights along the Wahaula tube overflowed, closing some of those at lower elevations. The upper skylights remained open, and observations of times required for logs thrown into the upper skylight to reach the lower skylight yielded lava velocities of 1.4 m/s.

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

Information Contacts: T. Moulds, HVO.


Langila (Papua New Guinea) — May 1991 Citation iconCite this Report

Langila

Papua New Guinea

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

All times are local (unless otherwise noted)


Ash emission resumes; steady glow

"After 7 months of quiescence, Crater 3 was reactivated. Resumption of activity, which started on 16 May, was manifested by the release of moderately thick white-to-grey vapour clouds with occasional blue vapours, and the recording of explosion earthquakes (2-20/day). After 18 May, deep rumbling noises and/or loud Vulcanian explosions were heard at the Cape Gloucester observation post . . . and light ashfalls occurred on the NW flank of the volcano. A weak steady red glow was observed over this crater at the end of the month.

"Activity at Crater 2 . . . did not seem to be affected. This crater kept on releasing moderate to weak emissions of white vapour and displayed a steady weak night glow."

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

Information Contacts: D. Lolok and P. de Saint-Ours, RVO.


Lascar (Chile) — May 1991 Citation iconCite this Report

Lascar

Chile

23.37°S, 67.73°W; summit elev. 5592 m

All times are local (unless otherwise noted)


High crater temperatures detected by satellite

On 8 January, radiant flux from the crater was near the highest levels since 1984, as demonstrated by Open Univ researchers using data from Landsat TM bands 5 and 7 (1.55-1.75 and 2.08-2.35 µm wavelength, respectively) (figure 8). The January images are the third in a set of three night images that have been used to provide improved estimates of radiated power output at Lascar. Previous estimates were based on daylight images (Glaze and others, 1989). No reflected sunlight is mingled with the thermal signal in night images, yielding more reliable thermal radiance values.

Figure (see Caption) Figure 8. Spectral radiance from Lascar measured in 2 short-wavelength infrared bands, 2 December 1984-8 January 1991. Solid line, Landsat TM band 7 (2.08-2.35 µm); dashed line, Landsat TM band 5 (1.55-1.75 µm). Courtesy of D. Rothery and C. Oppenheimer.

The following is from D. Rothery and C. Oppenheimer. "Two of the night images are shown in figure 9. The 12 November 1989 image shows a strong equidimensional radiant anomaly in a position that corresponds to the lava dome, with some isolated radiant pixels just beyond the edges that are probably sites of fumaroles. The 26 March 1990 image shows a much reduced radiant anomaly, following the 20 February 1990 explosive eruption.

Figure (see Caption) Figure 9. Night images of Lascar's active dome on 12 November 1989 (left) and 26 March 1990 (right), recorded at 2.08-2.35 µm wavelengths (Landsat TM band 7). N is toward the top. The individual pixels are ~30 m across. An image recorded on 8 January 1991 is almost identical to the 12 November 1989 image. Courtesy of D. Rothery and C. Oppenheimer.

"Field observations at the summit of Lascar on 23-24 March and 4 April 1990 showed that there were sites of incandescence over regions of the collapsed dome, and that some fumaroles elsewhere were also incandescent. Temperatures of up to 940°C were estimated by the use of an infrared thermometer.

"The most recent image (8 January 1991, not shown here) is almost indistinguishable from the 12 November 1989 image, which suggests a return to earlier conditions."

Reference. Glaze, L.S., Francis, P.W., and Rothery, D.A., 1989, Measuring Thermal Budgets of Active Volcanoes; Nature, v. 338, p. 144-146.

Geologic Background. Láscar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters. Prominent lava flows descend its NW flanks. An older, higher stratovolcano 5 km E, Volcán Aguas Calientes, displays a well-developed summit crater and a probable Holocene lava flow near its summit (de Silva and Francis, 1991). Láscar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires.

Information Contacts: D. Rothery and C. Oppenheimer, Open Univ.


Lewotobi (Indonesia) — May 1991 Citation iconCite this Report

Lewotobi

Indonesia

8.542°S, 122.775°E; summit elev. 1703 m

All times are local (unless otherwise noted)


Ash emission follows increased seismicity

Ash was erupted to 800 m height, and deposited to 7 km NE and 4 km NW, on 11-13 May. Gas emission continued through the end of May, with 84 emission events recorded during the last week. Twelve shallow and seven deep volcanic earthquakes were also recorded during the last week in May.

Geologic Background. The Lewotobi "husband and wife" twin volcano (also known as Lewetobi) in eastern Flores Island is composed of the Lewotobi Lakilaki and Lewotobi Perempuan stratovolcanoes. Their summits are less than 2 km apart along a NW-SE line. The conical Lakilaki has been frequently active during the 19th and 20th centuries, while the taller and broader Perempuan has erupted only twice in historical time. Small lava domes have grown during the 20th century in both of the crescentic summit craters, which are open to the north. A prominent flank cone, Iliwokar, occurs on the E flank of Perampuan.

Information Contacts: W. Modjo, VSI.


Lokon-Empung (Indonesia) — May 1991 Citation iconCite this Report

Lokon-Empung

Indonesia

1.358°N, 124.792°E; summit elev. 1580 m

All times are local (unless otherwise noted)


Increased gas emission, then ash eruption

Gas emissions to 450 m height were observed during the morning and afternoon of 10 May. One week later (17-18 May), ash was erupted to 200-400 m height. Seismicity then decreased, with one deep and three shallow volcanic earthquakes recorded during the last week of May, down from six deep and nine shallow events the second week of the month.

Geologic Background. The twin volcanoes Lokon and Empung, rising about 800 m above the plain of Tondano, are among the most active volcanoes of Sulawesi. Lokon, the higher of the two peaks (whose summits are only 2 km apart), has a flat, craterless top. The morphologically younger Empung volcano to the NE has a 400-m-wide, 150-m-deep crater that erupted last in the 18th century, but all subsequent eruptions have originated from Tompaluan, a 150 x 250 m wide double crater situated in the saddle between the two peaks. Historical eruptions have primarily produced small-to-moderate ash plumes that have occasionally damaged croplands and houses, but lava-dome growth and pyroclastic flows have also occurred. A ridge extending WNW from Lokon includes Tatawiran and Tetempangan peak, 3 km away.

Information Contacts: W. Modjo, VSI.


Manam (Papua New Guinea) — May 1991 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)


Ash ejection declines to weak vapor emission

". . . Manam has returned to the low non-erupting pattern displayed since early 1989. Both Main and Southern Craters released thin white vapour emissions. Grey ash-laden clouds commonly rose over Southern Crater until 20 May, associated with weak rumbling noises, presumably due to rockfalls within that crater. No night glow was reported from either crater. Tiltmeter measurements showed a slight radial inflation of ~1 µrad."

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: D. Lolok and P. de Saint-Ours, RVO.


Merapi (Indonesia) — May 1991 Citation iconCite this Report

Merapi

Indonesia

7.54°S, 110.446°E; summit elev. 2910 m

All times are local (unless otherwise noted)


Continued seismicity but lava dome unchanged

Seismic activity remained unchanged, with three volcanic earthquakes recorded during the first week in May, and seven during the last week in May. No changes were visible at the summit dome.

Geologic Background. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities.

Information Contacts: W. Modjo, VSI.


Obituary Notices (Unknown) — May 1991 Citation iconCite this Report

Obituary Notices

Unknown

Unknown, Unknown; summit elev. m

All times are local (unless otherwise noted)


Deaths of three volcanologists (Maurice and Katia Krafft, Harry Glicken) at Unzen

Volcanology has lost three of its most valuable professionals and our network has lost three of our most faithful contributors. Maurice and Katia Krafft, 45 and 44, were natives of Alsace who blended art and science in unique ways. They were famous not only for their superb photography and books, but for the enthusiasm and humor that made friends for them throughout the world. Always a close team, they were scholarly, selective collectors of volcanological literature and art. They had recently compiled guidebooks to the Comores and Zaire, a history of volcanology, a beautiful book of still photographs, and an informative IAVCEI video on volcanic hazards.

Harry Glicken, 33, was a Californian working as a post-doctoral fellow at Tokyo Metropolitan University. His study of the 1980 debris avalanche at Mt. St. Helens was a landmark. His brief but geographically diverse research career took him to Indonesia, Alaska, the Caribbean, and Japan, where he worked on the 1888 Bandai eruption, and most recently on pyroclastic surge deposits from Oshima volcano. All three of these fine people had much yet to give to volcanology, and we mourn their loss.

Geologic Background. Obituary notices for volcanologists are sometimes written when scientists are killed during an eruption or have had a special relationship with the Global Volcanism Program.

Information Contacts:


Ontakesan (Japan) — May 1991 Citation iconCite this Report

Ontakesan

Japan

35.893°N, 137.48°E; summit elev. 3067 m

All times are local (unless otherwise noted)


Earthquake swarms and tremor; renewed steam emission from 1979 vent

Many earthquakes and tremor episodes have been detected by a seismometer near the volcano since April, bringing seismicity to its highest levels since the start of regular seismic monitoring in 1988. Earthquake swarms were recorded on 20, 23, and 27 April, and 12 and 13 May, with tremor on 27 and 28 April, and 2 and 12-16 May (figure 8). In mid-May, steam began to emerge from a vent formed in the last eruption (in 1979) that had remained quiet since soon after the eruption ended. Similar seismicity continued in June, and as of the 19th, 170 earthquakes and eight tremor episodes had been recorded.

Figure (see Caption) Figure 8. Daily number of earthquakes (top) and tremor episodes (bottom) at On-take, January-May, 1991.

Geologic Background. The massive Ontakesan stratovolcano, the second highest volcano in Japan, lies at the southern end of the Northern Japan Alps. Ascending this volcano is one of the major objects of religious pilgrimage in central Japan. It is constructed within a largely buried 4 x 5 km caldera and occupies the southern end of the Norikura volcanic zone, which extends northward to Yakedake volcano. The older volcanic complex consisted of at least four major stratovolcanoes constructed from about 680,000 to about 420,000 years ago, after which Ontakesan was inactive for more than 300,000 years. The broad, elongated summit of the younger edifice is cut by a series of small explosion craters along a NNE-trending line. Several phreatic eruptions post-date the roughly 7300-year-old Akahoya tephra from Kikai caldera. The first historical eruption took place in 1979 from fissures near the summit. A non-eruptive landslide in 1984 produced a debris avalanche and lahar that swept down valleys south and east of the volcano. Very minor phreatic activity caused a dusting of ash near the summit in 1991 and 2007. A significant phreatic explosion in September 2014, when a large number of hikers were at or near the summit, resulted in many fatalities.

Information Contacts: JMA.


Pinatubo (Philippines) — May 1991 Citation iconCite this Report

Pinatubo

Philippines

15.13°N, 120.35°E; summit elev. 1486 m

All times are local (unless otherwise noted)


Major stratospheric cloud, pyroclastic flows, and new summit caldera; >300 killed by eruption and typhoon

After more than 2 months of increasing seismicity, deformation, and emission of small plumes, a series of strong explosions culminated in one of the largest eruptions of this century. The 15-16 June climactic phase lasted more than 15 hours, sending tephra to 30 km altitude, generating voluminous pyroclastic flows, and leaving a small caldera in the former summit region. Ten days later, the aerosol cloud formed a nearly continuous band that stretched 11,000 km from Indonesia to Central Africa. Timely evacuations saved many lives, but the combined effects of the eruption and a typhoon killed more than 300 people.

Figure (see Caption) Figure 4. Map of southern Luzon Is., showing some towns and river valleys.

Minor activity, April-May. Renewed activity was signaled by an explosion on 2 April, at the E end of Pinatubo's geothermal area, about 1.5 km NW of the summit (see 16:4). The explosion devastated about 1 km2 of forested land, stripped leaves and vegetation over several square kilometers, and ejected small steam/ash clouds, depositing ash 10 km away. About 2,000 people were evacuated from a zone of 10-km radius. After the explosion, a line of new fumaroles, roughly 1 km long with six main vents, had developed. Emissions, voluminous and at extremely high pressure, were carried W onto a zone of dead and dying vegetation. Respiratory and eye irritation forced about 5,000 W-flank residents to leave the area.

A seismometer installed on 5 April recorded 50-90 events/day through 10 May. Earthquakes (located beginning 6 May) were dominantly centered 4-8 km NW of the summit (figure 5) at 3-6 km depth, and had magnitudes of 0.1-1.5 (averaging about M 1.0).

Figure (see Caption) Figure 5. Epicenters of earthquakes (crosses) recorded near Pinatubo (dotted outline), 6-24 May (top), 25 May-5 June (middle), and 6-9 June (bottom) 1991. Courtesy of David Harlow.

Increased activity, late May-early June. Emissions from the vents increased in volume, with two large pulses observed on 25 and 26 May. Some ash was reported. SO2 flux, measured by COSPEC, rose from 500 t/d on 13 May to 5,000 t/d on 28 May, but dropped again to 1,700 t/d on 30 May and 1,800 t/d on 3 June. Seismicity continued slightly NW of the fumaroles (at 2-6 km depth), and an increasing number of earthquakes were recorded directly beneath the fumaroles (at 0-2 km depth) at the end of May. A "blast event" during the evening of 3 June produced ash and was immediately followed by harmonic tremor lasting 30 minutes. A similar tremor event was recorded the next day at around 1200. The SO2 flux had dropped to 280 t/d by 4 June.

Increased earthquake amplitudes and more frequent tremor were noted in early June. PHIVOLCS issued an Alert Level 3 announcement (indicating a possible major pyroclastic eruption within 2 weeks) on 5 June. Geologists interpreted the shallow seismicity and harmonic tremor to be caused by the upward movement of magma, and the drop in gas flux to suggest a blockage of escaping gas and an accompanying pressure buildup.

Seismicity increased over the next few days, from about 1,000 to 2,000 recorded earthquakes/day, associated with 25 microradians of tilt recorded on the upper E flank. Most epicenters were just NW of the summit. An explosion at 1640 on 7 June from the main vent near the center of the line of fumaroles (at the head of the Maronut River) ejected ash to 8,000 m height. The explosion occurred about 40 minutes into an hour-long episode of harmonic tremor. At 1700, PHIVOLCS announced an increase to Alert Level 4 (eruption possible within 24 hours) and ordered the evacuation of an area up to 21 km from the summit. About 12,000 residents were evacuated (from Zambales, Tarlac, and Pampanga Provinces).

Ash emission continued the next day, producing plumes about 5,000 m high and depositing ash to 25 km W. Helicopter reconnaissance in the morning confirmed the extrusion of a lava dome (100 x 60 m, and 30 m high) near the main vent on the volcano's N flank. The press reported that ash emission was continuing on 9 June (table 1) from two craters, with ash falling as far as the South China Sea (~35 km W). Seismographs near the volcano recorded continuous harmonic tremor.

Table 1. Eruptive episodes from Pinatubo, 9-17 June 1991. Times of eruption onsets are from PHIVOLCS and the USGS; times of initial satellite observations of eruptive episodes are shown in the second column. Plume altitudes are from NOAA. Altitudes given in the text are generally ground-based, and often higher than the NOAA estimates. Satellite data were compiled by James Lynch, NOAA/NESDIS, based on analysis of visible/infrared weather satellite imagery. Data in this table are very preliminary and will change as analyses of ground and satellite observations continue.

Date Eruption Time Detection Time Maximum Plume Altitude Direction of Movement Horizontal Extent (time after eruption)
09 Jun 1991 -- 0931 2 km NW less than 1 x 104 km2 (2 hrs)
11 Jun 1991 -- 1631 3.5 km WSW less than 1 x 104 km2 (2 hrs)
12 Jun 1991 0851 0931 17-19 km WSW 5.5 x 104 km2 (8 hrs)
12 Jun 1991 2250 2331 17-19 km WSW 1.1 x 105 km2 (8 hrs)
13 Jun 1991 0840 0931 17-19 km WSW 1 x 105 km2 (6 hrs)
14 Jun 1991 1309 1331 20-22 km WSW 5 x 104 km2 (4 hrs)
14 Jun 1991 1408 1431 20-22 km WSW 6 x 104 km2 (5 hrs)
14 Jun 1991 1853 1931 23-25 km WSW 7.5 x 104 km2 (6 hrs)
14 Jun 1991 2018 Indistinguishable from 1853 eruption on satellite images.
14 Jun 1991 2321 2331 23-25 km WSW 5 x 104 km2 (3 hrs)
15 Jun 1991 0114 0131 23-25 km WSW 1.5 x 105 km2 (4 hrs)
15 Jun 1991 0220 Indistinguishable from 0114 eruption on satellite images.
15 Jun 1991 0555 0631 20-22 km WSW 1.1 x 105 km2 (3 hrs)
15 Jun 1991 0611 Indistinguishable from 0555 eruption on satellite images.
15 Jun 1991 0809 0831 20-22 km WSW 1.1 x 105 km2 (3 hrs)
15 Jun 1991 0831 Indistinguishable from 0809 eruption on satellite images.
15 Jun 1991 1027 1031 35-40 km WSW 1 x 106 km2 (12 hrs)
15 Jun 1991 1027 1031 35-40 km WSW 1.5 x 106 km2 (18 hrs)
15 Jun 1991 1027 1031 35-40 km WSW 2.2 x 106 km2 (24 hrs)
15 Jun 1991 1027 1031 35-40 km WSW 2.7 x 106 km2 (36 hrs)
Initial, strongest phase of the climactic eruption, apparent on infrared imagery until 2131; column over the volcano reached 35-40 km height; extensive ash plume at 25-30 km. Ash from this phase comprised >95% of the extensive plume.
15 Jun 1991 1117 Indistinguishable from the 1027 eruption on satellite images.
15 Jun 1991 1221 Indistinguishable from the 1027 eruption on satellite images.
15 Jun 1991 1252 Indistinguishable from the 1027 eruption on satellite images.
15 Jun 1991 1342 Indistinguishable from the 1027 eruption on satellite images.
15 Jun 1991 1342 2231 26-28 km WSW --
The second phase of the climactic eruption continued until 0231 on 16 Jun, with a ball-shaped column over the volcano.
16 Jun 1991 -- 0331 23-25 km WSW --
The third phase, smaller than the second,, was characterized by a wedge-shaped plume from the volcano; apparent on satellite imagery until 0731.
16 Jun 1991 -- 1031 5-6 km WSW 1.5 x 104 km2 (3 hrs)
16 Jun 1991 -- 1231 5-6 km WSW less than 1 x 104 km2 (2 hrs)
16 Jun 1991 -- 1431 5-6 km WSW 1.5 x 104 km2 (3 hrs)
16 Jun 1991 -- 2031 4-5 km WSW less than 1 x 104 km2 (2 hrs)
17 Jun 1991 1300 1300 3.5 km WSW less than 1 x 104 km2 (2 hrs)

The evacuation of Clark Air Base (~15 km E of the volcano) was ordered by the U.S. Air Force at 0500 on 10 June. Almost 14,500 servicemen and their families were moved to Subic Bay Naval Base (30 km SSW), while 1,500 personnel remained at Clark. Preliminary hazard maps placed Clark Air Base at the E edge of pyroclastic-flow hazard zones, and flanked by potential mudflow hazard zones. Voluminous ash-laden steam clouds were emitted on 11 June.

Initial strong explosions, 12-early 15 June. A tephra column rose to about 20 km on 12 June, as an explosive episode at 0851 signalled the start of a major pyroclastic phase. The explosions were preceded by around 12-16 hours of continuous tremor and several smaller explosions. Numerous shocks had been felt by scientists working on the volcano earlier in the morning. Pyroclastic flows advanced at least 5 km and perhaps as much as 15 km down the Maronut, O'Donnell, and Marella Rivers on the NW, N, and SW flanks of the volcano, respectively. Six hundred of the remaining 1,500 military personnel at Clark Air Base were evacuated and thousands of people fled adjacent Angeles (population 300,000). All residents within a 20-km radius of the volcano were warned to leave.

The press reported that a smaller explosion occurred at 1149, then explosive activity declined after a few hours. Prevailing winds carried the eruption plume WSW, depositing ash more than 30 km away, but ashfall also apparently occurred N of the volcano, reportedly covering an aerial gunnery range. A small rain-induced mudflow occurred in the Maronut River valley at about 1830 on 12 June.

Weather satellite images showed that the eruption plume had separated from the volcano by 1330, after reaching about 330 km length (figure 6). By 1830, winds had sheared the plume into three different layers; material at 15-18 km altitude traveling WSW at 100 km/hour; at 6-9 km altitude, W at 55 km/hour; and at 6-9 km altitude, WNW at 35 km/hour. The Nimbus-7 satellite's TOMS instrument detected a significant amount of SO2 during its pass over the area about 2.5 hours after the onset of the explosion. Aviation authorities warned aircraft to avoid the plumes and closed several air routes W of the volcano (A461, A583, B460, R77, R93, R468, and R471).

Figure (see Caption) Figure 6. Infrared image from the NOAA 10 polar-orbiting weather satellite on 15 June at about 1830, showing the massive cloud from the climactic explosive phase. Temperature estimates suggest that the main body of the plume is at about 30 km altitude, with the eruption column directly over the volcano rising to 35-40 km. The apparent boundary between sections of the cloud is probably a sampling artifact. Material NE of the volcano is probably at a lower altitude than the bulk of the cloud to the W and SW. Numerous faint bands are evident within the plume in false-color versions of the image. Courtesy of NOAA/NESDIS.

Another large explosive pulse occurred between 2250 and 2305 on 12 June, producing an eruption column that briefly rose to 25 km altitude before declining to a sustained elevation of about 20 km. Tephra fell to the W, NW, and SW, with pumice lapilli falling to 15 km distance, and coarse sand-sized tephra to more than 20 km from the volcano. A similar explosion at 0840 on 13 June lasted for 8 minutes and sent an ash column to 25 km altitude, following about an hour of long-period earthquakes. Satellite images showed large plumes extending [WSW] from the volcano after both explosions.

After a lull of about 28 hours, explosions resumed at 1309 on 14 June, ejecting tephra to 25 km altitude. Intermittent small pulses occurred at 1353 and 1408. Pyroclastic flows in the NW flank's Maronut valley extended 15 km to Sitio Ugik, site of an evacuation camp until increased shallow seismicity prompted additional warnings just before the start of the latest series of explosions. Ash fell to the S, SE, and SW. Another explosion at 1853 sent ash to 24 km altitude and additional pyroclastic flows to the NW. Strong rains during several of the explosive pulses generated mudflows in drainages where pyroclastic-flow deposits and airfall tephra had previously been emplaced.

By 14 June, 79,000 people had been evacuated, including about 15,000 from Clark Air Base. Civil Defense officials reported that four people had been killed, 24 injured, and four were missing in the series of explosions.

A small explosion at 2018 on 14 June sent an ash cloud to 6 km. A period of harmonic tremor preceded a strong explosion at 2321 that produced a column to >20 km [see also 16:6]. Ashfall was reported in San Marcelino (25 km SW) and San Narciso (30 km WSW). Explosions on 15 June at 0114 and about 0220 produced pyroclastic flows that moved down the SW flank.

Climactic explosions, 15-16 June. An explosion at 0555 on 15 June fed a 20-22 km-high ash column [see also 16:6], marking the onset of strong sustained activity that included the climactic explosions and lasted until early 16 June. Effects of the eruption were exacerbated by heavy rains and strong winds from typhoon Yunya. Much of the summit region was removed by explosions or collapse, leaving a caldera 2-3 km in diameter centered slightly north of the former summit.

Pyroclastic flows generated by the first 15 June explosion extended 8-10 km down the N, NNE, NNW flanks. Additional explosions were reported at 0611, 0809, and 0831. Before the strongest activity began, PHIVOLCS expanded the radius of the official danger zone from 30 to 40 km and expressed concern about the possibility of a caldera-forming eruption. The expanded danger zone included Clark Air Base, Subic Naval Base, and their neighboring cities of Angeles and Olongapo. Additional evacuees brought the total to about 200,000. Several thousand military dependents were sent back to the United States.

Satellite data suggested that the climactic phase began with an explosion detected by a nearby barograph at 1027, and continued with recorded explosions at 1117, 1221, and 1252, although ground reports indicated that the strongest activity started with an explosion at 1342 (table 1). A column remained fixed over the volcano through 2131, feeding a massive cloud (figure 7). Comparison of satellite-derived eruption column temperatures with atmospheric temperature profiles from nearby radiosondes yielded an altitude of 25-30 km as the cloud spread WSW toward mainland Asia, and elevations of 35-40 km for the eruption column over the volcano. The maximum altitude of a plume can be underestimated by this technique if its temperature has not fully equilibrated with that of the surrounding air, or if more diffuse material extends above the plume's densest region. Satellite data suggest that more than 95% of the cloud was produced by this 12-hour phase. Visible-band images showed ejection of very dark-colored material throughout the day (from 0631 until 1631), in contrast to the light-colored plumes generated by other phases of the eruption. Noticeably less violent activity, seen on images from 2231 on 15 June until 0231 on 16 June, sustained a ball-shaped cloud over Pinatubo at 26-28 km altitude. Activity had declined further during a third period, from 0331 through 0731, when a wedge-shaped plume extended from the volcano.

Figure (see Caption) Figure 7. Infrared image from the NOAA 10 polar orbiting weather satellite on 15 June at about 1830, showing the massive cloud from the climactic explosive phase. Temperature estimates suggest that the main body of the plume is at about 30 km altitude, with the eruption column directly over the volcano rising to 35-40 km. The apparent boundary between sections of the cloud is probably a sampling artifact. Material NE of the volcano is probably at lower altitude than the bulk of the cloud to the W and SW (figure 7-19). Numerous faint concentric bands are evident within the plume in false-color versions of the image.

The bulk of the tephra fell to the SE, S, and SW, but airfall distribution was complicated by the typhoon's winds. Ash was carried by the typhoon to Palawan Island, 500 km SSW of the volcano. The press reported slight ashfall 150 km S (in Batangas Province) and clumps of mud fell on Clark Air Base, Angeles, and the volcano's W flank. Some falling pumice was reportedly apricot-sized. Pumice the size of marbles fell 33 km SSW (at Olongapo) where tephra fall reached 15-30 cm and more than 30 injuries and some deaths were reported. The cloud darkened Manila by 1545, 3 hours before its usual nightfall, although most ashfall amounts there were less than about 1 cm [see also 16:6].

The stratospheric cloud expanded rapidly WSW, and by 1030 the next day, its leading edge had reached the Bangkok area, more than 2,000 km away (figure 8). Preliminary Nimbus-7 satellite data showed very high concentrations of SO2 over a broad area (figure 9), with a total mass that appeared to be approximately double that of the 1982 injection from El Chichón. Light ashfalls were reported in southern Vietnam (from Da Nang to the Mekong Delta, 1,400 km W-1,800 km WSW), northern Borneo (Sabah and Sarawak, 1,000-2,000 km SW), and Singapore (2,500 km SW). By 23 June, a nearly continuous zone of enhanced SO2 as much as 30° wide extended from south of Indochina about 11,000 km to central Africa (figure 10). A small zone of apparent aerosol material had reached about 40°W. [See the Atmospheric Effects chapter for more information about the stratospheric cloud].

Figure (see Caption) Figure 8. Sketch of the major eruption cloud from Pinatubo as seen on satellite imagery on 16 June at about 1030, about 21 hours after the onset of strongest activity, and 1 hour before the SO2 data in figure 7-20. Courtesy of SAB.
Figure (see Caption) Figure 9. Preliminary SO2 data from the Total Ozone Mapping Spectrometer on the Nimbus-7 satellite, showing the major eruption cloud from Pinatubo on 16 June at about 1130, 22 hours after the start of the climactic explosions. Each number or letter represents the average SO2 value within an area 50 km across. 0 = 10-35 milliatmosphere-cm (100-350 ppm-m), 1 = 36-60 matm-cm, 2 = 61-85 matm-cm, etc.; 9 is followed by A, B, etc. Data were lost in the barred zone. Courtesy of Scott Doiron.
Figure (see Caption) Figure 10. Preliminary SO2 data from the Total Ozone Mapping Spectrometer on the Nimbus-7 satellite, showing the major eruption cloud from Pinatubo on 23 June, eight days after the climactic phase. The main body of the cloud, 11,000 km long, has reached central Africa, but a smaller advance segment apparently extended over the eastern Atlantic Ocean, bisected by the 30°W meridian. Only values > 18 matm-cm are shown. Highest values within the dense cloud reached about 75 matm-cm (over Saudi Arabia). Courtesy of Scott Doiron.

Smaller explosions continued during the next several days, but the strongest activity appeared to have ended, and people began to return to their homes. PHIVOLCS reported three periods of ash emission accompanied by tremor on 17 June. Satellite data revealed a small explosion at 1300 and a column to 5-6 km altitude was observed.The Worldwide Standardized Seismic Net detected shallow earthquakes near Pinatubo on 15 June at 1539 (M 4.9), 1831 (M 4.4), 1841 (M 5.4), 1911 (M 4.6), 1915 (M 5.5), and 2026 (M 4.7), on 16 June at 0349 (M 4.9), 0359 (M 4.8), 1008 (M 5.6), 1458 (M 4.9), 1751 (M 5.1), and 2127 (M 4.9), on 17 June at 0441 (M 5.3) and 2333 (M 4.6), and on 18 June at 1120 (M 4.6).

On 18 June geologists reported preliminary cumulative ashfall thicknesses of 15-30 cm at Clark Air Base, 15-30 cm in Olongapo, and an unconfirmed 35.5 cm in some parts of SW Luzon. At a site along the Abacan River, 37 km E of the summit, debris-flow deposits were sandwiched between a coarse basal layer and finer, sand-sized tephra. Several homes at this site had been inundated, and several others swept away by lateral stream erosion, with some resulting casualties. A similar situation was found at a second site along the Baluyot River, 34 km ESE of the summit. Several homes had been lost or buried by mud, but no deaths had occurred.

The leading edge of typhoon Yunya had reached the area by 14 June at about 2000, and strong storms began moving over the volcano at about 0500 on 15 June. The storm had weakened to light-moderate showers 24 hours later, but these persisted through the 16th. Heavy rains soaked the recently fallen tephra, adding substantially to its weight, and the wet tephra soon hardened to a concrete-like material, making it very difficult to remove. Numerous roof and building collapses resulted, and were responsible for many of the casualties from the combined effects of the eruption and typhoon. As of 19 June, the death toll had risen to more than 300.

The 15 June activity forced closure of Manila's international and domestic airports, which remained closed to arriving jet aircraft through 18 June. A limited number of outgoing flights were permitted beginning early 19 June, and propeller-driven aircraft, less vulnerable to the effects of ash clouds, offered limited air service to and from Manila. Preliminary reports indicate that [14] jets encountered ash during the eruption, most on 15 June (table 2). All landed safely, but some sustained engine and/or exterior damage.

Table 2. Preliminary summary of aircraft encounters with clouds from Pinatubo, 12-18 June 1991. Courtesy of T. Casadevall. [Including additional encounters reported in BGVN 16:07.]

Date Time Duration Location Comments
12 Jun 1991 -- 3 minutes Descent into Manila --
13 Jun 1991 0030 20 minutes S China Sea Electrostatic discharge on windscreen; no damage.
14 Jun 1991 early AM 15 minutes 750 km W of Pinatubo, 11 km altitude No significant damage.
14 or 15 Jun 1991 -- 29 minutes -- Two engines replaced; impact damage and ash buildup on engines.
15 Jun 1991 -- 15-20 minutes -- Flew through "heavy ash;" cockpit and cabin contaminated by ash.
15 Jun 1991 early AM -- 1,100 km W, 9 km altitude All four engines damaged.
15 Jun 1991 -- 12 minutes 10.5 km altitude Temperatures of all four engines rose and fluctuated; sparks from windows; ash hit aircraft; no significant exterior or engine damage.
15 Jun 1991 1600 -- Approach to Manila from S Vietnam Much ash in engines; exterior abrasion.
15 Jun 1991 evening -- Leaving Manila Black marks on exterior of left wing.
15 Jun 1991 2347 -- Approach to Manila from S Vietnam Ash, sulfur odor, electrostatic discharge, and blue-green light. No significant damage
16 Jun 1991 0130 25 minutes S China Sea Electrostatic discharge on windscreen; no damage.
16 Jun 1991 0310 30 minutes S China Sea Electrostatic discharge on windscreen; no damage.
17 Jun 1991 -- -- -- Engine 3 shutdown; heavy ash buildup in engines.
18 Jun 1991 0200 -- 11 km altitude Engine 1 stalled, engine 4 lost power; descended to 9 km to restart. Engine 1 replaced.

Further References. Pinatubo Volcano Observatory Team, 1991, Lessons from a major eruption: Mt. Pinatubo, Phillipines: EOS, v. 72, p. 545, 552-3, 555.

Woods, A. and Self, S., 1992, Thermal disequilibrium at the top of volcanic clouds and its effect on estimates of the column height: Nature, v. 355, p. 628-630.

Geologic Background. Prior to 1991 Pinatubo volcano was a relatively unknown, heavily forested lava dome complex located 100 km NW of Manila with no records of historical eruptions. The 1991 eruption, one of the world's largest of the 20th century, ejected massive amounts of tephra and produced voluminous pyroclastic flows, forming a small, 2.5-km-wide summit caldera whose floor is now covered by a lake. Caldera formation lowered the height of the summit by more than 300 m. Although the eruption caused hundreds of fatalities and major damage with severe social and economic impact, successful monitoring efforts greatly reduced the number of fatalities. Widespread lahars that redistributed products of the 1991 eruption have continued to cause severe disruption. Previous major eruptive periods, interrupted by lengthy quiescent periods, have produced pyroclastic flows and lahars that were even more extensive than in 1991.

Information Contacts: R. Punongbayan, PHIVOLCS; R. Janda and J. Ewert, CVO; SAB; Scott Doiron, GSFC; Chris Newhall and Ellen Limburg-Santistevan, USGS Reston; David Harlow, USGS Menlo Park; T. Casadevall, USGS Denver; Nicholas Krull, FAA; Tom Fox, ICAO; NEIC; AP; UPI; Reuters.


Poas (Costa Rica) — May 1991 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Strong gas emission; rain adds water to nearly dry crater lake

Strong sulfur-gas emission continued from crater fumaroles in May. The crater lake, nearly dry since March, began to refill during the third week of May because of increased rainfall. Small pools coalesced to cover the entire crater floor, and warm mud was frequently ejected to several meters height from the center of the lake. The largest fumarole was in the crater's N sector, and other smaller ones were in the W and SE. Microseismicity decreased at the end of May and the volcano was considered by geologists to have returned to normal rainy season conditions. A new network of five digital seismometers was installed near the volcano by a joint RSN-French group.

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

Information Contacts: R. Barquero, ICE.


Rabaul (Papua New Guinea) — May 1991 Citation iconCite this Report

Rabaul

Papua New Guinea

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

All times are local (unless otherwise noted)


Continued low-level seismicity; slight uplift

"Seismicity was at a low level in May. The month's total number of earthquakes was 102 (compared to 126-140 over the last 3 months). Only five earthquakes were locatable, distributed on the NE and W sides of the caldera seismic zone. Levelling measurements on 24 May showed a slight uplift (3.5 mm at the SE end of Matupit Island)."

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

Information Contacts: D. Lolok and P. de Saint-Ours, RVO.


Rincon de la Vieja (Costa Rica) — May 1991 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)


More details on 8 May eruption and deposits

The following, from the Univ Nacional, supplements last month's report from ICE.

A phreatic eruption on 8 May ejected lake sediments and ash, and produced small mudflows. The eruption followed several low-frequency earthquakes during the night of 6-7 May, and a low-frequency earthquake with a 155-second duration at 0811 on 7 May. Reports from residents of Dos Ríos de Upala (8 km NW) and from guards at Parque Nacional Rincón de la Vieja described an accompanying explosion and a 1-km-high light-colored plume with ash that traveled NW.

Seven low-frequency microearthquakes preceded the 8 May phreatic eruption. An earthquake that lasted 120 seconds, possibly associated with a small explosion, occurred 18 minutes prior to the eruption, and low-frequency tremor began 7 minutes before it.

The sound wave of the main explosion arrived at the seismometer (6 km SW) 6 seconds after the start of the eruption signal at 1017, and the instrument was saturated for 25 seconds. The subsequent 150-second signal was interpreted to record strong degassing and the initiation of mudflows. Low-frequency harmonic tremor was recorded for 30 minutes, gradually decreasing below detection limits. The main explosion produced a gray ash cloud, 5 km high, that was carried NW. Ash was deposited to 14 km NW from this (figure 1) and the approximately 10 small (columns

Figure (see Caption) Figure 1. Map showing deposits from the 8 May 1991 phreatic eruption at Rincón de la Vieja. Site numbers correspond to cross-sections in figures 2 and 3, and table 1. Courtesy of OVSICORI.

Table 1. Field observations of 8 May 1991 mudflow deposits from Rincón de la Vieja. Sites correspond to locations in figure 1. Courtesy of OVSICORI.

Site Distance Deposit width Channel width Max. flow height Deposit description
1 7.2 km 41 m 10 m 4-6 m 1.65 m of erosion.
2 6.6 km 185 m 12 m 2-3 m ~8 m deposited.
3 7.0 km 239 m -- 4-5 m 2-60 cm of fine (2-16 mm) material.
4 16.6 km -- -- 2.15 m Blocks (to 1.5 x 2.0 m) and tree trunks (50 cm diameter); 10-50-cm mantle of fine sediment.

Mudflows traveled down the N flank (along the Quebrada Azufrosa, and Río Pénjamo), destroying two small bridges and cutting off access to the towns of Buenos Aires (~12 km NE) and Gavilán. Several smaller mudflows traveled down tributaries to the Río Azul (also to the N). Erosion occurred predominantly between 1,500 and 500 m elevation. Field observations of the mudflow deposits were made at several sites (figures 2 and 3; table 1). Park guards reported small quantities of sediment transported by the Río Colorado (S flank), but no effects on the ecosystem were observed.

Figure (see Caption) Figure 2. Cross-section of 8 May 1991 Rincón de la Vieja mudflow deposits near a bridge over the Río Azul. Site location is marked in figure 1. Courtesy of OVSICORI.
Figure (see Caption) Figure 3. Cross-section of 8 May 1991 Rincón de la Vieja mudflow deposits near a bridge over the Río Pénjamo. Site location is marked in figure 1. Courtesy of OVSICORI.

Blocks (to 40 x 50 cm) with impact craters and ejected lake sediments were found near the summit during a 9 May visit. Acidity and sediment-fall had variable impacts on nearby vegetation, ranging to complete defoliation. Fumarolic activity continued, as evidenced by a strong sulfur odor, eye irritation, and breathing difficulties near the crater. Rain collected 3 km S had a pH of 3.85.

Seismicity declined to 9 low-frequency recorded earthquakes/day (9 May), with only sporadic (1-2/day) events on later days.

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: E. Fernández S., Jorge Brenes M., V. Barboza M., and Tomás Marino H., Observatorio Vulcanológico y Sismológico de Costa Rica, Univ Nacional.


Nevado del Ruiz (Colombia) — May 1991 Citation iconCite this Report

Nevado del Ruiz

Colombia

4.892°N, 75.324°W; summit elev. 5279 m

All times are local (unless otherwise noted)


Frequent lithic ash emissions; occasional vigorous earthquake swarms

Lithic ash emissions were frequent during May, depositing material to Manizales (30 km WNW) on 1 May. Short pulses of shallow tremor were associated with the emissions. High-frequency seismicity reached very high levels during a swarm on 8 May (figure 45), which included a M 2.1 earthquake, 2.5 km N of Arenas crater at 5 km depth. A similar swarm occurred on 14 May. Low-frequency seismicity was at a moderate level in May, with peaks of vigorous seismicity on 4 days. Deformation measurements showed no significant changes. The SO2 flux was low; the monthly average was 930 t/d, compared to ~2,740 t/d in April.

Figure (see Caption) Figure 45. Daily number of seismic events (bottom) and energy release (top) at Ruiz, May 1991. Solid line, high-frequency events; dashed line, low-frequency events. Courtesy of INGEOMINAS.

Geologic Background. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.

Information Contacts: C. Carvajal, INGEOMINAS, Manizales.


Sabancaya (Peru) — May 1991 Citation iconCite this Report

Sabancaya

Peru

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

All times are local (unless otherwise noted)


Vigorous Vulcanian activity; mudflows force daily clearing of river channel

Strong Vulcanian explosions were observed during a visit on 13-19 April. The explosions, occurring every 20-30 minutes, lasted ~ 1 minute and produced 3-4-km-high, medium-gray ash clouds. Small avalanches were produced by falling blocks at the base of the eruptive columns. Quiet degassing continued between explosions. Light-gray ashfall was frequent during the visit, depositing 2 mm one night ~9.5 km SE of the summit (at Cajamarcana).

The volcano began erupting in late May 1990, reportedly ejecting ash to 7 km. By late June 1990 (15:7), activity had decreased to periodic explosions with weak ash columns 2-3 km high, but then increased slowly through November. High-frequency seismicity (>122 events recorded over one 2-week period) was usually centered ~ 10 km NE, although two earthquakes occurred under the crater. Several tremor episodes were recorded, starting in October.

The plume was black and heavy with ash during an overflight on 10 November, rising an estimated 5-8 km in distinct, but almost continuous pulses. Ash deposited on Hualca Hualca (4 km N) caused increased melting of the glaciers (estimated 20 cm of snow above the ice and berm) producing numerous mudflows. These moved down the N flank nightly, dumping an estimated 13,000 m3 of debris/day into the Majes River drainage system ~ 5 km N of the volcano. Construction crews cleared the channel daily. Airfall deposits were composed of 80% lithics and 20% glassy fragments and breadcrusted material. At one outcrop, the 1990 ash accumulations were 1 cm thick, overlying at progressively greater depth 30 cm soil, 2 cm ash, 40 cm soil, and another 2 cm ash. Eruptive activity observed on 22 December appeared about the same as it was on 10 November.

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: P. Vetsch and R. Haubrichs, SVG, Switzerland; N. Banks, CVO; Instituto Geofísico del Perú, Lima.


San Jose (Chile-Argentina) — May 1991 Citation iconCite this Report

San Jose

Chile-Argentina

33.789°S, 69.895°W; summit elev. 6070 m

All times are local (unless otherwise noted)


New fumarole field on upper S flank

A new fumarole field, 150 m below the rim on the S flank . . . was first observed in late February (figures 1 and 2). On 14 May, geologists from the Univ de Chile noted that the new activity was similar to that of earlier fumaroles associated with a small andesitic dome within the central crater.

Figure (see Caption) Figure 1.Sketch of view looking E at the San José complex, 14 May 1991. Vapor rises from within the crater and from the February 1991 fumarole field. Courtesy of O. González-Ferrán.
Figure (see Caption) Figure 2. Sketch map showing the summit region and craters of the San José complex, May 1991. Courtesy of O. González-Ferrán.

Although no earthquakes were detected at the volcano, an increase in seismicity was recorded by the Univ de Chile's seismic network throughout the roughly N-S fault zone that separates the Valle Central and the Cordillera Andina. Four events were recorded in February, 8 in March, 9 in April, and 14 in May, the largest (M 4.0 and M 3.5) on 8 and 11 April, respectively (figure 3).

Figure (see Caption) Figure 3. Sketch showing the location of San José and the epicenters of two large earthquakes, April 1991. Courtesy of O. González-Ferrán.

Geologic Background. Volcán San José lies along the Chile-Argentina border at the southern end of a volcano group that includes the Pleistocene volcanoes of Marmolejo and Espíritu Santo. The glaciated 6070-m-high Marmolejo stratovolcano is truncated by a 4-km-wide caldera, breached to the NW, that has been the source of a massive debris avalanche. San José is a 5856-m-high stratovolcano of Pleistocene-Holocene age with a broad 2 km x 0.5 km summit region containing overlapping and nested craters, pyroclastic cones, and blocky lava flows. Volcán la Engorda and Volcán Plantat, located SW of Marmolejo and NW of San Jose, have also been active during the Holocene. An 8-km-long lava flow traveled to the SW from the 1-km-wide summit crater of Espíritu Santo volcano, which overlaps the southern slope of Marmolejo. Mild phreatomagmatic eruptions were recorded from San José in the 19th and 20th centuries.

Information Contacts: O. González-Ferrán, Univ de Chile; P. Acevedo, Univ de la Frontera, Temuco.


Soputan (Indonesia) — May 1991 Citation iconCite this Report

Soputan

Indonesia

1.112°N, 124.737°E; summit elev. 1785 m

All times are local (unless otherwise noted)


Explosion sounds and incandescence; frequent seismicity

On 22-24 May... loud booming sounds and night glow were reported from the main crater. Up to 100 seismic events were recorded/6-hour period on 28 May.

Geologic Background. The Soputan stratovolcano on the southern rim of the Quaternary Tondano caldera on the northern arm of Sulawesi Island is one of Sulawesi's most active volcanoes. The youthful, largely unvegetated volcano is located SW of Riendengan-Sempu, which some workers have included with Soputan and Manimporok (3.5 km ESE) as a volcanic complex. It was constructed at the southern end of a SSW-NNE trending line of vents. During historical time the locus of eruptions has included both the summit crater and Aeseput, a prominent NE-flank vent that formed in 1906 and was the source of intermittent major lava flows until 1924.

Information Contacts: W. Modjo, VSI.


Stromboli (Italy) — May 1991 Citation iconCite this Report

Stromboli

Italy

38.789°N, 15.213°E; summit elev. 924 m

All times are local (unless otherwise noted)


More frequent explosions

The number of seismically recorded explosions increased briefly in late March and persistently from mid-April (figure 13). After mid-April, the number of earthquakes exceeding instrument saturation level decreased from an average of ~20/day since January to

Figure (see Caption) Figure 13. Average number of seismically recorded explosion events/hour at Stromboli, 15 March-15 May 1991. The mean value for the period is shown. Courtesy of M. Riuscetti.
Figure (see Caption) Figure 14. Daily number of seismometer-saturating events (lower curve); and average tremor amplitude (upper curve) at Stromboli, 15 March-15 May 1991. Courtesy of M. Riuscetti.

Volcano guides reported infrequent small explosive activity at the 3 craters during visits to the summit on 10, 15, and 16 April, and 1 May. In early May, the first complete gas sampling at Stromboli was made during an inter-explosive phase at fumaroles (410°C) on the NW rim of the active crater complex (table 1).

Table 1. Chemical composition (in volume %) of fumarolic gases from Stromboli, early May 1991. Courtesy of M. Martini.

Gas Volume %
H2O 60.29
CO2 29.68
H2S --
HCl 0.28
HF 0.041
H2 --
N2 6.90
O2 1.29
B 0.0014
Br 0.00017
CO 0.00007
NH4 0.00006
CH4 --

Local residents reported a significant increase in the number of explosions on 19 May, after several weeks of weak activity. During a visit to the summit on the evening of 21 May, frequent strong explosions were observed at craters 1 and 3, with large ejections of incandescent material. Thirty explosions were counted between 2000 on the 21st and 0600 the next day. Many ejecta fell onto the N flank's Sciara del Fuoco. Crater 2 and the small cones continuously emitted gas and vapor.

Geologic Background. Spectacular incandescent nighttime explosions at this volcano have long attracted visitors to the "Lighthouse of the Mediterranean." Stromboli, the NE-most of the Aeolian Islands, has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent horseshoe-shaped scarp formed about 5,000 years ago due to a series of slope failures that extend to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Information Contacts: M. Riuscetti, Univ di Udine; M. Martini, Univ di Firenze; H. Gaudru, Société Volcanologique Européenne (SVE), Switzerland.


Ulawun (Papua New Guinea) — May 1991 Citation iconCite this Report

Ulawun

Papua New Guinea

5.05°S, 151.33°E; summit elev. 2334 m

All times are local (unless otherwise noted)


Large gas plume and numerous weak earthquakes

"Activity remained at the low, non-erupting level displayed since January 1990, gently releasing a white vapour plume and generating an average of ~200 very small low-frequency earthquakes/day.

"An aerial inspection and ground deformation survey was carried out 14-16 May. The plume emitted by the crater, although of moderate volume, seemed rich in SO2 and could distinctly be seen stretching horizontally >40 km downwind. No significant changes were noted in summit crater morphology since the last inspection in May 1990, apart from a series of cracks on the terminal cone's upper W flank, suggesting a slight inward sagging of this side of the crater rim.

"EDM and dry tilt measurements suggest that no significant deformation has occurred over the last 12 months."

Geologic Background. The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Information Contacts: D. Lolok and P. de Saint-Ours, RVO.


Unzendake (Japan) — May 1991 Citation iconCite this Report

Unzendake

Japan

32.761°N, 130.299°E; summit elev. 1483 m

All times are local (unless otherwise noted)


41 killed by pyroclastic flow from lava dome

On 3 June a large pyroclastic flow formed near the summit of Fugen-dake cone and moved down the E flank, reaching the outskirts of Kita-Kamikoba, 3 km from the 20 May lava dome. Forty people were killed, including volcanologists Harry Glicken, and Maurice and Katia Krafft. The pyroclastic flow and accompanying fires destroyed more than 56 houses and portions of Shimabara were blanketed with wet ash. A larger pyroclastic flow, on 8 June, destroyed an additional 73 houses in Shimabara and Fukae, but no injuries were reported. On 11 June, ejecta from an explosive event, not associated with pyroclastic-flow activity, damaged houses and car windows in Shimabara. Ashfall was reported 250 km to the NE. Dome extrusion and pyroclastic-flow activity at Unzen continued as of 24 June.

Premonitory activity and small ash emission. Increased seismicity was initially centered in Chijiiwa Bay, 13 km W, in November 1989, and gradually migrated E in July-October 1990, when seismicity increased further and the first volcanic tremor was recorded. Following several earthquake swarms, including one on 13-14 November (centered 5 km W of the summit at shallow depth), the volcano erupted on 17 November, weakly emitting ash to heights of 300-400 m from two newly formed vents (Jigoku-ato and Tsukumo-jima) within existing craters roughly 650 m E of the summit (figure 17). Ash emissions, tremor, and swarm activity quickly ceased, but steam emission continued and seismicity remained at high levels. An earthquake swarm occurred on 15 January and tremor resumed on 25 January (figure 18).

Figure (see Caption) Figure 17. Map showing the distribution of the three facies of the 3 June pyroclastic flow at Unzen. Crosses represent locations of recovered bodies. Data from Kyushu and Kagoshima universities. Body locations from The Japan Times. Courtesy of JMA.
Figure (see Caption) Figure 18. Daily number of earthquakes (top) and tremor episodes (bottom) at Unzen, January-18 June 1991. Arrows represent resumption of explosive activity on 12 February and dome appearance on 20 May 1991. Courtesy of JMA.

Phreato-magmatic activity, February-May. A second eruption on 12 February produced 500-m ash plumes from a new 50-m-long line of small vents (named Byobu-iwa) 170 m WSW of Jigoku-ato crater and 500 m E of the summit. Deposits of ash and lapilli reached 30 cm thick (10 m E of the vent) but no incandescence was seen and no juvenile material was detected in the ash. Frequent small ash emissions continued from Byobu-iwa vent and seismicity remained at high levels.

In early April, ash emissions resumed at Jigoku-ato vent, which widened and began to eject bombs. By mid-April, Jigoku-ato was the site of the most intense activity. The Geographic Survey Institute detected a summit offset of 11 cm to the W on 12 April.

Juvenile volcanic glass was first recognized on 12 May, although emissions remained small. Shallow microseismicity beneath Jigoku-ato rose sharply the next day, and EDM measurements showed rapid inflation of the summit region.

Debris flows, 15 and 19 May. Heavy rains on accumulated ash deposits triggered debris flows along the Mizunashi River on 15 and 19 May that destroyed two bridges and caused the temporary evacuation of about 1,300 people from Shimabara.

Lava extrusion, 20-23 May. On 20 May, high-silica dacite (table 6) lava extrusion began in Jigoku-ato crater. By the following day large fractures had appeared and the dome had separated into four parts. Debris flows along the Mizunashi River continued; after the fourth debris flow, at 0252 on 21 May, about 1,100 people were evacuated. Water level in the river dropped following a debris flow at 0445, and people were allowed to return home at 0555.

Table 6. Chemical composition of eruptive products from Unzen. Sample 1 - block from 24 May 1991 pyroclastic flow. Sample 2 - surface of lava dome 1 June 1991. Sample 3 - pumice block from 8 June 1991 pyroclastic flow. Sample 4 - 1792 lava flow. Total Fe as Fe2O3. Analyses performed by XRF at Kyushu Univ, normalized anhydrous.

Component Sample 1 Sample 2 Sample 3 Sample 4
SiO2 65.92 66.03 66.18 66.1
TiO2 0.66 0.64 0.65 0.65
Al2O3 15.46 15.47 15.46 15.8
Fe2O3* 4.18 4.14 4.07 4.28
MnO 0.09 0.08 0.08 0.09
MgO 2.39 2.37 2.34 2.24
CaO 4.90 4.98 4.86 4.56
Na2O 3.85 3.77 3.80 3.78
K2O 2.39 2.35 2.41 2.39
P2O5 0.16 0.17 0.16 0.13
Total 100.02 100.00 100.01 100.02

The dome continued to grow, reaching about 110 m diameter and 44 m height (a few tens of meters above the crater rim) on 23 May, when material began spalling from its margins down the steep outer slopes. Large blocks, to 5 m in diameter (60-70 m3 volume), were observed falling from the dome, and explosive events produced grayish clouds to 100 m height. The Geological Society of Japan reported that Fugen-dake cone had expanded 89 cm from 10 to 22 May (figure 19), and that the lava dome front was moving E at 70-80 cm/hour.

Figure (see Caption) Figure 19. Results of EDM measurements between points T1 and F2 on the S flank of Fugen-dake cone at Unzen, 10 May-8 June. Shortening of this line reflects expansion of the cone as F2 moves toward T1. Data from the GSJ. Courtesy of JMA.

Pyroclastic flows begin, 24 May. At 0810 on 24 May, a large explosion was heard as a portion of the lava dome collapsed, producing a pyroclastic flow that traveled about 1 km down the E flank to within 2 km of Kita-Kamikoba. The flow discolored trees and transported blocks 10 m in diameter. Smaller collapse/pyroclastic flow events occurred at 1755 and 1920.

About 1,300 people were evacuated on 24 May because of increasing mudflow hazard along the Mizunashi River, as volcanic debris accumulated and heavy rains continued. During the evening, workers dredged material from above a dam (2 km from the summit) constructed after the November 1990 eruption to reduce the mudflow danger. By 0600 the following morning the evacuation recommendation was withdrawn and residents were allowed to return home.

Heavy rain on 25 May made observation difficult, but dust and ash from a pyroclastic flow was seen at around 1145. The lava dome continued to grow at an estimated rate of 80,000 m3/day. Rain continued on 26 May, and ash plumes 600 m high were reported, but little is known about activity at the dome.

At 1130 on 26 May, a pyroclastic flow traveled into the Mizunashi valley, injuring a worker (2.6 km from the crater) who had climbed up from the dredging area for better views of the volcano. The flow traveled 3 km, to within 600 m of Kita-Kamikoba, and deposited ash 5 km E on Shimabara. Bursts of tremor accompanied this flow and the prior pyroclastic flow at 1113, suggesting that the tremor signal could be used to detect and count pyroclastic flows (figure 20).

Figure (see Caption) Figure 20. Daily number of pyroclastic flows determined seismically at Unzen, 20 May-18 June 1991. Number represents counts of tremor lasting >30 seconds with amplitudes larger than an empirical threshold. Courtesy of JMA.

The 1130 pyroclastic flow, and the continued accumulation of debris in the river channel, prompted the evacuation of around 3,500 people from the surrounding valley. Several mudflows were reported during that evening, and rain soaked previously-deposited dust and ash to create more mud. Many people were allowed to return home the next day when the rain ceased.

Observations of the dome (27 May) revealed a v-shaped vent, from which a 60-m-wide tongue of lava was being extruded. Pyroclastic flows spawned from the margins of the lava tongue traveled along E and SE paths that joined at mid-flank. On 28 May, fluid (no longer blocky) lava overflowed the crater's E rim and moved down the outer flank, reaching about 700 m elevation by midnight.

The 26 May evacuation order was extended. Pyroclastic flows continued to form, reaching to within 500 m of Kita-Kamikoba on the 29th, and within 200 m on the 30th. Trees in the valley were burned to charcoal, suggesting that flow temperatures had increased. On 31 May, lava was observed emerging from the vent, and then avalanching 1 km down the steep slope in 30 seconds, producing a roaring sound that was heard 6 km E in Shimabara.

Pyroclastic flow kills 41, 3 June. At about 1610 on 3 June, an audible explosion and 6 minutes of recorded tremor signaled the collapse of a portion of the summit dome and lava flow. The resulting large pyroclastic flow moved down the Mizunashi River at reported speeds of up to 100 km/hour and entered Kita-Kamikoba. The core of the pyroclastic flow traveled about 3.2 km (figure 17) over a vertical drop of 1,000 m. An ash cloud surge apparently detached from the flow and traveled an additional 0.8 km, knocking down trees, burning houses, and leaving deposits up to 30 cm thick. Blasted zones occurred in places along the margins of the flow and surge. The volume of the deposits was estimated to be 7.3 x 105 m3.

All of the casualties were within an evacuated "forbidden" zone and all were caused by the detached surge. The victims consisted of: 15 members of the Japanese press, three volcanologists, four taxi drivers, a few local residents, and members of police and fire brigades. Of the 41 people listed dead, 27 bodies were recovered, four remain missing and are presumed dead, and 10 died in hospitals from burns.

Pyroclastic flows continued over the next several days, hampering rescue and recovery efforts, but were less frequent. Lava effusion occurred at a constant rate of around 105 m3/day, producing a tongue 70-80 m wide and 100 m long by 5 June. Periodic explosions produced gas/ash columns 100 m high. One helicopter was grounded due to ash-related engine problems on 6 June. On 7 June, the evacuated zone was widened to include an additional 1,500 people, bringing the total number of evacuees to more than 7,200, and a fine of $75 was imposed on people entering the evacuated area. Observers reported that despite continued growth of the dome it had not yet recovered half of its pre-3 June size.

Large pyroclastic flow, 8 June. An increase in pyroclastic flow activity occurred in the afternoon of 8 June, with numerous small flows over a 5-hour period leading to a larger flow at 1723. The evacuation zone was again widened, to include parts of Fukae, bringing the total number evacuated to about 8,500. Multiple pyroclastic flows began at 1930. Finally, from 1951 to 2016, a continuous series of pyroclastic flows traveled 5.5 km down the Mizunashi River, through parts of Shimabara and Fukae, to within 50 m of Highway 57 (2 km from the sea). Deposits reached 100 m wide and had an estimated volume of ~1.0 x 106 m3. The flows destroyed 73 houses, but no injuries were reported.

Activity continued, with an explosion (detected by infrared camera) at 2007 and a small pyroclastic flow at 2120. Ashfall from the explosion was deposited 90 km NE (in Hida) and 80 km N (in Fukuoka). Clasts 5 cm in diameter fell to 5 km.

Evacuation zones were expanded on 9 June and again on 10 June, to a total of 9,800 people. Mudflow hazards were considered high given the more than 1 x 106 m3 of debris that completely filled the Mizunashi River channel and covered the surrounding valley.

Large explosive event, 11 June. By 11 June, a 50-m-wide dome partly filled the large horseshoe-shaped depression that formed 8 June on the E side of the summit dome. A large explosive ash emission, not associated with pyroclastic-flow formation, occurred at 2359-0003, accompanied by strong tremor and sharp deflation (10 µrad; figure 21). Houses, car windows, and two helicopters were damaged by tephra clasts (d = 1.0-2.0 g/cm3) >=15 cm in diameter that fell to 3.5 km (figure 22). Ash was deposited to 130 km NE (Oita) and 250 km NE (Matsuyama, Shikoku Is.). Two hours after the explosion, 25 µrad of inflation was recorded over a 10-hour period, suggesting rising magma.

Figure (see Caption) Figure 21. Change of ground tilt 850 m W of Unzen's dome, 6-15 June, 1991. Arrows represent large eruptive events on 8 and 11 June. E up corresponds to inflation of the summit area. Data from the Joint Monitoring Group of National Universities. Courtesy of JMA.
Figure (see Caption) Figure 22. Isopleth map of maximum pumice clast sizes from the explosion at Unzen on 11 June at 2359. Data from Kyushu and Kagoshima universities. Courtesy of JMA.

Continued activity. Dome extrusion and pyroclastic-flow formation continued at Unzen as of 24 June. On 14 June, the dome was 100 m wide and 50 m high; it grew another 20 m in height by 16 June. Cracks in the dome emitted gas to 200-300 m height, and periodic explosions produced 1-km-high ash columns. The evacuation area was again expanded on 17 June, bringing the total number of evacuees to more than 10,000.

Actions by Coordinating Committee. The following is from Daisuke Shimozuru, Chairman of the Coordinating Committee for the Prediction of Volcanic Eruptions. "The Japan Meteorological Agency (JMA) dispatched an observation team in mid-October to intensify seismic observation, assisting JMA's local observatory. Early in November, volcanic tremors were observed. We were very worried about an impending eruption, and asked the Ministry for financial aid for observations by university scientists. On 9 November, the Ministry decided to provide financial aid for observations by 6 universities. The university team set up seismic and deformation nets, in cooperation with Shimabara Volcano Observatory of Kyushu Univ." A chronology of Unzen's activity and statements and warnings issued by the Coordinating Committee is shown in table 7 (see following report).

Geologic Background. The massive Unzendake volcanic complex comprises much of the Shimabara Peninsula east of the city of Nagasaki. An E-W graben, 30-40 km long, extends across the peninsula. Three large stratovolcanoes with complex structures, Kinugasa on the north, Fugen-dake at the east-center, and Kusenbu on the south, form topographic highs on the broad peninsula. Fugendake and Mayuyama volcanoes in the east-central portion of the andesitic-to-dacitic volcanic complex have been active during the Holocene. The Mayuyama lava dome complex, located along the eastern coast west of Shimabara City, formed about 4000 years ago and was the source of a devastating 1792 CE debris avalanche and tsunami. Historical eruptive activity has been restricted to the summit and flanks of Fugendake. The latest activity during 1990-95 formed a lava dome at the summit, accompanied by pyroclastic flows that caused fatalities and damaged populated areas near Shimabara City.

Information Contacts: JMA; D. Shimozuru, Tokyo Univ of Agriculture; H. Kamata, GSJ; Public Works Research Institute, Ministry of Construction; K. Uto, USGS; M. Takahashi, SI; Kyodo News Service; The Japan Times; Asahi Shinbun; Yomiuri Shinbun; AP; UPI; Reuters.


Whakaari/White Island (New Zealand) — May 1991 Citation iconCite this Report

Whakaari/White Island

New Zealand

37.52°S, 177.18°E; summit elev. 294 m

All times are local (unless otherwise noted)


Ash emission from new vent; continued deformation

Ash-laden steam emission was reported starting 23 April and continued as of 27 May. An 18 May visit revealed that activity was centered at a newly formed vent in the NE part of 1978/91 Crater (figure 13), near a zone of hot ground first observed on 21 April. Considerable ash accumulation had already occurred in the surrounding area.

Figure (see Caption) Figure 13. Sketch map of White Island on 27 May 1991, showing the new May 91 Vent. Dots mark deformation bench marks. Contour interval, 40 m. Courtesy of DSIR.

During 27May fieldwork, the new vent (named May 91) almost continuously (>=1 pulse/second) emitted a column of gas and minor ash 500-600 m high, depositing dry material, plus some moist sub-millimeter aggregates. The vent, against the NE crater wall, was surrounded by a tuff cone 35-40 m in diameter and 8-10 m high, but no ballistic ejecta were visible. Orca and TV1 Craters quietly emitted weak steam.

Up to 95 mm of ash had accumulated since 21 May at a site 125 m SSE of May 91 vent, of which at least 25 mm was from the new vent. Tephra had infilled the small lake in the vicinity of R.F. Vent (near the SE wall of 1978/90 Crater), and small mudflows traveled across the crater floor. Ash contained a high proportion of fresh material, but lacked vesiculated clasts.

Little change was observed at the 40-45-m-deep collapse pit NW of formerly active Donald Duck Crater. Two passages (20-30 m wide) led from the pit; one connected to Donald Duck Crater (to the SE), and the other headed at least 50-60 m N towards Noisy Nellie. The SE passage contained large sulfur stalactites and stalagmites.

Deformation measurements on 27 May showed that subsidence centered at Donald Mound and Noisy Nellie continued, but at lower rates than the last measurements on 13 February. Minor uplift was measured ~200 m S of Donald Mound.

Seismicity (typically small A- and B-type earthquakes) remained at low levels since 21 April, with periods of 2-3 days without recorded events. One uncharacteristically large E-type event, similar to an event preceding the formation of TV1 Crater (BGVN 15:09) was recorded at 0538 on 23 May. Weak low-frequency tremor has been recorded since 10 May.

Geologic Background. The uninhabited Whakaari/White Island is the 2 x 2.4 km emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes. The SE side of the crater is open at sea level, with the recent activity centered about 1 km from the shore close to the rear crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. The formation of many new vents during the 19th and 20th centuries caused rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities. The official government name Whakaari/White Island is a combination of the full Maori name of Te Puia o Whakaari ("The Dramatic Volcano") and White Island (referencing the constant steam plume) given by Captain James Cook in 1769.

Information Contacts: B. Scott and B. Houghton, DSIR Geology & Geophysics, Rotorua; J. Cole, Univ of Canterbury, Christchurch.

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