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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

Sarychev Peak (Russia) Ash eruption in March 2020; lava extrusion in August filled and then overflowed the crater in January 2021

Ol Doinyo Lengai (Tanzania) Small lava flows in the summit crater during September 2020-February 2021

Manam (Papua New Guinea) Ash plumes, SO2 plumes, and thermal anomalies continued during October 2020-March 2021

Dukono (Indonesia) Ash and sulfur dioxide plumes during October 2020-March 2021

Sinabung (Indonesia) Block avalanches, pyroclastic flows, and ash explosions continue through February 2021

Barren Island (India) Ash emissions in November and December 2020, then thermal anomalies through February 2021

Merapi (Indonesia) New domes appear in January and February 2021; large explosion on 27 January

Yasur (Vanuatu) Gas-and-ash emissions, SO2 plumes, and thermal anomalies during September 2020-February 2021

Rincon de la Vieja (Costa Rica) Frequent small phreatic explosions through 13 December 2020

Kilauea (United States) New eruption in December 2020 with an active lava lake, lava flows, spattering, and a dome fountain

Pacaya (Guatemala) Increasing activity with ash emissions, explosions, and lava flows on multiple flanks during December 2020-February 2021

Villarrica (Chile) Explosions, ash plumes, crater incandescence, and an active lava lake during September 2020-February 2021



Sarychev Peak (Russia) — May 2021 Citation iconCite this Report

Sarychev Peak

Russia

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

All times are local (unless otherwise noted)


Ash eruption in March 2020; lava extrusion in August filled and then overflowed the crater in January 2021

Sarychev Peak forms the surface of Matua Island in the Kurile Islands with reported activity dating back to around 1765. Recent activity that started in May 2019 included ash and gas emission and elevated temperatures within the summit crater detected by satellite sensors, with the last reported activity being an ash plume reaching 2.7 km altitude on 10 August and thermal anomalies present until 7 October 2019 (BGVN 44:11). This bulletin summarizes activity during November 2019-April 2021 using reports by the Sakhalin Volcanic Eruption Response Team (SVERT) and the Kamchatka Volcanic Eruptions Response Team (KVERT), along with satellite data.

No cloud-free satellite images were found of the summit in November 2019, but Sentinel-2 satellite images showed weak gas-and-steam emissions on 2 and 20 December. Cloud-free Sentinel-2 images showed gas-and-steam emission through January 2020, and a thermal anomaly was detected in the crater on the 29th (figure 30). No clear satellite images of the summit area were found, but there is evidence of gas emission in February. Evidence of a new eruption is seen in satellite imagery of thin linear ash deposits across the snow on 1, 19, and 30 March 2020, all extending SE from the crater (figure 31). The crater was obscured by gas emissions on the 19th and a clear view of the crater floor showed no thermal anomaly on the 31st.

Figure (see Caption) Figure 30. These thermal satellite images show the Sarychev Peak summit area in December 2019 and January 2020. The images from 2 December 2019, 6 January, and 19 January 2020 show gas emissions (solid arrows). The 29 January image shows a small area with an elevated temperature on the crater floor (dashed arrow). Sentinel-2 thermal satellite images with false color (urban) (bands 12, 11, 4) rendering. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 31. Three ashfall deposits are visible SW of the Sarychev Peak summit through March 2020. Based on satellite images, the deposit at the top was emplaced during an event that occurred during 28 February (ash-free image) and 1 March, the middle during 17 (ash-free image) and 19, and the bottom during 26 (ash-free image) and 29 March. Gas-and-steam emissions are obscuring the view into the crater. All images are at the same scale. Sentinel-2 satellite image with natural (bands 4, 3, 2) rendering. Courtesy of Planet Labs.

The MIROVA system began detecting elevated temperatures in early April 2020, which corresponded to the Sentinel-2 thermal sensor detecting high temperatures on the crater floor (figures 32 and 33). Satellite images also showed continued gas emissions, some days obscuring the view of the crater floor.

Figure (see Caption) Figure 32. This plot shows thermal energy detected at Sarychev Peak by the MIROVA system during March 2020-March 2021. there was an increase in energy detected in April 2020, which was intermittent through to October. After a few months the system detected thermal energy again in mid-January through to early February with a higher output. Courtesy of MIROVA.
Figure (see Caption) Figure 33. Satellite images showing the Sarychev Peak summit crater on 4, 5, 18, and 20 April 2020. The first (top left) PlanetScope image shows the snow-covered summit area with a darker snow-free area on the crater floor. The other three images are Sentinel-2 thermal satellite images with the yellow to red colors indicating high temperatures on the crater floor. There is gas and steam in the crater on the 18th. The high temperature areas correlate to the darker snow-free area in NW part of the crater in the first image; blue colors in the thermal images are snow. Sentinel-2 thermal satellite images have false color (urban) (bands 12, 11, 4) rendering. Courtesy of Planet Labs and Sentinel Hub Playground.

The thermal anomaly on the crater floor continued through May and June, with cloud-free images showing the same area of elevated temperature as the previous months. By 20 May 2019 data from Sentinel-1 Synthetic Aperture Radar (SAR) showed morphological change in the crater associated with the area of high temperature, and this change continued through June. The TROPOspheric Monitoring Instrument (TROPOMI) detected sulfur dioxide (SO2) content within the plume on 27 May (figure 34). Gas-and-steam emission also continued in June, with more substantial plumes visible on 22 and 27 June (figure 35). TROPOMI again detected SO2 on 24 and 25 June; the plume on 24 June was also visible in Sentinel-2 imagery (figure 36).

Figure (see Caption) Figure 34. This image shows a weak gas plume from Sarychev Peak dispersing to the SE on 27 May 2020, as well as other volcanoes in Kamchatka. TROPOspheric Monitoring Instrument (TROPOMI) data showing sulfur dioxide (SO2) in Dobson Units (DU). Courtesy of NASA Global Sulfur Dioxide Monitoring Page.
Figure (see Caption) Figure 35. These Planet Scope satellite scenes show gas-and-steam plumes emanating from the Sarychev Peak summit crater and dispersing SSW (left) and NW (right) on 22 and 27 June 2020, respectively. Courtesy of Planet Labs.
Figure (see Caption) Figure 36. Weak gas emission at Sarychev Peak detected by satellite sensors on 25 and 26 June 2020. The top image and the bottom-left images were acquired on the 25th and show the plume being redirected by a meteorological vortex northward before curving to the W and N. Top: Sentinel-2 satellite image with natural color (bands 4, 3, 2) rendering. Courtesy of Planet Labs. Bottom: TROPOspheric Monitoring Instrument (TROPOMI) data showing sulfur dioxide (SO2) in Dobson Units (DU). Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Throughout July satellite data show thermal emission and gas-and-steam emission, mostly within plumes dispersing from the summit crater in different directions and sometimes restricted to within the crater (figure 37). On 18 July a PlanetScope image showed lava extrusion in the crater, at the location of the elevated temperature. Sentinel-2 thermal satellite images showed weak thermal energy detected in the same location during August, and degassing continued (figure 38). By 12 August the deformation on the crater floor was clear in SAR data (figure 39), matching the PlanetScope and Sentinel-2 data. From 21 August through to 12 October there was a reduction in thermal energy detected in Sentinel-2 TIR data, with many days not having clear views of the crater floor. Plume emission continued throughout this time. There were no images showing elevated temperatures during November and December when clouds frequently covered the crater area, and there were also no anomalies detected by the MIROVA system.

Figure (see Caption) Figure 37. The PlanetScope natural color (top) and Sentinel-2 thermal (bottom) satellite images indicate lava in the crater during July 2020. Gas emission is also visible in the images. Sentinel-2 thermal satellite images have false color (urban) (bands 12, 11, 4) rendering. Courtesy of Planet Labs and Sentinel Hub Playground.
Figure (see Caption) Figure 38. PlanetScope and Sentinel-2 satellite images acquired during August 2020 show lava in the crater and gas-and-steam plumes being dispersed in different directions by winds. Sentinel-2 satellite image with natural color (bands 4, 3, 2) rendering. Courtesy of Planet Labs and Sentinel Hub Playground.
Figure (see Caption) Figure 39. These satellite images show the morphological change in the Sarychev Peak summit crater between 10 November 2019 and 12 August 2020. The three gray-scale images use Sentinel-1 Synthetic Aperture Radar (SAR) data acquired on 10 November 2019, 20 May, and 12 August 2020. The color image in the lower left is a Sentinel-2 thermal image acquired on 22 June 2020. The SAR images show morphological changes in the crater in the same location as the elevated temperatures in the thermal images, indicating lava extrusion. Sentinel-1 SAR images are VV, decibel gamma0, and orthorectified. Sentinel-2 thermal satellite images have false color (urban) (bands 12, 11, 4) rendering. Courtesy of Sentinel Hub Playground.

On 11 January 2021 KVERT released a Volcano Observatory Notice for Aviation (VONA) with an elevation of the Aviation Color Code from Green to Yellow. The temperature within the crater had increased above background levels by 79.8°?, indicating that renewed lava extrusion had begun in the crater on the 10th. A gas-and-steam plume extended 36 km NE on the 12th. On 15 January KVERT reported that moderate activity continued, including a gas-and-steam plume that extended 40 km NE. SAR data through January shows the lava volume increasing before flowing over the NW rim and down a preexisting channel on the flank (figure 40). KVERT reported that a lava flow on the northern flank had reached 400 m by the 20th. Lava extrusion with associated moderate gas and steam emission continued throughout the month.

Figure (see Caption) Figure 40. These SAR images of Sarychev Peak during 3 January to 20 February 2021 show lava extrusion filling the summit crater and descending a channel on the NW flank. Note that the 6 January image has a different look angle to the other images, and this alters how the surface appears. Sentinel-1 SAR images are VV, decibel gamma0, and orthorectified. Courtesy of Sentinel Hub Playground.

A 3 February satellite image of the NW flank showed that the lava flow front had reached approximately 1.9 km from the crater rim where it had overflowed (figure 41). The Aviation Color Code was lowered to Green on the 18th with KVERT reporting that the eruption had ended, though thermal anomalies and gas-and-steam emission continued.

Figure (see Caption) Figure 41. Satellite image scenes show the lava flow at Sarychev Peak on 3 and 14 February 2021. Top: PlanetScope image from 3 February showing the lobate lava flow front approximately 1.9 km from the NW crater rim. Bottom: Sentinel-2 satellite scenes from 14 February (thermal infrared to the left and natural color to the right) showing the summit crater area with lava extrusion and the lava flow overtopping the NW rim. Sentinel-2 satellite images have natural color (bands 4, 3, 2) rendering, and thermal false color (urban) (bands 12, 11, 4) rendering. Courtesy of Planet Labs and Sentinel Hub Playground.

Satellite images of the lava flow acquired during March and April show the narrow lava lobe with pressure ridges and levees (figure 42). A comparison between a September 2019 satellite image and a clear 29 April 2021 image shows the change to the crater after the lava emplacement. The last Sentinel-2 image acquired within this period showing elevated temperatures within the crater was on 19 March and there was no more thermal energy detected by the MIROVA system by early February.

Figure (see Caption) Figure 42. The PlanetScope satellite images across the top of this figure show the lava flow on the NW flank of Sarychev Peak during March-April 2021. The different degrees of snow cover show different surface morphological aspects like pressure ridges and levees. The bottom images show the crater on 7 September 2019 for comparison (left) and the lava within the summit crater on 29 April 2021 (right). Fumaroles are also visible around the crater walls in the 2019 image. The top images and bottom right image are PlanetScope satellite images and the lower left image is by CNES/Airbus through Google Earth. Courtesy of Planet Labs and U.S. Dept. of State Geographer Data via Google Earth, ©2019 Google.

Geologic Background. Sarychev Peak, one of the most active volcanoes of the Kuril Islands, occupies the NW end of Matua Island in the central Kuriles. The andesitic central cone was constructed within a 3-3.5-km-wide caldera, whose rim is exposed only on the SW side. A dramatic 250-m-wide, very steep-walled crater with a jagged rim caps the volcano. The substantially higher SE rim forms the 1496 m high point of the island. Fresh-looking lava flows, prior to activity in 2009, had descended in all directions, often forming capes along the coast. Much of the lower-angle outer flanks of the volcano are overlain by pyroclastic-flow deposits. Eruptions have been recorded since the 1760s and include both quiet lava effusion and violent explosions. Large eruptions in 1946 and 2009 produced pyroclastic flows that reached the sea.

Information Contacts: Sakhalin Volcanic Eruption Response Team (SVERT), Institute of Marine Geology and Geophysics, Far Eastern Branch, Russian Academy of Science, Nauki st., 1B, Yuzhno-Sakhalinsk, Russia, 693022 (URL: http://www.imgg.ru/en/, http://www.imgg.ru/ru/svert/reports); Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); Google Earth (URL: https://www.google.com/earth/).


Ol Doinyo Lengai (Tanzania) — April 2021 Citation iconCite this Report

Ol Doinyo Lengai

Tanzania

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

All times are local (unless otherwise noted)


Small lava flows in the summit crater during September 2020-February 2021

Ol Doinyo Lengai is located near the southern end of the East African Rift in Tanzania. It is known for its unique low-temperature carbonatitic lava. Activity primarily occurs in the crater offset to the N about 100 m below the summit where hornitos (small cones) and pit craters produce lava flows and spattering. Eruptions have been recorded since the late 19th century; the current eruptive period began in April 2017 and has recently been characterized by small lava flows in the crater (BGVN 45:09). This report covers similar activity during September 2020 through February 2021 using information primarily from satellite data.

During September 2020 to February 2021 both thermal and natural color satellite imagery showed small lava flows in the summit crater. A total of six weak thermal anomalies were identified in MIROVA data during September (2), October (3), and November (1) 2020 (figure 211). No thermal anomalies were detected after late November, according to the MIROVA graph. Sentinel-2 satellite imagery showed small lava flows within the summit crater throughout the reporting period. On clear weather days, infrequent and faint thermal anomalies were observed in thermal satellite imagery within the crater; new lava flows were identified due to the change in shape, volume, and location of the thermal anomaly (figure 212). On 31 August a faint thermal anomaly was visible in the NW side of the summit crater. On 15 September fresh black lava was observed in the center of the summit crater spreading to the NW and E. Two small thermal anomalies were present on the W and E side of the crater on 20 September. On 24 December both thermal and Natural Color images showed the location of a lava flow as a thermal anomaly and as fresh lava in the center and W side of the crater. On 7 February a gas-and-steam plume was observed drifting E from the crater.

Figure (see Caption) Figure 211. Intermittent low-level thermal anomalies were recorded at Ol Doinyo Lengai, based on the MIROVA thermal data graph (Log Radiative Power) during late August through late November 2020; a total of six weak thermal anomalies were detected between September through November 2020. The black lines are distant anomalies (more than 5 km from the summit) not related to volcanism. Courtesy of MIROVA.
Figure (see Caption) Figure 212. Sentinel-2 thermal and natural color imagery of Ol Doinyo Lengai from 31 August 2020 to 7 February 2021. On clear weather days, thermal anomalies (bright yellow-orange) were faintly visible in the summit crater on 31 August (top left) on the NW side. On 15 September (top right) fresh black lava, which quickly cools to a whitish-brown color, was seen in the crater, reflecting the position of the anomalies visible in the thermal image. Two anomalies were visible on 20 September (middle left) on the W and E side. Two black dots which represent cooled lava and thermal anomalies on the W side of the crater were visible in both 24 December (bottom left) thermal and Natural Color images. A small lava flow was observed in the center of the crater on 7 February (bottom right) 2021. Images are marked with “Atmospheric penetration” rendering (bands 12, 11, 8A) and “Natural Color” rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

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

Information Contacts: 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).


Manam (Papua New Guinea) — April 2021 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 plumes, SO2 plumes, and thermal anomalies continued during October 2020-March 2021

Manam is located 13 km off the N coast of mainland Papua New Guinea and has had eruptions documented since 1616. It contains two active summit craters, Main and South, which have been characterized by occasional Strombolian activity, lava flows, pyroclastic avalanches, and ash plumes. The current eruption period has been ongoing since 2014 with more recent activity consisting of intermittent ash plumes, thermal anomalies, and sulfur dioxide emissions (BGVN 45:10). This report describes similar activity and covers October 2020 through March 2021 using information primarily from the Darwin Volcanic Ash Advisory Center (VAAC) and various satellite data.

Explosive and thermal activity was relatively low during this reporting period. Three ash plumes were reported by the Darwin VAAC based on imagery from the HIMIWARI-8 satellite. On 6 December 2020 an ash plume rose to 2.4 km altitude and drifted SW. The next VAAC notice was for ash detected on 23 January 2021 rising to 4.9 km and drifting SE and N. Then on 21 February an ash plume rose to a maximum altitude of 6 km and drifted W. Intermittent sulfur dioxide plumes were detected using the TROPOMI instrument on the Sentinel-5P satellite, some of which reached at least two Dobson Units (DU) and drifted in multiple directions (figure 79). On 6 December and 23 January, the ash plume that was described in the Darwin VAAC advisory was accompanied by an SO2 plume. SO2 plumes that reached a minimum of two DU were recorded for at least 12 days during October, 13 days during November, 15 days during December, 10 days during January, 3 days during February, and 6 days during March.

Figure (see Caption) Figure 79. Distinct sulfur dioxide plumes rising from Manam and drifting in different directions were detected using data from the TROPOMI instrument on the Sentinel-5P satellite on 9 October (top left), 3 November (top right), 6 December (middle left) 2020, 13 January (middle right), 18 February (bottom left), and 18 March (bottom right) 2021. Courtesy of the NASA Global Sulfur Dioxide Monitoring Page.

Thermal activity during October 2020 through March 2021 was relatively low in power and frequency compared to August and September, as recorded by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system. Two brief pulses of activity were detected during mid-November and late December to mid-January (figure 80). A total of 14 low-power anomalies were recorded: one in early October, three in mid-November, two in December, a maximum number of six in January, one in late February, and one in late March. Some of this activity was captured in Sentinel-2 thermal satellite imagery on clear weather days in both the Main and South summit craters (figure 81).

Figure (see Caption) Figure 80. Thermal activity at Manam was low to moderate in power during October 2020 through March 2021, with notable brief pulses during mid-November and late December through mid-January, as shown on this MIROVA Log Radiative Power graph. One anomaly was detected in early October, three in mid-November, two in December, six in January, one in late February, and one in late March. Courtesy of MIROVA.
Figure (see Caption) Figure 81. Sentinel-2 thermal satellite images show a persistent thermal anomaly (bright yellow-orange) at both of Manam’s summit craters (Main and South) on clear weather days during November 2020 through March 2021. Occasional gas-and-steam emissions accompanied the thermal anomalies as seen on 25 November 2020 (top left), 29 January (top right), 8 February (bottom left), and 20 March (bottom right) 2021. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

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: 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/); NASA 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).


Dukono (Indonesia) — April 2021 Citation iconCite this Report

Dukono

Indonesia

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

All times are local (unless otherwise noted)


Ash and sulfur dioxide plumes during October 2020-March 2021

Dukono, located in northernmost Halmahera, Indonesia, has been erupting continuously since 1933. Volcanism has recently been characterized by frequent ash explosions, ash plumes, and sulfur dioxide plumes (BGVN 45:10). This report updates activity consisting of white-and-gray plumes and sulfur dioxide plumes during October 2020-March 2021 using information primarily from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), the Darwin Volcanic Ash Advisory Centre (VAAC), and satellite data.

Volcanism at Dukono has been characterized by dominantly white-and-gray plumes, accompanied by intermittent ash plumes that drifted in multiple directions. On clear weather days, the ash plumes rose to 1.5-2.4 km altitude, or about 270-1,200 m above the crater, according to PVMBG and the Darwin VAAC advisories (table 23).

Table 23. Monthly summary of reported ash plumes from Dukono during October 2020-March 2021. The direction of drift for the ash plumes was highly variable; notable plume drifts each month were only indicated in the table if at least two weekly reports were consistent. Data courtesy of PVMBG and the Darwin VAAC.

Month Plume altitude (km) Notable plume drift
Oct 2020 1.8-2.4 W, N, NE, E, SW
Nov 2020 1.5-2.1 Multiple directions
Dec 2020 1.5-2.4 SE, E
Jan 2021 1.5-2.1 SW, E
Feb 2021 1.5-2.1 Multiple directions
Mar 2021 1.5-2.4 Multiple directions

Activity during October 2020 primarily consisted of near daily white-and-gray plumes that rose 100-700 m above the crater and drifted in multiple directions (figure 19). Ash plumes during this month rose between 1.8 and 2.4 km altitude and drifted W, N, NE, E, SW, according to PVMBG VONA notices and the Darwin VAAC advisories. Frequent white gas-and-steam emissions were also observed in webcam images. Similar activity continued in November, with almost daily white-and-gray plumes rising 100-800 m above the crater and drifting in multiple directions. On clear weather days ash plumes were observed up to 2.1 km altitude; on 12 November the ash plume rose up to 2.1 km altitude and drifted SW (figure 19).

Figure (see Caption) Figure 19. Webcam images of white-and-gray plumes rising from Dukono on 8 October (left) and an ash plume on 12 November (right) 2020. Courtesy of MAGMA Indonesia.

In December and January 2021, white-and-gray plumes were 100-700 m above the crater and drifted in multiple directions, dominantly E and W in December and SW in January. According to Darwin VAAC advisories during these two months, ash plumes were seen rising to 2.4 km altitude and drifted notably SE, E, and SW.

Activity in February persisted with white-and gray plumes rising 100-600 m above the crater and drifting dominantly SW and E (figure 20). Intermittent ash plumes rose to 2.1 km altitude during February and 2.4 km altitude during March, drifting in multiple directions. Gas-and-steam plumes were also frequent. During March, almost daily white-and-gray plumes rose 100-800 m above the crater and drifted in multiple directions (figure 20).

Figure (see Caption) Figure 20. Webcam images of white-and-gray plumes rising from Dukono on 25 February (left) and 22 March (right) 2021. Courtesy of MAGMA Indonesia.

The NASA Global Sulfur Dioxide page, using data from the TROPOMI instrument on the Sentinel-5P satellite, showed strong SO2 plumes rising from Dukono and drifting in various directions (figure 21). In addition to SO2 plumes, Sentinel-2 thermal satellite imagery showed thermal anomalies of variable intensities on clear weather days (figure 22). Intermittent thermal anomalies recorded by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system during early December 2020 through mid-March 2021 were low in power (figure 23). A brief break in thermal activity occurred during mid- to late-February.

Figure (see Caption) Figure 21. Strong sulfur dioxide emissions rose from Dukono and drifted in multiple directions were detected using the TROPOMI instrument on the Sentinel-5P satellite. SO2 plumes drifted N on 10 October (top left), generally E on 28 November (top right), 13 December (middle left) 2020, and 11 February 2021 (bottom left), SE on 9 January (middle right) 2021, and W on 4 March (bottom right) 2021. Courtesy of the NASA Global Sulfur Dioxide Monitoring Page.
Figure (see Caption) Figure 22. Sentinel-2 thermal satellite imagery showing a thermal anomaly in the summit crater on 1 November (top left) 2020, 10 January (middle right), 1 March (bottom left), and 16 March (bottom right) 2021, frequently accompanied by gas-and-steam and ash plumes. On 11 November (top right) and 6 December (middle left) 2020 a Natural Color image showed a grayish white ash plume drifting SW and SE, respectively. Sentinel-2 satellite images with “Natural Color” rendering (bands 4, 3, 2) on 11 November and 6 December 2020, all other images use “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 23. MIROVA (Log Radiative Power) thermal data for Dukono from 3 June 2020 through March 2021 showed intermittent low power thermal activity during early December 2020 through mid-March 2020. A brief break in activity occurred during mid- to late-February. Courtesy of MIROVA.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); 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/); NASA 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).


Sinabung (Indonesia) — March 2021 Citation iconCite this Report

Sinabung

Indonesia

3.17°N, 98.392°E; summit elev. 2460 m

All times are local (unless otherwise noted)


Block avalanches, pyroclastic flows, and ash explosions continue through February 2021

Indonesia’s Sinabung volcano in north Sumatra had its first confirmed Holocene eruption during August and September 2010. It remained quiet until September 2013 when a new eruptive phase began that continued through mid-2018. Dome growth and destruction resulted in block avalanches, multiple explosions with ash plumes, and deadly pyroclastic flows during the period. After a pause in activity from September 2018 through April 2019, explosions resumed during May and June 2019. Dome growth began again with an explosion on 8 August 2020, and similar activity continued through October 2020. This report covers ongoing activity from November 2020 through February 2021 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, and the Darwin Volcanic Ash Advisory Centre (VAAC). Additional information comes from satellite instruments and local news reports.

Activity at Sinabung during November 2020-February 2021 was characterized by tens of daily rock avalanches, periodic pyroclastic flows, and ash-bearing explosions. The rock avalanches traveled up to 1,000 m down the E and SE flanks. The pyroclastic flows also traveled down the E and SE flanks, and the largest reached 2.5 km from the summit. Periodic explosions produced ash plumes that rose up to 2 km above the summit and drifted in multiple directions. Although cloudy much of the time, intermittent satellite images showing two thermal anomalies at the summit suggested that the dome remained active (figure 85).

Figure (see Caption) Figure 85. Two thermal anomalies were present at the summit of Sinabung several times during the report period from November 2020-February 2021, including on 2 December 2020 and 10 February 2021, suggesting ongoing dome activity. In addition, frequent pyroclastic flows produced incandescent anomalies on the E flank multiple times including on 10 February 2021. Sentinel-2 images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

White steam emissions rose 50-500 m above the summit of Sinabung during most days in November 2020. Block avalanches were frequent during the first half of the month, traveling 200-1,000 m down the S and SE flanks. The Darwin VAAC reported small ash plumes from block avalanches on 1 and 2 November that rose to 3 km altitude and quickly dissipated. Clouds prevented observations during the last week of the month, but tens of seismic events interpreted by PVMBG as block avalanches were detected. Pyroclastic flows were either observed visually or measured seismically on 2-7, 10, 12, 16, 18 and 19 November (figure 86). They most often occurred on the E or SE flanks and traveled 1,500-2,500 m. Seismic signals indicating lahars were recorded on 26, 27, and 30 November.

Figure (see Caption) Figure 86. A pyroclastic flow descended the S flank of Sinabung on 7 November 2020. Courtesy of Rizal.

Nine explosions with ash plumes were reported during November 2020. On 2 November a gray ash plume rose 1,500 m above the summit, to about 3.9 km altitude, and drifted E. The next day the Darwin VAAC reported an explosion to 3.7 km altitude that drifted E. An ash explosion on 4 November was recorded seismically for 117 seconds but was not seen due to fog. An explosion on 10 November produced an ash plume that rose 2 km above the summit and drifted E, along with pyroclastic flows that traveled 1,500-2,500 m down the E and SE flanks. On 18 November an explosion created an ash plume that rose to 3.7 km altitude and drifted SW; it was measured seismically as a continuous volcanic tremor that lasted for 160 seconds. Seismic activity confirmed an explosion on 21 November, but meteoric clouds obscured observations of ash. An ash plume drifting SW at 3 km altitude, about 500 m above the summit, was reported on 25 November. On 29 November an explosion produced an ash plume to the same altitude that drifted E (figure 87). The next day seismic activity indicated another explosion, but it was not observed due to cloudy weather.

Figure (see Caption) Figure 87. An ash plume at Sinabung rose to 3 km altitude and drifted E on 29 November 2020. Courtesy of PVMBG and MAGMA Indonesia.

Explosive activity decreased during December 2020. Steam plumes rose 50-500 m and tens of rock avalanches were recorded seismically every day. On 6 December block avalanches rolled 300-500 m down the E and SE flanks; they traveled 500-1,000 m down the SE flank on 8 December. During 12-14 December they traveled 1,000-1,500 m down the E and S flanks. On 30 and 31 December they were seen moving 500-1,000 m down the same flanks. Lahars were measured seismically on 4 and 5 December with no reports of damage.

An explosion on 2 December produced an ash plume that rose about 500 m above the summit and drifted ESE. Clouds and rain prevented views of the summit on 5 December, but the seismogram recorded an explosive event that lasted for 168 seconds (figure 88). The Darwin VAAC reported an ash plume moving ESE at 3 km altitude on 13 December. Sentinel-2 satellite imagery captured a thermal anomaly on the E flank on 17 December that was likely from a pyroclastic flow (figure 89). Two explosions were recorded each day on 28 and 29 December. On the first day the ash plume from the first explosion rose to 500 m and drifted S. The second explosion was not observed due to weather, but a thermal anomaly was intermittently visible. The explosions on 29 December were only recorded seismically, as was one explosion on 30 December.

Figure (see Caption) Figure 88. The KESDM seismogram at Sinabung recorded an explosive event on 5 December 2020 that lasted for 168 seconds. Courtesy of PVMBG and MAGMA Indonesia.
Figure (see Caption) Figure 89. A thermal anomaly on the E flank of Sinabung on 17 December 2020 was likely from a pyroclastic flow. The summit is obscured by clouds. Sentinel-2 image with Atmospheric penetration rendering (bands 12, 11, and 8a). Courtesy of Sentinel Hub Playground.

Tens of daily rock avalanches continued to be recorded during January 2021, although most were not observed. During 2-5 January they traveled 500-1,200 m down the E and SE flanks, and on 14 January they fell 700-1,000 m down the SE flank. The number of explosions with ash plumes increased significantly from December. On 3 January two explosions were recorded seismically; an ash plume from the first rose 1,000 m above the summit and drifted NW in the morning. A few hours later a second explosion was recorded but not observed due to clouds. Three explosions were recorded each day on 4 and 5 January. The first on 4 January produced a 700-m-high ash plume, the second and third sent ash 1,000 m above the summit to the W and NW (figure 90). The next day, the first explosion sent an ash plume 800 m above the summit that drifted E and SE; the other two were recorded seismically but not observed due to weather. One or two explosions were recorded daily during 6-10 January; most were obscured by clouds. One of the explosions on 8 January produced an ash plume that rose to 700 m and drifted N, and the explosion on 9 January rose to 1,000 m and drifted N and NE. Two explosions were recorded on 12 January, and two or three explosions were reported daily during 16-18 January. Explosions were also recorded on 20-21, 23, 25-27, and 29 January. The three ash plumes on 17 January all rose 500 m above the summit and drifted E, NE, or SE; the plumes on 21 and 27 January rose 500 m and drifted E and SE.

Figure (see Caption) Figure 90. An explosion at Sinabung on 4 January 2021 produced an ash emission that rose 1,000 m above the summit and drifted W and NW. Courtesy of PVMBG and MAGMA Indonesia.

Steam emissions rose 50-700 m above the summit throughout February 2021. Over 100 seismic events from rock avalanches were reported daily; on 6 February a maximum of 231 events were recorded. Numerous explosions, many with pyroclastic flows, were only detected seismically on 5-12, 14, 17, 22, 25, and 28 February. On 6 February the Darwin VAAC reported a continuous ash eruption identified in satellite imagery at 3.1 km altitude drifting NW. PVMBG also reported a pyroclastic flow that traveled 2,500 m down the S flank that day. The Antara News Agency reported an ash plume rising 1,000 m above the summit from a pyroclastic flow and drifting E, SE, and S on 7 February, and another pyroclastic flow on 9 February that traveled 1,000 m down the SE flank (figure 91). Cloudy weather obscured views on most days, but during 12-14 February blocks traveled 500-1,500 m down the S, SE, and E flanks.

Figure (see Caption) Figure 91. A pyroclastic flow traveled 1,000 m down the SE flank of Sinabung on 9 February 2021. Courtesy of Anadolu Agency.

The Darwin VAAC received a report on 10 February of an ash plume at 4.6 km altitude moving E; it was not identifiable in satellite imagery due to meteoric clouds. Two pyroclastic flows on 12 February moved as far as 2,000 m down the E and SE flanks. On 17 February an ash plume rose 1,000 m above the summit and drifted S and W and a pyroclastic flow was reported. A lahar was reported on 21 February. A pyroclastic flow on 22 February traveled 2,000 m down the E and SE flanks. The ash plume from the 25 February event rose to 1,500 m above the summit to about 3.9 km altitude and drifted E and SE (figure 92) and was accompanied by four pyroclastic flows that traveled 500-1,000 m down the E and SE flanks. A discrete ash plume was reported by the Darwin VAAC on 28 February that rose to 3.1 km altitude and drifted SW, dissipating withing six hours. Pyroclastic flow were observed that day moving 1,000-1,250 m down the S, SE, and E flanks.

Figure (see Caption) Figure 92. The ash plume at Sinabung from a 25 February 2021 explosion rose to 1,500 m above the summit and drifted E and SE. Courtesy of PVMBG and MAGMA Indonesia.

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/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); 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); Rizal (URL: https://twitter.com/Rizal06691023/status/1324972883634917376); Antara News Agency (URL: https://www.antaranews.com/berita/1986704/guguran-abu-gunung-sinabung-teramati-setinggi-1000-meter); Anadolu Agency (URL: https://www.aa.com.tr/ba/svijet/indonezija-u-vulkanu-sinabung-odjeknula-eksplozija/2138389).


Barren Island (India) — March 2021 Citation iconCite this Report

Barren Island

India

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

All times are local (unless otherwise noted)


Ash emissions in November and December 2020, then thermal anomalies through February 2021

Barren Island, an uninhabited possession of India in the Andaman Sea, had numerous historical eruptions observed during 1787-1832. No further evidence of activity was found until 1991 when ash plumes, Strombolian explosions, and lava flows that reached the ocean were observed. Intermittent similar eruptions since 2005 have lasted for months to years. Its remoteness makes ground observations rare, but satellite data and reports from the Darwin VAAC (Volcanic Ash Advisory Center) suggest that the most recent eruption which began in September 2018 with lava fountaining, lava flows, and ash emissions has continued with intermittent thermal anomalies at the summit and minor ash emissions since early 2019. This report covers activity from July 2020-February 2021.

The MIROVA thermal anomaly data from April 2020 through February 2021 indicate low levels of thermal activity from April through October 2020. Pulses of activity in early November and late January-early February 2021 correspond to increased thermal activity seen in satellite images during that time (figure 47). Ash emissions were reported by the Darwin VAAC in early November and early December 2020. A strong thermal anomaly was present in satellite imagery on 11 November, and moderate anomalies appeared during February 2021. In addition, during November-February faint thermal anomalies and/or small ash emissions were present in one or more satellite images each month.

Figure (see Caption) Figure 47. The MIROVA thermal anomaly data from April 2020 through February 2021 indicate low levels of thermal activity from April through October 2020. Pulses of activity in early November and late January-early February 2021 corresponded to increased thermal activity seen in satellite images. Courtesy of MIROVA.

After a small ash plume was observed on 24 June 2020 in Sentinel-2 satellite imagery (BGVN 45:08), the only evidence of further activity was a very weak thermal anomaly present inside the summit crater of the pyroclastic cone on 19 July 2020. Satellite images were mostly cloudy during August-October 2020, although the few clear images each month showed no sign of thermal anomalies or ash emissions. Single MODVOLC thermal alerts were issued for Barren Island on 2 and 4 November 2020. The Darwin VAAC reported continuous ash emissions drifting SW at 1.5 km altitude on 5 November. A very faint thermal anomaly was present inside the summit of the pyroclastic cone the next day. A large thermal anomaly and small ash plume were captured in satellite images on 11 November (figure 48). The bright anomaly at the center of the cone was surrounded by a weaker anomaly suggesting incandescent ejecta on the flanks of the cone. A smaller thermal anomaly and similar ash plume were visible in the 16 November 2020 Sentinel-2 satellite images (figure 49).

Figure (see Caption) Figure 48. A large thermal anomaly and small ash plume at Barren Island were captured in Sentinel-2 satellite images on 11 November 2020. In the left image the bright anomaly at the center of the cone was surrounded by a weaker anomaly suggesting incandescent ejecta on the flanks of the cone. Image uses Atmospheric penetration rendering (bands 12, 11, 8a). The ash emission immediately W of the summit crater is more visible in the Natural color rendering (right, bands 4,3,2). Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 49. A thermal anomaly at the summit and a discrete ash emission slightly W of the summit of Barren Island were captured in Sentinel-2 satellite imagery on 16 November 2020. Left image uses Atmospheric penetration rendering (bands 12, 11, 8a) and right image shows a closeup of the summit and ash plume in Natural color rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

The Darwin VAAC issued an ash advisory on 8 December 2020 of an ash plume drifting W at 1.8 km altitude. It was only visible in satellite imagery for about two hours before dissipating. A small thermal anomaly appeared at the summit on 21 December. During January 2021 faint thermal anomalies were visible on 5, 20, and 25 January, and ash plumes could be seen on 15 and 25 January in Sentinel-2 images (figure 50). The strength of the thermal activity increased during February 2021, with satellite evidence recorded on 4, 9, 19, and 24 February; an ash emission was visible on 9 February (figure 51).

Figure (see Caption) Figure 50. Ash plumes and thermal anomalies at Barren Island were present in Sentinel-2 satellite images several times during January 2021. The left image from 15 January shows an ash plume drifting W from the summit using Natural color rendering (bands 4, 3, 2). The right image shows a weak thermal anomaly at the summit on 25 January with an ash plume drifting S using Atmospheric penetration rendering (bands 12, 11, and 8A). Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 51. Sentinel-2 satellite images showed thermal anomalies at Barren Island several times during February 2020 including on 4 (left) and 9 (right) February. An ash emission drifted S from the summit on 9 February. Images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

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


Merapi (Indonesia) — March 2021 Citation iconCite this Report

Merapi

Indonesia

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

All times are local (unless otherwise noted)


New domes appear in January and February 2021; large explosion on 27 January

Merapi volcano in central Java, Indonesia, has a lengthy history of major eruptive episodes. Activity has included lava flows, pyroclastic flows, lahars, Plinian explosions with heavy ashfall, incandescent block avalanches, block-and-ash flows, and dome growth and destruction. Fatalities from these events were reported in 1994, 2006, and in 2010 when hundreds of thousands of people were evacuated. Renewed phreatic explosions in May 2018 cancelled airline fights and generated significant SO2 plumes. A new lava dome appeared in early August 2018; gradual dome growth and then destruction was accompanied by rockfalls, block-and-ash flows, periodic explosions, and pyroclastic flows through June 2020. The period from October 2020 through February 2021 is covered in this report and includes the growth of two new domes in early 2021. Information is provided primarily by Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG), the Center for Research and Development of Geological Disaster Technology, a branch of PVMBG, which monitors activity specifically at Merapi, the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), and the Darwin Volcanic Ash Advisory Centre (VAAC).

Measurements in late July 2020 showed no change in the dome (BGVN 45:10), though satellite evidence for weak thermal activity near the NW crater rim persisted during August-October 2020 (figure 98). A significant increase in the deformation rate and the appearance of numerous rock avalanches at the end of October led PVMBG to raise the Alert Level from II to III and evacuate hundreds of local residents. During November and December 2020 the deformation rate continued to increase and numerous rock avalanches were reported. Incandescent block avalanches were first reported on 4 January 2021. Block-and-ash flows began on 7 January and increased in frequency throughout the month; a new dome was confirmed that day. The deformation rate decreased significantly as the dome grew in size during January. Hundreds of incandescent block avalanches were recorded through the end of the month. A large explosion on 27 January produced a 12.2-km-high ash plume and a large pyroclastic flow; ashfall was reported in numerous communities. Incandescent block avalanches and block-and-ash flows continued frequently during February 2021; a second dome was reported growing near the center of the summit crater on 17 February.

Figure (see Caption) Figure 98. A very small thermal anomaly was recorded in Sentinel-2 satellite data near the NW crater rim at the summit of Merapi during August-October 2020, along with gas emissions. Images are from 21 August 2020 (top left), 15 September 2020 (top right), 20 October 2020 (bottom left), and 13 January 2021 (bottom right). The January anomaly was much larger, noticeable even through cloud cover, six days after PBBTKG scientists confirmed the presence of a new dome growing near the SW crater rim. Courtesy of Sentinel Hub Playground.

The deformation rate at the summit, shortening determined by Electronic Distance Measurements (EDM) interpreted by PBBTK as inflation related to magma moving towards the surface, remained between 1-2 cm per week during August through early -October with just steam-and-gas plumes rising 150-250 m. During the week of 9-15 October PBBTKG reported a deformation rate of 1 cm/day. Drone photographs confirmed no change in the size or shape of the dome on 18 October 2020. The shortening rate increased to 2 cm/day during 16-22 October and the steam-and-gas plumes rose up to 500 m above the summit; the shortening rate increased to 4 cm/day during 23-29 October. PVMBG reported on 28 October that rock avalanches were heard twice in Babadan and Jrakah over the previous 24 hours, but fog prevented observations.

PVMBG raised the Alert Level from II to III on 5 November 2020 based on an increase in both seismicity and the deformation rate. Rock avalanches were heard that day from Babadan. Analyses of the crater area based on photographs from 30 October and 3 November did not show any morphological changes at the dome. The shortening rate, however, increased to 9-10 cm/day during the first three weeks of the month. Rock avalanches were observed on 8 November on the W flank moving as far as 3 km downslope and moving 2 km on 14 November. Photos comparing the SE flank on 11 and 19 November showed that part of the 2018 lava dome had collapsed. Drone images on 16 November also showed a collapse of part of the crater wall. On 22 November rock avalanches from the crater rim moved 1 km down the W flank. Steam and gas emissions were observed from the Babadan Observation Post rising 200-750 m above the summit during the second half of November (figure 99. A photo analysis on 26 November indicated that part of the 1954 lava dome had collapsed since 19 November. The deformation rate had increased to 11 cm/day by the last week of the month. During overflights on 26 and 27 November BNPB and BPPTKG observers noted many new avalanche deposits on the NW, W, and SW flanks. As of 27 November, there were 2,318 people who had been evacuated from the area around the volcano.

Figure (see Caption) Figure 99. Steam and gas emissions at Merapi were observed from the Babadan Observation Post rising 200-750 m above the summit during the second half of November, including on 25 November 2020 shown here. Courtesy of MAGMA Indonesia Volcano Photo Gallery.

Steam and gas plumes rose 150-400 m above the summit throughout December 2020. Rock avalanches were heard but not seen due to foggy weather during the first few days of the month. On 8 December they were seen falling 200 m upstream of Kali Lamat on the W flank and on 14 December they were observed moving downslope 1.5 km on the NW flank upstream of the Senowo River. Rock avalanches were also observed on 23 December moving 1.5 km down the W flank above Kali Sat ravine and on 31 December moving the same distance above the Senowo River. The deformation rate remained high during December, ranging from 9-11 cm/day through 24 December; it rose to 14 cm/day during the last week. Minor changes were seen in photographs of the summit area, but drone data on 5 and 14 December showed no new lava dome. No lava dome was visible in a clear view of the upper part of the SW flank on 20 December (figure 100); the head of BPPTKG-PVMBG noted that the first observed incandescence in that area was on 31 December.

Figure (see Caption) Figure 100. No lava dome was visible in a clear view of the upper part of the SW flank of Merapi on 20 December 2020, although rock avalanches had occurred a number of times during the month; the head of BPPTKG-PVMBG noted that the first observed incandescence in that area was on 31 December. Courtesy of BPPTKG and MAGMA Indonesia Volcano Photo Gallery.

The deformation rate remained very high at 15 cm/day during the first week of January 2021. Rock avalanches were observed on 1 and 3 January that moved 1.5 km from the summit towards Kali Lamat and Kali Senowo on the W and NW flanks. On 4 January incandescent material was observed with a thermal webcam, and rock avalanches were heard at the Babadan Observation Post (figure 101). Incandescent block avalanches were observed 19 times during 4-7 January, traveling 800 m to the upper reaches of Kali Krasak (figure 102). Four block-and-ash flows occurred on 7 January, moving less than 1 km downslope. Comparison of images between 24 December and 7 January revealed a new lava dome. Hanik Humaida, the head of BPPTKG-PVMBG concluded that incandescent lava had appeared at the bottom of the 1997 dome and noted that incandescence had first been observed late on 31 December. PVMBG issued VONAs on 7 and 9 January reporting block-and-ash flows that produced ash plumes which rose to 3.2 km altitude and drifted SW and NW.

Figure (see Caption) Figure 101. Incandescence from the growth of a new dome at Merapi on the SW flank appeared in a thermal webcam image on 4 January 20201. Courtesy of BPPTKG (Terjadi Peningkatan Aktivitas Vulkanik, Teramati Guguran Lava Pijar di Gunung Merapi, 5 January 2021).
Figure (see Caption) Figure 102. Numerous incandescent blocks fell down the SW flank of Merapi from the new lava dome, seen here on 6 January 2021. Courtesy of BPPTKG and MAGMA Indonesia Volcano Photo Gallery.

Incandescent block avalanches were observed 128 times during the second week of January moving as far as 900 m down the SW flank to the upper reaches of Kali Krasak. Two block-and-ash flows were also reported. On 14 January 2021, the measured volume of the new dome was 46,766 m3 with a growth rate of about 8,500 m3/day. Deformation decreased significantly to a shortening rate of 6 cm/day during the second week of the month. Incandescent avalanches continued at a high rate and were reported 282 times during the third week of January (figure 103); they traveled as far as 1,000 m to the upper reaches of the Kali Krasak and Kali Boyong. Block-and-ash flows were recorded 19 times during 15-21 January moving 1,800 m downslope to the SW (figure 104). Compared to the previous week, as measured on 21 January, the new dome had more than doubled in size to 104,000 m3 with an average growth rate of 8,600 m3/day.

Figure (see Caption) Figure 103. There were 20 incandescent block avalanches that fell up to 1,000 m down the SW flank of Merapi from the new dome on 16 January 2021. Courtesy of BPPTKG.
Figure (see Caption) Figure 104. PVMBG reported a block-and-ash flow (referred to as Awan Panas Guguran or APG) at Merapi that traveled approximately 1,000 m down the SW flank towards Kali Krasak on 18 January 2021. Courtesy of BPPTKG and BNPB (Gunung Merapi Kembali Keluarkan Awan Panas Guguran Sejauh 1.000 Meter, 18 January 2021).

The deformation rate decreased further to less than 1 cm/day by the end of the third week of January. A substantial block-and-ash flow on 19 January that moved 1,800 m down the Krasak and Boyong rivers produced a 500-m-high ash plume that drifted E. According to detikNews, ash fell on 19 January in several villages in Musuk and Tamansari Districts in the Boyolali Regency, and in the Kemalang District in the Klaten Regency (figure 105). The Darwin VAAC reported ash visible in the webcam on 20 and 26 January that drifted downwind close to the summit. Over 200 incandescent block avalanches were observed during the last week of January; the maximum distance traveled was 1,500 m down the SW flank. Block-and-ash flow activity increased significantly during 25-27 January with four flows on 25 January and 13 flows on 26 January which produced ash plumes that rose 300-400 m above the summit and traveled 600-1,500 m down the SW flank. PVMBG reported 31 block-and-ash flows on 27 January that traveled as far as 3 km down the SW flank (figure 106).

Figure (see Caption) Figure 105. Ash from Merapi covered plants in Tegalmulyo Village, in the Klaten Regency on 19 January 2021. Photo by Achmad Syauqi, courtesy of detik.com.
Figure (see Caption) Figure 106. A block-and-ash flow at Merapi with it’s associated ash plume seen here on 27 January 2021 was one of 36 such events reported by BPPTKG that day; they traveled up to 3 km from the summit down the SW flank. Courtesy of BNPB (Gunung Merapi Erupsi Besar, Begini Penjelasan BPPTKG, 27 January 2021).

The volume of the 2021 lava dome on 25 January 2021 was 157,000 m3, but by 28 January it was only 62,000 m3 as a result of block-and-ash flows, explosions, and pyroclastic flows that occurred on 26-27 January. An explosion on 27 January was reported by the Darwin VAAC, based on multiple ground reports of a significant eruption, although meteoric clouds obscured most ground observations. The ash plume rose to 12.2 km altitude, drifted NW, and was visible in satellite images. Ash emissions from a superheated pyroclastic flow rose to 6.1 km altitude and drifted NE (figure 107). Satellite imagery and pilot reports indicated that the 12.2 km ash plume dissipated after about five hours, while the plumes generated by the pyroclastic flow continued moving E at 3.7 km altitude for several more hours. Sand-sized ash was reported in several villages in the Tamansari District in Boyolali Regency on the E flank including the Dukuh Beling area, Sudimoro (Sangup Village), Lanjaran Village, Mriyan and in Boyolali City, Central Java on 27 January. Dense ash was also reported in Tegalmulyo Village; Sruni Village and Cluntang in the Musuk District also reported ashfall.

Figure (see Caption) Figure 107. A significant explosion at Merapi on 27 January 2021 produced an ash plume to 12.2 km altitude that drifted NW and a pyroclastic flow that sent ash to 6.1 km altitude and drifted NE. The pyroclastic flow is seen here from Ngrangkah, Umbulharjo, Cangkringan, Sleman Regency. Photo by Jauh Hari Wawan S, courtesy of detik.com.

Multiple incandescent rock avalanches were observed during the first week of February 2021. They traveled 500-1,200 m down the SW flank. On 4 February the volume of the 2021 lava dome on the SW flank was measured at 117,400 m3; the growth rate since 28 January was 12,600 m3/day. On 8 February, 23 incandescent block avalanches were reported that traveled as far as 1,500 m from the summit down the SW flank upstream of Kali Krasak and Kali Boyong. Six incandescent avalanches were reported on 9 February; webcams indicated multiple daily incandescent block avalanches for the rest of the month. When measured on 11 February, the dome had grown significantly to 295,000 m3 at a growth rate of 48,900 m3/day (figure 108).

Figure (see Caption) Figure 108. The 2021 lava dome at Merapi was located at the head of the SW flank, and was almost 300,000 m3 in size on 11 February, two days before this image taken on 13 February 2021. Courtesy of PVMBG and Rizal.

A drone observation on 17 February noted two lava domes at the summit. The first (the 2021 lava dome) was located on the SW flank and was attached to the 1997 lava dome, and a second new dome had appeared more in the center of the summit crater. Based on calculations from aerial photographs, the dome on the SW flank was 258 m long, 133 m wide, and 30 m high, with a volume of 397,500 m3 and growth rate of 25,200 m3/day. The lava dome in the center of the summit crater was 160 m long, 120 m wide, and 50 m high, with a volume of 426,000 m3 and an average growth rate of 10,000 m3/day. Deformation data showed no changes during February. During 24-27 February one or two block-and-ash flows occurred each day, the largest travelled 1,900 m SW (figure 109). The block-and-ash flow on 25 February 2021 at 1652 local time (WIB) produced traces of ashfall in Kali Tengah Lor, Kali Tengah Kidul, Deles, and Tlukan. The volume of the lava dome on the SW flank on 25 February was 618,700 m3 with a growth rate of 13,600 m3/day.

Figure (see Caption) Figure 109. A block-and-ash flow at Merapi on 27 February 2021 descended hundreds of meters down the SW flank and sent ash drifting E mostly below the level of the summit. Courtesy of BPPTKG and MAGMA Indonesia Volcano Photo Gallery.

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: 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/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1, https://magma.esdm.go.id/v1/gunung-api/gallery); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG), Center for Research and Development of Geological Disaster Technology (URL: http://merapi.bgl.esdm.go.id/, https://twitter.com/BPPTKG/status/1350508928740675584); 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/); Detik news (URL: https://news.detik.com/, https://news.detik.com/berita-jawa-tengah/d-5339832/hujan-abu-gunung-merapi-jangkau-desa-di-wilayah-krb-ii-klaten, https://news.detik.com/berita-jawa-tengah/d-5350542/gunung-merapi-erupsi-sirene-bahaya-meraung-warga-turun-ke-tempat-aman, https://news.detik.com/berita-jawa-tengah/d-5350625/gunung-merapi-erupsi-besar-boyolali-diguyur-hujan-abu-campur-pasir?_ga=2.230047007.2076450499.1612195171-14950811.1611700211); Rizal (URL: https://twitter.com/Rizal06691023/status/1360488059649757191).


Yasur (Vanuatu) — April 2021 Citation iconCite this Report

Yasur

Vanuatu

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

All times are local (unless otherwise noted)


Gas-and-ash emissions, SO2 plumes, and thermal anomalies during September 2020-February 2021

Yasur, located at the SE tip of Tanna Island, contains a 400-m-wide summit crater within the small Yenkahe caldera. Its current eruption has been ongoing since at least 1774 and has consisted of Strombolian and Vulcanian activity. More recently, Strombolian activity and gas-and-ash explosions have been reported (BGVN 45:03 and 45:09). This report covers activity from September 2020 through February 2021 that is characterized by ongoing explosions, gas-and-ash emissions, SO2 plumes, and thermal anomalies. Information primarily comes from monthly bulletins of the Vanuatu Meteorology and Geo-Hazards Department (VMGD) and various satellite data.

VMGD reported that ongoing explosions and gas-and-ash emissions continued at an elevated level throughout this reporting period, based on ground observations and seismic data. On clear weather days these emissions were captured by Sentinel-2 satellite imagery (figure 75). Some of the more intense explosions may result in larger ejecta falling in or around the summit crater. On 18 January 2021 a webcam image captured a gas-and-ash emission rising above the crater rim at 1500 (figure 76).

Figure (see Caption) Figure 75. Sentinel-2 satellite images showing gas-and-ash emissions rising from the summit crater of Yasur on clear weather days. Ash is visible during 17 October (left) and 21 December 2020 (middle), while white gas-and-steam emissions are observed on 14 February 2021 (right). Sentinel-2 satellite images with “Natural Color” (bands 4, 3, 2) rendering. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 76. Webcam photo of a gas-and-ash emission rising from Yasur on 18 January 2021 taken at 1500. Courtesy of VMGD.

Sulfur dioxide emissions were measured using the Sentinel-5P/TROPOMI satellite instrument for multiple days each month from September through February 2021 (figure 77). The density and drift direction of these SO2 plumes varied. During 17-19 January relatively dense SO2 plumes were detected consecutively, and drifted SE (figure 78).

Figure (see Caption) Figure 77. Occasional SO2 plumes of varying densities were observed from Yasur during each month of September 2020 through February 2021. Plumes drifted generally W on 28 September (top left), 29 October (top right), 6 December (middle right), 25 December 2020 (bottom left), slightly N on 14 November (middle left), and SW on 19 February 2021 (bottom right). Courtesy of NASA Global Sulfur Dioxide Monitoring Page.
Figure (see Caption) Figure 78. Relatively high-density SO2 plumes from Yasur during 17 (left), 18 (middle), and 19 (right) January 2021 were observed consecutively using the TROPOMI imaging spectrometer on the Sentinel-5P satellite. The plumes drifted SE on each of the days. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Intermittent thermal anomalies recorded by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system during September 2020 through February 2021 were low to moderate in power (figure 79). Brief noticeable break in activity occurred during early December 2020 and for much of January 2021. The MODVOLC thermal alert data recorded 41 thermal signatures primarily within the summit crater over a total of 25 different days during September 2020-February 2021. Some of these thermal anomalies were also captured in Sentinel-2 thermal satellite imagery; thermal anomalies were visible in the N and S vents in the summit crater (figure 80).

Figure (see Caption) Figure 79. MIROVA (Log Radiative Power) thermal data for Yasur from 26 May 2020 through February 2021 showed persistent low to moderate thermal activity. A brief but noticeable break in activity occurred during early December, early January, and late January. Courtesy of MIROVA.
Figure (see Caption) Figure 80. Sentinel-2 thermal satellite images showing strong thermal anomalies (yellow-orange) in the N and S vents of the summit crater at Yasur each month from September 2020 through February 2021. During 22 September (top left), 17 October (top right), and 26 November (middle left), the two thermal anomalies in the crater were roughly the same intensity. On 21 December (middle right) the anomaly was accompanied by a small, gray ash plume. On 15 January (bottom left) and 24 February (bottom right) the intensity of the anomaly in the N vent and then the S vent had decreased slightly. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Geologic Background. Yasur, the best-known and most frequently visited of the Vanuatu volcanoes, has been in more-or-less continuous Strombolian and Vulcanian activity since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island, this mostly unvegetated pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide, horseshoe-shaped caldera associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD), Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); 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/); NASA 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).


Rincon de la Vieja (Costa Rica) — March 2021 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 through 13 December 2020

Recent activity at Rincón de la Vieja has been dominated by frequent weak phreatic explosions, with an occasional ash plume, along with gas-and-steam emissions. Sporadic lahars have also been recently reported (BGVN 45:10). The volcano has a hot, churning, acid lake in its main crater. The current report describes activity during October 2020-February 2021, a continuation of the most recent eruptive period that began in January 2020. The primary information source for this report is weekly bulletin from the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA).

According to OVSICORI-UNA, small but frequent hydrothermal explosions continued in October through mid-December 2020, although less energetic than during previous months (figure 34). During the first half of October there were 1-2 daily small explosions. Plumes often rose 500-800 m above the crater rim, but on 1 and 6 October they rose 1 km. Then the number briefly increased to 5-7 small daily explosions before decreasing during the latter part of October; one explosion seen in webcam images on 24 October sent a plume to 1 km above the crater (figure 35).

Figure (see Caption) Figure 34. Graph showing the number of daily eruptions at Rincón de la Vieja during 2020. Following frequent phreatic explosions during April-June, weak intermittent explosions were detected again starting in late July and continuing through December 2020. Courtesy of OVSICORI-UNA.
Figure (see Caption) Figure 35. Webcam photo of Rincón de la Vieja taken on 24 October 2020 at 0808 local time. According to OVSICORI-UNA, the explosion lasted for about a minute and the resulting plume rose to 1 km above the crater. Courtesy of OVSICORI-UNA, as reported by The Nacion.

OVSICORI-UNA reported that in November small-to-moderate hydrothermal explosions increased in amplitude, but became more sporadic and by the end of the month had decreased to only one per day. An explosion at 0835 on 3 November produced a plume that rose 800 m above the crater rim. According to OVSICORI’s weekly bulletin for 23 November, there had been 1,437 explosions since the beginning of 2020. A large explosion on 13 December was the last through at least February 2021. During the week of 18 January OVSICORI changed the Alert Level from 3 to 2 due to the low level of activity.

Geodesic monitoring at the summit by GPS indicated no deformation trend in October, significant contraction in November, some extension in December, but then no significant changes through at least February 2021. Aerial observations on 13 February indicated that the crater lake was at a low water level and had sustained convection. The lake level had dropped 15-20 m since February 2020, and 5-10 m since May 2020. Gas monitoring during October 2020-February 2021 was carried out at the Ojo de Agua Santuarium (4 km N of the active crater); sulfur dioxide in the plume was not detected in significant quantities.

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/); The Nacion (URL: https://www.nacion.com/).


Kilauea (United States) — March 2021 Citation iconCite this Report

Kilauea

United States

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

All times are local (unless otherwise noted)


New eruption in December 2020 with an active lava lake, lava flows, spattering, and a dome fountain

Kilauea, which overlaps the E flank of the Mauna Loa shield volcano, is the southeastern-most volcano in Hawaii. It’s East Rift Zone (ERZ) has been intermittently active for at least 2,000 years; the most recent eruption period began in January 1983 and was characterized by open lava lakes and lava flows from the summit caldera and the East Rift Zone. During May 2018 lava migrated into the Lower East Rift Zone (LERZ) and opened 24 fissures along a 6-km-long NE-trending fracture zone that produced lava flows traveling in multiple directions. Lava fountaining was reported in these fissures and the lava lake in the Halema’uma’u crater drained (BGVN 43:10).

September 2018 marked the end of the previous eruption period after 36 years of continuous activity. A new eruption began during December 2020 in the Halema’uma’u crater, characterized by a new lava lake, lava flows, lava fountaining, and gas-and-steam emissions. This report covers the activity from December 2020 through January 2021 using information provided from the US Geological Survey's (USGS) Hawaiian Volcano Observatory (HVO) in the form of daily reports, volcanic activity notices, and abundant photo, map, and video data.

Monitoring through mid-December 2020. Monitoring data from HVO since the end of the previous eruption in September 2018 included variable rates of seismicity and ground deformation, low rates of sulfur dioxide emissions, and minor morphological changes. Areas of elevated ground temperatures and minor gas emissions persisted in the vicinity of the 2018 LERZ fissures. Since March 2019, GPS stations and tiltmeters at the summit had detected deformation consistent with slow magma accumulation approximately 1-2 km below ground level. In addition, GPS stations in the upper ERZ recorded increased rates of uplift beginning in September. The HVO seismic network recorded 1,450 earthquakes in September, a significant increase over previous months, followed by another increase to 2,100 events in October. The pond at the bottom of the Halema’uma’u crater, which appeared on 25 July 2019, continued to collect water over time, slowly expanding and deepening from 23 m in early January 2020 to 48 m by 3 November 2020 (figure 467).

Figure (see Caption) Figure 467. Photos comparing the growth of the water lake in the Halema’uma’u crater at Kilauea on 18 December 2019 (left) and 23 September 2020 (right). During this time, the lake had risen approximately 25 m and had a surface area of 0.033 km2, compared to December 2019 (0.011 km2). Photos taken from the E rim of Halema’uma’u by K. Mulliken and M. Patrick; courtesy of USGS HVO.

The number of earthquakes detected in November was 1,350, less than what was recorded in October. By late November seismic stations recorded an average of at least 480 shallow, small-magnitude, earthquakes per week underneath the summit and upper ERZ; during 29-30 November HVO recorded over 80 earthquakes beneath the summit, beginning at 2300 on 29 November and continuing for 11 hours. On 2 December, spikes in seismicity were reported, consistent with a small dike intrusion under the S part of the caldera; tiltmeters at the summit detected about 8 cm of caldera floor uplift. At 1745 earthquakes intensified and another spike occurred after 0000 to an average rate of 10-12 earthquakes per hour. Within 24 hours, up to 220 earthquakes were recorded, occurring in clusters under the caldera and upper ERZ, according to HVO. By the afternoon of 3 December, seismicity and ground deformation rates at the summit had decreased and returned to near background levels. On 17 December, the number and duration of long-period seismic signals increased.

Eruptive activity during 20-21 December 2020. On the evening of 20 December at 2030 an earthquake swarm was recorded, accompanied by ground deformation detected by tiltmeters. Shortly after 2130 HVO reported an orange glow within the Halema’uma’u crater at Kilauea’s summit caldera, observed on an infrared monitoring camera, as well as a vigorous gas-and-steam plume, which marked the beginning of the eruption. At 2236 an M 4.4 earthquake was detected below the S flank. The Volcano Alert Level (VAL) was raised to Warning and the Aviation Color Code was raised to Red.

An HVO Volcanic Activity Notice issued on 21 December at 1014 stated that the water lake in the summit crater had boiled away due to new effusive activity, producing a large gas-and-steam emission (figure 468). Three vents in the N, NW, and W walls of the Halema’uma’u crater generated lava flows that fed a growing lava lake at the base of the crater (figure 469). Minor lava fountaining at these vents rose 25 m high; the highest fountain reached 50 m high in the N fissure. The lava lake began rising several meters per hour since the start of the eruption and exhibited a circulating perimeter, but a stagnant center (figure 470). Occasional blasts originated from the ponded lava in the crater. The eruption was confined to the Halema’uma’u crater. On 21 December the VAL was lowered to Warning and the Aviation Color Code decreased to Orange. Sulfur dioxide emission rates remained high at around 30,000 tons/day. In comparison, the emission rates from the pre-2018 lava lake ranged between 3,000-6,500 tons/day.

Figure (see Caption) Figure 468. Webcam image of the summit of Kilauea at 0630 on 21 December 2020. The water lake had been replaced by a lava lake as fissure vents in the wall of Halema’uma’u effused lava into the crater. Strong gas-and-steam emissions were visible. Courtesy of HVO.
Figure (see Caption) Figure 469. Map of the Halema’uma’u crater at Kilauea showing the location of volcanic activity shortly after 2130 on 20 December 2020. The red spots are the approximate locations of the three initial fissure vents effusing lava into the bottom of the Halema’uma’u crater. The water lake at the base of the crater had been replaced with a growing lava lake. The lava is deeper by at least 10 m compared to the water lake in this base map. The base map is from imagery collected on 23 September 2020. The eastern-most vent was characterized by lava fountains up to 50 m high with minor fountaining on the W side. Courtesy of HVO.
Figure (see Caption) Figure 470. Aerial view of the summit of Kilauea during an overflight at 1120 on 21 December 2020 showing two active fissure vents that effused lava into the growing lava lake in the Halema’uma’u crater. The N fissure (right-most) is the dominant stream of lava. The fresh cooling lava appears black, surrounding the center of the lake, which was described as stagnant. Courtesy of HVO.

Activity during 22-25 December 2020. The effusive eruption continued on 22 December from at least two vents on the N and W sides of Halema’uma’u; the third vent between the N and W vents paused between 0730 and 0800. The middle and W vents became inundated by the growing lava lake, while the northern-most vent remained vigorous. As of 1151 the crater lake had grown to 487 m below the crater rim, which suggests that the lake had filled 134 m from the crater floor; the rate at which the lake rose was more than 1 m per hour. Measurements made on 22 December showed that approximately 10-12 million cubic meters of lava had been erupted to that point, with a surface area of about 0.13-0.22km2 (figure 471). Another measurement made during the afternoon showed that the volume of the lava lake grew an additional two million cubic meters. The dimensions of the lake were 690 m E-W and 410 m N-S. Overflights were made on 21 and 22 December to obtain natural color and thermal infrared images of the growing lava lake (figure 472).

Figure (see Caption) Figure 471. Location map showing the activity from the new eruption at the summit of Kilauea in the Halema’uma’u crater updated on 22 December 2020 at 1400. Two active fissure vents (orange dots) on the N and W side of the crater fed lava into the growing lava lake (red). The blue dashed line represents the extent of the former water lake (July 2019 to December 2020) that was present in the crater before the eruption and the black dashed line represents the extent of the lava lake that was present during 2008-2018. The current lava lake is larger than both the previous lakes and has formed slightly more N compared to the former lava lake. Map created by M. Zoeller; courtesy of USGS HVO.
Figure (see Caption) Figure 472. Comparison of thermal images taken on 21 December at 1120 (top) and 22 December 2020 at 1130 (bottom) showing the rise and infilling of the lava lake from wall vents in the Halema’uma’u crater at Kilauea’s summit. Images by M. Patrick; courtesy of HVO.

By 23 December the lava lake had deepened to 155 m (figure 473). Two fissure vents on the N and W walls remained active; the W vent fed two narrow channels into the lake and the N vent remained the most vigorous. An island of cooler, solidified, lava within the lava lake that measured 115 x 260 m was drifting slowly eastward, based on a thermal map. During an overflight made later in the day, the approximate surface area was 0.25 km2, with dimensions of 460 x 715 m. High SO2 emissions were an estimated 30,000-40,000 tons/day, based on measurements made on 21 and 23 December.

Figure (see Caption) Figure 473. Plot showing the increasing depth in Kilauea’s summit lava lake since the beginning of the eruption on 20 December 2020 at 2130. A laser rangefinder was used to take measurements of the lava lake surface about 2-3 times per day. The depth of the lake was about 155 m on 23 December at 0630 (top right) compared to 87 m on 21 December at 0630 (bottom right). In comparison, the water lake that was observed in Halema’uma’u before the start of the eruption was 51 m at its deepest. Plot by H. Dietterich; courtesy of HVO.

Measurements taken on 24 and 25 December showed a continuously growing lava lake that was 169 and 176 m deep, respectively, and the volume of the lake had reached 21 million cubic meters. By 25 December the vigorously erupting N fissure vent was starting to become inundated and the W vent displayed intermittent spattering (figure 474). Around 1400 the lake level had dropped by 2 m to reveal a narrow black ledge around the N edge of the crater. The rate of SO2 emissions decreased to 16,000-20,000 tons/day during 25 December.

Figure (see Caption) Figure 474. Photo of the Halema’uma’u crater at the summit of Kilauea at 0230 on 25 December 2020 showing lava flows and lava fountaining feeding the lake. The main N vent started to become inundated by the growing lava lake. Intermittent activity continued at the W vent. Photo taken from the S rim of the crater by J. Schmith and C. Parcheta; courtesy of HVO.

Activity during 26-31 December 2020. During the morning of 26 December, at 0240, the N vent continued to erupt lava into the lake while the W vent began to effuse more vigorously with up to three narrow lava flows feeding the lake (figure 475). The depth and volume of the lake remained the same as on 25 December: 176 m deep and 21 million cubic meters. Lava fountaining was visible up to 10 m high above the W vent. After 0300, the N vent declined in activity and started to drain lava from the lake. Summit tiltmeters continued to record some deformation. Effusive activity remained confined to Halema’uma’u; the lava lake was 177 m deep as of 0700 m on 27 December. The SO2 emissions continued to decrease to about 3,300-5,500 tons/day during 27-28 December. Summit tiltmeters continued to record weak inflation.

Figure (see Caption) Figure 475. Photo of the W vent in Halema’uma’u at Kilauea’s summit shows the effusive activity increased on 26 December 2020. Some lava fountaining in this vent was visible while lava flows continued to feed the lake from the N vent. The lava fountaining in the W vent rose at least 10 m high. Photo was taken at 0515 by H. Dietterich; courtesy of HVO.

On 28 December the volume of the lava lake had grown to 21.5 million cubic meters and a thermal map updated on 26 December showed the new dimensions of the lava lake were 520 x 790 m, covering a surface area of 0.29 km2. The narrow black ledge visible above the N edge of the crater was about 1-2 m above the lake surface. During 27-28 December the main central island of cooler, solidified, lava drifted slowly W and measured about 110 x 225 m. The island surface was about 6 m above the lake surface and was covered in tephra, possibly remnants of explosive activity generated when lava first reached the water lake. Reduced, but still elevated, SO2 emissions were 3,300 tons/day; the emission plume carried Pele’s Hair and Pele’s Tears SW, depositing the tephra in areas downwind.

Effusive activity continued, with the lava lake measuring 179-180 m deep with a narrow black ledge around it as of 0400 on 29 December. Multiple narrow lava channels from the W vent fed into the crater. The lava lake volume was slightly more than 22 million cubic meters. The central 135 x 250 m island of solidified lava had drifted slowly W until 2200 on 28 December, then during the morning of 29 December it stalled and began rotating. There were about 10 smaller islands to the E.

On the morning of 30 December, at 0345, the lava lake was 181 m deep with the narrow black ledge around it; the lava lake was an estimated volume of 23 million cubic meters. A spatter cone built around the W vent, while lava effused through crusted-over channels. The main central island was about 6-8 m above the surface of the lake. The rate of SO2 emissions were 3,800 tons/day.

Similar observations were made during 31 December; the lava lake continued to grow, with the depth of the lake measuring 181-186 m and dimensions of 530 x 800 m, based on thermal mapping. The total surface area was 0.33 km2. Spattering continued in the W vent while lava flowed through crusted-over channels into the lake (figure 476). The main island in the lake continued to drift slowly W while roughly 10 smaller islands were observed around the E end of the crater (figure 477). The SO2 emission rate increased to 4,500-6,300 tons/day, compared to the previous day.

Figure (see Caption) Figure 476. Photo of the active W vent in Halema’uma’u at the summit of Kilauea, viewed from the W crater rim on 31 December 2020 with incandescence, spattering, and a prominent spatter cone; the lava lake is visible in the right background. Photo by B. Carr; courtesy of HVO.
Figure (see Caption) Figure 477. Annotated photo taken from the S rim of Halema’uma’u at the summit of Kilauea at 1700 on 30 December 2020 showing the location of the main central island and the smaller islands located on the eastern part of the crater. The W vent continued to effuse lava, as well as some spattering, while the N vent was inactive. Photo by K. Lynn; courtesy of HVO.

Activity during January 2021. Effusive activity continued within Halema’uma’u during January 2021. Lava originated from the NW side of the crater, with the W vents exhibiting spattering and lava effusions through crusted-over channels into the lava lake. A levee had also begun to develop around the perimeter of the lake (figure 478), creating what is known as a “perched” lake. According to HVO, this is common in lava lakes at Kilauea, and is due to repeated small overflows and the rafting and piling of surface crust that fuses together to form a barrier. During 31 December and 1 January the main island of solidified lava (135 x 250 m) had moved W while the other 10 smaller islands remained near the E side of the lake. Summit tiltmeters recorded weak deflation during 1-2 January. Both SO2 emission rates and seismicity remained elevated; the SO2 emission rate was 4,400 tons/day on 1 January.

Figure (see Caption) Figure 478. Photo of the lava lake in Halema’uma’u at Kilauea on 1 January 2021 that has developed a levee (darker black) around the perimeter, allowing the lake to be slightly perched above its base. Photo by M. Patrick; courtesy of HVO.

During 2-3 January the depth of the lake had grown to 189-190 m, had a volume of 26 million cubic meters, and still maintained the narrow black ledge around its perimeter. Measurements on 3 January showed that the lake was perched about a meter above its E and W edges, and discontinuously on the N edge. A thermal webcam showed spatter originating from two places in the W vents and a small dome fountain above the lake crust in front of the W vents (figure 479). The dome fountain had formed where lava was entering the lake from a submerged inlet at the base of the W vent. The height of the dome fountain reached 5 m and the width was an estimated 10 m. The main island, about 6 m above the lake surface, continued to drift W in front of the W vents while the 10 smaller islands remained relatively stationary near the E end of the lake.

Figure (see Caption) Figure 479. Video data showed the lava at Kilauea’s summit crater formed a dome fountain at the inlet to the lava lake in Halema’uma’u during 2-3 January 2021. The fountain is located near the base of the W vents where the inlet had become partially submerged. The 5-m-high dome fountain was about 10 m wide. Video by H. Dietterich; courtesy of HVO.

Lava effusion continued during 4-5 January from vents on the NW side of the crater. The lava lake was perched 1-2 m above its edge and had deepened to 191-192 m (figure 480). A thermal map from 5 January showed the perched lake dimensions had slightly decreased in size to 520 x 760 m, with a volume of about 27 million cubic meters. Summit tiltmeters continued to record weak deflation. Spatter in the W vents was visible from the top of a small cone on the NW wall of Halema’uma’u; the dome fountain persisted in front of the W vents (figure 481). The main island was rotating counterclockwise in front of the W vent while the now 11 smaller islands had generally stayed in the E side of the crater. Measurements on 4 January showed that the island was 7-8 m above the lake surface.

Figure (see Caption) Figure 480. A comparison of the Digital Elevation Model (DEM) and topographic profiles of the Halema’uma’u crater at Kilauea created from aerial imagery collected during helicopter overflights, showing the change in depth and elevation of the lava lake between 26 December 2020 (left) and 5 January 2021 (right). The N vent remained inactive as it became inundated by the rising lava. The central island had migrated W and rotated by 5 January. The depth of the lava lake was 192 m on 5 January. DEMs created by B. Carr, graphic created by K. Mulliken; courtesy of USGS HVO.
Figure (see Caption) Figure 481. Photo of the Halema’uma’u crater at Kilauea at 0545 on 5 January 2021 showing ongoing activity at the W vent, generating a lava flow that feeds both the lake and the dome fountain. Photo by K. Lynn; courtesy of USGS HVO.

HVO continued to monitor the changes in the active lava lake on 6 January, which was 194 m deep and remained perched 1-2 m above its edge. At 1500 rapid deflationary tilt was recorded overnight into 7 January. Lava from the W vents continued to feed the dome fountain through crusted-over channels on the W side of the crater. During the morning of 7 January the dome fountain weakened giving way to spattering at the top of the vent and the formation of a second cone. A thermal map on 7 January showed that the lake size had decreased to 470 x 760 m, covering 0.28 km2; more of the E part appeared to be stagnant while solidified lava was being progressively pulled beneath the molten surface (figure 482). SO2 emissions were still elevated at 3,400 tons/day on 6 January, but had decreased to 2,700 tons/day the next day. During 7-8 January incandescence was visible from two small cones on the NW wall of Halema’uma’u while lava flowed into the lake through a crusted channel. The main island remained 135 x 250 m; it had moved slightly E while the 11 smaller islands remained stationary.

Figure (see Caption) Figure 482. Thermal image (top) and photo (bottom) of the lava lake at Kilauea showing the larger central island on the W side of the Halema’uma’u crater and 11 smaller islands on the E side of the crater, taken on 7 and 9 January 2021, respectively. The lake is slightly perched and surrounded by a lower ledge of cooler lava along the perimeter (appears pink-purple in the thermal image along the perimeter). The lava effusion at the W vent has become less intense and much of the E half of the lake has stagnated completely, likely because the lake level has not changed significantly in the last three days. Image by M. Patrick (top) and photo by H. Dietterich (bottom); courtesy of HVO.

Incandescence and spatter continued on 9 January at the two W vents as lava descended through a crusted channel into the lake. Summit tiltmeters recorded weak deflation since 1 January, but on the evening of 9 January weak inflation was detected. A newly installed instrument during 9-10 January showed that the lake had risen about a meter since the switch to inflationary tilt. The depth of the lake slightly increased to 196 m below the W vents on the morning of 10 January. The W vents exhibited strong lava flows during the afternoon with spattering and spatter-fed lava flows from the top of the small cones on the NW wall of Halema’uma’u; lava also flowed through crusted-over channels into the lake. Low lava fountaining was also visible during 10-11 January. The SO2 emission rates were 2,300 tons/day and 2,500 tons/day on 10 and 11 January, respectively.

During the morning of 12 January the lava lake remained at a depth of 196 m below the W vents; the stagnant E half of the lake was about 4 m shallower and had subsided below its perched rims. Low lava fountaining and flows through channels from the top of the small cones were visible. Measurements of the main island on 12 January showed that it was 8 m above the surface, with the highest point at 23 m. By 13 January, the depth of the lake had increased to 198 m. On 13 January a small portion of the active cone had collapsed, causing a second vent to open adjacent to the main vent and effuse lava for less than 20 minutes.

Activity continued in Halema’uma’u with low fountaining, lava flows, and spattering from the W vent through 22 January (figure 483). The depth of the lake continued to increase slowly to 204 m on 22 January. The entire lake was perched 1-2 m above the crust between the levees along the perimeter and the crater wall. All of the islands of solidified lava within the lake were stagnant; the dimensions of the main island were unchanged since 10 January. On 14 January the SO2 emissions increased to 4,700 tons/day, then decreased to 2,500 tons/day on 16 January. On 19 January at 1746 field crews observed a minor collapse event from the spatter cone on its N rim and open channel margins at the W vent (figure 484). Summit tiltmeters began to detect some deflation on 20 January; the rate of which began to slow by 21 January. Measurements on 22 January showed that the S end of the main island was 12 m above the lava lake surface, with the highest point still around 23 m.

Figure (see Caption) Figure 483. Photo of low fountaining and an accompanying lava flow at the W vent of Halema’uma’u at Kilauea on 15 January 2021. The vent formed a spatter cone around the fountaining as the flow moved through an open channel into the lake. Photo by M. Patrick; courtesy of HVO.
Figure (see Caption) Figure 484. Series of photos showing the W vent at Kilauea (seen from the S rim looking NW) that continued to feed the growing lava lake in Halema’uma’u through an open channel. At 1746 on 19 January field crews observed a minor collapse on the N rim of the spatter cone and channel margins. The photo at 1731 (top left) shows the vent just before the collapse; the photo at 1746 (top right) shows just after the collapse; the photos at 1749 (bottom left) and at 1811 (bottom right) show the destabilization and movement of the portion of the remaining cone flank surrounded by incandescence. Photos by H. Dietterich; courtesy of HVO.

During the morning of 23-25 January the lava lake was about 205 m deep; the W half remained active with low fountaining and a lava flow while the E half was stagnant (figure 485). The E side of the lake was elevated about 1-2 m and the W half was elevated about 4 m above the solidified lava adjacent to the crater wall. HVO reported that summit tiltmeters continued to record variable inflation and deflation. On 23 January SO2 emission rates were 2,200 tons/day.

Figure (see Caption) Figure 485. Map of the Halema’uma’u crater at the summit of Kilauea on 25 January 2021 showing the locations of the active lava lake (red), the extent of the lava lake (light red), the major islands of solidified lava (yellow), the active W vent (orange), and the inactive N vent (maroon). The depth of the lake is 205 m, the size of the lake is 0.1 km2, and the total lake volume is 31 million cubic meters. In comparison, the dashed blue line represents the final extent of the water lake that evaporated on 20 December 2020 and the dashed black line represents the extent of the 2008-2018 lava lake. Courtesy of USGS HVO.

The depth of the lava lake continued to deepen, and by the evening of 27 January it was 209 m, while the stagnant E half remained up to 5 m lower. The active lake surface no longer extended around the E side of the central island; surface circulation was limited to the W, N, and S sides of the island. Activity in the W vents consisted of slow surface movements at the base of the lava flow and overturning of the crust near its margins. The E side of the lake was elevated approximately 1 m while the W was 3 m above the solidified lava adjacent to the crater wall. All the islands within the lake were stationary. By 28 January only the W part of the lava lake was active. On 29 January, measurements made on the main island showed its edges were 7-8 m above the lake surface.

On the morning of 30 and 31 January, the active W part of the lava lake was 211 and 212 m deep, respectively; the W vent had crusted over except for a single (possibly two) openings that were mostly obscured by degassing, though several incandescent areas on the cone were visible. Surface lava continued to effuse into the central part of Halema’uma’u from the base of the cone (figure 486). A series of surface cracks separated the active and stagnant parts of the lake. During 30-31 January tiltmeters recorded inflation at the summit.

Figure (see Caption) Figure 486. Photo showing the leading edge of an active lava lobe moving S into the central part of Halema’uma’u at Kilauea on 31 January 2021. Photo by M. Patrick; courtesy of HVO.

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

Information Contacts: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawai'i National Park, HI 96718, USA (URL: http://hvo.wr.usgs.gov/).


Pacaya (Guatemala) — March 2021 Citation iconCite this Report

Pacaya

Guatemala

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

All times are local (unless otherwise noted)


Increasing activity with ash emissions, explosions, and lava flows on multiple flanks during December 2020-February 2021

Extensive lava flows, bomb-laden Strombolian explosions, and ash plumes emerging from Mackenney crater have characterized the persistent activity at Pacaya since 1961. The latest eruptive episode began with intermittent ash plumes and incandescence in June 2015; the growth of a new pyroclastic cone inside the summit crater was confirmed later that year. The cone has continued to grow, producing frequent loud Strombolian explosions rising above the crater rim and ongoing ash emissions. In addition, fissures on the flanks of the summit crater have been the source of an increasing number of lava flows traveling distances of over one kilometer down multiple flanks during 2019 and into 2021. Increasing explosive and effusive activity during December 2020-February 2021 is covered in this report with information provided by Guatemala's Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), multiple sources of satellite data, and numerous photographs from observers on the ground.

Eruptive activity increased substantially during December 2020-February 2021. During December, ash emissions were reported fewer than half the days of the month; by February, dense ash emissions drifted many kilometers most days, and ashfall was reported numerous times in the surrounding communities. Strombolian explosions in December generally rose 50-125 m above the summit of the pyroclastic cone; by February they were commonly rising 300 m or more and sending ejecta 500 m from the summit. Numerous lava flows were reported on the NW, W, and S flanks during the period; a flow that emerged on the SSW flank on 7 January 2021 persisted through the end of February and was 800-1,200 m long. Strombolian activity also occurred at the fissure where the flow emerged, and incandescent blocks rolled hundreds of meters beyond the front of the flow. A steady increase in thermal activity was recorded with the MIROVA Log Radiative Power graph during December 2020 – February 2021 (figure 145). This corresponded to the persistent lava flows on multiple flanks and constant Strombolian activity. Multiple MODVOLC thermal alerts were issued many days each month during the period.

Figure (see Caption) Figure 145. The MIROVA graph of thermal anomalies at Pacaya from 13 May 2020 through February 2021 shows activity increasing in frequency and intensity beginning in late August 2020. Multiple lava flows from fissures on the flanks and Strombolian activity from the pyroclastic cone inside Mackenney crater were reported throughout the period. Courtesy of MIROVA.

The Washington VAAC reported an ash emission at Pacaya that rose to 3.0 km altitude and drifted WSW on 3 December 2020; it dissipated within a few hours. INSIVUMEH reported daily gas and steam plumes that rose a few hundred meters and sometimes drifted as far as 10 km. They also reported ash emissions along with the gas and steam on 10, 12-14, 16-18, 24-25, and 28 December. The ash plumes usually rose 300-400 m and drifted a few kilometers with the wind. On the evening of 28 December ash reached populated places including San José El Rodeo. Strombolian explosions at the summit occurred daily and rose 50-125 m above the Mackenney crater rim (figure 146). Ejecta was reported to heights of 250 m on 13 December and 200 m on 21 December.

Figure (see Caption) Figure 146. Explosions sent ejecta up to 125 meters above the Mackenney cone crater at Pacaya on 29 December 2020. In addition, lava flows with multiple branches were active on the W flank. Courtesy of CONRED (LAVA FLOWS IN PACAYA VOLCANO CONTINUE ACTIVE, 29 December 2020, Informative Bulletin No. 582-2020).

Lava flow activity continued on the SW flank throughout December 2020 and high winds remobilized ash on the flanks a number of times during the month. On 1 December the flow was about 675 m long and moving to the SW. Two branches were active the next day and three were reported on 6 December. A second flow appeared on the NW flank on 9 December on the plateau near Cerro Chino and grew to 250 m long (figure 147). Both flows had incandescent block avalanches spalling off their fronts and rolling at least 100 m. The SW-flank flow remained 450-550 m long through 11 December, and then grew to around 700 m the next day. Branches from both flows extended 700-1,000 m by 15 December and were moving NW, W, and SW. The NW-flank flow was growing through 16 December. Three 600-m-long branches were active on the SW-flank flow on 21 December. In a special bulletin released on 23 December, INSIVUMEH noted that the SW-flank flow was still active from the same mid-flank fissure where it originated on 20 October 2020, and consisted of 5-7 branches with lengths varying from 600-750 m (figure 148). For the remainder of December, multiple branches of the active SW-flank flow were between 525 and 650 m long, with block avalanches falling off the front that generated ash clouds.

Figure (see Caption) Figure 147. Sentinel 2 satellite imagery of Pacaya from 10 December 2020 revealed a thermal anomaly at the summit (lower right of center image), a multi-branch flow 550 meters long on the W flank (left of center image), and a small anomaly from the beginning of a new flow on the NW flank. Courtesy of INSIVUMEH (BOLETÍN VULCANOLÓGICO ESPECIAL BEPAC # 119-2020, Guatemala, 10 de diciembre de 2020, 19:30 horas (Hora Local), “ACTUALIZACIÓN DE LA ACTIVIDAD VOLCÁNICA”).
Figure (see Caption) Figure 148. Sentinel 2 satellite imagery of Pacaya on 20 (left) and 30 (right) December 2020 indicated thermal activity at the summit and on the NW and W flanks. The NW-flank lava flow was active from 9-16 December, and still cooling in the 20 December image. The WSW-flank lava flow had multiple branches between 525 and 650 m long for the last half of the month. Images use Atmospheric Penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

In a special bulletin issued on 1 January 2021 INSIVUMEH reported an increase in eruptive activity that produced Strombolian explosions which sent ejecta 300 m high and up to 100 m from the summit. Constant rumblings like a train and shock waves were heard and felt in nearby communities. Strombolian explosions continued to rise 75-200 m above the rim throughout the month, and numerous gas emissions rose 100-300 m and drifted as far as 10 km (figure 149). Ash emissions were noted on 1, 6, 7, 11, 13, 18, 19, 21-23, 25, 27, and 31 January. On 7 January ash drifted SW at 3 km altitude and ejecta was reported 300 m from the summit. INSIVUMEH noted that the columns of ash reached 300-500 m above the crater that day, generating loud rumbling and shock waves that vibrated roofs and windows in nearby villages. On 12 January explosions sent material 300 m high. A VAAC report on 22 January noted an ash plume drifting NW from the summit at 3.4 km altitude. INSIVUMEH remarked in a special report that day that ash fell in San Vicente Pacaya and in San Francisco de Sales. The ash emissions on 25 January were brown to gray, sporadic overnight and more continuous in the early morning, drifting 1-4 km W. On 27 and 31 January ash drifted 10 km W.

Figure (see Caption) Figure 149. Strombolian explosions rose 75-200 m above the summit of the pyroclastic cone inside Pacaya’s Mackenney crater on 7 January 2020 and throughout the month. On the NW flank, multiple branches of lava appeared as red to white areas in this thermal image. Thermal image courtesy of INSIVUMEH (BOLETÍN VULCANOLÓGICO ESPECIAL BEPAC002-2021, 12:00 horas (Hora Local), EXPLOSIONES CON CENIZA).

Multiple lava flows emerged from the flanks of Pacaya during January 2021. The lava flow that began on 20 October 2020 on the W flank continued to be active through about 8 January with branches flowing 400-600 m W and SW. A flow on the SSW flank began on 2 January from a vent 200 m below the rim of Mackenney crater. By 6 January it was feeding 3-4 flows from the same point, each 400 m long with block avalanches falling off the fronts and moving W, SW, and S down the flanks (figure 150). In the morning of 7 January two flows were seen on the N flank, 200 and 50 m long. Later that night another flow appeared on the SSW flank that lengthened rapidly, reaching 425 m the next day, and was 1,200 m long on 9 January (figure 151). High temperatures were still present on the W and SW flanks from the earlier flows. The SSW flow reached 1,500 m in length on 10 January and fluctuated between 1,200 and 1,600 m through 17 January when Strombolian activity ejecting material 5-10 m high was reported from the fissure. More Strombolian activity at the fissure was noted on 22 January, and the flow remained 800-1,150 m long through the 23rd. The flow reached 1,700 m in length on 25 January; for the rest of the month, it was reported as 800-1,000 m long, with block avalanches traveling an additional 200-400 m from the flow front. Strombolian activity reached 65 m high from the fissure at the head of the flow on 28 January. On 30 January multiple branches of the SSW flow were visible from a vantage point south of the volcano (figure 152).

Figure (see Caption) Figure 150. Multiple flows emerged from a single vent at Pacaya on 5 January 2021. The fissure was located about 300 m below the rim of Mackenney crater on the SSW flank. Incandescent debris falls from the front of the flow generated an ash plume seen at the bottom center of the image. Copyrighted photo by Deybin Fotografia, used with permission.
Figure (see Caption) Figure 151. A lava flow at Pacaya that first emerged on 7 January 2021 on the SSW flank grew quickly to over a kilometer long by 9 January and remained 800-1,000 m long for the rest of the month, often with incandescent blocks falling several hundred meters beyond the front of the flow. A thermal anomaly persisted at the summit of the pyroclastic cone inside Mackenney crater as well from constant Strombolian activity. A weak anomaly was also visible on the NW flank from earlier activity. Atmospheric penetration rendering (bands 12, 11, 8a) of Sentinel 2 images. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 152. Multiple branches of Pacaya’s SSW-flank-flow that began on 7 January 2021 were visible from a vantage point S of the volcano on 30 January. The branches were at least 700 m long with incandescent blocks falling several hundred meters farther down the flanks. The white lights below the flow are from people approaching the flow. Courtesy of David Rojas, used with permission.

Increased Strombolian activity during February 2021 was accompanied by frequent ash emissions that rose to 3.0-3.5 km altitude. The explosions often reached 225 m above the crater rim, and higher during pulses of increased activity. On 5 February ash drifted W, NW, and SW about 4 km and ashfall was reported in San Francisco de Sales, Concepcion el Cedro, and Calderas. A pulse of increased Strombolian activity on 6 February sent ejecta 400-500 m around the pyroclastic cone and columns of ash drifted 6 km NW and N. Ashfall was reported in the same areas as the day before, plus in El Bejucal, Mesías Altas and other communities in that region. Abundant ash emissions were reported by INSIVUMEH overnight on 7-8 February; variable winds dispersed the ash 30 km to the NW and W and 10 km N (figure 153). The ash emissions were accompanied by ejecta that landed 300 m from the summit. By the next day, ash had drifted as far as 66 km W and NW and ashfall was reported in El Patrocinio, El Rodeo, and El Caracol. Prolonged rumbling as loud as an airplane engine was reported from strong degassing. The Washington VAAC reported ash emissions in satellite imagery on 9 February at 3.8 km altitude drifting NW about 65 km from the summit.

Figure (see Caption) Figure 153. Dense ash emissions increased in frequency at Pacaya during February 2021. Ash emissions on 6 (left) and 8 (right) February resulted in ashfall in multiple communities around the volcano and were accompanied by incandescent ejecta falling hundreds of meters from the summit. Courtesy of INSIVUMEH (BOLETÍN VULCANOLÓGICO ESPECIAL BEPAC 006-2021, 009-2021).

High levels of similar activity continued through 10 February when 500-m-high ejecta was observed inside Mackenney crater. An increase in the seismic amplitude on 11 February was accompanied by ash plumes rising to 3.0-3.2 km altitude and drifting 15-20 km W and SW. Ashfall was reported in Patrocinio and El Rodeo. The next day ashfall was reported in San Francisco de Sales, San Jose Calderas, and Concepción el Cedro. On 13 February the Washington VAAC reported ash plumes visible in satellite imagery at 4.3 km altitude moving ENE, and ash fell in Santa Elena Barillas, Mesillas Bajas, and Mesillas Altas as the wind carried ash 6 km W, N, and NE; ash on 14 February drifted 5 km E. A new pulse of activity late on 16 February, the third in a week, produced incandescent material 400 m high; high-pressure gas also created plane engine noises, with roofs and windows rattled in nearby communities. Ashfall from the event was reported in Los Llanos, Los Pocitos, El Cedro, and other communities within 4 km. Another pulse on 18 February sent ejecta 200 m high, variable winds sent ash primarily NE and S. Two more pulses of activity on the morning of 19 February were recorded as increases in seismic amplitude by the PCG5 seismic station (figure 154). The first pulse was accompanied by a new lava flow appearing on the NW flank. The second pulse coincided with ash emissions that rose 500 m above the crater and drifted 8 km S, producing ashfall in Los Pocitos and plantations in that vicinity.

Figure (see Caption) Figure 154. Two increases in seismic amplitude at Pacaya were recorded during the morning of 19 February 2021 at seismic station PCG5. The first corresponded to the effusion of a new lava flow on the NW flank (left), and the second coincided with a pulse of ash plumes that drifted S (right). Courtesy of INSIVUMEH (BOLETÍN VULCANOLÓGICO ESPECIAL BEPAC 31-2021, Incremento de actividad por emission de ceniza y surgimiento de nuevo flujo de lava).

Ash emissions from explosions on 20 February drifted 10-25 km S and SW, resulting in ashfall in El Rodeo and El Patrocinio. That evening incandescent material rose 300-400 m above the summit and ejecta reached 500 m down the flanks of the cone (figure 155). The next day ash plumes rose to 2.8-3.2 km altitude and drifted SW with ashfall reported in San Francisco de Sales, El Cedro, and other plantations in the area (figure 156). During 22-24 February ash emissions rose as high as 800 m above the summit and drifted 3-5 km W, SW, and S. Ashfall drifted over 30 km S and SW on 24 February with ashfall reported in the villages of Los Pocitos, Pacaya, El Rodeo, and El Patrocinio. Pulses of increased activity on 26 February produced an ash plume 2.5 km above the summit. With variable wind directions at different altitudes, the ash drifted both N and S. The Washington VAAC reported the plume drifting N at 3.9 km altitude. This activity was accompanied by incandescent explosions that rose 500 m above the Mackenney crater, and noises as loud as an airplane engine. Similar pulses of activity continued through the end of the month, producing ash plumes that rose to 3.5 km altitude and drifted W and SW; ashfall was reported in El Patrocinio on 28 February.

Figure (see Caption) Figure 155. During the weekend of 20-21 February 2021 when this photo was taken, Strombolian explosions at Pacaya sent ejecta 400 m above the summit of the cone and 500 m down the flanks, while a lava flow remained active on the SSW flank. Copyrighted photo by David Rojas, used with permission.
Figure (see Caption) Figure 156. On 21 February 2021, ash plumes at Pacaya rose to 2.8-3.2 km altitude and drifted SW with ashfall reported in San Francisco de Sales, El Cedro, and other plantations in the area. Courtesy of Luis Figueroa.

The lava flow on the SSW flank was about 900 m long at the beginning of February with block avalanches falling about 100 m from the front of the flow, and Strombolian explosions active at the fissure at the head of the flow. Two distinct branches of the flow were visible on 6 February, one 1,200 and one 800 m long; multiple branches were active throughout the month (figure 157). High levels of activity continued; during 10-12 February the flow was 1,200-1,300 m long and loose blocks were descending an additional 200 m. During 13-18 February high temperature zones were still present on the N and NW flanks from earlier flows. From 14-18 February the S-flank flow was 900-1,100 m long with multiple branches and Strombolian activity at the vent (figure 158). A new flow appeared briefly on the NW flank during 19-20 February. High-temperature zones remained on the NW flank during 22-24 February. The S-flank flow remained active throughout the rest of February and was 800-1,100 m long, with incandescent blocks traveling up to 600 m beyond the flow fronts (figure 159).

Figure (see Caption) Figure 157. Multiple branches of the S-flank lava flow at Pacaya were active throughout February 2021. Strombolian activity was observed at the fissure where the flow emerged, and incandescent blocks rolled hundreds of meters beyond the flow front. The fissure was located about 300 m below the crater rim. The thermal anomaly from the Strombolian activity at the summit of the pyroclastic cone inside Mackenney crater was also visible in most satellite images. Atmospheric penetration rendering of Sentinel 2 image uses bands 12, 11, 8a. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 158. A lava flow about 1 km long on the S flank of Pacaya was active throughout the month; on 16 February 2021 Strombolian activity at the summit and at the head of the flow were visible. Multiple branches of the flow sent incandescent blocks hundreds of meters beyond the flow front. Copyrighted image by Berner Villela, used with permission.
Figure (see Caption) Figure 159. The lava flow on the S flank of Pacaya had several active branches as seen in this thermal image on 21 February 2021. The source fissure vent was about 300 m below the rim of Mackenney crater. Incandescent blocks fell hundreds of meters beyond the fronts of the flows. Courtesy of INSIVUMEH and Roberto Iboy.

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

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), 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/); 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); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Deybin Fotografía (URL: https://www.facebook.com/Deybin-fotografía-2316704905277353, https://twitter.com/UniversoNews1/status/1347037016324792327); David Rojas (URL: https://twitter.com/DavidRojasGt/status/1360789438545149957); Luis Figueroa (URL: https://twitter.com/luisficarpediem/status/1363664541318598657); Berner Villela (URL: https://bernervillela.com/galerias/naturaleza, https://twitter.com/soy_502/status/1362846917743366146); Roberto Iboy (URL: https://twitter.com/IboyRoberto/status/1363688900401709057).


Villarrica (Chile) — March 2021 Citation iconCite this Report

Villarrica

Chile

39.42°S, 71.93°W; summit elev. 2847 m

All times are local (unless otherwise noted)


Explosions, ash plumes, crater incandescence, and an active lava lake during September 2020-February 2021

Villarrica, located in Chile, has had historical eruptions dating back to 1558. The current eruption period began in December 2014 and more recently has been characterized by summit crater incandescence, Strombolian explosions, and ash emissions (BGVN 45:09). This report covers activity during September 2020 through February 2021, which consists of an active lava lake, explosions, ash plumes, and nighttime crater incandescence. Information is provided by the Southern Andes Volcano Observatory (Observatorio Volcanológico de Los Andes del Sur, OVDAS), part of Chile's National Service of Geology and Mining (Servicio Nacional de Geología y Minería, SERNAGEOMIN), the Projecto Observación Villarrica Internet (POVI), part of the Fundacion Volcanes de Chile, a private research group that studies volcanoes across Chile, the Buenos Aires Volcanic Ash Advisory Center (VAAC), and various satellite data.

Activity during September 2020 was characterized by an active lava lake, white gas-and-steam plumes that rose 500 m above the crater, nighttime crater incandescence that could be observed on clear days, and sporadic ash emissions produced by minor explosions. During 5 and 7 September tephra deposits extended up to 36 m on the E and SE flanks, according to satellite data. On 25 September the seismic network recorded a long-period earthquake associated with a moderate explosion at 1350, which produced an ash plume that rose 800 m above the crater and drifted ENE (figure 104); blocks of ejecta were deposited around the crater. A second explosion was recorded at 1829 in conjunction with another long-period event, which generated an ash plume that rose 450 m above the crater (figure 104). Sentinel L2 A satellite images were used to determine that ashfall extended 3.8 km SSE, 865 m SE, and 275 m N as a result of the explosions during the day. The POVI webcam captured incandescent ejecta at night on 27 September (figure 105).

Figure (see Caption) Figure 104. Explosions at Villarrica on 25 September 2020 at 1350 (top) and 1829 (bottom) produced a long-period seismic signal and ash plumes that rose 800 m and 450 m above the crater, respectively and drifted ENE. Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcanica (REAV), Region De La Araucania y Los Rios, Volcan Villarrica, 25 de septiembre de 2020, 14:35 Hora local y 25 de septiembre de 2020, 19:20 Hora local).
Figure (see Caption) Figure 105. Incandescent ejecta up to 100 m above the summit of Villarrica was captured in the POVI webcam at night on 27 September 2020. Courtesy of POVI.

Intermittent white gas-and-steam plumes, ash explosions, and nighttime crater incandescence continued during October. On 4 October SERNAGEOMIN reported a long-period event accompanied by a moderate explosion at 1130, generating an ash plume that rose 450 m above the crater and drifted NE. The next day on 5 October two long-period events were recorded at 1343 and 1347 associated with explosions, resulting in ash plumes that rose to 400 m above the crater and drifted SE (figure 106). On 12 October a satellite image showed an ash plume drifting 2.5 km NE and a strip of tephra deposits measuring 200 m wide and 3 km long on the NE flank, as a result of two eruptive events on 9 October, according to POVI and Sentinel-2 satellite imagery.

Figure (see Caption) Figure 106. Explosions at Villarrica on 5 October 2020 produced a long-period seismic signal and an ash plume that rose 400 m above the crater and drifted SE. Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcanica (REAV), Region De La Araucania y Los Rios, Volcan Villarrica, 5 de octubre de 2020, 14:20 Hora local).

Moderate explosions were detected at 0534 and 0804 on 15 October, associated with two long-period earthquakes. As a result, ash plumes rose as high as 900 m above the crater and gas-and-steam plumes rose to 450 m, according to SERNAGEOMIN. The explosion at 0534 was accompanied by crater incandescence and incandescent ejecta that were deposited on the E flank as far as 3 km. An analysis of Planet Scope and Sentinel-2 satellite images showed that ash deposits extended 4.4 km NE. On 20 October an explosion and long-period event were recorded at 1722 that resulted in an ash plume 240 m above the crater that drifted S (figure 107). Explosions recorded during 22-23 October produced ash plumes that rose 780 m and 180 m above the crater, respectively, according to a Buenos Aires VAAC report and SERNAGEOMIN. The event on 22 October deposited tephra up to 3.8 km on the E flank.

Figure (see Caption) Figure 107. An explosion at Villarrica on 20 October 2020 at 1722 was characterized by a long-period earthquake and a dense, gray ash plume that rose 240 m above the crater and drifted S. Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcanica (REAV), Region De La Araucania y Los Rios, Volcan Villarrica, 20 de octubre de 2020, 18:00 Hora local).

Ash explosions continued in November, accompanied by intermittent nighttime crater incandescence and white gas-and-steam plumes. On 5 November a pulse of ash was observed at 1442 that rose 350 m above the crater and drifted NW. Similar activity was noted on 6 November at 0757 and 0808 when ash rose 350 m above the crater and at 1412 when ash rose 250 m above the crater, both of which drifted NW (figure 108). According to a Buenos Aires VAAC report on 7 November, an isolated ash plume was detected in satellite images up to 4.3 km altitude, drifted ESE. A Differential Absorption Optical Spectroscopy Unit (DOAS) showed average values of SO2 totaling 140 tons/day during 7-8 and 15 November with a maximum daily value of 168 tons/day on 7 November. An explosive event at 0051 on 8 November ejected incandescent material and produced an ash plume that rose 220 m above the crater (figure 108). On 10 November OVDAS reported an ash plume rose 320 m above the crater and drifted SSW, accompanied by continuous seismic tremor at 1514. Ash continued to be reported during 16-17 November rising 160 m above the crater and to 3.7 km altitude, respectively. Data from the DOAS showed that SO2 emissions had slightly increased to an average of 166 tons/day during 16-30 November, with a maximum daily value of 549 tons/day on 22 November.

Figure (see Caption) Figure 108. Explosions that generated ash and incandescent ejecta at the summit of Villarrica were captured by the POVI webcam during 6-8 November 2020 (left to right). Courtesy of POVI.

The number of ash events decreased in December compared to the previous months, though similar activity persisted. On clear nights, crater incandescence was visible, accompanied by white gas-and-steam emissions. SERNAGEOMIN reported a single long-period earthquake associated with a moderate explosion at 1844 on 5 December with a resulting ash plume that rose 160 m above the crater and drifted SSE; some ashfall was detected within 500 m of the crater, based on Sentinel-2, Pleiades, and SkySat data, and incandescent material was deposited on the SSE flanks (figure 109). According to POVI, during an overflight on 9 December scientists observed a lava lake 10-15 m in diameter that was partially covered by solidified floating black lava. Small pulses of gas and ash were observed in the lava lake. Additionally, ballistic blocks and pyroclasts that measured a maximum of 20 cm in diameter had been ejected up to 800 m from the crater during previous eruptive events. The average SO2 value was 178 tons/day with a maximum daily value of 353 tons/day on 7 December 2020, according to DOAS data.

Figure (see Caption) Figure 109. An explosion at Villarrica on 5 December 2020 at 1844 produced a long-period seismic signal along with an ash plume that rose 160 m crater and drifted SSE. Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcanica (REAV), Region De La Araucania y Los Rios, Volcan Villarrica, 5 de diciembre de 2020, 19:50 Hora local).

On 16 December at both 1146 and 1156 SERNAGEOMIN reported two ash pulses associated with long-period events. The first ash emission rose 160 m above the crater and drifted NW; the second rose 280 m above the crater and drifted 500 m NE. On 17 December at 1716 another ash plume associated with a long-period event rose 720 m above the crater and drifted ESE (figure 110). Pyroclastic deposits were reported up to 1.3 km N, 3.3 km E, 5 km SE, and 1.8 km SW from the crater, according to data obtained from Sentinel-2 and SkySat. During 18-19 December seismicity increased, intense crater incandescence was visible, and a notable sulfur odor was noted, according to POVI reports. Minor ash emissions rose to low heights on 22 December.

Figure (see Caption) Figure 110. An explosion at Villarrica on 17 December 2020 at 1716 produced an ash plume that rose 720 m above the crater and drifted ESE. Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcanica (REAV), Region De La Araucania y Los Rios, Volcan Villarrica, 17 de diciembre de 2020, 17:50 Hora local).

During January 2021, the number of explosions with ash plumes continued to decrease compared to the previous months. On clear weather days, occasional nighttime crater incandescence was observed, as well as white gas-and-steam emissions of variable intensities. During an overflight on 2 January scientists observed an incandescent vent at the bottom of the crater that had a solidified lava bridge connecting across a partially crusted-over top (figure 111). DOAS data showed that the average mass of SO2 plumes had increased compared to November and December to 318 tons/day with a maximum daily value of 789 tons/day on 12 January. During 1-15 January, the highest ash plume reported rose 700 m above the crater, though it was mostly composed of gas-and-steam emissions. During 16-31 January gas-and-steam emissions continued, rising to 1.3 km above the crater on 20 January. The average value of SO2 plumes increased again to 430 tons/day with a maximum daily value of 789 tons/day on 22 January.

Figure (see Caption) Figure 111. Webcam image of two incandescent vents at Villarrica on 2 January 2021. A bridge of solidified lava separates the two sections and extends across the active lava lake. Courtesy of POVI.

Activity during February continued to decrease compared to the previous months and consisted of primarily white gas-and-steam plumes, nighttime crater incandescence, and SO2 plumes. On 10 February dense, white gas-and-steam plumes rose 700 m above the crater. During 1-15 February, the average value of SO2 plumes was 181 tons/day with a maximum daily value of 369 tons/day on 2 February. Long-period earthquakes were recorded by the seismic network at 1146 and 1156 on 16 February with an associated explosion that generated ash plumes 160 m above the crater that drifted NW and 280 m that drifted NE, respectively. During 16-28 February white gas-and-steam plumes rose to a high of 780 m above the crater; SO2 plumes were an average value of 402 tons/day with a maximum daily value of 1,026 tons/day on 21 February.

Low-power thermal activity was detected during September 2020 through January 2021, according to the MIROVA Log Radiative Power graph using MODIS infrared satellite information (figure 112). Three thermal anomalies were recorded in September, one in October, and four in November; a single stronger anomaly was observed in early November. The number of anomalies increased in late December through late January 2021, though they remained low in power. On clear weather days, a strong thermal anomaly in the summit crater was visible in Sentinel-2 thermal satellite imagery during each month of the reporting period; in February, the strength of the anomaly had slightly decreased compared to previous months (figure 113).

Figure (see Caption) Figure 112. Low-power thermal anomalies were detected in the MIROVA graph (Log Radiative Power) at Villarrica during September 2020 through late January 2021. A pulse of thermal anomalies was recorded during late December 2020 through late January 2021 compared to the previous month but remained low in power. Courtesy of MIROVA.
Figure (see Caption) Figure 113. Sentinel-2 thermal satellite images showing strong thermal anomalies on clear weather days in the summit crater of Villarrica each month from September 2020 through February 2021. The strength of the thermal anomaly in February decreased slightly compared to previous months. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

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

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

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Scientific Event Alert Network Bulletin - Volume 08, Number 10 (October 1983)

Managing Editor: Lindsay McClelland

Arenal (Costa Rica)

Continued lava extrusion

Atmospheric Effects (1980-1989) (Unknown)

Lower stratospheric layer; source uncertain

Chichon, El (Mexico)

Fumarole and crater lake temperatures decline

Colo (Indonesia)

July- August explosion times, plume heights, and photos

Irazu (Costa Rica)

Fumarolic activity

Kilauea (United States)

10th and 11th major phases of E Rift Zone eruption

Kusatsu-Shiranesan (Japan)

Explosions eject large tephra

Langila (Papua New Guinea)

Moderate Vulcanian activity; explosion events; tremor

Manam (Papua New Guinea)

Tephra clouds; glow; rumbling; increased seismicity

Miyakejima (Japan)

Four lava flows, four explosion craters from 10-hour eruption

Pagan (United States)

Explosive eruption on 26 September

Pavlof (United States)

Large eruption column; tremor

Poas (Costa Rica)

Strong continuous gas emission

Rabaul (Papua New Guinea)

Large increases in seismicity and ground deformation

St. Helens (United States)

Deformation, SO2 emission, and seismicity increase as lava extrusion pattern changes

Tangkuban Parahu (Indonesia)

Seismicity continues to increase

Turrialba (Costa Rica)

Fumarolic activity

Veniaminof (United States)

Lava fountains and flow; ash emission; increased tremor

Villarrica (Chile)

Continuous explosions emit tephra; pyroclastic flows; summit glow suggests lava fountaining



Arenal (Costa Rica) — October 1983 Citation iconCite this Report

Arenal

Costa Rica

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

All times are local (unless otherwise noted)


Continued lava extrusion

The lava flow that was advancing rapidly down the NW flank in April stopped in July with its front at an elevation of 625 m. A new flow, the 42nd since 1968, began to emerge in July and by September had reached 1,380 m elevation. Gas emission was continuous and strong rumblings were heard.

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: J. Barquero H., E. Fernández S., Univ. Nacional, Heredia.


Atmospheric Effects (1980-1989) (Unknown) — October 1983 Citation iconCite this Report

Atmospheric Effects (1980-1989)

Unknown

Unknown, Unknown; summit elev. m

All times are local (unless otherwise noted)


Lower stratospheric layer; source uncertain

Lidar data from Hampton, Virginia showed a sharp increase in backscattering from aerosols in the lower stratosphere on 27 October. Accompanying the enhanced aerosols was a lowered, multiple tropopause, with sever al temperature inversions (the strongest at 9.4 km) instead of the single one that usually marks the boundary between the troposphere and the stratosphere. Poor weather had prevented observations since 3 October, when backscattering integrated from the tropopause to 30 km altitude was only half the 27 October value. Four nights later, lower stratospheric backscattering had declined but was still somewhat enhanced, and the altitude of the tropopause was 2 km higher. Preliminary analysis of 8 November data indicated an additional decrease in the amount of lower stratospheric aerosols and a further rise in the tropopause altitude. The source of the enhanced aerosols could not be determined but NASA scientists suggested either a recent eruption (perhaps the 3 October Miyakejima activity) or El Chichón material transported southward by an arctic air mass from high latitudes, where it has recently been concentrated. No lower stratospheric layers were reported in October from Fukuoka, Japan.

From Jeddah, Saudi Arabia, Edward Brooks reported variable dawns and dusks; some were brief because aerosols were at lower elevation than before. Dusk on 28 September ended quickly and was the same color as the sun, indicating that the scatterers were at low altitude and relatively large. Two distinct periods of enhanced colors were observed at dusk 2 October and dawn on the 8th, suggesting illumination of layers at 2 altitudes. Dusks 10-11 October and dawn on the 11th ended quickly, indicating that the scattering layer was at low altitude. Dusks 29 September and 9 October produced no significant color enhancement.

Geologic Background. 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 here.

Information Contacts: W. Fuller and P. McCormick, NASA; M. Fujiwara and M. Hirono, Kyushu Univ., Japan; E. Brooks, Saudi Arabia.


El Chichon (Mexico) — October 1983 Citation iconCite this Report

El Chichon

Mexico

17.36°N, 93.228°W; summit elev. 1150 m

All times are local (unless otherwise noted)


Fumarole and crater lake temperatures decline

A team of scientists descended into the crater during the week of 16 October. They found no new tephra or other signs of recent eruptive activity. The temperature of the crater lake had decreased to 42°C from 52-58°C during the previous descent in late January. The lake had receded substantially between the late January visit and observations from the crater rim 21 April but lake level was not appreciably lower in October. Average fumarole temperatures had dropped from 116°C in January to 99° in October. In the talus rampart just above the crater floor, a small low-pressure fumarole that had registered a temperature of 446°C in January was no longer active in October. No other notable changes in fumarole position were noted. No significant seismic activity has been recorded at El Chichón in recent months although some tectonic seismicity has occurred SE of the volcano.

Further Reference. Casadevall, T., de la Cruz-Reyna, S., Rose, W.I. Jr., Bagley, S., Finnegan, D.L., and Zoller, W.H., 1984, Crater lake and post-eruption hydrothermal activity, El Chichón Volcano, México: JVGR, v. 23, p. 163-191.

Geologic Background. El Chichón is a small, but powerful trachyandesitic tuff cone and lava dome complex that occupies an isolated part of the Chiapas region in SE México far from other Holocene volcanoes. Prior to 1982, this relatively unknown volcano was heavily forested and of no greater height than adjacent nonvolcanic peaks. The largest dome, the former summit of the volcano, was constructed within a 1.6 x 2 km summit crater created about 220,000 years ago. Two other large craters are located on the SW and SE flanks; a lava dome fills the SW crater, and an older dome is located on the NW flank. More than ten large explosive eruptions have occurred since the mid-Holocene. The powerful 1982 explosive eruptions of high-sulfur, anhydrite-bearing magma destroyed the summit lava dome and were accompanied by pyroclastic flows and surges that devastated an area extending about 8 km around the volcano. The eruptions created a new 1-km-wide, 300-m-deep crater that now contains an acidic crater lake.

Information Contacts: S. de la Cruz-Reyna, UNAM, México.


Colo (Indonesia) — October 1983 Citation iconCite this Report

Colo

Indonesia

0.162°S, 121.601°E; summit elev. 404 m

All times are local (unless otherwise noted)


July- August explosion times, plume heights, and photos

A VSI team monitored the eruption from near the island [beginning 23 July, and observed 22 distinct explosions (table 2). Many, but not all of these explosions were detected by satellite (table 1).]

Table 2. Times of Una Una eruption clouds with heights estimated by VSI geologists [23 July-26 August 1983.].

Date Time Plume height (km)
23 Jul 1983 1623 10
25-26 Jul 1983 2325-0021 7.5
27 Jul 1983 0400-0605 7.5
27 Jul 1983 1500-2010 7
28 Jul 1983 0002-0045 8
28 Jul 1983 1630-1730 8
30 Jul 1983 1615-? 6
01 Aug 1983 1834-2000 7
01-02 Aug 1983 2130-0230 6
02 Aug 1983 0314-0600 8
02 Aug 1983 0800-0900 8
02-03 Aug 1983 1905-0200 5
04 Aug 1983 0915-1100 6
06 Aug 1983 1520-? 6
07 Aug 1983 1100-1900 10
11 Aug 1983 1115-1135 8
12 Aug 1983 0047-0147 9
18 Aug 1983 1013-1240 12
22 Aug 1983 1203-? 8
24 Aug 1983 2148-2220 4
25 Aug 1983 1847-2000 5.5
26 Aug 1983 1023-1139 10

Maurice Krafft visited Una Una in mid-Aug. He observed and photographed the 22 Aug explosion (table 2 and figure 3) and pyroclastic flow deposits from previous explosions (figure 4). The entire island had been devastated except for a narrow strip of undamaged vegetation and villages along the E coast.

Figure (see Caption) Figure 3. Explosion photographed from the S on 22 August 1983. Pyroclastic flows from this explosion continued 500 m beyond the SSW coast of the island and 1 km beyond the NNW coast. Courtesy of Maurice Krafft.
Figure (see Caption) Figure 4. Coconut trees uprooted by pyroclastic flows on the SE side of the island, photographed 19 August 1983. Pyroclastic flow deposits from the major 23 July explosion were 5 m thick on the island's SW side. A plume from the summit is in the background. Courtesy of Maurice Krafft.

Further Reference. Katili, J.A., and Sudradjat, A., 1984, The devastating 1983 eruption of Colo volcano, Una Una Island, central Sulawesi, Indonesia: Geologisches Jahrbuch, v. A75, p. 27-47.

Geologic Background. Colo volcano forms the isolated small island of Una Una in the middle of the Gulf of Tomini in northern Sulawesi. The broad, low volcano contains a 2-km-wide caldera with a small central cone. Only three eruptions have been recorded in historical time, but two of those caused widespread damage over much of the island. The last eruption, in 1983, produced pyroclastic flows that swept over most of the island shortly after all residents had been evacuated.

Information Contacts: A. Sudradjat, VSI; M. Krafft, Cernay.


Irazu (Costa Rica) — October 1983 Citation iconCite this Report

Irazu

Costa Rica

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

All times are local (unless otherwise noted)


Fumarolic activity

Fumarolic activity continued on the NW flank with a mean temperature of 77°C. No activity was observed in the craters.

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: J. Barquero H. and E. Fernández S., Univ. Nacional, Heredia.


Kilauea (United States) — October 1983 Citation iconCite this Report

Kilauea

United States

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

All times are local (unless otherwise noted)


10th and 11th major phases of E Rift Zone eruption

EPISODE 10

"The 10th major episode of Kilauea's prolonged E rift zone eruption occurred in early October. As in episodes 4-9, the active vent was at the growing spatter cone, now tentatively named Pu'u O [later Pu`u `O`o, see 10:4], approximately 750 m NE of Pu'u Kamoamoa (figure 20).

Figure (see Caption) Figure 20. Distribution of Kilauea lavas and vent deposits of episodes 8, 9, and 10. Courtesy of HVO.

"Low-level eruptive activity marking the onset of episode 10 began at about 0800 on 2 October when a small lava flow, about 300-500 m3 in volume, was extruded onto the floor of the crater within Pu'u O. Some of the lava drained back into the open, glowing, 4-m-diameter conduit, which had been preserved near the center of the crater floor at the end of episode 9. No further activity was observed until 4 October when small bursts of spatter were intermittently emitted, most of which fell back into the conduit.

"Beginning at about 0100 on 5 October, harmonic tremor increased above the low repose-period background level, and lava began to spill through a deep breach in the NE wall of the spatter cone. Intensity of both harmonic tremor and eruptive activity increased over the next several hours. By 0330, tremor amplitude had increased by an order of magnitude, and by 0400 the glow was visible and the roar of the vent was audible 20 km away at HVO. Near dawn, the 300-m-high fountain was visible from the coast at the Wahaula Visitor Center (approximately 11 km S of the active vent). Late on 5 October, tremor amplitude increased to a maximum exceeding that of the previous eruptive episode, consistent with a trend of progressively increasing tremor that began with episode 4. High tremor occurred throughout vigorous episode 10 lava emission.

"After initially high activity, the fountains became erratic, changing rapidly in height from a few tens of meters to a maximum of about 250 m. At times, 3-4 distinct fountains were observed within the crater; sometimes high jetting fountains and a relatively low dome fountain played simultaneously from different parts of the lava pond surface.

"On 5-6 October, a thick slow-moving aa flow advanced 3.7 km ESE from Pu'u O, and rapidly moving pahoehoe formed superimposed sheets over an elongated area that extended about 2 km from the vent. By 7 October, the aa flow had stagnated, and the pahoehoe issuing to the NE had become confined to a channel in which a vigorously flowing lava river supplied a flow of pahoehoe and aa that eventually extended 4 km NE (figure 21).

Figure (see Caption) Figure 21. Lava flows and vent deposits of Kilauea episodes 11 and 12. Courtesy of HVO.

"Eruptive activity waned between about 1630 and 1700 on 7 October; harmonic tremor amplitude decreased rapidly at about 1650, and, after 1700, assumed the low level typical of repose-period activity. Such low-level tremor continued in the E rift zone for the remainder of October.

"As in the previous several episodes, episodes 10 basalt is characterized by the occurrence of scattered small olivine phenocrysts. Lava temperatures measured by thermocouple ranged from 1134° to 1142°C; the latter is the highest lava temperature measured since the beginning of eruptive activity on 3 January.

"Episode 10 produced nearly 14 x 106 m3 of lava for a total erupted volume since 3 January of approximately 120 x 106 m3 distributed over about 23 x 106 m2 of the rift zone. At the end of episode 10, Pu'u O was approximately 600 m in diameter and 80 m high. A chaotic jumble of disrupted blocks of agglutinated spatter covered the crater floor and the spillway through which the NE flow exited. The blocks, which were apparently transported as the last lava drained back into the eruptive conduit, choked the central conduit, which had stood open after episode 9. Oxidized fume issued from the margins of the crater floor and from the nearby parts of the interior walls of the crater but not from the rubble-covered floor.

"During episode 10, summit subsidence was recorded by nearly 19 µrad of ESE tilt change at the Uwekahuna vault on the NW rim of the caldera. This corresponds to a summit volume decrease of about 7.5 x 106 m3, bringing the total deflationary volume loss since January to about 130 x 106 m3. Summit inflation from the end of episode 10 to the end of October was sufficient for the Uwekahuna tiltmeter to more than recover the deflationary tilt change of episode 10."

Addendum: Episode 11 began with an increase in harmonic tremor amplitude at 2314 on 5 November and the onset of eruptive activity around midnight. Summit deflation began at about 0200 on 6 November. An overflight at 0730 revealed a discontinuous line of fountains up to 40 m high extending approximately 200 m up and down rift from the spatter cone (Pu'u O) active in previous eruptive episodes. Vents high on the W flank of the spatter cone fed 2 lava flows which that 4 and 1.5 km S before activity ceased there late on 6 November. The main vent, on the E summit and flank of the spatter cone, produced lava fountains 10-40 m high and fed the main lava flow that extended 8 km NE [it reached 9.5 km length; 8:11]. At 1840 on 7 November, the amplitude of harmonic tremor decreased sharply; lava fountaining from the main vent ceased later on 7 November, and inflation of the summit region resumed.

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: E. Wolfe, A. Okamura, and R. Koyanagi, HVO.


Kusatsu-Shiranesan (Japan) — October 1983 Citation iconCite this Report

Kusatsu-Shiranesan

Japan

36.618°N, 138.528°E; summit elev. 2165 m

All times are local (unless otherwise noted)


Explosions eject large tephra

UPI reported that thunderous explosions ejected tephra on 13 November at 1144. [Blocks fell a few hundred meters from the vent; original press reports of a more distant fall of large tephra were incorrect.] Tephra [reached a town] (Nakanojo) 40 km SE of the volcano. A "secondary" eruption occurred 25 minutes later. No injuries were reported.

Geologic Background. The Kusatsu-Shiranesan complex, located immediately north of Asama volcano, consists of a series of overlapping pyroclastic cones and three crater lakes. The andesitic-to-dacitic volcano was formed in three eruptive stages beginning in the early to mid-Pleistocene. The Pleistocene Oshi pyroclastic flow produced extensive welded tuffs and non-welded pumice that covers much of the E, S, and SW flanks. The latest eruptive stage began about 14,000 years ago. Historical eruptions have consisted of phreatic explosions from the acidic crater lakes or their margins. Fumaroles and hot springs that dot the flanks have strongly acidified many rivers draining from the volcano. The crater was the site of active sulfur mining for many years during the 19th and 20th centuries.

Information Contacts: UPI.


Langila (Papua New Guinea) — October 1983 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)


Moderate Vulcanian activity; explosion events; tremor

"Moderate explosive activity persisted at Crater 2 during the first week of October, but from the 8th until the end of the month, eruptive activity was at a low level.

"During 1-7 October, activity at Crater 2 consisted of weak-strong ash emission accompanied by explosion and rumbling sounds heard 10 km away. Weak red night glow from the crater was observed 3-7 October. Seismically this activity was represented by occasional large Vulcanian explosion earthquakes (2-5 per day), numerous smaller explosion shocks, and rare periods of continuous and discontinuous harmonic tremor. Ashfall was experienced in coastal inhabited areas about 10 km N and NW of the volcano on 2 October.

"From the 8th until the end of the month, Crater 2 released white emissions in small to moderate quantities. However, Vulcanian explosions accompanied by loud detonation sounds and ejections of incandescent material took place on 24 and 27 October. Seismicity was at a low level 8-31 October, but rare Vulcanian explosion events were also recorded. Crater 3 released small volumes of white and occasionally blue vapours throughout the month."

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: C. McKee, RVO.


Manam (Papua New Guinea) — October 1983 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)


Tephra clouds; glow; rumbling; increased seismicity

"Activity intensified somewhat at Manam's Main crater in October, while Southern crater activity was generally mild with forceful ejections of tephra on 2 days. The intensified Main crater activity took place in several brief periods. Explosive eruption sounds (rumbling, roaring, and booming) were heard about 4-5 km away on 14-15, 23-25, and 29-31 October, and crater glow was seen on 14, 23-24, and 29-30 October. Moderate, pale grey-brown emissions were observed during these periods, but at other times only small to moderate amounts of tephra-poor vapour were emitted.

"For most of the month, Southern crater emissions consisted of pale grey-brown ash clouds, but on 16 and 31 October impulsive, dense ejections of tephra and vapour to 200-250 m above the crater occurred. On 20, 22, and 31 October the emissions from both craters combined to form a plume several tens of kilometers long.

"Amplitudes of volcanic earthquakes were mainly steady at about 2-3 times normal levels, but increased 15-25 October. Daily earthquake totals remained around 2,700 for the first half of the month, decreased to about 1,900 at mid-month, and approached 2,600 on 31 October. A small down-tilt of about 1 µrad to the N (deflation) accumulated steadily during the month."

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: C. McKee, RVO.


Miyakejima (Japan) — October 1983 Citation iconCite this Report

Miyakejima

Japan

34.094°N, 139.526°E; summit elev. 775 m

All times are local (unless otherwise noted)


Four lava flows, four explosion craters from 10-hour eruption

A SW-flank fissure eruption that began 3 October in mid-afternoon reached maximum intensity soon after it started and had subsided by the next morning. Frequent explosions and lava fountaining occurred from vents along a 4-km-long fissure extending SW from the island volcano's summit to the coast (figure 1), fountaining along the upper 2 km and phreatomagmatic explosions along the lower 2 km of the fissure. Lava buried 80% of the coast town of Ako, and heavy tephra falls occurred on the SE part of the island.

Figure (see Caption) Figure 1. Sketch map of Miyake-jima after the eruption of 3-4 October 1983. Craters are indicated by hachured circles. Values in centimeters within the stippled area are thicknesses of new tephra at those locations. Mt. Oyama is the summit cone of Miyake-jima volcano. Courtesy of JMA.

Pre-eruption studies. The JMA Mobile Observation Team had investigated Miyake-jima 20 August-8 September 1983 and found no unusual activity. During this investigation seismometers recorded a swarm of microearthquakes a few tens of kilometers S of the island, and another a similar distance N, but none with epicenters on the island. Temperatures, ground water chemistry and height of the steam column showed no anomalous values. From 27 December 1982 to 18 January 1983 many earthquakes, the largest of magnitude 6.1 (Ms) [JMA magnitude 6.4] at 1537 on 28 December, occurred 40 km S of the volcano, (figure 1), but no relation between them and the eruption is known.

Eruption chronology and products. JMA personnel judged that the eruption began at 1523, when the amplitude of recorded continuous tremor began to increase (figure 2). Tremor was saturating instruments by 1527. A dark eruption cloud that had reached 3 km altitude was observed from an [All Nippon Airways] airliner at 1529. People living at the foot of the volcano heard explosions at around 1530, and saw incandescent blocks and voluminous clouds of tephra ejected from points on the SW flank. Ash began to fall at the airport at 1540. The eruption column had reached an altitude of 10 km by around 1600. Lava flowing W was 0.5 km from Ako by 1630, and began surrounding and igniting houses around 1800. The southernmost lava flow entered the sea about 3.5 km SE of Ako at about 1900.

Figure (see Caption) Figure 2. Seismicity at Miyake-jima recorded at the JMA weather station on the N side of the island, 3-8 October 1983. Data shows the number of earthquakes felt per hour (top) and amplitude of continuous tremor (bottom). On the tremor graph, the broken line indicates approximately measured data and the heavy line above the graph diagramatically shows the period of eruptive activity. Courtesy of JMA.

Phreatomagmatic explosions began at a newly formed explosion crater (named [Shinmyo] Pond Crater) near the S end of the fissure at around 1640. At 1722, a strong explosion near the seashore, perhaps at the same crater, produced an incandescent column. Lapilli started to fall in Tsubota (about 4 km E) at 1646. The lapilli fall was heavy enough to break car windshields at around 1700, but began to decline at 1834 and ceased at 1910 as wet muddy ashfall started. At 2140 a strong explosion occurred near the shore, and about an hour later many incandescent columns were observed there but this activity paused at about 2300. A submarine phreatomagmatic explosion at the SW end of the fissure was observed from a fishing boat at around 2310. At about 0145 occasional submarine explosions were seen . . . in the same area.

A member of the JMA Mobile Observation Team arrived at Miyake-jima on 4 October at 0500. Sea and air observations at that time revealed that the fountaining had ended, perhaps about an hour earlier, and observers in aircraft saw neither explosions nor lava extrusion. Four main lava flows had moved down the SW flank. Steam rose weakly from some places on the flows, and voluminously from the SW end of the fissure where phreatic activity had occurred. Small flames seen on flow surfaces were probably from burning trees [or houses]. Lava had virtually stopped flowing, although surveyors who landed at Ako by boat observed a flow front advancing slightly. A series of pits and cinder cones had formed along the fissure in [a slightly curved line] (figure 1). Along the lower 2 km of the fissure there were four explosion craters. The largest, 300 m in diameter, was the site of submarine explosions seen during the night. It had added new land at the shore and was given the name "Mippana Crater."

The largest of the lava flows had buried 80% of Ako. It was 50 m wide in valleys, 500 m wide in the town, and 5 m thick at its front. Several homes and two schools afire at the flow front were observed from the air at 0500 on 4 October. Part of the flow advanced a few meters 4-6 October; on the 6th sea water was sprayed at 40 places along the front to halt it. At 38 of these, the flow had stopped by the next day, but spraying continued until 8 October. The E half of the island was covered with dark tephra, 15 cm deep at Tsubota, 10 cm at the airport, and 1 cm on the NE coast. The coast road around the island was closed at many places by lava flows and tephra.

Volcanologists from the Universities of Tokyo, Tohoku, Chiba, and other institutions arrived on the island 4-5 October to study the eruption and its products. Shigeo Aramaki's preliminary estimate of the volume of material ejected was [4.7] x 106 m3 of lava and [7.4] x 106 m3 of tephra (table 1).

Table 1. Estimated ejecta volumes of eruptions at Miyake-jima during 1940, 1962, and 1983 (in millions of cubic meters).

Year Lava Tephra
1940 11 greater than 1962
1962 9 0.3
1983 4.7 7.4

Seismicity. Five earthquakes were felt between 1448 and 1522 on 3 October , but with the steep increase in [continuous volcanic] tremor amplitude at the start of the eruption, felt shocks stopped (figure 2). Earthquake activity remained low from 1522-1800, the most vigorous phase of the fissure eruption, then increased gradually from 1812 until 2233 when a 5.7 (Ms) [JMA magnitude 6.2] event shook the island. The few shocks felt 5-6 October represent stronger than usual seismicity. The last felt event occurred 15 October and the total since the beginning of the activity was 101. Although landslides occurred at about 10 sites along roads, there were no casualties. The number of small earthquakes then gradually decreased, but remained above background level on 27 October. . . . The amplitude of recorded continuous tremor decreased rapidly late 3 October, reaching its usual low level on 5 October, but increased again briefly early 7 October without . . . eruptive activity.

Human effects. The JMA weather station issued an alert on 3 October at 1545. Evacuation of Ako's 1400 inhabitants by fishing boat, private car and bus began immediately, as the instruction to go to Izu, on the N shore, was repeated through loudspeakers. Eleven buses moved about 1,000 persons in two round trips before the road was cut by lava at around 1730. Fishing boats transported the remaining 70. Eleven ships (from JMSA and JSDF) arrived the evening of 3 October, in case the entire island population of 4,400 needed evacuation. Food, blankets, and tanks of water were shipped from Tokyo.

Electricity was restored to all areas except Tsubota within 24 hours. Water supply to half the island was cut off because of damage to a major conduit (from Tairo-ike Pond). Telephone service was interrupted on 4 October when a switching station in Ako failed, but emergency radio service was established the same day. Tephra deposits at the airport ware cleared after 4 days, allowing it to reopen. The Tokyo government planned to build temporary housing for evacuees.

Further References. Aramaki, S., Hayakawa, Y., Fujii, T., Nakamura, K., and Fukuoka, T., 1986, The October 1983 eruption of Miyake-jima volcano: JVGR, v. 29, p. 203-230.

Special Issue -- The 1983 eruption of Miyake-jima: Bulletin of the Volcanological Society of Japan, v. 29, December 1984, 349 pp. (32 papers).

Geologic Background. The circular, 8-km-wide island of Miyakejima forms a low-angle stratovolcano that rises about 1,100 m from the sea floor in the northern Izu Islands about 200 km SSW of Tokyo. The basaltic volcano is truncated by small summit calderas, one of which, 3.5 km wide, was formed during a major eruption about 2,500 years ago. Parasitic craters and vents, including maars near the coast and radially oriented fissure vents, dot the flanks of the volcano. Frequent historical eruptions have occurred since 1085 CE at vents ranging from the summit to below sea level, causing much damage on this small populated island. After a three-century-long hiatus ending in 1469, activity has been dominated by flank fissure eruptions sometimes accompanied by minor summit eruptions. A 1.6-km-wide summit caldera was slowly formed by subsidence during an eruption in 2000; by October of that year the crater floor had dropped to only 230 m above sea level.

Information Contacts: JMA, Tokyo.


Pagan (United States) — October 1983 Citation iconCite this Report

Pagan

United States

18.13°N, 145.8°E; summit elev. 570 m

All times are local (unless otherwise noted)


Explosive eruption on 26 September

Several former residents of Pagan, including Mayor Dan Castro, spent September on the island. The only activity they observed was an explosive eruption accompanied by glow that began at 0640 on the 26th. That evening, glow remained visible. Ash that fell on the village was collected from concrete slabs. The ash has been identified as magmatic, of medium-sand size, and depleted in fines.

Since Pagan's major eruption in May 1981, six or seven explosions have ejected enough tephra to cause ashfall in the village. The 26 September ash was the first to fall on the concrete slabs since they were swept clean in July.

Geologic Background. Pagan Island, the largest and one of the most active of the Mariana Islands volcanoes, consists of two stratovolcanoes connected by a narrow isthmus. Both North and South Pagan stratovolcanoes were constructed within calderas, 7 and 4 km in diameter, respectively. North Pagan at the NE end of the island rises above the flat floor of the northern caldera, which may have formed less than 1,000 years ago. South Pagan is a stratovolcano with an elongated summit containing four distinct craters. Almost all of the recorded eruptions, which date back to the 17th century, have originated from North Pagan. The largest eruption during historical time took place in 1981 and prompted the evacuation of the sparsely populated island.

Information Contacts: N. Banks, HVO.


Pavlof (United States) — October 1983 Citation iconCite this Report

Pavlof

United States

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

All times are local (unless otherwise noted)


Large eruption column; tremor

Strong tremor started to appear on local seismic records on 14 November at about 1500 and by 1800 was saturating the instruments. The mayor of Sand Point, about 90 km E of Pavlof, saw glow over the volcano at 2330 that night. At 1220 the next day, an airline pilot reported an eruption column rising to about 5.5 km altitude through weather clouds that covered the summit and obscured the vent area. Twenty minutes later, the column had reached 7.5 km altitude. Tephra emission was continuing at 1300. The plume blew S and SE, and spread to about 50 km width, 50 km S of the volcano. Aircraft were diverted from the area. Tremor continued to saturate the seismic instruments through the afternoon.

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

Information Contacts: T. Miller, USGS, Anchorage; S. McNutt, LDGO.


Poas (Costa Rica) — October 1983 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 continuous gas emission

Fumarolic activity continued with strong continuous gas emission from the eroded cone (table 4). The crater lake remained hot (table 3) and the water level descended about 10 m.

Further Reference. Barquero, J., 1983, Termometría de la fumarola del Volcán Poás: Boletín de Vulcanología, no. 13, p. 11-12.

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: J. Barquero H., E. Fernández S., Univ. Nacional, Heredia.


Rabaul (Papua New Guinea) — October 1983 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)


Large increases in seismicity and ground deformation

"Further dramatic increases in seismicity and ground deformation rates took place in October. The total number of caldera earthquakes for the month was 5198, about 2.5 times the total for September and about 35 times the average monthly total since the last peak of activity in March 1982. A large proportion of events occurred in seismic crises on 15-16 October (daily earthquake totals of 868 and 305) and 28-29 October (daily totals of 338 and 513 events). The strongest earthquakes had magnitudes (ML) of about 4, and subterranean rumblings accompanied many of the felt events. The earthquakes continued to be concentrated in the E and NE parts of the caldera at depths of about 0-3 km.

"Tilt measurements showed maximum values around Tavurvur Cone in the NE part of the caldera. Tilts of up to about 20 µrad accumulated gradually until the seismic crisis at the end of the month, when step-wise changes of up to about 40 µrad were measured. Ground cracks were found on the W flank of Tavurvur after the seismic crisis of 28-29 October.

"Interpretation of the tilting using a point-source model indicates that the centre(s) of deformation could be immediately offshore about 1 km below the SW flank of Tavurvur. The increase in volume of the deforming source(s) is estimated to be of the order of 1 x 106 m3."

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: C. McKee, RVO.


St. Helens (United States) — October 1983 Citation iconCite this Report

St. Helens

United States

46.2°N, 122.18°W; summit elev. 2549 m

All times are local (unless otherwise noted)


Deformation, SO2 emission, and seismicity increase as lava extrusion pattern changes

Growth of the composite lava dome continued through October. At the end of September, the pattern of lava extrusion began to change, with lava redirected southward along the margin of the active lobe. Examination of daily airphotos indicated that by 6 October a substantial area of uplift had developed along the S edge of the lobe and a spine was emerging from a point about 50 m WSW of the vent that had fed the active lobe since the beginning of May. The spine grew 1.5-2 m per day until 15 October, then its growth slowed to about 0.5 m/day for the next 2 weeks. The spine reached 30 m in height, 17 m higher than any other point on the dome. From the spine, a sharp, lateral ridge extended about 100 m NE. By 31 October, this feature had crumbled. The spine remained nearly intact, but had stopped growing and some crumbling had occurred.

As the spine grew, lava emerged from a "spreading center" just to the S, pushing the spine slowly NW. Lava advanced S and SE along the periphery of the May lobe at roughly 1-2 m/day through October, thickening this portion of the lobe by a factor of 4-5. As this area of the lobe grew, advance of the NE end of the lobe slowed and had nearly stagnated by the end of October.

Although deformation of the S and SE flanks of the dome stopped accelerating about 6 October as the spine began to emerge, outward movement of this part of the dome continued at high but relatively stable rates of as much as 120 cm/day through October as the active lobe advanced and thickened. The crater floor adjacent to the S and SE flanks of the dome also continued to deform slightly through October, with a maximum uplift of 6-8 cm and maximum horizontal strain of about 20 cm during the month.

SO2 emission averaged 75 ± 45 t/d in October. Several days of elevated SO2 emission 1-8 October (reaching 210 t/d on the 1st) accompanied the onset of the changed lava extrusion pattern on the dome. From 8 October through the end of the month, rates dropped to 30-80 t/d. Several small gas-and-ash ejections from an explosion pit near the summit of the dome continued to occur daily, elevating SO2 flux to 3-4 times background, usually for only a few minutes but occasionally for tens of minutes. Plumes were usually grayish-white and contained only a little tephra. Sand-size and occasionally cobble-size fragments fell near the vent, but only small quantities of very fine material were deposited on the crater rim.

Since November 1980, a drainage system has developed in the 1980 pyroclastic-flow deposits. In the late spring of 1983, steam was noted in the drainage system for the first time. A zone of six to eight small hot springs had developed near the N edge of the crater at the contact between hydrothermally altered ancestral dacite and the pyroclastic-flow deposits. Flow rates were typically less than 1 liter per second. Temperatures measured at the springs in September and on 26 October ranged from 76 to 91°C, pH was 7.1-8.2, and specific conductance was 3,300-5,800 mhos. Travertine was being deposited at one of the springs.

Seismic energy release declined in mid-September, but a gradual increase began in early October, leveling off about 9-10 October at roughly twice the late September rate. A small decrease in the slope of the energy release curve occurred in late October but poor weather may have caused instrumental interference. By early November, the mid-October rates had been regained. Little change in surface events was observed in October. In the summer, many surface seismic events were the result of seasonal avalanching from the crater walls, but in October most were caused by steam ejections.

Geologic Background. Prior to 1980, Mount St. Helens formed a conical, youthful volcano sometimes known as the Fujisan of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Mount St. Helens was formed during nine eruptive periods beginning about 40-50,000 years ago and has been the most active volcano in the Cascade Range during the Holocene. Prior to 2,200 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older edifice, but few lava flows extended beyond the base of the volcano. The modern edifice consists of basaltic as well as andesitic and dacitic products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the north flank, and were witnessed by early settlers.

Information Contacts: D. Swanson, T. Casadevall, USGS CVO, Vancouver, WA; R. Norris, University of Washington.


Tangkuban Parahu (Indonesia) — October 1983 Citation iconCite this Report

Tangkuban Parahu

Indonesia

6.77°S, 107.6°E; summit elev. 2084 m

All times are local (unless otherwise noted)


Seismicity continues to increase

Seismicity continued to increase through mid-October but no surface changes have been noted. Tectonic earthquakes and both A-and B-type microtremors were recorded. A-type events occurred irregularly, usually at 1-3 per day, but as many as five were detected on several days. B-type earthquakes increased substantially, as shown in table 1.

Table 1. Number of B-type events/day at Tangkubanparahu, May to mid-October 1983.

Time Period Daily Average Maximum / day
May-Jul 1983 3 7
Aug 1983 (first weeks) 10 19
Aug 1983 (last week) 14 25
Sep 1983 (first half) 70 120
Sep 1983 (second half) 57 103
Oct 1983 (first half) 72 127

Ground deformation did not show regular changes. From 10 to 25 mm of irregular inflation and deflation were detected but their significance is doubtful. Fumarole temperatures remained stable at 96°C in the three fumarole fields (Baru, Ratu, and Upas). The previously declared forbidden zone of 3-km-radius remained in effect.

Geologic Background. Gunung Tangkuban Parahu is a broad shield-like stratovolcano overlooking Indonesia's former capital city of Bandung. The volcano was constructed within the 6 x 8 km Pleistocene Sunda caldera, which formed about 190,000 years ago. The volcano's low profile is the subject of legends referring to the mountain of the "upturned boat." The Sunda caldera rim forms a prominent ridge on the western side; elsewhere the rim is largely buried by deposits of the current volcano. The dominantly small phreatic eruptions recorded since the 19th century have originated from several nested craters within an elliptical 1 x 1.5 km summit depression.

Information Contacts: A. Sudradjat, VSI.


Turrialba (Costa Rica) — October 1983 Citation iconCite this Report

Turrialba

Costa Rica

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

All times are local (unless otherwise noted)


Fumarolic activity

Fumarolic activity continued in the central and W craters, where a mean temperature of 89°C was measured.

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

Information Contacts: J. Barquero H. and E. Fernández S., Univ. Nacional, Heredia.


Veniaminof (United States) — October 1983 Citation iconCite this Report

Veniaminof

United States

56.17°N, 159.38°W; summit elev. 2507 m

All times are local (unless otherwise noted)


Lava fountains and flow; ash emission; increased tremor

Eruptive activity continued through early November. On the night of 23-24 October, Perryville residents observed lava fountains at the summit, and on 30 October they observed lava flowing down the SW flank of the intra-caldera cone. On 31 October and 1 November, an ash cloud rose 1 km above the vent.

Bad weather prevented overflights by USGS personnel during late October. During a 4 November overflight, a very light-colored vapor plume containing a little ash rose approximately 100 m and was blown S. Lava flowed down the SW side of the intra-caldera cone, extending the lava delta to the S. They did not observe any water in the large ice pits previously melted into the caldera ice by the lava flows, but their view was obscured by the eruption cloud.

Seismic records available through 8 October showed low-amplitude continuous volcanic tremor beginning 1 October at 1200. On 2 October the amplitude increased to slightly less than half that during the June eruption (8:5, 8). The tremor remained continuous and of about this amplitude through 8 October. Some slightly larger bursts of tremor were recorded 4-8 October. The eruptive activity reported on 3 October by Perryville residents was not distinguishable on the seismic record.

Geologic Background. Veniaminof, on the Alaska Peninsula, is truncated by a steep-walled, 8 x 11 km, glacier-filled caldera that formed around 3,700 years ago. The caldera rim is up to 520 m high on the north, is deeply notched on the west by Cone Glacier, and is covered by an ice sheet on the south. Post-caldera vents are located along a NW-SE zone bisecting the caldera that extends 55 km from near the Bering Sea coast, across the caldera, and down the Pacific flank. Historical eruptions probably all originated from the westernmost and most prominent of two intra-caldera cones, which rises about 300 m above the surrounding icefield. The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

Information Contacts: M.E. Yount, USGS, Anchorage; S. McNutt, LDGO.


Villarrica (Chile) — October 1983 Citation iconCite this Report

Villarrica

Chile

39.42°S, 71.93°W; summit elev. 2847 m

All times are local (unless otherwise noted)


Continuous explosions emit tephra; pyroclastic flows; summit glow suggests lava fountaining

"Forest guards in the Villarrica National Park reported that the volcano entered into a remarkable eruptive stage on 14 October, after a long period of moderate activity. Continuous explosions with tephra emissions and some black pyroclastic flows over the ice-covered slopes have been observed. By night, a red glow over the summit indicates that a lava fountain is filling the crater. Since the big lava and pyroclastic eruptions of October-December 1971, active fumaroles have been present in the main crater."

Further Reference. Muñoz, M., 1984, Probabilidad de erupción en el Volcán Villarrica en los próximos años: Tralka, v. 2, no. 3, p. 323-325.

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

Information Contacts: H. Moreno R., Univ. de Chile, Santiago.

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