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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

Karangetang (Indonesia) Incandescent block avalanches through mid-January 2020; crater anomalies through May

Masaya (Nicaragua) Lava lake level drops but remains active through May 2020; weak gas plumes

Shishaldin (United States) Intermittent thermal activity and a possible new cone at the summit crater during February-May 2020

Krakatau (Indonesia) Strombolian explosions, ash plumes, and crater incandescence during April 2020

Taal (Philippines) Eruption on 12 January with explosions through 22 January; steam plumes continuing into March

Unnamed (Tonga) Additional details and pumice raft drift maps from the August 2019 submarine eruption

Klyuchevskoy (Russia) Strombolian activity November 2019 through May 2020; lava flow down the SE flank in April

Nyamuragira (DR Congo) Intermittent thermal anomalies within the summit crater during December 2019-May 2020

Nyiragongo (DR Congo) Activity in the lava lake and small eruptive cone persists during December 2019-May 2020

Kavachi (Solomon Islands) Discolored water plumes seen using satellite imagery in 2018 and 2020

Kuchinoerabujima (Japan) Eruption and ash plumes begin on 11 January 2020 and continue through April 2020

Soputan (Indonesia) Minor ash emissions during 23 March and 2 April 2020



Karangetang (Indonesia) — June 2020 Citation iconCite this Report

Karangetang

Indonesia

2.781°N, 125.407°E; summit elev. 1797 m

All times are local (unless otherwise noted)


Incandescent block avalanches through mid-January 2020; crater anomalies through May

The Karangetang andesitic-basaltic stratovolcano (also referred to as Api Siau) at the northern end of the island of Siau, north of Sulawesi, Indonesia, has had more than 50 observed eruptions since 1675. Frequent explosive activity is accompanied by pyroclastic flows and lahars, and lava-dome growth has created two active summit craters (Main to the S and Second Crater to the N). Rock avalanches, observed incandescence, and satellite thermal anomalies at the summit confirmed continuing volcanic activity since the latest eruption started in November 2018 (BGVN 44:05). This report covers activity from December 2019 through May 2020. Activity is monitored by Indonesia's Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), and ash plumes are monitored by the Darwin VAAC (Volcanic Ash Advisory Center). Information is also available from MODIS thermal anomaly satellite data through both the University of Hawaii's MODVOLC system and the Italian MIROVA project.

Increased activity that included daily incandescent avalanche blocks traveling down the W and NW flanks lasted from mid-July 2019 (BGVN 44:12) through mid-January 2020 according to multiple sources. The MIROVA data showed increased number and intensity of thermal anomalies during this period, with a sharp drop during the second half of January (figure 40). The MODVOLC thermal alert data reported 29 alerts in December and ten alerts in January, ending on 14 January, with no further alerts through May 2020. During December and the first half of January incandescent blocks traveled 1,000-1,500 m down multiple drainages on the W and NW flanks (figure 41). After this, thermal anomalies were still present at the summit craters, but no additional activity down the flanks was identified in remote satellite data or direct daily observations from PVMBG.

Figure (see Caption) Figure 40. An episode of increased activity at Karangetang from mid-July 2019 through mid-January 2020 included incandescent avalanche blocks traveling down multiple flanks of the volcano. This was reflected in increased thermal activity seen during that interval in the MIROVA graph covering 5 June 2019 through May 2020. Courtesy of MIROVA.
Figure (see Caption) Figure 41. An episode of increased activity at Karangetang from mid-July 2019 through mid-January 2020 included incandescent avalanche blocks traveling up to 1,500 m down drainages on the W and NW flanks of the volcano. Top left: large thermal anomalies trend NW from Main Crater on 5 December 2019; about 500 m N a thermal anomaly glows from Second Crater. Top center: on 15 December plumes of steam and gas drifted W and SW from both summit craters as seen in Natural Color rendering (bands 4,3,2). Top right: the same image as at top center with Atmospheric penetration rendering (bands 12, 11, 8a) shows hot zones extending WNW from Main Crater and a thermal anomaly at Second Crater. Bottom left: thermal activity seen on 14 January 2020 extended about 800 m WNW from Main Crater along with an anomaly at Second Crater and a hot spot about 1 km W. Bottom center: by 19 January the anomaly from Second Crater appeared slightly stronger than at Main Crater, and only small anomalies appeared on the NW flank. Bottom right: an image from 14 March shows only thermal anomalies at the two summit craters. Courtesy of Sentinel Hub Playground.

A single VAAC report in early April noted a short-lived ash plume that drifted SW. Intermittent low-level activity continued through May 2020. Small SO2 plumes appeared in satellite data multiple times in December 2019 and January 2020; they decreased in size and frequency after that but were still intermittently recorded into May 2020 (figure 42).

Figure (see Caption) Figure 42. Small plumes of sulfur dioxide were measured at Karangetang with the TROPOMI instrument on the Sentinel-5P satellite multiple times during December 2019 (top row). They were less frequent but still appeared during January-May 2020 (bottom row). Larger plumes were also detected from Dukono, located 300 km ESE at the N end of North Maluku. Courtesy of Global Sulfur Dioxide Monitoring Page.

PVMBG reported in their daily summaries that steam plumes rose 50-150 m above the Main Crater and 25-50 m above Second Crater on most days in December. The incandescent avalanche activity that began in mid-July 2019 also continued throughout December 2019 and January 2020 (figure 43). Incandescent blocks from the Main Crater descended river drainages (Kali) on the W and NW flanks throughout December. They were reported nearly every day in the Nanitu, Sense, and Pangi drainages, traveling 1,000-1,500 m. Incandescence from both craters was visible 10-25 m above the crater rim most nights.

Figure (see Caption) Figure 43. Incandescent block avalanches descended the NW flank of Karangetang as far as 1,500 m frequently during December 2019 and January 2020. Left image taken 13 December 2019, right image taken 6 January 2020 by PVMBG webcam. Courtesy of PVMBG, Oystein Anderson, and Bobyson Lamanepa.

A few blocks were noted traveling 800 m down Kali Beha Barat on 1 December. Incandescence above the Main crater reached 50-75 m during 4-6 December. During 4-7 December incandescent blocks appeared in Kali Sesepe, traveling 1,000-1,500 m down from the summit. They were also reported in Kali Batang and Beha Barat during 4-14 December, usually moving 800-1,000 m downslope. Between 5 and 14 December, gray and white plumes from Second Crater reached 300 m multiple times. During 12-15 December steam plumes rose 300-500 m above the Main crater. Activity decreased during 18-26 December but increased again during the last few days of the month. On 28 December, incandescent blocks were reported 1,500 m down Kali Pangi and Nanitu, and 1,750 m down Kali Sense.

Incandescent blocks were reported in Kali Sesepi during 4-6 January and in Kali Batang and Beha Barat during 4-8 and 12-15 January (figure 44); they often traveled 800-1,200 m downslope. Activity tapered off in those drainages and incandescent blocks were last reported in Kali Beha Barat on 15 January traveling 800 m from the summit. Incandescent blocks were also reported traveling usually 1,000-1,500 m down the Nanitu, Sense, and Pangi drainages during 4-19 January. Blocks continued to occasionally descend up to 1,000 m down Kali Nanitu through 24 January. Pulses of activity occurred at the summit of Second Crater a few times in January. Steam plumes rose 25-50 m during 8-9 January and again during 16-31 January, with plumes rising 300-400 m on 20, 29, and 31 January. Incandescence was noted 10-25 m above the summit of Second Crater during 27-30 January.

Figure (see Caption) Figure 44. Incandescent material descends the Beha Barat, Sense, Nanitu, and Pangi drainages on the NW flank of Karangetang in early January 2020. Courtesy of Bobyson Lamanepa; posted on Twitter on 6 January 2020.

Activity diminished significantly after mid-January 2020. Steam plumes at the Main Crater rose 50-100 m on the few days where the summit was not obscured by fog during February. Faint incandescence occurred at the Main Crater on 7 February, and steam plumes rising 25-50 m from Second Crater that day were the only events reported there in February. During March, steam plumes persisted from the Main Crater, with heights of over 100 m during short periods from 8-16 March and 25-30 March. Weak incandescence was reported from the Main Crater only once, on 25 March. Very little activity occurred at Second Crater during March, with only steam plumes reported rising 25-300 m from the 22nd to the 28th (figure 45).

Figure (see Caption) Figure 45. Steam plumes at Karangetang rose over 100 m above both summit craters multiple times during March, including on 26 March 2020. Courtesy of PVMBG and Oystein Anderson.

The Darwin VAAC reported a continuous ash emission on 4 April 2020 that rose to 2.1 km altitude and drifted SW for a few hours before dissipating. Incandescence visible 25 m above both craters on 13 April was the only April activity reported by PVMBG other than steam plumes from the Main Crater that rose 50-500 m on most days. Steam plumes of 50-100 m were reported from Second Crater during 11-13 April. Activity remained sporadic throughout May 2020. Steam plumes from the Main Crater rose 50-300 m each day. Satellite imagery identified steam plumes and incandescence from both summit craters on 3 May (figure 46). Faint incandescence was observed at the Main Crater on 12 and 27 May. Steam plumes rose 25-50 m from Second Crater on a few days; a 200-m-high plume was reported on 27 May. Bluish emissions were observed on the S and SW flanks on 28 May.

Figure (see Caption) Figure 46. Dense steam plumes and thermal anomalies were present at both summit craters of Karangetang on 3 May 2020. Sentinel 2 satellite image with Natural Color (bands 4, 3, 2) (left) and Atmospheric Penetration rendering (bands 12, 11, 8a) (right); courtesy of Sentinel Hub Playground.

Geologic Background. Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi island. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia's most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented in the historical record (Catalog of Active Volcanoes of the World: Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.

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/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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/); 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/); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: http://www.oysteinlundandersen.com); Bobyson Lamanepa, Yogyakarta, Indonesia, (URL: https://twitter.com/BobyLamanepa/status/1214165637028728832).


Masaya (Nicaragua) — June 2020 Citation iconCite this Report

Masaya

Nicaragua

11.985°N, 86.165°W; summit elev. 594 m

All times are local (unless otherwise noted)


Lava lake level drops but remains active through May 2020; weak gas plumes

Masaya, which is about 20 km NW of the Nicaragua’s capital of Managua, is one of the most active volcanoes in that country and has a caldera that contains a number of craters (BGVN 43:11). The Santiago crater is the one most currently active and it contains a small lava lake that emits weak gas plumes (figure 85). This report summarizes activity during February through May 2020 and is based on Instituto Nicaragüense de Estudios Territoriales (INETER) monthly reports and satellite data. During the reporting period, the volcano was relatively calm, with only weak gas plumes.

Figure (see Caption) Figure 85. Satellite images of Masaya from Sentinel-2 on 18 April 2020, showing and a small gas plume drifting SW (top, natural color bands 4, 3, 2) and the lava lake (bottom, false color bands 12, 11, 4). Courtesy of Sentinel Hub Playground.

According to INETER, thermal images of the lava lake and temperature data in the fumaroles were taken using an Omega infrared gun and a forward-looking infrared (FLIR) SC620 thermal camera. The temperatures above the lava lake have decreased since November 2019, when the temperature was 287°C, dropping to 96°C when measured on 14 May 2020. INETER attributed this decrease to subsidence in the level of the lava lake by 5 m which obstructed part of the lake and concentrated the gas emissions in the weak plume. Convection continued in the lava lake, which in May had decreased to a diameter of 3 m. Many landslides had occurred in the E, NE, and S walls of the crater rim due to rock fracturing caused by the high heat and acidity of the emissions.

During the reporting period, the MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system recorded numerous thermal anomalies from the lava lake based on MODIS data (figure 86). Infrared satellite images from Sentinel-2 regularly showed a strong signature from the lava lake through 18 May, after which the volcano was covered by clouds.

Figure (see Caption) Figure 86. Thermal anomalies at Masaya during February through May 2020. The larger anomalies with black lines are more distant and not related to the volcano. Courtesy of MIROVA.

Measurements of sulfur dioxide (SO2) made by INETER in the section of the Ticuantepe - La Concepción highway (just W of the volcano) with a mobile DOAS system varied between a low of just over 1,000 metric tons/day in mid-November 2019 to a high of almost 2,500 tons/day in late May. Temperatures of fumaroles in the Cerro El Comalito area, just ENE of Santiago crater, ranged from 58 to 76°C during February-May 2020, with most values in the 69-72°C range.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras caldera and is itself a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The Nindirí and Masaya cones, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6,500 years ago. Historical lava flows cover much of the caldera floor and there is a lake at the far eastern end. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals have caused health hazards and crop damage.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); 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).


Shishaldin (United States) — June 2020 Citation iconCite this Report

Shishaldin

United States

54.756°N, 163.97°W; summit elev. 2857 m

All times are local (unless otherwise noted)


Intermittent thermal activity and a possible new cone at the summit crater during February-May 2020

Shishaldin is located near the center of Unimak Island in Alaska, with the current eruption phase beginning in July 2019 and characterized by ash plumes, lava flows, lava fountaining, pyroclastic flows, and lahars. More recently, in late 2019 and into January 2020, activity consisted of multiple lava flows, pyroclastic flows, lahars, and ashfall events (BGVN 45:02). This report summarizes activity from February through May 2020, including gas-and-steam emissions, brief thermal activity in mid-March, and a possible new cone within the summit crater. The primary source of information comes from the Alaska Volcano Observatory (AVO) reports and various satellite data.

Volcanism during February 2020 was relatively low, consisting of weakly to moderately elevated surface temperatures during 1-4 February and occasional small gas-and-steam plumes (figure 37). By 6 February both seismicity and surface temperatures had decreased. Seismicity and surface temperatures increased slightly again on 8 March and remained elevated through the rest of the reporting period. Intermittent gas-and-steam emissions were also visible from mid-March (figure 38) through May. Minor ash deposits visible on the upper SE flank may have been due to ash resuspension or a small collapse event at the summit, according to AVO.

Figure (see Caption) Figure 37. Photo of a gas-and-steam plume rising from the summit crater at Shishaldin on 22 February 2020. Photo courtesy of Ben David Jacob via AVO.
Figure (see Caption) Figure 38. A Worldview-2 panchromatic satellite image on 11 March 2020 showing a gas-and-steam plume rising from the summit of Shishaldin and minor ash deposits on the SE flank (left). Aerial photo showing minor gas-and-steam emissions rising from the summit crater on 11 March (right). Some erosion of the snow and ice on the upper flanks is a result of the lava flows from the activity in late 2019 and early 2020. Photo courtesy of Matt Loewen (left) and Ed Fischer (right) via AVO.

On 14 March, lava and a possible new cone were visible in the summit crater using satellite imagery, accompanied by small explosion signals. Strong thermal signatures due to the lava were also seen in Sentinel-2 satellite data and continued strongly through the month (figure 39). The lava reported by AVO in the summit crater was also reflected in satellite-based MODIS thermal anomalies recorded by the MIROVA system (figure 40). Seismic and infrasound data identified small explosions signals within the summit crater during 14-19 March.

Figure (see Caption) Figure 39. Sentinel-2 thermal satellite images (bands 12, 11, 8A) show a bright hotspot (yellow-orange) at the summit crater of Shishaldin during mid-March 2020 that decreases in intensity by late March. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 40. MIROVA thermal data showing a brief increase in thermal anomalies during late March 2020 and on two days in late April between periods of little to no activity. Courtesy of MIROVA.

AVO released a Volcano Observatory Notice for Aviation (VONA) stating that seismicity had decreased by 16 April and that satellite data no longer showed lava or additional changes in the crater since the start of April. Sentinel-2 thermal satellite imagery continued to show a weak hotspot in the crater summit through May (figure 41), which was also detected by the MIROVA system on two days. A daily report on 6 May reported a visible ash deposit extending a short distance SE from the summit, which had likely been present since 29 April. AVO noted that the timing of the deposit corresponds to an increase in the summit crater diameter and depth, further supporting a possible small collapse. Small gas-and-steam emissions continued intermittently and were accompanied by weak tremors and occasional low-frequency earthquakes through May (figure 42). Minor amounts of sulfur dioxide were detected in the gas-and-steam emissions during 20 and 29 April, and 2, 16, and 28 May.

Figure (see Caption) Figure 41. Sentinel-2 thermal satellite images (bands 12, 11, 8A) show occasional gas-and-steam emissions rising from Shishaldin on 26 February (top left) and 24 April 2020 (bottom left) and a weak hotspot (yellow-orange) persisting at the summit crater during April and early May 2020. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 42. A Worldview-1 panchromatic satellite image showing gas-and-steam emissions rising from the summit of Shishaldin on 1 May 2020 (local time) (left). Aerial photo of the N flank of Shishaldin with minor gas-and-steam emissions rising from the summit on 8 May (right). Photo courtesy of Matt Loewen (left) and Levi Musselwhite (right) via AVO.

Geologic Background. The beautifully symmetrical Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steam plume often rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the W and NE sides at 1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of Strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.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).


Krakatau (Indonesia) — June 2020 Citation iconCite this Report

Krakatau

Indonesia

6.102°S, 105.423°E; summit elev. 155 m

All times are local (unless otherwise noted)


Strombolian explosions, ash plumes, and crater incandescence during April 2020

Krakatau, located in the Sunda Strait between Indonesia’s Java and Sumatra Islands, experienced a major caldera collapse around 535 CE, forming a 7-km-wide caldera ringed by three islands. On 22 December 2018, a large explosion and flank collapse destroyed most of the 338-m-high island of Anak Krakatau (Child of Krakatau) and generated a deadly tsunami (BGVN 44:03). The near-sea level crater lake inside the remnant of Anak Krakatau was the site of numerous small steam and tephra explosions. A larger explosion in December 2019 produced the beginnings of a new cone above the surface of crater lake (BGVN 45:02). Recently, volcanism has been characterized by occasional Strombolian explosions, dense ash plumes, and crater incandescence. This report covers activity from February through May 2020 using information provided by the Indonesian Center for Volcanology and Geological Hazard Mitigation, also known as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), the Darwin Volcanic Ash Advisory Center (VAAC), and various satellite data.

Activity during February 2020 consisted of dominantly white gas-and-steam emissions rising 300 m above the crater, according to PVMBG. According to the Darwin VAAC, a ground observer reported an eruption on 7 and 8 February, but no volcanic ash was observed. During 10-11 February, a short-lived eruption was detected by seismograms which produced an ash plume up to 1 km above the crater drifting E. MAGMA Indonesia reported two eruptions on 18 March, both of which rose to 300 m above the crater. White gas-and-steam emissions were observed for the rest of the month and early April.

On 10 April PVMBG reported two eruptions, at 2158 and 2235, both of which produced dark ash plumes rising 2 km above the crater followed by Strombolian explosions ejecting incandescent material that landed on the crater floor (figures 108 and 109). The Darwin VAAC issued a notice at 0145 on 11 April reporting an ash plume to 14.3 km altitude drifting WNW, however this was noted with low confidence due to the possible mixing of clouds. During the same day, an intense thermal hotspot was detected in the HIMAWARI thermal satellite imagery and the NASA Global Sulfur Dioxide page showed a strong SO2 plume at 11.3 km altitude drifting W (figure 110). The CCTV Lava93 webcam showed new lava flows and lava fountaining from the 10-11 April eruptions. This activity was evident in the MIROVA (Middle InfraRed Observation of Volcanic Activity) graph of MODIS thermal anomaly data (figure 111).

Figure (see Caption) Figure 108. Webcam (Lava93) images of Krakatau on 10 April 2020 showing Strombolian explosions, strong incandescence, and ash plumes rising from the crater. Courtesy of PVMBG and MAGMA Indonesia.
Figure (see Caption) Figure 109. Webcam image of incandescent Strombolian explosions at Krakatau on 10 April 2020. Courtesy of PVMBG and MAGMA Indonesia.
Figure (see Caption) Figure 110. Strong sulfur dioxide emissions rising from Krakatau and drifting W were detected using the TROPOMI instrument on the Sentinel-5P satellite on 11 April 2020 (top row). Smaller volumes of SO2 were visible in Sentinel-5P/TROPOMI maps on 13 (bottom left) and 19 April (bottom right). Courtesy of NASA Global Sulfur Dioxide Monitoring Page.
Figure (see Caption) Figure 111. Thermal activity at Anak Krakatau from 29 June-May 2020 shown on a MIROVA Log Radiative Power graph. The power and frequency of the thermal anomalies sharply increased in mid-April. After the larger eruptive event in mid-April the thermal anomalies declined slightly in strength but continued to be detected intermittently through May. Courtesy of MIROVA.

Strombolian activity rising up to 500 m continued into 12 April and was accompanied by SO2 emissions that rose 3 km altitude, drifting NW according to a VAAC notice. PVMBG reported an eruption on 13 April at 2054 that resulted in incandescence as high as 25 m above the crater. Volcanic ash, accompanied by white gas-and-steam emissions, continued intermittently through 18 April, many of which were observed by the CCTV webcam. After 18 April only gas-and-steam plumes were reported, rising up to 100 m above the crater; Sentinel-2 satellite imagery showed faint thermal anomalies in the crater (figure 112). SO2 emissions continued intermittently throughout April, though at lower volumes and altitudes compared to the 11th. MODIS satellite data seen in MIROVA showed intermittent thermal anomalies through May.

Figure (see Caption) Figure 112. Sentinel-2 thermal satellite images showing the cool crater lake on 20 March (top left) followed by minor heating of the crater during April and May 2020. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

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

Information Contacts: 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.vsi.esdm.go.id/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Taal (Philippines) — June 2020 Citation iconCite this Report

Taal

Philippines

14.002°N, 120.993°E; summit elev. 311 m

All times are local (unless otherwise noted)


Eruption on 12 January with explosions through 22 January; steam plumes continuing into March

Taal volcano is in a caldera system located in southern Luzon island and is one of the most active volcanoes in the Philippines. It has produced around 35 recorded eruptions since 3,580 BCE, ranging from VEI 1 to 6, with the majority of eruptions being a VEI 2. The caldera contains a lake with an island that also contains a lake within the Main Crater (figure 12). Prior to 2020 the most recent eruption was in 1977, on the south flank near Mt. Tambaro. The United Nations Office for the Coordination of Humanitarian Affairs in the Philippines reports that over 450,000 people live within 40 km of the caldera (figure 13). This report covers activity during January through February 2020 including the 12 to 22 January eruption, and is based on reports by Philippine Institute of Volcanology and Seismology (PHIVOLCS), satellite data, geophysical data, and media reports.

Figure (see Caption) Figure 12. Annotated satellite images showing the Taal caldera, Volcano Island in the caldera lake, and features on the island including Main Crater. Imagery courtesy of Planet Inc.
Figure (see Caption) Figure 13. Map showing population totals within 14 and 17 km of Volcano Island at Taal. Courtesy of the United Nations Office for the Coordination of Humanitarian Affairs (OCHA).

The hazard status at Taal was raised to Alert Level 1 (abnormal, on a scale of 0-5) on 28 March 2019. From that date through to 1 December there were 4,857 earthquakes registered, with some felt nearby. Inflation was detected during 21-29 November and an increase in CO2 emission within the Main Crater was observed. Seismicity increased beginning at 1100 on 12 January. At 1300 there were phreatic (steam) explosions from several points inside Main Crater and the Alert Level was raised to 2 (increasing unrest). Booming sounds were heard in Talisay, Batangas, at 1400; by 1402 the plume had reached 1 km above the crater, after which the Alert Level was raised to 3 (magmatic unrest).

Phreatic eruption on 12 January 2020. A seismic swarm began at 1100 on 12 January 2020 followed by a phreatic eruption at 1300. The initial activity consisted of steaming from at least five vents in Main Crater and phreatic explosions that generated 100-m-high plumes. PHIVOLCS raised the Alert Level to 2. The Earth Observatory of Singapore reported that the International Data Center (IDC) for the Comprehensive test Ban Treaty (CTBT) in Vienna noted initial infrasound detections at 1450 that day.

Booming sounds were heard at 1400 in Talisay, Batangas (4 km NNE from the Main Crater), and at 1404 volcanic tremor and earthquakes felt locally were accompanied by an eruption plume that rose 1 km; ash fell to the SSW. The Alert Level was raised to 3 and the evacuation of high-risk barangays was recommended. Activity again intensified around 1730, prompting PHIVOLCS to raise the Alert Level to 4 and recommend a total evacuation of the island and high-risk areas within a 14-km radius. The eruption plume of steam, gas, and tephra significantly intensified, rising to 10-15 km altitude and producing frequent lightning (figures 14 and 15). Wet ash fell as far away as Quezon City (75 km N). According to news articles schools and government offices were ordered to close and the Ninoy Aquino International Airport (56 km N) in Manila suspended flights. About 6,000 people had been evacuated. Residents described heavy ashfall, low visibility, and fallen trees.

Figure (see Caption) Figure 14. Lightning produced during the eruption of Taal during 1500 on 12 January to 0500 on 13 January 2020 local time (0700-2100 UTC on 12 January). Courtesy of Chris Vagasky, Vaisala.
Figure (see Caption) Figure 15. Lightning strokes produced during the first days of the Taal January 2020 eruption. Courtesy of Domcar C Lagto/SIPA/REX/Shutterstock via The Guardian.

In a statement issued at 0320 on 13 January, PHIVOLCS noted that ashfall had been reported across a broad area to the north in Tanauan (18 km NE), Batangas; Escala (11 km NW), Tagaytay; Sta. Rosa (32 km NNW), Laguna; Dasmariñas (32 km N), Bacoor (44 km N), and Silang (22 km N), Cavite; Malolos (93 km N), San Jose Del Monte (87 km N), and Meycauayan (80 km N), Bulacan; Antipolo (68 km NNE), Rizal; Muntinlupa (43 km N), Las Piñas (47 km N), Marikina (70 km NNE), Parañaque (51 km N), Pasig (62 km NNE), Quezon City, Mandaluyong (62 km N), San Juan (64 km N), Manila; Makati City (59 km N) and Taguig City (55 km N). Lapilli (2-64 mm in diameter) fell in Tanauan and Talisay; Tagaytay City (12 km N); Nuvali (25 km NNE) and Sta (figure 16). Rosa, Laguna. Felt earthquakes (Intensities II-V) continued to be recorded in local areas.

Figure (see Caption) Figure 16. Ashfall from the Taal January 2020 eruption in Lemery (top) and in the Batangas province (bottom). Photos posted on 13 January, courtesy of Ezra Acayan/Getty Images, Aaron Favila/AP, and Ted Aljibe/AFP via Getty Images via The Guardian.

Magmatic eruption on 13 January 2020. A magmatic eruption began during 0249-0428 on 13 January, characterized by weak lava fountaining accompanied by thunder and flashes of lightning. Activity briefly waned then resumed with sporadic weak fountaining and explosions that generated 2-km-high, dark gray, steam-laden ash plumes (figure 17). New lateral vents opened on the N flank, producing 500-m-tall lava fountains. Heavy ashfall impacted areas to the SW, including in Cuenca (15 km SSW), Lemery (16 km SW), Talisay, and Taal (15 km SSW), Batangas (figure 18).

Figure (see Caption) Figure 17. Ash plumes seen from various points around Taal in the initial days of the January 2020 eruption, posted on 13 January. Courtesy of Eloisa Lopez/Reuters, Kester Ragaza/Pacific Press/Shutterstock, Ted Aljibe/AFP via Getty Images, via The Guardian.
Figure (see Caption) Figure 18. Map indicating areas impacted by ashfall from the 12 January eruption through to 0800 on the 13th. Small yellow circles (to the N) are ashfall report locations; blue circles (at the island and to the S) are heavy ashfall; large green circles are lapilli (particles measuring 2-64 mm in diameter). Modified from a map courtesy of Lauriane Chardot, Earth Observatory of Singapore; data taken from PHIVOLCS.

News articles noted that more than 300 domestic and 230 international flights were cancelled as the Manila Ninoy Aquino International Airport was closed during 12-13 January. Some roads from Talisay to Lemery and Agoncillo were impassible and electricity and water services were intermittent. Ashfall in several provinces caused power outages. Authorities continued to evacuate high-risk areas, and by 13 January more than 24,500 people had moved to 75 shelters out of a total number of 460,000 people within 14 km.

A PHIVOLCS report for 0800 on the 13th through 0800 on 14 January noted that lava fountaining had continued, with steam-rich ash plumes reaching around 2 km above the volcano and dispersing ash SE and W of Main Crater. Volcanic lighting continued at the base of the plumes. Fissures on the N flank produced 500-m-tall lava fountains. Heavy ashfall continued in the Lemery, Talisay, Taal, and Cuenca, Batangas Municipalities. By 1300 on the 13th lava fountaining generated 800-m-tall, dark gray, steam-laden ash plumes that drifted SW. Sulfur dioxide emissions averaged 5,299 metric tons/day (t/d) on 13 January and dispersed NNE (figure 19).

Figure (see Caption) Figure 19. Compilation of sulfur dioxide plumes from TROPOMI overlaid in Google Earth for 13 January from 0313-1641 UT. Courtesy of NASA Global Sulfur Dioxide Monitoring Page and Google Earth.

Explosions and ash emission through 22 January 2020. At 0800 on 15 January PHIVOLCS stated that activity was generally weaker; dark gray, steam-laden ash plumes rose about 1 km and drifted SW. Satellite images showed that the Main Crater lake was gone and new craters had formed inside Main Crater and on the N side of Volcano Island.

PHIVOLCS reported that activity during 15-16 January was characterized by dark gray, steam-laden plumes that rose as high as 1 km above the vents in Main Crater and drifted S and SW. Sulfur dioxide emissions were 4,186 t/d on 15 January. Eruptive events at 0617 and 0621 on 16 January generated short-lived, dark gray ash plumes that rose 500 and 800 m, respectively, and drifted SW. Weak steam plumes rose 800 m and drifted SW during 1100-1700, and nine weak explosions were recorded by the seismic network.

Steady steam emissions were visible during 17-21 January. Infrequent weak explosions generated ash plumes that rose as high as 1 km and drifted SW. Sulfur dioxide emissions fluctuated and were as high as 4,353 t/d on 20 January and as low as 344 t/d on 21 January. PHIVOLCS reported that white steam-laden plumes rose as high as 800 m above main vent during 22-28 January and drifted SW and NE; ash emissions ceased around 0500 on 22 January. Remobilized ash drifted SW on 22 January due to strong low winds, affecting the towns of Lemery (16 km SW) and Agoncillo, and rose as high as 5.8 km altitude as reported by pilots. Sulfur dioxide emissions were low at 140 t/d.

Steam plumes through mid-April 2020. The Alert Level was lowered to 3 on 26 January and PHIVOLCS recommended no entry onto Volcano Island and Taal Lake, nor into towns on the western side of the island within a 7-km radius. PHIVOLCS reported that whitish steam plumes rose as high as 800 m during 29 January-4 February and drifted SW (figure 20). The observed steam plumes rose as high as 300 m during 5-11 February and drifted SW.

Sulfur dioxide emissions averaged around 250 t/d during 22-26 January; emissions were 87 t/d on 27 January and below detectable limits the next day. During 29 January-4 February sulfur dioxide emissions ranged to a high of 231 t/d (on 3 February). The following week sulfur dioxide emissions ranged from values below detectable limits to a high of 116 t/d (on 8 February).

Figure (see Caption) Figure 20. Taal Volcano Island producing gas-and-steam plumes on 15-16 January 2020. Courtesy of James Reynolds, Earth Uncut.

On 14 February PHIVOLCS lowered the Alert Level to 2, noting a decline in the number of volcanic earthquakes, stabilizing ground deformation of the caldera and Volcano Island, and diffuse steam-and-gas emission that continued to rise no higher than 300 m above the main vent during the past three weeks. During 14-18 February sulfur dioxide emissions ranged from values below detectable limits to a high of 58 tonnes per day (on 16 February). Sulfur dioxide emissions were below detectable limits during 19-20 February. During 26 February-2 March steam plumes rose 50-300 m above the vent and drifted SW and NE. PHIVOLCS reported that during 4-10 March weak steam plumes rose 50-100 m and drifted SW and NE; moderate steam plumes rose 300-500 m and drifted SW during 8-9 March. During 11-17 March weak steam plumes again rose only 50-100 m and drifted SW and NE.

PHIVOLCS lowered the Alert Level to 1 on 19 March and recommended no entry onto Volcano Island, the area defined as the Permanent Danger Zone. During 8-9 April steam plumes rose 100-300 m and drifted SW. As of 1-2 May 2020 only weak steaming and fumarolic activity from fissure vents along the Daang Kastila trail was observed.

Evacuations. According to the Disaster Response Operations Monitoring and Information Center (DROMIC) there were a total of 53,832 people dispersed to 244 evacuation centers by 1800 on 15 January. By 21 January there were 148,987 people in 493 evacuation. The number of residents in evacuation centers dropped over the next week to 125,178 people in 497 locations on 28 January. However, many residents remained displaced as of 3 February, with DROMIC reporting 23,915 people in 152 evacuation centers, but an additional 224,188 people staying at other locations.

By 10 February there were 17,088 people in 110 evacuation centers, and an additional 211,729 staying at other locations. According to the DROMIC there were a total of 5,321 people in 21 evacuation centers, and an additional 195,987 people were staying at other locations as of 19 February.

The number of displaced residents continued to drop, and by 3 March there were 4,314 people in 12 evacuation centers, and an additional 132,931 people at other locations. As of 11 March there were still 4,131 people in 11 evacuation centers, but only 17,563 staying at other locations.

Deformation and ground cracks. New ground cracks were observed on 13 January in Sinisian (18 km SW), Mahabang Dahilig (14 km SW), Dayapan (15 km SW), Palanas (17 km SW), Sangalang (17 km SW), and Poblacion (19 km SW) Lemery; Pansipit (11 km SW), Agoncillo; Poblacion 1, Poblacion 2, Poblacion 3, Poblacion 5 (all around 17 km SW), Talisay, and Poblacion (11 km SW), San Nicolas (figure 21). A fissure opened across the road connecting Agoncillo to Laurel, Batangas. New ground cracking was reported the next day in Sambal Ibaba (17 km SW), and portions of the Pansipit River (SW) had dried up.

Figure (see Caption) Figure 21. Video screenshots showing ground cracks that formed during the Taal unrest and captured on 15 and 16 January 2020. Courtesy of James Reynolds, Earth Uncut.

Dropping water levels of Taal Lake were first observed in some areas on 16 January but reported to be lake-wide the next day. The known ground cracks in the barangays of Lemery, Agoncillo, Talisay, and San Nicolas in Batangas Province widened a few centimeters by 17 January, and a new steaming fissure was identified on the N flank of the island.

GPS data had recorded a sudden widening of the caldera by ~1 m, uplift of the NW sector by ~20 cm, and subsidence of the SW part of Volcano Island by ~1 m just after the main eruption phase. The rate of deformation was smaller during 15-22 January, and generally corroborated by field observations; Taal Lake had receded about 30 cm by 25 January but about 2.5 m of the change (due to uplift) was observed around the SW portion of the lake, near the Pansipit River Valley where ground cracking had been reported.

Weak steaming (plumes 10-20 m high) from ground cracks was visible during 5-11 February along the Daang Kastila trail which connects the N part of Volcano Island to the N part of the main crater. PHIVOLCS reported that during 19-24 February steam plumes rose 50-100 m above the vent and drifted SW. Weak steaming (plumes up to 20 m high) from ground cracks was visible during 8-14 April along the Daang Kastila trail which connects the N part of Volcano Island to the N part of the main crater.

Seismicity. Between 1300 on 12 January and 0800 on 21 January the Philippine Seismic Network (PSN) had recorded a total of 718 volcanic earthquakes; 176 of those had magnitudes ranging from 1.2-4.1 and were felt with Intensities of I-V. During 20-21 January there were five volcanic earthquakes with magnitudes of 1.6-2.5; the Taal Volcano network (which can detect smaller events not detectable by the PSN) recorded 448 volcanic earthquakes, including 17 low-frequency events. PHIVOLCS stated that by 21 January hybrid earthquakes had ceased and both the number and magnitude of low-frequency events had diminished.

Geologic Background. Taal is one of the most active volcanoes in the Philippines and has produced some of its most powerful historical eruptions. Though not topographically prominent, its prehistorical eruptions have greatly changed the landscape of SW Luzon. The 15 x 20 km Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2 surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, and several eruptive centers lie submerged beneath the lake. The 5-km-wide Volcano Island in north-central Lake Taal is the location of all historical eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones that have grown about 25% in area during historical time. Powerful pyroclastic flows and surges from historical eruptions have caused many fatalities.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Disaster Response Operations Monitoring and Information Center (DROMIC) (URL: https://dromic.dswd.gov.ph/); United Nations Office for the Coordination of Humanitarian Affairs, Philippines (URL: https://www.unocha.org/philippines); James Reynolds, Earth Uncut TV (Twitter: @EarthUncutTV, URL: https://www.earthuncut.tv/, YouTube: https://www.youtube.com/user/TyphoonHunter); Chris Vagasky, Vaisala Inc., Louisville, Colorado, USA (URL: https://www.vaisala.com/en?type=1, Twitter: @COweatherman, URL: https://twitter.com/COweatherman); Earth Observatory of Singapore, Nanyang Technological University, 50 Nanyang Avenue, Singapore (URL: https://www.earthobservatory.sg/); 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/); Relief Web, Flash Update No. 1 - Philippines: Taal Volcano eruption (As of 13 January 2020, 2 p.m. local time) (URL: https://reliefweb.int/report/philippines/flash-update-no-1-philippines-taal-volcano-eruption-13-january-2020-2-pm-local); Bloomberg, Philippines Braces for Hazardous Volcano Eruption (URL: https://www.bloomberg.com/news/articles/2020-01-12/philippines-raises-alert-level-in-taal-as-volcano-spews-ash); National Public Radio (NPR), Volcanic Eruption In Philippines Causes Thousands To Flee (URL: npr.org/2020/01/13/795815351/volcanic-eruption-in-philippines-causes-thousands-to-flee); Reuters (http://www.reuters.com/); Agence France-Presse (URL: http://www.afp.com/); Pacific Press (URL: http://www.pacificpress.com/); Shutterstock (URL: https://www.shutterstock.com/); Getty Images (URL: http://www.gettyimages.com/); Google Earth (URL: https://www.google.com/earth/).


Unnamed (Tonga) — March 2020 Citation iconCite this Report

Unnamed

Tonga

18.325°S, 174.365°W; summit elev. -40 m

All times are local (unless otherwise noted)


Additional details and pumice raft drift maps from the August 2019 submarine eruption

In the northern Tonga region, approximately 80 km NW of Vava’u, large areas of floating pumice, termed rafts, were observed starting as early as 7 August 2019. The area of these andesitic pumice rafts was initially 195 km2 with the layers measuring 15-30 cm thick and were produced 200 m below sea level (Jutzeler et al. 2020). The previous report (BGVN 44:11) described the morphology of the clasts and the rafts, and their general westward path from 9 August to 9 October 2019, with the first sighting occurring on 9 August NW of Vava’u in Tonga. This report updates details regarding the submarine pumice raft eruption in early August 2019 using new observations and data from Brandl et al. (2019) and Jutzeler et al. (2020).

The NoToVE-2004 (Northern Tonga Vents Expedition) research cruise on the RV Southern Surveyor (SS11/2004) from the Australian CSIRO Marine National Facility traveled to the northern Tonga Arc and discovered several submarine basalt-to-rhyolite volcanic centers (Arculus, 2004). One of these volcanic centers 50 km NW of Vava’u was the unnamed seamount (volcano number 243091) that had erupted in 2001 and again in 2019, unofficially designated “Volcano F” for reference purposes by Arculus (2004) and also used by Brandl et al. (2019). It is a volcanic complex that rises more than 1 km from the seafloor with a central 6 x 8.7 km caldera and a volcanic apron measuring over 50 km in diameter (figures 19 and 20). Arculus (2004) described some of the dredged material as “fresh, black, plagioclase-bearing lava with well-formed, glassy crusts up to 2cm thick” from cones by the eastern wall of the caldera; a number of apparent flows, lava or debris, were observed draping over the northern wall of the caldera.

Figure (see Caption) Figure 19. Visualization of the unnamed submarine Tongan volcano (marked “Volcano F”) using bathymetric data to show the site of the 6-8 August 2020 eruption and the rest of the cone complex. Courtesy of Philipp Brandl via GEOMAR.
Figure (see Caption) Figure 20. Map of the unnamed submarine Tongan volcano using satellite imagery, bathymetric data, with shading from the NW. The yellow circle indicates the location of the August 2019 activity. Young volcanic cones are marked “C” and those with pit craters at the top are marked with “P.” Courtesy of Brandl et al. (2019).

The International Seismological Centre (ISC) Preliminary Bulletin listed a particularly strong (5.7 Mw) earthquake at 2201 local time on 5 August, 15 km SSW of the volcano at a depth of 10 km (Brandl et al. 2019). This event was followed by six slightly lower magnitude earthquakes over the next two days.

Sentinel-2 satellite imagery showed two concentric rings originating from a point source (18.307°S 174.395°W) on 6 August (figure 21), which could be interpreted as small weak submarine plumes or possibly a series of small volcanic cones, according to Brandl et al. (2019). The larger ring is about 1.2 km in diameter and the smaller one measures 250 m. By 8 August volcanic activity had decreased, but the pumice rafts that were produced remained visible through at least early October (BGVN 44:11). Brandl et al. (2019) states that, due to the lack of continued observed activity rising from this location, the eruption was likely a 2-day-long event during 6-8 August.

Figure (see Caption) Figure 21. Sentinel-2 satellite image of possible gas/vapor emissions (streaks) on 6 August 2019 drifting NW, which is the interpreted site for the unnamed Tongan seamount. The larger ring is about 1.2 km in diameter and the smaller one measures 250 m. Image using False Color (urban) rendering (bands 12, 11, 4); courtesy of Sentinel Hub Playground.

The pumice was first observed on 9 August occurred up to 56 km from the point of origin, according to Jutzeler et al. (2020). By calculating the velocity (14 km/day) of the raft using three satellites, Jutzeler et al. (2020) determined the pumice was erupted immediately after the satellite image of the submarine plumes on 6 August (UTC time). Minor activity at the vent may have continued on 8 and 11 August (UTC time) with pale blue-green water discoloration (figure 22) and a small (less than 1 km2) diffuse pumice raft 2-5 km from the vent.

Figure (see Caption) Figure 22. Sentinel-2 satellite image of the last visible activity occurring W of the unnamed submarine Tongan volcano on 8 August 2019, represented by slightly discolored blue-green water. Image using Natural Color rendering (bands 4, 3, 2) and enhanced with color correction; courtesy of Sentinel Hub Playground.

Continuous observations using various satellite data and observations aboard the catamaran ROAM tracked the movement and extent of the pumice raft that was produced during the submarine eruption in early August (figure 23). The first visible pumice raft was observed on 8 August 2019, covering more than 136.7 km2 between the volcanic islands of Fonualei and Late and drifting W for 60 km until 9 August (Brandl et al. 2019; Jutzeler 2020). The next day, the raft increased to 167.2-195 km2 while drifting SW for 74 km until 14 August. Over the next three days (10-12 August) the size of the raft briefly decreased in size to less than 100 km2 before increasing again to 157.4 km2 on 14 August; at least nine individual rafts were mapped and identified on satellite imagery (Brandl et al. 2019). On 15 August sailing vessels observed a large pumice raft about 75 km W of Late Island (see details in BGVN 44:11), which was the same one as seen in satellite imagery on 8 August.

Figure (see Caption) Figure 23. Map of the extent of discolored water and the pumice raft from the unnamed submarine Tongan volcano between 8 and 14 August 2019 using imagery from NASA’s MODIS, ESA’s Sentinel-2 satellite, and observations from aboard the catamaran ROAM (BGVN 44:11). Back-tracing the path of the pumice raft points to a source location at the unnamed submarine Tongan volcano. Courtesy of Brandl et al. (2019).

By 17 August high-resolution satellite images showed an area of large and small rafts measuring 222 km2 and were found within a field of smaller rafts for a total extent of 1,350 km2, which drifted 73 km NNW through 22 August before moving counterclockwise for three days (figure f; Jutzeler et al., 2020). Small pumice ribbons encountered the Oneata Lagoon on 30 August, the first island that the raft came into contact (Jutzeler et al. 2020). By 2 September, the main raft intersected with Lakeba Island (460 km from the source) (figure 24), breaking into smaller ribbons that started to drift W on 8 September. On 19 September the small rafts (less than 100 m x less than 2 km) entered the strait between Viti Levu and Vanua Levu, the two main islands of Fiji, while most of the others were stranded 60 km W in the Yasawa Islands for more than two months (Jutzeler et al., 2020).

Figure (see Caption) Figure 24. Time-series map of the raft dispersal from the unnamed submarine Tongan volcano using multiple satellite images. A) Map showing the first days of the raft dispersal starting on 7 August 2019 and drifting SW from the vent (marked with a red triangle). Precursory seismicity that began on 5 August is marked with a white star. By 15-17 August the raft was entrained in an ocean loop or eddy. The dashed lines represent the path of the sailing vessels. B) Map of the raft dispersal using high-resolution Sentinel-2 and -3 imagery. Two dispersal trails (red and blue dashed lines) show the daily dispersal of two parts of the raft that were separated on 17 August 2019. Courtesy of Jutzeler et al. (2020).

References: Arculus, R J, SS2004/11 shipboard scientists, 2004. SS11/2004 Voyage Summary: NoToVE-2004 (Northern Tonga Vents Expedition): submarine hydrothermal plume activity and petrology of the northern Tofua Arc, Tonga. https://www.cmar.csiro.au/data/reporting/get file.cfm?eovpub id=901.

Brandl P A, Schmid F, Augustin N, Grevemeyer I, Arculus R J, Devey C W, Petersen S, Stewart M , Kopp K, Hannington M D, 2019. The 6-8 Aug 2019 eruption of ‘Volcano F’ in the Tofua Arc, Tonga. Journal of Volcanology and Geothermal Research: https://doi.org/10.1016/j.jvolgeores.2019.106695

Jutzeler M, Marsh R, van Sebille E, Mittal T, Carey R, Fauria K, Manga M, McPhie J, 2020. Ongoing Dispersal of the 7 August 2019 Pumice Raft From the Tonga Arc in the Southwestern Pacific Ocean. AGU Geophysical Research Letters: https://doi.orh/10.1029/2019GL086768.

Geologic Background. A submarine volcano along the Tofua volcanic arc was first observed in September 2001. The newly discovered volcano lies NW of the island of Vava'u about 35 km S of Fonualei and 60 km NE of Late volcano. The site of the eruption is along a NNE-SSW-trending submarine plateau with an approximate bathymetric depth of 300 m. T-phase waves were recorded on 27-28 September 2001, and on the 27th local fishermen observed an ash-rich eruption column that rose above the sea surface. No eruptive activity was reported after the 28th, but water discoloration was documented during the following month. In early November rafts and strandings of dacitic pumice were reported along the coast of Kadavu and Viti Levu in the Fiji Islands. The depth of the summit of the submarine cone following the eruption determined to be 40 m during a 2007 survey; the crater of the 2001 eruption was breached to the E.

Information Contacts: Jan Steffen, Communication and Media, GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany; Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Klyuchevskoy (Russia) — June 2020 Citation iconCite this Report

Klyuchevskoy

Russia

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

All times are local (unless otherwise noted)


Strombolian activity November 2019 through May 2020; lava flow down the SE flank in April

Klyuchevskoy is part of the Klyuchevskaya volcanic group in northern Kamchatka and is one of the most frequently active volcanoes of the region. Eruptions produce lava flows, ashfall, and lahars originating from summit and flank activity. This report summarizes activity during October 2019 through May 2020, and is based on reports by the Kamchatkan Volcanic Eruption Response Team (KVERT) and satellite data.

There were no activity reports from 1 to 22 October, but gas emissions were visible in satellite images. At 1020 on 24 October (2220 on 23 October UTC) KVERT noted that there was a small ash component in the ash plume from erosion of the conduit, with the plume reaching 130 km ENE. The Aviation Colour Code was raised from Green to Yellow, then to Orange the following day. An ash plume continued on the 25th to 5-7 km altitude and extending 15 km SE and 70 km SW and reached 30 km ESE on the 26th. Similar activity continued through to the end of the month.

Moderate gas emissions continued during 1-19 November, but the summit was obscured by clouds. Strong nighttime incandescence was visible at the crater during the 10-11 November and thermal anomalies were detected on 8 and 10-13 November. Explosions produced ash plumes up to 6 km altitude on the 20-21st and Strombolian activity was reported during 20-22 November. Degassing continued from 23 November through 12 December, and a thermal anomaly was visible on the days when the summit was not covered by clouds. An ash plume was reported moving to the NW on the 13th, and degassing with a thermal anomaly and intermittent Strombolian activity then resumed, continuing through to the end of December with an ash plume reported on the 30th.

Gas-and-steam plumes continued into January 2020 with incandescence noted when the summit was clear (figure 33). Strombolian activity was reported again starting on the 3rd. A weak ash plume produced on the 6th extended 55 km E, and on the 21st an ash plume reached 5-5.5 km altitude and extended 190 km NE (figure 34). Another ash plume the next day rose to the same altitude and extended 388 km NE. During 23-29 Strombolian activity continued, and Vulcanian activity produced ash plumes up to 5.5 altitude, extending to 282 km E on the 30th, and 145 km E on the 31st.

Figure (see Caption) Figure 33. Incandescence and degassing were visible at Klyuchevskoy through January 2020, seen here on the 11th. Courtesy of KVERT.
Figure (see Caption) Figure 34. A low ash plume at Klyuchevskoy on 21 January 2020 extended 190 km NE. Courtesy of KVERT.

Strombolian activity continued throughout February with occasional explosions producing ash plumes up to 5.5 km altitude, as well as gas-and-steam plumes and a persistent thermal anomaly with incandescence visible at night. Starting in late February thermal anomalies were detected much more frequently, and with higher energy output compared to the previous year (figure 35). A lava fountain was reported on 1 March with the material falling back into the summit crater. Strombolian activity continued through early March. Lava fountaining was reported again on the 8th with ejecta landing in the crater and down the flanks (figure 36). A strong persistent gas-and-steam plume containing some ash continued along with Strombolian activity through 25 March (figure 37), with Vulcanian activity noted on the 20th and 25th. Strombolian and Vulcanian activity was reported through the end of March.

Figure (see Caption) Figure 35. This MIROVA thermal energy plot for Klyuchevskoy for the year ending 29 April 2020 (log radiative power) shows intermittent thermal anomalies leading up to more sustained energy detected from February through March, then steadily increasing energy through April 2020. Courtesy of MIROVA.
Figure (see Caption) Figure 36. Strombolian explosions at Klyuchevskoy eject incandescent ash and gas, and blocks and bombs onto the upper flanks on 8 and 10 March 2020. Courtesy of IVS FEB RAS, KVERT.
Figure (see Caption) Figure 37. Weak ash emission from the Klyuchevskoy summit crater are dispersed by wind on 19 and 29 March 2020, with ash depositing on the flanks. Courtesy of IVS FEB RAS, KVERT.

Activity was dominantly Strombolian during 1-5 April and included intermittent Vulcanian explosions from the 6th onwards, with ash plumes reaching 6 km altitude. On 18 April a lava flow began moving down the SE flank (figures 38). A report on the 26th reported explosions from lava-water interactions with avalanches from the active lava flow, which continued to move down the SE flank and into the Apakhonchich chute (figures 39 and 40). This continued throughout April and May with sustained Strombolian and intermittent Vulcanian activity at the summit (figures 41 and 42).

Figure (see Caption) Figure 38. Strombolian activity produced ash plumes and a lava flow down the SE flank of Klyuchevskoy on 18 April 2020. Courtesy of IVS FEB RAS, KVERT.
Figure (see Caption) Figure 39. A lava flow descends the SW flank of Klyuchevskoy and a gas plume is dispersed by winds on 21 April 2020. Courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.
Figure (see Caption) Figure 40. Sentinel-2 thermal satellite images show the progression of the Klyuchevskoy lava flow from the summit crater down the SE flank from 19-29 April 2020. Associated gas plumes are dispersed in various directions. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 41. Strombolian activity at Klyuchevskoy ejects incandescent ejecta, gas, and ash above the summit on 27 April 2020. Courtesy of D. Bud'kov, IVS FEB RAS, KVERT.
Figure (see Caption) Figure 42. Sentinel-2 thermal satellite images of Klyuchevskoy show the progression of the SE flank lava flow through May 2020, with associated gas plumes being dispersed in multiple directions. Courtesy of Sentinel Hub Playground.

Geologic Background. Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


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

Nyamuragira

DR Congo

1.408°S, 29.2°E; summit elev. 3058 m

All times are local (unless otherwise noted)


Intermittent thermal anomalies within the summit crater during December 2019-May 2020

Nyamuragira (also known as Nyamulagira) is located in the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo and consists of a lava lake that reappeared in the summit crater in mid-April 2018. Volcanism has been characterized by lava emissions, thermal anomalies, seismicity, and gas-and-steam emissions. This report summarizes activity during December 2019 through May 2020 using information from monthly reports by the Observatoire Volcanologique de Goma (OVG) and satellite data.

According to OVG, intermittent eruptive activity was detected in the lava lake of the central crater during December 2019 and January-April 2020, which also resulted in few seismic events. MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows thermal anomalies within the summit crater that varied in both frequency and power between August 2019 and mid-March 2020, but very few were recorded afterward through late May (figure 88). Thermal hotspots identified by MODVOLC from 15 December 2019 through March 2020 were mainly located in the active central crater, with only three hotspots just outside the SW crater rim (figure 89). Sentinel-2 thermal satellite imagery also showed activity within the summit crater during January-May 2020, but by mid-March the thermal anomaly had visibly decreased in power (figure 90).

Figure (see Caption) Figure 88. The MIROVA graph of thermal activity (log radiative power) at Nyamuragira during 27 July through May 2020 shows variably strong, intermittent thermal anomalies with a variation in power and frequency from August 2019 to mid-March 2020. Courtesy of MIROVA.
Figure (see Caption) Figure 89. Map showing the number of MODVOLC hotspot pixels at Nyamuragira from 1 December 2019 t0 31 May 2020. 37 pixels were registered within the summit crater while 3 were detected just outside the SW crater rim. Courtesy of HIGP-MODVOLC Thermal Alerts System.
Figure (see Caption) Figure 90. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) confirmed ongoing thermal activity (bright yellow-orange) at Nyamuragira from February into April 2020. The strength of the thermal anomaly in the summit crater decreased by late March 2020, but was still visible. Courtesy of Sentinel Hub Playground.

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

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


Nyiragongo (DR Congo) — June 2020 Citation iconCite this Report

Nyiragongo

DR Congo

1.52°S, 29.25°E; summit elev. 3470 m

All times are local (unless otherwise noted)


Activity in the lava lake and small eruptive cone persists during December 2019-May 2020

Nyiragongo is located in the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo, part of the western branch of the East African Rift System and contains a 1.2 km-wide summit crater with a lava lake that has been active since at least 1971. Volcanism has been characterized by strong and frequent thermal anomalies, incandescence, gas-and-steam emissions, and seismicity. This report summarizes activity during December 2019 through May 2020 using information from monthly reports by the Observatoire Volcanologique de Goma (OVG) and satellite data.

In the December 2019 monthly report, OVG stated that the level of the lava lake had increased. This level of the lava lake was maintained for the duration of the reporting period, according to later OVG monthly reports. Seismicity increased starting in November 2019 and was detected in the NE part of the crater, but it decreased by mid-April 2020. SO2 emissions increased in January 2020 to roughly 7,000 tons/day but decreased again near the end of the month. OVG reported that SO2 emissions rose again in February to roughly 8,500 tons/day before declining to about 6,000 tons/day. Unlike in the previous report (BGVN 44:12), incandescence was visible during the day in the active lava lake and activity at the small eruptive cone within the 1.2-km-wide summit crater has since increased, consisting of incandescence and some lava fountaining (figure 72). A field survey was conducted on 3-4 March where an OVG team observed active lava fountains and ejecta that produced Pele’s hair from the small eruptive cone (figure 73). During this survey, OVG reported that the level of the lava lake had reached the second terrace, which was formed on 17 January 2002 and represents remnants of the lava lake at different eruption stages. There, the open surface lava lake was observed; gas-and-steam emissions accompanied both the active lava lake and the small eruptive cone (figures 72 and 73).

Figure (see Caption) Figure 72. Webcam image of Nyiragongo in February 2020 showing an open lava lake surface and incandescence from the active crater cone within the 1.2 km-wide summit crater visible during the day, accompanied by white gas-and-steam emissions. Courtesy of OVG (Rapport OVG February 2020).
Figure (see Caption) Figure 73. Webcam image of Nyiragongo on 4 March 2020 showing an open lava lake surface and incandescence from the active crater cone within the 1.2 km-wide summit crater visible during the day, accompanied by white gas-and-steam emissions. Courtesy of OVG (Rapport OVG Mars 2020).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data continued to show frequent strong thermal anomalies within 5 km of the summit crater through May 2020 (figure 74). Similarly, the MODVOLC algorithm reported multiple thermal hotspots almost daily within the summit crater between December 2019 and May 2020. These thermal signatures were also observed in Sentinel-2 thermal satellite imagery within the summit crater (figure 75).

Figure (see Caption) Figure 74. Thermal anomalies at Nyiragongo from 27 July through May 2020 as recorded by the MIROVA system (Log Radiative Power) were frequent and strong. Courtesy of MIROVA.
Figure (see Caption) Figure 75. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) showed ongoing thermal activity (bright yellow-orange) in the summit crater at Nyiragongo during January through April 2020. Courtesy of Sentinel Hub Playground.

Geologic Background. One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes of a stratovolcano contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

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


Kavachi (Solomon Islands) — May 2020 Citation iconCite this Report

Kavachi

Solomon Islands

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

All times are local (unless otherwise noted)


Discolored water plumes seen using satellite imagery in 2018 and 2020

Kavachi is a submarine volcano located in the Solomon Islands south of Gatokae and Vangunu islands. Volcanism is frequently active, but rarely observed. The most recent eruptions took place during 2014, which consisted of an ash eruption, and during 2016, which included phreatomagmatic explosions (BGVN 42:03). This reporting period covers December 2016-April 2020 primarily using satellite data.

Activity at Kavachi is often only observed through satellite images, and frequently consists of discolored submarine plumes for which the cause is uncertain. On 1 January 2018 a slight yellow discoloration in the water is seen extending to the E from a specific point (figure 20). Similar faint plumes were observed on 16 January, 25 February, 2 March, 26 April, 6 May, and 25 June 2018. No similar water discoloration was noted during 2019, though clouds may have obscured views.

Figure (see Caption) Figure 20. Satellite images from Sentinel-2 revealed intermittent faint water discoloration (yellow) at Kavachi during the first half of 2018, as seen here on 1 January (top left), 25 February (top right), 26 April (bottom left), and 25 June (bottom right). Images with “Natural color” rendering (bands 4, 3, 2); courtesy of Sentinel Hub Playground.

Activity resumed in 2020, showing more discolored water in satellite imagery. The first instance occurred on 16 March, where a distinct plume extended from a specific point to the SE. On 25 April a satellite image showed a larger discolored plume in the water that spread over about 30 km2, encompassing the area around Kavachi (figure 21). Another image on 30 April showed a thin ribbon of discolored water extending about 50 km W of the vent.

Figure (see Caption) Figure 21. Sentinel-2 satellite images of a discolored plume (yellow) at Kavachi beginning on 16 March (top left) with a significant large plume on 25 April (right), which remained until 30 April (bottom left). Images with “Natural color” rendering (bands 4, 3, 2); courtesy of Sentinel Hub Playground.

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

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


Kuchinoerabujima (Japan) — May 2020 Citation iconCite this Report

Kuchinoerabujima

Japan

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

All times are local (unless otherwise noted)


Eruption and ash plumes begin on 11 January 2020 and continue through April 2020

Kuchinoerabujima encompasses a group of young stratovolcanoes located in the northern Ryukyu Islands. All historical eruptions have originated from the Shindake cone, with the exception of a lava flow that originated from the S flank of the Furudake cone. The most recent previous eruptive period took place during October 2018-February 2019 and primarily consisted of weak explosions, ash plumes, and ashfall. The current eruption began on 11 January 2020 after nearly a year of dominantly gas-and-steam emissions. Volcanism for this reporting period from March 2019 to April 2020 included explosions, ash plumes, SO2 emissions, and ashfall. The primary source of information for this report comes from monthly and annual reports from the Japan Meteorological Agency (JMA) and advisories from the Tokyo Volcanic Ash Advisory Center (VAAC). Activity has been limited to Kuchinoerabujima's Shindake Crater.

Volcanism at Kuchinoerabujima was relatively low during March through December 2019, according to JMA. During this time, SO2 emissions ranged from 100 to 1,000 tons/day. Gas-and-steam emissions were frequently observed throughout the entire reporting period, rising to a maximum height of 1.1 km above the crater on 13 December 2019. Satellite imagery from Sentinel-2 showed gas-and-steam and occasional ash emissions rising from the Shindake crater throughout the reporting period (figure 7). Though JMA reported thermal anomalies occurring on 29 January and continuing through late April 2020, Sentinel-2 imagery shows the first thermal signature appearing on 26 April.

Figure (see Caption) Figure 7. Sentinel-2 thermal satellite images showed gas-and-steam and ash emissions rising from Kuchinoerabujima. Some ash deposits can be seen on 6 February 2020 (top right). A thermal anomaly appeared on 26 April 2020 (bottom right). Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

An eruption on 11 January 2020 at 1505 ejected material 300 m from the crater and produced ash plumes that rose 2 km above the crater rim, extending E, according to JMA. The eruption continued through 12 January until 0730. The resulting ash plumes rose 400 m above the crater, drifting SW while the SO2 emissions measured 1,300 tons/day. Ashfall was reported on Yakushima Island (15 km E). Minor eruptive activity was reported during 17-20 January which produced gray-white plumes that rose 300-500 m above the crater. On 23 January, seismicity increased, and an eruption produced an ash plume that rose 1.2 km altitude, according to a Tokyo VAAC report, resulting in ashfall 2 km NE of the crater. A small explosion was detected on 24 January, followed by an increase in the number of earthquakes during 25-26 January (65-71 earthquakes per day were registered). Another small eruptive event detected on 27 January at 0148 was accompanied by a volcanic tremor and a change in tilt data. During the month of January, some inflation was detected at the base on the volcano and a total of 347 earthquakes were recorded. The SO2 emissions ranged from 200-1,600 tons/day.

An eruption on 1 February 2020 produced an eruption column that rose less than 1 km altitude and extended SE and SW (figure 8), according to the Tokyo VAAC report. On 3 February, an eruption from the Shindake crater at 0521 produced an ash plume that rose 7 km above the crater and ejected material as far as 600 m away. As a result, a pyroclastic flow formed, traveling 900-1,500 m SW. The previous pyroclastic flow that was recorded occurred on 29 January 2019. Ashfall was confirmed in the N part of Yakushima Island with a large amount in Miyanoura (32 km ESE) and southern Tanegashima. The SO2 emissions measured 1,700 tons/day during this event.

Figure (see Caption) Figure 8. Webcam images from the Honmura west surveillance camera of an ash plume rising from Kuchinoerabujima on 1 February 2020. Courtesy of JMA (Weekly bulletin report 509, February 2020).

Intermittent small eruptive events occurred during 5-9 February; field observations showed a large amount of ashfall on the SE flank which included lapilli that measured up to 2 cm in diameter. Additionally, thermal images showed 5-km-long pyroclastic flow deposits on the SW flank. An eruption on 9 February produced an ash plume that rose 1.2 km altitude, drifting SE. On 13 February a small eruption was detected in the Shindake crater at 1211, producing gray-white plumes that rose 300 m above the crater, drifting NE. Small eruptive events also occurred during 20-21 February, resulting in gas-and-steam emissions that rose 200 m above the crater. During the month of February, some horizontal extension was observed since January 2020 using GNSS data. The total number of earthquakes during this month drastically increased to 1225 compared to January. The SO2 emissions ranged from 300-1,700 tons/day.

By 2 March 2020, seismicity decreased, and activity declined. Gas-and-steam emissions continued infrequently for the duration of the reporting period. The SO2 emissions during March ranged from 700-2,100 tons/day, the latter of which occurred on 15 March. Seismicity increased again on 27 March. During 5-8 April 2020, small eruptive events were detected, generating ash plumes that rose 900 m above the crater (figure 9). The SO2 emissions on 6 April reached 3,200 tons/day, the maximum measurement for this reporting period. These small eruptive events continued from 13-20 and 23-25 April within the Shindake crater, producing gray-white plumes that rose 300-800 m above the crater.

Figure (see Caption) Figure 9. Webcam images from the Honmura Nishi (top) and Honmura west (bottom) surveillance cameras of ash plumes rising from Kuchinoerabujima on 6 March and 5 April 2020. Courtesy of JMA (Weekly bulletin report 509, March and April 2020).

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

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


Soputan (Indonesia) — May 2020 Citation iconCite this Report

Soputan

Indonesia

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

All times are local (unless otherwise noted)


Minor ash emissions during 23 March and 2 April 2020

Soputan is a stratovolcano located in the northern arm of Sulawesi Island, Indonesia. Previous eruptive periods were characterized by ash explosions, lava flows, and Strombolian eruptions. The most recent eruption occurred during October-December 2018, which consisted mostly of ash plumes and some summit incandescence (BGVN 44:01). This report updates information for January 2019-April 2020 characterized by two ash plumes and gas-and-steam emissions. The primary source of information come from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) and the Darwin Volcanic Ash Advisory Center (VAAC).

Activity during January 2019-April 2020 was relatively low; three faint thermal anomalies were observed at the summit at Soputan in satellite imagery for a total of three days on 2 and 4 January, and 1 October 2019 (figure 17). The MIROVA (Middle InfraRed Observation of Volcanic Activity) based on analysis of MODIS data detected 12 distal hotspots and six low-power hotspots within 5 km of the summit during August to early October 2019. A single distal thermal hotspot was detected in early March 2020. In March, activity primarily consisted of white to gray gas-and-steam plumes that rose 20-100 m above the crater, according to PVMBG. The Darwin VAAC issued a notice on 23 March 2020 that reported an ash plume rose to 4.3 km altitude; minor ash emissions had been visible in a webcam image the previous day (figure 18). A second notice was issued on 2 April, where an ash plume was observed rising 2.1 km altitude and drifting W.

Figure (see Caption) Figure 17. Sentinel-2 thermal satellite imagery detected a total of three thermal hotspots (bright yellow-orange) at the summit of Soputan on 2 and 4 January and 1 October 2019. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 18. Minor ash emissions were seen rising from Soputan on 22 March 2020. Courtesy of MAGMA Indonesia.

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

Information Contacts: 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.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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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Bulletin of the Global Volcanism Network - Volume 16, Number 04 (April 1991)

Managing Editor: Lindsay McClelland

Aira (Japan)

Continued vigorous explosions

Alcedo (Ecuador)

Sonic activity and felt earthquakes decline; minor changes to hydrothermal system

Arenal (Costa Rica)

Strombolian activity; explosions; lava extrusion

Asamayama (Japan)

Continued steam emission; seismicity increases after 2 months of quiet

Colima (Mexico)

Lava advances down SW flank after partial collapse of summit dome; rock avalanches from flow margins

Fernandina (Ecuador)

Large SO2-rich plumes deposit ash; lava fountains and flows from 1988 vent area

Fukutoku-Oka-no-Ba (Japan)

Water discoloration during one of five overflights

Galeras (Colombia)

Frequent ash emission and seismicity

Gede-Pangrango (Indonesia)

Earthquake swarm

Hakoneyama (Japan)

Brief earthquake swarm in center of caldera

Ijen (Indonesia)

Crater lake changes from gray and bubbling to light green

Kavachi (Solomon Islands)

Submarine eruption builds new island

Kilauea (United States)

Lava breakout from tube system feeds new ocean entry

Klyuchevskoy (Russia)

Small summit plume; ash on SE flank

Kozushima (Japan)

Earthquake swarm but no surface activity

Kusatsu-Shiranesan (Japan)

Continued seismicity

Langila (Papua New Guinea)

Ash emission and glow

Lewotobi (Indonesia)

Brief increase in seismicity

Manam (Papua New Guinea)

Tephra emission from two craters

Merapi (Indonesia)

High-temperature fumaroles; no changes evident to summit dome

Ontakesan (Japan)

Earthquake swarms and tremor; no change in steam emission

Pacaya (Guatemala)

Strombolian activity declines to ash emission as seismicity decreases

Pinatubo (Philippines)

Phreatic explosion devastates 1 km2 forested area; seismicity and gas emission continue; 2,000 evacuated

Poas (Costa Rica)

Increased gas emission; continued seismicity

Rabaul (Papua New Guinea)

Low-level seismicity; minor deflation

Rincon de la Vieja (Costa Rica)

Ash ejection and lahars

Ruiz, Nevado del (Colombia)

Tremor precedes several days of ash emission

Santa Maria (Guatemala)

Strong explosion and pyroclastic flow; continued lava extrusion feeds rock avalanches

Semeru (Indonesia)

Continued explosions and seismicity

Sheveluch (Russia)

Possible new tephra deposit on E flank

Stromboli (Italy)

Explosive activity from a single crater; strong seismicity

Submarine Volcano NNE of Iriomotejima (Japan)

Strong felt seismicity but no surface changes

Taal (Philippines)

Continued seismicity and changes to crater lake

Turrialba (Costa Rica)

New fractures found after major 22 April earthquake

Unzendake (Japan)

Ash emission from two vents; frequent seismicity; lava dome extruded into summit crater

Vulcano (Italy)

Fumarole temperatures increase

Whakaari/White Island (New Zealand)

Renewed ash emission; new collapse pit



Aira (Japan) — April 1991 Citation iconCite this Report

Aira

Japan

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

All times are local (unless otherwise noted)


Continued vigorous explosions

Explosive activity has remained at high levels since mid-January, totaling . . . 42 [explosions] in April (the highest monthly total since April 1986), and 15 through 16 May . . . . The explosions caused no damage. The highest April ash cloud rose 3,000 m on the 30th. April ashfall was 187 g/m2 [at KLMO]. Earthquake swarms were recorded on four days, a normal monthly total for the volcano.

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

Information Contacts: JMA.


Alcedo (Ecuador) — April 1991 Citation iconCite this Report

Alcedo

Ecuador

0.43°S, 91.12°W; summit elev. 1130 m

All times are local (unless otherwise noted)


Sonic activity and felt earthquakes decline; minor changes to hydrothermal system

Late-April fieldwork revealed continued but diminished sonic activity, no evidence of an eruption, and only minor changes to the volcano's hydrothermal system.

Biologist Milton Friere, working on the island since February, reported that he felt a strong shock, apparently on 9 March at about 1900. Hunters on Santiago Island, 35 km NE of Alcedo, also felt a large earthquake around that time but there is uncertainty about the date and the WWSSN recorded only the 3 March event (16:3). Immediately after the felt earthquake, explosion sounds began to be heard daily at Friere's camp on the caldera's N rim. The initial sounds were the most intense and frequent, then they declined gradually, and by late April were heard only once every few days from the N rim camp. Fewer than 5 earthquakes were felt at the camp until 5 April. Others were documented on 5 April at 1740, 7 April at 1700, and 17 April at 1725. Events of similar intensity may have gone unnoticed during active fieldwork.

While camped on the caldera's S rim during a 23-28 April field survey, Dennis Geist heard eight explosion sounds in 3 days, compared to 2-13 heard daily by Tui DeRoy and Mark Jones in late March (16:3). All were heard in camp, with none noticed during fieldwork. The sounds, consisting of deep rumbling lasting about a second, were likened to thunder generated ~ 10 km away. Although the sounds were clearly directional, each seemed to come from a different direction. None were accompanied by discernible changes in fumarole output, but two were followed 10-15 seconds later by a felt earthquake. The stronger earthquake lasted 5-10 seconds, whereas the weaker one continued for more than 30 seconds after a strong initial jolt.

The seismicity and sonic activity were preceded by the first heavy rains in the Galápagos for several years. Between 26 February and 4 March, 5-10 cm of rain fell daily on Alcedo. Heavy rains also fell on 6, 8, 10, 19, and 30 March, and 10 and 15 April.

Geist noted only subtle changes to the hydrothermal system. Before the 1991 activity, hundreds of fumaroles were distributed around both the southern ring faults and a vent that erupted voluminous rhyolitic pumice and obsidian flows about 90,000 years ago. Fewer than 10 small new fumaroles (identified by remains of recently killed plants) were observed, and no significant increase in total gas output was evident. A large fumarole (called "the Geyser" because it formerly ejected water) may have been somewhat more vigorous than during Geist's previous visits in 1989 and 1983. The vapor plume from this fumarole varied dramatically over periods of hours, and at times there was no visible cloud. No recently formed fissures or fault scarps were observed.

Geologic Background. Alcedo is one of the lowest and smallest of six shield volcanoes on Isabela Island. Much of the flanks and summit caldera are vegetated, but young lava flows are prominent on the N flank near the saddle with Darwin volcano. It is the only Galapagos volcano known to have erupted rhyolite as well as basalt, producing about 1 km3 of late-Pleistocene rhyolitic tephra and lava flows from several vents late in its history. Recent faulting has produced a moat around part of the 7-8 km caldera floor, which is elongated N-S and appears to be migrating to the south. Fewer circumferential fissures occur on Alcedo than on other western Galápagos volcanoes. An eruption attributed to Alcedo in 1954 (Richards, 1957) is more likely to have been from neighboring Sierra Negra (Simkin 1980, pers. comm.). Photo-geologic mapping by K.A. Howard (pers. comm.) revealed only one flow on 30 October 1960 photographs that does not appear on 30 May 1946 photos. That is near Cartago Bay, low on the SE flank, rather than the 610-m, NE-flank elevation listed for the 1954 eruption. An active hydrothermal system is located within the caldera.

Information Contacts: D. Geist, Univ of Idaho.


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

Arenal

Costa Rica

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

All times are local (unless otherwise noted)


Strombolian activity; explosions; lava extrusion

Strombolian activity, with sporadic small explosions, lava extrusion, and voluminous gas emission, continued during April. Tremor, associated with lava extrusion, dominated seismicity during the first half of the month. Following 15 April, the number of explosions increased and tremor diminished.

The following is a report by W. Melson. "From 7 to 17 April, continuous 24 hour/day seismic, sound, and visual observations from the Arenal Observatory . . . revealed that; 1) blocky lava flows are moving down and have covered the S slope to about 900 m elevation. None are now active in the previous long-term channel on the N slopes into the Río Tabacón drainage; one small 200-m-long flow was active on the WNW slope. 2) The level of pyroclastic activity ranged from 3 events/day (10 April) to 46/day (14-15 April) (figure 37). 3) Episodic periods of intense harmonic tremor are common. Compared to 11 other periods of close monitoring, beginning in 1987, the pyroclastic activity is low (figure 38)."

Figure (see Caption) Figure 37. Daily number of pyroclastic events at Arenal, 7-17 April 1991. Event types are characterized by sound; 'Whooshes' are intense gas, block, and bomb fountains;'Chugs' are rhythmic, less intense gas emissions, commonly accompanied by blocks and bombs. Observations were made from Arenal Observatory Lodge, 2.7 km S of the summit. Courtesy of W. Melson.
Figure (see Caption) Figure 38. Average daily number of pyroclastic events at Arenal, during 12 approximately 10-day periods, 1987-91. Observations were made from Arenal Observatory Lodge (2.7 km S of the summit) by Earthwatch and Smithsonian Volunteer Expeditions personnel. Courtesy of W. Melson.

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: W. Melson, SI; V. Barboza, E. Fernández, J. Barquero, and R. Sáenz, OVSICORI.


Asamayama (Japan) — April 1991 Citation iconCite this Report

Asamayama

Japan

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

All times are local (unless otherwise noted)


Continued steam emission; seismicity increases after 2 months of quiet

Strong seismicity . . . declined during February and March 1991. Only 19 earthquakes and no tremor episodes were recorded in March. Seismicity increased again 8-18 April and a monthly total of 250 earthquakes and 17 tremor episodes were recorded (figure 13). Steam emission remained unchanged with a plume height of a few hundred meters.

Figure (see Caption) Figure 13. Daily number of recorded earthquakes (top) and tremor episodes (bottom) at Asama, January 1989-early May 1991. Arrow marks small ash eruptions on 20 July 1990. Courtesy of JMA.

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

Information Contacts: JMA.


Colima (Mexico) — April 1991 Citation iconCite this Report

Colima

Mexico

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

All times are local (unless otherwise noted)


Lava advances down SW flank after partial collapse of summit dome; rock avalanches from flow margins

The following is from Ana Lillian Martín del Pozzo and colleagues.

The new summit-dome lobe grew from about 6 m high and 20 m in diameter on 2 March to 36 m high and 109 m across on 14 April, but geodetic measurements on 15 April showed a reduction in its diameter due to the beginning of its emplacement down the SW flank. Seismicity recorded by four portable seismographs increased dramatically beginning on 12 April, saturating records; avalanche signals and both A-and B-type events were detected. Most seismicity after 15 April was related to avalanching (see also seismic data from RESCO instruments reported in 16:03). During the morning of 16 April, avalanching from the dome occurred every 3-5 minutes, increasing to constant landsliding about noon. Large Merapi-type avalanches began around 1515, with maximum intensity between 1700 and 1800. During that time, three distinct plumes were visible: a white gas column, fine gray ash being carried E, and fine-grained material produced by the avalanches. Colima airport was closed because of ashfall, although <5 mm of ash were measured there. Data from four dry-tilt stations N and S of the summit showed <10 µrad of deformation for the period 14-23 April. Weekly spring-water monitoring showed no pH or temperature changes, although sulfate and boron contents varied, having increased before 16 April. Declines in the levels of nearby lakes appear to have been caused by normal withdrawal of irrigation water.

The following is from a Centro Internacional de Ciencias de la Tierra (CICT) team, including geologists and geophysicists from the Universidad de Colima, UNAM, Univ de Guadalajara, Arizona State, and Louisiana State Universities.

Avalanches generated voluminous dilute dust clouds, mainly produced by the crumbling of blocks falling from the dome and the receding crater rim, and by reactivation of previously deposited dust. The component of hot new magma apparently contributed to the seemingly fluidized character of the avalanches [and the resulting Merapi-type block-and-ash flows].

After the partial collapse of the summit-dome lobe, a block lava flow emerged from the SW part of the dome and began to move down the SW flank. The flow, 70 m long and 40 m wide on 18 April, was about 100 m wide and at least 1,150 m long by the morning of 26 April, with its 25-m-thick front at 2,680 m altitude. Dimensions were similar on 18 May, and the flow was widening at its top. Small avalanches occurred from the flow front, from the crater rim adjacent to the flow levees, and from the levees themselves, especially the E levee. Blocks reached about 2,300 m elevation (~4,000 m outward from the summit) during the largest avalanche associated with the 16 April collapse. Dust clouds extended beyond the range of the avalanche blocks, and three canyons of the volcano's main drainage system on the SW and S flanks were filled with avalanche-derived clastic material, mostly very fine powder. This material has not been compacted and has a volume on the order of 106 m3. A lahar warning has been issued for the coming rainy season, which usually begins in early June. Lava extruded from the SW part of the dome was pushing older dome material toward the W and NW. Unstable material was accumulating, and geologists noted that additional avalanches could be expected in those areas.

Winds in the area have dominantly blown toward the SE to NE recently, and some light ashfall has been reported from towns in that sector up to 30 km away. Seismic records showed events with small wave packages that at times seemed to correlate with explosive summit degassing activity, but their number and amplitude were decreasing as of late April.

Observations of the summit area revealed that the 2 July 1987 crater on the E side of the dome (Flores and others, 1987, and 12:07, 13:09, and 15:12) had a ring-like pattern of fumaroles around its rim. A pair of whitish plumes persistently issued from the N part of the zone of lava extrusion, where some incandescence has been observed. Plume heights during similar wind conditions ranged from a few tens of meters to 1,500 m. As of 18 May, the summit-dome lobe was growing toward the edge of the pre-existing W dome. Geologists noted that if activity continues at the same rate, a new block lava flow will begin to develop, probably on the W or NW side of the volcano, in the next 2-3 weeks.

Airborne COSPEC measurements that began 25 April showed SO2 emission rates on the order of 300 t/d, similar to those observed in 1982 by Casadevall and others (1984) and in 1985 by geologists from Dartmouth College. Geologists noted that these stable low levels were consistent with the absence of significant deep seismicity or harmonic tremor and support an interpretation that the present cycle of activity does not include the ascent of significant new magma or magmatic gases from depth.

Alert warnings have been issued and transportation made available for possible evacuation of towns in the risk area, which extends to 12 km on the SW flank. However, geologists noted that no evacuations have occurred, since the volume of rock avalanches was limited to a few hundred thousand m3 and seismicity has remained at relatively low levels, without harmonic tremor or low-frequency earthquakes.

The following, from J.B. Murray, describes ground deformation work 1-7 March.

"Ten kilometers of levelling lines, established in 1982, were measured 1-4 March, as were five of six dry-tilt stations. The 6th, on the W side of the cone, could not be measured, because repeated rock avalanches from the dome made it extremely hazardous to approach this side of the mountain.

"The levelling traverse was last occupied in March 1990, and results show that there have been no large changes since then. There was a slight subsidence of the stations nearest to the summit (just over 1 km from the dome), which have dropped 2.5 cm relative to the farthest stations, 3 km from the summit and outside the caldera. Within the precision of the method, the subsidence appears to be radial to the summit, or perhaps between the summit and the parasitic vent Volcancito (on the upper NE flank).

"The three dry-tilt stations within the caldera all showed tilts to the S over the past year. Those on the Playon (the caldera floor at the NW foot of the active cone) had small tilts of 9 and 15 µrad. The station on Volcancito has tilted 39 µrad, although this value is less reliable because the combination of benchmarks used was different than in 1990. The other two stations (at Nevado de Colima and Barranca La Arena), 6 km N and 9 km S of the summit, were vandalized or otherwise disturbed.

"At first sight these results appear reassuring, as one would expect more pronounced deformation if there were any major increase in magma supply that might be associated with a cataclysmic event. However, caution must be exercised, since (a) ground deformation prior to a major eruption has not been measured at Colima before, and is poorly known on this type of volcano, and (b) the levelling traverse and two of the three dry-tilt stations are N of the volcano where the ground rises toward Nevado de Colima, whereas most of the deformation could be occurring on the unbutressed S flank.

"Many large rock avalanches were seen on 1 March, but from 2 March, the rate declined somewhat. During the levelling 2-4 March, avalanches were noted at the overall rate of 3.2/hour down the N and W sides. From the same area, avalanches were noted at the hourly rate of 1.4 on 29 March-1 April 1990; 0.4 on 4-5 February 1986; and 1.5 on 3-7 December 1982. These figures underplay the 1991 activity, because the avalanches were much larger this year and continued for much longer."

References. Casadevall, T.J., Rose, W.I., Fuller, W., Hunt, W., Hart, M., Moyers, J., Woods, D., Chuan, R., and Friend, J., 1984, Sulfur dioxide and particles in quiescent volcanic plumes from Poás, Arenal, and Colima Volcanoes, Costa Rica and México: JGR, v. 89, no. D6, p. 9633-9641.

Flores, J., and others, 1987, Informes de las recientes observaciones practicadas en el Volcán Colima: Revista del Instituto de Geografía y Estadística, Universidad de Guadalajara, México, v. 3, no. 2.

Further Reference. Rodríguez-Elizarrías, S., Siebe, C., Komorowski, J.-C., Espindola, J., and Saucedo, R., 1991, Field observations of pristine block- and-ash-flow deposits emplaced April 16-17, 1991 at Volcán de Colima, Mexico: JVGR, v. 48, p. 399-412.

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

Information Contacts: Francisco Núñez-Cornú, F.A. Nava, Gilberto Ornelas-Arciniega, Ariel Ramírez-Vázquez, R. Saucedo, G.A. Reyes-Dávila, R. García, Guillermo Castellanos, and Hector Tamez, CICT, Universidad de Colima; S. de la Cruz-Reyna, Z. Jiménez, J.M. Espindola, and Sergio Rodríguez, UNAM; Julián Flores, Instituto de Geografía y Estadística, Univ de Guadalajara; Claus Siebe and J-C. Komorowski, Arizona State Univ, USA; S. Williams, Louisiana State Univ, USA.Ana Lillian Martín del Pozzo, J. Panohaya, F. Sánchez, R. Maciel, and A. Aguayo, Instituto de Geofísica, UNAM; D. Barrera, Centro de Ciencias de la Tierra, Univ de Guadalajara; G. González, Univ Autónoma de Puebla; J.B. Murray, Open Univ, UK.


Fernandina (Ecuador) — April 1991 Citation iconCite this Report

Fernandina

Ecuador

0.37°S, 91.55°W; summit elev. 1476 m

All times are local (unless otherwise noted)


Large SO2-rich plumes deposit ash; lava fountains and flows from 1988 vent area

The eruption . . . began on 19 April and ended in the early morning hours of 24 April. It was observed by several groups both on and near Fernandina, providing documentation that is unusually detailed for this uninhabited island volcano.

The start of the eruption was witnessed at about 1300 by Kirstin and Feo Pitcairn while sailing towards Fernandina ~30 km to its N. A "towering column" developed within only a few minutes, and one hour later a second plume, from a source N of the first, was recognized. David Day. . . reported that the main vent was near the base of the ESE caldera wall at the 1988 eruption site, with another vent ~3 km to the NW, also on the main caldera boundary fault and near the easternmost 1978 eruption vent. At 1500, Day, then sailing near Isla Santiago, noted that the leading edge of the cloud had already reached that island's high point, ~ 90 km ENE of its source.

Shortly after 1500, cloud development accelerated. Kirstin Pitcairn described a "big white mushroom cloud above the N plume" and estimated the height of the rapidly rising S plume at 4-6 km. Day described the distant cloud as building slowly after 1510, and both observers remarked on the increased density of the ash cloud. At 1535 a new plume joined the other two, nearer the S plume, and rose very rapidly, but the S plume remained dominant and Pitcairn saw pink coloration to its top in daytime. Starting about 1600, ash fell at Cabo Hammond, on Fernandina's SW corner, where Markus Horning and assistants were studying fur seals. Ashfall was continuous for 3 hours and intermittent until about 2230, with an estimated accumulation of 5-10 mm for the full eruption. At 2015 Horning first heard noise from the eruption, a strong continuous rumbling without booms or explosions, that continued until well after midnight. A single explosion was heard by Milton Friere, 50 km E on Volcán Alcedo, at 1630 ( ± 15 minutes).

At 1830 David Day, then 110 km ESE, saw "the first of 3 large dark clouds punch up quickly above the low cloud covering Isabela . . . over a 10-minute period," and estimated the cloud height at 3-4 km.

That night the Pitcairns watched and videotaped the eruption from Punta Espinoza on Fernandina's NE coast. They described a varying spectacle including "flame-shaped jets shooting high into the billowing column," alternation of brightness between the two main plumes, and cessation of the central plume at 2043. At Cabo Hammond, Horning routinely measured incident light intensity at sea level every night, and his readings indicated maximum light emission/reflection that night from about 2000 to 2200. He noted that this was the only night in which glow from two vents was visible (only the S vent being active in later nights). Although it was a dark night (new moon 14 April), the peak glow corresponded to roughly 2/3 the light measured on clear full-moon nights.

The eruption was quieter on the early morning of 20 April, but zoologists N.P. and M.J. Ashmole, also at Espinoza, described renewed activity around 0845, including audible explosions, ash, and reappearance of the central column. On the opposite corner of the island, Horning experienced a heavy, dense fog that obscured the summit, but he heard strong explosions at 0857 and 1116. The Pitcairns described a huge dark cloud forming at 0910, and in late morning they sailed W to circle the island, but encountered heavy ashfall off the WNW coast. At 1152 the Nimbus-7 . . . TOMS instrument measured a strong SO2 plume to the SW, with the greatest concentration 500-600 km SSW and trace values to the W. A preliminary estimate of the total mass of SO2 was 1.7 x 105 metric tons. The combination of ash and aerosol that stung the eyes caused the Pitcairn group to turn back about 1500. Ashfall increased to the N in late afternoon, and they experienced (decreasing) ashfall all the way back to Punta Espinoza. Very little ash fell at Cabo Hammond.

Activity had declined by the morning of 21 April, with only the S plume continuing and at decreased height. By mid-morning the summit was obscured by low cloud cover, but at 1120 Pitcairn saw all three plumes active (although the N one was small). From the summit of Sierra Negra, 65 km SE of Fernandina, David Day photographed "a medium-size eruption cloud" at noon. At the same time, however, the TOMS instrument detected virtually no SO2 over Galápagos but a low concentration 600 km W, on the equator. That night, Day sailed around Isabela and briefly saw faint glow over Fernandina as he approached it from the S.

On the morning of 22 April, . . . Day landed at NW Fernandina and noted 1 mm of fresh ash. At about 1040, while still low on the NW flank, he heard roaring from the vent, then roughly 12 km distant. This apparently marked a renewal of activity, for the TOMS instrument measured a strong concentration of SO2 immediately over Fernandina at 1046. Day reached the rim at 1730 and described 50-100-m fountains from the 1988 vent area, low on the opposite caldera wall. Fresh aa flows covered an estimated 80% of the low caldera floor, with only the higher lobes of the 1988 debris avalanches still visible. Most flows were to the NW, but a smaller flow went W below the SE bench. The aforementioned northerly vent, on the E side of the NW bench, had fed "a small flow" to join the others on the NW floor, and fumarolic activity was vigorous at the vent.

Day reported that the eruption continued with the same intensity all night, and the next day he explored to the S, finding that the maximum thickness of new tephra on the W rim was 1 cm at a point WNW of the main vent. Pele's hair was "fairly abundant." On this day (23 April), the GOES satellite detected a 105-km plume at 0900 that grew to 320 km SSW at 1300 and had dissipated by 1600 (16:3). At 1103 the TOMS instrument detected a strong SO2 concentration ~ 90 km SW and lower values to ~ 225 km SW; a preliminary estimate of the total mass was ~4 x 104 metric tons. Day was on the S rim of the caldera at 1205, when he saw "a mass of landslides round and above the main vent" that was immediately followed by increased activity at the vent. Fountain height increased by almost 50% and his group (~ 3 km SW of the vent) experienced light scoria fall 10 minutes later that lasted for 15 minutes. Noise and fountaining, after almost ceasing, resumed at 2006 that evening and Day saw additional flareups at 2019, 2037, and 2100. Day observed a small flow NW from the main vent from 2100 to 2122, with no noise, but reported no further observations or sounds overnight.

Horning had reached the SW rim at 1700 and watched the S vent continue producing lava until at least 0100 on 24 April, but it had ceased by 0530. Day also noted no activity between dawn and his leaving the rim at 0630 that morning. Horning's SW-rim camp received 1 mm or less of ash overnight, but when they returned to their coastal camp that evening ~ 1-2 mm had accumulated in their absence. No glow was observed during the nights of 24 and 25 April.

Geologist Dennis Geist was on the summit of Alcedo from 24 April and reported that the only sign of a Fernandina eruption was a small (~ 3 km diameter) white cloud above the caldera. No glow was observed that night, either from Alcedo or N of the volcano (where Day was sailing around N Isabela). The small white cloud persisted over Fernandina at least until 27 April when Geist left Alcedo.

Geologic Background. Fernandina, the most active of Galápagos volcanoes and the one closest to the Galápagos mantle plume, is a basaltic shield volcano with a deep 5 x 6.5 km summit caldera. The volcano displays the classic "overturned soup bowl" profile of Galápagos shield volcanoes. Its caldera is elongated in a NW-SE direction and formed during several episodes of collapse. Circumferential fissures surround the caldera and were instrumental in growth of the volcano. Reporting has been poor in this uninhabited western end of the archipelago, and even a 1981 eruption was not witnessed at the time. In 1968 the caldera floor dropped 350 m following a major explosive eruption. Subsequent eruptions, mostly from vents located on or near the caldera boundary faults, have produced lava flows inside the caldera as well as those in 1995 that reached the coast from a SW-flank vent. Collapse of a nearly 1 km3 section of the east caldera wall during an eruption in 1988 produced a debris-avalanche deposit that covered much of the caldera floor and absorbed the caldera lake.

Information Contacts: D. Day, Isla Santa Cruz; F. Pitcairn and K. Pitcairn, Bryn Athyn, PA, USA; M. Horning, Seeweisen, Germany; S. Doiron, GSFC; N. Ashmole and M. Ashmole, Univ of Edinburgh, Scotland; D. Geist, Univ of Idaho, USA.


Fukutoku-Oka-no-Ba (Japan) — April 1991 Citation iconCite this Report

Fukutoku-Oka-no-Ba

Japan

24.285°N, 141.481°E; summit elev. -29 m

All times are local (unless otherwise noted)


Water discoloration during one of five overflights

A blue water discoloration, extending 2 km E-W, was observed during a 6 February overflight by the JMSA. Overflights on 18 January, 12 March, 15 April, and 10 May revealed no abnormal water.

Geologic Background. Fukutoku-Oka-no-ba is a submarine volcano located 5 km NE of the pyramidal island of Minami-Ioto. Water discoloration is frequently observed from the volcano, and several ephemeral islands have formed in the 20th century. The first of these formed Shin-Ioto ("New Sulfur Island") in 1904, and the most recent island was formed in 1986. The volcano is part of an elongated edifice with two major topographic highs trending NNW-SSE, and is a trachyandesitic volcano geochemically similar to Ioto.

Information Contacts: JMA.


Galeras (Colombia) — April 1991 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


Frequent ash emission and seismicity

Following the pattern begun in March, activity continued to increase during April, when ash emissions from the main crater and associated seismicity were very frequent (table 5). Fieldwork revealed new fissures and vents on the crater's W wall, increases in the area of incandescence, and slumping of loose material. Analyses of gas samples from Deformes and Besolima fissure fumaroles suggest an increasingly magmatic composition. At Calvache fumarole, the ratio of CO2/SO2 has increased steadily (figure 36), while H2S and HCl have shown no significant variations. Besolima fissure fumarole temperatures continued to decline, from 514°C in March to 468°C on 2 April.

Table 5. Eruptive activity and associated seismicity at Galeras, 1-19 April 1991. Atmospheric conditions prevented direct observations 20-30 April. "Inc" means increased, column heights are in meters, and durations are in seconds.

Date Time Activity Column height Signal Type Signal Duration
01 Apr 1991 0640 Ash emission -- Long-period 34 s
01 Apr 1991 0905 Inc sulfur odor -- Tremor 1800 s
02 Apr 1991 0620 Inc column size 300 m Tremor 159 s
02 Apr 1991 0711 Ash emission 900 m Tremor 275 s
02 Apr 1991 1014 Ash emission -- Tremor 116 s
02 Apr 1991 1029 Ash emission -- Long-period 42 s
03 Apr 1991 0741 Ash emission -- Tremor 89 s
05 Apr 1991 0500 Inc noise -- Tremor 475 s
06 Apr 1991 0002 Inc incandescence -- Tremor 182 s
07 Apr 1991 1757 Ash emission 700 m Long-period 52 s
07 Apr 1991 1823 Ash emission 500 m Tremor 140 s
08 Apr 1991 1717 Ash emission -- Tremor 135 s
09 Apr 1991 1827 Ash emission 400 m Tremor 130 s
10 Apr 1991 0608 Ash emission 1100 m Tremor 89 s
10 Apr 1991 0644 Ash emission 200 m Tremor 71 s
10 Apr 1991 1010 Ash emission 700 m Tremor 230 s
10 Apr 1991 1643 Inc noise -- Tremor 110 s
10 Apr 1991 1820 Ash emission -- Long-period 50 s
10 Apr 1991 1820 Inc noise -- Long-period 61 s
10 Apr 1991 1820 Inc incandescence -- Tremor 165 s
10 Apr 1991 1916 Ash emission -- Long-period 30 s
11 Apr 1991 0320 Ash emission, inc incandescence -- Tremor 170 s
11 Apr 1991 0324 Ash emission -- Long-period 17 s
11 Apr 1991 0324 Inc incandescence -- Long-period 29 s
11 Apr 1991 0605 Ash emission 200 m Long-period 44 s
11 Apr 1991 0611 Ash emission 400 m Long-period 58 s
11 Apr 1991 1508 Ash emission -- Tremor 131 s
11 Apr 1991 1758 Ash emission 1700 m Tremor 120 s
11 Apr 1991 1836 Ash emission 200 m Long-period 26 s
11 Apr 1991 1841 Ash emission 800 m Tremor 115 s
12 Apr 1991 0806 Ash emission -- Tremor 295 s
12 Apr 1991 0826 Ash emission -- Tremor 250 s
12 Apr 1991 0854 Ash emission -- Long-period 46 s
13 Apr 1991 0359 Ash emission -- Tremor 625 s
13 Apr 1991 0555 Inc column size 500 m Tremor 260 s
13 Apr 1991 0622 Inc column size 400 m Long-period 20 s
13 Apr 1991 0658 Ash emission 400 m Long-period 50 s
13 Apr 1991 0958 Ash emission, inc noise -- Tremor 91 s
14 Apr 1991 0632 Ash emission 800 m Tremor 83 s
14 Apr 1991 0735 Ash emission 1100 m Tremor 130 s
14 Apr 1991 0808 Ash emission 700 m Long-period 56 s
14 Apr 1991 0845 Ash emission, explosions, inc sulfur odor 1500 m Tremor 179 s
15 Apr 1991 0757 Ash emission 1500 m Tremor 137 s
15 Apr 1991 1355 Ash emission, explosions -- Long-period; tremor 380 s
15 Apr 1991 1509 Ash emission, explosions -- Tremor 82 s
15 Apr 1991 1921 Ash emission, inc incandescence -- Tremor 130 s
16 Apr 1991 0559 Ash emission -- Tremor 111 s
16 Apr 1991 0711 Ash emission -- Long-period 40 s
16 Apr 1991 0815 Ash emission 800 m Long-period 34 s
16 Apr 1991 0835 Ash emission 1500 m Tremor 600 s
16 Apr 1991 1004 Ash emission 1500 m Tremor 171 s
16 Apr 1991 1107 Ash emission -- Tremor 145 s
17 Apr 1991 0711 Ash emission -- Long-period 47 s
17 Apr 1991 0740 Ash emission -- Long-period 57 s
17 Apr 1991 0752 Ash emission -- Tremor 122 s
17 Apr 1991 1742 Ash emission -- Tremor 205 s
17 Apr 1991 1802 Ash emission -- Tremor 370 s
17 Apr 1991 1948 Ash emission -- Tremor 1500 s
18 Apr 1991 0706 Ash emission -- Tremor 190 s
18 Apr 1991 0918 Ash emission -- Long-period 70 s
19 Apr 1991 0627 Ash emission -- Long-period 21 s
19 Apr 1991 0728 Ash emission -- Tremor 76 s
19 Apr 1991 0855 Ash emission -- Tremor 180 s
Figure (see Caption) Figure 36. Concentration of CO2 (squares) and SO2 (circles) in Calvache fumarole gas at Galeras, April 1988-early April 1991. Courtesy of INGEOMINAS.

A significant increase in high-frequency seismicity was recorded during the second half of April, including swarms of events on the 18th and 29th. The earthquakes (M<=2.9) were mostly located SSW of the crater at 1-5 km depth (figure 37). Long-period seismicity was at high levels, and the daily reduced displacement on 13 April was the highest recorded since monitoring began in February 1989 (figure 38). The amplitudes and durations of tremor pulses fluctuated; deep tremor and low-frequency, modulating tremor were also recorded.

Figure (see Caption) Figure 37. Epicenter map of 36 high-frequency earthquakes at Galeras, April 1991. Courtesy of INGEOMINAS.
Figure (see Caption) Figure 38. Daily reduced displacement of long-period earthquakes at Galeras, April 1991. Courtesy of INGEOMINAS.

The electronic tiltmeter 0.9 km E of the crater (at "Crater" station) showed continued inflation, with 85 and 48 µrad of accumulated tangential and radial inflation, respectively, since September 1990 (figure 39). Three km E of the crater, dry tilt (El Pintado station) showed very low, but consistent inflation. Geologists interpreted the inflation as volcanic deformation or neotectonic tilt along the Buesaco fault.

Figure (see Caption) Figure 39. Tangential (top curve) and radial (bottom curve) deformation 0.9 km E of the crater ("Crater" electronic tiltmeter) at Galeras, May 1990-April 1991. Courtesy of INGEOMINAS.

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

Information Contacts: INGEOMINAS-OVP.


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

Gede-Pangrango

Indonesia

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

All times are local (unless otherwise noted)


Earthquake swarm

A swarm of 100 volcanic earthquakes (40 deep and 60 shallow) was recorded on 29 April, an increase from the previous daily average of 10-15 events. Tectonic earthquakes averaged 1-2/day. Seismicity had been increasing since February. No surface activity was observed.

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

Information Contacts: W. Modjo, VSI.


Hakoneyama (Japan) — April 1991 Citation iconCite this Report

Hakoneyama

Japan

35.233°N, 139.021°E; summit elev. 1438 m

All times are local (unless otherwise noted)


Brief earthquake swarm in center of caldera

A swarm of ~300 earthquakes (M <= 2.5) was recorded between 1000 and 1300 on 22 April. Several of the earthquakes, located at 5 km depth in the central part of the caldera, were felt by area residents. Seismicity gradually declined, and had returned to normal by 24 April. No changes in surface activity were observed. Earthquake swarms have been recorded about once a year, including one in August 1990 (M <= 5.1), at the volcano's E foot. Hakone erupted phreatically about 3,000 years ago, and many fumaroles and hot springs remain active.

Geologic Background. Hakoneyama volcano is truncated by two overlapping calderas, the largest of which is 10 x 11 km wide. The calderas were formed as a result of two major explosive eruptions about 180,000 and 49,000-60,000 years ago. Scenic Lake Ashi lies between the SW caldera wall and a half dozen post-caldera lava domes that were constructed along a NW-SE trend cutting through the center of the calderas. Dome growth occurred progressively to the NW, and the largest and youngest of these, Kamiyama, forms the high point. The calderas are breached to the east by the Hayakawa canyon. A phreatic explosion about 3000 years ago was followed by collapse of the NW side of Kamiyama, damming the Hayakawa valley and creating Lake Ashi. The latest magmatic eruptive activity about 2900 years ago produced a pyroclastic flow and a lava dome in the explosion crater, although phreatic eruptions took place as recently as the 12-13th centuries CE. Seismic swarms have occurred during the 20th century. Lake Ashi, along with the thermal areas in the caldera, is a popular resort destination SW of Tokyo.

Information Contacts: JMA.


Ijen (Indonesia) — April 1991 Citation iconCite this Report

Ijen

Indonesia

8.058°S, 114.242°E; summit elev. 2769 m

All times are local (unless otherwise noted)


Crater lake changes from gray and bubbling to light green

The crater lake (45°C) was light green in March and April, a change from its previous gray color, when large bubbles were visible on the surface. A total of one deep and two shallow volcanic earthquakes and one tectonic event were recorded. Tremor was recorded on 25, 26, and 28 March.

Geologic Background. The Ijen volcano complex at the eastern end of Java consists of a group of small stratovolcanoes constructed within the large 20-km-wide Ijen (Kendeng) caldera. The north caldera wall forms a prominent arcuate ridge, but elsewhere the caldera rim is buried by post-caldera volcanoes, including Gunung Merapi, which forms the high point of the complex. Immediately west of the Gunung Merapi stratovolcano is the historically active Kawah Ijen crater, which contains a nearly 1-km-wide, turquoise-colored, acid lake. Picturesque Kawah Ijen is the world's largest highly acidic lake and is the site of a labor-intensive sulfur mining operation in which sulfur-laden baskets are hand-carried from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of cones forms an E-W zone across the southern side of the caldera. Coffee plantations cover much of the caldera floor, and tourists are drawn to its waterfalls, hot springs, and volcanic scenery.

Information Contacts: W. Modjo, VSI.


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

Kavachi

Solomon Islands

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

All times are local (unless otherwise noted)


Submarine eruption builds new island

A newly emergent volcanic island near previously active Kavachi was observed ejecting lava and ash during a helicopter overflight on 4 May. John Starcy (Australian High Commissioner, Honiara, Solomon Islands) reported that "the volcanic action had already formed a thick rim of black material above sea level, inside which a large body of molten lava was churning and spewing out rocks." At the time, the island was estimated to be ~300x150 m in diameter and ~30 m high, with a lava pond ~50 m in diameter. Red Marsden (a Rabaul-based pilot) flew over the volcano on 12 May. The island had a regular conical shape that he estimated was ~15-20 m high. The volcano continued to eject incandescent lava fragments and some dark material to ~50 m height. White vapor emission occurred between ejections, and considerable steam rose from along the water line. Activity continued as of 13 May and the size of the cone continued to increase.

The location of the new island remains uncertain (figure 5) [but more precise navigation linked it to Kavachi; see 16:7]. It was reported at 8.88°S, 157.88°E, 20 km NW of Kavachi, by Starcy, and ~38 km SW of Kavachi (at 9.23°S, 157.70°E; within the Woodlark Basin) by Ted Tame (Rabaul representative of the Papua New Guinea National Disaster and Emergency Services). A submarine volcano was shown on Admiralty Chart 3995 at ~25 km W of Kavachi (at 9.0°S, 157.8°E), between the two reported positions, but the Machias 1981 bathymetry survey failed to find this feature (Exon and Johnson, 1986). Instead, the survey located a bathymetric high 10 km to the WNW that is probably a southward-trending ridge originating on Tetepare Island.

Figure (see Caption) Figure 5. Map of the western Solomon Islands. Crosses represent reported new island locations, triangles mark the New Georgia Group volcanoes (Pliocene to Recent), and the filled circle represents the unnamed submarine volcano on Admiralty Chart 3995. Modified from Exon and Johnson (1986).

Reference. Exon, N.E., and Johnson, R.W., 1986, The elusive Cook volcano and other submarine forearc volcanoes in the Solomon Islands: BMR Journal of Australian Geology & Geophysics, v. 10, p. 77-83.

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

Information Contacts: G. Wheller, CSIRO, Australia; C. McKee, RVO.


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

Kilauea

United States

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

All times are local (unless otherwise noted)


Lava breakout from tube system feeds new ocean entry

Lava . . . continued to enter the ocean . . . on the W side of the flow field through April (figure 77). The tube supplying lava to the coast divided just above the sea cliff. Its W branch fed a single entry site, where repeated collapse of the fragile lower lava bench caused nearly continuous explosive activity in early April. Bench collapse episodes left the lava tube perched in the sea cliff, and lava poured into the ocean in an arching stream. The explosive activity built a littoral cone >3 m high that was >90% covered by spatter. The two entry sites fed by the tube's E branch have built a large bench below the (pre-autumn 1990) sea cliff.

In mid-April, lava broke out of the tube system near 150 m (500 ft) elevation, generating a large pahoehoe flow that was diverted E by 1990 and 1991 flows and reached the ocean ~1.5 km E of the W entry sites. By 22 April, it had built a new bench below the sea cliff, and had an active front ~300 m wide that extended no more than 20 m offshore. Lava continued to pour into the sea until the beginning of May, when only three sluggish streams of lava were observed at the ocean front. Behind the active entry, small viscous surface flows broke out from the main flow. Despite the apparently diminished supply of lava to the E entry, large volumes of lava continued to flow into the sea at the W entry sites in early May. Surface flows, noted during April along the tube system between ~430 and 340 m (1,400-1,100 ft) elevation, covered a previously lava-free area (kipuka) on the W side of the flow field.

Skylights in the tube system at the base of Kupaianaha shield revealed lava velocities of ~1.5 m/s in late April. The uppermost skylight, at ~620 m (2,050 ft) elevation, was fuming heavily, but very little degassing was occurring from the vicinity of Kupaianaha and its former lava pond, which remained sealed through the month. Three kilometers uprift, the lava pond in the base of Pu`u `O`o crater, ~60 m below the rim, remained active through April. The pond covered less than half of the crater floor, but sometimes overflowed onto more. The walls of Pu`u `O`o remained unstable and collapse continued.

Since the intrusive swarm seismicity in late March seismic activity has returned to lower levels. Low-amplitude volcanic tremor continued along the East rift zone, with some variability at stations near Kupaianaha and Pu`u `O`o. Increases in summit-area microearthquakes were recorded 9-10, 14, and 26-27 April, but events were very small and did not appear to be associated with changes in eruptive activity.

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

Information Contacts: T. Moulds and P. Okubo, HVO.


Klyuchevskoy (Russia) — April 1991 Citation iconCite this Report

Klyuchevskoy

Russia

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

All times are local (unless otherwise noted)


Small summit plume; ash on SE flank

A Space Shuttle photograph on 29 April at 1248 shows a plume, apparently containing ash, rising about 1 km above the summit and extending about 15 km downwind. Snow on the SE flank appeared to be ash-covered. A small summit eruption occurred on 8 April, but no additional eruptive activity has been reported.

Geologic Background. Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Information Contacts: C. Evans, Lockheed, Houston.


Kozushima (Japan) — April 1991 Citation iconCite this Report

Kozushima

Japan

34.219°N, 139.153°E; summit elev. 572 m

All times are local (unless otherwise noted)


Earthquake swarm but no surface activity

An earthquake swarm (M <= 4.0) occurred from 2100 to 2400 on 23 April, with seismicity gradually returning to normal levels by the following day. Many of the earthquakes were felt by residents (to JMA intensity IV). Swarm events were centered from the W coast to 20 km SW of the island (figure 1), at 0-10 km depth. No surface activity was reported.

Figure (see Caption) Figure 1. Epicenter map (top) and space/time diagram (bottom) showing seismicity around Kozu-shima and Nii-jima volcanoes, January 1991-June 1992. Courtesy of JMA.

Geologic Background. A cluster of rhyolitic lava domes and associated pyroclastic deposits form the small 4 x 6 km island of Kozushima in the northern Izu Islands. Kozushima lies along the Zenisu Ridge, one of several en-echelon ridges oriented NE-SW, transverse to the trend of the northern Izu arc. The youngest and largest of the 18 lava domes, 574-m-high Tenjoyama, occupies the central portion of the island. Most of the older domes, some of which are Holocene in age, flank Tenjoyama to the north, although late-Pleistocene domes are also found at the southern end of the island. Only two possible historical eruptions, from the 9th century, are known. A lava flow may have reached the sea during an eruption in 832 CE. Tenjosan lava dome was formed during a major eruption in 838 CE that also produced pyroclastic flows and surges. Earthquake swarms took place during the 20th century.

Information Contacts: JMA.


Kusatsu-Shiranesan (Japan) — April 1991 Citation iconCite this Report

Kusatsu-Shiranesan

Japan

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

All times are local (unless otherwise noted)


Continued seismicity

In April, seismicity remained similar to previous months, with a total of 110 earthquakes and one tremor episode recorded... (figure 5). No surface activity was observed.

Figure (see Caption) Figure 5. Daily number of recorded earthquakes (top) and tremor episodes (bottom) at Kusatsu-Shirane, January 1989-April 1991. Courtesy of JMA.

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: JMA.


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

Langila

Papua New Guinea

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

All times are local (unless otherwise noted)


Ash emission and glow

"Activity declined in early April . . . . Emissions from Crater 2 consisted of moderate to weak white-grey ash and vapour. An explosion on 3 April produced a dark ash column that rose ~500 m above the crater and resulted in ashfall on the NW side of the volcano. Steady weak red glow from the crater was observed on most nights. Following the first few days of stronger seismicity, when up to four explosion earthquakes/day were recorded, the seismicity declined and on most days no explosion events were recorded."

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.


Lewotobi (Indonesia) — April 1991 Citation iconCite this Report

Lewotobi

Indonesia

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

All times are local (unless otherwise noted)


Brief increase in seismicity

A sudden increase in seismicity, from 7 to 60 earthquakes/day, was recorded at the end of March. Activity peaked on 26 March, then gradually decreased. No changes in surface activity were observed.

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

Information Contacts: W. Modjo, VSI.


Manam (Papua New Guinea) — April 1991 Citation iconCite this Report

Manam

Papua New Guinea

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

All times are local (unless otherwise noted)


Tephra emission from two craters

"The increased activity at Main Crater in late March continued until mid-April, then declined. However, Southern Crater then became more active.

"Main Crater emissions consisted of weak to moderate white-grey ash and vapour with occasional thin blue vapour from 1 to 14 April. Emission clouds reached heights of 180-1,000 m above the crater rim. Light ashfall was noted 5 km downwind on 4 April. Deep roaring noises were heard on most days during this period. Weak red glow was seen above the crater 1-11 April, with some incandescent lava ejections on the 4th.

"Southern Crater activity increased for the first time since August 1990. From about mid-April, emissions consisted of weak to moderate white-grey vapour and ash. Light ashfalls were reported 23 and 25 April on the E side of the volcano, ~5 km from the summit. Low rumbling noises associated with the vapour and ash emissions were heard on 16 and 23-25 April.

"The seismograph at Manam became inoperable from 8 April. Before this time, seismic amplitudes remained at about the same level as at the end of March (~3x normal levels), although the daily totals of recorded volcanic shocks dropped from ~550 to 100. Tiltmeter measurements showed a slight radial deflation of ~1.5 µrad."

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

Information Contacts: C. McKee, RVO.


Merapi (Indonesia) — April 1991 Citation iconCite this Report

Merapi

Indonesia

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

All times are local (unless otherwise noted)


High-temperature fumaroles; no changes evident to summit dome

No changes were visible at the summit dome, whose volume remained at ~6.8 x 106 m3. Diffuse to dense gas plumes rose to 450 m above the summit. Temperatures of 832 and 543°C were measured at the dome's Gendol and Woro solfataras, respectively. The temperature measured through cracks in the 1956 lava was 86°C on 20 April. There was no significant change in seismicity, although the weekly number of volcanic earthquakes briefly rose to 17 during the second week in April from the long-term average of 1-4. One multiphase event and 3-10 tectonic earthquakes were recorded/week.

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

Information Contacts: W. Modjo, VSI.


Ontakesan (Japan) — April 1991 Citation iconCite this Report

Ontakesan

Japan

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

All times are local (unless otherwise noted)


Earthquake swarms and tremor; no change in steam emission

Three earthquake swarms (20, 23, and 27 April) and four tremor episodes (27-28 April and 2 May) were recorded during late April-early May. The strongest swarm, on 20 April, lasted a few hours and included a M 1.6 event. None of the shocks were felt, and it was not possible to locate them accurately, but they were believed to be in the summit area. The 27 April tremor episode was the largest (table 1), and accompanying seismicity was the strongest registered (figure 5), since installation of the current seismometer, in July 1988.

Table 1. Tremor episodes recorded at On-take, 15 July 1988-11 May 1991.

Date Time Amplitude (N) Duration (min)
02 Oct 1988 0132 0.1 1
06 Oct 1988 1035 0.1 1
12 Jan 1989 1725 0.6 1
19 Aug 1989 1313 0.4 2
11 Apr 1990 1808 0.2 2
27 Apr 1991 0716 2.3 4
27 Apr 1991 1201 0.1 2
28 Apr 1991 1309 1.4 3
02 May 1991 0938 0.3 3
Figure (see Caption) Figure 5. Daily number of recorded earthquakes at On-take, 15 July 1988-5 May 1991. Courtesy of JMA.

White steam emissions, unchanged from previous months (figure 6), rose 200 m from summit vents formed during a small phreatic eruption in October 1979. That eruption emitted ash for 1 day; steam emission declined, but has remained steady since then.

Figure (see Caption) Figure 6. Plume heights at On-take, 20 July 1988-13 May 1991. Courtesy of JMA.

A M 6.8 earthquake, 12 km SE of the summit on 14 September 1984, triggered a landslide on the S slope of the volcano that killed 29 people. Aftershocks were distributed on the volcano's S flank in an elliptical zone that may mark a 20-km-long WSW-ENE fault (figure 7). Steam emission and surface activity were unchanged by the 1984 earthquake.

Figure (see Caption) Figure 7. Epicenter map of 138 earthquakes at On-take, January 1990-May 1991. Locations of the three swarms are not shown, but are considered to be in the summit area (triangle). The largest shock, M 1.8, was centered just W of the summit. The group of events in an E-W line 15 km S of the summit are aftershocks from a M 6.8 earthquake in 1984. Courtesy of JMA.

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

Information Contacts: JMA.


Pacaya (Guatemala) — April 1991 Citation iconCite this Report

Pacaya

Guatemala

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

All times are local (unless otherwise noted)


Strombolian activity declines to ash emission as seismicity decreases

In comparison with observations made in early February (16:02), visits to the volcano in mid-March-early April revealed a decrease in eruptive activity. A small vent with night glow on the W flank (50 m below the summit), periodically the source of incandescent lava fragments that rolled down the upper flank, had disappeared by 21 March. Strombolian activity from a cinder cone in the W quarter of MacKenney Cone's 1987 crater ejected material to 100-150 m height. The number of explosions declined from about 20 to 1-2/hour over the mid March-early April observation period, and during the first week of April, the primary ejecta changed from lava spatter to ash. Some collapse occurred on the cone's interior walls. Two explosions, observed during a 3-hour period on 10 April, emitted ash clouds hundreds of meters high. Lava flow activity, prominent from mid-November through February (15:11-12 and 16:02), declined, and ceased entirely by 10 April. A decrease in seismicity, coincident with the decrease of eruptive activity, began about 1 April and continued as of 19 April.

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

Information Contacts: Otoniel Matías and Rodolfo Morales, Sección de Vulcanología, INSIVUMEH; Michael Conway, Michigan Technological Univ, Houghton, USA; P. Vetsch, SVG, Switzerland; Thierry Basset, Univ de Genève, Switzerland; Alan Deino, Berkeley Geochronology Laboratory, Institute of Human Origins, USA.


Pinatubo (Philippines) — April 1991 Citation iconCite this Report

Pinatubo

Philippines

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

All times are local (unless otherwise noted)


Phreatic explosion devastates 1 km2 forested area; seismicity and gas emission continue; 2,000 evacuated

The following includes a more detailed account of events reported in 16:3.

On 2 April, an explosion at the E end of Pinatubo's geothermal area (about 1.5 km NW of the summit and 2/3 of the way down the flank) ejected clouds of steam and minor quantities of ash to 500-800 m height. Ash fell 2 km away, primarily to the NW and SW, and covered an area of about 10,000 m2, including part of one village, from which about 2,000 people were evacuated. No injuries or deaths were reported. The ash was composed of sub-angular material, none of which was freshly vesiculated, with a mineralogy of plagioclase, hornblende, small amounts of biotite, and possible quartz. About 1 km2 of forested land was devastated by the explosion, extending about 500 m from the explosion site, and leaves and vegetation were stripped over several square kilometers. Downed trees were preferentially oriented N.

Following the explosion, an ENE-WSW-trending line (roughly 1 km long at 1,100-1,350 m elevation - summit elevation is 1,745 m) of new fumaroles with six main vents had developed. The most intense activity was located at the W end of the line, while the blast site, at the E end of the line, had ceased activity (figure 2). Vent emissions, voluminous and at extremely high pressure, consisted mainly of steam, with an H2S odor and an associated gray haze. Plumes (~200-500 m high in mid- to late-April, 100-300 m high in early May) were carried W by the prevailing wind, onto a zone of dead and dying vegetation. Respiratory and eye irritation forced about 5,000 W-flank residents to leave the area. Increased discharge from springs near the fumaroles caused rapid downward erosion in stream beds, and muddy water was reported in the N drainages.

Figure (see Caption) Figure 2. Sketch looking SSE at Pinatubo on 27 April 1991, from about 1 km distance (at geothermal well site PN-3, drilled in 1989 by PNOC). Fumaroles are labeled A-E, and the explosion site is labeled Z. Courtesy of David Sussman.

A seismometer installed on 5 April recorded 223 high-frequency volcano-tectonic earthquakes over a 24-hour period (figure 3). Seismicity rapidly decreased, with 50-90 events recorded/day 8 April-10 May (the seismometer did not function 6-8 April). Earthquake location became possible on 6 May with the completion of a seismic network at the volcano. During the first few days of operation, earthquakes were centered [~4-8 km NW] of the summit at 3-6 km depth, and had magnitudes of 0.1-1.5 (averaging about M 1.0). The events all had the same first motions, suggesting that they had the same focal mechanisms. Seismicity increased on 10 May (167 recorded earthquakes/day) and remained high as of 12 May (120-150/day). No long-period events have been recorded.

Figure (see Caption) Figure 3. Daily number of recorded earthquakes at Pinatubo, 5 April-12 May 1991. Courtesy of PHIVOLCS.

Deformation measurements on the NW slope have not shown evidence of inflation.

The center of the Pinatubo geothermal area, previously the site of several low-discharge acid-sulfate springs and three steaming sulfur-depositing fumaroles (>90°C), was located within a crater-like structure largely related to collapse. Geologists believe that some of the breccias in the structure's wall are probably of hydrothermally explosive origin. "Numerous alleged eruptive activities have been reported in the area."

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

Information Contacts: R. Punongbayan, PHIVOLCS; Chris Newhall, USGS Reston; John Ewert, CVO; David Sussman and Areberto Arevalo, Philippine Geothermal Inc., Manila.


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

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Increased gas emission; continued seismicity

Gas emission increased in April. Fumaroles burned sulfur, produced loud jet-engine noises, and ejected small amounts of gray sediment that covered the W base of the crater. Acid rain continued to be a problem on the W flank of the volcano; rainwater pH was 3.4 at Cerro Pelón (2.5 km SW).

Seismicity levels in April were similar to March, with an average of 266 low-frequency earthquakes recorded/day (average frequency 2.2 Hz) and a monthly total of 26 high-frequency events (figure 37). Low-frequency tremor was recorded up to 22 hours/day on 20-21 April.

Figure (see Caption) Figure 37. Daily number of recorded earthquakes at Poás, April 1991. Courtesy of OVSICORI.

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

Information Contacts: E. Fernández, V. Barboza, and J. Barquero, OVSICORI.


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

Rabaul

Papua New Guinea

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

All times are local (unless otherwise noted)


Low-level seismicity; minor deflation

"Seismicity remained at a low level in April. The month's total number of earthquakes was 126 . . . with daily totals ranging from 0 to 19. Thirteen earthquakes were locatable and were distributed on the NW and W sides of the caldera seismic zone. Levelling measurements carried out between 8 March and 23 April showed 4 mm of subsidence at the SE end of Matupit Island."

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

Information Contacts: C. McKee, RVO.


Rincon de la Vieja (Costa Rica) — April 1991 Citation iconCite this Report

Rincon de la Vieja

Costa Rica

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

All times are local (unless otherwise noted)


Ash ejection and lahars

A [phreatomagmatic] eruption at 1015-1025 on 8 May ejected small quantities of [ash, bombs, blocks, and mud, and produced small lahars]. Gray lahars with a sulfur odor traveled N down the Río Pénjamo and Azul systems, destroying the forest along the rivers and two small bridges, and cutting off access to the towns of Buenos Aires (12 km NE) and Gavilán. At the distal end of the lahars, 15 km from the summit, the deposits reached 2 m in thickness, and covered the surface for several hundred meters on both sides of the Pénjamo river channels. Following passage of the lahars, the rivers were milky and had high acidity. The eruption followed two smaller explosive events on 6 and 7 May, but no other seismic precursors were recorded.

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: R. Barquero, ICE; J. Barquero and R. Sáenz, OVSICORI.


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

Nevado del Ruiz

Colombia

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

All times are local (unless otherwise noted)


Tremor precedes several days of ash emission

An increase in the number of tremor pulses preceded several days of ash emission at the end of April. Lithic and crystalline ash (<2 mm in diameter) was reported W of the volcano in Pereira (40 km from the summit), Santa Rosa de Cabal (35 km), Chinchiná (35 km), and Manizales (25 km), and NE of the volcano in Mariquita (55 km). High- and low-frequency seismicity was generally at low levels in April, with a slight increase in released energy from low-frequency events. The monthly average SO2 flux, measured by COSPEC, was ~2,740 t/d, up from 2,233 t/d in March.

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

Information Contacts: C. Carvajal, INGEOMINAS, Manizales.


Santa Maria (Guatemala) — April 1991 Citation iconCite this Report

Santa Maria

Guatemala

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

All times are local (unless otherwise noted)


Strong explosion and pyroclastic flow; continued lava extrusion feeds rock avalanches

Quoted material is a report from the Santiaguito Volcano Observatory.

"At 0903 on 10 April, a powerful pyroclastic eruption shook El Caliente vent. The eruption produced a vertical plume that rose 3.5 km above the vent, and a pyroclastic flow that moved a few kilometers down the Río Nimá II. Ash blanketed the area immediately SW to a maximum thickness of 1-2 mm, and noticeable ashfall was observed at Retalhuleu [25 km SSW]. The ash consisted of comminuted dacite, gray to black volcanic glass, plagioclase, and quartz. This eruption marked the first major pyroclastic event at Santiaguito since 23 November 1990 and could signal an increase in hazardous pyroclastic activity similar to the period April-November 1990. Seismic activity increased significantly during the final week of March, following a period of relative quiescence from January through mid-March (figure 20)."

Figure (see Caption) Figure 20. Daily explosions and avalanches at Santiaguito, January-March 1991. Dotted lines indicate no data. Courtesy of Otoniel Matías.

Smaller pyroclastic events, observed during fieldwork 24-27 March and 11-13 April, lasted about 4-7 minutes and were separated by tens of minutes to >1 hour. Eruptive plumes ranged from black to white and rose 500-1,500 m. On 11 April, observers measured a 20° initial eastward inclination of the explosion clouds, and plume heights of 3,000 m. The source of the explosions had migrated about 150-200 m NNE from the summit, which continued to degas quietly.

Numerous avalanches, with 150-400 recorded daily by seismometers (figure 20), occurred on the E flank of the volcano, sometimes accompanied by loud summit explosions. The block lava flow erupting from the E summit of Caliente continued to flow slowly (<100 m/month), with frequent collapses of the flow front sending block-and-ash debris avalanching [into] the Río Nimá II [drainage].

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

Information Contacts: Otoniel Matías and Rodolfo Morales, INSIVUMEH; Michael Conway, Michigan Technological Univ; P. Vetsch, SVG, Switzerland; Thierry Basset, Univ de Genève, Switzerland.


Semeru (Indonesia) — April 1991 Citation iconCite this Report

Semeru

Indonesia

8.108°S, 112.922°E; summit elev. 3657 m

All times are local (unless otherwise noted)


Continued explosions and seismicity

Explosions continued during April, with column heights averaging 300-400 m, and explosion earthquakes recorded an average of 112 times/day . . . . Seismographs also recorded 2-3 daily avalanches of material off the lava flow erupted 17 February. A total of one deep volcanic earthquake and 18 tectonic events were recorded.

Geologic Background. Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.

Information Contacts: W. Modjo, VSI.


Sheveluch (Russia) — April 1991 Citation iconCite this Report

Sheveluch

Russia

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

All times are local (unless otherwise noted)


Possible new tephra deposit on E flank

After the 8 April explosive eruption, satellite images showed an apparent narrow zone of tephra deposited SE from the summit to the coast. The NOAA 10 polar orbiter showed a second, similar deposit on 9 May at 1000, extending E from the summit then turning SE to parallel the 8 April material. . . .

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: W. Gould, NOAA/NESDIS.


Stromboli (Italy) — April 1991 Citation iconCite this Report

Stromboli

Italy

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

All times are local (unless otherwise noted)


Explosive activity from a single crater; strong seismicity

Explosive activity was at low levels from January through March, seldom exceeding the long-term average of six recorded explosions/hour (figure 11). Visits to the summit on 30 March and 9 April revealed that activity was restricted to Crater 1, and that the small cone 1 in Crater 3 had collapsed, forming a glowing red vent. The number of earthquakes exceeding instrument saturation level was quite high from the end of January to the beginning of February (~30/day), and 11-17 March (~19/day; figure 12). Average tremor amplitude returned to normal following a low in December.

Figure (see Caption) Figure 11. Daily average number of seismically recorded explosion events/hour at Stromboli, January-March 1991. The mean value for the period is shown. Courtesy of M. Riuscetti.
Figure (see Caption) Figure 12. Number of seismometer-saturating events/day (upper curve); and average tremor amplitude (lower curve) at Stromboli, January-March 1991. Courtesy of M. Riuscetti.

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

Information Contacts: M. Riuscetti, Univ di Udine.


Submarine Volcano NNE of Iriomotejima (Japan) — April 1991 Citation iconCite this Report

Submarine Volcano NNE of Iriomotejima

Japan

24.57°N, 123.93°E; summit elev. -200 m

All times are local (unless otherwise noted)


Strong felt seismicity but no surface changes

High levels of seismicity . . . suddenly declined in late April (figure 1). A total of 670 high-frequency earthquakes were felt by the end of April, including nine of JMA intensity IV, and a M 4.3 event on 31 March. The swarm was centered on the NW coast of the island (figure 2) at 0-10 km depth (the majority at ~5 km). No surface phenomena (steaming, bubbling, or water discoloration) were found despite frequent patrolling over the island and adjacent sea area by JMSA aircraft.

Figure (see Caption) Figure 1. Daily number of recorded earthquakes at Iriomote-jima island, 23 January-10 May 1991. Solid columns represent felt events. Courtesy of JMA.
Figure (see Caption) Figure 2. Epicenter map of earthquakes at Iriomote-jima island, 23 January-10 May 1991. A solid square marks the JMA weather station. Courtesy of JMA.

Geologic Background. The southernmost Ryukyu Islands volcano is a shallow submarine volcano 20 km NNE of Iriomotejima island and 35 km WSW of the northern tip of the island of Ishigakishima in an area with an estimated depth of 200-300 m. A major submarine eruption took place on 31 October 1924. It produced rhyolitic pumice rafts with an estimated volume of about 1 km3 that were carried by currents along both coasts of Japan as far north as Hokkaido. The largest pumice blocks exceeded 1 x 2 m in size, and the volume of ejecta places this poorly known eruption among the largest in historical time in Japan.

Information Contacts: JMA.


Taal (Philippines) — April 1991 Citation iconCite this Report

Taal

Philippines

14.002°N, 120.993°E; summit elev. 311 m

All times are local (unless otherwise noted)


Continued seismicity and changes to crater lake

High seismicity continued as of early May, with the daily number of earthquakes varying from 15 to 30 (figure 4). Felt earthquakes reached intensity IV. Acidity and chloride content of the volcano's crater lake continued to fluctuate, ranging from 2.4-2.8 and 9,630-11,720 ppm, respectively. Lake temperature increased slightly from 30° to 31°C, and lake level rose by 4 cm.

On 26 April, strong bubbling and increased steaming were observed in the N sector of the crater and at the base of the wall. Geysering, to 1.2 m height, was also noted near the NNE shore of the lake, where water temperatures of 99°C were measured.

Deformation measurements on Taal Volcano Island have found no inflation or swelling of the volcanic edifice.

Volcano Island has been partly evacuated since 23 March, but a small number of residents have remained, particularly near the PHIVOLCS station at the N end of the island.

Geologic Background. Taal is one of the most active volcanoes in the Philippines and has produced some of its most powerful historical eruptions. Though not topographically prominent, its prehistorical eruptions have greatly changed the landscape of SW Luzon. The 15 x 20 km Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2 surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, and several eruptive centers lie submerged beneath the lake. The 5-km-wide Volcano Island in north-central Lake Taal is the location of all historical eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones that have grown about 25% in area during historical time. Powerful pyroclastic flows and surges from historical eruptions have caused many fatalities.

Information Contacts: R. Punongbayan, PHIVOLCS.


Turrialba (Costa Rica) — April 1991 Citation iconCite this Report

Turrialba

Costa Rica

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

All times are local (unless otherwise noted)


New fractures found after major 22 April earthquake

Shortly after the [M 7.6] earthquake on 22 April [85 km WSW], numerous small concentric fractures were found along the S and SW rims of the central crater and the W rim of the main crater. Small landslides continued on the S, SW, and N walls of the main crater, and fumarole temperatures remained at 89°C.

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

Information Contacts: E. Fernández, V. Barboza, and J. Barquero, OVSICORI.


Unzendake (Japan) — April 1991 Citation iconCite this Report

Unzendake

Japan

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

All times are local (unless otherwise noted)


Ash emission from two vents; frequent seismicity; lava dome extruded into summit crater

Frequent, almost continuous, ash emissions (500 m high) continued in April from two vents. In mid-April, the most intense activity switched from Byobu-iwa vent . . . to Jigoku-ato vent . . . . No earthquake swarms were recorded in April, but seismicity remained high. A total of 733 earthquakes was recorded and 27 felt . . . compared to 734 recorded and 21 felt in March. Most of the events were located a few kilometers W of Fugen-dake peak . . . . The number of tremor episodes increased in April (181, compared to 99 in March), as did amplitudes and durations (figure 16).

Figure (see Caption) Figure 16. Daily number (top), amplitude (middle), and duration (bottom) of tremor episodes at Unzen, July 1990-early May 1991. Arrows at top mark eruptions on 17 November 1990 and 12 February 1991. Courtesy of JMA.

A swarm of microearthquakes, the first since July 1990, began 13 May and continued as of 17 May. Ash emissions were at low levels during this period. Heavy rains on recently fallen tephra caused lahars in at least one flank valley. The press reported that more than 1,200 people were evacuated on 19 May. A lava dome was extruded into the summit crater before dawn on 21 May. Small ash emissions occurred from the dome and fissures exposed its interior.

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

Information Contacts: JMA; H. Glicken, Tokyo Metropolitan Univ; AP.


Vulcano (Italy) — April 1991 Citation iconCite this Report

Vulcano

Italy

38.404°N, 14.962°E; summit elev. 500 m

All times are local (unless otherwise noted)


Fumarole temperatures increase

Observations at "La Fossa" crater in recent years have included changes in fumarole temperatures and chemical compositions, ground deformation, and opening of new fractures. Data collected since a systematic surveillance program began in 1977 have allowed geologists to identify different stages during which changing contributions of magmatic gases and water caused fluctuating fumarole outputs. The interaction of heat rising from depth with shallow aquifers has produced changes in water vaporization and pressure as the heat/water ratio varied.

Only minor crater activity occurred until 1987, probably because of the constraints imposed by a limited fracture system on the thermal input. Since then, a sharp change has been observed, with ground inflation and significant increases in the maximum temperature and water concentration of emitted fluids.

In 1990, a further increase in the maximum temperature (to 620°C) and decrease in water contents of fumarole fluids were interpreted as a consequence of increased heat flow, causing significant aquifer depletion (15:08).

The most recent (April 1991) observations indicate that fumarole temperatures are again increasing, and significant vaporization as well as new inflation can be expected. Geologists noted that the long-lasting instability of La Fossa's NW sector could result in some form of collapse that could create problems for the local community.

Further References. Falsaperla, S., Frazzetta, G., Neri, G., Nunnari, G., Velardita, R., and Villari, L., 1989, Volcano monitoring in the Aeolian Islands (southern Tyrrhenian Sea): the Lipari-Vulcano eruptive complex, in Latter, J.H., ed., Volcanic Hazards: Assessment and Monitoring: Springer-Verlag, p. 339-356.

Martini, M., 1989, The forecasting significance of chemical indicators in areas of quiescent volcanism: examples from Vulcano and Phlegrean Fields (Italy), in Latter, J.H., ed., Volcanic Hazards: Assessment and Monitoring: Springer-Verlag, p. 372-383.

Martini, M., Giannini, L., Buccianti, A., Prati, F., Legittimo, P.C., Iozelli, P., and Capaccioni, B., 1991, 1980-1990: Ten years of geochemical investigation at Phlegrean Fields (Italy): Journal of Volcanology and Geothermal Research, v. 48, p. 161-171.

Martini, M., Giannini, L., and Capaccioni, B., 1991, Geochemical and seismic precursors of volcanic activity: Acta Vulcanologia, v. 1, p. 7-11.

Martini, M., Giannini, L., and Capaccioni, B., 1991, The influence of water on chemical changes of fumarolic gases: different characters and their implications in forecasting volcanic activity: Acta Vulcanologia, v. 1, p. 13-16.

Geologic Background. The word volcano is derived from Vulcano stratovolcano in Italy's Aeolian Islands. Vulcano was constructed during six stages during the past 136,000 years. Two overlapping calderas, the 2.5-km-wide Caldera del Piano on the SE and the 4-km-wide Caldera della Fossa on the NW, were formed at about 100,000 and 24,000-15,000 years ago, respectively, and volcanism has migrated to the north over time. La Fossa cone, active throughout the Holocene and the location of most of the historical eruptions, occupies the 3-km-wide Caldera della Fossa at the NW end of the elongated 3 x 7 km island. The Vulcanello lava platform forms a low, roughly circular peninsula on the northern tip of Vulcano that was formed as an island beginning in 183 BCE and was connected to Vulcano in about 1550 CE. Vulcanello is capped by three pyroclastic cones and was active intermittently until the 16th century. The latest eruption from Vulcano consisted of explosive activity from the Fossa cone from 1898 to 1900.

Information Contacts: M. Martini, Univ di Firenze.


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

Whakaari/White Island

New Zealand

37.52°S, 177.18°E; summit elev. 294 m

All times are local (unless otherwise noted)


Renewed ash emission; new collapse pit

There was no evidence, during fieldwork 21 April, of eruptive activity since the 20-22 March eruption that formed Orca vent and was probably responsible for up to 10 mm of ash deposited on the 1978/91 Crater rim since 13 February. An increase in gas emission (compared to visits during February and March) was noted at Orca vent and TV1 Crater. . . . Intense gas emission also occurred from an area of hot ground NW of TV1.

Several morphologic changes were observed in the crater area. A second, smaller vent (~5 m in diameter) was found on the slope NW of Orca vent. A new collapse pit, ~20 m in diameter and 50 m deep, was located above the conduit that had previously fed Donald Duck Crater. The new pit, a few meters NW of the crater, looked fresh, suggesting that it had formed shortly before the 21 April visit.

Ash-laden steam emission reportedly began 23 April and was continuing as of 3 May. No significant volcanic tremor or other seismicity was recorded during this period.

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

Information Contacts: I. Nairn and B. Scott, DSIR Geology & Geophysics, Rotorua.

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