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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

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

Heard (Australia) Eruptive activity including a lava flow during October 2019-April 2020



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).


Heard (Australia) — May 2020 Citation iconCite this Report

Heard

Australia

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

All times are local (unless otherwise noted)


Eruptive activity including a lava flow during October 2019-April 2020

Heard Island is located on the Kerguelen Plateau in the southern Indian Ocean and contains Big Ben, a snow-covered stratovolcano with intermittent volcanism reported since 1910. Due to its remote location, visual observations are rare; therefore, thermal anomalies and hotspots detected by satellite-based instruments are the primary source of information. This report updates activity from October 2019 to April 2020.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed three prominent periods of strong thermal anomaly activity during this reporting period: late October 2019, December 2019, and the end of April 2020 (figure 41). These thermal anomalies were relatively strong and occurred within 5 km of the summit. Similarly, the MODVOLC algorithm reported a total of six thermal hotspots during 28 October, 1 November 2019, and 26 April 2020.

Figure (see Caption) Figure 41. Thermal anomalies at Heard from 29 April 2019 through April 2020 as recorded by the MIROVA system (Log Radiative Power) were strong and frequent in late October, during December 2019, and at the end of April 2020. Courtesy of MIROVA.

Six thermal satellite images ranging from late October 2019 to late March showed evidence of active lava at the summit (figure 42). These images show hot material, possibly a lava flow, extending SW from the summit; a hotspot also remained at the summit. Cloud cover was pervasive during the majority of this reporting period, especially in April 2020, though gas-and-steam emissions were visible on 25 April through the clouds.

Figure (see Caption) Figure 42. Thermal satellite images of Heard Island’s Big Ben showing strong thermal signatures representing a lava flow in the SW direction from 28 October to 17 December 2019. These thermal anomalies are located NE from Mawson Peak. A faint thermal anomaly is also captured on 26 March 2020. Satellite images with atmospheric penetration (bands 12, 11, and 8A), courtesy of Sentinel Hub Playground.

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

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

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Bulletin of the Global Volcanism Network - Volume 18, Number 04 (April 1993)

Managing Editor: Edward Venzke

Aira (Japan)

Explosive activity continues; windshield damaged

Akan (Japan)

Seismicity increases in April

Aracar (Argentina)

Ash column reported

Arenal (Costa Rica)

Explosions decrease as lava production increases

Avachinsky (Russia)

Fumarolic activity

Etna (Italy)

Steady degassing; seismicity low

Galeras (Colombia)

Two small eruptions; small swarm of earthquakes M 2.8-4.5

Kilauea (United States)

Lava continues to enter the ocean

Klyuchevskoy (Russia)

Small gas and ash explosions

Langila (Papua New Guinea)

Strombolian explosions continue

Lascar (Chile)

Eruption sends ash above 25 km altitude; pyroclastic flows travel 7.5 km

Lengai, Ol Doinyo (Tanzania)

Carbonatite lava production continues

Manam (Papua New Guinea)

Very low activity

Poas (Costa Rica)

Fumarolic activity continues; lake level drops

Rabaul (Papua New Guinea)

Seismic activity remains high; no ground uplift

Rincon de la Vieja (Costa Rica)

Seismic activity continues

Sheveluch (Russia)

Eruption sends ash cloud to 20 km altitude

Stromboli (Italy)

Explosive activity increases; detailed description of crater

Suwanosejima (Japan)

Sporadic, weak ash eruptions

Taftan (Iran)

Lava flow reported; no previous historical eruptions known

Turrialba (Costa Rica)

Fumarolic activity unchanged

Ulawun (Papua New Guinea)

Tremor level returns to background

Unzendake (Japan)

Pyroclastic flows increase in number; heavy rainfall produces large debris flows



Aira (Japan) — April 1993 Citation iconCite this Report

Aira

Japan

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

All times are local (unless otherwise noted)


Explosive activity continues; windshield damaged

Seven explosions . . . were recorded in April . . . . Lapilli from an explosion at 1425 on 7 April cracked the windshield of an automobile on the volcano's island. It was the first direct damage from an explosion since February when windshields from nine autos were damaged. An explosion at 0948 on 2 April produced the highest ash plume of the month, >3,200 m above the crater. No earthquake swarms were recorded.

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.


Akan (Japan) — April 1993 Citation iconCite this Report

Akan

Japan

43.384°N, 144.013°E; summit elev. 1499 m

All times are local (unless otherwise noted)


Seismicity increases in April

Microearthquake activity began to increase on 27 March and continued through April before declining in May. The monthly earthquake total for April was 295, far more than the background level of 10-20. Steam emissions remained steady with no observed changes.

Geologic Background. Akan is a 13 x 24 km caldera located immediately SW of Kussharo caldera. The elongated, irregular outline of the caldera rim reflects its incremental formation during major explosive eruptions from the early to mid-Pleistocene. Growth of four post-caldera stratovolcanoes, three at the SW end of the caldera and the other at the NE side, has restricted the size of the caldera lake. Conical Oakandake was frequently active during the Holocene. The 1-km-wide Nakamachineshiri crater of Meakandake was formed during a major pumice-and-scoria eruption about 13,500 years ago. Within the Akan volcanic complex, only the Meakandake group, east of Lake Akan, has been historically active, producing mild phreatic eruptions since the beginning of the 19th century. Meakandake is composed of nine overlapping cones. The main cone of Meakandake proper has a triple crater at its summit. Historical eruptions at Meakandake have consisted of minor phreatic explosions, but four major magmatic eruptions including pyroclastic flows have occurred during the Holocene.

Information Contacts: JMA.


Aracar (Argentina) — April 1993 Citation iconCite this Report

Aracar

Argentina

24.29°S, 67.783°W; summit elev. 6095 m

All times are local (unless otherwise noted)


Ash column reported

A steam plume was observed rising above Arácar on 28 March. Viewed from the town of Tolar Grande, 50 km SE, the plume persisted throughout the clear day. At least twice during the day, a large ash column slowly rose 2,000 m above the summit. The following day clouds prevented a clear view of the volcano, but an "ashy haze" in the sky was noted. A local observer indicated that the activity was not unusual.

Arácar has a base 10 km in diameter. It is located just E of the Argentina-Chile border, ~ 100 km S of Lascar and 80 km NE of Llullaillaco volcanoes. No historical eruptions have been recorded. Moyra Gardeweg provided the following background. "It is clearly younger than the surrounding Miocene volcanoes. Its steep conical edifice has been cut by some deep gorges and an uncovered alteration zone lies close to its summit on the NE flank. It has a well-developed and well-preserved summit crater (1-1.5 km diameter) that contains a tiny lake. Lava flows are well preserved at the base of the cone (below 4,500-m elev), a common feature of Pliocene-to-Quaternary volcanoes in the Central Andes. I have no information about its exact age, but the good preservation of the summit crater and lava flows suggest that it could be Quaternary, although I can only assume it is Pliocene or younger."

Geologic Background. Aracar is a steep-sided stratovolcano with a youthful-looking summit crater 1-1.5 km in diameter that contains a small lake. It is located just east of the Argentina-Chile border. The volcano was constructed during three eruptive cycles dating back to the Pliocene. The andesitic stratovolcano overlies dacitic lava domes. Lava flows found at the base of the volcano below 4500 m elevation are relatively well preserved, but upper-flank lavas, often an indication of youthful activity, are not present (de Silva, 2007 pers. comm.). There were reports of possible ash columns from the summit in 1993, but it is not known whether these were rockfall dust or eruption plumes.

Information Contacts: R. Trujillo, Colorado, USA; M. Gardeweg, SERNAGEOMIN, Santiago.


Arenal (Costa Rica) — April 1993 Citation iconCite this Report

Arenal

Costa Rica

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

All times are local (unless otherwise noted)


Explosions decrease as lava production increases

Gas emissions and lava flows continued from Crater C in April, and Strombolian activity vibrated windows of houses in La Palma, ~4 km N. Ash-laden columns were blown E on 15 April, and sporadic pyroclastic flows were observed. The character of the eruption changed on 20 April as the number of explosions decreased while degassing and effusion of lava increased.

The lava flow that started down the SW flank in March remained active. Its W lobe reached 1,050 m elevation and its SW lobe reached 1,000 m elevation. The flow descending the S flank halted at 1,400 m elevation. About the middle of the month a new flow began to descend the SW flank.

A seismograph ~2.7 km NE of the active crater recorded 1,314 explosions in April, an average of 44 explosions/day (figure 55, bottom). The highest daily total was 84 on April 21, and the lowest was 13 on 27 April. Some of the explosions were recorded by a new seismograph network 120 km distant. Tremor was most persistent on 7, 19 and 20 April with 19, 19, and 21 hours recorded respectively (figure 55, top). The tremor frequency was between 1.3 and 2.3 Hz.

Figure (see Caption) Figure 55. Hours of tremor/day (top) and explosions/day (bottom) recorded 2.7 km NE of Arenal. Courtesy of OVSICORI.

Activity 18-27 April was reported by W. Melson. "Arenal volcano was in continuous eruption. Loud explosions were common 18-19 April, but by 21 April were replaced by frequent chugging and whooshing sounds (figure 56) from summit scoria fountains. These fountains fed a slowly descending, viscous, blocky, highly phyric hypersthene-augite basaltic andesite flow, which spilled over the WSW side of the crater. The flow's advance was accompanied by spectacular avalanches of incandescent blocks from the flow front."

Figure (see Caption) Figure 56. Activity of Arenal, 18-27 April, as observed from Arenal Volcano Lodge, 2.8 km S of the summit craters. "Chug" and "whoosh" events are characterized by their sound. 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: E. Fernández, J. Barquero, V. Barboza, and W. Jimenez, OVSICORI; W. Melson, SI; S. McNutt, AVO.


Avachinsky (Russia) — April 1993 Citation iconCite this Report

Avachinsky

Russia

53.256°N, 158.836°E; summit elev. 2717 m

All times are local (unless otherwise noted)


Fumarolic activity

Fumarolic activity observed in late April from the crater area resulted from normal condensation of steam and was not caused by eruptive activity.

Geologic Background. Avachinsky, one of Kamchatka's most active volcanoes, rises above Petropavlovsk, Kamchatka's largest city. It began to form during the middle or late Pleistocene, and is flanked to the SE by the parasitic volcano Kozelsky, which has a large crater breached to the NE. A large horseshoe-shaped caldera, breached to the SW, was created when a major debris avalanche about 30,000-40,000 years ago buried an area of about 500 km2 to the south underlying the city of Petropavlovsk. Reconstruction of the volcano took place in two stages, the first of which began about 18,000 years before present (BP), and the second 7000 years BP. Most eruptive products have been explosive, with pyroclastic flows and hot lahars being directed primarily to the SW by the breached caldera, although relatively short lava flows have been emitted. The frequent historical eruptions have been similar in style and magnitude to previous Holocene eruptions.

Information Contacts: V. Kirianov, IVGG.


Etna (Italy) — April 1993 Citation iconCite this Report

Etna

Italy

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

All times are local (unless otherwise noted)


Steady degassing; seismicity low

Steady degassing from the summit craters followed the end of the 1991-93 eruption on 30 March (18:03). Increased gas emissions were noted at the central (Voragine) and SE craters (see figure 59) in April, but no morphological changes were detected. The floor of Northeast Crater sank a few meters in early April and remained obstructed by fallen material.

Seismic activity was low with only two volcano-tectonic events recorded. The highest magnitude event (M 2.7) occurred 14 April on the SE flank of the volcano at ~ 10 km depth. Long-period events were similar to those recorded in March, but fewer in number. There was also a decreasing trend in volcanic tremor spectral amplitude. No major changes were recorded by shallow bore-hole tilt stations on the slopes of the volcano.

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

Information Contacts: IIV.


Galeras (Colombia) — April 1993 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


Two small eruptions; small swarm of earthquakes M 2.8-4.5

Two small pyroclastic eruptions in the first half of April produced columns 6 km high. The first, at 1603 on 4 April, ejected 18 x 104 m3 of ash. Seismicity associated with the eruption reached M 3 and lasted for 123 seconds, saturating nearby stations (within 2 km) for the first 17 seconds. Analysis of records from stations >5 km away showed dominant frequencies of 4.9 and 12.6 Hz. Long-period seismicity increased slightly for 8 hours after the explosion. The second eruption occurred at 0321 on 13 April, with 21.7 x 104 m3 of ash and blocks ejected. The long-period event associated with this eruption reached M 3.1 and lasted for 140 seconds, saturating nearby stations for the first 33 seconds. The dominant frequencies were 9.8 and 12.4 Hz. Small-magnitude long-period seismicity continued for 30 minutes.

Seven high-frequency events were registered on 1 April, with a maximum magnitude of 4.5. The earthquakes occurred at 0048 (M 4.2), 0159 (M 4.5), 0204 (M 4.0), 0303 (M 3.5), 0508 (M 3.1), 0839 (M 3.0), and 2145 (M 2.8). High-frequency seismicity increased again 26 April, peaked the morning of the 27th (figure 66), and was continuing in early May. Another earthquake, M 3.6, occurred at 1030 on 29 April. All of these earthquakes, as well as 67 other events, had epicenters 3 km N of the active crater at depths of 2-8 km below the summit (figure 67). There were ~300 earthquakes recorded in April 1993.

Figure (see Caption) Figure 66. Daily number of earthquakes at Galeras, 1 January to 30 April 1993. Dashed line indicates long-period events; solid line indicates high-frequency events (very low until 27 April). Arrows at top indicate eruptions on 14 January, 23 March, 4 April, and 13 April. Courtesy of INGEOMINAS.
Figure (see Caption) Figure 67. Locations of high-frequency earthquakes at Galeras, 26-30 April 1993. Courtesy of INGEOMINAS.

"Screw-type" events, monochromatic long-period events characterized by a long, slowly decaying coda, reappeared on 8 April. A total of 18 of these events was recorded in April, the most significant at 0619 and 1030 on 10 April and at 0926 on 29 April, about an hour before an M 3.6 earthquake. This type of seismic signal has usually preceded eruptions, but was absent before the 4 April eruption. However, relatively small earthquakes, "hybrids between high-frequency and long-period," were registered at stations close to the crater. This activity, similar to that observed before other eruptions at Galeras, was more noticeable during the first half of the month, with swarms on 1, 2, 6, 8, and 9 April.

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: M. Calvache, INGEOMINAS, Pasto.


Kilauea (United States) — April 1993 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 continues to enter the ocean

The . . . eruption continued in April and early May as lava from E-51 and E-53 vents entered the ocean. Surface flows were rare during the second half of April, but lava continued to reach the coastline through tubes. The volume of lava entering the ocean at Lae Apuki and along the W edge of the Kamoamoa delta began to decline in the last few days of April and early May as surface flows began breaking out inland from the entry points. By 6 May only the W Kamoamoa entry remained slightly active. The same day, three large breakouts were observed on Pulama Pali and two large sheet flows appeared on the coastal plain at night. One flow emerged from a tube below Pali Uli (~1 km inland) and advanced down the W side of the Lae Apuki flow. The other flow broke out of the Kamoamoa lava tube and covered new land on the E margin of the Kamoamoa flow field. By 10 May, the flows at Lae Apuki were stagnant, but lava continued to enter the ocean on both the E and W sides of the Kamoamoa delta. The Pu`u `O`o lava pond was very active during this period, fluctuating between 75 and 79 m below the rim.

Eruption tremor along the East rift zone continued with tremor amplitude 2-3x background levels during this period. Microearthquake counts were low beneath the summit and slightly above average along the East rift zone. Seismicity associated with ocean front bench collapse/explosion was recorded at 0939 on 17 April across almost the entire network, with P-arrivals that appeared to have very long-period characteristics. Many smaller events were recorded locally by the Wahaula seismograph (~4 km NE).

A number of collapse events with slightly higher frequency characteristics, including six that were locatable, were detected between 2143 and 2158 on 19 April by the Wahaula station. Based on field evidence and tourist reports, a major bench collapse during that time period was followed by a steam explosion as sea water inundated newly exposed hot rocks (figure 90). One person disappeared into the ocean, and 22 others were treated for injuries caused by the explosion showering them with incandescent lithic blocks and from falls on older flows while fleeing the area. The collapsed bench measured 210 m parallel to the coast, 14 m wide, and 8 m maximum thickness. Ejecta from the steam explosion were directed NW. Blocks near the viewing area and trail were generally <25 cm in size; meter-sized blocks were restricted to within 20 m of the entry area. Blocks were observed up to 200 m from the coast.

Figure (see Caption) Figure 90. Map of the Lae Apuki ocean entry area following the bench collapse and steam explosion on 19 April 1993. Courtesy of HVO.

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

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


Klyuchevskoy (Russia) — April 1993 Citation iconCite this Report

Klyuchevskoy

Russia

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

All times are local (unless otherwise noted)


Small gas and ash explosions

IV noted an increase in activity . . . in mid-March 1993, after a short period of repose, when explosions in the central crater sent an ash-and-gas cloud 1-2 km above the summit. On 15 March, volcanic tremor was noted, increasing in amplitude after 15 April.

A significant increase in seismicity beneath the volcano 24-27 April was reported by IVGG. Observers reported a glow near the summit area during the night of 25-26 April. A snowstorm prevented observation of the volcano 28-29 April, as volcanic tremor continued. Small steam and ash bursts inside the crater rose 200-300 m above the rim on 6 May. The plume extended 40 km NW from the volcano. Volcanic tremor remained above background.

IVGG reported three ash explosions from the summit crater on 10 May between 2030 and 2045, producing a plume that rose ~1 km above the crater rim and extended 7 km about SE. That same day, tremor amplitude measured by IV reached a maximum of 2.4 µm. Occasional steam and ash bursts occurred in the summit crater again 14 May; the plume rose 0.5-1 km above the crater rim and extended 1-7 km SW. Tremor amplitude had decreased by 19 May.

IV geologists note that tremor at Kliuchevskoi is common and is related to eruptive activity in the summit crater and, to a lesser degree, to flank eruptions. Tremor amplitude is largely dependent on the style of volcanic activity: amplitudes <0.5 µm are associated with steam-gas emission; 0.5-3 µm with Vulcanian explosions; and >3 µm with Strombolian explosions or lava spouting. Aircraft observations on 4 April 1993 revealed a newly formed crater at the summit with a diameter of 500 m and a depth of 200 m. A July 1992 overflight by S. A. Fedotov (IV) had previously revealed the almost complete subsidence of the 1984-90 cone. The last episode of dome collapse followed by renewed dome growth took place during 1962-68 when a new small volcanic cone was seen on the floor of the crater and minor lava fountaining was observed from its vent.

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: V. Ivanov and V. Dvigalo, IV; V. Kirianov, IVGG


Langila (Papua New Guinea) — April 1993 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)


Strombolian explosions continue

"Eruptive activity was at a moderate-to-high level during April. A total of 134 Vulcanian explosion earthquakes was recorded, with the highest daily total of 17 events on 5 April.

"Incandescent Strombolian projections to 300 m above Crater 2 were seen on 2, 4, 5-10, and 23 April. Steady, weak glow was observed on 11, 19, 20, 24, and 26 April. Explosion and rumbling noises were heard throughout the month. Dark grey ash columns and moderate-to-strong white-grey vapour were released every day. Some ashfall to the SE and NW of the volcano was reported.

"Crater 3 was active until 13 April, producing moderate-to-strong ash emissions accompanied by deep explosion noises. Emissions then stopped until 22 April when weak blue and white vapours appeared. Emissions stopped again on 26 April. No glow or incandescent ejections were observed."

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: N. Lauer, R. Stewart, and C. McKee, RVO.


Lascar (Chile) — April 1993 Citation iconCite this Report

Lascar

Chile

23.37°S, 67.73°W; summit elev. 5592 m

All times are local (unless otherwise noted)


Eruption sends ash above 25 km altitude; pyroclastic flows travel 7.5 km

The largest historical eruption of Lascar began late on 18 April and sent ash 20-22 km above the . . . crater rim the following day. Pyroclastic flows traveled 7.5 km NW and light ashfall (<0.1 mm) was reported in Buenos Aires, Argentina, 1,500 km SE of the volcano.

A survey conducted from January to 14 March revealed that fumarolic activity persisted with columns sometimes absent but other times rising 500-1,000 m above the crater rim. A decrease in fumarolic activity 3-8 March preceded a small phreatomagmatic eruption on 10 March that produced a column 2,000 m high (Gardeweg and others, 1993). Similar activity had also been noted on 30 January when a higher eruption column followed a few days of low level activity. During 10-14 March, the column height remained at 500-1,000 m. Observations from 14 March to the evening of 20 April were made by Ibar Torrejón, a teacher in Talabre (17 km WNW) who maintains a log of Lascar's activity. From 8-17 April the column was also low: 100-200 m. The only other observed pre-eruption change was in the color of the column, from yellowish gray (8-11 April) to whitish pale-blue (12-17 April).

Eruptive activity. Activity on 18 April was primarily phreatic until 2200 when a large explosion threw incandescent material into the air. An explosion at 2300 produced a Plinian column. These initial explosions may have been related to the partial destruction of the dome that had filled the crater in March 1992 (17:3 and 5) and collapsed sometime between 12 November and 7 December.

At 0700 on 19 April, a low, dark, ash-laden Plinian column was observed, which slowly rose 5-10 km above the rim by 0900. (Initial reports of column heights were systematically high; corrected estimates are given here). Bombs were observed throughout the morning. At 1012 the column rose above 10 km, and the first pyroclastic flow down the N flank was seen: flows also descended the NE and SE flanks, but were not observed. Other large columns (10-15 km) accompanied by pyroclastic flows were recorded at 1030, 1205, and 1317. A witness in La Escondida mine (175 km SW) described these columns as much larger than those from the 1990 eruption (15:2). The explosion at 1317 produced a column that rose 20-22 km above the rim: it was accompanied by strong rumbling and ejection of bombs to heights > 2 km. The column dropped to 2 km height until an explosion at 1715 sent it back above 15 km. Nearly 30 minutes of continuous pyroclastic flow activity near the summit began at 1935. Large explosions at 2135-2148 and 2340-2350 preceded pyroclastic flows down the N and NW slopes. Ash was blown predominately ESE.

Activity declined until 0340 on 20 April when new Strombolian explosions began, ejecting incandescent spatter up to 1.5 km above the rim. Major explosive activity resumed at 0628, producing a column >10 km high and ejecting blocks to heights >1 km. The next large explosion, at 0920, was accompanied by strong rumbles and underground noises. It generated a column nearly 10 km high and its collapse produced the farthest-reaching pyroclastic flows (7.5 km NW). Seen from Sierra Gorda (165 km WNW), the column had a well-formed mushroom shape. It remained 2-4 km high until another large explosion at 1302, which sent the column to 8.5 km within 8 minutes before it began to drift NE. One observer reported two columns rising from the crater during this explosion, the W one a darker gray-brown. At 1500 the height of the yellow-gray column decreased to 3.5-4 km, and persisted at this height until 1915 when nightfall prevented further observations. During the night, no eruptions were recorded, and no incandescent material was seen above the crater or on the flanks of the volcano.

Observations at 0630 the following morning indicated that Lascar had returned to its normal fumarolic activity with weak columns that hardly rose above the crater rim. Small explosions on 22, 23, 26, and 29 April produced columns 1000 m above the rim, but the column otherwise remained low (100-300 m) and white with occasional ash explosions to 500-800 m high. This activity continued through 8 May. During this period 2 discrete fumarolic gas columns were again observed rising from the NE and W sides of the crater, suggesting changes in its morphology from March, when only one column was noted.

An overflight of the volcano on 26 April by the National Emergency Office of the Chilean Air Force provided aerial photography of the crater and surrounding area at scales of 1:33,000 and 1:3,500. From these photographs, a new lava dome was identified in the bottom of the crater, filling a much larger portion of the crater than either the 1989 or 1992 domes. The exposed base of the dome was ~60 m higher than the previous dome and 100 m above the known crater floor (5,145-m elev). A preliminary volume estimate of the new dome was 4.6 x 106 m3. The dome appeared as a flat surface with concentric cooling ridges and steep walls devoid of a talus apron. Fumarolic activity was restricted to the margins of the dome, primarily on the SE edge. Fresh tephra partially covered the walls of the active crater, particularly in the benches, and filled the E craters (figure 13). The crater showed no other remarkable morphological changes.

Figure (see Caption) Figure 13. Sketch map of the distribution of pyroclastic flows from the 19-20 April eruption of Lascar, based on photos taken on 26 April. Featured are (1) 19-20 April pumiceous pyroclastic-flow deposits, (2) 19-20 April undifferentiated pyroclastic material, (3) Previous lava flows partially covered by pyroclastic-flow deposits, (4) Pliocene welded ignimbrites, (5) Miocene to Pliocene domes, (6) the new lava dome, and (7) arrows indicating lava flows. Courtesy of M. Gardeweg, SERNAGEOMIN.

Five portable seismographs were installed around the volcano on the evening of 20 April. Preliminary analysis showed that the harmonic tremor recorded January-March 1993 was not initially present, but returned a couple of days after the eruption. A small number of high-frequency events occurred 21-25 April. A swarm of B-type events on 28 April may have been associated with the new dome formation, and an increase in activity on 30 April may have marked the injection of new magma.

Eruption products. M. Gardeweg characterized the eruption products as pyroclastic flows, co-ignimbrite fallout (pumice and ash) deposited mainly to the E, and projectiles (figure 13). The pyroclastic flows were small-volume ignimbrites composed of abundant rounded andesitic pumice in a gray ash matrix. Most flows traveled ~4 km from the crater, but some to the NW were channeled by the upper Talabre gorge and reached Tumbres, a swampy ground 7.5 km from the crater where springs supply water for the village of Talabre. The flow deposit was covered by a narrow, thin veneer of very fine-grained ash, which was constantly blown by the wind. Degassing pipes were observed in the Tumbres deposit. A day after the eruption, the flow front was still warm, but was cooling rapidly.

The water supply to Talabre was cut off by the pyroclastic flow, but a few hours after its emplacement, water eroded through the pyroclastic material, and developed a new creek in the gorge. Donkeys and small insects were back in Tumbres the day after the eruption. The water contained a large amount of ash, but its pH was 7.6-7.7, only slightly less than its normal 8.3. Grass samples from Tumbres that were covered by ash showed 33% more fluorine than samples of clean grass. Ash from Chilean volcanoes Hudson and Lonquimay also contained notable amounts of fluorine.

The lapilli varied from white and vesicular pumices to a denser scoriae. Banding evident in some lapilli mainly reflects different degrees of vesicularity. A few dense blocks (2(black scoriae) to 60.4% SiO2 (white pumices). The fine ash has a similar andesitic composition (60.3% SiO2) with slight K enrichment. Large blocks (>2 m) left 4-5 m diameter impact craters up to 7 km from the crater. In Lejía, 17 km SSE of the volcano, a thin cover of pumice fragments 6-9 cm in diameter was noted. Huaitiquina Pass, 65 km SE on the Chilean-Argentine border, received only a thin layer of fine ash (4-4.5 mm), largely blown by wind and concentrated below cliffs or in depressions. No fall-out was found in El Laco, 55 km SE (slightly S of Huaitiquina).

The eruption also affected Argentina and J. Viramonte provided the following information. The total volume of erupted material (excluding material injected into the stratosphere) was estimated to be 0.1 km3: 0.09 km3 proximal air fall, 0.0085 km3 distal air fall, and 0.0037 km3 pyroclastic flow.

Viramonte noted that pyroclastic-flow deposits W of the crater, 7.5 km long and 1.5-2 m thick, cut the road between Antofagasta, Chile, and Salta, Argentina. He described the deposits as 60% coarse juvenile andesitic pumice fragments (2-60 cm in diameter) mixed with a minor volume of dense andesitic blocks as large as 1 m in diameter (from the old summit lava dome), and 40% fine-grained andesitic material. A very fine-grained ash-cloud-surge deposit, 5-30 cm thick, that clearly burned vegetation, flanked the pyroclastic-flow deposits. On 23 April temperatures of the deposits were as high as 100°C. These units may have been emplaced during the continuous emission of pyroclastic flows that began at 1935 on 19 April.

Four superposed pyroclastic-flow units begin 3 km from the crater rim on the ESE flank of the volcano, and extend 3-4 km to the Pampa Lejía plain. They are 1.2-1.5 m thick and composed of mainly white juvenile pumice fragments and gray blocks from the lava dome (70-80%), and fine-grained material (20-30%). Many light-and-dark banded pumice fragments were present.

Three short pyroclastic-flow lobes on the E side of the volcano had been covered by air-fall pumice. Many fumaroles with white ammonium chloride crystals and red yellow iron chloride crystals were present on the flows. Fumarole temperatures were as high as 250°C. At the foot of the pyroclastic-flow deposits, a thin ground-surge deposit was identified 100-150 m up the side of Corona hill at the S end of Lascar.

Ejected bombs and blocks were abundant within a 3-3.5 km radius of the crater, becoming rare 4 km distant. The ballistic clasts were pumiceous black andesitic bombs and dense gray andesitic blocks from the lava dome. Rounded and strongly vesiculated bombs as large as 70 cm in diameter were found 3 km from the crater. The lava-dome blocks were irregular and often showed a bread-crust structure.

Tephra carried by strong high-altitude winds produced a large dispersion of airfall deposits to the ESE (figure 14). Wind speed and direction reported by the Servicio Metereorológico Nacional Argentina at different localities (table 2) are consistent with the evolution of the ash cloud as tracked by NOAA using weather satellites.

Figure (see Caption) Figure 14. Isopach map of tephra fallout from April 19-20 eruption of Lascar. Depths are in cm. Closed fields indicate salars, saline playa lakes. Courtesy of J. Viramonte, Instituto Geonorte.

Table 2. Wind speed and direction at selected cities (see figure 15) downwind of the 19-20 April eruption of Lascar. Data are from the Servicio Metereorológico Nacional Argentina. Courtesy of J. Viramonte, Instituto Geonorte.

Date Station Altitude (km) Direction (degrees) Velocity (km/hour)
19 Apr 1993 Resistencia 10.8 305 91
19 Apr 1993 Resistencia 12.3 270 41
19 Apr 1993 Resistencia 14.1 285 46
19 Apr 1993 Resistencia 16.5 275 41
19 Apr 1993 Córdoba 10.8 355 98
19 Apr 1993 Córdoba 12.3 345 59
19 Apr 1993 Córdoba 14.0 310 124
19 Apr 1993 Córdoba 16.4 300 56
19 Apr 1993 Salta 10.9 325 63
19 Apr 1993 Salta 12.3 310 91
19 Apr 1993 Salta 14.1 310 85
19 Apr 1993 Salta 16.5 295 91
20 Apr 1993 Resistencia 10.9 330 54
20 Apr 1993 Resistencia 12.4 320 72
20 Apr 1993 Resistencia 14.1 295 76
20 Apr 1993 Resistencia 16.6 290 65
20 Apr 1993 Córdoba 10.6 355 200
20 Apr 1993 Córdoba 12.1 355 202
20 Apr 1993 Córdoba 14.0 335 126
20 Apr 1993 Córdoba 16.4 300 115
20 Apr 1993 Salta 12.3 285 98
20 Apr 1993 Salta 14.1 285 83
20 Apr 1993 Salta 16.5 280 56
20 Apr 1993 Salta 18.6 260 44

The maximum diameter of air-fall clasts on the flanks of the volcano was 30-40 cm. The maximum tephra thickness was 0.6 m on the E side of Lascar where it intersects Aguas Calientes Volcano. Approximately 20,000 km2 received at least 1 mm of ash (figure 14), and over 850,000 km2, including parts of N-central Argentina, S Paraguay, Uruguay, and S Brazil, were covered by a thin (<0.1 mm) deposit of ash (figure 15).

Figure (see Caption) Figure 15. Approximate ash-fall distribution from the 18-20 April eruption of Lascar. The thick lines outline the area receiving ashfall according to news reports. Courtesy of M. Gardeweg, SERNAGEOMIN.

Satellite monitoring. GOES-7 visible and infrared imagery detected five major eruption pulses starting at 2300 on 19 April (table 3). The plume was very dark in the visible imagery, similar to the appearance of the 14-15 June 1991 clouds from Mount Pinatubo. A subtropical jetstream moved the plume rapidly ESE (figure 16) at ~93 km/hour.

Table 3. Summary of explosive phases of Lascar detected on 20 April with visible and infrared satellite imagery from GOES-7 and NOAA-11. The tropopause was at 15.7-km altitude in the region at 1200 GMT. Courtesy of Jim Lynch, NOAA/NESDIS.

Date Approximate Eruption Start Time Duration (hours) Maximum Altitude (km)
19 Apr 1993 2300 1.0 14-16
20 Apr 1993 0300 1.0 14-16
20 Apr 1993 0630 1.5 14-16
20 Apr 1993 0930 1.5 14-16
20 Apr 1993 1300 5.0 10-12
Figure (see Caption) Figure 16. Image of the plume of Lascar, 1600 on 20 April. The image was processed from NOAA-11 Advanced Very High Resolution Radiometer (AVHRR) channel 4 (thermal infrared) data. Compare with figure 3. Courtesy of G. Stephens, NOAA.

D. Rothery, C. Oppenheimer, and P. Francis noted the following changes in the active crater of Lascar using Landsat's TM. "We have been monitoring thermal events within Lascar's active crater for several years using the short wavelength infrared radiance of thermal origin. The latest image we have prior to the 20 April 1993 eruption was recorded by Landsat 5 on 24 February.

"Whereas our 1991 and 1992 data showed a strongly centered group of thermally radiant pixels that coincided with the lava dome (figure 17 bottom), there was a significant change visible on 24 February 1993 (figure 17 top). The central anomaly has decreased in size and magnitude, but there is a distinct subsidiary peak in thermal radiance to the E. This coincided with the position of a fumarole that had been more weakly radiant on previous images. This site lies about half-way down the wall of the active crater, which at this point is embedded in the floor of an old crater (see figure 13). We have no grounds for suggesting that this newly prominent site was the seat of the 19-20 April eruption. The nature of the central anomaly on 24 February, which had decreased to the approximate size and magnitude of the anomaly recorded from late 1987 until the end of 1989, suggests that the lava dome was still in existence on that date.

Figure (see Caption) Figure 17. Radiance in Landsat TM band 7 (2.08-2.35 micron) for a 15x15 pixel area encompassing Lascar's active crater, looking N. Data are from 24 February 1993 during the day (top), and 15 April 1992 during the night (bottom) (from figure 21b in Oppenheimer and others, 1993). Each pixel represents a 30 x 30 m ground area. Radiance is shown as DN, which is the number recorded by the sensor. In this example, areas with DN of about 50 or less are not thermally radiant and the DN represents reflected sunlight. Where DN exceeds about 100, the surface is radiating thermally, and the DN represents the sum of reflected sunlight and thermal radiance. Courtesy of D. Rothery, Open Univ.

"The summed spectral radiance of thermal origin in Landsat TM bands 5 and 7 showed a decline before the 1993 eruption similar to that before the September 1986 eruption (figure 18). There was no observed decline before the February 1990 eruption, though that could be the result of the lack of images before the eruption."

Figure (see Caption) Figure 18. Summed spectral radiance of thermal origin in Landsat TM bands 5 and 7 for the active crater of Lascar (from figure 18 in Oppenheimer and others, 1993 with data for 24 February 1993 added). Eruptions are noted by arrows. The decline in summed radiance prior to the 1993 eruption is similar to that preceding the 1986 eruption. There was no observed decline before the February 1990 eruption, though that could be the result of the lack of images during 1988-89. Courtesy of D. Rothery, Open Univ.

Effects and previous activity. The 70 [people] who live in Talabre and make their living as llama herders and weavers were evacuated [to the nearby village of Toconao for two nights] by authorities on 19 April. Initial reports indicated that there had been no injuries. However, many defied the order and returned to tend their homes and animals. As many as six people were listed as missing, having apparently gone searching for their animals on the SE side of the volcano. [The people listed as missing were forced to make a detour because their normal route was covered by pumice and ash, but they arrived safely 3 days after the eruption.]

References. Gardeweg, M.C., Sparks, S., Matthews, S., Fuentealba, G., Murillo, M, and Espinoza, A., 1993, V Informe sobre el comportamiento del Volcán Lascar (II Región): Enero Marzo 1993, Informe Inédito, Biblioteca Servicio Nacional de Geología y Minería, 14 p.

Oppenheimer, C., Francis, P.W., Rothery, D.A., Carlton, R.W.T., and Glaze, L.S., 1993, Infrared image analysis of volcanic thermal features: Lascar volcano, Chile, 1984-1992, Journal of Geophysical Research, v. 98, p. 4269-4286.

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

Information Contacts: M. Gardeweg and A. Espinoza, SERNAGEOMIN, Santiago; E. Medina, Univ Católica del Norte, Antofagasta; M. Murillo, Univ de la Frontera, Temuca, Chile; J. Viramonte, R. Marini, R. Bocchio, and R. Pereyra, Univ Nacional de Salta, Instituto Geonorte - CONICET, Argentina; R. Seggiaro, M. Bosso, N. Monegatti, and M. Bolli, Univ Nacional de Salta, Instituto Geonorte, Argentina; R. Ortiz Ramis, CSIC, J. Gutierrez Abascal, Spain; I. Torrejón, Esccuela Básica G-29, Talabre, Chile; D. Rothery, C. Oppenheimer, and P. Francis, Open Univ; J. Lynch, SAB; G. Stephens, NOAA; American Embassy, Santiago, Chile.


Ol Doinyo Lengai (Tanzania) — April 1993 Citation iconCite this Report

Ol Doinyo Lengai

Tanzania

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

All times are local (unless otherwise noted)


Carbonatite lava production continues

Carbonatite lava extrusion since February 1992 has centered on [T20] (figure 27). Lava production has continued since September [1992] as new lava flows from T20 have surrounded other cones with up to 4 m of new material.

Figure (see Caption) Figure 27. Panorama of Ol Doinyo Lengai crater on 23 February 1993 looking SW from the E rim (top) and looking E from the W rim (bottom). Crater diameter is ~330 m. Drawn by C. Nyamweru from photographs taken by H. Martin and P. Robinson.

Although no activity was observed on 23 February when David Peterson, Paul Robinson, and a group of St. Lawrence Univ students descended to the crater floor for ~3.5 hours in the morning, morphological changes indicated continued lava production from vent T20. Heather Martin reported that no liquid lava was visible in the vents or on the crater floor, but that steam was being emitted from almost all of the vents, especially T5/T9 and T20 (figure 27), and from the base of the W inner crater wall. There was also a strong smell of sulfur near the vents, and intermittent rumbling, thumping, and cracking noises were heard coming from beneath the crater floor and the two vents named above. The crater floor consisted of large, relatively smooth, but heavily cracked, pale grayish-tan plates. Crystalline sulfur deposits (green/yellow/rust/white) were present along cracks. No dark, fresh flows were observed. The E-W diameter of the crater was estimated to be 330 m, and the E wall behind T5/T9 was estimated to be 32 m high. Rim cone C1 and feature A5 were very pale compared to the color of the rest of the N wall.

The upper 5 m of cone T8 was still visible after being partially buried by several younger lava flows, now white in color. The vent on the E side of the summit of T14 remained open, although younger white-to-pale gray lavas have also surrounded this 6.4-m-high cone. Yellow sulfur staining was visible on the upper slopes of both the T8 and T14 cones. Vent T5/T9 (21 m high) remained the tallest feature on the crater floor, though the sharp junction at the base of the cone indicates that it has also been surrounded by younger flows. There have been no noticeable changes since last September to the 8-m-high T15 cone, which still has pale-gray lower slopes and jagged dark upper slopes. Vent T19 and feature D, possibly an older lava flow that has been visible for several years (figure 26), have apparently been completely buried by younger flows.

Based on the depth of lava that has surrounded the older T5/T9, T8, and T14 cones (1.5-4 m), the base of the crater wall, and the remains of the M2 spur, it is clear that a considerable volume of lava has been extruded since . . . 30 September 1992. The source of most or all of this lava appears to be the T20 vent . . . . Vent T20 has blackened upper slopes with an open vent on the W upper slope and a lava tunnel 2-3 m deep and 1-2 m high that extends ~50 m to the SE. The smooth lava that gently slopes up from the crater floor around T20 resulted in height estimates for T20 that varied between 7 and 14 m.

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

Information Contacts: C. Nyamweru, St. Lawrence Univ; D. Peterson, Arusha; P. Robinson, Nairobi, Kenya; H. Martin, Norwood, NY; A. Prime, Hingham, MA.


Manam (Papua New Guinea) — April 1993 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)


Very low activity

"Activity . . . continued at the very low level reported in March. Emissions from both summit craters consisted of weak-to-moderate white vapour. No night glow was reported. Seismic activity was low throughout April and the tilt measurements showed no trends."

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: N. Lauer, R. Stewart, and C. McKee, RVO.


Poas (Costa Rica) — April 1993 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Fumarolic activity continues; lake level drops

Fumarolic activity in the N part of the crater lake continued in April as gas columns rose to 500 m. One fumarole produced a jet-like sound, audible from an observation site 1 km S. Almost constant phreatic eruptions produced 1-2-m-high plumes in a light-green area near the center of the lake. The lake level dropped 1 m during April.

A seismograph located 2.7 km SW of the active crater recorded 4,115 low-frequency events (2-2.5 Hz) during April (figure 44). The highest daily total of the month was 319 on 5 April.

Figure (see Caption) Figure 44. Seismic events/day recorded 2.7 km SW of the main crater of Poás, April 1993. 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, J. Barquero, V. Barboza, and W. Jimenez, OVSICORI.


Rabaul (Papua New Guinea) — April 1993 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)


Seismic activity remains high; no ground uplift

"The number of earthquakes detected in April was 1,061, . . . still relatively high compared to background (250-350 earthquakes/month). Large swarms of >100 earthquakes occurred on 1, 3, and 21 April. No earthquakes were felt, suggesting that the largest event was M 2-2.5. The epicenters of the 52 accurately located earthquakes were mainly in the W and NE parts of the caldera seismic zone, similar to . . . March.

"Routine monthly levelling from Rabaul town to Matupit Island showed a small uplift at the S end of the island. Other parts of this levelling line showed no significant changes compared to March. Additional levelling along the N side of Greet Harbor showed a deflation of up to 13 mm since the last survey in August 1992.

"The relatively high level of seismicity with little or no associated ground uplift is reminiscent of activity recorded in mid-1986. The lack of significant uplift suggests that neither episode was related to any pronounced movement of magma within the caldera."

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: N. Lauer, R. Stewart, and C. McKee, RVO.


Rincon de la Vieja (Costa Rica) — April 1993 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)


Seismic activity continues

A seismograph about 5 km SW of the active crater recorded 28 microearthquakes and four high-frequency earthquakes in April (figure 7).

Figure (see Caption) Figure 7. Seismic events/day recorded 5 km SW of the active crater of Rincón de la Vieja. Courtesy of OVSICORA.

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

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


Sheveluch (Russia) — April 1993 Citation iconCite this Report

Sheveluch

Russia

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

All times are local (unless otherwise noted)


Eruption sends ash cloud to 20 km altitude

An explosive eruption 22 April followed more than a month of seismic and explosive precursors. Almost daily explosive bursts from 18 March to 4 April sent eruptive clouds to 1-4 km above the summit. Shallow earthquake swarms increased in early April from 14 earthquakes on 4 April to 90 distinct earthquakes in a continuous swarm on 7 April, when the Level of Concern Code was raised to orange by geologists at the IVGG. Magnitudes were estimated to be about M 2 on 6 April. Steam and gas explosions with some ash content continued over the next 3 days with seismicity remaining at high levels. Earthquakes increased in number and magnitude 12-15 April, with a maximum of 124 earthquakes on 14 April.

A snowstorm prevented observations 17-19 April, but explosions from the volcano were heard in Kliuchi (45 km SW) every few seconds on the 19th. Numerous gas and steam bursts occurred from the active dome 19-20 April. The gas-and-ash plume rose 800 m above the crater rim and drifted SW. Two spine-like or obelisk-shaped extrusions, 30-40 m high, were observed on the summit dome 20 April by geologists from IVGG and the IV. Shallow seismicity beneath the dome began to migrate towards the surface that same day. Seismicity began decreasing 19 April, and had declined sharply by the 21st. Gas and steam bursts rose to 600 m above the dome on 21 April.

The climactic eruption began the morning of 22 April. IV scientists reported explosions at the dome and from the crater near the dome beginning at 1030. The eruption cloud was ~7 km high by 1042 and >10 km high at 1313. The cloud obscured the volcano after the explosions until about 1600 when the lower part of the cloud was blown E and the upper part W. The eruption also produced pyroclastic flows and mud flows >10 km long.

The Level of Concern Code was raised to red on 22 April by IVGG geologists, who reported strong explosions at 1205 and 1230. At 1205 the eruptive cloud rose 6 km above the crater rim . . . and then to 15 km by 1330. The lower part of the ash cloud was moving WSW, and the upper portion was moving SE. Lightning was seen within the cloud. At 1340 the height of the eruption column was estimated to be 18 km (~20 km altitude). The ash cloud was detected drifting W by a weather satellite at 1432. By 1545, the ash cloud was moving WSW over the Kamchatka Peninsula. Pyroclastic flows down the flanks of the volcano reached 900 m elev, and mud flows extended 100 m lower.

The next morning, at 0530 on 23 April, another explosive ash eruption sent a column to 9-11 km altitude with the cloud moving in different directions at different altitudes. Bad weather prevented visual helicopter inspections of the crater area that day, but ash had started falling in . . . Kliuchi during the night and continued past 0800, stopping sometime later in the day. Strong winds rapidly redistributed the ash making thickness estimates difficult; however no more than 3 mm of ash appears to have fallen on the town, 45 km SW. Seismic activity decreased in the 24 hours after the eruption, and the Level of Concern Code was lowered to orange. No new pyroclastic flows or mudflows were observed on the lower flanks of the volcano.

IV also reported single explosions continuing on 23 April. The ash column was 3 km high and ashfall also occurred in Ust'-Kamchatsk (100 km SE). Baidarnaya station (8 km from active crater) registered 27 earthquakes on 23 April with amplitudes of 2-4 µm.

The volcano became visible 24 April, and a gas and steam column 4.5 km high was observed by IVGG at 2230, drifting to the N. Shimmering lights inside the crater were observed during the night. Seismicity was twice that recorded 22 April, and 20 earthquakes were detected in addition to constant low-amplitude tremor beneath the crater. An explosive burst was recorded seismically at 0619 on 25 April. A steam-and-ash column to 3.5 km above the crater was observed that day at 0530 and 0730, with a >30-km-long plume directed NNW.

Clouds again prevented visual observations 26-29 April, but the Level of Concern Code was lowered to yellow on 27 April because of the overall decline in volcanic activity. However, seismicity remained above background levels during this period with 36 earthquakes recorded on 27 April. Shallow, low-amplitude tremor was also continuing beneath the active dome.

Separate strong explosions were observed by IV geologists once every few days from 24 April to 3 May. The height of the ash cloud during the last days reached 1.5-2 km.

Thermal capacity and volume of ejected pyroclastics were calculated based on powerful explosions on 21 April at 2242-2258 (plume 6 km above the crater); 22 April at 0013-0026 (>10 km), 1104-1110, 1630 (7 km), and 2030, and 24 April at 1719 (3.5 km). Tremor amplitude was as much as 35 microns, with a period 0.6-0.9s (7.5 km from the active dome). Based on the height of the eruptive cloud and tremor, calculations indicate that the thermal capacity of the plume was about 1-50 x 109 MJ, with about 1-50 x 106 tons of ejected pyroclastics. Calculations were made by V. V. Ivanov (IV) using the methods of Fedotov (1985) and Firstov and others (1977).

References. Fedotov, S. A., 1985, Estimates of heat and pyroclast discharge by volcanic eruptions based upon the eruption cloud and steady plume observations: Journal of Geodynamics, v. 3, p. 275-302.

Firstov, P. P., Lemzikov, V. K., and Rulenko, O. P., 1977, Seismic regime of Karymsky volcano (1970-1973): Volcanism and Geodynamics, p. 161-179 (in Russian).

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: V. Kirianov, IVGG; S. Fedotov, V. Ivanov, G. Bogoyavlenskaya, V. Gavrilov, and N. Zharinov, IV; J. Lynch, SAB.


Stromboli (Italy) — April 1993 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 increases; detailed description of crater

Steve Matthews and Abigail Church observed vigorous Strombolian activity on 22 April at two 20-m-high hornitos in crater C1 (figure 29). Incandescent gas explosions occurred at 3-10 second intervals, followed ~0.5 seconds later by ejection of spatter. Semi-liquid bombs up to 2 m across reached up to 100 m above the vents. Stronger activity from all three craters every 10-20 minutes consisted of gas emissions lasting as long as 15 seconds that ejected spatter as high as 250 m. These stronger events appeared to occur in pairs from craters C3 and C2. An explosion from C3's vent 4 was often followed a few minutes later by an explosion from vent 2 in C2. Within C1, these larger explosions were only produced from the NE hornito (vent 1). Many incandescent fumaroles were visible on the hornitos and the floors of all three craters. Small amounts of spatter were also ejected from the fumaroles during the strongest explosive episodes. At about 2030, shortly after sunset, lava was observed flowing slowly from a breach or bocca in the SW hornito (vent 2) in C1. When observations ended at 2200, the lava flow had divided and was beginning to form a moat around the hornitos.

Figure (see Caption) Figure 29. Sketch of the summit craters and vents at Stromboli, 22 April (top), and 3 May 1993 (bottom). Crater walls could not be distinguished on 3 May due to the abundant gas and steam. Vent numbers are in parentheses. Field of view is ~200 m across. Courtesy of S. Matthews, A. Church, and S. O'Meara.

A high level of eruptive activity was reported by Steve O'Meara on 2-6 May. Roaring noises could be heard in San Vincenzo (~2.5 km NE) the afternoon of 2 May, which became periodic by late afternoon, occurring about once every 20-30 minutes. A gray fountain was observed from the lower NE slopes around 1830 that rose several hundred meters above the NE-most vent. Several strong explosions later that evening sent incandescent boulders rolling down the steep slope of the Sciara del Fuoco (figure 29). There were at least 8 vents active for several hours during summit observations the night of 3-4 May. Eruptive activity increased dramatically after the nearly full moon rose, peaked when the moon culminated in the southern sky, and waned before moonset. Lunar perigee (when the moon is closest to the Earth) occurred that night around 0100.

Vent 1 in crater C1 (figure 29) was a large dome-shaped mound with a summit crater and shallow floor filled with incandescent bombs from other vent explosions. Approximately every 30 minutes a powerful explosive blast, which sounded like a large cannon firing, violently blew the debris from the vent to heights of 200-300 m. Increased crater glow preceded these eruptions and most others. C1's vent 2 is a small cone with a peanut-shaped throat adjacent to and W of vent 1. This vent was continuously active with jetting sounds, blue flames, and spatter ejection. Thin streams of lava were erupted about every 5 minutes, with larger 100-m sprays of lava about every 15 minutes. Vent 3 in C1 (E of and adjacent to vent 1) exhibited continuous glow and erupted synchronously with either vent 1 or vent 2, ejecting material to a height of ~100 m. Occasionally, vents 1-3 would erupt together. Ejecta from vent 3 was directed slightly NE, while blasts from vents 1 and 2 were directed vertically. These explosions only lasted for a few seconds. Another less-active vent in C1, S of and adjacent to vent 1, also appeared to erupt synchronously with vents 1-3 to heights of tens of meters.

In crater C2, vent 1 had three glowing components, though only the western-most one produced sporadic minor eruptions, spraying lava ~10-30 m above its steep, narrow cone. Eruptions from vent 2 in C2 occurred every 30-45 minutes and lasted 20-40 seconds each. Eruptions began with a strong jetting sound, after which a thin spray of lava would shoot out, followed by more vigorous jetting and extensive lava production. Lava fountains reached heights of up to 150 m. Lava was visible in the vent for about a minute after each eruption, with the surface continually being fractured by escaping gases. The lava would then slowly sink into the vent until it was no longer visible, although glow remained.

Two small adjacent vents in crater C3 were each surrounded by wide, shallow cinder rims. Eruptions were more frequent at the W vent, where explosions sent material 300-400 m high about every 10 minutes during the most active periods. These eruptions occurred without warning and were accompanied by a loud roaring noise. The largest eruptions from this vent produced very broad, expansive plumes shaped like large evergreen trees, which reached 30 m above the summit of the volcano. Another vent farther S may also have erupted, but that area was obscured by fumes and steam.

The frequency of eruptions from each vent changed with time, but not the sounds, making it possible to know which vents were erupting. By the morning of 3 May, activity had declined to one large explosion and a couple of smaller ones approximately every 20 minutes. During the most active periods of the night, >20 strong eruptions occurred every hour. Activity increased again after moonrise on 4 May and remained strong into the early morning. Orange glow reflected by the clouds was observed that night in San Vincenzo. The next day, powerful eruptions continued from crater C3 and vent 1 in C1, but with less frequency. Vents 2 and 3 in C1 glowed but did not have any strong eruptions. Observations ended about 2400 on 5 May. Seven eruptions were seen from the ferry 2100-2200 on 6 May.

Marcello Riuscetti reports that Stromboli guides observed a new cone in crater C1 and renewed activity at the C3 spatter cone in mid-May. On 16 May a small lava emission occurred from the base of a cone in C3. During the night the flow traveled 30 m down the slope, reaching the feeding fissure of the 1985 eruption before stopping. The flow resumed 18 May, covering ~60 m of 1985 lava NE towards the Sciara del Fuoco. Strong tremor and frequent explosions accompanied the lava flow.

Seismicity (number and energy of shocks, tremor energy) increased in March and April after the low of 11 February (18:02). The level of seismicity was very high in April (figure 30), with nearly continuous explosions in the second and third weeks.

Figure (see Caption) Figure 30. Seismicity recorded at Stromboli, March-April 1993. Open bars show the number of recorded events/day, the solid bars those with ground velocities >100 mm/s. The lines show daily tremor energy computed by averaging hourly 60-second samples. The number of daily events are off the scale for the 2nd and 3rd weeks of April due to the nearly continuous explosions during that period. 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: S. Matthews, Univ College London, London; A. Church, Natural History Museum, London; S. O'Meara, Sky & Telescope; M. Riuscetti, Univ di Udine.


Suwanosejima (Japan) — April 1993 Citation iconCite this Report

Suwanosejima

Japan

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

All times are local (unless otherwise noted)


Sporadic, weak ash eruptions

Sporadic, weak ash eruptions continued in April. The island's residents heard explosions [during] 22-26 April.

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

Information Contacts: JMA.


Taftan (Iran) — April 1993 Citation iconCite this Report

Taftan

Iran

28.6°N, 61.13°E; summit elev. 3940 m

All times are local (unless otherwise noted)


Lava flow reported; no previous historical eruptions known

An eruption that sent a lava flow ~60 m downslope was reported on 25 April by the Islamic Republic News Agency. No additional information about the timing or location of the activity was available. There was apparently no immediate danger to the local population.

Geologic Background. Taftan is a strongly eroded andesitic stratovolcano with two prominent summits. The volcano was constructed along a volcanic zone in Beluchistan, SE Iran, that extends into northern Pakistan. The higher SE summit cone is well preserved and has been the source of very fresh-looking lava flows, as well as of highly active, sulfur-encrusted fumaroles. The deeply dissected NW cone is of Pleistocene age. In January 1902 the volcano was reported to be smoking heavily for several days, with occasional strong night-time glow. A lava flow was reported in 1993, but may have been a mistaken observation of a molten sulfur flow.

Information Contacts: AP; Reuters.


Turrialba (Costa Rica) — April 1993 Citation iconCite this Report

Turrialba

Costa Rica

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

All times are local (unless otherwise noted)


Fumarolic activity unchanged

Fumarolic activity continued in the N, W, and SW walls of the main crater. Temperatures at the fumaroles, 90°C, have remained relatively unchanged since 1982 (17:02). A condensate sample had a pH of 4.5, similar to the pH of 4.8 recorded in December 1992 (17:12). Small landslides from the N, S, and W walls continued.

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, J. Barquero, V. Barboza, and Walter Jimenez, OVSICORI.


Ulawun (Papua New Guinea) — April 1993 Citation iconCite this Report

Ulawun

Papua New Guinea

5.05°S, 151.33°E; summit elev. 2334 m

All times are local (unless otherwise noted)


Tremor level returns to background

"Activity continued at the low levels reported in the previous two months. Emissions of weak-to-moderate white vapour occurred throughout April, with stronger emissions on 3 and 6 April. Seismic activity was low throughout the month. RSAM showed that the slow decline in tremor amplitude seen in March continued until 20 April. After 20 April, the tremor amplitude remained constant, indicating that tremor had effectively ceased and the natural background noise was being recorded."

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

Information Contacts: N. LauerR. Stewart, and C. McKee, RVO.


Unzendake (Japan) — April 1993 Citation iconCite this Report

Unzendake

Japan

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

All times are local (unless otherwise noted)


Pyroclastic flows increase in number; heavy rainfall produces large debris flows

The swelling of dome 10 and local deformation of the basement rocks N of the dome complex had stopped by mid-April. Large blocks of dome 10 that overhung to the W and N collapsed and scattered around Jigokuato crater, filling it and covering a part of the 1663 lava flow.

Exogenous growth of dome 11 continued. The volume of dome 11 remained constant, implying that the volume of magma supplied to the dome was equal to that lost because of collapses. By mid-May, dome 11 was 150 m long, 150 m wide, and 70 m high.

The seismic network recorded ~ 10 pyroclastic flows/day until 27 April. On 28 and 29 April (both rainy days), 39 and 26 pyroclastic flows were detected, respectively. These were the highest daily totals since 25 September 1992. The monthly total of flows was 352, twice that of March.

The pyroclastic flows, almost all generated by collapses of dome 11, descended mainly E into Mizunashi Valley, NE into Oshiga Valley, and only rarely SE (figure 55). Several flows traveled through Oshiga Valley and entered the Mizunashi River, and some flows entered a headwater of the Nakao River, the upper stream of the Senbongi district. The limit of the flow deposits has been moving slowly N. The longest flow of the month occurred at 1016 on 29 April, traveling 3.5 km E from the dome complex and having a seismic duration of 160 seconds. Ash clouds from the flows rose ~ 1 km above the dome complex, generally higher than those of the past 4 months. The highest cloud rose 1.3 km on 26 April. A pilot reported a very dense, dark-gray column rising to 900 m above the summit and drifting SSE at 1818 on 25 April. The pyroclastic flows caused no damage.

Figure (see Caption) Figure 55. Map showing distribution of pyroclastic-flow and debris-flow deposits at Unzen, May 1993. Courtesy of S. Nakada.

Heavy rainfall on 28-29 April and 2 May generated the largest debris flows of the current eruption, both along the Mizunashi and Nakao rivers. Flows traveled E across highways 57 and 251, and the Shimabara railway, damaging about 500 houses. Prior to the flows, ~ 7,000 people had been asked to evacuate, and no injuries were reported. People were able to return after the rains. The highways were reopened 4 May after the sediment was removed, but the railway remained buried as of mid-May. The Civil Engineer of Nagasaki Prefectural Government estimated the total volume of debris in the Mizunashi River to be > 106 m3.

The number of microearthquakes detected under the dome complex declined . . . to 656 in April. A weak swarm occurred 19-24 April when daily totals increased by a factor of 5. Seismicity near the volcano was low.

The Geographical Survey Institute estimated the total volume of magma erupted from May 1991 to early-March 1993 to be 0.13 km3, and the volume of the dome complex to be 0.05 km3 based on digital mapping data. Over 2,000 residents remain evacuated from Shimabara and Fukae.

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; S. Nakada, Kyushu Univ; ICAO.

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