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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

Manam (Papua New Guinea) Few ash plumes during November-December 2022

Krakatau (Indonesia) Strombolian activity and ash plumes during November 2022-April 2023

Stromboli (Italy) Strombolian explosions and lava flows continue during January-April 2023

Nishinoshima (Japan) Small ash plumes and fumarolic activity during November 2022 through April 2023

Karangetang (Indonesia) Lava flows, incandescent avalanches, and ash plumes during January-June 2023

Ahyi (United States) Intermittent hydroacoustic signals and discolored plumes during November 2022-June 2023

Kadovar (Papua New Guinea) An ash plume and weak thermal anomaly during May 2023

San Miguel (El Salvador) Small gas-and-ash explosions during March and May 2023

Semisopochnoi (United States) Occasional explosions, ash deposits, and gas-and-steam plumes during December 2022-May 2023

Ebeko (Russia) Continued explosions, ash plumes, and ashfall during October 2022-May 2023

Home Reef (Tonga) Discolored plumes continued during November 2022-April 2023

Ambae (Vanuatu) New lava flow, ash plumes, and sulfur dioxide plumes during February-May 2023



Manam (Papua New Guinea) — July 2023 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)


Few ash plumes during November-December 2022

Manam is a 10-km-wide island that consists of two active summit craters: the Main summit crater and the South summit crater and is located 13 km off the northern coast of mainland Papua New Guinea. Frequent mild-to-moderate eruptions have been recorded since 1616. The current eruption period began during June 2014 and has more recently been characterized by intermittent ash plumes and thermal activity (BGVN 47:11). This report updates activity that occurred from November 2022 through May 2023 based on information from the Darwin Volcanic Ash Advisory Center (VAAC) and various satellite data.

Ash plumes were reported during November and December 2022 by the Darwin VAAC. On 7 November an ash plume rose to 2.1 km altitude and drifted NE based on satellite images and weather models. On 14 November an ash plume rose to 2.1 km altitude and drifted W based on RVO webcam images. On 20 November ash plumes rose to 1.8 km altitude and drifted NW. On 26 December an ash plume rose to 3 km altitude and drifted S and SSE.

Intermittent sulfur dioxide plumes were detected using the TROPOMI instrument on the Sentinel-5P satellite, some of which exceeded at least two Dobson Units (DU) and drifted in different directions (figure 93). Occasional low-to-moderate power thermal anomalies were recorded by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system; less than five anomalies were recorded each month during November 2022 through May 2023 (figure 94). Two thermal hotspots were detected by the MODVOLC thermal alerts system on 10 December 2022. On clear weather days, thermal activity was also captured in infrared satellite imagery in both the Main and South summit craters, accompanied by gas-and-steam emissions (figure 95).

Figure (see Caption) Figure 93. Distinct sulfur dioxide plumes were captured, rising from Manam based on data from the TROPOMI instrument on the Sentinel-5P satellite on 16 November 2022 (top left), 6 December 2022 (top right), 14 January 2023 (bottom left), and 23 March 2023 (bottom right). Plumes generally drifted in different directions. Courtesy of the NASA Global Sulfur Dioxide Monitoring Page.
Figure (see Caption) Figure 94. Occasional low-to-moderate power thermal anomalies were detected at Manam during November 2022 through May 2023, as shown in this MIROVA graph (Log Radiative Power). Only three anomalies were detected during late November, one in early December, two during January 2023, one in late March, four during April, and one during late May. Courtesy of MIROVA.
Figure (see Caption) Figure 95. Infrared (bands B12, B11, B4) satellite images show a consistent thermal anomaly (bright yellow-orange) in both the Main (the northern crater) and South summit craters on 10 November 2022 (top left), 15 December 2022 (top right), 3 February 2023 (bottom left), and 24 April 2023 (bottom right). Gas-and-steam emissions occasionally accompanied the thermal activity. Courtesy of Copernicus Browser.

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

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Krakatau (Indonesia) — July 2023 Citation iconCite this Report

Krakatau

Indonesia

6.1009°S, 105.4233°E; summit elev. 285 m

All times are local (unless otherwise noted)


Strombolian activity and ash plumes during November 2022-April 2023

Krakatau is located in the Sunda Strait between Java and Sumatra, Indonesia. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan cones and left only a remnant of Rakata. The post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former Danan and Perbuwatan cones; it has been the site of frequent eruptions since 1927. The current eruption period began in May 2021 and has recently consisted of explosions, ash plumes, and thermal activity (BGVN 47:11). This report covers activity during November 2022 through April 2023 based on information provided by the Indonesian Center for Volcanology and Geological Hazard Mitigation, referred to as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), MAGMA Indonesia, the Darwin Volcanic Ash Advisory Center (VAAC), and several sources of satellite data.

Activity was relatively low during November and December 2022. Daily white gas-and-steam plumes rose 25-100 m above the summit and drifted in different directions. Gray ash plumes rose 200 m above the summit and drifted NE at 1047 and at 2343 on 11 November. On 14 November at 0933 ash plumes rose 300 m above the summit and drifted E. An ash plume was reported at 0935 on 15 December that rose 100 m above the summit and drifted NE. An eruptive event at 1031 later that day generated an ash plume that rose 700 m above the summit and drifted NE. A gray ash plume at 1910 rose 100 m above the summit and drifted E. Incandescent material was ejected above the vent based on an image taken at 1936.

During January 2023 daily white gas-and-steam plumes rose 25-300 m above the summit and drifted in multiple directions. Gray-to-brown ash plumes were reported at 1638 on 3 January, at 1410 and 1509 on 4 January, and at 0013 on 5 January that rose 100-750 m above the summit and drifted NE and E; the gray-to-black ash plume at 1509 on 4 January rose as high as 3 km above the summit and drifted E. Gray ash plumes were recorded at 1754, 2241, and 2325 on 11 January and at 0046 on 12 January and rose 200-300 m above the summit and drifted NE. Toward the end of January, PVMBG reported that activity had intensified; Strombolian activity was visible in webcam images taken at 0041, 0043, and 0450 on 23 January. Multiple gray ash plumes throughout the day rose 200-500 m above the summit and drifted E and SE (figure 135). Webcam images showed progressively intensifying Strombolian activity at 1919, 1958, and 2113 on 24 January; a gray ash plume at 1957 rose 300 m above the summit and drifted E (figure 135). Eruptive events at 0231 and 2256 on 25 January and at 0003 on 26 January ejected incandescent material from the vent, based on webcam images. Gray ash plumes observed during 26-27 January rose 300-500 m above the summit and drifted NE, E, and SE.

Figure (see Caption) Figure 135. Webcam images of a strong, gray ash plume (left) and Strombolian activity (right) captured at Krakatau at 0802 on 23 January 2023 (left) and at 2116 on 24 January 2023 (right). Courtesy of PVMBG and MAGMA Indonesia.

Low levels of activity were reported during February and March. Daily white gas-and-steam plumes rose 25-300 m above the summit and drifted in different directions. The Darwin VAAC reported that continuous ash emissions rose to 1.5-1.8 km altitude and drifted W and NW during 1240-1300 on 10 March, based on satellite images, weather models, and PVMBG webcams. White-and-gray ash plumes rose 500 m and 300 m above the summit and drifted SW at 1446 and 1846 on 18 March, respectively. An eruptive event was recorded at 2143, though it was not visible due to darkness. Multiple ash plumes were reported during 27-29 March that rose as high as 2.5 km above the summit and drifted NE, W, and SW (figure 136). Webcam images captured incandescent ejecta above the vent at 0415 and around the summit area at 2003 on 28 March and at 0047 above the vent on 29 March.

Figure (see Caption) Figure 136. Webcam image of a strong ash plume rising above Krakatau at 1522 on 28 March 2023. Courtesy of PVMBG and MAGMA Indonesia.

Daily white gas-and-steam plumes rose 25-300 m above the summit and drifted in multiple directions during April and May. White-and-gray and black plumes rose 50-300 m above the summit on 2 and 9 April. On 11 May at 1241 a gray ash plume rose 1-3 km above the summit and drifted SW. On 12 May at 0920 a gray ash plume rose 2.5 km above the summit and drifted SW and at 2320 an ash plume rose 1.5 km above the summit and drifted SW. An accompanying webcam image showed incandescent ejecta. On 13 May at 0710 a gray ash plume rose 2 km above the summit and drifted SW (figure 137).

Figure (see Caption) Figure 137. Webcam image of an ash plume rising 2 km above the summit of Krakatau at 0715 on 13 May 2023. Courtesy of PVMBG and MAGMA Indonesia.

The MIROVA (Middle InfraRed Observation of Volcanic Activity) graph of MODIS thermal anomaly data showed intermittent low-to-moderate power thermal anomalies during November 2022 through April 2023 (figure 138). Some of this thermal activity was also visible in infrared satellite imagery at the crater, accompanied by gas-and-steam and ash plumes that drifted in different directions (figure 139).

Figure (see Caption) Figure 138. Intermittent low-to-moderate power thermal anomalies were detected at Krakatau during November 2022 through April 2023, based on this MIROVA graph (Log Radiative Power). Courtesy of MIROVA.
Figure (see Caption) Figure 139. A thermal anomaly (bright yellow-orange) was visible at Krakatau in infrared (bands B12, B11, B4) satellite images on clear weather days during November 2022 through May 2023. Occasional gas-and-steam and ash plumes accompanied the thermal activity, which drifted in different directions. Images were captured on 25 November 2022 (top left), 15 December 2022 (top right), 27 January 2023 (bottom left), and 12 May 2023 (bottom right). Courtesy of Copernicus Browser.

Geologic Background. The renowned Krakatau (frequently mis-named as Krakatoa) volcano lies in the Sunda Strait between Java and Sumatra. Collapse of an older edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of that volcano are preserved in Verlaten and Lang Islands; subsequently the Rakata, Danan, and Perbuwatan cones 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 caused more than 36,000 fatalities, most as a result of 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 Danan and Perbuwatan cones. 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.esdm.go.id/v1); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Stromboli (Italy) — July 2023 Citation iconCite this Report

Stromboli

Italy

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

All times are local (unless otherwise noted)


Strombolian explosions and lava flows continue during January-April 2023

Stromboli, located in Italy, has exhibited nearly constant lava fountains for the past 2,000 years; recorded eruptions date back to 350 BCE. Eruptive activity occurs at the summit from multiple vents, which include a north crater area (N area) and a central-southern crater (CS area) on a terrace known as the ‘terrazza craterica’ at the head of the Sciara del Fuoco, a large scarp that runs from the summit down the NW side of the volcano-island. Activity typically consists of Strombolian explosions, incandescent ejecta, lava flows, and pyroclastic flows. Thermal and visual monitoring cameras are located on the nearby Pizzo Sopra La Fossa, above the terrazza craterica, and at multiple flank locations. The current eruption period has been ongoing since 1934 and recent activity has consisted of frequent Strombolian explosions and lava flows (BGVN 48:02). This report updates activity during January through April 2023 primarily characterized by Strombolian explosions and lava flows based on reports from Italy's Istituto Nazionale di Geofisica e Vulcanologia (INGV) and various satellite data.

Frequent explosive activity continued throughout the reporting period, generally in the low-to-medium range, based on the number of hourly explosions in the summit crater (figure 253, table 16). Intermittent thermal activity was recorded by the MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data (figure 254). According to data collected by the MODVOLC thermal algorithm, a total of 9 thermal alerts were detected: one on 2 January 2023, one on 1 February, five on 24 March, and two on 26 March. The stronger pulses of thermal activity likely reflected lava flow events. Infrared satellite imagery captured relatively strong thermal hotspots at the two active summit craters on clear weather days, showing an especially strong event on 8 March (figure 255).

Figure (see Caption) Figure 253. Explosive activity persisted at Stromboli during January through April 2023, with low to medium numbers of daily explosions at the summit crater. The average number of daily explosions (y-axis) during January through April (x-axis) are broken out by area and as a total, with red for the N area, blue for the CS area, and black for the combined total. The data are smoothed as daily (thin lines) and weekly (thick lines) averages. The black squares along the top represent days with no observations due to poor visibility (Visib. Scarsa). The right axis indicates the qualitative activity levels from low (basso) to highest (altissimo) with the green highlighted band indicating the most common level. Courtesy of INGV (Report 17/2023, Stromboli, Bollettino Settimanale, 18/04/2023 - 24/04/2023).

Table 16. Summary of type, frequency, and intensity of explosive activity at Stromboli by month during January-April 2023; information from webcam observations. Courtesy of INGV weekly reports.

Month Explosive Activity
Jan 2023 Typical Strombolian activity with spattering and lava overflows in the N crater area. Explosions were reported from 4 vents in the N area and 1-2 vents in the CS area. The average hourly frequency of explosions was low-to-medium (1-12 events/hour). The intensity of the explosions varied from low (less than 80 m high) to medium (less than 150 m high) in the N crater area and up to high (greater than 150 m high) in the CS crater area.
Feb 2023 Typical Strombolian activity with spattering in the N crater area. Explosions were reported from 2-3 vents in the N area and 1-4 vents in the CS area. The average hourly frequency of explosions was low-to-medium (1-14 events/hour). The intensity of the explosions varied from low (less than 80 m high) to medium (less than 150 m high) in the N crater area and up to high (greater than 150 m high) in the CS crater area.
Mar 2023 Typical Strombolian activity with spattering and lava overflows in the N crater area. Explosions were reported from 2-3 vents in the N area and 2-4 vents in the CS area. The average hourly frequency of explosions was low-to-medium (1-18 events/hour). The intensity of the explosions varied from low (less than 80 m high) to medium (less than 150 m high) in the N crater area and up to high (greater than 150 m high) in the CS crater area.
Apr 2023 Typical Strombolian activity. Explosions were reported from 2 vents in the N area and 2-3 vents in the CS area. The average hourly frequency of explosions was low-to-high (1-16 events/hour). The intensity of the explosions varied from low (less than 80 m high) to medium (less than 150 m high) in both the N and CS crater areas.
Figure (see Caption) Figure 254. Intermittent thermal activity at Stromboli was detected during January through April 2023 and varied in strength, as shown in this MIROVA graph (Log Radiative Power). A pulse of activity was captured during late March. Courtesy of MIROVA.
Figure (see Caption) Figure 255. Infrared (bands B12, B11, B4) satellite images showing persistent thermal anomalies at both summit crater on 1 February 2023 (top left), 23 March 2023 (top right), 8 March 2023 (bottom left), and 27 April 2023. A particularly strong thermal anomaly was visible on 8 March. Courtesy of Copernicus Browser.

Activity during January-February 2023. Strombolian explosions were reported in the N crater area, as well as lava effusion. Explosive activity in the N crater area ejected coarse material (bombs and lapilli). Intense spattering was observed in both the N1 and N2 craters. In the CS crater area, explosions generally ejected fine material (ash), sometimes to heights greater than 250 m. The intensity of the explosions was characterized as low-to-medium in the N crater and medium-to-high in the CS crater. After intense spattering activity from the N crater area, a lava overflow began at 2136 on 2 January that flowed part way down the Sciara del Fuoco, possibly moving down the drainage that formed in October, out of view from webcams. The flow remained active for a couple of hours before stopping and beginning to cool. A second lava flow was reported at 0224 on 4 January that similarly remained active for a few hours before stopping and cooling. Intense spattering was observed on 11 and 13 January from the N1 crater. After intense spattering activity at the N2 crater at 1052 on 17 January another lava flow started to flow into the upper part of the Sciara del Fuoco (figure 256), dividing into two: one that traveled in the direction of the drainage formed in October, and the other one moving parallel to the point of emission. By the afternoon, the rate of the flow began to decrease, and at 1900 it started to cool. A lava flow was reported at 1519 on 24 January following intense spattering in the N2 area, which began to flow into the upper part of the Sciara del Fuoco. By the morning of 25 January, the lava flow had begun to cool. During 27 January the frequency of eruption in the CS crater area increased to 6-7 events/hour compared to the typical 1-7 events/hour; the following two days showed a decrease in frequency to less than 1 event/hour. Starting at 1007 on 30 January a high-energy explosive sequence was produced by vents in the CS crater area. The sequence began with an initial energetic pulse that lasted 45 seconds, ejecting predominantly coarse products 300 m above the crater that fell in an ESE direction. Subsequent and less intense explosions ejected material 100 m above the crater. The total duration of this event lasted approximately two minutes. During 31 January through 6, 13, and 24 February spattering activity was particularly intense for short periods in the N2 crater.

Figure (see Caption) Figure 256. Webcam images of the lava flow development at Stromboli during 17 January 2023 taken by the SCT infrared camera. The lava flow appears light yellow-green in the infrared images. Courtesy of INGV (Report 04/2023, Stromboli, Bollettino Settimanale, 16/01/2023 - 22/01/2023).

An explosive sequence was reported on 16 February that was characterized by a major explosion in the CS crater area (figure 257). The sequence began at 1817 near the S2 crater that ejected material radially. A few seconds later, lava fountains were observed in the central part of the crater. Three explosions of medium intensity (material was ejected less than 150 m high) were recorded at the S2 crater. The first part of this sequence lasted approximately one minute, according to INGV, and material rose 300 m above the crater and then was deposited along the Sciara del Fuoco. The second phase began at 1818 at the S1 crater; it lasted seven seconds and material was ejected 150 m above the crater. Another event 20 seconds later lasted 12 seconds, also ejecting material 150 m above the crater. The sequence ended with at least three explosions of mostly fine material from the S1 crater. The total duration of this sequence was about two minutes.

Figure (see Caption) Figure 257. Webcam images of the explosive sequence at Stromboli on 16 February 2023 taken by the SCT and SCV infrared and visible cameras. The lava appears light yellow-green in the infrared images. Courtesy of INGV (Report 08/2023, Stromboli, Bollettino Settimanale, 13/02/2023 - 19/02/2023).

Short, intense spattering activity was noted above the N1 crater on 27 and 28 February. A lava overflow was first reported at 0657 from the N2 crater on 27 February that flowed into the October 2022 drainage. By 1900 the flow had stopped. A second lava overflow also in the N crater area occurred at 2149, which overlapped the first flow and then stopped by 0150 on 28 February. Material detached from both the lava overflows rolled down the Sciara del Fuoco, some of which was visible in webcam images.

Activity during March-April 2023. Strombolian activity continued with spattering activity and lava overflows in the N crater area during March. Explosive activity at the N crater area varied from low (less than 80 m high) to medium (less than 150 m high) and ejected coarse material, such as bombs and lapilli. Spattering was observed above the N1 crater, while explosive activity at the CS crater area varied from medium to high (greater than 150 m high) and ejected coarse material. Intense spattering activity was observed for short periods on 6 March above the N1 crater. At approximately 0610 a lava overflow was reported around the N2 crater on 8 March, which then flowed into the October 2022 drainage. By 1700 the flow started to cool. A second overflow began at 1712 on 9 March and overlapped the previous flow. It had stopped by 2100. Material from both flows was deposited along the Sciara del Fuoco, though much of the activity was not visible in webcam images. On 11 March a lava overflow was observed at 0215 that overlapped the two previous flows in the October 2022 drainage. By late afternoon on 12 March, it had stopped.

During a field excursion on 16 March, scientists noted that a vent in the central crater area was degassing. Another vent showed occasional Strombolian activity that emitted ash and lapilli. During 1200-1430 low-to-medium intense activity was reported; the N1 crater emitted ash emissions and the N2 crater emitted both ash and coarse material. Some explosions also occurred in the CS crater area that ejected coarse material. The C crater in the CS crater area occasionally showed gas jetting and low intensity explosions on 17 and 22 March; no activity was observed at the S1 crater. Intense, longer periods of spattering were reported in the N1 crater on 19, 24, and 25 March. Around 2242 on 23 March a lava overflow began from the N1 crater that, after about an hour, began moving down the October 2022 drainage and flow along the Sciara del Fuoco (figure 258). Between 0200 and 0400 on 26 March the flow rate increased, which generated avalanches of material from collapses at the advancing flow front. By early afternoon, the flow began to cool. On 25 March at 1548 an explosive sequence began from one of the vents at S2 in the CS crater area (figure 258). Fine ash mixed with coarse material was ejected 300 m above the crater rim and drifted SSE. Some modest explosions around Vent C were detected at 1549 on 25 March, which included an explosion at 1551 that ejected coarse material. The entire explosive sequence lasted approximately three minutes.

Figure (see Caption) Figure 258. Webcam images of the lava overflow in the N1 crater area of Stromboli on 23 March 2023 taken by the SCT infrared camera. The lava appears light yellow-green in the infrared images. The start of the explosive sequence was also captured on 25 March 2023 accompanied by an eruption plume (e) captured by the SCT and SPT infrared webcams. Courtesy of INGV (Report 13/2023, Stromboli, Bollettino Settimanale, 20/03/2023 - 26/03/2023).

During April explosions persisted in both the N and CS crater areas. Fine material was ejected less than 80 m above the N crater rim until 6 April, followed by ejection of coarser material. Fine material was also ejected less than 80 m above the CS crater rim. The C and S2 crater did not show significant eruptive activity. On 7 April an explosive sequence was detected in the CS crater area at 1203 (figure 259). The first explosion lasted approximately 18 seconds and ejected material 400 m above the crater rim, depositing pyroclastic material in the upper part of the Sciara del Fuoco. At 1204 a second, less intense explosion lasted approximately four seconds and deposited pyroclastic products outside the crater area and near Pizzo Sopra La Fossa. A third explosion at 1205 was mainly composed of ash that rose about 150 m above the crater and lasted roughly 20 seconds. A fourth explosion occurred at 1205 about 28 seconds after the third explosion and ejected a mixture of coarse and fine material about 200 m above the crater; the explosion lasted roughly seven seconds. Overall, the entire explosive sequence lasted about two minutes and 20 seconds. After the explosive sequence on 7 April, explosions in both the N and CS crater areas ejected material as high as 150 m above the crater.

Figure (see Caption) Figure 259. Webcam images of the explosive sequence at Stromboli during 1203-1205 (local time) on 7 April 2023 taken by the SCT infrared camera. Strong eruption plumes are visible, accompanied by deposits on the nearby flanks. Courtesy of INGV (Report 15/2023, Stromboli, Bollettino Settimanale, 03/04/2023 - 09/04/2023).

On 21 April research scientists from INGV made field observations in the summit area of Stromboli, and some lapilli samples were collected. In the N crater area near the N1 crater, a small cone was observed with at least two active vents, one of which was characterized by Strombolian explosions. The other vent produced explosions that ejected ash and chunks of cooled lava. At the N2 crater at least one vent was active and frequently emitted ash. In the CS crater area, a small cone contained 2-3 degassing vents and a smaller, possible fissure area also showed signs of degassing close to the Pizzo Sopra La Fossa. In the S part of the crater, three vents were active: a small hornito was characterized by modest and rare explosions, a vent that intermittently produced weak Strombolian explosions, and a vent at the end of the terrace that produced frequent ash emissions. Near the S1 crater there was a hornito that generally emitted weak gas-and-steam emissions, sometimes associated with “gas rings”. On 22 April another field inspection was carried out that reported two large sliding surfaces on the Sciara del Fuoco that showed where blocks frequently descended toward the sea. A thermal anomaly was detected at 0150 on 29 April.

Geologic Background. Spectacular incandescent nighttime explosions at Stromboli have long attracted visitors to the "Lighthouse of the Mediterranean" in the NE Aeolian Islands. This volcano 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 scarp that formed about 5,000 years ago due to a series of slope failures which extends 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: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy, (URL: http://www.ct.ingv.it/en/); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Nishinoshima (Japan) — July 2023 Citation iconCite this Report

Nishinoshima

Japan

27.247°N, 140.874°E; summit elev. 100 m

All times are local (unless otherwise noted)


Small ash plumes and fumarolic activity during November 2022 through April 2023

Nishinoshima is a small island located about 1,000 km S of Tokyo in the Ogasawara Arc in Japan. The island is the summit of a massive submarine volcano that has prominent peaks to the S, W, and NE. Eruptions date back to 1973; the most recent eruption period began in October 2022 and was characterized by ash plumes and fumarolic activity (BGVN 47:12). This report describes ash plumes and fumarolic activity during November 2022 through April 2023 based on monthly reports from the Japan Meteorological Agency (JMA) monthly reports and satellite data.

The most recent eruptive activity prior to the reporting internal occurred on 12 October 2022, when an ash plume rose 3.5 km above the crater rim. An aerial observation conducted by the Japan Coast Guard (JCG) on 25 November reported that white fumaroles rose approximately 200 m above the central crater of a pyroclastic cone (figure 119), and multiple plumes were observed on the ESE flank of the cone. Discolored water ranging from reddish-brown to brown and yellowish-green were visible around the perimeter of the island (figure 119). No significant activity was reported in December.

Figure (see Caption) Figure 119. Aerial photo of gas-and-steam plumes rising 200 m above Nishinoshima on 25 November 2022. Reddish brown to brown and yellowish-green discolored water was visible around the perimeter of the island. Courtesy of JCG via JMA (monthly reports of activity at Nishinoshima, November 2022).

During an overflight conducted by JCG on 25 January 2023 intermittent activity and small, blackish-gray plumes rose 900 m above the central part of the crater were observed (figure 120). The fumarolic zone of the E flank and base of the cone had expanded and emissions had intensified. Dark brown discolored water was visible around the perimeter of the island.

Figure (see Caption) Figure 120. Aerial photo of a black-gray ash plume rising approximately 900 m above the crater rim of Nishinoshima on 25 January 2023. White fumaroles were visible on the E slope of the pyroclastic cone. Dense brown to brown discolored water was observed surrounding the island. Photo has been color corrected. Courtesy of JCG via JMA (monthly reports of activity at Nishinoshima, January, 2023).

No significant activity was reported during February through March. Ash plumes at 1050 and 1420 on 11 April rose 1.9 km above the crater rim and drifted NW and N. These were the first ash plumes observed since 12 October 2022. On 14 April JCG carried out an overflight and reported that no further eruptive activity was visible, although white gas-and-steam plumes were visible from the central crater and rose 900 m high (figure 121). Brownish and yellow-green discolored water surrounded the island.

Figure (see Caption) Figure 121. Aerial photo of white gas-and-steam plumes rising 900 m above Nishinoshima on 14 April 2023. Brown and yellow-green discolored water is visible around the perimeter of the island. Photo has been color corrected. Courtesy of JCG via JMA (monthly reports of activity at Nishinoshima, April, 2023).

Intermittent low-to-moderate power thermal anomalies were recorded in the MIROVA graph (Middle InfraRed Observation of Volcanic Activity) during November 2022 through April 2023 (figure 123). A cluster of six to eight anomalies were detected during November while a smaller number were detected during the following months: two to three during December, one during mid-January 2023, one during February, five during March, and two during April. Thermal activity was also reflected in infrared satellite data at the summit crater, accompanied by occasional gas-and-steam plumes (figure 124).

Figure (see Caption) Figure 123. Intermittent low-to-moderate thermal anomalies were detected at Nishinoshima during November 2022 through April 2023, according to this MIROVA graph (Log Radiative Power). A cluster of anomalies occurred throughout November, while fewer anomalies were detected during the following months. Courtesy of MIROVA.
Figure (see Caption) Figure 124. Infrared (bands B12, B11, B4) satellite images show a small thermal anomaly at the summit crater of Nishinoshima on 9 January 2023 (left) and 8 February 2023 (right). Gas-and-steam plumes accompanied this activity and extended S and SE, respectively. Courtesy of Copernicus Browser.

Geologic Background. The small island of Nishinoshima was enlarged when several new islands coalesced during an eruption in 1973-74. Multiple eruptions that began in 2013 completely covered the previous exposed surface and continued to enlarge the island. The island is the summit of a massive submarine volcano that has prominent peaks to the S, W, and NE. The summit of the southern cone rises to within 214 m of the ocean surface 9 km SSE.

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); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Karangetang (Indonesia) — July 2023 Citation iconCite this Report

Karangetang

Indonesia

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

All times are local (unless otherwise noted)


Lava flows, incandescent avalanches, and ash plumes during January-June 2023

Karangetang (also known as Api Siau), at the northern end of the island of Siau, Indonesia, contains five summit craters along a N-S line. More than 40 eruptions have been recorded since 1675; recent eruptions have included frequent explosive activity, sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters and collapses of lava flow fronts have produced pyroclastic flows. The two active summit craters are Kawah Dua (the N crater) and Kawah Utama (the S crater, also referred to as the “Main Crater”). The most recent eruption began in late November 2018 and has more recently consisted of weak thermal activity and gas-and-steam emissions (BGVN 48:01). This report updates activity characterized by lava flows, incandescent avalanches, and ash plumes during January through June 2023 using reports from Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, the Darwin VAAC (Volcano Ash Advisory Center), and satellite data.

Activity during January was relatively low and mainly consisted of white gas-and-steam emissions that rose 25-150 m above Main Crater (S crater) and drifted in different directions. Incandescence was visible from the lava dome in Kawah Dua (the N crater). Weather conditions often prevented clear views of the summit. On 18 January the number of seismic signals that indicated avalanches of material began to increase. In addition, there were a total of 71 earthquakes detected during the month.

Activity continued to increase during the first week of February. Material from Main Crater traveled as far as 800 m down the Batuawang (S) and Batang (W) drainages and as far as 1 km W down the Beha (W) drainage on 4 February. On 6 February 43 earthquake events were recorded, and on 7 February, 62 events were recorded. White gas-and-steam emissions rose 25-250 m above both summit craters throughout the month. PVMBG reported an eruption began during the evening of 8 February around 1700. Photos showed incandescent material at Main Crater. Incandescent material had also descended the flank in at least two unconfirmed directions as far as 2 km from Main Crater, accompanied by ash plumes (figure 60). As a result, PVMBG increased the Volcano Alert Level (VAL) to 3 (the second highest level on a 1-4 scale).

Figure (see Caption) Figure 60. Photos of the eruption at Karangetang on 8 February 2023 that consisted of incandescent material descending the flanks (top left), ash plumes (top right and bottom left), and summit crater incandescence (bottom right). Courtesy of IDN Times.

Occasional nighttime webcam images showed three main incandescent lava flows of differing lengths traveling down the S, SW, and W flanks (figure 61). Incandescent rocks were visible on the upper flanks, possibly from ejected or collapsed material from the crater, and incandescence was the most intense at the summit. Based on analyses of satellite imagery and weather models, the Darwin VAAC reported that daily ash plumes during 16-20 February rose to 2.1-3 km altitude and drifted NNE, E, and SE. BNPB reported on 16 February that as many as 77 people were evacuated and relocated to the East Siau Museum. A webcam image taken at 2156 on 17 February possibly showed incandescent material descending the SE flank. Ash plumes rose to 2.1 km altitude and drifted SE during 22-23 February, according to the Darwin VAAC.

Figure (see Caption) Figure 61. Webcam image of summit incandescence and lava flows descending the S, SW, and W flanks of Karangetang on 13 February 2023. Courtesy of MAGMA Indonesia.

Incandescent avalanches of material and summit incandescence at Main Crater continued during March. White gas-and-steam emissions during March generally rose 25-150 m above the summit crater; on 31 March gas-and-steam emissions rose 200-400 m high. An ash plume rose to 2.4 km altitude and drifted S at 1710 on 9 March and a large thermal anomaly was visible in images taken at 0550 and 0930 on 10 March. Incandescent material was visible at the summit and on the flanks based on webcam images taken at 0007 and 2345 on 16 March, at 1828 on 17 March, at 1940 on 18 March, at 2311 on 19 March, and at 2351 on 20 March. Incandescence was most intense on 18 and 20 March and webcam images showed possible Strombolian explosions (figure 62). An ash plume rose to 2.4 km altitude and drifted SW on 18 March, accompanied by a thermal anomaly.

Figure (see Caption) Figure 62. Webcam image of intense summit incandescence and incandescent avalanches descending the flanks of Karangetang on 18 March 2023. Photo has been color corrected. Courtesy of MAGMA Indonesia.

Summit crater incandescence at Main Crater and on the flanks persisted during April. Incandescent material at the S crater and on the flanks was reported at 0016 on 1 April. The lava flows had stopped by 1 April according to PVMBG, although incandescence was still visible up to 10 m high. Seismic signals indicating effusion decreased and by 6 April they were no longer detected. Incandescence was visible from both summit craters. On 26 April the VAL was lowered to 2 (the second lowest level on a 1-4 scale). White gas-and-steam emissions rose 25-200 m above the summit crater.

During May white gas-and-steam emissions generally rose 50-250 m above the summit, though it was often cloudy, which prevented clear views; on 21 May gas-and-steam emissions rose 50-400 m high. Nighttime N summit crater incandescence rose 10-25 m above the lava dome, and less intense incandescence was noted above Main Crater, which reached about 10 m above the dome. Sounds of falling rocks at Main Crater were heard on 15 May and the seismic network recorded 32 rockfall events in the crater on 17 May. Avalanches traveled as far as 1.5 km down the SW and S flanks, accompanied by rumbling sounds on 18 May. Incandescent material descending the flanks was captured in a webcam image at 2025 on 19 May (figure 63) and on 29 May; summit crater incandescence was observed in webcam images at 2332 on 26 May and at 2304 on 29 May. On 19 May the VAL was again raised to 3.

Figure (see Caption) Figure 63. Webcam image showing incandescent material descending the flanks of Karangetang on 19 May 2023. Courtesy of MAGMA Indonesia.

Occasional Main Crater incandescence was reported during June, as well as incandescent material on the flanks. White gas-and-steam emissions rose 10-200 m above the summit crater. Ash plumes rose to 2.1 km altitude and drifted SE and E during 2-4 June, according to the Darwin VAAC. Material on the flanks of Main Crater were observed at 2225 on 7 June, at 2051 on 9 June, at 0007 on 17 June, and at 0440 on 18 June. Webcam images taken on 21, 25, and 27 June showed incandescence at Main Crater and from material on the flanks.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed strong thermal activity during mid-February through March and mid-May through June, which represented incandescent avalanches and lava flows (figure 64). During April through mid-May the power of the anomalies decreased but frequent anomalies were still detected. Brief gaps in activity occurred during late March through early April and during mid-June. Infrared satellite images showed strong lava flows mainly affecting the SW and S flanks, accompanied by gas-and-steam emissions (figure 65). According to data recorded by the MODVOLC thermal algorithm, there were a total of 79 thermal hotspots detected: 28 during February, 24 during March, one during April, five during May, and 21 during June.

Figure (see Caption) Figure 64. Strong thermal activity was detected during mid-February 2023 through March and mid-May through June at Karangetang during January through June 2023, as recorded by this MIROVA graph (Log Radiative Power). During April through mid-May the power of the anomalies decreased, but the frequency at which they occurred was still relatively high. A brief gap in activity was shown during mid-June. Courtesy of MIROVA.
Figure (see Caption) Figure 65. Incandescent avalanches of material and summit crater incandescence was visible in infrared satellite images (bands 12, 11, 8A) at both the N and S summit crater of Karangetang on 17 February 2023 (top left), 13 April 2023 (top right), 28 May 2023 (bottom left), and 7 June 2023 (bottom right), as shown in these infrared (bands 12, 11, 8A) satellite images. The incandescent avalanches mainly affected the SW and S flanks. Sometimes gas-and-steam plumes accompanied the thermal activity. Courtesy of Copernicus Browser.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/); IDN Times, Jl. Jend. Gatot Subroto Kav. 27 3rd Floor Kuningan, Jakarta, Indonesia 12950, Status of Karangetang Volcano in Sitaro Islands Increases (URL: https://sulsel.idntimes.com/news/indonesia/savi/status-gunung-api-karangetang-di-kepulauan-sitaro-meningkat?page=all).


Ahyi (United States) — July 2023 Citation iconCite this Report

Ahyi

United States

20.42°N, 145.03°E; summit elev. -75 m

All times are local (unless otherwise noted)


Intermittent hydroacoustic signals and discolored plumes during November 2022-June 2023

Ahyi seamount is a large, conical submarine volcano that rises to within 75 m of the ocean surface about 18 km SE of the island of Farallon de Pajaros in the Northern Marianas. The remote location of the seamount has made eruptions difficult to document, but seismic stations installed in the region confirmed an eruption in the vicinity in 2001. No new activity was detected until April-May 2014 when an eruption was detected by NOAA (National Oceanic and Atmospheric Administration) divers, hydroacoustic sensors, and seismic stations (BGVN 42:04). New activity was first detected on 15 November by hydroacoustic sensors that were consistent with submarine volcanic activity. This report covers activity during November 2022 through June 2023 based on daily and weekly reports from the US Geological Survey.

Starting in mid-October, hydroacoustic sensors at Wake Island (2.2 km E) recorded signals consistent with submarine volcanic activity, according to a report from the USGS issued on 15 November 2022. A combined analysis of the hydroacoustic signals and seismic stations located at Guam and Chichijima Island, Japan, suggested that the source of this activity was at or near the Ahyi seamount. After a re-analysis of a satellite image of the area that was captured on 6 November, USGS confirmed that there was no evidence of discoloration at the ocean surface. Few hydroacoustic and seismic signals continued through November, including on 18 November, which USGS suggested signified a decline or pause in unrest. A VONA (Volcano Observatory Notice for Aviation) reported that a discolored water plume was persistently visible in satellite data starting on 18 November (figure 6). Though clouds often obscured clear views of the volcano, another discolored water plume was captured in a satellite image on 26 November. The Aviation Color Code (ACC) was raised to Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level (VAL) was raised to Advisory (the second lowest level on a four-level scale) on 29 November.

Figure (see Caption) Figure 6. A clear, true color satellite image showed a yellow-green discolored water plume extending NW from the Ahyi seamount (white arrow) on 21 November 2022. Courtesy of Copernicus Browser.

During December, occasional detections were recorded on the Wake Island hydrophone sensors and discolored water over the seamount remained visible. During 2-7, 10-12, and 16-31 December possible explosion signals were detected. A small area of discolored water was observed in high-resolution Sentinel-2 satellite images during 1-6 December (figure 7). High-resolution satellite images recorded discolored water plumes on 13 December that originated from the summit region; no observations indicated that activity breached the ocean surface. A possible underwater plume was visible in satellite images on 18 December, and during 19-20 December a definite but diffuse underwater plume located SSE from the main vent was reported. An underwater plume was visible in a satellite image taken on 26 December (figure 7).

Figure (see Caption) Figure 7. Clear, true color satellite images showed yellow-green discolored water plumes extending NE and W from Ahyi (white arrows) on 1 (left) and 26 (right) December 2022, respectively. Courtesy of Copernicus Browser.

Hydrophone sensors continued to detect signals consistent with possible explosions during 1-8 January 2023. USGS reported that the number of detections decreased during 4-5 January. The hydrophone sensors experienced a data outage that started at 0118 on 8 January and continued through 10 January, though according to USGS, possible explosions were recorded prior to the data outage and likely continued during the outage. A discolored water plume originating from the summit region was detected in a partly cloudy satellite image on 8 January. On 11-12 and 15-17 January possible explosion signals were recorded again. One small signal was detected during 22-23 January and several signals were recorded on 25 and 31 January. During 27-31 January a plume of discolored water was observed above the seamount in satellite imagery (figure 8).

Figure (see Caption) Figure 8. True color satellite images showed intermittent yellow-green discolored water plumes of various sizes extending N on 5 January 2023 (top left), SE on 30 January 2023 (top right), W on 4 February 2023 (bottom left), and SW on 1 March 2023 (bottom right) from Ahyi (white arrows). Courtesy of Copernicus Browser.

Low levels of activity continued during February and March, based on data from pressure sensors on Wake Island. During 1 and 4-6 February activity was reported, and a submarine plume was observed on 4 February (figure 8). Possible explosion signals were detected during 7-8, 10, 13-14, and 24 February. During 1-2 and 3-5 March a plume of discolored water was observed in satellite imagery (figure 8). Almost continuous hydroacoustic signals were detected in remote pressure sensor data on Wake Island 2,270 km E from the volcano during 7-13 March. During 12-13 March water discoloration around the seamount was observed in satellite imagery, despite cloudy weather. By 14 March discolored water extended about 35 km, but no direction was noted. USGS reported that the continuous hydroacoustic signals detected during 13-14 March stopped abruptly on 14 March and no new detections were observed. Three 30 second hydroacoustic detections were reported during 17-19 March, but no activity was visible due to cloudy weather. A data outage was reported during 21-22 March, making pressure sensor data unavailable; a discolored water plume was, however, visible in satellite data. A possible underwater explosion signal was detected by pressure sensors at Wake Island on 26, 29, and 31 March, though the cause and origin of these events were unclear.

Similar low activity continued during April, May, and June. Several signals were detected during 1-3 April in pressure sensors at Wake Island. USGS suggested that these may be related to underwater explosions or earthquakes at the volcano, but no underwater plumes were visible in clear satellite images. The pressure sensors had data outages during 12-13 April and no data were recorded; no underwater plumes were visible in satellite images, although cloudy weather obscured most clear views. Eruptive activity was reported starting at 2210 on 21 May. On 22 May a discolored water plume that extended 4 km was visible in satellite images, though no direction was recorded. During 23-24 May some signals were detected by the underwater pressure sensors. Possible hydroacoustic signals were detected during 2-3 and 6-8 June. Multiple hydroacoustic signals were detected during 9-11 and 16-17 June, although no activity was visible in satellite images. One hydroacoustic signal was detected during 23-24 June, but there was some uncertainty about its association with volcanic activity. A single possible hydroacoustic signal was detected during 30 June to 1 July.

Geologic Background. Ahyi seamount is a large conical submarine volcano that rises to within 75 m of the ocean surface ~18 km SE of the island of Farallon de Pajaros in the northern Marianas. Water discoloration has been observed there, and in 1979 the crew of a fishing boat felt shocks over the summit area, followed by upwelling of sulfur-bearing water. On 24-25 April 2001 an explosive eruption was detected seismically by a station on Rangiroa Atoll, Tuamotu Archipelago. The event was well constrained (+/- 15 km) at a location near the southern base of Ahyi. An eruption in April-May 2014 was detected by NOAA divers, hydroacoustic sensors, and seismic stations.

Information Contacts: US Geological Survey, Volcano Hazards Program (USGS-VHP), 12201 Sunrise Valley Drive, Reston, VA, USA, https://volcanoes.usgs.gov/index.html; Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Kadovar (Papua New Guinea) — June 2023 Citation iconCite this Report

Kadovar

Papua New Guinea

3.608°S, 144.588°E; summit elev. 365 m

All times are local (unless otherwise noted)


An ash plume and weak thermal anomaly during May 2023

Kadovar is a 2-km-wide island that is the emergent summit of a Bismarck Sea stratovolcano. It lies off the coast of New Guinea, about 25 km N of the mouth of the Sepik River. Prior to an eruption that began in 2018, a lava dome formed the high point of the volcano, filling an arcuate landslide scarp open to the S. Submarine debris-avalanche deposits occur to the S of the island. The current eruption began in January 2018 and has comprised lava effusion from vents at the summit and at the E coast; more recent activity has consisted of ash plumes, weak thermal activity, and gas-and-steam plumes (BGVN 48:02). This report covers activity during February through May 2023 using information from the Darwin Volcanic Ash Advisory Center (VAAC) and satellite data.

Activity during the reporting period was relatively low and mainly consisted of white gas-and-steam plumes that were visible in natural color satellite images on clear weather days (figure 67). According to a Darwin VAAC report, at 2040 on 6 May an ash plume rose to 4.6 km altitude and drifted W; by 2300 the plume had dissipated. MODIS satellite instruments using the MODVOLC thermal algorithm detected a single thermal hotspot on the SE side of the island on 7 May. Weak thermal activity was also detected in a satellite image on the E side of the island on 14 May, accompanied by a white gas-and-steam plume that drifted SE (figure 68).

Figure (see Caption) Figure 67. True color satellite images showing a white gas-and-steam plume rising from Kadovar on 28 February 2023 (left) and 30 March 2023 (right) and drifting SE and S, respectively. Courtesy of Copernicus Browser.
Figure (see Caption) Figure 68. Infrared (bands B12, B11, B4) image showing weak thermal activity on the E side of the island, accompanied by a gas-and-steam plume that drifted SE from Kadovar on 14 May 2023. Courtesy of Copernicus Browser.

Geologic Background. The 2-km-wide island of Kadovar is the emergent summit of a Bismarck Sea stratovolcano of Holocene age. It is part of the Schouten Islands, and lies off the coast of New Guinea, about 25 km N of the mouth of the Sepik River. Prior to an eruption that began in 2018, a lava dome formed the high point of the andesitic volcano, filling an arcuate landslide scarp open to the south; submarine debris-avalanche deposits occur in that direction. Thick lava flows with columnar jointing forms low cliffs along the coast. The youthful island lacks fringing or offshore reefs. A period of heightened thermal phenomena took place in 1976. An eruption began in January 2018 that included lava effusion from vents at the summit and at the E coast.

Information Contacts: Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


San Miguel (El Salvador) — June 2023 Citation iconCite this Report

San Miguel

El Salvador

13.434°N, 88.269°W; summit elev. 2130 m

All times are local (unless otherwise noted)


Small gas-and-ash explosions during March and May 2023

San Miguel in El Salvador is a broad, deep crater complex that has been frequently modified by eruptions recorded since the early 16th century and consists of the summit known locally as Chaparrastique. Flank eruptions have produced lava flows that extended to the N, NE, and SE during the 17-19th centuries. The most recent activity has consisted of minor ash eruptions from the summit crater. The current eruption period began in November 2022 and has been characterized by frequent phreatic explosions, gas-and-ash emissions, and sulfur dioxide plumes (BGVN 47:12). This report describes small gas-and-ash explosions during December 2022 through May 2023 based on special reports from the Ministero de Medio Ambiente y Recursos Naturales (MARN).

Activity has been relatively low since the last recorded explosions on 29 November 2022. Seismicity recorded by the San Miguel Volcano Station (VSM) located on the N flank at 1.7 km elevation had decreased by 7 December. Sulfur dioxide gas measurements taken with DOAS (Differential Optical Absorption Spectroscopy) mobile equipment were below typical previously recorded values: 300 tons per day (t/d). During December, small explosions were recorded by the seismic network and manifested as gas-and-steam emissions.

Gas-and-ash explosions in the crater occurred during January 2023, which were recorded by the seismic network. Sulfur dioxide values remained low, between 300-400 t/d through 10 March. At 0817 on 14 January a gas-and-ash emission was visible in webcam images, rising just above the crater rim. Some mornings during February, small gas-and-steam plumes were visible in the crater. On 7 March at 2252 MARN noted an increase in degassing from the central crater; gas emissions were constantly observed through the early morning hours on 8 March. During the early morning of 8 March through the afternoon on 9 March, 12 emissions were registered, some accompanied by ash. The last gas-and-ash emission was recorded at 1210 on 9 March; very fine ashfall was reported in El Tránsito (10 km S), La Morita (6 km W), and La Piedrita (3 km W). The smell of sulfur was reported in Piedra Azul (5 km SW). On 16 March MARN reported that gas-and-steam emissions decreased.

Low degassing and very low seismicity were reported during April; no explosions have been detected between 9 March and 27 May. The sulfur dioxide emissions remained between 350-400 t/d; during 13-20 April sulfur dioxide values fluctuated between 30-300 t/d. Activity remained low through most of May; on 23 May seismicity increased. An explosion was detected at 1647 on 27 May generated a gas-and-ash plume that rose 700 m high (figure 32); a decrease in seismicity and gas emissions followed. The DOAS station installed on the W flank recorded sulfur dioxide values that reached 400 t/d on 27 May; subsequent measurements showed a decrease to 268 t/d on 28 May and 100 t/d on 29 May.

Figure (see Caption) Figure 32. Webcam image of a gas-and-ash plume rising 700 m above San Miguel at 1652 on 27 May 2023. Courtesy of MARN.

Geologic Background. The symmetrical cone of San Miguel, one of the most active volcanoes in El Salvador, rises from near sea level to form one of the country's most prominent landmarks. A broad, deep, crater complex that has been frequently modified by eruptions recorded since the early 16th century caps the truncated unvegetated summit, also known locally as Chaparrastique. Flanks eruptions of the basaltic-andesitic volcano have produced many lava flows, including several during the 17th-19th centuries that extended to the N, NE, and SE. The SE-flank flows are the largest and form broad, sparsely vegetated lava fields crossed by highways and a railroad skirting the base of the volcano. Flank vent locations have migrated higher on the edifice during historical time, and the most recent activity has consisted of minor ash eruptions from the summit crater.

Information Contacts: Ministero de Medio Ambiente y Recursos Naturales (MARN), Km. 5½ Carretera a Nueva San Salvador, Avenida las Mercedes, San Salvador, El Salvador (URL: http://www.snet.gob.sv/ver/vulcanologia).


Semisopochnoi (United States) — June 2023 Citation iconCite this Report

Semisopochnoi

United States

51.93°N, 179.58°E; summit elev. 1221 m

All times are local (unless otherwise noted)


Occasional explosions, ash deposits, and gas-and-steam plumes during December 2022-May 2023

Semisopochnoi is located in the western Aleutians, is 20-km-wide at sea level, and contains an 8-km-wide caldera. The three-peaked Mount Young (formerly Cerberus) was constructed within the caldera during the Holocene. Each of these peaks contains a summit crater; the lava flows on the N flank appear younger than those on the S side. The current eruption period began in early February 2021 and has more recently consisted of intermittent explosions and ash emissions (BGVN 47:12). This report updates activity during December 2022 through May 2023 using daily, weekly, and special reports from the Alaska Volcano Observatory (AVO). AVO monitors the volcano using local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks.

Activity during most of December 2022 was relatively quiet; according to AVO no eruptive or explosive activity was observed since 7 November 2022. Intermittent tremor and occasional small earthquakes were observed in geophysical data. Continuous gas-and-steam emissions were observed from the N crater of Mount Young in webcam images on clear weather days (figure 25). On 24 December, there was a slight increase in earthquake activity and several small possible explosion signals were detected in infrasound data. Eruptive activity resumed on 27 December at the N crater of Mount Young; AVO issued a Volcano Activity Notice (VAN) that reported minor ash deposits on the flanks of Mount Young that extended as far as 1 km from the vent, according to webcam images taken during 27-28 December (figure 26). No ash plumes were observed in webcam or satellite imagery, but a persistent gas-and-steam plume that might have contained some ash rose to 1.5 km altitude. As a result, AVO raised the Aviation Color Code (ACC) to Orange (the second highest level on a four-color scale) and the Volcano Alert Level (VAL) to Watch (the second highest level on a four-level scale). Possible explosions were detected during 21 December 2022 through 1 January 2023 and seismic tremor was recorded during 30-31 December.

Figure (see Caption) Figure 25. Webcam image of a gas-and-steam plume rising above Semisopochnoi from Mount Young on 21 December 2022. Courtesy of AVO.
Figure (see Caption) Figure 26. Webcam image showing fresh ash deposits (black color) at the summit and on the flanks of Mount Young at Semisopochnoi, extending up to 1 km from the N crater. Image was taken on 27 December 2022. Image has been color corrected. Courtesy of AVO.

During January 2023 eruptive activity continued at the active N crater of Mount Young. Minor ash deposits were observed on the flanks, extending about 2 km SSW, based on webcam images from 1 and 3 January. A possible explosion occurred during 1-2 January based on elevated seismicity recorded on local seismometers and an infrasound signal recorded minutes later by an array at Adak. Though no ash plumes were observed in webcam or satellite imagery, a persistent gas-and-steam plume rose to 1.5 km altitude that might have carried minor traces of ash. Ash deposits were accompanied by periods of elevated seismicity and infrasound signals from the local geophysical network, which AVO reported were likely due to weak explosive activity. Low-level explosive activity was also detected during 2-3 January, with minor gas-and-steam emissions and a new ash deposit that was visible in webcam images. Low-level explosive activity was detected in geophysical data during 4-5 January, with elevated seismicity and infrasound signals observed on local stations. Volcanic tremor was detected during 7-9 January and very weak explosive activity was detected in seismic and infrasound data on 9 January. Weak seismic and infrasound signals were recorded on 17 January, which indicated minor explosive activity, but no ash emissions were observed in clear webcam images; a gas-and-steam plume continued to rise to 1.5 km altitude. During 29-30 January, ash deposits near the summit were observed on fresh snow, according to webcam images.

The active N cone at Mount Young continued to produce a gas-and-steam plume during February, but no ash emissions or explosive events were detected. Seismicity remained elevated with faint tremor during early February. Gas-and-steam emissions from the N crater were observed in clear webcam images on 11-13 and 16 February; no explosive activity was detected in seismic, infrasound, or satellite data. Seismicity has also decreased, with no significant seismic tremor observed since 25 January. Therefore, the ACC was lowered to Yellow (the second lowest level on a four-color scale) and the VAL was lowered to Advisory (the second lowest level on a four-color scale) on 22 February.

Gas-and-steam emissions persisted during March from the N cone of Mount Young, based on clear webcam images. A few brief episodes of weak tremor were detected in seismic data, although seismicity decreased over the month. A gas-and-steam plume detected in satellite data extended 150 km on 18 March. Low-level ash emissions from the N cone at Mount Young were observed in several webcam images during 18-19 March, in addition to small explosions and volcanic tremor. The ACC was raised to Orange and the VAL increased to Watch on 19 March. A small explosion was detected in seismic and infrasound data on 21 March.

Low-level unrest continued during April, although cloudy weather often obscured views of the summit; periods of seismic tremor and local earthquakes were recorded. During 3-4 April a gas-and-steam plume was visible traveling more than 200 km overnight; no ash was evident in the plume, according to AVO. A gas-and-steam plume was observed during 4-6 April that extended 400 km but did not seem to contain ash. Small explosions were detected in seismic and infrasound data on 5 April. Occasional clear webcam images showed continuing gas-and-steam emissions rose from Mount Young, but no ash deposits were observed on the snow. On 19 April small explosions and tremor were detected in seismic and infrasound data. A period of seismic tremor was detected during 22-25 April, with possible weak explosions on 25 April. Ash deposits were visible near the crater rim, but it was unclear if these deposits were recent or due to older deposits.

Occasional small earthquakes were recorded during May, but there were no signs of explosive activity seen in geophysical data. Gas-and-steam emissions continued from the N crater of Mount Young, based on webcam images, and seismicity remained slightly elevated. A new, light ash deposit was visible during the morning of 5 May on fresh snow on the NW flank of Mount Young. During 10 May periods of volcanic tremor were observed. The ACC was lowered to Yellow and the VAL to Advisory on 17 May due to no additional evidence of activity.

Geologic Background. Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island's northern part. The three-peaked Mount Cerberus (renamed Mount Young in 2023) was constructed within the caldera during the Holocene. Each of the peaks contains a summit crater; lava flows on the N flank appear younger than those on the south side. Other post-caldera volcanoes include the symmetrical Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented eruptions have originated from Young, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone could have been recently active.

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/).


Ebeko (Russia) — June 2023 Citation iconCite this Report

Ebeko

Russia

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

All times are local (unless otherwise noted)


Continued explosions, ash plumes, and ashfall during October 2022-May 2023

Ebeko, located on the N end of Paramushir Island in the Kuril Islands, consists of three summit craters along a SSW-NNE line at the northern end of a complex of five volcanic cones. Eruptions date back to the late 18th century and have been characterized as small-to-moderate explosions from the summit crater, accompanied by intense fumarolic activity. The current eruption period began in June 2022 and has recently consisted of frequent explosions, ash plumes, and thermal activity (BGVN 47:10). This report covers similar activity during October 2022 through May 2023, based on information from the Kamchatka Volcanic Eruptions Response Team (KVERT) and satellite data.

Activity during October consisted of explosive activity, ash plumes, and occasional thermal anomalies. Visual data by volcanologists from Severo-Kurilsk showed explosions producing ash clouds up to 2.1-3 km altitude which drifted E, N, NE, and SE during 1-8, 10, 16, and 18 October. KVERT issued several Volcano Observatory Notices for Aviation (VONA) on 7, 13-15, and 27 October 2022, stating that explosions generated ash plumes that rose to 2.3-4 km altitude and drifted 5 km E, NE, and SE. Ashfall was reported in Severo-Kurilsk (Paramushir Island, about 7 km E) on 7 and 13 October. Satellite data showed a thermal anomaly over the volcano on 15-16 October. Visual data showed ash plumes rising to 2.5-3.6 km altitude on 22, 25-29, and 31 October and moving NE due to constant explosions.

Similar activity continued during November, with explosions, ash plumes, and ashfall occurring. KVERT issued VONAs on 1-2, 4, 6-7, 9, 13, and 16 November that reported explosions and resulting ash plumes that rose to 1.7-3.6 km altitude and drifted 3-5 km SE, ESE, E, and NE. On 1 November ash plumes extended as far as 110 km SE. On 5, 8, 12, and 24-25 November explosions and ash plumes rose to 2-3.1 km altitude and drifted N and E. Ashfall was observed in Severo-Kurilsk on 7 and 16 November. A thermal anomaly was visible during 1-4, 16, and 20 November. Explosions during 26 November rose as high as 2.7 km altitude and drifted NE (figure 45).

Figure (see Caption) Figure 45. Photo of an ash plume rising to 2.7 km altitude above Ebeko on 26 November 2022. Photo has been color corrected. Photo by L. Kotenko, IVS FEB RAS.

Explosions and ash plumes continued to occur in December. During 1-2 and 4 December volcanologists from Severo-Kurilsk observed explosions that sent ash to 1.9-2.5 km altitude and drifted NE and SE (figure 46). VONAs were issued on 5, 9, and 16 December reporting that explosions generated ash plumes rising to 1.9 km, 2.6 km, and 2.4 km altitude and drifted 5 km SE, E, and NE, respectively. A thermal anomaly was visible in satellite imagery on 16 December. On 18 and 27-28 December explosions produced ash plumes that rose to 2.5 km altitude and drifted NE and SE. On 31 December an ash plume rose to 2 km altitude and drifted NE.

Figure (see Caption) Figure 46. Photo of an explosive event at Ebeko at 1109 on 2 December 2022. Photo has been color corrected. Photo by S. Lakomov, IVS FEB RAS.

Explosions continued during January 2023, based on visual observations by volcanologists from Severo-Kurilsk. During 1-7 January explosions generated ash plumes that rose to 4 km altitude and drifted NE, E, W, and SE. According to VONAs issued by KVERT on 2, 4, 10, and 23 January, explosions produced ash plumes that rose to 2-4 km altitude and drifted 5 km N, NE, E, and ENE; the ash plume that rose to 4 km altitude occurred on 10 January (figure 47). Satellite data showed a thermal anomaly during 3-4, 10, 13, 16, 21, 22, and 31 January. KVERT reported that an ash cloud on 4 January moved 12 km NE. On 6 and 9-11 January explosions sent ash plumes to 4.5 km altitude and drifted W and ESE. On 13 January an ash plume rose to 3 km altitude and drifted SE. During 20-24 January ash plumes from explosions rose to 3.7 km altitude and drifted SE, N, and NE. On 21 January the ash plume drifted as far as 40 km NE. During 28-29 and 31 January and 1 February ash plumes rose to 4 km altitude and drifted NE.

Figure (see Caption) Figure 47. Photo of a strong ash plume rising to 4 km altitude from an explosive event on 10 January 2023 (local time). Photo by L. Kotenko, IVS FEB RAS.

During February, explosions, ash plumes, and ashfall were reported. During 1, 4-5 and 7-8 February explosions generated ash plumes that rose to 4.5 km altitude and drifted E and NE; ashfall was observed on 5 and 8 February. On 6 February an explosion produced an ash plume that rose to 3 km altitude and drifted 7 km E, causing ashfall in Severo-Kurilsk. A thermal anomaly was visible in satellite data on 8, 9, 13, and 21 February. Explosions on 9 and 12-13 February produced ash plumes that rose to 4 km altitude and drifted E and NE; the ash cloud on 12 February extended as far as 45 km E. On 22 February explosions sent ash to 3 km altitude that drifted E. During 24 and 26-27 February ash plumes rose to 4 km altitude and drifted E. On 28 February an explosion sent ash to 2.5-3 km altitude and drifted 5 km E; ashfall was observed in Severo-Kurilsk.

Activity continued during March; visual observations showed that explosions generated ash plumes that rose to 3.6 km altitude on 3, 5-7, and 9-12 March and drifted E, NE, and NW. Thermal anomalies were visible on 10, 13, and 29-30 March in satellite imagery. On 18, 21-23, 26, and 29-30 March explosions produced ash plumes that rose to 2.8 km altitude and drifted NE and E; the ash plumes during 22-23 March extended up to 76 km E. A VONA issued on 21 March reported an explosion that produced an ash plume that rose to 2.8 km altitude and drifted 5 km E. Another VONA issued on 23 March reported that satellite data showed an ash plume rising to 3 km altitude and drifted 14 km E.

Explosions during April continued to generate ash plumes. On 1 and 4 April an ash plume rose to 2.8-3.5 km altitude and drifted SE and NE. A thermal anomaly was visible in satellite imagery during 1-6 April. Satellite data showed ash plumes and clouds rising to 2-3 km altitude and drifting up to 12 km SW and E on 3 and 6 April (figure 48). KVERT issued VONAs on 3, 5, 14, 16 April describing explosions that produced ash plumes rising to 3 km, 3.5 km, 3.5 km, and 3 km altitude and drifting 5 km S, 5 km NE and SE, 72 km NNE, and 5 km NE, respectively. According to satellite data, the resulting ash cloud from the explosion on 14 April was 25 x 7 km in size and drifted 72-104 km NNE during 14-15 April. According to visual data by volcanologists from Severo-Kurilsk explosions sent ash up to 3.5 km altitude that drifted NE and E during 15-16, 22, 25-26, and 29 April.

Figure (see Caption) Figure 48. Photo of an ash cloud rising to 3.5 km altitude at Ebeko on 6 April 2023. The cloud extended up to 12 km SW and E. Photo has been color corrected. Photo by L. Kotenko, IVS FEB RAS.

The explosive eruption continued during May. Explosions during 3-4, 6-7, and 9-10 May generated ash plumes that rose to 4 km altitude and drifted SW and E. Satellite data showed a thermal anomaly on 3, 9, 13-14, and 24 May. During 12-16, 23-25, and 27-28 May ash plumes rose to 3.5 km altitude and drifted in different directions due to explosions. Two VONA notices were issued on 16 and 25 May, describing explosions that generated ash plumes rising to 3 km and 3.5 km altitude, respectively and extending 5 km E. The ash cloud on 25 May drifted 75 km SE.

Thermal activity in the summit crater, occasionally accompanied by ash plumes and ash deposits on the SE and E flanks due to frequent explosions, were visible in infrared and true color satellite images (figure 49).

Figure (see Caption) Figure 49. Infrared (bands B12, B11, B4) and true color satellite images of Ebeko showing occasional small thermal anomalies at the summit crater on 4 October 2022 (top left), 30 April 2023 (bottom left), and 27 May 2023 (bottom right). On 1 November (top right) ash deposits (light-to-dark gray) were visible on the SE flank. An ash plume drifted NE on 30 April, and ash deposits were also visible to the E on both 30 April and 27 May. Courtesy of Copernicus Browser.

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

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Home Reef (Tonga) — June 2023 Citation iconCite this Report

Home Reef

Tonga

18.992°S, 174.775°W; summit elev. -10 m

All times are local (unless otherwise noted)


Discolored plumes continued during November 2022-April 2023

Home Reef is a submarine volcano located in the central Tonga islands between Lateiki (Metis Shoal) and Late Island. The first recorded eruption occurred in the mid-19th century, when an ephemeral island formed. An eruption in 1984 produced a 12-km-high eruption plume, a large volume of floating pumice, and an ephemeral island 500 x 1,500 m wide, with cliffs 30-50 m high that enclosed a water-filled crater. Another island-forming eruption in 2006 produced widespread pumice rafts that drifted as far as Australia; by 2008 the island had eroded below sea level. The previous eruption occurred during October 2022 and was characterized by a new island-forming eruption, lava effusion, ash plumes, discolored water, and gas-and-steam plumes (BGVN 47:11). This report covers discolored water plumes during November 2022 through April 2023 using satellite data.

Discolored plumes continued during the reporting period and were observed in true color satellite images on clear weather days. Satellite images show light green-yellow discolored water extending W on 8 and 28 November 2022 (figure 31), and SW on 18 November. Light green-yellow plumes extended W on 3 December, S on 13 December, SW on 18 December, and W and S on 23 December (figure 31). On 12 January 2023 discolored green-yellow plumes extended to the NE, E, SE, and N. The plume moved SE on 17 January and NW on 22 January. Faint discolored water in February was visible moving NE on 1 February. A discolored plume extended NW on 8 and 28 March and NW on 13 March (figure 31). During April, clear weather showed green-blue discolored plumes moving S on 2 April, W on 7 April, and NE and S on 12 April. A strong green-yellow discolored plume extended E and NE on 22 April for several kilometers (figure 31).

Figure (see Caption) Figure 31. Visual (true color) satellite images showing continued green-yellow discolored plumes at Home Reef (black circle) that extended W on 28 November 2022 (top left), W and S on 23 December 2022 (top right), NW on 13 March 2023 (bottom left), and E and NE on 22 April 2023 (bottom right). Courtesy of Copernicus Browser.

Geologic Background. Home Reef, a submarine volcano midway between Metis Shoal and Late Island in the central Tonga islands, was first reported active in the mid-19th century, when an ephemeral island formed. An eruption in 1984 produced a 12-km-high eruption plume, large amounts of floating pumice, and an ephemeral 500 x 1,500 m island, with cliffs 30-50 m high that enclosed a water-filled crater. In 2006 an island-forming eruption produced widespread dacitic pumice rafts that drifted as far as Australia. Another island was built during a September-October 2022 eruption.

Information Contacts: Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Ambae (Vanuatu) — June 2023 Citation iconCite this Report

Ambae

Vanuatu

15.389°S, 167.835°E; summit elev. 1496 m

All times are local (unless otherwise noted)


New lava flow, ash plumes, and sulfur dioxide plumes during February-May 2023

Ambae, also known as Aoba, is a large basaltic shield volcano in Vanuatu. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas. Periodic phreatic and pyroclastic explosions have been reported since the 16th century. A large eruption more than 400 years ago resulted in a volcanic cone within the summit crater that is now filled by Lake Voui; the similarly sized Lake Manaro fills the western third of the caldera. The previous eruption ended in August 2022 that was characterized by gas-and-steam and ash emissions and explosions of wet tephra (BGVN 47:10). This report covers a new eruption during February through May 2023 that consisted of a new lava flow, ash plumes, and sulfur dioxide emissions, using information from the Vanuatu Meteorology and Geo-Hazards Department (VMGD) and satellite data.

During the reporting period, the Alert Level remained at a 2 (on a scale of 0-5), which has been in place since December 2021. Activity during October 2022 through March 2023 remained relatively low and mostly consisted of gas-and-steam emissions in Lake Voui. VMGD reported that at 1300 on 15 November a satellite image captured a strong amount of sulfur dioxide rising above the volcano (figure 99), and that seismicity slightly increased. The southern and northern part of the island reported a strong sulfur dioxide smell and heard explosions. On 20 February 2023 a gas-and-ash plume rose 1.3 km above the summit and drifted SSW, according to a webcam image (figure 100). Gas-and-steam and possibly ash emissions continued on 23 February and volcanic earthquakes were recorded by the seismic network.

Figure (see Caption) Figure 99. Satellite image of the strong sulfur dioxide plume above Ambae taken on 15 November 2022. The Dobson Units (DU) exceeded 12. Courtesy of VMGD.
Figure (see Caption) Figure 100. Webcam image of a gas-and-ash plume rising above Ambae at 1745 on 20 February 2023. The plume drifted SSW. Courtesy of VMGD.

During April, volcanic earthquakes and gas-and-steam and ash emissions were reported from the cone in Lake Voui. VMGD reported that activity increased during 5-7 April; high gas-and-steam and ash plumes were visible, accompanied by nighttime incandescence. According to a Wellington VAAC report, a low-level ash plume rose as high as 2.5 km above the summit and drifted W and SW on 5 April, based on satellite imagery. Reports in Saratamata stated that a dark ash plume drifted to the WSW, but no loud explosion was heard. Webcam images from 2100 showed incandescence above the crater and reflected in the clouds. According to an aerial survey, field observations, and satellite data, water was no longer present in the lake. A lava flow was reported effusing from the vent and traveling N into the dry Lake Voui, which lasted three days. The next morning at 0745 on 6 April a gas-and-steam and ash plume rose 5.4 km above the summit and drifted ESE, based on information from VMGD (figure 101). The Wellington VAAC also reported that light ashfall was observed on the island. Intermittent gas-and-steam and ash emissions were visible on 7 April, some of which rose to an estimated 3 km above the summit and drifted E. Webcam images during 0107-0730 on 7 April showed continuing ash emissions. A gas-and-steam and ash plume rose 695 m above the summit crater at 0730 on 19 April and drifted ESE, based on a webcam image (figure 102).

Figure (see Caption) Figure 101. Webcam image showing a gas-and-ash plume rising 5.4 km above the summit of Ambae at 0745 on 6 April 2023. Courtesy of VMGD.
Figure (see Caption) Figure 102. Webcam image showing a gas-and-ash plume rising 695 m above the summit of Ambae at 0730 on 19 April 2023. Courtesy of VMGD.

According to visual and infrared satellite data, water was visible in Lake Voui as late as 24 March 2023 (figure 103). The vent in the caldera showed a gas-and-steam plume drifted SE. On 3 April thermal activity was first detected, accompanied by a gas-and-ash plume that drifted W (figure 103). The lava flow moved N within the dry lake and was shown cooling by 8 April. By 23 April much of the water in the lake had returned. Occasional sulfur dioxide plumes were detected by the TROPOMI instrument on the Sentinel-5P satellite that exceeded 2 Dobson Units (DU) and drifted in different directions (figure 104).

Figure (see Caption) Figure 103. Satellite images showing both visual (true color) and infrared (bands B12, B11, B4) views on 24 March 2023 (top left), 3 April 2023 (top left), 8 April 2023 (bottom left), and 23 April 2023 (bottom right). In the image on 24 March, water filled Lake Voui around the small northern lake. A gas-and-steam plume drifted SE. Thermal activity (bright yellow-orange) was first detected in infrared data on 3 April 2023, accompanied by a gas-and-ash plume that drifted W. The lava flow slowly filled the northern part of the then-dry lake and remained hot on 8 April. By 23 April, the water in Lake Voui had returned. Courtesy of Copernicus Browser.
Figure (see Caption) Figure 104. Images showing sulfur dioxide plumes rising from Ambae on 26 December 2022 (top left), 25 February 2023 (top right), 23 March 2023 (bottom left), and 5 April 2023 (bottom right), as detected by the TROPOMI instrument on the Sentinel-5P satellite. These plumes exceeded at least 2 Dobson Units (DU) and drifted in different directions. Courtesy of the NASA Global Sulfur Dioxide Monitoring Page.

Geologic Background. The island of Ambae, also known as Aoba, is a massive 2,500 km3 basaltic shield that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW-trending rift zone with numerous scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. That large central edifice is also called Manaro Voui or Lombenben volcano. Post-caldera explosive eruptions formed the summit craters about 360 years ago. A tuff cone was constructed within Lake Voui (or Vui) about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast.

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD), Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); Wellington Volcanic Ash Advisory Centre (VAAC), Meteorological Service of New Zealand Ltd (MetService), PO Box 722, Wellington, New Zealand (URL: http://www.metservice.com/vaac/, http://www.ssd.noaa.gov/VAAC/OTH/NZ/messages.html); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).

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Bulletin of the Global Volcanism Network - Volume 36, Number 08 (August 2011)

Managing Editor: Richard Wunderman

Changbaishan (China-North Korea)

Observatory notes high seismicity during mid-2002 to mid-2005

Cleveland (United States)

Dome growth during August-September 2011 seen evolving in radar data

Dukono (Indonesia)

Continued frequent minor ash plume at least as late as 13 September 2011

Ibu (Indonesia)

Frequent minor white-to-gray plumes and small avalanches

Krakatau (Indonesia)

2009-2011 eruptive phases; magma plumbing; date of ancestral eruption

Soufriere Hills (United Kingdom)

Extrusive pause follows 11 February 2010 partial dome collapse

Tambora (Indonesia)

Increased seismicity and minor steam venting in 2011

Tinakula (Solomon Islands)

MODVOLC thermal alerts extend through September 2011



Changbaishan (China-North Korea) — August 2011 Citation iconCite this Report

Changbaishan

China-North Korea

41.98°N, 128.08°E; summit elev. 2744 m

All times are local (unless otherwise noted)


Observatory notes high seismicity during mid-2002 to mid-2005

At the 25th General Assembly of the International Union of Geodesy and Geophysics (IUGG), the Chinese National Committee released an overview of data on Chinese volcanoes, especially Changbaishan volcano (figure 3), which they considered the most dangerous and the most likely to erupt (Fan and others, 2011; Liu and others 2011). Focusing on Changbaishan volcano and its summit caldera called Tianchi, Tianchi Volcano Observatory (TVO) released data collected since it formed in 1999. This report will summarize both the TVO's monitoring network and their findings from 1999 to 2010, focusing on the seismic crisis during mid-2002 to mid-2005. As clarification, the name Tianchi is used to refer to the ~ 5 km diameter summit caldera vent of the volcanic complex, and the name Changbaishan is used to refer to the complex in general. The latter name has many synonyms, including Baegdu, Baekdoosan, Baitoushan, Chang-pai-shan, Hakuto, and P'aektu-san.

Figure (see Caption) Figure 3. Geographic position of Changbaishan volcano, situated on the border between China and North Korea. Adapted from Machida and Arai (1983).

To continuously monitor seismicity, TVO's Changbaishan volcano center was built in the highlands 40 km from the volcano, and five, two, and four seismic stations were installed within 15, 25, and 50 km of the volcano, respectively. Liu and others (2011) report that TVO's system "can detect M 0.1 volcanic events and give the [detailed] location of M 1.0 and larger volcanic events."

Seismic crisis. Our previous report on Changbaishan briefly discussed an increase in seismicity centered at the volcano in 2003 (BGVN 35:08). Figure 4 and table 1 illustrate that the increased seismicity occurred both in terms of the magnitude and the number of seismic events recorded. A histogram of the annual number of earthquakes from 2002 through 2005 shows a peak in 2003. M 2 and larger earthquakes became common in 2002, and peaked in late 2004. Note that tectonic earthquakes of M 4.4 and 4.0 occurred on 17 December 2004 and 15 April 2005, respectively, and are not related to this trend or Tianchi volcano (Liu and others, 2011). Following the seismic crisis, the number of earthquakes declined slowly, reaching background levels by 2006 (Liu and others, 2011). Liu and others (2011) break the seismic data into three periods over the TVO monitoring history (table 1). As is common with earthquakes at volcanoes around the world, seismic activity at Changbaishan often occurred in swarms, especially from 2002 to 2003, when hundreds of seismic events were sometimes recorded within a single day (figure 4, table 1).

Figure (see Caption) Figure 4. Time distribution of seismic events recorded at Tianchi volcano (Changbaishan) from mid-1999 to mid-2010. Top plot indicates magnitude of each seismic event; bottom plot indicates number of seismic events per year. From Liu and others (2011).

Table 1. Tianchi volcano observatory (TVO) detected three distinct seismic episodes. * = Not including tectonic earthquakes of M 4.4 and 4.0 that occurred on 17 December 2004 and 15 April 2005, respectively. From Liu and others (2011).

Date Range Activity Max. Magnitude Number of events/time period
1999-Jun 2002 Background 1.5 Under 12/month.
Jul 2002-Jul 2005 Peak (crisis) 3.7* Over 100/day, in a series of swarms.
Aug 2005-present Recovery -- Under 12/month, generally.

The hypocenters of earthquakes occurring at Changbaishan, and specifically the Tianchi caldera, were calculated from 2001 to present (figure 5). The majority of the earthquakes originated within 3 km of the Tianchi caldera rim (map distance), and within 5 km depth from the caldera rim.

Figure (see Caption) Figure 5. Calculated hypocenters for earthquakes occuring at Changbaishan volcano since 2002. (Top) plan-view distribution: triangles are seismic stations, red circles are hypocenters. (Bottom) depth distribution: colors from green to red indicate increasing depth (0 = sea level). Most earthquakes originated directly under the Tianchi caldera, within 5 km of the surface. From Liu and others (2011).

Coinciding with the increased seismic activity from July 2002 to July 2005, the ground deformation of Changbaishan also entered into a period of inflation, as measured by GPS instruments (figure 6). Horizontal displacement reached a maximum of 4 cm between 2002 and 2003, and continued on a declining trend (figure 6; Liu and others, 2011). Similarly, vertical displacement reached a maximum of 38.6 mm between 2002 and 2003, and declined in the following years; a cumulative vertical displacement of 68.12 mm was measured from 2002 to 2005 (Liu and others, 2011). Vertical displacements of the N and W slopes of the volcano (measured once per year from 2006 to 2009) are presented in table 2.

Figure (see Caption) Figure 6. Horizontal displacement from GPS surveys from 2000 to 2007, showing inflation at Tianchi caldera of Changbaishan volcano. Reference arrow at the top of each frame is 10 mm/yr. From Liu and others (2011).

Table 2. Vertical displacement measurements of the N and W slopes of Changbaishan, measured once per year from 2006 through 2009. From Liu and others (2011).

Year Slope Elevation (mm) Difference from previous year (mm)
2006 North 901140.05 --
2007 North 901148.20 8.15
2008 North 901149.26 1.06
2009 North 901151.70 2.44
 
2006 West 1084636.20 --
2007 West 1084661.54 25.34
2008 West 1084659.21 -2.33
2009 West 1084653.77 -5.44

Magma source of Changbaishan. TVO monitored the gas flux of (among others) CO2, N2, He, H2, O2, and CH4, as well as the temperature of hot springs as a supplementary data set. Of particular interest is the measured helium (He) isotopic ratio, 3He/4He. The isotope 3He is often considered primordial. The concentration of 3He on Earth is considered to be essentially stable; the majority of 3He on Earth was trapped upon the formation of the Earth. 4He is a product of the alpha decay of heavy elements in the Earth's crust, and is still produced on Earth by alpha-particle emissions from heavy elements that have differentiated into the Earth's crust and then escape into the atmosphere. The mantle is depleted (relative to the crust and atmosphere) in 4He. 3He/4He ratios (R) of volcanic gases are compared with the common atmospheric 3He/4He ratio (Ra). If volcanic gases provide a particularly high R value (e.g., R = 5, or 5 Ra, indicating values 5 times the atmospheric 3He/4He ratio), then they are considered to be of mantle origin (i.e., depleted in 4He). Liu and others (2011) reported an average 3He/4He value of 5.61 Ra, and concluded that the gases being monitored are mantle sourced.

Liu and others (2011) also reported that He and H2 gas flux increased significantly in 2003 and 2004, associated with the above-mentioned increased volcano-seismicity of July 2002 to July 2005. They also reported He and H2 gas flux increases in October and November 2006, again associated with volcano-seismicity (as well as an M 2.6 tectonic earthquake on 11 November 2006).

From fluid geochemistry measurements, Liu and others (2011) reported that H2S and SO2 fluxes are low but suggested monitoring should increase in the event that the measured values increase.

References. Fan, Q., Sui, J., Zhao, Y., Li, N., and Sun, Q., 2011, Recent progress in active volcanoes in China, in China National Report on Volcanology and Chemistry of the Earth's Interior, for the 25th General Assembly of IUGG, Melbourne, Australia, 28 June-7 July 2011 (prepared by the Chinese National Committee for the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI)), pgs. 15-18.

Liu, G., Yang, J., Wang, L., and Sun, J., 2011, The active level analysis of Changbaishan volcano, in China National Report on Volcanology and Chemistry of the Earth's Interior, for the 25th General Assembly of IUGG, Melbourne, Australia, 28 June - 7 July 2011 (prepared by the Chinese National Committee for the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI)), pgs. 19-43.

Machida, H., and Arai, F., 1983, Extensive ash falls in and around the Sea of Japan from large late Quaternary eruptions, Journal of Volcanology and Geothermal Research, v. 18, p. 151-164.

Geologic Background. Massive Changbaishan stratovolcano (also known as Baitoushan and by the Korean names of Baegdu, Paektu, or P'aektu-san), is located along the China/Korea border. A 5-km-wide, 850-m-deep summit caldera is filled by Lake Tianchi (Sky Lake). The 60-km-diameter dominantly trachytic and rhyolitic volcano was constructed over the Changbaishan (Laoheidingzi) shield volcano. Satellitic cinder cones are aligned along a NNE trend. One of the largest known Holocene explosive eruptions took place here about 946 CE, depositing tephra as far away as northern Japan and forming in part the present caldera; Yang et al. (2021) estimated the total erupted volume to be 40-98 km3. Minor eruptions have been recorded since the 15th century.

Information Contacts: Changbaishan Tianchi Volcano Observatory (TVO), Antu 133613, China.


Cleveland (United States) — August 2011 Citation iconCite this Report

Cleveland

United States

52.825°N, 169.944°W; summit elev. 1730 m

All times are local (unless otherwise noted)


Dome growth during August-September 2011 seen evolving in radar data

Figure 10 shows the location of Cleveland volcano, the scene of significant changes in dome morphology in August and September 2011. On 31 March 2011 the Alaska Volcano Observatory (AVO) lowered the Volcano Alert Level and the Aviation Color Code for Cleveland to Unassigned, noting that no eruptive activity had been confirmed during the previous few months (BGVN 36:05). Cleveland lacks a real-time seismic network, which means AVO cannot track local earthquakes and estimate volcanic unrest. AVO notes that short-lived explosions with ash clouds that could exceed 6.1 km altitude can occur without warning and may go undetected on satellite imagery for hours. Low-level ash emissions at Cleveland occur frequently and do not necessarily mean a larger eruption is imminent. AVO continues to monitor the volcano using satellite imagery.

Figure (see Caption) Figure 10. Location of Cleveland volcano and other Aleutian volcanoes with respect to nearby cities and towns. Map created by Janet Schaefer and provided courtesy of AVO and the Alaska Division of Geological & Geophysical Surveys (ADGGS).

AVO reported that on 20 July 2011 the Volcano Alert Level for Cleveland was raised to Advisory, and the Aviation Color Code was raised to Yellow due to thermal anomalies visible in satellite imagery during 19-20 and 22 July 2011. Cloud cover prevented observations during 21 and 23-26 July.

During the week of 25-31 July 2011 elevated but weak thermal anomalies were observed in satellite images of during periods of clear weather. AVO found no evidence of ash emissions or eruptive activity. Observations on 29 July 2011 showed a small lava dome ~ 40 m in diameter in the summit crater, apparently formed since 19 July based on measured thermal anomalies. Observations on 2 August revealed growth of the lava dome from ~40 to 50 m in diameter. In response, AVO raised the Aviation Color Code to Orange and the Alert Level to Watch.

An animated sequence of satellite radar images revealed what was hard to see through persistent weather clouds. They portrayed dynamic growth of the lava dome during early August through at least late September 2011 (figure 11).

Figure (see Caption) Figure 11. A sequence of satellite radar images showing Cleveland volcano's summit crater and growth of its lava dome for 7, 18, and 29 August, and 9 and 20 September 2011. The radar data are from the TerraSAR-X sensor (wavelength 31 mm, frequency 9.6 GHz). The summit crater is ~ 200 m across. Note that satellite radar images have inherent topographic distortion (eg. foreshortening and layover) due to the manner in which they are collected. Image copyrighted in 2011 by the German Remote Sensing Data Center (DFD) and German Aerospace Center (DLR). Provided courtesy of Dave Schneider and Zhong Lu (Alaska Volcano Observatory, AVO) and the U.S. Geological Survey (USGS).

AVO reported weak thermal anomalies in satellite imagery during 2-3, 5, 7-9, and 13-14 August when cloud cover was limited or absent. They noted that a scientist flying N of the volcano on 14 August observed small white puffs of steam rising 30-60 m above the summit, even though most of the volcano was obscured by clouds.

During 17-23 August cloud cover over Cleveland prevented observations of the summit crater. On 21 August AVO noted that a weak, 1-pixel thermal anomaly was observed in a recent satellite view during a cloud break. On 30 August 2011, satellite observations during the previous two weeks indicated a pause in lava-dome growth. AVO lowered the Volcano Alert Level to Advisory and the Aviation Color Code to Yellow. Cloud cover prevented views of the summit crater during 31 August-2 September, but a thermal anomaly at the summit was observed during 3-5 September.

Observations on 6-7 September 2011 indicated that the lava dome had resumed growth (figure 11), reaching 120 m in diameter and filling the floor of the crater. AVO again raised the Volcano Alert Level to Watch and the Aviation Color Code to Orange. Although cloud cover often prevented observations of Cleveland during 7-12 September, a thermal anomaly on the lava dome was visible during 8-9 and 12 September, and a possible anomaly was visible on 10 September. These anomalies suggested that lava-dome growth was continuing, although no activity was observed in partly cloudy satellite images during 12-17 September. During 17-18 September a thermal anomaly was detected in imagery.

A report on 20 September noted that recent observations revealed the lava dome had grown to ~165 m in diameter. The dome remained contained within the ~ 200-m-diameter crater at Cleveland's summit, having advanced to ~ 20 m below the E crater rim.

During 20-22 September no observations of elevated surface temperatures or ash emissions from Cleveland were visible in partly cloudy satellite images. Elevated surface temperatures were observed in satellite images during 23-24 September, suggesting that the lava dome eruption was continuing. On 24-25 September 2011 elevated surface temperatures were absent in several clear satellite images. Cloud cover prevented observations on 26 September. Satellite views detected continued elevated summit temperatures over the period 27-28 September 2011. Satellite data also suggested ongoing eruption as the lava dome continued growing.

Geologic Background. The beautifully symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited Chuginadak Island. It lies SE across Carlisle Pass strait from Carlisle volcano and NE across Chuginadak Pass strait from Herbert volcano. Joined to the rest of Chuginadak Island by a low isthmus, Cleveland is the highest of the Islands of the Four Mountains group and is one of the most active of the Aleutian Islands. The native name, Chuginadak, refers to the Aleut goddess of fire, who was thought to reside on the volcano. Numerous large lava flows descend the steep-sided flanks. It is possible that some 18th-to-19th century eruptions attributed to Carlisle should be ascribed to Cleveland (Miller et al., 1998). In 1944 it produced the only known fatality from an Aleutian eruption. Recent eruptions have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey (USGS), 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: http://www.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 (ADGGS), 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://www.dggs.alaska.gov/).


Dukono (Indonesia) — August 2011 Citation iconCite this Report

Dukono

Indonesia

1.6992°N, 127.8783°E; summit elev. 1273 m

All times are local (unless otherwise noted)


Continued frequent minor ash plume at least as late as 13 September 2011

Frequent minor ash plumes have occurred at Dukono (see figure 4) since before July 2008 (BGVN 33:08, 33:11, 35:04, and 36:03). This report covers the time period subsequent to our previous report, which ended on 4 April 2011 (BGVN 36:03), through 13 September 2011. The Darwin Volcanic Ash Advisory Centre (VAAC) has provided continuous monitoring of the activity through satellite surveillance (table 12) during this time period.

Figure (see Caption) Figure 4. Map showing Dukono volcano, on the island of Halmahera, Indonesia. Courtesy of Google Maps (prepared by GVP editor Jeff Jessens).

Table 12. Ash plumes from Dukono detected in satellite images between 21 April 2011 and 13 September 2011. Each date or date range represents at least one plume. No plumes were reported between the end of the table in our previous report (4 April 2011) and 21 April 2011. Data from the Darwin Volcanic Ash Advisory Centre.

Date (UTC) Plume Altitude Plume Direction Plume Distance
21 Apr-22 Apr 2011 2.1 km NE and E Up to 85 km
28 Apr-02 May 2011 4.3 km NW, W, and SW 55-150 km
10 May-12 May 2011 4.3 km NE and E 75-110 km
16 May 2011 3 km E Over 90 km
19 May 2011 3 km NE 110 km
01 Jun 2011 3 km NE 110 km
01 Jul 2011 3 km E 110 km
06 Jul-07 Jul 2011 3 km NW 55 km
11 Aug 2011 3 km Various 14-93 km
14 Aug 2011 3 km NW 93 km
18 Aug-21 Aug 2011 3 km N and NE 110-150 km
13 Sep 2011 3 km NW 75 km

According to a news article (Metro TV News), seismic activity increased in August 2011. On 11 August, ash explosions were audible within a radius of about 7 km from the base of the volcano. Ash was ejected as high as 1 km above the crater, producing plumes that drifted E and S, and also approached Tobelo City (14 km ENE). The news article noted that seismographs at the Dukono observation post had recorded more than 100 eruption earthquakes during this time.

A news report posted on the web (YouTube, 2011) discussed an eruption at Dukono during first half of September 2011. The commentator spoke in Indonesian. The video shows a large column of ash rising what appears to be on the order of one or a few kilometers above the crater. This news report was discussed elsewhere as well on the web.

During this reporting period (21 April 2011 to 13 September 2011), there were no thermal alerts derived from the Hawai'i Institute of Geophysics and Planetology Thermal Alerts System (MODVOLC). The most recent MODVOLC thermal alert was on 20 November 2010.

Reference. YouTube (2011), Gunung Dukono letusan, Leputan 6.com, uploaded by szbrnr on 7 September 2011 (URL: http://www.youtube.com/watch?v=mb3We1MwXdg).

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

Information Contacts: 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/); Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Metro TV News (URL: http://www.metrotvnews.com).


Ibu (Indonesia) — August 2011 Citation iconCite this Report

Ibu

Indonesia

1.488°N, 127.63°E; summit elev. 1325 m

All times are local (unless otherwise noted)


Frequent minor white-to-gray plumes and small avalanches

Ibu (figure 9) has been intermittently active since 1998. Small explosions were noted during 2009 through January 2010 (BGVN 35:05). This report discuss seismic events from January 2011 to September 2011.

Figure (see Caption) Figure 9. Map showing Ibu volcano, on the island of Halmahera, Indonesia. Courtesy of Google Maps (prepared by GVP editor Jeff Jessens).

According to the Center of Volcanology and Geological Hazard Mitigation (CVGHM), during January 2011 to 8 September 2011, white-to-gray plumes rose 200-400 m above the craters. For 2011, CVGHM reported seismically detected avalanches, which on average occurred 45 times/day during January-April, 60 times/day during May-July, and 46 times/day during the first week of September. During much of 2011 seismicity fluctuated, but decreased towards September, prompting CVGHM to lower the Alert Level to 2 (on a scale of 1-4) on 8 September.

On 20 August 2011, observers from the nearby villages of Goin (exact location undisclosed) and Duono (5 km NW of Ibu) noted multiple eruptions from the S, E, and N craters. Plumes rose 50-250 m above the craters and an avalanche traveled 300 m in undisclosed direction.

During 2010, MODVOLC thermal alerts appeared about once per week on average, whereas, during 1 January 2011 through 13 September 2011, these alerts only appeared about once every 2.4 weeks on average. (Those alerts are derived from satellite data collected by the MODIS instrument and processed by the Hawai'i Institute of Geophysics and Planetology.)

Geologic Background. The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, has contained several small crater lakes. The 1.2-km-wide outer crater is breached on the N, creating a steep-walled valley. A large cone grew ENE of the summit, and a smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. The first observed and recorded eruption was a small explosion from the summit crater in 1911. Eruptive activity began again in December 1998, producing a lava dome that eventually covered much of the floor of the inner summit crater along with ongoing explosive ash emissions.

Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Saut Simatupang, 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/); Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).


Krakatau (Indonesia) — August 2011 Citation iconCite this Report

Krakatau

Indonesia

6.1009°S, 105.4233°E; summit elev. 285 m

All times are local (unless otherwise noted)


2009-2011 eruptive phases; magma plumbing; date of ancestral eruption

Anak Krakatau (the active post-collapse cone of Krakatau volcano, figure 23) began another eruptive [period] around 25 October 2010, characterized by up to hundreds of explosions per day (e.g., 251 explosions during 31 October-1 November 2010 as noted in the Jakarta Post). In November 2010, Arnold Binas documented explosive activity, ballistic bombs, column collapse generating pyroclastic flows, and volcanic lightning... (figure 24).

Figure (see Caption) Figure 23. Topography and bathymetry of the Sunda Arc showing several noteworthy features including Krakatau. Inset shows the active Anak Krakatau, a comparatively small island. The star symbol shows the location of the Great Sumatran Earthquake of 2004. Adapted from Jaxybulatov and others (2011).
Figure (see Caption) Figure 24. Photographs of explosive activity at Anak Krakatau during November 2010, within approximately one month of the onset of the eruptive phase beginning around 25 October 2010. (top) An explosive plume and column collapse generating a pyroclastic flow (note the material falling from the plume). (bottom) An explosion at night, capturing the parabolic arcs of red, glowing bombs thrown from the crater and the brilliant white tracks of lightning. Courtesy of Arnold Binas.

According to the Center for Volcanology and Geological Hazard Mitigation (CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC), ash plumes reached heights of 2.4 km altitude on 24 December 2010 and 12 January 2011; on 15 January 2011, an ash plume reached 3 km altitude. Ashfall in early January 2011 covered the solar panels running seismometers monitoring Anak Krakatau, rendering them inoperative until rainfall cleared the ash from the solar panels. Following the seismometer failure and amid continued activity of the volcano, the South Lampung Disaster Mitigation Agency (BPBD) ordered the evacuation of seven districts (of the 17 districts of South Lampung Regency) on 11 January 2011 (Jakarta Post).

In March 2011, the activity at Anak Krakatau decreased and the eruption was considered to be over. According to a local news service (TO:DAY), the head of the Anak Krakatau monitoring post reported that in the previous month, volcanic earthquakes became fewer and at greater focal depths. They had ranged from a high of 500-600 shallow earthquakes per day, declining to dozens per day in March 2011. The eruptive pause lasted, at most, until 31 July 2011 when NASA's Earth Observing-1 (EO-1) satellite observed a diffuse plume drifting W (figure 25).

Figure (see Caption) Figure 25. Natural color satellite image of a diffuse plume drifting W from Anak Krakatau on 31 July 2011. Image acquired by NASA's Earth Observing-1 (EO-1) satellite. Courtesy of NASA Earth Observatory.

In August, Andi Rosadi reported on the Volcano Discovery website that the seismometer monitoring Anak Krakatau was again damaged by explosions venting from the summit crater, noting "many quite big new bombs around the old crater." CVGHM reported that GPS measurement stations had been damaged as well. Rosadi also described and photographed large areas of incandescence within the summit crater on 8 August 2011, reporting a lava dome or "dry lava lake glowing in the central crater" (figure 26). The Volcano Discovery website noted that on 6 September 2011, Chris Weber reported fire fountaining reaching ~10 m high.

Figure (see Caption) Figure 26. Incandescence within the summit crater of Anak Krakatau seen from similar perspectives on 8 August 2011, at 1731 (top), and at 1830 (bottom). Courtesy of Andi Rosadi, Volcano Discovery.

On 30 September, CVGHM reported that the seismometers were again operational following 18 September, and increased the Alert Level from 2 to 3 (on a scale from 1 to 4), citing visual and seismic observations. Visually, while no ash producing eruptions had occurred from 14-30 September, CVGHM reported that the E flank of the volcano was covered in solfataras, with thin gusts of smoke within the crater and along crater walls. They also reported vibration in the body of the volcano within distances of 700 m from the summit. Seismically, from 18-30 September, CVGHM reported persistent volcanic earthquakes (volcanic earthquake swarms), noting that volcanic earthquakes had reached a level of 4-5 events per minute. As of 3 October, the Alert Level remained at 3, and residents and tourists were prohibited within 2 km of the crater.

Plumbing of the Krakatau system.Three recent publications addressed magma generation and plumbing of the Krakatau system from different disciplinary approaches. Employing mineral-melt equilibria thermo-barometry on Krakatau's phenocryst phases of clinopyroxene and plagioclase, Dahren and others (2010) demonstrated that clinopyroxene crystallizes at 8-12 km depth, while plagioclase crystallizes at 4-6 km depth. The two crystallization depth ranges could suggest multiple magma storage regions in the Krakatau system. They also noted that clinopyroxenes erupted before 1981 recorded deeper crystallization (and thus storage) - depths of 8-22 km - indicating a shallowing of the plumbing system over the last ~ 40 years.

From seismic tomography and inversion, Jaxybulatov and others (2011) reported a multi-layered structure beneath the Krakatau system (figure 27). They found their model similar to the one noted above (Dahren and others, 2010). They also reported that the deep-focus earthquakes they studied (100-160 km focal depths) were likely related to phase transitions and fluid fluxes in the subducting slab. They suggested these could lead to diapirism and formation of magma chambers in the overlying mantle wedge and crust.

Figure (see Caption) Figure 27. Interpretive model of Jaxybulatov and others (2011) highlighting multiple storage chambers and depths of the Krakatau magmatic system. Petrologic comments reflect data from mineral-melt equilibria studies. Background coloration indicates distribution of seismic velocity (Vp/Vs) ratios. Orange dots depict seismicity in the section. Krakatau caldera and the active Anak Krakatau vent are shown schematically.

In their spatial and temporal analysis of seismological data from 1964-2005, Špièák and others (2011) reported both deepening and shallowing of earthquake foci over the past 40 ? 5 years (figure 28). This result is not dissimilar to that of Dahren and others (2010), but ?pièák and others (2011) concluded that the pattern reflects "depth variations of tectonic stress concentration rather than vertical migration of the source of magma." Similar to Jaxybulatov and others (2011), ?pièák and others (2011) also reported that the deepest events (~100 km) constrain the primary magma generation of the system to depths greater than 100 km. They further noted an aseismic gap in the Wadati-Benioff zone of the subducting plate at 100-120 km depth. They inferred that this gap is likely the consequence of partial melting "inhibiting stress concentration necessary to generate stronger earthquakes," while an increased occurrence of earthquakes in the lithospheric wedge above probably reflects magma ascent.

Figure (see Caption) Figure 28. Teleseismic earthquake foci located at Krakatau during 1964-2005. Each panel (depth vs horizontal position) indicates the overall cluster of earthquakes, but emphasizes the earthquakes within the designated time interval (symbols in red). The panels are oriented trending N30W. Open and red symbols represent body-wave magnitudes (mb) as shown in the legend at bottom. From ?pièák and others (2011).

Revised first millenium eruption date. Prior to 2000, a caldera-forming event at Krakatau ("Proto-Krakatau") was hypothesized to have occurred circa 416 CE. From an intensive, multi-disciplinary approach, Wohletz (2000) hypothesized that the catastrophic event actually occurred in the year prior to widespread climate perturbation during 535-536 CE. He noted that the 338th century of the Shaka calendar was probably previously mis-aligned to 416 CE of the western calendar. Since Wohletz (2000), the date of this eruption is widely accepted as 535 CE (see inset of figure 23 for map representation of the caldera's topographic margin).

References. Dahren, B., Troll., V.R., Andersson, U., Chadwick, J.P., and Gardner, M.F., 2010, Investigating magma plumbing beneath Anak Krakatau volcano, Indonesia: evidence for multiple magma storage regions, Geophysical Research Abstracts, v. 12, 1607-7962; in7th EGU General Assembly, 2010.

Jaxybulatov, K., Koulakov, I., Ibs-von Seht, M., Klinge, K., Reichert, C., Dahren, B., and Troll, V.R., 2011, Evidence for high fluid/melt content beneath Krakatau volcano (Indonesia) from local earthquake tomography, Journal of Volcanology and Geothermal Research, v. 206, p. 96-105.

Špièák, A., Van?k, J., and Hanu?, V., 2011, Recent plumbing system of the Krakatau volcano revealed by teleseismic earthquake distribution, International Journal of Earth Sciences, v. 100, p. 1375-1381.

Wohletz K.H., 2000, Were the Dark Ages triggered by volcano-related climate changes in the 6th century? EOS Transactions of the American Geophys. Union, v. 48(81), F1305.

Geologic Background. The renowned Krakatau (frequently mis-named as Krakatoa) volcano lies in the Sunda Strait between Java and Sumatra. Collapse of an older edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of that volcano are preserved in Verlaten and Lang Islands; subsequently the Rakata, Danan, and Perbuwatan cones 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 caused more than 36,000 fatalities, most as a result of 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 Danan and Perbuwatan cones. Anak Krakatau has been the site of frequent eruptions since 1927.

Information Contacts: Center for Volcanology and Geological Hazard Mitigation (CVGHM), Jl. Diponegoro 57, Bandung, West Java, Indonesia, 40 122 (URL: http://www.vsi.esdm.go.id/); Arnold Binas, Sydney, Australia (URL: http://www.arnoldbinas.com); Darwin Volcanic Ash Advisory Centre (VAAC) (URL: http://www.bom.gov.au/info/vaac/); The Jakarta Post (URL: http://www.thejakartapost.com/); TO:DAY (URL: http://today.co.id/); NASA Earth Observatory, NASA Goddard Space Flight Center (URL: http://earthobservatory.nasa.gov/); Andi Rosadi, Chris Weber, and Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/).


Soufriere Hills (United Kingdom) — August 2011 Citation iconCite this Report

Soufriere Hills

United Kingdom

16.72°N, 62.18°W; summit elev. 915 m

All times are local (unless otherwise noted)


Extrusive pause follows 11 February 2010 partial dome collapse

Our previous report on Soufrière Hills volcano, Montserrat, (BGVN 35:03), was published in the month following the 11 February 2010 partial dome collapse, which consisted of 40-50 x 106 m3 of material (~20% of the dome's pre-collapse volume) and left a collapse scar ~ 300 m wide on the N flank of the dome. The ash column from this event reached ~15 km altitude, and large pyroclastic flows extended the island's E shoreline, creating ~1 km2 of new land surface. This event marked the end of Extrusive Phase 5, the most recent phase of extrusive activity since the volcano's awakening in 1995 (figure 88). Since then, and as recently as 9 September 2011, Soufrière Hills experienced a low level of activity with pyroclastic flows and rockfalls, but no significant extrusion of lava; a behavior typical of pauses in extrusion at this volcano since 1995 (figure 88). The Hazard Level remained at 3 (on a scale from 1 to 5). Most of the data and information in this report is from Cole and others, 2010 and Cole and others, 2011. Information has also been contributed by the Montserrat Volcano Observatory (MVO).

Figure (see Caption) Figure 88. Extrusive phases (red areas) and pauses (green areas) of the Soufrière Hills eruption, Montserrat, from 1 January 1995 to 30 April 2011, based on seismic, GPS, and SO2 monitoring data. Top: number of seismic events detected. Middle: GPS data from three stations smoothed with a 7-day running mean filter. Bottom: Measured SO2 flux filtered with a 7-day running median filter. From Cole and others, 2011.

Pyroclastic flows and rockfalls removed 3.65 x 106 m3 (~ 1.9 % volume) of the dome from 12 February 2010 to 30 April 2011. Of these events, 54 were small pyroclastic flows (maximum runout of 1 km) and 31 were moderate-large pyroclastic flows (maximum runout of 2 km), generated mainly from three source regions:(1) above Gages Valley (W side); (2) N of the head of the 11 February 2010 collapse scar; and (3) at the head of the Tar River Valley (ESE side).

Undercutting of the dome face above Gages Valley (W side) by heavy summer rainfall in 2010 compromised dome stability and led to the largest pyroclastic flows. Pyroclastic flows occasionally generated small plumes and ashfall in inhabited areas of the island.

Lahars in the Belham Valley (on the volcano's W side) decreased from 40 measurable events (during late February-October 2010) to 10 measurable events (during November 2010-April 2011). The lahars were well correlated with peak rainfall events, and the 40 lahars occurring from 28 February to 31 October 2010 were attributed to especially heavy rainfall occurring in the months of April, late July, September, and October 2010. Figure 89 shows a house in Belham Valley partially covered by lahar deposits.

Figure (see Caption) Figure 89. A house on the S side of the golf course that used to occupy the mouth of Belham Valley, Montserrat (Old Road Bay can be seen in the background). Photo by Robert Dennen (Global Volcanism Program) taken July 2010.

As of 9 September 2011 the Washington Volcanic Ash Advisory Center (VAAC) reported eruptive plumes only a handful of times since 28 February 2010. Based on a METAR weather report and analyses of satellite imagery, on 10 August 2010 a narrow plume drifted 100 km WNW. According to the Washington VAAC, on 2 October 2010 the MVO reported that an ash plume rose to an altitude of 2.1 km altitude and drifted W. The next day an ash plume seen in satellite imagery drifted 55 km WNW and NW. A few hours later, an area of ash at an altitude of 2.1 km altitude was observed 140 km to the WNW. On 11 October a diffuse steam-and-gas plume drifted NNW.

Seismicity generally remained low, with low-frequency seismicity, long-period (LP), hybrid, and LP-rockfall events detected between 1 November 2010 and 9 September 2011 (figure 88). Short periods of volcano-tectonic (VT) earthquake activity on 25 June and 2 July 2010 were followed by ash venting; roaring could be heard N of the volcano. Another VT short swarm on 3 December 2010 was associated with an increase in gas emission and additional minor ash venting.

SO2 flux also remained low, with the daily average from 28 February 2010 to 30 April 2011 measured at 375 tons/day; low values typical of periods of pause. Elevated SO2 flux occurred in early May 2010 (up to 1,250 tons/day), November 2010, and March 2011 (figure 88).

During the reporting interval, mid-February 2010 to 9 September 2011, steady but weak inflation occurred, with only minor changes to the dome. The changes stemmed from mass wasting such as rockfalls and from pyroclastic flows.

Incandescence from various places on the lava dome was observed and analyzed (figure 90). The largest feature was a fumarolic gas vent on the floor of the 11 February collapse scar (see "Gas vent", figure 90 B, D). From the incandescent color, the temperature is estimated to be 500-600°C. Dome interior temperatures are considered likely nearly magmatic.

Figure (see Caption) Figure 90. Four labeled images of Soufrière Hills calling attention to thermal features in the vent and dome area. The top two (A and B) represent night-time, long-exposure photographs. (A) An 11 November 2010 view from MVO (203 second exposure time). (B) A 12 November 2010 view from Jack Boy Hill (30 second exposure time). Features labeled X and Y are the most prominent incandescent/thermal features in the headwall of the 11 February 2010 collapse scar. (C and D) Photos with infrared enhancements indicated by colored zones (red representing hottest temperatures). (C) A 15 February 2011 view from MVO. (D) A 25 February 2011 view from Jack Boy Hill. Features labeled X and Y are as described above; those labeled Z were source areas for pyroclastic flows and rockfalls. From Cole and others, 2011.

References. Cole, P., Bass, V., Christopher, T., Eligon, C., Murrell, C., Odbert, H., Smith, P., Stewart, R., Stinton, A., Syers, R., Robertson, R., and Williams, P., 2010, Report to the Scientific Advisory Committee on Volcanic Activity at Soufrière Hills Volcano Montserrat, Report on Activity between 28 February 2010 and 31 October 2010, Open File Report OFR 10-02a, Prepared for SAC 15: 15 ? 17 November 2010. Monsterrat Volcano Observatory (MVO).

Cole, P., Bass, V., Christopher, T., Murrell, C., Odbert, H., Smith, P., Stewart, R., Stinton, A., Syers, R., and Williams, P., 2011, MVO scientific report for volcanic activity between 1 November 2010 and 30 April 2011, Open File Report OFR 11-01. Monsterrat Volcano Observatory (MVO).

Geologic Background. The complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. The volcano is flanked by Pleistocene complexes to the north and south. English's Crater, a 1-km-wide crater breached widely to the east by edifice collapse, was formed about 2000 years ago as a result of the youngest of several collapse events producing submarine debris-avalanche deposits. Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits, including those from an eruption that likely preceded the 1632 CE settlement of the island, allowing cultivation on recently devegetated land to near the summit. Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but no historical eruptions were recorded until 1995. Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth and pyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption.

Information Contacts: Montserrat Volcano Observatory (MVO), Fleming, Montserrat, West Indies (URL: http://www.mvo.ms/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/).


Tambora (Indonesia) — August 2011 Citation iconCite this Report

Tambora

Indonesia

8.25°S, 118°E; summit elev. 2850 m

All times are local (unless otherwise noted)


Increased seismicity and minor steam venting in 2011

Beginning in April 2011, Tambora volcano, Indonesia (figure 1), experienced increased seismic activity and minor steam venting. As a result, the Center for Volcanology and Geological Hazard Mitigation (CVGHM) raised the Alert Level for Tambora. This report will summarize the increased activity from April 2011 through 8 September 2011, as reported by CVGHM.

Figure (see Caption) Figure 1. Regional (top) and local (bottom) geographic setting of Tambora volcano, Indonesia. Courtesy of Wilford (2006) and the New York Times.

Seismicity at Tambora increased steadily from April 2011 to at least 8 September. CVGHM reported six seismic signals that were monitored: volcanic earthquakes (VA), shallow volcanic earthquakes (VB), distant tectonic earthquakes (TJ), local tectonic earthquakes (TL), low-frequency earthquakes (LF), and volcanic tremor. Seismic activity from April through August is summarized in figure 2. In addition to increased seismicity, ground-based observers described dense white plumes rising 50-75 m above the caldera rim in April and June.

Figure (see Caption) Figure 2. Reported seismic activity at Tambora cumulative by month from April through August 2011. Onset of continuous volcanic tremor on 29 August is not represented. Data from CVGHM.

Volcanic tremor started 29 August and continued every day since, with the exception of 3 September (table 1). The tremor was accompanied by diffuse plumes rising 10-20 m above the caldera rim on 29 August and 5 September. Based on seismic activity and visual observations, CVGHM raised the Alert Level to 2 (on a scale from 1 to 4) on 30 August, and forbade access to the peak of Tambora.

Table 1. Summary of seismicity at Tambora since the onset of volcanic tremor on 29 August 2011. On both 29 August and 5 September seismicity was accompanied by plumes rising 10-20 m above the caldera rim. Data from CVGHM.

Date Volcanic A-type Volcanic B-type Local tectonic Low-frequency Tremor
29 Aug 2011 14 -- 3 -- continuous
30 Aug 2011 9 5 2 1 continuous
31 Aug 2011 6 5 -- 2 continuous
01 Sep 2011 15 -- 2 2 continuous
02 Sep 2011 6 4 4 6 11
03 Sep 2011 5 5 4 4 --
04 Sep 2011 6 1 3 4 11
05 Sep 2011 11 7 3 1 4
06 Sep 2011 7 4 -- -- continuous
07 Sep 2011 40 6 1 -- continuous

Along with the continuation of the tremor after 29 August, CVGHM reported an increase in other types of seismic activity from 30 August to 7 September. On 5 September an earthquake was felt by residents (exact location undisclosed). Instruments recorded 40 volcanic earthquakes on 7 September (table 1); 32 of those were recorded within 6 hours. On 8 September, CVGHM raised the Alert Level to 3, invoked a 3 km exclusion zone, and prohibited access to Disaster Prone Areas III, summarized in table 2. The Disaster Prone Areas were largely based on the devastating 1815 eruption of Tambora. As of 21 September, the Alert Level remained at 3.

Table 2. Summary of Disaster Prone Areas at Tambora defined on the basis of radial distance from the peak of Tambora. Courtesy of CVGHM.

Area Radius from Tambora Potential hazards
Disaster Prone Area I 8 km Lahars, ash fall, and incandescent bombs.
Disaster Prone Area II 5 km Pyroclastic flows, lava flows, toxic gases, incandescent bombs, ash fall, lahars/mudflows, and high acidity in water.
Disaster Prone Area III 3 km Pyroclastic flows, lava flows, toxic gases, incandescent bombs, and heavy ash fall.

References. Wilford, J.N., 2006, Under an 1815 Volcano Eruption, Remains of a 'Lost Kingdom', the New York Times, URL: http://www.nytimes.com/2006/02/28/science/28volc.html; Posted 28 February 2006; accessed 26 September 2011.

Geologic Background. The massive Tambora stratovolcano forms the entire 60-km-wide Sanggar Peninsula on northern Sumbawa Island. The largely trachybasaltic-to-trachyandesitic volcano grew to about 4,000 m elevation before forming a caldera more than 43,000 years ago. Late-Pleistocene lava flows largely filled the early caldera, after which activity changed to dominantly explosive eruptions during the early Holocene. Tambora was the source of history's largest explosive eruption, in April 1815. Pyroclastic flows reached the sea on all sides of the peninsula, and heavy tephra fall devastated croplands, causing an estimated 60,000 fatalities. The eruption of an estimated more than 150 km3 of tephra formed a 6-km-wide, 1250-m-deep caldera and produced global climatic effects. Minor lava domes and flows have been extruded on the caldera floor at Tambora during the 19th and 20th centuries.

Information Contacts: Center for Volcanology and Geological Hazard Mitigation (CVGHM), Jl. Diponegoro 57, Bandung, West Java, Indonesia, 40 122 (URL: http://www.vsi.esdm.go.id/).


Tinakula (Solomon Islands) — August 2011 Citation iconCite this Report

Tinakula

Solomon Islands

10.386°S, 165.804°E; summit elev. 796 m

All times are local (unless otherwise noted)


MODVOLC thermal alerts extend through September 2011

Our previous report on Tinakula (BGVN 35:01) summarized MODVOLC thermal alert data through 27 February 2010. This report notes MODVOLC alerts through September 2011. Tinakula is a rarely visited or monitored island in the Santa Cruz Island complex, which is part of the Solomon Island group in the South Pacific ocean (figures 8-10).

Figure (see Caption) Figure 8. The location of Tinakula in the Santa Cruz Islands. Courtesy of McCoy and Cleghorn (1988).
Figure (see Caption) Figure 9. Sketch map of Tinakula island based on work and publications by G.W. Hughes (1972) and colleagues, and summarized by Eissen and others (1991). (This previously appeared in BGVN 28:01.)
Figure (see Caption) Figure 10. Stamp from the British Solomon Islands showing Tinakula. Top stamp shows the summit crater emitting a plume and well-developed radial channels with abundant material deposited on the volcano's lower right flank. Bottom stamp illustrates the large scar across the island's NW side. These stamps were featured on the website of Iomoon.com.

An image captured on 25 May 2010 by the MODIS instrument aboard the Aqua satellite, showed an ash plume from the volcano. It is not known whether plumes during the time period of this report were frequent.

MODVOLC thermal alerts continued through the rest of 2010 and through at least September 2011. During March 2010 through October 2010, the number of alerts ranged from zero to three per month. The number of alerts rose to 10 in November and to 20 in December, then decreased to 11 in January 2011. Between February and 26 September 2011, the number of alerts ranged from two to 12 per month. In July 2011, the two recorded alerts were 4 pixels each, a high during the time period for this report.

References. Eissen, J-P., Blot, C., and Louat, R., 1991, Chronology of the historic volcanic activity of the New Hebrides island arc from 1595 to 1991: Rapports Scientifiques et Technique, Sciences de la Terre, No. 2, ORSTOM, France.Hughes, G.W., 1972, Geological map of Tinakula: Nendö sheet EOI 1, Soloman Geol. Survey, Honiara.McCoy, P.C., and Cleghorn, 1988, Archaeological Excavations on Santa Cruz (Nendö), Southeast Solomon Islands: Summary Report, pp. 104-115 (map on 105 and at URL: http://www.jstor.org/stable/40386813?seq=2),in Archaeology in Oceania.

Geologic Background. The small 3.5-km-wide island of Tinakula is the exposed summit of a massive stratovolcano at the NW end of the Santa Cruz islands. It has a breached summit crater that extends from the summit to below sea level. Landslides enlarged this scarp in 1965, creating an embayment on the NW coast. The Mendana cone is located on the SE side. The dominantly andesitic volcano has frequently been observed in eruption since the era of Spanish exploration began in 1595. In about 1840, an explosive eruption apparently produced pyroclastic flows that swept all sides of the island, killing its inhabitants. Recorded eruptions have frequently originated from a cone constructed within the large breached crater. These have left the upper flanks and the steep apron of lava flows and volcaniclastic debris within the breach unvegetated.

Information Contacts: 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/); Iomoon.com (URL: http://www.iomoon.com/).

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