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 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 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 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 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).

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 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 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 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 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 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 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 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/).

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 25. Webcam image of a gas-and-steam plume rising above Semisopochnoi from Mount Young on 21 December 2022. Courtesy of AVO.

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/).

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 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 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 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 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 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 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/).

Persistent eruptive activity since April 2008 at Ibu, a stratovolcano on Indonesian’s Halmahera Island, has consisted of daily explosive ash emissions and plumes, along with observations of thermal anomalies (BGVN 47:04). The current eruption continued during October 2022-May 2023, described below, based on advisories issued by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), daily reports by MAGMA Indonesia (a PVMBG platform), and the Darwin Volcanic Ash Advisory Centre (VAAC), and various satellite data. The Alert Level during the reporting period remained at 2 (on a scale of 1-4), except raised briefly to 3 on 27 May, and the public was warned to stay at least 2 km away from the active crater and 3.5 km away on the N side of the volcano.

According to MAGMA Indonesia, during October 2022-May 2023, daily gray-and-white ash plumes of variable densities rose 200-1,000 m above the summit and drifted in multiple directions. On 30 October and 11 November, plumes rose a maximum of 2 km and 1.5 km above the summit, respectively (figures 42 and 43). According to the Darwin VAAC, discrete ash emissions on 13 November rose to 2.1 km altitude, or 800 m above the summit, and drifted W, and multiple ash emissions on 15 November rose 1.4 km above the summit and drifted NE. Occasional larger ash explosions through May 2023 prompted PVMBG to issue Volcano Observatory Notice for Aviation (VONA) alerts (table 6); the Aviation Color Code remained at Orange throughout this period.

Figure 42. Larger explosion from Ibu’s summit crater on 30 October 2022 that generated a plume that rose 2 km above the summit. Photo has been color corrected. Courtesy of MAGMA Indonesia.

Figure 43. Larger explosion from Ibu’s summit crater on 11 November 2022 that generated a plume that rose 1.5 km above the summit. Courtesy of MAGMA Indonesia.

Table 6. Volcano Observatory Notice for Aviation (VONA) ash plume alerts for Ibu issued by PVMBG during October 2022-May 2023. Maximum height above the summit was estimated by a ground observer. VONAs in January-May 2023 all described the ash plumes as dense.

Sentinel-2 L1C satellite images throughout the reporting period show two, sometimes three persistent thermal anomalies in the summit crater, with the most prominent hotspot from the top of a cone within the crater. Clear views were more common during March-April 2023, when a vent and lava flows on the NE flank of the intra-crater cone could be distinguished (figure 44). White-to-grayish emissions were also observed during brief periods when weather clouds allowed clear views.

Figure 44. Sentinel-2 L2A satellite images of Ibu on 10 April 2023. The central cone within the summit crater (1.3 km diameter) and lava flows (gray) can be seen in the true color image (left, bands 4, 3, 2). Thermal anomalies from the small crater of the intra-crater cone, a NE-flank vent, and the end of the lava flow are apparent in the infrared image (right, bands 12, 11, 8A). Courtesy of Copernicus Browser.

The MIROVA space-based volcano hotspot detection system recorded almost daily thermal anomalies throughout the reporting period, though cloud cover often interfered with detections. Data from imaging spectroradiometers aboard NASA’s Aqua and Terra satellites and processed using the MODVOLC algorithm (MODIS-MODVOLC) recorded hotspots on one day during October 2022 and December 2022, two days in April 2023, three days in November 2022 and May 2023, and four days in March 2023.

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: 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 (Multiplatform Application for Geohazard Mitigation and Assessment in Indonesia), Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/); 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/).

Dukono, a remote volcano on Indonesia’s Halmahera Island, has been erupting continuously since 1933, with frequent ash explosions and sulfur dioxide plumes (BGVN 46:11, 47:10). This activity continued during October 2022 through May 2023, based on reports from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG; also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), the Darwin Volcanic Ash Advisory Centre (VAAC), and satellite data. During this period, the Alert Level remained at 2 (on a scale of 1-4) and the public was warned to remain outside of the 2-km exclusion zone. The highest reported plume of the period reached 9.4 km above the summit on 14 November 2022.

According to MAGMA Indonesia (a platform developed by PVMBG), white, gray, or dark plumes of variable densities were observed almost every day during the reporting period, except when fog obscured the volcano (figure 33). Plumes generally rose 25-450 m above the summit, but rose as high as 700-800 m on several days, somewhat lower than the maximum heights reached earlier in 2022 when plumes reached as high as 1 km. However, the Darwin VAAC reported that on 14 November 2022, a discrete ash plume rose 9.4 km above the summit (10.7 km altitude), accompanied by a strong hotspot and a sulfur dioxide signal observed in satellite imagery; a continuous ash plume that day and through the 15th rose to 2.1-2.4 km altitude and drifted NE.

Figure 33. Webcam photo of a gas-and-steam plume rising from Dukono on the morning of 28 January 2023. Courtesy of MAGMA Indonesia.

Sentinel-2 images were obscured by weather clouds almost every viewing day during the reporting period. However, the few reasonably clear images showed a hotspot and white or gray emissions and plumes. Strong SO₂ plumes from Dukono were present on many days during October 2022-May 2023, as detected using the TROPOMI instrument on the Sentinel-5P satellite (figure 34).

Figure 34. A strong SO2 signal from Dukono on 23 April 2023 was the most extensive plume detected during the reporting period. Courtesy of the NASA Global Sulfur Dioxide Monitoring Page.

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: 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 (Multiplatform Application for Geohazard Mitigation and Assessment in Indonesia), Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Sabancaya is located in Peru, NE of Ampato and SE of Hualca Hualca. Eruptions date back to 1750 and have been characterized by explosions, phreatic activity, ash plumes, and ashfall. The current eruption period began in November 2016 and has more recently consisted of daily explosions, gas-and-ash plumes, and thermal activity (BGVN 47:11). This report updates activity during November 2022 through April 2023 using information from Instituto Geophysico del Peru (IGP) that use weekly activity reports and various satellite data.

Intermittent low-to-moderate power thermal anomalies were reported by the MIROVA project during November 2022 through April 2023 (figure 119). There were few short gaps in thermal activity during mid-December 2022, late December-to-early January 2023, late January to mid-February, and late February. According to data recorded by the MODVOLC thermal algorithm, there were a total of eight thermal hotspots: three in November 2022, three in February 2023, one in March, and one in April. On clear weather days, some of this thermal anomaly was visible in infrared satellite imagery showing the active lava dome in the summit crater (figure 120). Almost daily moderate-to-strong sulfur dioxide plumes were recorded during the reporting period by the TROPOMI instrument on the Sentinel-5P satellite (figure 121). Many of these plumes exceeded 2 Dobson Units (DU) and drifted in multiple directions.

Figure 119. Intermittent low-to-moderate thermal anomalies were detected during November 2022 through April 2023 at Sabancaya, as shown in this MIROVA graph (Log Radiative Power). There were brief gaps in thermal activity during mid-December 2022, late December-to-early January 2023, late January to mid-February, and late February. Courtesy of MIROVA.

Figure 120. Infrared (bands 12, 11, 8A) satellite images showed a constant thermal anomaly in the summit crater of Sabancaya on 14 January 2023 (top left), 28 February 2023 (top right), 5 March 2023 (bottom left), and 19 April 2023 (bottom right), represented by the active lava dome. Sometimes gas-and-steam and ash emissions also accompanied this activity. Courtesy of Copernicus Browser.

Figure 121. Moderate-to-strong sulfur dioxide plumes were detected almost every day, rising from Sabancaya by the TROPOMI instrument on the Sentinel-5P satellite throughout the reporting period; the DU (Dobson Unit) density values were often greater than 2. Plumes from 23 November 2022 (top left), 26 December 2022 (top middle), 10 January 2023 (top right), 15 February 2023 (bottom left), 13 March 2023 (bottom middle), and 21 April 2023 (bottom right) that drifted SW, SW, W, SE, W, and SW, respectively. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

IGP reported that moderate activity during November and December 2022 continued; during November, an average number of explosions were reported each week: 30, 33, 36, and 35, and during December, it was 32, 40, 47, 52, and 67. Gas-and-ash plumes in November rose 3-3.5 km above the summit and drifted E, NE, SE, S, N, W, and SW. During December the gas-and-ash plumes rose 2-4 km above the summit and drifted in different directions. There were 1,259 volcanic earthquakes recorded during November and 1,693 during December. Seismicity also included volcano-tectonic-type events that indicate rock fracturing events. Slight inflation was observed in the N part of the volcano near Hualca Hualca (4 km N). Thermal activity was frequently reported in the crater at the active lava dome (figure 120).

Explosive activity continued during January and February 2023. The average number of explosions were reported each week during January (51, 50, 60, and 59) and February (43, 54, 51, and 50). Gas-and-ash plumes rose 1.6-2.9 km above the summit and drifted NW, SW, and W during January and rose 1.4-2.8 above the summit and drifted W, SW, E, SE, N, S, NW, and NE during February. IGP also detected 1,881 volcanic earthquakes during January and 1,661 during February. VT-type earthquakes were also reported. Minor inflation persisted near Hualca Hualca. Satellite imagery showed continuous thermal activity in the crater at the lava dome (figure 120).

During March, the average number of explosions each week was 46, 48, 31, 35, and 22 and during April, it was 29, 41, 31, and 27. Accompanying gas-and-ash plumes rose 1.7-2.6 km above the summit crater and drifted W, SW, NW, S, and SE during March. According to a Buenos Aires Volcano Ash Advisory Center (VAAC) notice, on 22 March at 1800 through 23 March an ash plume rose to 7 km altitude and drifted NW. By 0430 an ash plume rose to 7.6 km altitude and drifted W. On 24 and 26 March continuous ash emissions rose to 7.3 km altitude and drifted SW and on 28 March ash emissions rose to 7.6 km altitude. During April, gas-and-ash plumes rose 1.6-2.5 km above the summit and drifted W, SW, S, NW, NE, and E. Frequent volcanic earthquakes were recorded, with 1,828 in March and 1,077 in April, in addition to VT-type events. Thermal activity continued to be reported in the summit crater at the lava dome (figure 120).

Geologic Background. Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning "tongue of fire" in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions date back to 1750.

Information Contacts: Instituto Geofisico del Peru (IGP), Centro Vulcanológico Nacional (CENVUL), Calle Badajoz N° 169 Urb. Mayorazgo IV Etapa, Ate, Lima 15012, Perú (URL: https://www.igp.gob.pe/servicios/centro-vulcanologico-nacional/inicio); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard MD 20771, USA (URL: https://so2.gsfc.nasa.gov/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).

Sheveluch (also spelled Shiveluch) in Kamchatka, has had at least 60 large eruptions during the last 10,000 years. The summit is truncated by a broad 9-km-wide caldera that is breached to the S, and many lava domes occur on the outer flanks. The lava dome complex was constructed within the large open caldera. Frequent collapses of the dome complex have produced debris avalanches; the resulting deposits cover much of the caldera floor. A major south-flank collapse during a 1964 Plinian explosion produced a scarp in which a “Young Sheveluch” dome began to form in 1980. Repeated episodes of dome formation and destruction since then have produced major and minor ash plumes, pyroclastic flows, block-and-ash flows, and “whaleback domes” of spine-like extrusions in 1993 and 2020 (BGVN 45:11). The current eruption period began in August 1999 and has more recently consisted of lava dome growth, explosions, ash plumes, and avalanches (BGVN 48:01). This report covers a significant explosive eruption during early-to-mid-April 2023 that generated a 20 km altitude ash plume, produced a strong sulfur dioxide plume, and destroyed part of the lava-dome complex; activity described during January through April 2023 use information primarily from the Kamchatka Volcanic Eruptions Response Team (KVERT) and various satellite data.

Satellite data. Activity during the majority of this reporting period was characterized by continued lava dome growth, strong fumarole activity, explosions, and hot avalanches. According to the MODVOLC Thermal Alerts System, 140 hotspots were detected through the reporting period, with 33 recorded in January 2023, 29 in February, 44 in March, and 34 in April. Frequent strong thermal activity was recorded during January 2023 through April, according to the MIROVA (Middle InfraRed Observation of Volcanic Activity) graph and resulted from the continuously growing lava dome (figure 94). A slightly stronger pulse in thermal activity was detected in early-to-mid-April, which represented the significant eruption that destroyed part of the lava-dome complex. Thermal anomalies were also visible in infrared satellite imagery at the summit crater (figure 95).

Figure 94. Strong and frequent thermal activity was detected at Sheveluch during January through April 2023, according to this MIROVA graph (Log Radiative Power). These thermal anomalies represented the continuously growing lava dome and frequent hot avalanches that affected the flanks. During early-to-mid-April a slightly stronger pulse represented the notable explosive eruption. Courtesy of MIROVA.

Figure 95. Infrared (bands B12, B11, B4) satellite imagery showed persistent thermal anomalies at the lava dome of Sheveluch on 14 January 2023 (top left), 26 February 2023 (top right), and 15 March 2023 (bottom left). The true color image on 12 April 2023 (bottom right) showed a strong ash plume that drifted SW; this activity was a result of the strong explosive eruption during 11-12 April 2023. Courtesy of Copernicus Browser.

During January 2023 KVERT reported continued growth of the lava dome, accompanied by strong fumarolic activity, incandescence from the lava dome, explosions, ash plumes, and avalanches. Satellite data showed a daily thermal anomaly over the volcano. Video data showed ash plumes associated with collapses at the dome that generated avalanches that in turn produced ash plumes rising to 3.5 km altitude and drifting 40 km W on 4 January and rising to 7-7.5 km altitude and drifting 15 km SW on 5 January. A gas-and-steam plume containing some ash that was associated with avalanches rose to 5-6 km altitude and extended 52-92 km W on 7 January. Explosions that same day produced ash plumes that rose to 7-7.5 km altitude and drifted 10 km W. According to a Volcano Observatory Notice for Aviation (VONA) issued at 1344 on 19 January, explosions produced an ash cloud that was 15 x 25 km in size and rose to 9.6-10 km altitude, drifting 21-25 km W; as a result, the Aviation Color Code (ACC) was raised to Red (the highest level on a four-color scale). Another VONA issued at 1635 reported that no more ash plumes were observed, and the ACC was lowered to Orange (the second highest level on a four-color scale). On 22 January an ash plume from collapses and avalanches rose to 5 km altitude and drifted 25 km NE and SW; ash plumes associated with collapses extended 70 km NE on 27 and 31 January.

Lava dome growth, fumarolic activity, dome incandescence, and occasional explosions and avalanches continued during February and March. A daily thermal anomaly was visible in satellite data. Explosions on 1 February generated ash plumes that rose to 6.3-6.5 km altitude and extended 15 km NE. Video data showed an ash cloud from avalanches rising to 5.5 km altitude and drifting 5 km SE on 2 February. Satellite data showed gas-and-steam plumes containing some ash rose to 5-5.5 km altitude and drifted 68-110 km ENE and NE on 6 February, to 4.5-5 km altitude and drifted 35 km WNW on 22 February, and to 3.7-4 km altitude and drifted 47 km NE on 28 February. Scientists from the Kamchatka Volcanological Station (KVS) went on a field excursion on 25 February to document the growing lava dome, and although it was cloudy most of the day, nighttime incandescence was visible. Satellite data showed an ash plume extending up to 118 km E during 4-5 March. Video data from 1150 showed an ash cloud from avalanches rose to 3.7-5.5 km altitude and drifted 5-10 km ENE and E on 5 March. On 11 March an ash plume drifted 62 km E. On 27 March ash plumes rose to 3.5 km altitude and drifted 100 km E. Avalanches and constant incandescence at the lava dome was focused on the E and NE slopes on 28 March. A gas-and-steam plume containing some ash rose to 3.5 km altitude and moved 40 km E on 29 March. Ash plumes on 30 March rose to 3.5-3.7 km altitude and drifted 70 km NE.

Similar activity continued during April, with lava dome growth, strong fumarolic activity, incandescence in the dome, occasional explosions, and avalanches. A thermal anomaly persisted throughout the month. During 1-4 April weak ash plumes rose to 2.5-3 km altitude and extended 13-65 km SE and E.

Activity during 11 April 2023. The Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS) reported a significant increase in seismicity around 0054 on 11 April, as reported by strong explosions detected on 11 April beginning at 0110 that sent ash plumes up to 7-10 km altitude and extended 100-435 km W, WNW, NNW, WSW, and SW. According to a Tokyo VAAC report the ash plume rose to 15.8 km altitude. By 0158 the plume extended over a 75 x 100 km area. According to an IVS FEB RAS report, the eruptive column was not vertical: the initial plume at 0120 on 11 April deviated to the NNE, at 0000 on 12 April, it drifted NW, and by 1900 it drifted SW. KVS reported that significant pulses of activity occurred at around 0200, 0320, and then a stronger phase around 0600. Levin Dmitry took a video from near Békés (3 km away) at around 0600 showing a rising plume; he also reported that a pyroclastic flow traveled across the road behind him as he left the area. According to IVS FEB RAS, the pyroclastic flow traveled several kilometers SSE, stopping a few hundred meters from a bridge on the road between Klyuchi and Petropavlovsk-Kamchatsky.

Ashfall was first observed in Klyuchi (45 km SW) at 0630, and a large, black ash plume blocked light by 0700. At 0729 KVERT issued a Volcano Observatory Notice for Aviation (VONA) raising the Aviation Color Code to Red (the highest level on a four-color scale). It also stated that a large ash plume had risen to 10 km altitude and drifted 100 km W. Near-constant lightning strikes were reported in the plume and sounds like thunderclaps were heard until about 1000. According to IVS FEB RAS the cloud was 200 km long and 76 km wide by 0830, and was spreading W at altitudes of 6-12 km. In the Klyuchi Village, the layer of both ash and snow reached 8.5 cm (figure 96); ashfall was also reported in Kozyrevsk (112 km SW) at 0930, Mayskoye, Anavgay, Atlasovo, Lazo, and Esso. Residents in Klyuchi reported continued darkness and ashfall at 1100. In some areas, ashfall was 6 cm deep and some residents reported dirty water coming from their plumbing. According to IVS FEB RAS, an ash cloud at 1150 rose to 5-20 km altitude and was 400 km long and 250 km wide, extending W. A VONA issued at 1155 reported that ash had risen to 10 km and drifted 340 km NNW and 240 km WSW. According to Simon Carn (Michigan Technological University), about 0.2 Tg of sulfur dioxide in the plume was measured in a satellite image from the TROPOMI instrument on the Sentinel-5P satellite acquired at 1343 that covered an area of about 189,000 km² (figure 97). Satellite data at 1748 showed an ash plume that rose to 8 km altitude and drifted 430 km WSW and S, according to a VONA.

Figure 96. Photo of ash deposited in Klyuchi village on 11 April 2023 by the eruption of Sheveluch. About 8.5 cm of ash was measured. Courtesy of Kam 24 News Agency.

Figure 97. A strong sulfur dioxide plume from the 11 April 2023 eruption at Sheveluch was visible in satellite data from the TROPOMI instrument on the Sentinel-5P satellite. Courtesy of Simon Carn, MTU.

Activity during 12-15 April 2023. On 12 April at 0730 satellite images showed ash plumes rose to 7-8 km altitude and extended 600 km SW, 1,050 km ESE, and 1,300-3,000 km E. By 1710 that day, the explosions weakened. According to news sources, the ash-and-gas plumes drifted E toward the Aleutian Islands and reached the Gulf of Alaska by 13 April, causing flight disruptions. More than 100 flights involving Alaska airspace were cancelled due to the plume. Satellite data showed ash plumes rising to 4-5.5 km altitude and drifted 400-415 km SE and ESE on 13 April. KVS volcanologists observed the pyroclastic flow deposits and noted that steam rose from downed, smoldering trees. They also noted that the deposits were thin with very few large fragments, which differed from previous flows. The ash clouds traveled across the Pacific Ocean. Flight cancellations were also reported in NW Canada (British Columbia) during 13-14 April. During 14-15 April ash plumes rose to 6 km altitude and drifted 700 km NW.

Alaskan flight schedules were mostly back to normal by 15 April, with only minor delays and far less cancellations; a few cancellations continued to be reported in Canada. Clear weather on 15 April showed that most of the previous lava-dome complex was gone and a new crater roughly 1 km in diameter was observed (figure 98); gas-and-steam emissions were rising from this crater. Evidence suggested that there had been a directed blast to the SE, and pyroclastic flows traveled more than 20 km. An ash plume rose to 4.5-5.2 km altitude and drifted 93-870 km NW on 15 April.

Figure 98. A comparison of the crater at Sheveluch showing the previous lava dome (top) taken on 29 November 2022 and a large crater in place of the dome (bottom) due to strong explosions during 10-13 April 2023, accompanied by gas-and-ash plumes. The bottom photo was taken on 15 April 2023. Photos has been color corrected. Both photos are courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.

Activity during 16-30 April 2023. Resuspended ash was lifted by the wind from the slopes and rose to 4 km altitude and drifted 224 km NW on 17 April. KVERT reported a plume of resuspended ash from the activity during 10-13 April on 19 April that rose to 3.5-4 km altitude and drifted 146-204 km WNW. During 21-22 April a plume stretched over the Scandinavian Peninsula. A gas-and-steam plume containing some ash rose to 3-3.5 km altitude and drifted 60 km SE on 30 April. A possible new lava dome was visible on the W slope of the volcano on 29-30 April (figure 99); satellite data showed two thermal anomalies, a bright one over the existing lava dome and a weaker one over the possible new one.

Figure 99. Photo showing new lava dome growth at Sheveluch after a previous explosion destroyed much of the complex, accompanied by a white gas-and-steam plume. Photo has been color corrected. Courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.

References. Girina, O., Loupian, E., Horvath, A., Melnikov, D., Manevich, A., Nuzhdaev, A., Bril, A., Ozerov, A., Kramareva, L., Sorokin, A., 2023, Analysis of the development of the paroxysmal eruption of Sheveluch volcano on April 10–13, 2023, based on data from various satellite systems, ??????????? ???????? ??? ?? ???????, 20(2).

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1,300 km3 andesitic volcano is one of Kamchatka's largest and most active volcanic structures, with at least 60 large eruptions during the Holocene. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes occur on its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large open caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: 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/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Kamchatka Volcanological Station, Kamchatka Branch of Geophysical Survey, (KB GS RAS), Klyuchi, Kamchatka Krai, Russia (URL: http://volkstat.ru/); 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/); 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/); Kam 24 News Agency, 683032, Kamchatka Territory, Petropavlovsk-Kamchatsky, Vysotnaya St., 2A (URL: https://kam24.ru/news/main/20230411/96657.html#.Cj5Jrky6.dpuf); Simon Carn, Geological and Mining Engineering and Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA (URL: http://www.volcarno.com/, Twitter: @simoncarn).

Bezymianny is located on the Kamchatka Peninsula of Russia as part of the Klyuchevskoy volcano group. Historic eruptions began in 1955 and have been characterized by dome growth, explosions, pyroclastic flows, ash plumes, and ashfall. During the 1955-56 eruption a large open crater was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater. The current eruption period began in December 2016 and more recent activity has consisted of strong explosions, ash plumes, and thermal activity (BGVN 47:11). This report covers activity during November 2022 through April 2023, based on weekly and daily reports from the Kamchatka Volcano Eruptions Response Team (KVERT) and satellite data.

Activity during November and March 2023 was relatively low and mostly consisted of gas-and-steam emissions, occasional small collapses that generated avalanches along the lava dome slopes, and a persistent thermal anomaly over the volcano that was observed in satellite data on clear weather days. According to the Tokyo VAAC and KVERT, an explosion produced an ash plume that rose to 6 km altitude and drifted 25 km NE at 1825 on 29 March.

Gas-and-steam emissions, collapses generating avalanches, and thermal activity continued during April. According to two Volcano Observatory Notice for Aviation (VONA) issued on 2 and 6 April (local time) ash plumes rose to 3 km and 3.5-3.8 km altitude and drifted 35 km E and 140 km E, respectively. Satellite data from KVERT showed weak ash plumes extending up to 550 km E on 2 and 5-6 April.

A VONA issued at 0843 on 7 April described an ash plume that rose to 4.5-5 km altitude and drifted 250 km ESE. Later that day at 1326 satellite data showed an ash plume that rose to 5.5-6 km altitude and drifted 150 km ESE. A satellite image from 1600 showed an ash plume extending as far as 230 km ESE; KVERT noted that ash emissions were intensifying, likely due to avalanches from the growing lava dome. The Aviation Color Code (ACC) was raised to Red (the highest level on a four-color scale). At 1520 satellite data showed an ash plume rising to 5-5.5 km altitude and drifting 230 km ESE. That same day, Kamchatka Volcanological Station (KVS) volcanologists traveled to Ambon to collect ash; they reported that a notable eruption began at 1730, and within 20 minutes a large ash plume rose to 10 km altitude and drifted NW. KVERT reported that the strong explosive phase began at 1738. Video and satellite data taken at 1738 showed an ash plume that rose to 10-12 km altitude and drifted up to 2,800 km SE and E. Explosions were clearly audible 20 km away for 90 minutes, according to KVS. Significant amounts of ash fell at the Apakhonchich station, which turned the snow gray; ash continued to fall until the morning of 8 April. In a VONA issued at 0906 on 8 April, KVERT stated that the explosive eruption had ended; ash plumes had drifted 2,000 km E. The ACC was lowered to Orange (the third highest level on a four-color scale). The KVS team saw a lava flow on the active dome once the conditions were clear that same day (figure 53). On 20 April lava dome extrusion was reported; lava flows were noted on the flanks of the dome, and according to KVERT satellite data, a thermal anomaly was observed in the area. The ACC was lowered to Yellow (the second lowest on a four-color scale).

Figure 53. Photo showing an active lava flow descending the SE flank of Bezymianny from the lava dome on 8 April 2023. Courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.

Satellite data showed an increase in thermal activity beginning in early April 2023. A total of 31 thermal hotspots were detected by the MODVOLC thermal algorithm on 4, 5, 7, and 12 April 2023. The elevated thermal activity resulted from an increase in explosive activity and the start of an active lava flow. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system based on the analysis of MODIS data also showed a pulse in thermal activity during the same time (figure 54). Infrared satellite imagery captured a continuous thermal anomaly at the summit crater, often accompanied by white gas-and-steam emissions (figure 55). On 4 April 2023 an active lava flow was observed descending the SE flank.

Figure 54. Intermittent and low-power thermal anomalies were detected at Bezymianny during December 2022 through mid-March 2023, according to this MIROVA graph (Log Radiative Power). In early April 2023, an increase in explosive activity and eruption of a lava flow resulted in a marked increase in thermal activity. Courtesy of MIROVA.

Figure 55. Infrared satellite images of Bezymianny showed a persistent thermal anomaly over the lava dome on 18 November 2022 (top left), 28 December 2022 (top right), 15 March 2023 (bottom left), and 4 April 2023 (bottom right), often accompanied by white gas-and-steam plumes. On 4 April a lava flow was active and descending the SE flank. Images using infrared (bands 12, 11, 8a). Courtesy of Copernicus Browser.

Geologic Background. The modern Bezymianny, much smaller than its massive neighbors Kamen and Kliuchevskoi on the Kamchatka Peninsula, was formed about 4,700 years ago over a late-Pleistocene lava-dome complex and an edifice built about 11,000-7,000 years ago. Three periods of intensified activity have occurred during the past 3,000 years. The latest period, which was preceded by a 1,000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large open crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Kamchatka Volcanological Station, Kamchatka Branch of Geophysical Survey, (KB GS RAS), Klyuchi, Kamchatka Krai, Russia (URL: http://volkstat.ru/); 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/); 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/).

Chikurachki, located on Paramushir Island in the northern Kuriles, has had Plinian eruptions during the Holocene. Lava flows have reached the sea and formed capes on the NW coast; several young lava flows are also present on the E flank beneath a scoria deposit. Reported eruptions date back to 1690, with the most recent eruption period occurring during January through October 2022, characterized by occasional explosions, ash plumes, and thermal activity (BGVN 47:11). This report covers a new eruptive period during January through February 2023 that consisted of ash explosions and ash plumes, based on information from the Kamchatka Volcanic Eruptions Response Team (KVERT) and satellite data.

According to reports from KVERT, an explosive eruption began around 0630 on 29 January. Explosions generated ash plumes that rose to 3-3.5 km altitude and drifted 6-75 km SE and E, based on satellite data. As a result, the Aviation Color Code (ACC) was raised to Orange (the second highest level on a four-color scale). At 1406 and 1720 ash plumes were identified in satellite images that rose to 4.3 km altitude and extended 70 km E. By 2320 the ash plume had dissipated. A thermal anomaly was visible at the volcano on 31 January, according to a satellite image, and an ash plume was observed drifting 66 km NE.

Occasional explosions and ash plumes continued during early February. At 0850 on 1 February an ash plume rose to 3.5 km altitude and drifted 35 km NE. Satellite data showed an ash plume that rose to 3.2-3.5 km altitude and drifted 50 km NE at 1222 later that day (figure 22). A thermal anomaly was detected over the volcano during 5-6 February and ash plumes drifted as far as 125 km SE, E, and NE. Explosive events were reported at 0330 on 6 February that produced ash plumes rising to 4-4.5 km altitude and drifting 72-90 km N, NE, and ENE. KVERT noted that the last gas-and steam plume that contained some ash was observed on 8 February and drifted 55 km NE before the explosive eruption ended. The ACC was lowered to Yellow and then Green (the lowest level on a four-color scale) on 18 February.

Figure 22. Satellite image showing a true color view of a strong ash plume rising above Chikurachki on 1 February 2023. The plume drifted NE and ash deposits (dark brown-to-gray) are visible on the NE flank due to explosive activity. Courtesy of Copernicus Browser.

Geologic Background. Chikurachki, the highest volcano on Paramushir Island in the northern Kuriles, is a relatively small cone constructed on a high Pleistocene edifice. Oxidized basaltic-to-andesitic scoria deposits covering the upper part of the young cone give it a distinctive red color. Frequent basaltic Plinian eruptions have occurred during the Holocene. Lava flows have reached the sea and formed capes on the NW coast; several young lava flows are also present on the E flank beneath a scoria deposit. The Tatarinov group of six volcanic centers is located immediately to the south, and the Lomonosov cinder cone group, the source of an early Holocene lava flow that reached the saddle between it and Fuss Peak to the west, lies at the southern end of the N-S-trending Chikurachki-Tatarinov complex. In contrast to the frequently active Chikurachki, the Tatarinov centers are extensively modified by erosion and have a more complex structure. Tephrochronology gives evidence of an eruption around 1690 CE from Tatarinov, although its southern cone contains a sulfur-encrusted crater with fumaroles that were active along the margin of a crater lake until 1959.

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

Lava flows, pyroclastic flows, loud noises, and repeated forceful emissions were witnessed during June 2007-March 2008. Previously, there were brief periods of effusive activity and almost daily thermal anomalies during June 2006 through May 2007 (BGVN 32:04). Emissions during June 2007 consisted largely of steam of variable density.

On 12 June, there was a particularly forceful emission. Glow was observed on the night of 14 June. This kind of behavior continued into July. On 8 July observers saw glow and watched a single forceful release of pale gray ash.

On 14 July, Bagana generated a particularly forceful release that generated a pyroclastic flow. The release spewed out thick, dark-gray ash. The pyroclastic flow descended the S flank of the volcano stopping at the base near a small hot-spring-fed lake located at the head of the Torokina river. Since that event, rock falls from the edge of the active lava flow triggered thin ash clouds of light brown color from the S flank. This was accompanied by a loud roaring noise persisting into 15 July.

On 6 August, some emissions occasionally contained gray ash. The lava flow from the summit crater on the SE flank became active again and continued through 23 August. Thick white plumes escaped forcefully during 13-16 August. Ash clouds seen then were attributed to rock falls from collapse at the edges of the active lava flow. The Darwin VAAC reported that a diffuse plume rose to an altitude of 3.7 km on 23 August.

A particularly forceful emission occurred on 25 August and 12 September and the latter generated thin gray ash clouds directed over the SE flank.

Into October, the summit continued to release gentle emission of thin to thick white vapor. A weak to bright fluctuating glow was visible at night from 2-5 October and a continuous rumbling noise that lasted about an hour was heard on 5 October. On 6 October, there was a particularly forceful emission and the lava flow on the SE flank became active. Observers saw the lava flow emitting glow as it passed down the SE flank on 6-7, 10-12, and 17 October. Occasional thin pale gray ash clouds observed at the edges of the active lava flow were visible on 9-10, and 14-15 October. Based on satellite imagery, the Darwin VAAC reported that ash plumes drifted N then NW on 19 October.

White vapor escaped through November and into December. It was occasionally accompanied by plumes containing ash that were generated along the lava flow.

Two explosions sent forth ash plumes on 19 and 27 November. The SE-flank lavas descended almost continuously and lava fragments vented at the summit on 7 and 9 December. On 9 December an ash plume rose to an altitude of 2.8 km; another on 17 December rose to uncertain height; and one on 26-27 December rose to 3 km altitude and drifted W.

Activity in January through March was generally weak but persistent, with earthquakes absent. Satellite imagery and information from RVO led the Darwin VAAC to report a diffuse plume on 3 March. It rose to an altitude of less than 3 km and drifted SW. Later that day, an ash-and-steam plume drifted SW.

Throughout the reporting period, the MODVOLC satellite system typically detected multiple thermal anomalies monthly. The system uses MODIS (the Moderate Resolution Imaging Spectroradiometer) and a processing algorithm and staff at HIGP (see Information Contacts, below).

Geologic Background. Bagana volcano, in a remote portion of central Bougainville Island, is frequently active. This massive symmetrical cone was largely constructed by an accumulation of viscous andesitic lava flows. The entire edifice could have been constructed in about 300 years at its present rate of lava production. Eruptive activity is characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although occasional explosive activity produces pyroclastic flows. Lava flows with tongue-shaped lobes up to 50 m thick and prominent levees descend the flanks on all sides.

Information Contacts: Herman Patia, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, Northern Territory 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP) Hot Spots System, University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

Olga Girina of the Kamchatka Volcanic Eruptions Response Team (KVERT) reported no eruptive activity at Chikurachki volcano [activity that began 4 March 2007 (BGVN 32:05)] after about 18 April 2007. The following report was based primarily on information found on the KVERT website. Chikurachki is not monitored with seismic instruments, but KVERT has satellite monitoring and receives occasional reports of visual observations (figure 5).

Figure 5. Ash plume extending to the ESE from Chikurachki on 8 September 2007. Photo by L. Kotenko, supported by JSPS (Japan Society for the Promotion of Science); courtesy of KVERT Current Activity of Chikurachki website.

According to observations, no eruptive activity was noted on 12 and 14 August. However, visual information from Podgorny (20 km SSE) indicated that an eruption began on 18 August 2007 at 2200 UTC. Ashfall was noted in Podgorny at that time and on 19-20 August, and satellite data showed an ash plume extending about 120 km SE (figure 6). An ash plume extending about 100 km SE at an altitude of 5 km was observed by pilots on 20 August 20 at 0140 UTC. An ash plume extending about 160 km to the NNE at an altitude of 3 km and ashfall on Alaid volcano were noted by volcanologists on 21 August. Table 2 lists observations, when available, of the ash plume during this eruption.

Figure 6. Plume from Chikurachki taken 19 August 2007 by the Moderate Resolution Imaging Spectroradiometer (MODIS) flying on NASA's Aqua satellite. Besides Chikurachki, whose plume blows SE over the ocean, the image captures the summits of neighboring volcanos Atlasova Island and Fuss Peak above the cloud cover. Courtesy of NASA Earth Observatory.

Table 2. Ash plume observations for the eruption of Chikurachki beginning 18 August 2007. Clouds obscured the volcano on most days not noted. Courtesy of KVERT.

The eruption continued through at least 25 October 2007, and perhaps through 8 November. Clouds obscured the volcano on many days, making estimates of the continuity of this eruption and its ending date difficult. KVERT has reported no later plumes observed over Chikurachki to mid-April 2008. No thermal anomalies were measured by the MODIS satellites during 2007 or 2008 to 20 April.

Geologic Background. Chikurachki, the highest volcano on Paramushir Island in the northern Kuriles, is a relatively small cone constructed on a high Pleistocene edifice. Oxidized basaltic-to-andesitic scoria deposits covering the upper part of the young cone give it a distinctive red color. Frequent basaltic Plinian eruptions have occurred during the Holocene. Lava flows have reached the sea and formed capes on the NW coast; several young lava flows are also present on the E flank beneath a scoria deposit. The Tatarinov group of six volcanic centers is located immediately to the south, and the Lomonosov cinder cone group, the source of an early Holocene lava flow that reached the saddle between it and Fuss Peak to the west, lies at the southern end of the N-S-trending Chikurachki-Tatarinov complex. In contrast to the frequently active Chikurachki, the Tatarinov centers are extensively modified by erosion and have a more complex structure. Tephrochronology gives evidence of an eruption around 1690 CE from Tatarinov, although its southern cone contains a sulfur-encrusted crater with fumaroles that were active along the margin of a crater lake until 1959.

Information Contacts: Olga Girina, Kamchatka Volcanic Eruptions Response Team (KVERT), a cooperative program of the Institute of Volcanic Geology and Geochemistry, Far East Division, Russian Academy of Sciences, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia, the Kamchatka Experimental and Methodical Seismological Department (KEMSD), GS RAS (Russia), and the Alaska Volcano Observatory (USA) (URL: http://www.kscnet.ru/ivs/kvert/updates.shtml); Alaska Volcano Observatory (AVO), a cooperative program of the U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), the Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and the Alaska Division of Geological and Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA; NASA Earth Observatory Natural Hazards (URL: http://earthobservatory.nasa.gov/NaturalHazards/); KVERT Current Activity of Chikurachki (URL: http://www.kscnet.ru/ivs/kvert/current/chkr/).

The Mt. Erebus Volcano Observatory (MEVO) website activity log gives information on each eruption of the volcano detected. Daily activity that usually includes several eruptions. Erebus eruption sizes are measured in the pressure unit of Pascals (Pa) from the infrasonic overpressure (at Station E1S.IS1). The eruption size index scale is divided into events classified as small (0-19 Pa), medium (20-39 Pa), large (40-59 Pa), and very large (>= 60 Pa).

Table 2 lists large and very large eruptions for the period December 2006 through 23 October 2007 (BGVN 31:12 gave a similar list for the year 2006 through November). The absence of recorded eruptions from 13 April 2007 to 29 August 2007 is notable. No eruptions were reported on the website during 23 October 2007 to 29 April 2008.

Table 2. Eruptions recorded at Erebus in the instrumentally derived categories "large" and "very large" during December 2006-23 October 2007. Courtesy of MEVO.

Thermal anomalies over Erebus, measured from the MODIS (Moderate Resolution Imaging Spectroradiometer) satellite images were analyzed by the Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC algorithm. They commonly appeared throughout the 2007 due to the presence of a molten lava lake within the crater.

Geologic Background. Mount Erebus, the world's southernmost historically active volcano, overlooks the McMurdo research station on Ross Island. It is the largest of three major volcanoes forming the crudely triangular Ross Island. The summit of the dominantly phonolitic volcano has been modified by one or two generations of caldera formation. A summit plateau at about 3,200 m elevation marks the rim of the youngest caldera, which formed during the late-Pleistocene and within which the modern cone was constructed. An elliptical 500 x 600 m wide, 110-m-deep crater truncates the summit and contains an active lava lake within a 250-m-wide, 100-m-deep inner crater; other lava lakes are sometimes present. The glacier-covered volcano was erupting when first sighted by Captain James Ross in 1841. Continuous lava-lake activity with minor explosions, punctuated by occasional larger Strombolian explosions that eject bombs onto the crater rim, has been documented since 1972, but has probably been occurring for much of the volcano's recent history.

Information Contacts: Philip R. Kyle and Kyle Jones, Mt. Erebus Volcano Observatory (MEVO), New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA (URL: https://nmtearth.com/); Hawai'i Institute of Geophysics and Planetology (HIGP) MODIS Thermal Alerts, 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/).

As reported in (BGVN 31:07) Galeras displayed dome growth and elevated seismicity from November 2005 through mid-August 2006; ~ 10,000 residents evacuated but the crisis later abated. The key source of this report was the Instituto Colombiano de Geologia y Mineria (INGEOMINAS). This report follows the August 2006 events and covers the period through April 2008.

In September 2006, INGEOMINAS recorded continuing low-level minor earthquakes, M 1.4, corresponding to the movement of fluids at depths between 4 and 8 km and low SO₂ fluxes. A fly-over observed gas and steam emissions from the periphery of the active cone with diminished intensity through early November.

Beginning in late November and continuing through December 2006, an increase in the level of the volcanic activity occurred indicating the movement of solid material at focal depths to 9.6 km and at intensities to M 2.1. INGEOMINAS raised the Alert Level from 3 to 2 elevating the hazard status to "likely eruption in days or weeks" on 22 November 2006. The scale extends from 4 (lowest) to 1 ( highest hazard). The change was based on the increase in activity, behavior resembling characteristics that preceded earlier eruptions, i.e., increased earthquake activity associated with rock fractures within 2 km of the surface and weak gas emissions caused by the apparent capping of the lava dome.

On 2 March 2007, a tectonic earthquake was recorded ~ 2 km NNW of Galeras at M 3.5 and focal depth of 8.2 km. On 15 March, observations made with the support of the Colombian Air Force (FACE), showed continuing low rates of gas discharge continuing from secondary craters and fumaroles mainly located in the periphery of the main crater. On 20 March, because of decreased seismicity, low gas emissions, and no indication of changes below the surface of the dome, the Alert Level shifted towards less severe, from 2 to 3 (to "changes in the behavior of volcanic activity have been noted").

On 19 and 21 May 2007, two earthquakes registered, M 3.0 and M 2.1 respectively. These earthquakes were located SW of Galeras and felt by residents. The inclinometer to the SW of the active crater continued showing deformation indicating deeper volcanic activity.

Little volcanic activity occurred through September 2007. From October 2007 through January 2008, INGEOMINAS and the Washington Volcanic Ash Advisory Center reported an increase in gas-and steam plumes emitted from Galeras (table 8). During an overflight on 27 November, thermal images recorded by INGEOMINAS indicated an increase in temperatures at the point sources of emissions. The Alert Level remained at 3. Occasional gas and steam eruptions continued through January 2008.

Table 8. Summary of activity reported at Galeras from October 2007 through January 2008. Based on information from INGEOMINAS and the Washington Volcanic Ash Advisory Center.

On 11 January 2008, INGEOMINAS noted variations in seismicity associated with greater volumes of gas discharge. On 16-17 January, 5 tremors were recorded near the active cone. Early on 17 January, INGEOMINAS noted the similarity of these events to those preceding the eruptions of 1992, 1993, and 2004-2006.

Later, on the 17th, an explosive eruption was registered by the seismic network and prompted INGEOMINAS to raise the Alert Level from 3 ("changes in the behavior of volcanic activity have been noted") to 1 ("imminent eruption or in course"). The Washington VAAC reported that an ash plume rose to an altitude of 11 km and drifted W. According to a news article, small settlements to the N were ordered to evacuate; about 100 people moved to shelters.

About 2 km away from the main crater, military personnel saw blocks 1.5 m in diameter on a highway. Several impact craters of 17 January were spotted; the largest, ~ 15 m across and ~ 5 m deep (figure 111).

Figure 111. A composite of several photos showing a large impact crater formed by the Galeras eruption of 17 January 2008. The impact site was 1.5 km S of the main crater. Courtesy of INGEOMINAS.

On 19 January 2008, INGEOMINAS lowered the Alert Level to 2 ("likely eruption in days of weeks") because seismic events decreased in occurrence and energy and on 21 January, INGEOMINAS further lowered the Alert Level to 3 and reported that the initial ash plume from the eruption drifted SW, then W. Through February and into March seismic activity remained low. However, in mid-March, a a cluster of earthquakes (several events in a relatively short time interval), associated mainly with movement of magmatic fluids to the interior of the volcanic system were recorded. Volcanic gas and steam columns were routinely observed between 200 and 450 m from the top of Galeras, with variable directions of dispersion depending on the wind direction. Seismicity decreased in early April and SO₂ emissions remained low.

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

Information Contacts: Diego Gomez Martinez, Observatorio Vulcanológico y Sismológico de Pasto (OVSP), INGEOMINAS, Carrera 31, 1807 Parque Infantil, PO Box 1795, Pasto, Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html; Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Associated Press (URL: http://www.ap.org/).

During late 2007 and continuing into 2008, it became clear the Karkar's vegetation had suffered and seismicity was significant (tens of earthquakes per day). Herman Patia of the Rabaul Volcano Observatory (RVO) reported that the Bagiai cone situated in the inner caldera of Karkar volcano continued to release thin to moderate white vapor while a RVO team was at the volcano from 27-31 December 2007. The white vapor plume was also visible from the mainland. Prior to the visit, communities on the W and SW had heard occasional roaring noises associated with the gas emission from the Bagiai cone. The last Bulletin (BGVN 25:11) discussed light ashfall ultimately attributed to Ulawun. In early November 2007, RVO had reported vegetation die-back and increased fumarolic activity at Bagiai cone on the floor of the inner caldera (figure 5). Latest images sent to RVO by Sir Peter Barter on 11 December 2007 indicated that vegetation on the SE flank had withered completely. According to RVO, the last eruption of Karkar was in 1979.

Figure 5. Vegetation die-back and increased fumarolic activity on Bagiai cone at Karkar; (top) photo taken early in 2007, (bottom) photo taken during the last week of October 2007. Courtesy of RVO; photos by Paul Goodyear.

During the team's December visit, they deployed three portable seismic recorders on the NW, SW, and E sides of the island (figure 6, open triangles). Preliminary results indicated a total of 30 high-frequency (HF) earthquakes recorded during the 3 days of deployment. These events were interpreted as indicative of rock-breaking due to magma movement under the volcano. The overall seismicity was low.

Figure 6. A map of the island of Karkar showing morphology. Open triangles indicate seismograph stations during 28-31 December 2007 (KSUG, KWAD, and KKEV). The filled triangles indicate seismograph stations during 24 January-3 February 2008 (KMAT, KARS, and KMID). The outlined oval-shaped region endorses the approximate area where the high-frequency earthquakes had epicenters. The regions decorated with square dots indicate channels, which provide possible pathways for mudflows and pyroclastic flows. Small dots villages, some of which lie within these channels. Courtesy of RVO.

Bagiai cone continued to release variable volumes of white vapor towards the end of January 2008. A second phase of seismic monitoring at Karkar was carried on from 24 January to 3 February 2008. (figure 6, filled triangles). The closest seismometer to the cone was placed ~ 3 km away Seismic activity was low, dominated by high-frequency earthquakes, but low-frequency earthquakes also occurred. About 15?20 earthquakes were recorded daily during the first 3 days of recording (24-28 January), the earthquakes occurring near Bagiai cone in the center of the inner caldera.

The two phases of seismic monitoring detected both high-frequency volcano-tectonic (VT) earthquakes and low-frequency earthquakes. VT earthquakes were taken to indicate magma intrusion underneath or near Karkar volcano and were detected during the December 2007 deployment by two of the three stations (KWAD and KKEV) on the E and SE side. Station KSUG did not record the HF earthquakes.

The seismic monitor installed about 3 km from Bagiai cone (KMAT), at a spot adjacent to the thermal activity, recorded LF earthquakes as well. LF earthquakes were presumed to be associated with movement of steam and gas and the hydrothermal activity at Bagiai cone.

To provide continuous seismic monitoring at Karkar, on 3 February 2008 a portable seismic recorder was installed 9 km N of the cone. RVO intends to download and analyze the data every 2 months.

For several weeks during late February into early March 2008, RVO scientists visited Karkar to monitor the increased seismic activity first monitored during December 2007. Once again, the group reported that thermal activity from within the cone had caused the vegetation to die and turn brown. On this visit, withered and dry vegetation could be observed on Bagiai's flanks. Seismicity was continuing, but at low levels. On this visit, three portable seismic recorders were deployed close to the summit area on the outer caldera, 3.5 km from Bagiai. They recorded 15-20 volcanic earthquakes per day.

There have been no thermal anomalies measured over Karkar by MODIS instruments since at least the beginning of 2007 through mid-April 2008.

Geologic Background. Karkar is a 19 x 25 km forest-covered island that is truncated by two nested summit calderas. The 5.5 km outer caldera was formed during one or more eruptions, the last of which occurred 9,000 years ago. The steep-walled 300-m-deep, 3.2 km diameter, inner caldera was formed sometime between 1,500 and 800 years ago. Cones are present on the N and S flanks of this basaltic-to-andesitic volcano; a linear array of small cones extends from the northern rim of the outer caldera nearly to the coast. Recorded eruptions date back to 1643 from Bagiai, a pyroclastic cone constructed within the inner caldera, the floor of which is covered by young, mostly unvegetated andesitic lava flows.

Information Contacts: Herman Patia, Rabaul Volcanological Observatory (RVO), P.O. Box 3386, Kokopo, Papua New Guinea; MODVOLC Hawai'i Institute of Geophysics and Planetology (HIGP) 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/).

The extrusion of a substantial dome into the center of the active crater lake at Kelut (also spelled Kelud) started in early November 2007. The volcano and lake are among the most historically active and dangerous in Indonesia (Thouret and others, 1998). They were studied by members of the Volcanological Survey of Indonesia (VSI), Alain Bernard, and colleagues. During about 15 years prior to the eruption, the crater lake showed considerable hydrothermal influence, with temperatures several degrees above the ambient air temperature of 19°C, but with near-neutral pH. Prior to this eruption, the lake was ~ 34 m deep, ~ 350 m in diameter, and it held ~ 2.1 x 10⁶ m³ of water (Bernard and Mazot, 2004).

Lava was clearly seen emerging from the center of the lake on 4 November 2007. The activity was passive, even at the contact between the dome and lake. Neither water nor substantial ash were thrown forcefully out of the lake and onto the flanks. The dome rose rapidly above the lake, building a steep construct surrounded by a placid but dwindling lake. A well-defined depression crossed the dome's center, dividing its top surface in two. A few undated photos showed a mildly explosive phase. During 29-30 November the still-erupting dome was stable. As of early May 2008, tentative reports suggested that dome extrusion had ceased or paused. A lake still existed at that point.

Setting, historical lahars, and morphology. The volcano resides in a densely populated part of Java (1,800 people/km²) and could threaten over 3 million residents (Bernard, 2000). Bernard (2000) also noted that Kelut's approximately 30 historical eruptions have caused over 15,000 deaths since 1500 AD. Kelut's last eruption occurred in 1990 (BGVN 15:01). One of the most detailed VSI reports on Kelud's pre-eruptive behavior was issued 30 October 2007 (Surono, 2007).

Although lahars were absent during the 2007 eruption, lahars were associated with eruptions in 1919 and 1966; post-1996 lahars came in response to rainfall (figure 2). To control lahars and related problems, decades before engineers had driven a complex series of drainage tunnels through the edifice's walls, draining much of the lake.

Figure 2. Map of Kelut showing prominent drainages on the W side and key settlements such as Kediri, Tulungagung, and Blitar (respective populations, 252,000, 970,000 and 1,200,000), and three sets of lahars. Heavy (often straight) lines indicate some local political boundaries. The 2007 eruption did not trigger lahars. After Rodolfo (1999).

Lake chemistry. Active crater lakes such as Kelut's trap some fraction of the heat and fluids escaping the magmatic and hydrothermal system (Delmelle and Bernard, 1999), and their study has led to breakthroughs in eruption prediction. One example of this kind of study (figure 3) presents various heat and mass-balance factors in a model of Kelut's lake (Bernard and Mazot, 2004). Heat is derived from the enthalpy (E) of hydrothermal fluids (Ebrine + steam) and from solar and atmospheric radiation (Erad). Heat is lost by evaporation (Eevap), conduction (Econd), radiation (Erad), and by the overflow (Eover) of hot waters through the drainage tunnel.

Figure 3. A sketch of Kelut's summit crater made prior to the 2007 eruption, looking E. The 2007 eruption built a dome in the lake's center. The irregular high area on the far wall of the crater (labeled "dome") is called Gunung Kelut, and is but one of many domes at the complex. The arrows are explained in the text. The dashed 'drainage tunnel' through the edifice walls is schematic, the actual tunnels consist of a network built in successive stages. Diagram after Bernard and Mazot (2004).

Monitoring instrumentation is in place on and around the lake (figure 4). Fieldwork is also performed to measure the flux of CO₂ emitted at the lake surface (figure 5). Numerous CO₂-bearing gas bubbles rising to the surface were seen in July 2006. Bubbles were also widespread on bathymetric soundings (eg. detected at 50 and 200 kHz) in July 2007, and in some cases observers witnessed frequent discontinuous gas releases (puffing) from bottom fumaroles.

Figure 4. A pre-eruption photo showing Kelut's lake from a high point on the rim. Numbered sites are monitoring stations, as follows: 1) temperature and conductivity at 15 m depth and meteorological conditions (air temperature, relative humidity, and wind velocity), 2-4) lake level sensors, where the pressure difference between stations 3 and 4 functions as a N-S tilt meter), and 5) a radon sensor. Instrumentation also monitors the runoff volume in the drainage tunnel. A buoy (at 1) was one of three ultimately installed in the lake. A service road down the crater wall leads to the lake end of a drainage tunnel. Courtesy of A. Bernard.

Figure 5. (bottom left) A July 2006 photo at Kelut of the team taking a CO2 flux measurement at a sample site. The team consisted of (left to right) Loic Peiffer, Khirul Huda from VSI, and Alain Bernard. The team used a floating accumulation chamber connected by tubing to a dedicated spectrometer residing in the boat. (top left) A graph of 2007 spectrometer data from a sampling cycle with the accumulation chamber. After a lag time of ~ 30 seconds, the accumulation rate was stable at a slope of ~ 400 ppm/s. (right) Resulting map of lake surface showing CO2 flux per unit area (in the units of grams per square meter per day, g/(m2/d)). The map resulted from 230 spot measurements taken between 30 July and 2 August 2007. Courtesy of Alain Bernard.

The CO₂ flux from the lake's surface was measured by IR spectrophotometry using a Dr?ger Polytron instrument. Bernard's team modified a technique initially developed for monitoring the flux of gases in soil (Chiodini and others, 1996), applying this method by means of the floating accumulation chamber at multiple sites.

According to the VSI report, carbon dioxide (CO₂) concentrations measured during 30 July to 2 August 2007 ranged from below 500 g/m²/d to hotspots of 12,000 g/m²/d, especially in the E portion of the lake. The overall flux of CO₂ from the lake reached more than 500 tons/day on 11 September 2007, about ten times greater than measurements made in 2005 and 2006 (figure 6).

Figure 6. A plot for Kelut from 2001 through 2 August 2007 showing water temperature and total CO2 flux from the lake. The total CO2 flux was estimated by normalizing the data to the relevant lake area at Kelut, 103,600 m2). The latest CO2 field measurements were made during 30 July to 2 August 2007. The line shows lake temperature readings (taken at uncertain depth and location, but presumably more consistently measured than temperature data shown on table 2. Unfortunately, these plotted temperature data do not extend into late 2007 when table 2 suggests lake temperatures rose more than 50°C higher, to ~ 78°C).

Data on lake chemistry (table 2) was compiled by Surono (2007) and Bernard (2000). The water chemistry of the active crater lake showed both stable and variable parameters. Comparatively stable ones included pH and during various time periods (including 2007), some chemical species. Among the largest perturbations were a sudden, almost two-fold rise in SO₂ during September-October 2007; and a rapid increase in lake water temperature during November 2007. Soluble Cl stood over 1,000 ppm during 1993 and dropped sharply reaching a low of 67 ppm on 20 August 2007. It climbed after that, reaching 354 ppm in the last (11 November) measurement, a value taken about a week after the dome broke the lake surface.

Table 2. A compilation for Kelut's lake water showing temperature, pH, and chemical concentration data from VSI for 2007 (Surono, 2007) and Alain Bernard (2000) during 1993 to 2005. Some of the data presented here were rounded and the number of significant figures reduced. The 23 October 2007 Cl value was variously reported. Some of the original data were presumably collected at different locations and depths; and some of the original data included additional parameters such as total dissolved solids (see cited publications). Eruptions began on 3 November 2007, and the dome emerged above the lake surface on 4 November.

Monitoring, hazards status, and dome extrusion. Visual monitoring was carried out by means of a closed-circuit video monitor installed on Mount Lirang, as well as from photographs taken in or near the crater. During 15-28 September, gas emissions from the crater lake increased and spread over a zone within a radius of ~ 5 m.

According to Surono (2007), pre-eruption CO₂ fluxes from the lake were typically 50 metric tons/day. During August 2007 they rose to 333 tons/day; during late August to early September they reached 500 tons/day.

During 2006, the Darwin Volcanic Ash Advisory Center (VAAC) reported a pilot observation. An ash plume on 18 May 2006 allegedly reached an altitude of 5.5 km.

On 17 October 2007 Kelut was the subject of further VAAC reports, first noting the elevation of the hazard status to 4 (the highest level, indicating an eruption imminent). On 23 October there was a brief noting evidence from a satellite of a eruption (to ~ 6 km altitude) but ground observers suggested that it was a meteorological cloud. A VAAC report on 4 November noted "ash not identifiable on satellite imagery." On 8 November an advisory noted the continued absence of identifiable ash.

Seismicity rose suddenly on 10 September 2007 (figure 7). It peaked on 16 October at all four seismic stations on or adjacent the volcano, at 510 events. The next day, the number of earthquakes still stood quite high, 151.

Figure 7. Kelut seismicity, lake-water temperature, and Alert Levels registered during June to early November October 2007. After plots by Surono (2007) and Bernard.

Cross sections showing hypocenters for 10-11 and 26-29 September 2007 depicted them broadly centered below the edifice but distributed around 2.5 km depth; they were initially absent in a zone about 2-3 km below the summit . During mid-October the hypocenters became more closely packed along a narrow vertical band beneath the edifice. They then filled a zone 0.7-1.2 km beneath the summit, with a few other hypocenters centered ~ 2 km below the summit. During 24-29 October, many hypocenters clustered ~ 6 km below the summit, but others strung out on or about a vertical line intersecting near the summit. The shallowest events plotted were then ~ 1 km below the summit. Reports also noted tremor was common during 24 October through 4 November.

VSI issued a series of increases in Kelut's hazard status (a scale of 1-4, figure 7). On 11 September 2007, VSI raised the status from 1 to 2. This corresponded to the CO₂ flux mentioned above, a sudden jump in seismicity on 10 September (figure 7), and changes in both lake temperature and color, which shifted from its usual green, becoming yellow in some areas and blue-white in others. On 29 September, the status went from 2 to 3 based on visual observations, increased seismicity, deformation measurements, and further changes of crater lake water chemistry and temperature.

VSI brought the status to 4 on 16 October (figure 7). Factors included the sudden rise in seismicity, and the summit's inflation during 13-16 October. Before the crisis of 16 October the lake water was whitish green; after the crisis, dominantly green. VSI to recommend that villagers within a 10-km radius evacuate. According to a United Nations report, local authorities evacuated ~ 117,000 people within this radius. The UN report cited Indonesian media as stating that an eruption could affect as many as ~ 290,000 people (figure 8).

Figure 8. A map of a portion of E Java that indicates the location of Kelut (sometimes written as "Kelud," as is the case here) and the major city Surabaya (~ 85 km NE; population, ~ 4 million). The map was issued after the alert status was raised to the highest level ("4"; at 1800 on 16 October) and indicates the number of people in two adjacent jurisdictions that could be affected by its eruption. Courtesy of Relief Web (United Nations); boundaries and names shown and the designations used on this map do not imply official endorsement or acceptance by the United Nations.

According to a news article, thousands returned to their homes on 17 October to tend to crops and animals, and to retrieve food. On 8 November the status fell to 3 and residents were allowed to return home. On 29 November the status fell from 3 to 2 following both decreased seismicity and a lack of deformation. At this stage, people were advised to remain at least 1.5 km from the lake.

During 24-31 October, a series of regional earthquakes occurred, dominated by shallow events and tremor. Seismicity intensified during 2-3 November, but then decreased on 4 November.

Dome emerges during 3-4 November 2007. On 3 November, VSI and news media mentioned plumes, and possibly some evidence of erupted solids entering the lake. Also, their buoy ceased functioning. On 4 November, white plumes rose to an altitude of 2.2 km and drifted N.

Plumes on the 4th came from a fresh black lava dome, protruding from the then turbid green lake. Monitoring cameras showed copious steam obscuring the dome. The exposed mass grew quickly. Although steaming continued, relative calm usually prevailed at both the dome and the lake. Although the dome steadily displaced the lake, the water did not undergo violent broad-scale boiling.

According to VSI, the temperature at the surface of the crater lake on 6 November had climbed to over 75°C. The newly exposed dome surface was 150-210°C. Plumes generally inhibited clear views.

On 8 November, VSI reported a decrease in seismicity, and deformation-monitoring suggested greater stability. An infrared camera (FLIR) captured images of the dome on 9 November as it emerged from the lake. The images revealed considerable radiant heat in the FLIR-sensitive wavelengths (figure 9).

Figure 9. On 9 November 2007, scientists looking at Kelut's new dome took these two photos, and at right, coinciding infrared (FLIR) images. The scale bars on the FLIR images indicate that the highest temperatures were on the order of 135°C. The hottest zones occurred both over a large area at the dome's top and along a band following the dome near the lake surface. Courtesy of VSI and taken from Bernard (2007).

According to a news article by Agence France Presse on 12 November, a volcanologist reported that the lava dome had reached 250 m in diameter and was 120 m above the lake surface.

November photos and videos. On 11 November, a plume rose to an altitude of 3.7 km and ashfall was reported in several areas. News accounts indicated that tremors continued and that Kelut was spewing ash and lava. More photos of the dome, particularly during 10-29 November, would be useful for understanding activity in this period.

An undated video provides views of a short-lived avalanche down from the new dome's upper walls. Based on the size of the dome then, the scene was probably captured in mid- to late November (it was posted on 7 December; Masdjawa, 2007). The avalanche initially contained on the order of 5-20 m³ of loose material, much of it incandescent in daylight. A large portion of this material bounced downslope into the steaming lake. When sufficient fragmental material entered the lake an intense phreatic eruption took place. The clouds rose vertically; they were initially jet black, but within tens of seconds became dominantly white steam, hiding the dome for ~ 1-2 minutes.

Daniel Brazilier visited during 25-26 November and saw mildly to moderately explosive activity; his photos appeared in Societe de Volcanologie Geneve reports (SVG, 2007). Many of his photos were taken during daylight from ~ 1.5 km away; they showed several explosions with billowing white-to-tan clouds. The foreground, the W crater wall, contained small amounts of tephra and some bombs. The billowing clouds appeared to contain minor ash; they vented from the dome upper area or side, and accompanied numerous steaming bombs, which from their arcing trails, seemed destined to land within the crater. Night photos disclosed large areas of incandescence on the W side.

Tom Pfeiffer took a series of remarkable photos on 29-30 November 2007, documenting a surprisingly large and clearly fast-growing dome. He posted over 60 photos on the Volcano Discovery website and elsewhere, and several of them appear here (figures 10, 11, and 12).

Figure 10. Kelut's dome seen in low-light conditions on 29 or 30 November 2007 in a view looking towards the E. Myriad incandescent fragments detached from the dome, leaving incandescent scars in the middle to upper dome area. The dome's summit area and much of its lower skirt are chiefly dark, except in the latter case for the trails of material bouncing and falling past. The much reduced lake was calm and wrapping around the dome's left (N) side. The segment of the crater rim towering above the new dome's right side is the older dome mentioned in figure 3. Copyrighted photo by Tom Pfeiffer (Volcano Discovery).

Figure 11. A NE view under dark conditions of Kelut's growing dome at a time on 29 or 30 November when dome incandescence was particularly high. In the foreground is the pathway leading to the lake. Comparatively few bombs littered the curbing along the pathway, but pelting from bombs had apparently damaged the steel hand-rail in a few places. Copyrighted photo by Tom Pfeiffer (Volcano Discovery).

Figure 12. Kelut's new lava dome had reduced the crater lake to a narrow band by 29-30 November 2007. This low-light photo looking NE captured the shrinking lake and its contact with the new dome. At right is a prominent avalanche chute choked with the incandescent trails of bouncing blocks. Upon entry into the lake some of the trails made a second bounce. Copyrighted photo by Tom Pfeiffer (Volcano Discovery).

Note that Pfeiffer's photos are night-time shots with long exposures and thus the impression of large glowing areas implies more activity than really occurred at any one time. The dome had clearly crowded out the then green or brownish lake, which in the field of view had been reduced to an arcuate sliver. The extent of the lake on the dome's W and SW sides was unclear from his perspective.

Particularly on figures 10 and 11, the dome was rife with abundant glowing zones and numerous red traces due to incandescent dome rocks bouncing downslope. Abundant were glowing avalanche trails, and large rockfall scars. The photos also suggest possible lava seeps and narrow lava flows, although Tom Pfeiffer attributed most of the incandescence to mobile and solidified material, rather than narrow zones occupied by fluid moving lava.

A few of the glowing traces in the photos terminate upon entering the crater lake (figure 12). After their first contact with the water, some of those descending traces also seemingly shattered and bounced, producing one or more secondary arcs (akin to a skipping stone).

Pfeiffer described the scene as "filled with the noises of cracking lava, falling debris, and chilled lava blocks that splashed into the lake." He went on to note the lack of "explosions, or major ash emissions attached to the activity. The lava dome was simply growing quietly and not doing anything else than what is visible on the photos." He was struck by the observation "that the lake was simply there and NOT boiling. A sign how well rock insulates. Also, the upper 10 meters of the dome, its very top, were rather inactive, like the top of a mushroom being lifted up. The most active zones were just underneath that upper crust . . .."

References. Bernard A., and Mazot A., 2004, Geochemical evolution of the young crater lake of Kelud volcano in Indonesia: Proceedings of the Eleventh International Symposium on Water-Rock Interaction, Saratoga Springs, New York, USA, v. 1, p. 87-90.

Bernard, A., 2000, Geochemistry of the crater lake of Kelut volcano, Indonesia: Essay labeled "in preparation" on the http://www.ulb.ac.be/ website.

Bourdier, J. L., Pratomo, I., Thouret, J.C., Boudon, G. and Vincent, P.M., 1997. Observations, stratigraphy and eruptive processes of the 1990 eruption of Kelut volcano, Indonesia: J. Volcanol. Geotherm. Res., v. 79, p. 181-203.

Delmelle, P., and Bernard, A., 1999, Volcanic lakes, in Encyclopedia of volcanoes, H. Sigurdsson (ed.): Academic Press, p. 877-895.

Masdjawa, 2007, Kelud-Kubah Lava: Kelud_03.mpg (23.2 Mb), 2 min 20 sec; http://masdjawa.multiply.com/video/item/4

Rodolfo, K. S., 1999, The hazard from lahars and Jökulhaups, in Encyclopedia of volcanoes, H. Sigurdsson (ed.): Academic Press, p. 973-995.

Surono, 2007, Pusat Vulkanologi Dan Mitigasi Bencana Geologi, Pos Pengamatan Gunungapi Kelut (Hasil evaluasi tingkat kegiatan G. Kelut): Departemen Energi Dan Sumber Daya Mineral, Republik Indonesia, Badan Geologi, Nomor, 112/GK/X/2007, 30 Oktober 2007.

Thouret, J. C., Abdurachman, K. E., and Bourdier, J. L., 1998, Origin, characteristics, and behavior of lahars following the 1990 eruption of Kelud volcano, eastern Java (Indonesia): Bull. Volcanol., v. 59, p. 460-480.

Geologic Background. The relatively inconspicuous Kelud stratovolcano contains a summit crater lake that has been the source of some of Indonesia's most deadly eruptions. A cluster of summit lava domes cut by numerous craters has given the summit a very irregular profile. Satellitic cones and lava domes are also located low on the E, W, and SSW flanks. Eruptive activity has in general migrated in a clockwise direction around the summit vent complex. More than 30 eruptions have been recorded since 1000 CE. The ejection of water from the crater lake during the typically short but violent eruptions has created pyroclastic flows and lahars that have caused widespread fatalities and destruction. After more than 5,000 people were killed during an eruption in 1919, an engineering project to drain the crater lake lowered the surface by more than 50 m. The 1951 eruption deepened the crater by 70 m, leaving 50 million cubic meters of water after the damaged drainage tunnels were repaired. Following more than 200 deaths in the 1966 eruption, a new deeper tunnel was constructed, and the lake's volume before the 1990 eruption was only about 1 million cubic meters.

Information Contacts: Volcanological Survey of Indonesia, Center of Volcanology and Geological Hazard Mitigation, Saut Simatupang, 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/); Alain Bernard, Free University of Brussels, CP 160/02, 50, avenue F, Roosevelt, 1050 Brussels, Belgium (URL: http://www.ulb.ac.be/sciences/cvl/); Relief Web, United Nations Office for the Coordination of Humanitarian Affairs, Resident Coordinator's Office, Jakarta, Indonesia (URL: https://reliefweb.int/, http://www.unocha.org/); Darwin Volcanic Ash Advisory Center, Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, Northern Territory 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Tom Pfeiffer, Volcano Discovery (URL: http://www.VolcanoDiscovery.com/); Daniel Brazilier, France.

On 28 March 2008, reporter Michael Field noted that an eruption of the submarine volcano Monowai was taking place. Olivier Hyvernaud was quoted in the article as saying that they recorded on the Polynesian Seismic Network (Réseau Sismique Polynésien, or RSP) a "big acoustic event" on 8 February. [He also noted that the volcano was in an eruptive phase, but it was not clear if it was a strong eruption.] The news article went on to say that, according to geologist Cornel de Ronde, the French Polynesian RSP currently receives submarine hydrophone signals from Monowai eruptions more easily than stations in New Zealand. The article concluded that this activity went unnoticed as its location is off the main shipping routes.

Ian Wright of the New Zealand National Institute of Water and Atmospheric Research (NIWA) informed us about new volcano discoveries along the S-central Kermadec arc and some recent mapping results from Monowai. In recent years, New Zealand scientists have mapped, using soundings made by multibeam acoustic arrays, most of the Kermadec arc, with the consequent discovery and naming of a number of 'new' arc volcanoes. Some of the more recent work for the 30°-35°S latitude sector was published in Wright and others (2006). A second manuscript detailing the 25°-30°S latitude sector will be completed soon for publication by Graham and others.

Wright and his colleagues mapped Monowai using the multibeam system in 1998 and again in 2004, identifying drastic changes in morphology during that 6-year period. They found edifice collapse and cone regrowth. They interpreted these changes in morphology in the context of T-wave data recorded by Hyvernaud and his colleague Dominique Reymond [Wright and others, 2008 (in press); BGVN 32:01].

As indicated on figures 20 and 21, the group subsequently re-mapped Monowai in mid-2007 for a third time, again finding drastic changes coinciding with a period of ongoing and high T-wave activity. They are currently preparing a manuscript detailing these latter changes (Chadwick and others, in preparation). According to Bill Chadwick, while the research ship was on site conducting the 2007 survey and attempting some remotely operated vehicle (ROV) dives, scientists heard booming sounds and saw slicks and bubbles on the surface.

Figure 20. Multibeam bathymetry and shaded terrain model of the Monowai volcanic complex, including its caldera and cone. Isobaths are shown at 50 m intervals. Courtesy of Wright and others, 2008 (in press).

Figure 21. Cumulative number of T-wave events centered at Monowai during the latter half of 2002 through 2007 from monitoring data at RSP (covering the times of the September 2004 and May 2007 bathymetric surveys, and the anomalous 24 May 2002 swarm, as reported in BGVN 27:05 and 32:01). Courtesy of Hyvernaud and Reymond, Laboratoire de Geophysique (LDG); from Chadwick and others (in preparation).

Bob Dziak of NOAA informed the Bulletin staff that Monowai T-phases are recorded on the NOAA East Pacific Rise hydrophone arrays, but analysis of data from those arrays await their retrieval of recording packages from ocean deployment sites. (In contrast, Hyvernaud of LDG in French Polynesia recovers data in real-time.) Dziak also mentioned that, from time to time, T-phase events from what is likely volcanic activity in the Izu-Bonin Mariana region are recorded by the NOAA real-time system in the North Pacific. He offered to provide a later Bulletin report.

A recent paper by de Rhonde and others (2008) noted that all the major submarine volcanic centers on the Kermadec intraoceanic arc NE of New Zealand (including Monowai) are hydrothermally active. The Monowai volcanic complex has two separate and extensive hydrothermal fields associated with the Monowai caldera and the Monowai cone, respectively.

References. Wright, I.C., Worthington, T.J., and Gamble, J.A., 2006, New multibeam mapping and geochemistry of the 30°-35°S sector, and overview, of southern Kermadec arc volcanism, Journal of Volcanology and Geothermal Research, v. 149, p. 263-296.

Wright, I. C., Chadwick, W., de Ronde, C. E. J., Reymond, D., Hyvernaud, O., Gennerich, H., Stoffers, P., Mackay, K., Dunkin, M., and Bannister, S., 2008 (in press), Collapse and reconstruction of Monowai submarine volcano, Kermadec arc, 1998-2004, Journal of Geophysical Research, doi:10.1029/2007JB005138.

de Ronde, C.E.J., Baker, E.T., Lupton, J.L., Sprovieri, M., Bruno, P.P., Faure, K., Leybourne, M.I., Walker, S.L., Italiano, F., Embley, R.W., Graham, I., Greene, R.R., Wright, I.C., and NZAPLUME III & Aeolian'07 shipboard parties, 2008, Contrasting examples of submarine hydrothermal venting along the Kermadec intraoceanic arc and the Aeolian island arc, Geophysical Research Abstracts, v. 10, EGU2008-A-05597, 2008 (SRef-ID: 1607-7962/gra/EGU2008-A-05597).

Geologic Background. Monowai, also known as Orion seamount, is a basaltic stratovolcano that rises from a depth of about 1,500 to within 100 m of the ocean surface about halfway between the Kermadec and Tonga island groups, at the southern end of the Tonga Ridge. Small cones occur on the N and W flanks, and an 8.5 x 11 km submarine caldera with a depth of more than 1,500 m lies to the NNE. Numerous eruptions have been identified using submarine acoustic signals since it was first recognized as a volcano in 1977. A shoal that had been reported in 1944 may have been a pumice raft or water disturbance due to degassing. Surface observations have included water discoloration, vigorous gas bubbling, and areas of upwelling water, sometimes accompanied by rumbling noises. It was named for one of the New Zealand Navy bathymetric survey ships that documented its morphology.

Information Contacts: Ian Wright, New Zealand National Institute of Water and Atmospheric Research (NIWA), Private Bag 14-901, Wellington, 6003, New Zealand; Cornel de Ronde, GNS Science, Lower Hutt, 5040 New Zealand; Olivier Hyvernaud and Dominique Reymond, Laboratoire de Géophysique, Commissariat a l'Energie Atomique (CEA/DASE/LDG), PO Box 640, Papeete, Tahiti, French Polynesia; GNS Science, Wairakei Research Center, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Michael Field, Fairfax Media, Auckland, New Zealand; William Chadwick and Robert Dziak, NOAA and Cooperative Institute for Marine Resources Studies at Oregon State University, 2115 SE OSU Drive, Newport, OR 97365.

An ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometry) satellite image became available, showing a Montagu Island plume blowing NNE on 17 December 2006 (figure 19). A persistent ash plume over Montagu was previously noted in October 2006 ASTER imagery (BGVN 31:11).

Figure 19. ASTER near-infrared image of Montagu Island volcano at 1115 UTC on 17 December 2006. Courtesy of ASTER Volcano Archive.

Thermal anomalies from Montagu were often detected by MODIS satellite instruments nearly weekly from at least 2006 until 20 September 2007. However, during that interval anomalies were absent for more than two months, from January 2007 through late March 2007. Anomalies were also absent from 21 September 2007 to 17 April 2008. The absence of anomalies could be due to lack of visibility, or the chilling of lava flows after the end of an eruptive phase.

Geologic Background. The largest of the South Sandwich Islands, Montagu consists of a massive shield volcano cut by a 6-km-wide ice-filled summit caldera. The summit of the 11 x 15 km island rises about 3,000 m from the sea floor between Bristol and Saunders Islands. Around 90% of the island is ice-covered; glaciers extending to the sea typically form vertical ice cliffs. The name Mount Belinda has been applied both to the high point at the southern end of the summit caldera and to the young central cone. Mount Oceanite, an isolated peak at the SE tip of the island, was the source of lava flows exposed at Mathias Point and Allen Point. There was no record of Holocene activity until MODIS satellite data, beginning in late 2001, revealed thermal anomalies consistent with lava lake activity. Apparent plumes and single anomalous pixels were observed intermittently on AVHRR images from March 1995 to February 1998, possibly indicating earlier volcanic activity.

Information Contacts: ASTER Volcano Archive (URL: http://ava.jpl.nasa.gov/); Hawai'i Institute of Geophysics and Planetology (HIGP) 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/);.

This report describes ash plumes (figure 48) and explosions (table 9) located at Tavurvur, a cone located on the NE flank of Rabaul caldera. Tavurvur's summit sits at ~ 240 m elevation. The largest nearby settlement is Rabaul Town. Throughout the course of this report, audible sounds such as roaring, glowing of the cone, incandescent events, and hydrogen-sulfide (H₂S) odor were frequently reported. RVO interpreted high-frequency earthquakes as rocks breaking or explosion events, and low-frequency earthquakes driven by fluids, steam or gas (rarely liquid magma), their motions imparting a slower shaking or rocking to the ground.

Figure 48. MODIS satellite image of a Rabaul ash plume on 18 March 2008.The plume can be seen over 150 km. Courtesy of NASA Earth Observatory.

Table 9. Summary of events at Rabaul's Tavurvur cone during August 2007 to April 2008. Not all events are reported here. Further details of some of the events can be found in the text. Some data such as plume height or direction of plume were not measured. Areas effected by ashfall can generally be found in the text. Courtesy of the Darwin VAAC.

Low eruptive activity such as reported in this issue have been periodically occurring since the powerful explosion in 1994. Our last report (BGVN 32:06) reported the six explosions that occurred in June and July (2007) at Tavurvur cone that produced shockwaves that rattled windows of houses in Rabaul Town and surrounding areas. The explosions also showered the flanks with lava fragments and conveyed ashfall and sulfurous odors to the NW.

RVO stated that there was no indication of any build up that might lead to significant eruptive activity like in October 2006. Ground deformation remains to be in a deflated but stable state. Seismic activity remains at a moderate to high level dominated by low-frequency earthquakes.

Throughout the entire period covered by these observations and reports, authorities have been regularly advising the public not to venture close to the volcano due to the possibility of rocks being expelled during the occasional eruptions.

Late July 2007. Rabaul Volcanic Observatory (RVO) described this time as marked by minor eruptions. The activity consisted of emission of thin to thick, white, and bluish vapor, which rose to an altitude of ~ 0.9 km and drifted NNW. Roaring noises were occasionally heard and incandescence was intermittently visible at the crater rim.

Red glow was visible at night, associated with a small lava dome centrally located within Tavurvur's wide vent. A weak smell of sulphur was evident on the downwind side of the vapor plume on 25 July. Occasional low roaring noise continued to be heard and a weak to bright red glow was visible above the crater rim on 28 and 29 July. On 30 July, a white plume with little ash content rose to an altitude of 2.7 km and drifted SW.

Seismicity was low but it and deformation were consistent with a dynamic and restless caldera. The real-time GPS at the caldera's center of the showed that centimeter-scale movements often occurred over a few hours. Small inflation events sometimes preceded activity by 6-12 hours. Only 17 low-frequency earthquakes were recorded between 22 and 27 July. One high-frequency earthquake was recorded on 26 July which originated NE of the caldera. Ground deformation continued to show a slow inflation trend with movement N.

August 2007. August activity was characterized by Tarvurvur emitting almost continuous ash and vapor plumes. During 1-7 August 2007, ashfall was reported at Rabaul Town (~ 6.5 km NW of the vent) and surrounding areas. Seismicity was generally moderate during the earlier part of August but increased to higher levels between 22-29 August. Activity was usually low frequency earthquakes, with occasional high-frequence earthquakes between 25-29 August. Five weak explosions were recorded on 27 August.

Ground deformation was stable until the middle of August when minor uplifts were noted. On 22 August, a marked uplift began and then subsided with the resumption of ash emissions. The subsidence continued until 28 August when a minor uplift began but subsided on 30 August.

A total of 1,087 low frequency earthquakes were recorded during 28-31 August. Three weak explosions were recorded on 30 August, but no high-frequency earthquakes were recorded. Ash emission persisted before declining significantly on the night of 30 August. A total of 150 low-frequency earthquakes were recorded on 31 August. After a momentary eruptive interlude took place at the end of August, blending into early September

September 2007. On 2 September, fine ashfall continued on Rabaul Town. Seismicity continued at a moderate level, dominated by bands of irregular tremor and discrete low-frequency earthquakes. A total of 886 low-frequency earthquakes were recorded during 1-5 September; no high-frequency events were recorded. During 6-10 September there was little or no ash emitted. Emissions consisted of billowing white fume when atmospheric conditions were humid or cool. During hot dry periods, observers saw clear air above the cone, with a white plume appearing several hundred meters higher. On 8 September, odors of H₂S became noticeable downwind; this coincided with a blue tinge to the plume. Ground deformation measurements indicated an uplift. Emissions began again on 20 September, with ashfall in Rabaul Town and areas downwind, including Namanula Hill (3 km W). On 27 September, a large explosion was noted. During 30 September-2 October, incandescent fragments were ejected from the summit and rolled down the flanks.

October 2007. On 3 October ashfall was reported from areas downwind, including Rabaul Town. On 4 October ash plumes resulted in ashfall in Matupit Island (3.3 km SE), Malaguna. Incandescent fragments were ejected from the summit. On 5 October, vapor plumes with minor ash content were noted. During 8-23 October, occasional explosions produced ash plumes. Ashfall was reported at Namanula Hill and surrounding areas. Continuous weak glow was visible at night and incandescence at the summit was observed. The glow was bright on the night of 17 October. On 29-30 October ashfall was reported in Rabaul Town. Seismicity continued at moderate to moderately high level between the 17th and 20th. One high-frequency event was recorded on 21 October from NE of Rabaul.

November 2007. In late November, after five weeks of low-level activity, Tavurvur began to emit ash from a new vent on the NE crater rim. The new vent was formed as a result of the lava dome blocking the vent on the crater floor. The activity progressed and on 8-9 December emissions were thick white gray ash. The new dome has been the source of the continuous red glow visible at night.

December 2007. There was a slight increase in seismicity during December, but it was still low. The average daily number of low-frequency earthquakes was 20 during 1-3 December, before increasing to 55 during 4- 6 December, and 85 during 7- 8 December. The activity was accompanied by low-level sub-continuous signals. Two high-frequency earthquakes were recorded on 3 December which originated NE of the caldera. Ashfall continued downwind, including Rabaul Town. During 13-18 December, white plumes were observed and a strong smell of H₂S gas was reported.

January 2008. January 2008 continued the December activity. White ash and vapor plumes continued from the Tavurvur cone. The eruptive activity came from vents based on the inner eastern wall. One vigorous coneless fumarole on the upper outer eastern flank occasionally erupted ash. Unfortunately, NW winds carried ash towards the Provincial Airport (5.3 km NW) on a few occasions, causing closures.

During 11-12 January slight ashfall was reported about 20 km SE of Tokua. On 17 January ashfall at Tokua, prompted Air Niugini to cancel some flights. During 18-20 January, the ash plumes were released at 10-20 minute intervals. Slight ashfall was reported in areas on the E coast. Incandescence from the center of the crater was visible at night throughout most of January.

Deformation-monitoring instruments indicated that uplift started on 23 January and peaked during 25-26 January with 2 cm of inflation. On 26 January, ashfall was quite heavy but died down on the morning of 27 January. Seismicity remained moderately high, with small sub-continuous low-frequency signals dominating. In the preceeding 24 hrs there were 400 low-frequency events and 3 explosion type signals, most of them were not associated with the seen emissions. There were no high-frequency or hybrid events. There were small explosion type signals, even when ash was not emitted. Deformation monitoring showed a slight uplift superimposed on the gradual 6 month long subsidence. On 29 January two small, instrumentally recorded, high-frequency events occured within the caldera, one between Tavurvur and Rabalanakia and the other just off the E coast of Vulcan (the first here since the '94 eruption). Deformation monitoring showed that the center of the caldera underwent a rapid centimetre scale uplift and matching deflation on 31 January.

February 2008. There was little variance in the activity at Tarvurur which was essentially a continuation of the January activity. Because of light winds, the plumes reached 1 km above Tavurvur. Drift was predominantly E. During 1-3 February ashfall was reported in Kokopo (20 km SE). On 4 February, a strong smell of H₂S gas was reported from Rabaul Town (3-5 km NW). Incandescence from the center of the crater was visible almost every night.

Low-frequency seismicity was moderately high and increased slightly, with occasional low-frequency signals dominating. Some hybrid events were also recorded. Seismic activity did not always appear to be related to the observed events. Deformation monitoring showed that the center of the caldera remaining reasonable stable during the early part of the month, although the trend was towards inflation. On 5 February, deformation monitoring showed some small, but significant movements with horizontal strain greater than vertical. A slight deflation was noted.

Toward the middle of February, ashfall was reported everyday in areas downwind, including Matupit, Kokopo, and Rabaul Town, and surrounding areas. Incandescence at the summit was noted and incandescent material was propelled from a vent on the inner E wall of the crater. Seismic activity remained at moderate levels; but again, the activity did not always appear to be related to observed events. Deflation appeared to continue but only slightly. Occasional periods of high level seismic activity were dominated by low-frequency volcanic earthquakes. A total of over 1,570 events were recorded during 7-8 February. Ground deformation showed no significant movement although the trend after 9 February was towards inflation.

From 13-19 February, ashfall was reported in Barovon, Lalakua, Raluana, Kokopo, and surrounding villages. During 19-20 February, incandescence at the summit was accompanied by projections of lava fragments. Ground deformation as indicated by both the GPS and water-tube tiltmeter continued to indicate a trend towards inflation. On 25 February an explosion showered the flanks with lava fragments. On 26 February a large explosion occurred. The flanks were again showered with lava fragments. Ashfall was reported in Kokopo and surrounding areas.

March 2008. Tavurvur's activity during March was a continuation of the preceeding months. During 27 February-4 March ashfall was reported in areas downwind, including Matupit. A smell of H₂S gas was again reported in Rabaul Town. During 3-7 March, incandescence at the summit. A slight smell of H₂S was reported in areas to the S on 5 March. During 8-11 March, ash fall was reported in areas downwind, including Kokopo town (SE), and Rabaul Town (NW) on 11 and 13 March. Seismic activity often remained at a high level during March, but, the instrument's batteries died during 10-11 March. A total of over 980 events were recorded on 9 March. No high-frequency earthquakes were recorded. Deformation continued to indicate an inflationary trend after 8 March. On 13 March fine ash fell upon Rabaul Town. Ground deformation began towards an inflation trend after previous indications towards deflation. Unlike most plume eruptions, on 13 March sounds were not recorded. On 17 March moderate to heavy ash fall rained on Matupit island and surrounding areas.

At 1105 on 20 March a large explosion occurred showering the flanks with lava fragments. The shockwave rattled windows in Rabaul Town. At 1730 on 22 March 2008 an explosion occurred showering the flanks with lava fragments. During 22-23 March areas downwind had ashfall.

On 25 March 2008 ash clouds formed a broad fan from S at Barovon/Ialakua to Kokopo. The cloud drifted SE towards Tokua later that morning. During the morning on 26 March 2008 ash plumes caused Air Niugini flights into Tokua to be affected.

During 27 March into July 2007 overall deflation was 5 cm of subsidence, step-wise with small superimposed up lifts. RVO suggested that low-pressure intrusions were periodically rising in an open conduit causing the uplift before intersecting with the surface. The overall deflation implied that the deeper source was being depleted. The deformation measurements were made at Matupit. Constant expansion and degassing of magma in the recent weeks had apparently kept the conduit open. Pressure and debris have started to block the mouth of the vent by compaction and partial welding of molten material. This would lead to pressure build-up causing periodic explosions, in a plausible waning explosive phase.

April-May 2008. On 2 April ground deformation was stable with small and continued rapid fluctuations due to the repeating sealing and rupturing of the shallow conduit. Seismicity generally became moderate, but still generally dominated by low-frequency earthquakes. Activity was no longer preceded by notable explosions. The vent would be clear for a period of time. On 7 April a high-frequency event occurred NE of the caldera. On 9-10 April 9 mm of uplift occurred. On 11 April moderate ashfall was noted in Rabaul Town. Fine ashfall occurred in Matupit island. Seismic activity returned to a high level dominated by low-frequency earthquakes. On 11 April a total of 1,000 earthquakes were recorded. At 1100 on 22 April a modest explosion occurred. On 23 April 1-2 mm of non compacted flocculated pale ash was deposited in a sector from Malaguna E to S of Matupit. The cone was obscured to vision. On 28 April ground deformation was in a deflated but stable state. Ashfalls on 2 May left 3-4 cm in eastern Rabaul and 1-2 cm in western Rabaul.

Geologic Background. The low-lying Rabaul caldera on the tip of the Gazelle Peninsula at the NE end of New Britain forms a broad sheltered harbor utilized by what was the island's largest city prior to a major eruption in 1994. The outer flanks of the asymmetrical shield volcano are formed by thick pyroclastic-flow deposits. The 8 x 14 km caldera is widely breached on the east, where its floor is flooded by Blanche Bay and was formed about 1,400 years ago. An earlier caldera-forming eruption about 7,100 years ago is thought to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the N and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and W caldera walls. Several of these, including Vulcan cone, which was formed during a large eruption in 1878, have produced major explosive activity during historical time. A powerful explosive eruption in 1994 occurred simultaneously from Vulcan and Tavurvur volcanoes and forced the temporary abandonment of Rabaul city.

Information Contacts: Steve Saunders and Herman Patia, Rabaul Volcanological Observatory (RVO), Department of Mining, Private Mail Bag, Port Moresby Post Office, National Capitol District, Papua New Guinea (URL: http://www.pngndc.gov.pg/); NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/).

Our previous report on Sangay (BGVN 21:03) described occasional, but sometimes conspicuous, steam and/or ash plumes between January 2004 and January 2006. The current report continues coverage of plume emissions through December 2007.

Sangay has continued to erupt, sending ash plumes up to an altitude of about 11 km. A summary of plume activity is indicated in table 1. The information is from the Washington Volcanic Ash Advisory Center (VAAC), and is based on reports from the Guayaquil Meteorologic Watch Office, pilot reports, satellite imagery, and the Instituto Geofísico-Departamento de Geofísica (Escuela Politécnica Nacional). We did not receive any report of activity during the period February 2006 through September 2006, or during the first three months of 2008.

Table 1. Ash plume advisories about Sangay activity, October 2006 through December 2007. Courtesy of the Washington VAAC.

According to a report from the Instituto Geofísico, activity at Sangay increased at the end of 2006 through the beginning of 2007. They reported that a thermal anomaly was detected by satellite imagery during several days in December 2006. During that time, mountain guides near the volcano observed the fall of incandescent rocks down the volcano's flanks at night and a recent deposit of ash that was sufficiently deep to affect birds, rabbits, and other small animals. The report indicated that the Instituto Geofísico has not installed monitoring instrumentation near Sangay because of a significant logistics problem in maintaining them in this inhospitable area, and also because the area is uninhabited and thus poses no direct human risk. However, the report notes that because ash emissions from Sangay may pose problems for aircraft in the S, SE, and SW parts of the country, the Instituto maintains contact with the civil aviation authority.

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

Information Contacts: Washington Volcanic Ash Advisory Center, 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/); P. Ramón, Instituto Geofísico-Departamento de Geofísica (IG), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador.

This report updates activity through March 2008. Our last overview of Ulawun (BGVN 32:02) reported little activity of note other than frequent ash plumes from March 2006 to January 2007. Typical activity at Ulawun has consisted of gentle emission of thin-to-thick white vapor from the summit Based on satellite imagery and information from the Rabaul Volcano Observatory (RVO), the Darwin VAAC reported that diffuse plumes from Ulawun drifted N on 28 April 2007. On 1 May, an ash plume rose to an altitude of 4 km and drifted W.

[On 29 May 2007, RVO reported thick white vapor; there were no audible noises or night glow.] The two N valley vents remained quiet. Seismicity was at a low to moderate level dominated by low-frequency earthquakes. Through May, between 500 and 1,265 low frequency events were recorded daily with the most recorded on 28 and 29 May.

Similar conditions continued through the end of 2007 with only minor incidental variation. On 6 June, the elevated characteristics of the forceful emissions of 28-29 May were repeated. The daily total number of low-frequency earthquakes fluctuated between 400 and 1,042 events with the highest numbers recorded on 24 June (1,032) and 8 August (1,042). A high-frequency earthquake was recorded on 1 August. On 3 September forceful emissions were recorded sending the vapor plume ~ 1 km above the summit before being blown SE. On 25 December, based on satellite imagery observations, the Darwin VAAC reported that an ash-and-steam plume from Ulawun drifted W.

Low levels of activity continued from January through March 2008. Emissions consisted of thin to thick white vapor and with no audible noises and no glow visible at night. Seismicity continued at moderate level dominated by low frequency volcanic earthquakes. Variable amounts of white fume were emitted, sometimes forcefully. The two N valley vents continued to remain quiet.

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

Information Contacts: Herman Patia, Rabaul Volcano Observatory (RVO), P. O. Box 386, Rabaul, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Commonwealth Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); US Air Force Weather Agency (AFWA), Satellite Applications Branch, Offutt AFB, NE 68113-4039, USA; Hawai'i Institute of Geophysics and Planetology (HIGP) 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/); James Mori, Disaster Prevention Research Institute, Kyoto University, Uji, Kyoto 611-0011, Japan (URL: http://eqh.dpri.kyoto-u.ac.jp/~mori/).