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/).

According to the Sakurajima Volcano Research Center (SVRC) at Kyoto University, an eruption started on 4 June 2006 at the Showa crater, a spot that differs from vents active in recent decades at the summit of Minami-dake ("south mountain"; BGVN 31:06 and many previous reports). The Showa crater resides on the E slope of Minami-dake at an elevation of ~ 800 m (figures 23, 24, and 25). Showa crater was formed in a 1946 eruption; the 1946 vent was the source of lava flows that spread E and then branched to travel S and ENE (figure 25).

Figure 23. Map images showing Sakura-jima stratovolcano and environs on Japan's Kyushu island (~ 1,000 km S of Tokyo). (left) Image from Google Earth showing the S end of Kyushu Island. Population centers are labeled. Sakura-jima forms the dominant topographic feature in Kagoshima Bay. The Osumi Peninsula is to the E; the Satsuma Peninsula to the W. (right) Image from Google Earth showing terrain features looking NW towards the upper portions of Kagoshima Bay. Courtesy of Google Earth.

Figure 24. A sketch map focused on the geologic context of Sakura-jima, the Aira caldera, and adjacent calderas. The Kagoshima graben forms the Bay of the same name. The graben also lies coincident with several caldera margins. Sakura-jima resides at the S portion of Aira caldera. Modified slightly from Okuno and others (1998).

Figure 25. A geological map of Sakura-jima shown with several key features and eruptive dates labeled. Topographic highs from N to S include Kita-dake (K), Nika-dake (N), and Minami-dake (M). Craters at the summit of Minami-dake have been the active in past decades, but the eruption that started on 4 June eruption vented at Showa crater (S). An E flank lava flow (the Taisho Lava of 1914-1915) joined what had been an island's SE side to the shore (arrow at lower right labeled "j" aims at the zone of contact). Fringing the roughly circular former island are several areas of submarine volcanic and intrusive deposits (labeled here with the abbreviation "subm."). For example, the large area budding NE from the island consists of submarine and intrusive rocks of 1779-1780. Many of the Holocene eruptive deposits are dacites and andesites. They commonly bear pyroxene (and also sometimes, olivine). Besides lava flows, deposits include welded air-fall and pyroclastic-flow deposits (in some cases showing rheomorphosed textures indicative of movement downslope after forming a welded mass). From the Geologic Survey of Japan, AIST website (after Fukuyama and Ono, 1981 and Kobayashi, 1988).

Unfortunately, at press time many details still remained unavailable to Bulletin editors regarding the duration and character of the return of venting at Showa crater. It is also unclear to what extent the Minami-dake summit craters continued to participate in the emissions.

The 4 June 2006 eruption continued intermittently, including an evening eruption on 7 June which sent an ash column ~ 1 km above the crater. Figure 26 shows one such eruption on 6 June.

Figure 26. A photograph of Sakura-jima erupting at 1231 on 6 June 2006 from Showa crater. Courtesy of SVRC, Disaster Prevention Research Institute, Kyoto University.

A series of plots describe the short- and long-term seismicity and volume of magma supplied at Sakura-jima (figures 27 and 28). The number of shallow earthquakes had increased since the middle of March 2006 (figures 26 and 27), and small volcanic tremors with a duration shorter than 2 minutes had increased since the middle of May 2006. GPS data showed continued inflation in the N part of the Aira caldera, an observation attributed to incoming magma. Kazuhiro Ishihara, director of SVRC, commented that the present eruption was considered to be related to magma accumulating in the Aira caldera and searching for an exit.

Figure 27. A multi-year (1995 to mid-2006) view of Sakura-jima's activity: (top) monthly A-type earthquakes, (middle) monthly number of explosions (determined geophysically, exact method undisclosed), and (bottom) the cumulative volume of magma supplied. Courtesy of SVRC, Disaster Prevention Research Institute, Kyoto University.

Figure 28. Plot of the daily number of volcanic earthquakes at Sakura-jima for the period 1 January-7 June 2006. Courtesy of SVRC, Disaster Prevention Research Institute, Kyoto University.

Table 14 presents a chronology of ash-plume observations made since the previous Bulletin report (BGVN 31:06). The table is based primarily on reports from Tokyo Volcanic Ash Advisory Center (VAAC) and covers the interval 7 June 2006 to 20 March 2007. Most of the plumes described did not exceed 3 km altitude. The tallest plume recorded on the table, an ash plume on 20 March 2007, rose to 3.7 km altitude.

Table 14. Heights and drift of plumes and their character at Sakurajima from June 2006-March 2007. Some of the data during mid-June 2006 were previously reported, but new information has emerged. Courtesy of SVRC and Tokyo Volcanic Ash Advisory Center.

Volcanic hazards research. Lee and others (2005) reported the successful remote measurement of significant amounts of ClO (as well as BrO and SO₂) in a volcanic plume from Sakura-jima during May 2004. Near the volcano they also observed halogen-catalyzed, local surface ozone depletion. The investigators employed ground-based, multi-axis, differential optical absorption spectroscopy. Their results help document the presence of a wide range of chemical species that have potential health implications for populations living nearby.

The center of Kagoshima City (population ~ 550,000) sits ~ 10 km from Minami-dake's summit and ~ 4 km from Sakura-jima's E shore (just off figure 24, but along the trend of the arrow labeled KC). According to Durand and others (2001), "Since 1955 the city has been subjected to ashfall from Sakura-jima. Until 1990 ashfalls occurred up to twice per week, although this has decreased in frequency in recent years."

Durand and others (2001) comment that "[Kagoshima City] presents a good opportunity to study the impacts of volcanic ash on key services, or 'lifelines.' In addition, the city provides a chance to see how lifelines have been adapted to counter any problems presented by ashfalls." They also noted that, "The advice from Kagoshima would seem to be that during an ashfall event, people should bring in the washing and shut the doors and windows. People who have to go out and work in ashfall should wear goggles and a face mask. In Kagoshima, umbrellas are the only form of protection for many people going to work during ashfall events."

References. Durand, M.; Gordon, K .; Johnston, D. ; Lorden, R. ; Poirot ,T. ; Scott, J. ; and Shephard, B.; 2001; Impacts of, and responses to ashfall in Kagoshima from Sakurajima Volcano?lessons for New Zealand. Science report 2001/30, Institute of Geological & Nuclear Sciences; Lower Hutt, New Zealand, November 2001 53p. (ISSN 1171-9184, ISBN 0-478-09748-4).

Fukuyama, H. and Ono, K., 1981, Geological Map of Sakura-jima, scale 1:25,000

Kobayashi, Tetsuo, 1988, Geological Map of Sakurajima Volcano, A Guidebook for Sakura-jima Volcano, in Kagoshima International Conference on Volcanoes, 1988 (1:50,000).

Lee, C., Kim, Y. J., Tanimoto, H., Bobrowski, N., Platt, U., Mori, T., Yamamoto, K., and Hong, C. S., 2005, High ClO and ozone depletion observed in the plume of Sakurajima volcano, Japan, Geophysical Research Letters, v. 32, L21809, doi:10.1029/2005GL023785.

Okuno, Mitsuru; Nakamura, Toshio, and Kobayashi, Tetsuo, 1998, AMS ¹⁴C dating of historic eruptions of the Kirishima, Sakura-jima and Kaimon-dake volcanoes, Southern Kyushu, Japan. Proceedings of the 16th International ¹⁴C Conference, edited by W. G. Mook and van der Plicht, RADIOCARBON, Vol. 40, No. 2, 1998, P. 825,832.

Geologic Background. The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan's most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim and built an island that was joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4,850 years ago, after which eruptions took place at Minamidake. Frequent eruptions since the 8th century have deposited ash on the city of Kagoshima, located across Kagoshima Bay only 8 km from the summit. The largest recorded eruption took place during 1471-76.

Information Contacts: Sakura-jima Volcano Research Center, Disaster Prevention Research Institute (DPRI), Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan (URL: http://www.dpri.kyoto-u.ac.jp/~kazan/default_e.html); Tokyo Volcanic Ash Advisory Center (VAAC), Japan Meteorological Agency (JMA) (URL: http://ds.data.jma.go.jp/svd/vaac/data/).

Brief periods of effusive activity took place during January to mid-April 2006 (BGVN 31:05), with ash-and-steam emissions reported as late as 18 June 2006. Activity has continued since that time through early June 2007, with evidence coming from either MODIS thermal satellite data, observations of glow, or plume observations from the ground or satellites (figure 8). It appears that there were three episodes of increased plume generation, two periods of frequent glow observations, and almost daily MODIS anomalies over that one-year time frame.

Figure 8. Summary of daily activity at Bagana, 18 June 2006-5 June 2007. Plumes are all varieties (steam or ash) reported by RVO or Darwin VAAC; glow as reported by RVO; MODIS data indicates days with at least one thermal pixel detected. Compiled from MODIS/HIGP data, Darwin VAAC reports, and RVO reports.

The Rabaul Volcano Observatory (RVO) noted that between 18 September and 4 December 2006 only white vapor was released; some of these emissions were forceful. Jet engine-like roaring noises were heard on 11 and 20 November. Variable glow was visible on 25-26 September, 15, 20, and 29 October, 15-21 November, and 4 December. The lava flow on the S flank was active only on 15 October.

There were no aviation warnings after June until a diffuse plume became visible on satellite imagery on 22 November. Based on satellite imagery, the Darwin Volcanic Ash Advisory Centre (VAAC) reported subsequent plumes on 5 December (ash), 21-22 December (ash-and steam), and 9 January 2007.

RVO reported that white vapor emissions from the summit crater continued during 10 January-21 May 2007. Emissions were occasionally forceful and were accompanied by ash clouds on 3 and 17 March, as well as 1 and 3-5 April. Summit incandescence was visible on 7, 8, 20, and 24 March, and 17 May. Based on satellite imagery, the Darwin VAAC reported diffuse plumes to altitudes of 2.4 and 3 km on 10 March and 20 May, respectively. Forceful, white emissions on 21 May produced plumes that rose to an altitude of 2.3 km and drifted W. Diffuse ash-and-steam plumes were seen in satellite images again on 22 and 28 May, rising to altitudes of 3.7 and 3 km, respectively.

Moderate Resolution Imaging Spectroradiometers (MODIS) satellite thermal anomaly data reported by the Hawai'i Institute of Geophysics and Planetology (HIGP) revealed frequent thermal anomalies during 20 June-24 July 2006, 16 August-3 October 2006, 9 November 2006-23 January 2007, and 13 February-2 June 2007.

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/).

Activity declined at Bulusan in late June 2006 after a series of 10 explosions that began on 19 March 2006 (BGVN 31:09). Between 30 August and 1 September steam plumes reached up to 350 m above the summit; the plumes drifted NW and SE. This report summarizes Bulusan's activity from 10 October 2006 through 12 May 2007 (table 4). Hazard maps created by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) illustrate the risks to the large numbers of cummunities in the vicinity of the volcano (figure 7). Review of the available MODIS data indicates no thermal alerts during the year prior to 31 May 2007.

Table 4. An overview of Bulusan's activity, as noted by PHIVOLCS during 10 October 2006 through 12 May 2007. Courtesy of PHIVOLCS.

Figure 7. Hazards maps for Bulusan showing susceptibility to pyroclastic flows and surges (left), and lava flows and lahars (right). Courtesy of PHIVOLCS.

PHIVOLCS reported an explosion from Bulusan on 10 October that produced an ash-and-steam plume that rose to 4.5 km altitude and drifted mainly SE and SSW. Light ashfall (1.5-5.0 mm thick) was reported in neighboring towns downwind. Based on seismic data, the activity lasted for 9 minutes. On 11 and 12 October, steam plumes drifted SW and SSW. Another explosion occurred on 19 October. The following day, steam plumes drifted W and WSW. On 23 October, an explosion produced a brownish ash plume that rose to about 2.6 km and drifted SE and SW. Light ashfall (trace to 0.5 mm thick) from the 19 and 23 Cctober explosions was reported from neighborhoods in the municipality of Irosin, about 7 km S of the summit.

During 25-26 October, PHIVOLCS reported a lahar that deposited sediments 15 cm thick along a tributary leading to the Gulang-gulang River. According to news articles, the lahar mobilized boulders as large as trucks and caused at least 96 people to evacuate. During 30-31 October, ash explosions generated a light gray ash-and-steam plume that rose to 2.3 km and drifted NNE. Later field inspection revealed ashfall (trace to 1 mm) N of the volcano, as well as in the municipalities of Casiguran and Gubat, about 12 km SSE and 18 km NNE, respectively, from the summit. Two explosion-type earthquakes recorded late on 31 October were followed by ashfall in Casiguran, Malapatan, and Irosin.

News articles and wire services reported that Bulusan emitted ash accompanied by rumbling noises and lightning flashes on 20 December. Clouds hindered a view of the summit. Ash deposits up to 4 mm thick were noted in several villages in the foothills. A news report in News Balita noted a plume of gas and "white ash" on 22 December.

In January 2007, PHIVOLCS reported that an explosion from the summit on 24 January lasted about 10 minutes, based on seismic interpretation. Observation was inhibited due to cloud cover. Ashfall was reported SW of the volcano.

On 15 March, news media reported that ash fell on Bulusan's SW slopes and nearby villages. A resident volcanologist stated that ashfall was caused by voluminous steaming during 12-15 March, not explosions. Other news articles stated that eruptions on 8 April produced ash plumes that rose to altitudes of 3.1-6.6 km.

PHIVOLCS reported another ash explosion on 12 May 2007 with an eruption column reaching a maximum height of 4 km above the summit before drifting to the WSW and WNW. The activity was accompanied by rumbling sounds and was recorded by the seismic network as an explosion type earthquake that lasted for about 35 minutes. Prior to the explosion, during 9-12 May, an increase in the daily number of volcanic earthquakes was noticed, with 42, 65 and 97 events recorded.

Geologic Background. Luzon's southernmost volcano, Bulusan, was constructed along the rim of the 11-km-diameter dacitic-to-rhyolitic Irosin caldera, which was formed about 36,000 years ago. It lies at the SE end of the Bicol volcanic arc occupying the peninsula of the same name that forms the elongated SE tip of Luzon. A broad, flat moat is located below the topographically prominent SW rim of Irosin caldera; the NE rim is buried by the andesitic complex. Bulusan is flanked by several other large intracaldera lava domes and cones, including the prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the NE. The summit is unvegetated and contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Many moderate explosive eruptions have been recorded since the mid-19th century.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph); Tokyo Volcanic Ash Advisory Center, Tokyo, Japan (URL: http://www.jma.go.jp/jma/jma-eng/jma-center/vaac/index/html); Inquirer.net, Philippines (URL: http://www.inquirer.net/); Associated Press (URL: http://www.ap.org/); News Balita, Philippines (URL: http://news.balita.ph/).

The new island at Home Reef that was constructed by the 8-11 August 2006 felsic shallow marine explosive eruption (BGVN 31:09) was visited on 18 February 2007 by Scott Bryan (Kingston University, United Kingdom), Alex Cook (Queensland Museum, Australia), and Peter Colls (University of Queensland, Australia). The initial aim of field research was to map and describe the volcanic geology of the new island at Home Reef and to collect samples for comparison to floating pumice generated by the eruption (Bryan, 2007).

Island observations. Satellite imagery on 4 October 2006 showed an 800-m-long elongate island (0.23-0.26 km²), which was being rapidly modified by wave erosion (BGVN 31:10). An overflight by the RNZAF on 7 December 2006 revealed a roughly circular island, 450 m in diameter and up to 75 m above the water line (BGVN31:12). Upon arrival on 18 February 2007, the scientists found that only a small (50-75 m diameter) <5 m high low-relief wave-reworked "pumice mound" remained at the southern windward end of the Home Reef shoal (figure 23). Due to strong winds and large swells, landing on the tidally-exposed mound was not possible and it could only be viewed from a couple of hundred meters offshore. The location of the mound (18.993°S 174.758°W) is close to that reported for the circular island observed on 7 December 2006. Swells 2-m high or greater were strongly impacting the mound, with the largest waves almost completely engulfing and sweeping over the mound at half-tide.

Figure 23. View to the NW of the wave-reworked pumice mound at Home Reef, as seen on 18 February 2007. The diameter of the mound is ~ 75 m. Note the scattered large blocks on the upper surface of the mound. Late Island is in the background at right. Courtesy of Scott Bryan.

The morphology of the island suggests that no primary subaerial island-building deposits remain from the eruption and that complete reworking has occurred of the previously observed cone. On the southern side of the pumice mound were scattered large (>1 m diameter), outsized blocks (10-20 in number) on the mound surface (figure 23) that were largely immobile in the waves. Slopes of the mound reflected wave run-up and the pumiceous material comprising the mound appeared to be relatively coarse and well-sorted. There was little entrained particulate material in the water column downwind and downcurrent, but considerable amounts of material within the surf zone surrounding the island, coloring the water brown. A considerable area of discolored water (green, translucent milky) extended N of the mound for more than 500 m. Several smaller lobes or plumes extended off the W side of the main body of discoloration.

A strong sulfurous odor was detected downwind (NW) of the mound, indicating that magma was continuing to cool and degas at shallow levels in the seamount seven months after the eruption; no surface plume was visible. Surface water temperature measurements did not detect any thermal anomalies, recording ambient water temperatures (28-29°C).

Local pumice sightings. Downwind and downcurrent of the mound were small scattered pumice stringers forming orange-brown slicks a few meters to tens of meters long, characterized by low pumice clast abundance and size (usually 0.5-1 cm diameter). The pumice fragments were generally moderate to high sphericity grains, but some more platy pumice fragments were also sampled. Some clasts had orange to brown surface stains, reflecting hydrothermal alteration since the eruption. Most grains showed some signs of abrasion. Orange-brown algal clumps or coagulates floating on the ocean surface were associated with the stringers.

Small pumice rafts were also encountered around some of the islands at the SW end of the Vava'u Group during the week of 17-24 February (figure 24). The pumice rafts had lateral extents of tens of meters, but other flotsam (leaf, twig, sea grass and plastics) was also present. Pumice clast sizes ranged from ~ 2 mm up to 6 cm, and some of the gray pumice possessed orange-brown surface hydrothermal staining. Some rafts had abundant attached fauna, dominated bygoose barnacles (Lepas sp.) ~ 2-7 mm long. Much of these pumice rafts reflected remobilization of previously stranded material from neighboring beaches, and many SE-facing beaches had been stripped of pumice by strong SE trade winds.

Figure 24. Pumice slick from Home Reef found on the W side of Nuatapu Island, 21 February 2007. Note other flotsam (leaves, plastic) within the slick. Courtesy of Scott Bryan.

Many beaches had several pumice strandline deposits, the lowermost of which reflected tidal sorting. Dominantly lapilli-sized gray pumice formed the deposits, whereas a black glassy, moderately vesicular pumice of higher density was a notable feature of the highest strandlines. There were also abundant pumice clasts with an orange-brown staining on clast surfaces.

Floating pumice reaches Australia. Pumice rafts and beach strandings were reported previously as the pumice drifted westward past the Lau and Fiji islands and on to Vanuatu in November 2006. A major influx of pumice reached the E coast of northeastern Australia during March and April 2007, seven to eight months after the eruption. Pumice was first noticed passing the offshore islands of Willis Island (16.30°S, 149.98°E) in early February, and Lizard Island (14.66°S 145.47°E) the last week of February. Pumice strandings along the eastern Australian coast began in March in northern Queensland, with a substantial stranding occurring in mid-April corresponding to a change to easterly and northeasterly onshore wind conditions and king tides. This stranding event extended for more than 1,300 km along the Queensland and northern New South Wales coast.

Most stranded pumice clasts ranged in size from 1-4 cm diameter, with the largest clasts up to 17 cm diameter. Pumice clasts were fouled by a variety of organisms, primarily goose barnacles (Lepas sp.) up to 2.7 cm long, molluscs, bryozoa, and dark green algae (figure 25), with serpulids, oysters and other species of algae (e.g., Halimeda) less abundant. A substantial proportion of stranded pumice material remains on beaches inshore from the Great Barrier Reef. However, little stranded material has remained on exposed beaches south of 25°S, to the extent that some beaches still have more pumice preserved from the 2001 eruption of an unnamed Tongan seamount about 85 km NW of Home Reef.

Figure 25. Closeup of a pumice clast from Home Reef that reached Marion Reef (19.095°S, 152.390°E), Australia, fouled by goose barnacles (Lepas sp.), bryozoa, and mollusc. Coin is 2 cm in diameter. Courtesy of Scott Bryan.

Seismicity. Although no seismicity has been reported that was detected during the eruption, Robert Dziak identified seismic signals from Home Reef in March 2006. The East Pacific hydrophone array maintained by NOAA recorded 52 earthquakes over a 12-hour period beginning at 1700 UTC on 12 March 2006. The arrivals were all very clear and had medium to low T-wave amplitudes.

Reference. Bryan, S.E., 2007, Preliminary Report: Field investigation of Home Reef volcano and Unnamed Seamount 0403-091: Unpublished Report for Ministry of Lands, Survey, Natural Resources and Environment, Tonga, 9 p.

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: Scott Bryan, School of Earth Sciences & Geography, Kingston University, Kingston Upon Thames, Surrey KT1 2EL, United Kingdom; Peter Colls, School of Physical Sciences, University of Queensland, St Lucia, Queensland 4072, Australia; Robert Dziak, NOAA Pacific Marine Environmental Laboratory (PMEL), Hatfield Marine Science Center, 2115 SE Oregon State University Drive, Newport, OR 97365, USA.

Eruptive activity at Manam has generally been low following a significant explosion in late February 2006 (BGVN 31:02). Between March and July 2006 the Rabaul Volcano Observatory (RVO) reported intermittent, milder, ash explosions (BGVN 31:06). Similar variable activity has continued into early May 2007, with plumes frequently identified on satellite imagery by the Darwin Volcanic Ash Advisory Centre (VAAC).

RVO received a report that four people were swept away by a mudflow in the early hours of 13 March following heavy rainfall on the northern part of the island. A 5th person was reportedly critically wounded and in a hospital.

Activity during August-December 2006. On 4 and 5 August, an ash plume was visible on satellite imagery extending 30 km NW. Ash plumes were emitted again during 14-15August. Over the next couple of days, the emissions became more diffuse and weak incandescence was observed at night. Based on pilot reports and satellite imagery, continuous emissions during 17-21 August eached altitudes of 3.7 km and drifted NW. Eruptive activity from Main Crater during 22-23 August consisted mainly of dark brown-to-gray ash plumes that rose 1-2 km above the summit and drifted W and NW. The Darwin VAAC reported that eruption plumes were visible on satellite imagery on 23 and 26 August, extending NW. Southern Crater continued to release only diffuse white vapor.

From the end of August to 5 September 2006, the Darwin VAAC reported that ash-and-steam plumes reached altitudes of 4.6 km and drifted W. Steam plumes with possible ash were visible on imagery below 3 km and drifted NE. RVO reported mild eruptive activity during 15-17 October that consisted of steam and ash plumes. White vapor plumes were visible from Southern Crater and intermittently from Main Crater. Main Crater produced gray ash plumes on 19 October. Weak incandescence was seen during 15-17 and 29 October.

During 1-13 November, white vapor plumes rose from Southern and Main craters. Incandescence was noted from both craters during 8-10 November and from Main Crater on 12 November. On 13 November a diffuse plume seen on satellite imagery drifted W. Steady incandescence was again observed from Main Crater during 8-10 December and bluish white vapor emissions during 6-9 December changed to a darker gray on 10 December. Weak glow continued from Main Crater during 14-18 December and a white vapor plume rose just above 2 km altitude. Based on satellite imagery, diffuse plumes drifted mainly W during 13-15 December. The daily number of volcanic earthquakes fluctuated between 700 and 1,000.

Activity during January-May 2007. RVO reported that mild eruptive activity and emissions of white vapor plumes from Main Crater were observed during 1-14 January. Brown-to-gray ash plumes accompanied emissions on 6 and 9-11 January; and nighttime incandescence was observed intermittently. White vapor clouds were occasionally released from Southern Crater. Seismic activity was at low to moderate levels; the daily number of low-frequency earthquakes fluctuated between 500 and 1,000.

Satellite imagery showed diffuse plumes drifting WSW on 15 February. Southern Crater emitted gray ash plumes during 15-19 February and white vapor plumes on 21 February. Continuous gray ash plumes from Main Crater rose to an altitude of 2.3 km and drifted SE during 19-21 February. The daily number of low-frequency earthquakes fluctuated between 400 and 500 during 22-24 February before the seismograph developed technical problems.

Mild eruptive activity continued during 22 February-10 March. Main Crater forcefully released variable gray ash clouds on 22 February that rose less than 1 km above the summit before being blown SE. Incandescence was also visible that day. Poor weather prevented observations for the remainder of the month. When the clouds cleared on 3 March, Main Crater was seen sending ash clouds less than 500 m high. Glow was visible during 2-5 and 9-10 March. Southern Crater released occasional diffuse gray ash clouds on 3-4 and 6 March, but only white vapor on 5 and 7-11 March.

Main Crater continued to release occasional low-level ash clouds through 6 April. Incandescence was visible during clear weather on the nights of 11-12 and 16-18 March. Southern Crater released diffuse white vapor on 11-12 and 15 March; however, diffuse ash clouds were reported on 16-20 March. Weak roaring noises were heard on 24 March, and on 7, 12, and 26 April. Low-level plumes were seen during 25-26 April, and a small plume was blowing W on 28 April. Weak incandescence was again visible from Main Crater on 2 and 4 May. Diffuse plumes were seen in satellite imagery on 6 and 23 May. Seismic activity was at a low level, with the daily number of volcanic earthquakes between 800 and 1,000 events.

Thermal satellite data. Thermal anomalies were not detected by Moderate Resolution Imaging Spectroradiometers (MODIS) for 9 months after events related to the 27-28 February 2006 explosion. Anomalies reappeared in December, with hot pixels detected on 5, 7, 9, 10, 12, and 14 December 2006. Another anomaly was recorded on 19 April 2007. Additional thermal anomalies were present on 16 and 23 May 2007. Most of the pixels were located near the summit, or slightly towards the NE. The May anomalies were the furthest down the NE Valley.

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

Information Contacts: Herman Patia and Steve Saunders, 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/); NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/).

Centro Nacional de Prevencion de Desastres (CENAPRED) reported only sporadic, modest activity at Popocatépetl during early 2006 through April 2007. Based on information from the Mexico City Meteorological Watch Office (MWO), and the Washington Volcanic Ash Advisory Center (VAAC), there were five occasions when ash plumes rose substantially. On 25 and 27 July 2006 ash plumes rose to an altitude of ~ 9.8 km. On 18 and 20 December 2006, ash plumes rose to an altitude of ~ 6.7 km and 7.9 km, respectively. In April 2007, ash plumes rose to ~ 7.6 km on the 1st, and to ~ 7.3 km on the 3rd.

In August 2006, the lava dome that had been irregularly growing since July 2005 covered the floor of the internal crater and began a piston-like growth on the top of the previous dome. The enlarged dome can be seen in an aerial photography taken in 24 November 2006 (figure 51). This formation of the dome was the twenty-sixth such event since 1996.

Figure 51. Aerial photo taken 24 November 2006 showing the growing lava dome at Popocatépetl.The dashed white line defines the dome edge. The lava dome that started growing in July 2005 has covered the floor of the internal crater and began growing on the top of the previous dome. The white areas outside the inner-crater rim are snow cover. Courtesy of the government of the State of Puebla, Mexico.

On 4-5 August and 1-3 November 2006 episodes of large-amplitude harmonic tremor (figure 52) were believed to reflect an increased rate of dome growth. The accumulated volume of the lava dome between November of 2005 and November of 2006 was estimated to be 1,299,000 m³. The average rate growth over that interval is around 0.04 m?/s. Assuming that the dome grows only during the tremor episodes, the rate would be ~ 6.75 m³/s.

Figure 52. Evidence of a large-amplitude, multiband harmonic tremor, showing clear frequency peaks in its spectrum detected in August 2006 at Popocatépetl. The combination of the frequencies appear as moiré shadows in the paper recording.Courtesy of CENAPRED.

Incandescence at the summit was recorded by the CENAPRED camera on 3 August and 4-5 September 2006. Over 27-29 October 2006, eigth small explosions ejected incandescent debris on the slopes surrounding the crater. During November and December 2006, more episodes of low amplitude tremors were recorded. From August to December 2006, 77 volcano-tectonic micro-earthquakes were detected, with magnitudes ranging between 2.0 and 3.0. From these, 66 were located below the crater at depths ranging between 3 and 7 km (figure 53).

Figure 53. Location and depth of micro-earthquakes on Popocatépetl recorded during August to December 2006. Courtesy of CENAPRED.

Hot spots at the summit were detected on satellite imagery by the Washington Volcanic Ash Advisory Center (VAAC) on 7-8 January 2007. According to the Washington VAAC, a puff with little ash content emitted from Popocatépetl was reported from the MWO and visible from the camera operated by CENEPRED on 14 February 2007. A very diffuse plume was seen drifting to the E on satellite imagery. Base on an aerial photograph taken on 24 January 2007, CENEPRED reported that the lava-dome dimensions have slightly increased since 24 November 2006.

Geologic Background. Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Information Contacts: Centro Nacional de Prevención de Desastres (CENAPRED), Av. Delfín Madrigal No.665. Coyoacan, México D.F. 04360, México (URL: https://www.gob.mx/cenapred/); Alicia Martinez Bringas and Angel Gómez Vázquez, CENAPRED; Servando de la Cruz Reyna, Insituto de Geofisica UNAM. Ciudad Universitaria, s/n. Circuito Institutos . Coyoacan México D.F. México; 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/).

This report discusses evidence for the end of the March 2006 eruption, and press releases announcing newly acquired multibeam bathymetry that disclosed submarine calderas on the flanks of Raoul Island and some adjacent volcanoes.

End of the March 2006 eruption. After the 17 March 2006 eruption (BGVN 31:03), volcanic activity decreased significantly. On 18 September 2006 the Alert Level was lowered to 0.

GeoNet Science (GNS) summarized the decreased activity in their Volcano Alert Bulletin of 18 September 2006. The report noted an absence of significant earthquakes within ~ 30 km of Raoul Island. The water level in Green Lake had continued to drop and was close to the pre-eruption level by 18 September. On 27 August the lake temperature was 20.3°C, well within the seasonal range. The level of ongoing hydrothermal activity (upwelling in Green Lake, nearby hot pools, and steaming ground) was commensurate with that expected six months after an eruption like that seen in March. Chemical analyses of samples recently collected from some of the thermal features were typical of volcano-hydrothermal features in this environment.

GNS reported that the water level in Green Lake, which had risen significantly during the week after the March 2006 eruption and had drowned several new steam vents, still remained above pre-eruption levels as of July 2006, but thereafter dropped slowly. Upwelling and bubbling of springs indicated the volcanic-hydrothermal system was still weakly active 3 months after the eruption. The water temperature, obtained from a thermal infrared satellite image taken on 11 April 2006, was 39.2°C, was 7°C above the average water temperature in April, but had returned to seasonal temperatures by August 2006.

Only 1 to 5 earthquakes were recorded per day in the months following the eruption. The number of earthquakes 30-40 km offshore was slightly higher than normal.

New submarine volcanoes discovered. Marine geologists who had investigated two volcanoes in the Kermadec Arc during May 2007, discovered two new submarine volcanoes near Raoul Island. The geologists were on a scientific expedition mounted by New Zealand's National Institute of Water & Atmospheric Research (NIWA) and the University of Auckland aboard NIWA's deepwater research vessel Tangaroa. They investigated volcanoes on the two largest Kermadec Islands (Raoul and Macauley) and their submerged flanks.

A 22 May 2007 press release by NIWA reported that new seafloor observations revealed for the first time the presence of two submerged calderas. Both calderas were relatively small, ~ 4 km in diameter. One caldera was very deep, measuring ~ 1 km from the rim to the crater floor. Both volcanoes appeared geologically young, on the order of thousands of years old, but laboratory analysis of sediments will be needed to better quantify their age.

The expedition took sediment samples and mapped the contours of the volcanoes both above and below sea level (the latter using multibeam sonar). A series of sediment cores taken from E and W of both islands revealed at least six eruptions from the two islands, recorded as centimeter-thick layers up to 100 km from the islands.

Geologic Background. Anvil-shaped Raoul Island is the largest and northernmost of the Kermadec Islands. During the past several thousand years volcanism has been dominated by dacitic explosive eruptions. Two Holocene calderas exist, the older of which cuts the center the island and is about 2.5 x 3.5 km wide. Denham caldera, formed during a major dacitic explosive eruption about 2200 years ago, truncated the W side of the island and is 6.5 x 4 km wide. Its long axis is parallel to the tectonic fabric of the Havre Trough that lies W of the volcanic arc. Historical eruptions during the 19th and 20th centuries have sometimes occurred simultaneously from both calderas, and have consisted of small-to-moderate phreatic eruptions, some of which formed ephemeral islands in Denham caldera. An unnamed submarine cone, one of several located along a fissure on the lower NNE flank, has also erupted during historical time, and satellitic vents are concentrated along two parallel NNE-trending lineaments.

Information Contacts: Steve Sherburn, GeoNet Science (GNS), Wairakei Research Centre, Private Bag 2000, Taupo, New Zealand; Ian Wright, Ocean Geology group, National Institute of Water & Atmospheric Research (NIWA), PO Box 14901, Wellington, New Zealand (URL: http://www.niwascience.co.nz); Roger Matthews, North Shore City Council, 1 The Strand, Takapuna Private Bag 93500, Takapuna, North Shore City, New Zealand (URL: http://www.northshorecity.govt.nz/).

Our last report (BGVN 31:01) discussed post-eruption lahars following the sudden 1 October 2005 eruption (BGVN 30:09). This report contains two sections. The first section addresses regional processes such as vegetation loss, ash accumulation, and lahars on and beyond the E flank of Santa Ana (also known as Ilamatepec) to the shores of Lake Coatepeque. Those lahars began soon after the 1 October 2005 eruption. The information on these lahars chiefly came from a report (SNET, 2006) authored by El Salvador's Servicio Nacional de Estudios Territoriales (SNET).

The second section addresses monitoring and observations such as extensive steaming and drop in the surface elevation of the lake in the summit crater. Material for this section, primarily found on the SNET website, covers January-April 2006, when activity was fumarolic with no large eruptions. The 1 October 2005 eruption was possibly followed by a second one two days later on 3 October (SNET, 2006). A 3 October eruption was not mentioned in previous Bulletin reports.Carlos Pullinger explained that the evidence for the second eruption was tremor that day, but that could stemmed from other causes such as geysers in the summit crater lake, so the evidence for a 3 October eruption remains equivocal.

E-flank issues. October 2005 volcanism took place coincident with unusually high rains during tropical storm Stan (1-10 October 2005). On the E flank, the October 2005 eruptive episode killed extensive vegetation and left loose ash deposits covering the upper slopes (figure 7).

Figure 7. A November 2005 photo looking southward showing Santa Ana in the foreground, along with denuded, ash-laden vegetation. A wisp of steam escapes the summit crater, a basin hosting an acidic crater lake. Santa Ana's plumes and October 2005 ash deposits, coupled with other factors such as steep slopes, stress to vegetation, the lack of surviving permeable soils, and regional rainfall have led to a rash of new E-flank lahars. Peaks beyond Santa Ana include its satellitic cone Cerro Verde and then Izalco (sharp peak beyond the notch). Photo from SNET (2006).

Based on a rain gauge 5 km W of the crater (national meteorological station Los Naranjos), rainfall in October averages 193 mm; the yearly average is 2,155 mm. In the months prior to October 2006, rainfall at that station remained at normal values, always below 460 mm per month. In contrast, rainfall reached 865 mm during October 2006. During the peak of the storm, 3-6 October 2005, the Los Naranjos rain gauge collected more than 100 mm per day; the highest reading of 320 mm was on 5 October.

The lahars on Santa Ana's E slope consisted of both material from the October 2005 eruption as well as previous deposits. The first lahar seen by local witnesses took place on the night of 2 October 2005. It carried material up to 2 m in diameter. The lahars that produced most of the damage were those that occurred immediately after the eruption and reached a maximum thickness of 1.5 m. Other lahars descended later in the storm, persisting well into 2006.The 2006 rainy season did not generate damaging lahars, just heavy runoff with minor sediment. In all, SNET seismically registered 22 lahar events, all of which were confirmed by local residents. The communities used tractors used to keep the main drainages open and to build levees, which confined the lahars inside main drainage areas. The SNET website mentioned several lahar episodes during 2006. Some of these episodes occurred in May, June, and July 2006.

A large scallop in the topographic margin of Coatepeque caldera results in Planes de la Laguna (an area of ~ 10 km²), which was where lahars eventually deposited (figures 8 and 9). This area of less steeply sloped, and in places comparatively level, ground contains numerous coffee plantations and small settlements. The largest settlement is El Javillal (figure 8, adjacent Lake Coatepeque).

Figure 8. Lahars displayed as trains of heavy dots on a topographic base map of the E-central side of Santa Ana and the adjacent W side of Lake Coatepeque. (N is towards the top; light grid-lines are 1 km apart, so the distance from the summit on the W to the large lake on the E is ~ 6.5 km.) In general, the lahars descended from W to E. Coatepeque is a 7 x 10 km caldera and the series of dashed lines across the map indicate the caldera's steep-sided topographic margin in. Several caldera domes are labeled, including Cerro Pacho and Cerro Afate. Note the lahar entering the settlement adjacent Lake Coatepeque ("Caserío El Javillal"). From SNET (2006).

Figure 9. An E-W topographic profile with Santa Ana on the W across to the E side of Lake Coatepeque on the E. Dashed lines indicate the location of Coatepeque's caldera wall. From SNET (2006).

The upslope areas contained numerous channels carrying lahars (figure 8). Several kilometers into the caldera the channels merge as they cross the less steeply sloped Planes de Laguna. The channels eventually grow into two primary channels, La Mina on the S and El Javillal on the N (figure 10). The La Mina channel led directly towards the Cerro Pacho dome, where the lahars proceeded to branch into multiple routes (A, B, C, and D) before entering El Javillal (figure 11).

Figure 10. Annotated aerial photo at unknown date showing part of Coatepeque's Planes de Laguna, W of Santa Ana, taken looking roughly S. The view illustrates lahars in and around El Javillal.The lahars entered the area along two drainages (Quebradas La Mina and El Javillal), both flowing from right to left (arrows). Adjacent to the domes and settlements, the flow patterns become quite complex (as indicated by flow directions A, B, C, and D). Lake Coatepeque appears at the upper left. The steep caldera wall lies along the photo's margin from the upper center to right corner. The large circular dome is Cerro Pacho; the smaller dome to the right is Cerro Guacamayero. Photo from SNET (2006).

Figure 11. Photos showing October 2005 lahar deposits from Santa Ana in El Javillal. Deposits included lava blocks of differing sizes, and a mixture of soil, tree parts, mud, and water. Photos from SNET (2006).

Given the lack of soils and the state of vegetation, lahars were viewed as a potential ongoing hazard. To control lahars, SNET (2006) proposed excavating two channels from the vicinity of the domes to Lake Coatepeque, to carry sediment farther towards the lake. The proposed artificial channels are 2 m deep, with sides that slope at 45° outwards, and with a flat floor 5 m across. One proposed channel follows the S margin of the Cerro Pacho dome, the other follows a path similar to arrow A on figure 10.

Pullinger noted that the jocote de corona crop harvest was not affected because it came out just after the eruption. However, coffee was damaged wherever ash fell. Lahars did not directly hurt coffee plantations, but access roads were damaged and labor for harvesting was minimal, after much of the population had fled.

Monitoring. Moderate seismic activity and steam emissions continued during 2006. During 2006, seismicity was slightly above normal levels. Small earthquakes were interpreted as being associated with gas pulses.

Degassing continued in January 2006 with sporadic gas-and-steam emissions which rose approximately 200 m before dispersing. The SO₂ flux ranged between 163 and 1,578 metric tons/day.

On 2 February, there was an increase in seismicity, possibly related to an earthquake on the coast of Guatemala. From 1-7 February the SO₂ flux averaged 2,000 metric tons per day. A drop in the water level of the steaming, green-colored acidic lake in the summit crater revealed a local topographic high in the lake's center, which took the form of an irregular island (figure 12).

Figure 12. Photo showing the crater lake at Santa Ana volcano. The decrease in the water level has revealed an island of rocks and sediments that was previously covered by the crater lake. Photo taken on 17 February 2006 and provided courtesy of SNET.

Intense bubbling and fumarole activity during 27 February-23 March disturbed the lake's surface and made it difficult to assess the level of the water. During April, instability in the crater led to periodic landslides. One significant landslide deposited material in the SW section of the beach of the crater lake.

Reference. Servicio Nacional de Estudios Territoriales (SNET), 2006, Flujos de escombros en la Ladera Oriente del Volcán Ilamatepec, Departamento de Santa Ana: Perfil de Obras de Mitigacion, Enero de 2006, 12 p.

Geologic Background. Santa Ana (also known as Ilamatepec), is a massive, dominantly andesitic-to-trachyandesitic stratovolcano in El Salvador immediately W of Coatepeque Caldera. Collapse during the late Pleistocene produced a voluminous debris avalanche that swept into the Pacific Ocean, forming the Acajutla Peninsula. Reconstruction of the volcano subsequently filled most of the collapse scarp. The broad summit is cut by several crescentic craters, and a series of vents and cones have formed along a 20-km-long fissure system that extends from near the town of Chalchuapa NNW of the volcano to the San Marcelino and Cerro la Olla cinder cones on the SE flank. Small to moderate explosive eruptions from both summit and flank vents have been documented since the 16th century. The San Marcelino cinder cone on the SE flank produced a lava flow in 1722 that traveled 13 km E.

Information Contacts: Carlos Pullinger, Servicio Nacional de Estudios Territoriales (SNET), Alameda Roosevelt y 55 Avenida Norte, Edificio Torre El Salvador, Quinta Planta, San Salvador, El Salvador (URL: http://www.snet.gob.sv).

Activity returned to normal levels following the strong explosive episode of 10 September 2006 (BGVN 31:09). Activity after September included an occasional minor explosions, rockfalls, minor pyroclastic flows, venting of ash and gases and steam with emissions reaching up to 3 km altitude, minor ashfalls, and mudflows during heavy rains. In September and October, the minor pyroclastic flows primarily moved down the N and NE flanks of the dome. In January, pyroclastic flows traveled down the Gages Valley, Tyres Ghaut, Belham Valley, Tuits Ghaut, Farrells Plain, and especially the lower Tar River Valley E of the volcano.

Lava-dome growth slowed in March, and by the end of April it appeared to have ceased. On 1 June Montserrat Volcano Observatory (MVO) (figure 75) warned that, while the lava extrusion had ceased and the dome may not be actively growing, it remains as a large mass of partially molten lava capable of collapsing or exploding. According to MVO, the amount of material above Tyres Ghaut to the NW was sufficient to generate pyroclastic flows and surges capable of affecting the lower Belham Valley and other areas.

Figure 75. Map of Montserrat showing the pre-eruption topography of Soufrière Hills. The black circle shows the location of the MVO. The approximate outline of the Tar River delta in July 2004 is shown. Courtesy of Wadge and others (2005).

Data provided by MVO (table 64) shows the elevated seismicity (hybrid earthquakes and rockfall signals) related to the increased activity in late August and early September (BGVN 31:09). The high number of long-period earthquakes in late June reflects the dome collapse at that time (BGVN 31:05). The dramatic decrease in long-period events and rockfalls in mid-March corresponds to the observed reduction in dome growth.

Table 64. Seismicity at Soufrière Hills between 16 June 2006 and 25 May 2007. * Data for the first 4 days only. VT: volcanic tectonic; LP: long-period. Courtesy of MVO.

Strong activity during mid-September 2006. On 9 and 10 September, vigorous ash venting from the Gages Wall was accompanied by small explosions. Pyroclastic flows from fountain collapse occurred on all sides of the dome and reached 1 km W down Gages valley. On 11 September, the collapse of an overhanging lava lobe produced pyroclastic flows NE down the Tar River valley. One pyroclastic flow in the same area on 13 September reached the sea. On 14 September, vigorous ash venting resumed. Continuous ash and gas emissions during 13-19 September produced plumes that reached altitudes of 2.4-3.7 km. The Gages Wall vent continued to produce ash and gas emissions into mid-October.

Activity during September-December 2006. During 15 September-6 October the lava dome continued to grow at a moderate rate in the summit area and on the S and E sides of the dome. On 22 September the volume of the dome was about 80 million cubic meters. Lava-dome growth was concentrated on the NE part of the edifice from 6 October until 15 December, when growth moved to the SW part of the dome. A new E-facing shear lobe with a smooth, curved back enlarged during 13-20 October.

During 24 November-1 December, the two cracks in the curved back of the shear E-facing lobe on the summit propagated downward and divided the lobe into three blocks. The dome overtopped the NE crater wall and fresh rock and boulder deposits were observed in that region. During 22-29 December, lava-dome growth was focused on the W, where gas-and-ash venting occurred. A high whaleback lobe directed SW was observed on 26 December.

Aviation notices reported continuous ash and gas emissions almost every day from 15 September through 14 November, with plumes rising above 2 km to a maximum of 4.6 km altitude. Plumes extended 140 km W on 2-3 October. During 17-24 November, ash venting originated from the westernmost of two cracks in the curved back of the shear E-facing lobe on the summit. An explosion produced an ash plume that rose to altitudes of 1.5-1.7 km.

Pyroclastic flows occurred regularly as collapses from the dome sent material in all directions. Pyroclastic flows reached both the upper region of Tuitts Ghaut (N) and the sea via the Tar River Valley (E) on 23 November.

Activity during January-March 2007. Rapid lava-dome growth, pyroclastic flows, and ash venting increased during 3-9 January. Dome growth was concentrated in the NW, the highest part of the dome. Pyroclastic flows were observed in Tyres Ghaut (NW), Gages Valley (W), and N, behind Gages Mountain and accompanied by ash venting. On 4 January, simultaneous pyroclastic flows descended Tyres Ghaut and Gages Valley, and a resultant ash cloud reached an altitude of 2.5 km. The maximum distance for the Gages Valley flow was 4 km. During 6-9 January, distances of pyroclastic flows increased in Tyres Ghaut and possibly exceeded 1.5 km.

During 10-16 January, lava-dome growth was focused on the NW quadrant. During 10-11 January, one pyroclastic flow was observed to the W in Gages Valley and one to the NW in Tyres Ghaut. On 15 January, a relatively large pyroclastic flow traveled E down the Tar River Valley. After 15 January, measurable activity was low. Gas and ash venting that originated from the W side of the dome continued. A clear view on 22 January revealed that the collapse scar from the 8 January event was filled in. A small spine was noted on the W side. On 23 January, a large pyroclastic flow traveled down Gages Valley. The Washington VAAC reported that ash plumes were visible during 26-27 January. On 28 January, a large pyroclastic flow traveled down the Tar River Valley and reached the sea. A diffuse plume rose to an altitude of 1.5 km on 31 January.

During 7-13 February, growth of the lava dome continued on the W side, then was concentrated on the E and N sides for the rest of the month. The lava-dome volume in mid-February was estimated at 200 million cubic meters based on LIDAR data. Previous measurements over-estimated the lava-dome volume due to the perceived location of the dome and the lack of data from inside the crater. Small pyroclastic traveled in multiple directions throughout February. Moderate pyroclastic flows traveled down the Tar River Valley during 24-25 and 27 February. Continuous ash emissions were reported during 14 February-6 March, with plumes to altitudes of 2.1-6.1 km.

Lava-dome growth during 2-9 March was concentrated on an E-facing lobe topped with blocky, spine-like protrusions. Rockfalls affected the E and NE flanks. Pyroclastic flows traveled 2 km in the Tar River Valley. Heightened pyroclastic activity on 7 March resulted in an ash plume that rose to an estimated 2.4 km. On 11 March, a pyroclastic flow traveled down the NE flank into White's Ghaut.

During 9-26 March, lava-dome growth was concentrated on the NE side. Intermittent pyroclastic flows traveled E down the Tar River valley and produced ash plumes. One plume on 12 March rose to 3 km altitude. Pyroclastic flows were observed NW in Tyre's Ghaut and ashfall was reported from the Salem /Old Towne areas. During 23 March-3 April, dome growth apparently stopped.

MODIS thermal data indicated hot pixels at the dome and from pyroclastic flows on 24 March. Another thermal anomaly from a pyroclastic flow Tar River was detected on 29 March. No futher anomalies had been recorded by the HIGP Hotspot system through May. However, the Washington VAAC reported that a SW-drifting, diffuse plume and a hotspot were visible on satellite imagery on 2 April.

During 30 March-13 April, small, intermittent pyroclastic flows from the E-facing shear lobe occurred in the Tar River valley (figure 76). Incandescent rockfalls were seen at night during 5-9 April. On 17 April, a small pyroclastic flow was observed to the NW in the upper part of Tyres Ghaut. In mid-April MVO estimated that the lava-dome volume was about 208 million cubic meters.

Figure 76. Photograph taken 4 April 2007 of southern Montserrat and Soufrière Hills from the NE, showing from left the Tar River Delta and the debris fans spilling from Tuitts and Whites Ghauts. Courtesy MVO.

The sulfur dioxide (SO₂) flux rate during 6-13 April was high, with an average value of 3,114 metric tons per day (t/d), well above the long-term average for the eruption. The previous week averaged 1,035 t/d, from a low of 71 to a high of 3,818 t/d. The three days from 8 to 10 April showed markedly elevated emissions: 3,550, 7,396 peaking at 7,471 t/d, whereas the remaining days' emissions were extremely low, some below 100 t/d.

During 13-20 April, material originating from the lava dome's E-facing shear lobe was shed down the Tar River Valley. A bluish haze containing sulfur dioxide was observed flowing down the N flanks on 18-20 April. Pyroclastic activity was ongoing on the E and NE sides of the dome during 27 April-4 May. After 4 May the overall structure of the dome changed very little. Low-level rockfall and pyroclastic-flow activity continued into late May.

Reference. Wadge, G., Macfarlane, D.G., Robertson, D.A., Hale, A.J., Pinkerton, H., Burrell, R.V., Norton, G.E., and James, M.R., 2005, AVTIS: a novel millimetre-wave ground based instrument for volcano remote sensing: J. Volcanology and Geothermal Research, v. 146, no. 4, p. 307-318.

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

Information Contacts: Montserrat Volcano Observatory (MVO), Fleming, Montserrat, West Indies (URL: http://www.mvo.ms/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Hawai'i Institute of Geophysics and Planetology, MODIS Thermal Alert System, School of Ocean and Earth Sciences and Technology (SOEST), University of Hawai'i, 2525 Correa Road, Honolulu, HI, USA (URL: http://modis.higp.hawaii.edu/).

According to Sonia Calvari of Istituto Nazionale di Geofisica e Vulcanologia (INGV-CT), a flank eruption started on Stromboli volcano on 27 February 2007 and continued to at least 15 March. Compared to the previous flank eruption during 2002-2003, lava effusion was about an order of magnitude greater. Initially, a NE fissure opened on the NE flank of the NE-crater, and lava emitted from the fissure formed three branches and rapidly reached the sea (figure 75).

Figure 75. Lava from Stromboli reaching the sea on 27 February 2007. Courtesy of the INGV-CT 2007 Stromboli eruption web site.

Late on the eruption's first day, the three initial flows stopped and a new vent opened at the E Margin of the Sciara del Fuoco at about 400 m elevation. In a few days, this vent emitted sufficient lava to build a lava bench several tens of meters wide, which significantly modified the coastline. These lava emissions stopped for a few hours on 9 March, after which another vent opened at about 550 m elevation on the N flank of the NE-crater, almost in the same position as one of the vents of the 2002-2003 eruption. The 550-m vent was active for less than 24 hours and, when it ceased emitting lava, the 400-m vent reopened, again feeding lava to the sea.

On 15 March 2007, while the effusion from the 400-m vent continued, a major explosion occurred at 2137 (2037 UTC). This event, similar to that on 5 April 2003 (BGVN 28:04), was recorded by all the INGV-CT monitoring web cams. As in 2003, the 2007 event occurred during a flank effusive eruption, when the summit craters were obstructed by debris fallen from the crater rims. Still images and videos can be downloaded from the INGV-CT webpage dedicated to the 2007 Stromboli eruption.

Satellite imagery. Satellite imagery revealed an ash plume fanning SSE from the eruption site beginning at 1215 UTC on 27 February 2007. Another eruption was observed on MET-8 split-window IR (infrared) imagery on the same day at 1830 UTC. Ash then blew SSE at 46-56 km/hour.

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

Information Contacts: Sonia Calvari, Istituto Nazionale di Geofisica e Vulcanologia Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/); INGV-CT 2007 Stromboli eruption website (URL: http://www.ct.ingv.it/stromboli2007/main.htm); U.S. Air Force Weather Agency (AFWA)/XOGM, Offutt Air Force Base, NE 68113, USA.

New and revised information has emerged regarding the behavior of the Sulu Range (Johnson, 1971), a volcanic field adjacent to and immediately E of Walo hot springs along the coast in the N-central part of New Britain Island (BGVN 31:07 and 31:09; figure 3). Initial Rabaul Volcanological Observatory (RVO) reports mentioned apparent steam and ash emission during mid-July 2006, but although weak-to-moderate vapor emission occured, and a later section of this report discusses heightened hot spring activity, the reported "forceful dark emissions" have been instead linked to dust during mass wasting.

Figure 3. A sketch map of New Britain island showing a small portion of the main island of Papua New Guinea (lower left) and New Ireland (upper right). Volcanoes on or adjacent New Britain are labeled. Volcanoes active and erupting frequently in the last decade include (from the SW) Langila, Ulawun, and Rabaul. Volcanoes that have erupted or undergone anomalous unrest in the past few years include (from the SW) Ritter Island, the Garbuna group, Pago, Sulu Range, and Bamus.

In a 12 April Email message, Steve Saunders clarified the latest RVO views on Sulu's behavior. He noted that ". . . Sulu did not erupt! It was purely a series of seismic cris[es]. The 'emissions' which were reported before we got there turned out to be dust from landslides."

Unusually vigorous hot springs, declining seismicity. Following the first two weeks of unrest during mid-July at Sulu Range, an RVO report discussing 31 July to 2 August activity stated that area hot springs such as those at Walo were undergoing unusually strong activity. This included expelled mud, the emergence of geysers, and abnormal quantities of steam.

RVO noted waning seismicity in late July. Seismicity had declined to relatively low levels, although small volcano-tectonic events continued to be recorded. The small earthquakes were centered around the settlements of Silanga, Sege, and Sale (figure 4; respectively, from Mt.Ruckenberg's summit, located 12.7 km to the SW; 7.2 km SW, and 5.5 km S). The 31 July to 2 August earthquakes were described as more irregular and less frequent than those in preceeding weeks.

Figure 4. Geological map showing the cluster of overlapping cones of the Sulu Range. Walo village lies just off the map near the coast within a few kilometers of the map 's W margin. The thermal area by the same name lies ~ 5 km SW of Lava Point. The prominent cone on the N edge of the Range is called Mount Ruckenberg or Mount Karai. The initial "vent location" was 2 km SW of Mount Karai between Ubia and Ululu volcanoes. Part of that area is crossed by two parallel, closely spaced faults. The narrow zone between those faults was down-thrown. A SW-directed debris flow was also mapped near this area. Three centers in the N, Ruckenberg (Karai), Kaiamu maar, and Voku, are specifically mentioned in the text as areas with recently documented Holocene activity. Modified from a map by Chris McKee, RVO.

The pattern of located earthquakes defined an irregular ellipse, with major axis 9 km E-W. Two earthquakes represented a 1-2 km extension N from the ellipse under Bangula Bay. There were also two earthquakes offshore about 4-5 km due N of Cape Reilnitz, a broad promontory the most extreme point of which lies 18 km to the W of Mt. Ruckenberg's summit. As of the end of July an area devoid of earthquakes remained; it was 2-3 km in diameter and centered on Walo village.

The RVO estimated that the top of the underlying magma body was 10-15 km deep when volcano-tectonic earthquakes began on 6 July 2006. They judged that volatiles or heat escaping from the magma were responsible for onset of the mud and water ejections at the once quiet hot springs.

Postulated intrusion. Randy White (US Geological Survey) analyzed the July seismic crisis, which in his interpretation did not follow the pattern of a tectonic earthquake with a main shock and associated aftershocks, but did follow behavior of many earthquakes accompanying the onset of volcanic unrest. He attributed the seismicity to a dike intruded to shallow depth (and confined to the subsurface). According to White, the epicenters well outboard of, but surrounding the area of intrusion, occurred in a pattern similar to those accompanying many shallow intrusions.

The elevated seismicity began after a volcano-tectonic earthquake, M ~ 6 on 19 July (BGVN 31:07). It was located on the N side of New Britain, slightly offshore, and a few ten's of kilometers from the Sulu Range. The focal depth was thought to be in the 10-20 km range. White noted that soon after the 19 July earthquake, Australia provided portable seismometers. Once those arrived and began recording data, computed moment tensors indicated that subsequent earthquakes were very shallow. Epicenters occurred slightly W of the Sulu Range.

Short level-lines installed by RVO in August 2006 showed, by November, ~ 2 cm of deflation of the Kaiamu area in relation to a datum ~ 1 km E on the Kaiamu-Sulu track. By April 2006 the measured levels had returned to approximately the August datum line.

To the W of the area at Lasibu a similar pattern existed, with over 2.5 cm of deflation locally measured by November and an approximate return to the datum-line by April 2006. The center of the area delimited by seismicity is swamp and difficult to access. Google satellite images show an interesting series of raised shorelines W of Kaiamu.

Upon prompting from White, Chuck Wicks acquired satellite radar (L-band imagery) from Japanese collaborators for the Sulu Range. The radar data were taken weeks before and weeks after the July seismicity. When processed to obtain radar interferometry, the data indicated over 80 cm of vertical surface deformation. The deformation was centered in a region W of the Sulu Range along an area along the coast ~ 5 km W of Lava Point (Lara Point on some maps). It trends ENE. The data were interpreted as a shallow dike intrusion on the order of ~ 8 m wide trending out beneath Bangula Bay.

Wick's preliminary analysis suggests the intrusion's volume may be on the order of one cubic kilometer. White's qualitative estimate of the volume, from the intensity, style, and duration of the seismicity, were consistent with that analysis. In addition, the strike-slip focal mechanisms seen in the seismic data suggested the dike-intrusion episode caused movement along a nearby strike-slip fault.

Geological investigations conducted in the past several months by Herman Patia and Chris McKee indicated that Sulu Range has been quite active 'recently.' The latest eruptive phase at Kaiamu maar was radiocarbon-dated at 1,300 BP. Since that time at least seven eruptions have taken place at other vents, notably Voko, involving phreatomagmatic eruptions. Ruckenberg (Karai) appears to be the source of the most recent activity. Within the last 200 years it produced lava flows.

Reference. Johnson, RW., 1971, Bamus volcano, Lake Hargay area, and Sulu Range, New Britain: Volcanic geology and petrology: Australia Department of National Development, Bureau of Mineral Resources, Geology and Geophysics, Record 1971/55.

Geologic Background. The Sulu Range consists of a cluster of partially overlapping small stratovolcanoes and lava domes in north-central New Britain off Bangula Bay. The 610-m Mount Malopu at the southern end forms the high point of the basaltic-to-rhyolitic complex. Kaiamu maar forms a peninsula with a small lake extending about 1 km into Bangula Bay at the NW side of the Sulu Range. The Walo hydrothermal area, consisting of solfataras and mud pots, lies on the coastal plain west of the SW base of the Sulu Range. No historical eruptions are known from the Sulu Range, although some of the cones display a relatively undissected morphology. A vigorous new fumarolic vent opened in 2006, preceded by vegetation die-off, seismicity, and dust-producing landslides.

Information Contacts: Steve Saunders, Herman Patia, and Chris McKee, Rabaul Volcanological Observatory (RVO), Department of Mining, Private Mail Bag, Port Moresby Post Office, National Capitol District, Papua New Guinea; USGS Earthquakes Hazard Program (URL: http://earthquakes.usgs.gov/); Randy White and Chuck Wicks, US Geological Survey, 345 Middlefield Rd., MS 977, Menlo Park, CA 94025, USA; United Nations Office for the Coordination of Humanitarian Affairs (URL: https://reliefweb.int/).

This report covers the time interval early January to 2 March 2007, based on Special Reports of the Ecuadorian Geophysical Institute (IG). This reporting interval was mainly one of relative quiet. In contrast, our previous report (BGVN 32:12), covered IG reports describing energetic eruptions of July and August 2006. Those IG reports also mentioned eruption-related fatalities and the discovery of a new growing bulge on the volcano's N flank. A map and geographic background were tabulated in BGVN 29:01.

Relative quiet prevails and some residents return. As touched on in BGVN 32:12, after August 2006, the volcanic vigor at Tungurahua was minimal and of low energy. The decrease in activity was gradual through mid-December 2006. The vigor remained low until mid-January 2007. Ash emissions did occur but were consistently minor.

IG reports noted that the relative tranquility at Tungurahua could reflect a pattern similar to that seen there in 1918. That was a case when various months of volcanic quiet occurred, only to be followed by explosive eruptions of large size. The latter generated pyroclastic flows.

During the quiet that followed the July and August 2006 eruptions, residents who had evacuated from the margins of the volcano returned to their properties. The IG noted that, unfortunately, these returning residents became more vulnerable to volcanic hazards and made emergency response more difficult.

Vigor increases. Between 20 January and 5 February 2007 internal seismic activity resumed, behavior consisting of a few earthquakes inferred as associated with fractures (volcano-tectonic earthquakes, VTs). On 13 February the volcano emitted an eruptive column with moderate ash content. After 19 February there was a reoccurrence of seismic VTs. These were of shorter duration but higher intensity than those that occurred during the previous period.

During 23-24 February 2007, volcanic tremors and seismic LP's were registered at the Volcanic Observatory of Tungurahua (VOT). At 0310 on 24 February, VOT staff and local observers reported continuous roars of moderate intensity, and discharge of incandescent material that both rose to ~ 800 m above the summit and descended ~ 1000 m down the volcano's flanks.

The emission column headed NW. Fine tephra fell, followed by a thick ashfall that was black in color. It left a deposit 3 mm thick in the towns of Pillate and San Juan. Reports received from Cotaló, Bilbao, Manzano, and Choglontús that indicate a thick, dark ashfall in those spots left a deposit 2 mm thick. Ashfall was also reported in the area of Quero.

Seismic activity decreased on 24 February as well as the intensity and frequency of the roars. As of 2 March, sporadic explosions of ash and incandescent material had been observed. Around this time some bad weather prevented clear views of the upper volcano; however, some reporters noted minor ashfall along the SW portion of the crater. Additionally, the SO₂ flux increased to ~ 2,000 metric tons a day for the first time since the beginning of the year. The IG's "Seismic Activity Index" indicated an increase of the volcano's internal activity.

Two scenarios envisioned. Given the available data, the IG concluded that the volcano had received a new influx of magma. They proposed two potential scenarios: (1) the current levels of activity will continue and constant emissions of ash, (potentially more intense) will be generated. Ash clouds will be blown by winds that at this time of the year are predominantly westerly, with occasional S and NW variations. These ash clouds could generate heavy ashfall in the towns downwind from the volcano; or (2) the volume and speed of ascent of the magmatic gases originating from the new magma will increase dramatically, in which case, new explosive eruptions of pyroclastic flows similar to those on 14 July and 16 August could occur.

Geologic Background. Tungurahua, a steep-sided andesitic-dacitic stratovolcano that towers more than 3 km above its northern base, is one of Ecuador's most active volcanoes. Three major edifices have been sequentially constructed since the mid-Pleistocene over a basement of metamorphic rocks. Tungurahua II was built within the past 14,000 years following the collapse of the initial edifice. Tungurahua II collapsed about 3,000 years ago and produced a large debris-avalanche deposit to the west. The modern glacier-capped stratovolcano (Tungurahua III) was constructed within the landslide scarp. Historical eruptions have all originated from the summit crater, accompanied by strong explosions and sometimes by pyroclastic flows and lava flows that reached populated areas at the volcano's base. Prior to a long-term eruption beginning in 1999 that caused the temporary evacuation of the city of Baños at the foot of the volcano, the last major eruption had occurred from 1916 to 1918, although minor activity continued until 1925.

Information Contacts: Geophysical Institute (IG), Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/).