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/).

As described in the previous Arenal report (BGVN 29:08), on 6 July 2004 a series of pyroclastic flows descended the NE flank. These flows resulted from the collapse of the upper portions of a lava flow, and affected areas beyond those affected by pyroclastic flows during 1999-2003. Similar events have been common in recent years on the volcano's N and NE sides, as Crater C continued to emit gases, lava flows, and sporadic strombolian eruptions through 2004 and at least as late as November 2005. Throughout the period of this report (August 2004-September 2005) the lava flow that began to be emitted towards the NE flank in June 2004 remained active. Occasional blocks spalled off the N edge of the crater towards the NE. The NE and SE flanks continued to be affected by pyroclastic flows and acid rain. Crater D displayed fumarole activity from July 2004 through September 2005. The seismograph station VACR (2.9 km NE of the active Crater C) was out of service from 24 June 2004 until 20 August 2004. Table 24 summarizes the seismicity registered at VACR from August 2004 to September 2005.

Table 24. Seismic activity registered at Arenal's station VACR, August 2004 - September 2005. From 24 June to 20 August 2004 VACR was not operating. No data were reported for December 2004. Courtesy of OVSICORI-UNA.

During July 2004-January 2005, pyroclastic flows were produced by the collapse of the active lava flow front. In August 2004 some eruptions generated ash columns higher than 500 m above Crater C.

Through most of February 2005 Arenal was hidden by storm clouds, but late in the month it could be observed that the lava flow formerly active on the NE flank had stopped, and no other active flow was seen. The number of eruptions and the amount of ejected pyroclastic material were both reduced in February, and few eruptions produced plumes as high as 500 m. The dome in Crater C continued to grow.

At the beginning of March a SW-trending lava flow was observed, and blocks were ejected to the W. During April 2005 this flow continued, and ejected blocks caused small fires in the surrounding vegetation. A new lava flow began on the SE flank, and blocks ejected to the S and SE again caused fires. In May and June 2005 the SW flow continued. In July the SW lava flow deposited blocks towards the SW, the W and the NW. The SE lava flow released small avalanches off its front and sides. Occasional eruptions produced ash columns higher than 500 m above Crater C.

In August 2005 the SE lava flow stopped. Few eruptions produced ash columns higher than 500 m above Crater C. During September 2005 the SW lava flow was active and deposited blocks to the SW, the W and the NW. The NE and SE flanks continued to be affected by the fall of pyroclastic material and acid rain.

Observatorio Vulcanológico y Sismológico de Costa Rica -Universidad Nacional (OVSICORI-UNA) reported that around 1500 on 2 November a pyroclastic flow was observed on the SE flank of Arenal. On 3 November researchers from OVSICORI-UNA visited the affected area and, contrary to what witnesses had reported, determined that the 2 November event took place on the W flank of the volcano. The mid-size pyroclastic flow produced gas, dust, and ash that were carried by strong winds towards the SE.

Despite the rainy and hazy conditions during the fieldwork it was possible to confirm the affected area and deposits. The movement of lava flows on the SW flank had been observed for the last several months. Materials descending from the summit bifurcate, covering a wide fan that ranges from the W to the SW flank. The main pyroclastic flow affected an area from the summit down to ~ 1000 m altitude. A smooth alley was carved in the steep walls of upper W flank by the transport of incandescent material. Most of the material was deposited in a distal zone 75 m wide, at the break in the steep upper cone slope.

Samples were taken from hot loose blocks spalled from the lava flow; one block was still at 154°C, and was accompanied by several other massive blocks that were fractured by rapid cooling and rough transport. There is evidence that the fine fall material was only deposited in the upper and middle part of the edifice towards the SE.

Given the sustained deposition of material in the area, visitors were advised to follow instructions and safety measures and adhere to the advice of the Park Rangers and tour guides.

Geologic Background. Conical Volcán Arenal is the youngest stratovolcano in Costa Rica and one of its most active. The 1670-m-high andesitic volcano towers above the eastern shores of Lake Arenal, which has been enlarged by a hydroelectric project. Arenal lies along a volcanic chain that has migrated to the NW from the late-Pleistocene Los Perdidos lava domes through the Pleistocene-to-Holocene Chato volcano, which contains a 500-m-wide, lake-filled summit crater. The earliest known eruptions of Arenal took place about 7000 years ago, and it was active concurrently with Cerro Chato until the activity of Chato ended about 3500 years ago. Growth of Arenal has been characterized by periodic major explosive eruptions at several-hundred-year intervals and periods of lava effusion that armor the cone. An eruptive period that began with a major explosive eruption in 1968 ended in December 2010; continuous explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows characterized the eruption from vents at the summit and on the upper western flank.

Information Contacts: Eliecer Duarte, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica. (URL: http://www.ovsicori.una.ac.cr/).

At 1631 on 26 February 2005 (0031 UTC on 27 February), a hydroacoustic network detected the start of what became an intense earthquake swarm (Ridge 2000 TCS (Time Critical Studies) Oversight Committee, 2005). The source of the swarm was on the Endeavour segment of the northern Juan de Fuca Ridge (JdFR) (figure 1).

Figure 1. Location map of the February 2005 earthquake swarm on the Juan de Fuca ridge along the Endeavour Segment. Courtesy Ridge 2000 TCS Oversight Committee, 2005.

More than 3,740 earthquakes were detected over a 5.5-day period (figure 2). Event counts were as high as 50-70 per hour, which is similar in scale to event counts associated with sea-floor-spreading events on the ridge at both the Middle Valley segment in September 2001 and at the Endeavour segment in 1999. The hydroacoustic array is the Sound Surveillance System (SOSUS) of the National Oceanic and Atmospheric Administration (NOAA).

Figure 2. Histogram showing the number of seismic events per hour on the Endeavour segment of the Juan de Fuca ridge. The x-axis extends over Julian days 56-64, 2005 (25 February-5 March 2005). Courtesy National Oceanic and Atmospheric Agency (NOAA) Vents web site, 2005.

The preliminary location of the swarm's epicenters was 48°14.5'N, 128°57.6'W (figure 2), ~ 36 km NNE of the Main Endeavour vent field and a few kilometers E of the intersection of the Heck Seamounts with the JdFR axis. The sequence also produced three large earthquakes (mb 4.5, 4.8, and 4.9) detected by instruments of the National Earthquake Information Center (NEIC), the University of Washington, and the Pacific Northwest Seismograph Network (PNSN). The February-March 2005 seismic swarm also maintained an elevated, nearly constant rate of similar-magnitude earthquakes for several days, behavior consistent with magma intrusion and in contrast to the "mainshock-aftershock" sequence characteristic of tectonic events.

Research response personnel were on station by 6 March, just six days after notification of the seismic swarm, a task that often requires a lead time of over a year. Results from the response cruise indicate that it is unlikely that the February-March 2005 earthquake swarm (figure 3) induced any corresponding expression at the sea floor (i.e., eruption of a lava flow) or in the water column (i.e., formation of new hydrothermal venting, either chronic or event plumes).

Figure 3. Epicenters of the 305 larger earthquakes along the Endeavour Segment. Those indicated by the larger red dots were located using 4 or more hydrophones.The epicenters indicated by the smaller black dots were smaller events located using three hydrophones, and they may not be as well constrained. Epicenters are plotted through 1 March 2005 and comprise 305 events. Courtesy National Oceanic and Atmospheric Agency (NOAA) Vents web site, 2005.

In-situ and shipboard physical and chemical data from the three long tow-yo casts and seven vertical casts revealed no water-column signal that can be clearly associated with the recent earthquake swarm, whether magmatic or tectonic. Initial calculations of methane to hydrogen ratios from the Main Endeavour Field, and from Mothra, High Rise, or Salty Dawg vent fields along the Endeavour segment are comparable to historical (2003) values from vent fluids. No evidence of any temperature or optical anomalies was seen in the near-bottom camera tow data (CTD or MAPR) overlying an axial magma chamber reflector, close to the region of the February/March swarm. Camera images of the sea floor revealed no fresh basalt; rather, the entire camera tow track documented lavas with moderate to heavy sediment cover. Finally, no bathymetric anomalies were detected as the cruise scientists searched for evidence of new lava flows in the earthquake area by comparing before and after high-resolution multibeam bathymetry data. The earthquake swarm was thus thought to reflect a magmatic intrusion that failed to generate measurable changes in the sea floor or an intrusive magmatic event that did not reach sufficiently shallow crustal depths to lead to extrusion (eruptive flows) or stimulate venting at new or existing vent fields as discernable via surface-ship sampling.

References. Ridge 2000 TCS (Time Critical Studies) Oversight Committee, 2005, Recent detected events on the Juan de Fuca Ridge, Status report on time critical studies: Ridge 2000 Events, v. 3 (Spring 2005), p. 14-15.

Davis, E.E., and Currie, R.G., 1993, Geophysical observations of the northern Juan de Fuca Ridge system: Lessons in sea-floor spreading: Canadian Journal of Earth Sciences, v. 30 (2), p. 278-300.

Geologic Background. The Endeavour Segment (or Ridge) lies near the northern end of the Juan de Fuca Ridge, W of the coast of Washington and SW of Vancouver Island. The northern end is offset to the east with respect to the West Valley Segment, which extends north to the triple junction with the Sovanco Fracture Zone and the Nootka Fault. The 90-km-long, NNE-SSW-trending segment lies at a depth of more than 2,000 m and is the site of vigorous high-temperature hydrothermal vent systems that were discovered in 1981. Five major vent fields that include sulfide chimneys and black smoker vents are spaced at about 2-km intervals in a 1-km-wide axial valley at the center of the ridge. Preliminary uranium-series dates of Holocene age were obtained on basaltic lava flows, and other younger "zero-age" flows were sampled. Seismic swarms were detected in 1991 and 2005.

Information Contacts: Pacific Marine Environmental Laboratory (PMEL), National Oceanic and Atmospheric Agency (NOAA), 7600 Sand Point Way NE, Building 3, Seattle, WA 98115-6349, and Hatfield Marine Science Center, 2115 SE Oregon State University Drive, Newport, OR 97365 (URL: https://www.pmel.noaa.gov/eoi/); Robert Dziak, NOAA PMEL, Hatfield Marine Science Center, 2115 SE Oregon State University Drive, Newport, OR 97365.

Vigorous eruptive activity was observed in July 2004, and visitors in January 2005 noted that a new crater rim overflow area had developed along the N rim (see report and map in BGVN 30:04). The mountain guide for Martin Haigh reported on 15 May that last lava flows had occurred in March.

Activity during 3-5 July 2005. During 3-5 July 2005 Bernard Marty and others visited the crater to conduct gas sampling. His report follows.

At the time of arrival (0800 on 3 July), sporadic lava flows of the aa type were emitted from a vent at the base of T56B, which was itself disrupted by an explosion, leaving an open cavity about 15 m in diameter. The lava was flowing toward the E overflow, but never reached the crater rim. At about 1130, lava was spilling violently from T58B and flowing towards the E overflow.

Sampling had to be interrupted at T46 due to the risk of a sudden lava flood in the sampling area, a real possibility if the thin W wall of T58B fractured following thermal erosion of the wall by molten lava in the lava lake. One hundred meters S of T46, close to the base of T47, a deep hole ~ 1.5 m diameter and bordered by lava splashes emitted a piercing sound. A pahoehoe lava flow was emitting high temperature gases with no visible steam.

A lava pond, not directly observed but for which bubble explosions were clearly visible, was discharging surges of lava towards the E rim while the adjacent T58C cone, now higher than T58B, was discharging high-velocity gases that occasionally splashed lava. The eruption lasted all day and the following night, with variations from steady-state outpouring with lower degassing, to bursts of large bubbles with enhanced lava emission. By the afternoon of 4 July the lava, which was then overflowing the E slope of the volcano, ignited a bush fire. The lava emission rate was estimated at about 0.3 m³/s, with a speed of ~ 2 m/s in the flat area toward the volcano's flank.

At 0500 on 5 July lava flows suddenly invaded the mountain camp's kitchen area to a depth of one meter. Fortunately no one was hurt, but the episode illustrated that there was no safe area within the N crater.

Activity during 19 July-9 August 2005. During 19 July-9 August a team of observers led by Fred Belton camped in the inactive S crater. They submitted the following report of the active N crater as viewed from the SE crater rim.

Activity during the past year was confined to the crater's central portion. Since its initial violent eruption from a hole in the crater floor on 15 July 2004, T58C has grown to a height of ~ 12 m and is at the time of this report the second highest cone in the crater, tall and narrow with large blocks scattered about the crater floor below, indicating that it has undergone some flank collapses in the preceding months. T49B has grown significantly taller since July 2004 and is the tallest feature in the crater, rising at least 15 m above its base.

T56B, which has remained open to the SE since July 2004, has grown a small cone on its SE flank. The new cone, which has not been named because it is so high on the flank of T56B, is being undermined by a large tunnel. The tunnel begins at the SE base of the small unnamed cone and extends under it to the open vent of T56B. Clearly the tunnel was a recent active feature, and the tunnel entrance appears to be the result of collapse during or after an eruption.

T58B contained a large and deep (10-12 m) open pit, which clearly indicated the presence of past lava-lake activity at two levels. The solid crust of a former lava lake about 4 m below the rim contained a hole near its center that opened into a much deeper chamber. At some point during the night of 4 August this deeper pit was filled by lava so that only the upper level remained.

T57B appeared unchanged from July 2004 until its S half was covered by a thick layer of fused spherical lapilli from a short but powerful eruption of T58C on 20-21 July (figure 85).

Figure 85. At 0100 on 21 July a short but powerful eruption from Ol Doinyo Lengai's T58C vent produced these fresh black lava flows and a lapilli field on the flank of T57B. This view is looking NW. Courtesy of Fred Belton.

Spatter cones T40, T46, T47, T51, T45, T37, T37B, and the ash cones have continued to be gradually covered by lava flows from the active cone group in the central crater. In particular, T40, which was the primary active cone during much of 1999, is now well on its way to disappearing under the lava. Lava flows from the central cone area have continued to build up the height of the mound in the central crater so that several cones are easily visible from Engare Sero village. T53 (~ 80 m NW of T40) no longer existed. A deep hole in the crater floor, just N of T47 and surrounded by recent pahoehoe flows from T58B, is possibly all that remains of the summit vent of T39. The hole was degassing at a high temperature but did not show any evidence of recent effusive activity. An area in the E part of the crater, which is sheltered by outcroppings and sometimes used by campers, had been covered by a thick flow of slabby pahoehoe lava from T58B. A large amount of vegetation on the E flank of Lengai had also been burned by lava flowing through the E-crater-rim overflow (figure 86). Several locations on the N crater rim had become crossed by small lava flows.

Figure 86. The light-colored stripe represents the overflow of recent lavas from Ol Doinyo Lengai down the E flank, as photographed on 7 Aug 2005 from the S crater. The blackened area represents burned vegetation from the bush fire reported by Bernard Marty on 4 July 2005. The lavas, termed natrocarbonatites, turn light colored on the surfaces upon cooling and absorbing moisture. Courtesy of Fred Belton.

Table 10 shows a multi-year set of measurements of the width of crater rim overflows. The N rim overflow was first measured on 7 August 2005.

Table 10. Measurements of the widths of lava overflowing the crater rim at Ol Doinyo Lengai. The values represent the arc length of the crater rim covered by lava flows on the various dates. Measurements were made by pacing the distance several times and averaging the results. The dashes mean that the overflow had not yet come into existence on the date indicated. The lengths of the flows beyond the crater rim are not shown on this table. Courtesy of Fred Belton and Chris Weber.

Although there was no activity on 19 July, an unobserved eruption may have begun around 2300 on 20 July and probably ended by 0130 on 21 July, according to reports by a camping group in the W portion of the crater floor. The activity reached its peak between 0100 and 0130 and involved strong lava fountains from a vent about halfway up the E side of T58C. The fountains deposited a deep (at least 0.5 m) bed of lapilli around the base and on the S flank and top of cone T57B, and sent pahoehoe and aa flows to the E. One of the flows traveled tens of meters down Lengai's E slopes. The lapilli consisted mostly of hollow spheroids with diameters up to 1.2 cm. Many of the lapilli were fused, and sections of the field broke apart under their own weight, leaving a blocky, fissured surface.

On 21 July at 1511 lava flowed from T58B's active vent during a 12-minute eruption. At 2100 on the same day a third eruption sent strong surges of lava from the same vent and continued throughout the night. Atmospheric clouds prevented detailed observations, but clear conditions at 0500 on 22 July revealed that a large lava channel had formed just E of T58B and had been thermally eroded to a depth of more than one meter. Maximum flow rate during the eruption was estimated to be 0.5 m³/s. The eruption continued until about 1800 and deposited pahoehoe flows over a large part of the SE crater floor.

With the exception of a very minor lava flow from T58C at 1930 on 26 July and the brief (unobserved) appearance of a lava lake in T58B on the night of 4 August, no further activity occurred through 9 August. There were frequent sounds of lava at depth near the base of T58C and inside the open vent of T58B. The lava lake that briefly occupied T58B filled up its deep inner pit and then solidified, leaving a flat surface of new lava about 4 m below the lowest place on the cone's rim. During 4-9 August lava could be heard moving near the surface somewhere inside T58B's vent, but it never became visible. Observations ended at 0800 on 9 August 2005.

Activity during September and October 2005. Kees DeJong reported the following, which was posted on Belton's website: "We climbed Oldonyo Lengai 13 September 2005, arriving at the crater rim [at 0710]. Tourists that had camped in the crater said that eruptions began at midnight (and that there were no eruptions the previous days). Lava kept flowing until about [0846]; we left the crater at [1300] that day."

Photos that Kees made indicated that lava was flowing from about halfway up the side of T48B and across the crater floor toward the W, but that it was not a particularly large eruption. Earlier, probably on 11 September, a small amount of lava flowed down the N flank of T49B and a short distance across the crater floor. Other photos indicated (by comparing specific lava flows on the crater floor with the same lava flows in 7 August photos) a high probability that there were no lava flows at all between 9 August and 11 September. On 19 September Burra Gadiye reported to Roger Mitchell that he had seen no activity that day.

Anatoly Zaytsev climbed on 30 September and reported that they did not see eruptive activity during their visit (between 1100 and 1500). They did see some natrocarbonatite lavas with estimated ages of 2-3 weeks. These were probably the flows from 13 September described above.

Following a visit during 1-3 October, Jaco de Borst reported the following. "During the first of October there was also no activity, only 'smoke' from several cones and cracks. On the second of October there were several 'small' eruptions. In daylight and at night, the cone that was erupting was the biggest and close to the overflow where the trail reaches the crater. Lava only reached the foot of the cone [Belton noted that he was describing T49B]. We left in the morning of 3 October, I think at about 1000. When we left there was no activity... [other] than some noise and 'smoke.' The night eruptions we saw... I think [occurred] about 5 o'clock in the morning [on 3 October]."

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

Information Contacts: Christoph Weber, Volcano Expeditions International, Muehlweg 11, 74199 Untergruppenbach, Germany (URL: http://www.v-e-i.de/); Celia Nyamweru, Department of Anthropology, St. Lawrence University, Canton, NY 13617, USA (URL: http://blogs.stlawu.edu/lengai/); Frederick Belton, Developmental Studies Department, PO Box 16, Middle Tennessee State University, Murfreesboro, TN 37132, USA (URL: http://oldoinyolengai.pbworks.com/); Bernard Donth, Waldwiese 5, 66123 Saarbruecken, Germany.

Our last report (BGVN 30:09) described the first five days of this eruption, and was taken largely from a valuable joint report of Ecuador's Instituto Geofísico and Parque Nacional Galápagos. Here we report information from several sources on these topics: (a) initial observations of the eruption, (b) caldera-floor deformation prior to the eruption, (c) observations of the eruption's progress during 26 to 30 October (when it ended), and (d) satellite infrared observations of thermal fluxes associated with the eruption.

Eruption's start and subsequent plumes. As noted previously (BGVN 30:09), the eruption began around 1730 on 22 October 2005, when an explosion was heard by many residents of the volcano's S flank. Satellite images showed no activity at 1715, but revealed a large eruption at 1745 local time (2345 UTC). The eruption cloud reached an estimated altitude of at least 15 km (50,000 ft) and was moving SW.

At about this time, passengers and crew on Lindblad Expeditions' 80 passenger vessel M/N Polaris had an excellent view of the eruptive plume (figure 5). Lucho Verdesoto, the expedition leader, reported that the ship was then at Cerro Dragon, Santa Cruz island. Sunset was at 1753. As night fell they sailed to a position ~ 18 km NE of the volcano, where they had clear views of flows descending the volcano's upper NE flank (figure 6).

Figure 5. Early photo of the Sierra Negra plume from the cruise ship Polaris, anchored off NW Santa Cruz island around sunset on 22 October 2005. Courtesy of Lucho Verdesoto.

Figure 6. Lava spews skyward from circumferential fissure vents near the N rim of Sierra Negra caldera as flows descend the upper N flank. The photos were taken on 22 October, during the first few hours of the eruption, from the Polaris. Courtesy of Lucho Verdesoto.

Naturalist Carman Guzman wrote, "After sunset the show was fascinating so we decided to move the Polaris to a much closer location. After dinner, we were only eleven miles from the eruption itself. What a thrill! The darkness of the night enhanced the beauty of the fiery reds and oranges that were seen at the top of the caldera. We spent several hours enjoying this rare and fantastic event. Rivers of lava were running down the slopes of the volcano and enormous flames were lighting up the sky."

According to NASA MODIS imagery and VAAC/NOAA reports, on 25 October 2005 a large plume of gases and steam was observed in GOES 12 imagery for 1545 local time (2145 UTC). The plume extended ~ 460 km W and SW of the summit at an altitude of ~ 4.6 km. Figure 7 shows the average concentration of SO₂ over the Sierra Negra plume as imaged by NASA's Aura satellite for the period 23 October-1 November.

Figure 7. The average concentration of sulfur dioxide (SO2) over Sierra Negra from 23 October-1 November measured by the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite. In agreement with reports from the ground, OMI stopped seeing measurable sulfur dioxide coming from the volcano on 31 October. The column abundances of SO2 appear on the associated key (in Dobson Units, DU, a product of concentration and pathlength that reflects the number of SO2 molecules in a unit area of the atmospheric column). Courtesy of NASA Earth Observatory/Natural Hazards website.

Deformation monitoring. In the early stages of this eruption, Bill Chadwick (NOAA) submitted a report on pre-eruption deformation (figure 8). The plot shows both Synthetic Aperture Radar (InSAR) and GPS data on vertical deformation of the caldera floor. Chadwick wrote that he, Dennis Geist (University of Idaho), and Dan Johnson (University of Puget Sound, recently deceased) installed a 27 station GPS network at Sierra Negra in 2000, that was reoccupied in 2001 and 2002 (Geist and others, in press). With help from UNAVCO (a consortium supporting high-precision deformation measurements), the group then added a 6-station, continuous GPS network in 2002. Since then, there occurred a change from caldera subsidence to caldera uplift in March 2003. During this uplift, an M 4.6 earthquake on 16 April 2005 marked trapdoor faulting. The continuous GPS network measured a surface displacement of 85 cm within 10 seconds. Both this event and the previous case of trapdoor faulting in 1997-8-documented by satellite measurements using Interferometric Synthetic Aperture Radar (InSAR) (Amelung and others, 2000)-were preceded by over a meter of inflation (Jónsson and others, 2005). Both the 1997-98 and 2005 trapdoor movements occurred along the caldera floor's S side.

Figure 8. Recent history of uplift at the center of Sierra Negra's caldera. The data plotted are only through April 2005 when the trapdoor faulting event occurred. Although not plotted, GPS data since April has continued to indicate robust deformation. Courtesy Bill Chadwick, NOAA.

Aside from its immediate affects, the April 2005 earthquake left the later inflation rate unchanged. Caldera-centered uplift has continued since then without pause at about the same high rate. During the interval from March 2002 to April 2005 there was about ~ 1.2 m of uplift. Rates after the April 2005 earthquake are not plotted but were roughly the same as those during the interval March 2002-April 2005. The only other large earthquakes at Sierra Negra in the last year were an M 4.0 on 23 February 2005, which was associated with a small (2 cm) displacement near the trapdoor fault, an M 4.6 on 19 September 2005 that caused no obvious displacements, and an M 5.5, just 3 hours before the 22 October eruption started. The GPS data has not yet been processed.

Field descriptions of the eruption. The eruption began on 22 October with venting along a 2-km fissure near the caldera's N rim (figure 6). The fissure descended the caldera's inner wall at its E end. Flows were fed both northward down the outer N flank and southward onto the NE caldera floor. Although flows reached 5 km down the outer flank, flow into the caldera soon dominated, with strong channels descending inner caldera slopes before combining to form a wide aa flow banked against the caldera's E wall and moving steadily southward (see figures and discussion, BGVN 30:09).

Figure 9 is a photo taken by Greg Estes on 24 October. It highlights the vigorous venting and intracaldera flows at that point in the eruption. Figure 10, a post-eruption satellite photo, illustrates the broad pattern of still-cooling, erupted lavas (which appear as light colored areas on this 2 November thermal-infrared image). Although this may represent the best overview of the new lavas at this time, some of the thinnest flows or chilled flow features may not appear on this image.

Figure 9. The Sierra Negra eruption setting as viewed from the E caldera rim. The fissure vent was vigorously emitting fountains, and there were several anastomosing lava flows pouring into the caldera. Photo was taken at night on 24 October 2005, day 3 of the eruption. The scattered glow in the foreground was due to ponded lava covering the caldera's E floor. Courtesy of Greg Estes (Galápagos resident and Park Guide).

Figure 10. The Sierra Negra eruption setting as viewed from space in a false color ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) infrared image taken at night on 2 November, ~ 3 days after the eruption ended. N is towards the top. Caldera is 7 x 10.5 km across. Note the extra-caldera, N-flank lava flows, the lunate zone of ponded lavas along the E caldera. NASA image created by Jesse Allen, Earth Observatory, using data provided courtesy of Eric Fielding (NASA/JPL), the NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team.

By 26 October, fissure activity had narrowed to one major vent very near the N rim, but at 0830 on the 27th, eyewitness Godfrey Merlin reported that a second vent opened downslope and SE of the first. This new vent did not diminish the activity of the first, meaning that the total flux of erupting lava nearly doubled.

By about 1400 on the 27th, a team including Dennis Geist (University of Idaho), Terry Naumann (University of Alaska), and Karen Harpp (Colgate University) had arrived at the E caldera rim and began sending back a series of valuable reports. Their first report noted a major vent immediately below GPS station SN12 on the rim NE of the caldera's center. This vent emitted a large intracaldera aa flow.

Some active N-flank vents stood about 300-400 m NW of a station (GV01) on the caldera's N rim . There, two major vents fed lava fountains up to 50 m high. Most lava being erupted was flowing into the caldera, although some of the scoria from the fountains was falling outside the caldera and then forming a short, sluggish flow. Lava inside the caldera was cascading from the vents down the slope on the N edge of the caldera in 3 main channels, each 30-40 m across, with lava flowing at ~10 m/s (36 km/h) and in some cases over 10 m/s, and coalescing into a major aa flow to the S. On the caldera floor these channels merged into one big aa channel about 100 m wide that flowed more slowly both to the S, clockwise along the base of the E caldera wall, and into the moat along the S edge of the caldera floor. Pahoehoe outbreaks occurred along the margins of the major aa flow. New aa lava covered an estimated one-third of the caldera floor.

The report for 28 October noted that the eruption was still going strong. There were no significant new events on this day, but it appeared that the lava flux had increased because the vents looked wider and there seemed to be a lot more gas emitted. The lava continued to feed from the vents to the caldera floor in two large streams, each ~ 20 m across with lava traveling at 5-10 m/s, adding up to probably hundreds of millions of cubic meters of lava per day. The aa field continued to grow. The group reached the caldera floor and were able to sample both lava and tephra.

By 0700 on the 29th some of the vents had shut down and the two lava channels to the W (previously fed by the upper vent) stopped moving. The lower vent still emitted lava and fed one channel E of the others. The team estimated the channel to be ~10 m wide and moving ~5 m/s. Assuming a 2-m depth, the lava flux was 5 to 10 million cubic meters per day, about half that seen the morning of the 29th.

The emission rate continued to diminish throughout the 29th and by the evening it was only 10-20% of that seen on the 28th. In addition, the amount of gases emitted decreased such that the gas plume only rose ~1 km, whereas earlier plumes had risen to several kilometers. The lower vent was no longer fountaining continuously as it had on the 28th; instead the fountaining came in bursts at intervals of about 1-30 seconds. A lava lake sloshed around in the lower vent's crater; some lava escaped this crater along a breach in the crater rim. The upper vent (the one that shut off) was still incandescent with a lot of gas coming out, so it was possible that there was a lava lake there too.

The eruption appeared to end on the 30th. Glow was observed at 0200, but had ceased by 0400. The vents still emitted gas, but not fresh lava. However, it was possible that there was still N-flank activity. There were reports of lava flows there, and while it was certain that at least some of these flows were clastogenic (composed of spatter from fire fountains that accumulated and then began to flow), it was uncertain whether there were also actively erupting flank vents. The team remained separated from this area by hot lava, thwarting reconnaissance. Initial estimates of the coverage of the caldera floor were an area of ~14 km². Assuming a 3-4 m average flow thickness, this was ~0.05 km³ (50,000,000 m³) of lava. There were obviously high error bars on this estimate, but it was clearly much less than the ~1 km³ extruded in the 1979 eruption.

MODVOLC Thermal Alerts. A large set of thermal hotspots in multispectral imagery was observed beginning late 22 October (local time and date) and continuing through 16 November 2005 (figure 11). Although MODVOLC data were missing for some days and reduced for others (presumably due to cloud cover screening the radiation from the satellite) these hot-spot pixels dramatically document the course of the eruption. Data on figure 11 appear consistent with in situ observations, in that by the second day, lava was at least 5 km down the outer N slope and covering much of the E caldera floor. By the 8th day (30 October), the outer slope flows had cooled significantly, but flows inside the caldera had continued their clockwise advance, filling all low points to the extreme SW corner of the caldera. Ten days later (9 November), the eruption had ended and only flows from the vents to the SE caldera floor were still emitting detectable heat. The last pixels observed, two above the original vent area on the N rim, were on 16 November.

Figure 11. Selected images of MODVOLC thermal anomalies for Sierra Negra measured from satellite (MODIS) data at three days during and after the 2005 eruption. Part A presents an overview of the region (smaller scale than the other images) on 24 October. Parts B-D give a zoom-in on the 7 x 10.5 km caldera. Part B represents 24 October; Part C, 30 October; and part D, 9 November 2005. Since the eruption ended 30 October, the latter two images must thus portray the post-eruptive thermal inertial of the cooling lavas. Courtesy of Hawai`i Institute of Geophysics and Planetology, University of Hawai`i.

References. Amelung, F., Jónsson, S., Zebker, H., and Segall, P., 2000, Widespread uplift and 'trapdoor' faulting on Galápagos volcanoes observed with radar interferometry: Nature, v. 407, p. 993-996.

Geist, D.J., Chadwick, W.W., Jr., and Johnson, D.J., in press, Results from new GPS monitoring networks at Fernandina and Sierra Negra volcanoes, Galápagos, 2000-2002: Journal of Volcanology and Geothermal Research (in press).

Jónsson, S., H. Zebker, and F. Amelung, 2005, On trapdoor faulting at Sierra Negra volcano, Galápagos; Journal of Volcanology and Geothermal Research, v. 144, p. 59-71.

Geologic Background. The broad shield volcano of Sierra Negra at the southern end of Isabela Island contains a shallow 7 x 10.5 km caldera that is the largest in the Galápagos Islands. Flank vents abound, including cinder cones and spatter cones concentrated along an ENE-trending rift system and tuff cones along the coast and forming offshore islands. Although it is the largest of the five major Isabela volcanoes, it has the flattest slopes, averaging less than 5° and diminishing to 2° near the coast. A sinuous 14-km-long, N-S-trending ridge occupies the west part of the caldera floor, which lies only about 100 m below its rim. The Volcán de Azufre fumarolic area lies within a graben between this ridge and the west caldera wall. Lava flows from a major eruption in 1979 extend all the way to the north coast from circumferential fissure vents on the upper northern flank.

Information Contacts: Lucho Verdesoto and Carman Guzman, M/NPolaris, Galápagos Islands, Ecuador; Francisco Dousdebes, Galápagos Expedition Manager, Metropolitan Touring, Ecuador; Lindblad Expeditions (URL: http://www.expeditions.com/); U.S. National Aeronautical and Space Administration (NASA) (URL: http://earthobservatory.nasa.gov/); Bill Chadwick, Cooperative Institute for Marine Resources Studies (CIMRS), National Oceanic and Atmospheric Agency (NOAA) Pacific Marine Environmental Laboratory (PMEL), Oregon State University, 2115 SE OSU Drive, Newport, OR 97365, USA; Dennis Geist, Department of Geological Sciences, University of Idaho, Moscow, ID 83844-3022 USA; Terry Naumann, Department of Geology, University of Alaska at Anchorage, Anchorage, AK 99598, USA (URL: https://www.uaa.alaska.edu/academics/college-of-arts-and-sciences/departments/geology/); Karen Harpp, Department of Geology, Colgate University, 408 Lathrop Hall, Hamilton, NY 13346, USA (URL: http://www.colgate.edu/facultysearch/FacultyDirectory/karen-harpp); MODVOLC Alerts Team, Hawaii Institute of Geophysics and Planetology (HIGP), University of Hawaii at Manoa, 1680 East-West Road, Post 602, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

In a recent publication, Rubin and van der Zander (2005) discuss radiometric methods for dating lavas as one means to establish eruption chronologies. Some of their techniques were applied to samples of fresh lava (erupted September-October 2003) found on the East Pacific Rise (EPR) at 10°44'N (Voight and others, 2004). This location lies ~ 1,900 km WNW of the Galápagos Islands. During a November 2003 biological sampling visit to the EPR at 10°44'N, divers in the submersible Alvin expected to be revisiting an established hydrothermal vent field. Instead, they found indicia all of which were consistent with a recent eruption, notably fresh lava, bacterial mats, and diffuse snow- blower vents issuing from lava collapses. The team acted immediately after the cruise by sending the lava samples to the University of Hawai`I for dating. Researchers there determined that an eruption had occurred within 1 to 2 months prior to the site visit. A hydrophone array (designated N-EPR) nominally monitored this part of the EPR since 1996, but not in real time. Unfortunately, the system failed to record data during the 2002-2004 interval due to a hardware problem.

Ages for lavas erupted within the past 1.5-2 years were determined with the ²¹⁰Po-²¹⁰Pb dating method (Rubin and others, 1994). To use this method, analyses should begin as soon as possible after samples are collected from suspected eruption locales. Radioactive disequilibrium is largest, and temporal resolution of the method is highest, immediately following eruption. According to Rubin and van der Zander (2005, p. 28) "Polonium is volatile at magmatic temperatures and degasses from magmas when they erupt. This creates an initial ²¹⁰Po (half-life = 138.4 day) deficit relative to grand parental ²¹⁰Pb in freshly erupted magmas. This deficit is subsequently erased with time via radioactive ingrowth toward secular equilibrium."

References. Rubin, K.H., Macdougall, J.D., and Perfit, M.R., 1994, ²¹⁰Po-²¹⁰Pb dating of recent volcanic eruptions on the seafloor: Nature, v. 368, p. 841-844.

Rubin, K., and van der Zander, I., 2005, Obtaining high-resolution chronologies of submarine lava eruptions: Better dating through radiochemistry: Ridge 2000 Events, v. 3 (Spring 2005), p. 28-30.

Voight, J. R., Zierenberg, R.A., McClain, J., and the Science Party: Batson, P., Beers, K., Daly, M., Dushman, B., Gollner, S., Govenar, B., Haney, T.A., Hourdez, S., Liow, L.H., Parker, C., Von Damm, K., Zekley, J., and Zelnio, K.A., 2004, FIELD cruise to the northern EPR: Discoveries made during biological investigations from 8°37'N to 12°48'N: Ridge 2000 Events, v. 2(1), p. 22-24.

Geologic Background. Divers in the submersible Alvin discovered an extremely fresh lava flow in an unexpected location at 10°44'N on the East Pacific Rise during an expedition in November 2003. The young flow was covered by bacterial mats, had large amounts of bacterial floc ("snow-blowers") issuing from diffuse vents, and was sparsely populated by small animals. Uranium-series dating indicated that the eruption had taken place within a time window only a few months to weeks prior to the observations. This segment of the East Pacific Rise, located just north of the Clipperton Transform Fault, is an area with an estimated low magma production rate.

Information Contacts: Ken Rubin, Department of Geology and Geophysics, SOEST, University of Hawai`I, 1680 East West Road, Honolulu, HI 96822, USA.

Frequent steam plumes through 2002 and 2003 indicated that Pacaya was active, although incandescence from the long-term lava lake ended after June 2001. During the latter half of October 2003 constant steam and abundant emissions of water and gas were being blown to the NNW and W of the volcano (BGVN 28:10). All of the following information is derived from the reports of Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH).

Throughout November and December 2003 and the first half of 2004, abundant clouds and columns of white and off-white gases and steam were expelled from Pacaya, generally reaching less than 400 m above the volcano and dispersing mostly to the W and SW; these were occasionally visible from Guatemala City, 30 km to the NNE.

During June, July, and August 2004, near-continuous tremor and frequent long-period earthquakes were recorded at seismograph station PCG (~ 1.4 km to the W of Pacaya). On 14 June, weak incandescence was observed in the central crater of MacKenney Cone for the first time since August 2000. Pacaya continued to expel off-white smoke and/or steam which usually drifted to the S and SW and rose to 150-300 m above the volcano. On 19 July, ejection of small lava fragments began to form a cone in the bottom of the central crater of MacKenney Cone.

During September-November 2004, tremor increased somewhat (from ~ 2mm in June, July, and September to 4-7 mm in December), and white steam and/or gas plumes rose 300-500 m above MacKenney Cone. Incandescence was observed throughout this time and lava clasts were expelled from the MacKenney Cone on 7-9 December.

On 3 January 2005, small expulsions of incandescent lava clasts rose from the central crater, and a narrow lava flow from the S rim of the crater reached 75-100 m down the flank. Station PCG continued to register tremor, and incandescence and white plumes persisted. On 10 January, lava flowed ~ 30 m from the SW rim of the central crater of MacKenney Cone. On 12 January, two lava flows, one to the S ( ~ 125 m) and one to the SW (~ 50 m) left the central crater. Observers saw incandescent lava fragments rising <10 m above the mouth of the intra-crater cone, and "smoke" whiffs rising from the MacKenney Cone. During the last 5 days of January 2005, numerous small lava flows descended the S and SW flanks of the volcano.

During February, March, and April 2005, incandescence, tremor, and minor lava flows continued. On 2 February observers reported that avalanches from the lava flow fronts during the previous days formed a debris fan covering about 2/3 of the SW flank. On 28 February expulsion of incandescent lava fragments reached heights of 10-50 m for brief periods. On 1 March INSIVUMEH recommended that park officials prevent tourists from climbing Pacaya because of avalanches, lava expulsion, and gas emissions. In March and April explosions of lava reached 100 m in height, and smoke/gas emissions continued.

Lava emission continued during May. On 4 May, three flows were active, extending up to 100 m down the SW flank and 150 m W in the direction of Cerro Chino. On 9 May two active flows from the base of the intracrater cone reached 200 m down the W flank. Plumes from the MacKenney Cone rose as high as 800 m above the crater. Ejection of incandescent material continued throughout the month. Lava flows moving to the SW and W in the direction of Cerro Chino reached lengths of 150-250 m.

During early June, incandescent lava clasts were ejected as high as ~ 75 m above Pacaya's crater. An intra-crater lava flow extended ~ 300 m from the SW base of the central cone. On 6 June, a lava flow traveled ~ 200 m down the volcano's W flank. By 27 June a lava flow extended ~ 300 m down the SW flank. A white steam column rose ~ 150 m over the central crater and drifted SW. Incandescent lava expulsions reached heights of 15-50 m. On the night of 27 June two rivers of lava, 75 and 150 m long, were observed in front of Cerro Chino. Constant expulsions of pyroclastic material rose 20-30 m above the crater.

Lava flows in July traveled 200-300 m down the SW flank. Small plumes emitted from the volcano's central crater rose to low altitudes. Avalanches of incandescent volcanic blocks produced small ash clouds to low levels.

During 7-11 September, occasional Strombolian activity occurred. Volcanic bombs from two craters rose up to 30 m above their rims. Incandescence from lava flows on the SE flank was visible on several nights.

Geologic Background. Eruptions from Pacaya are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the older Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1,500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate scarp inside which the modern Pacaya volcano (Mackenney cone) grew. The NW-flank Cerro Chino crater was last active in the 19th century. During the past several decades, activity has consisted of frequent Strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and covered the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit.

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); 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/).

Prior to the period covered by this report, recent activity at Santa María was characterized by weak-to-moderate explosions producing ash, crater-rim collapses and avalanches of block lava and ash, pyroclastic flows, and an active lava flow (BGVN 28:10). Activity was similar from October 2003 to June 2004, consisting mostly of explosions from Santiaguito, a lava-dome complex that includes the Caliente vent. The explosions produced ash plumes, and there were numerous block-lava-and-ash avalanches from Caliente collapses (BGVN 29:06). From July 2004 until October 2005, these types of activity continued.

Activity during July-September 2004. During July to September 2004, weak-to-moderate explosions at Santiaguito produced plumes to a maximum height of ~ 1.5 km above the volcano. Frequent avalanches of volcanic material including blocks and ash traveled SE and SW down Caliente cone. In early September 2004, several weak-to-moderate explosions produced ash clouds to a maximum height of 2 km above the volcano. Partial collapses of the lava dome caused pyroclastic flows to travel down the volcano's NE and SW flanks. On 27 September, several avalanches of volcanic material from active lava-flow fronts traveled SW.

Activity during October 2004. During October 2004 moderate explosions produced ash-and-gas plumes that rose to a maximum altitude of 9 km. Explosions on 4 October produced small pyroclastic flows to the SW. On 11 October, a partial lava-dome collapse to the SW produced a pyroclastic flow that traveled toward the Nimá Segundo River. An ash cloud formed that rose to a height of ~ 500 m and covered most of the dome complex. The collapse was preceded by an explosion that produced an ash-and-gas cloud to ~ 1.5 km above the volcano. Small explosions on 12 October produced small lava-dome collapses to the SW that generated avalanches of lava blocks and ash.

Small lahars traveled down San Isidro ravine on 14 and 15 October. A small collapse of the SW edge of the lava dome in the Caliente crater produced a pyroclastic flow on 17 October. The flow traveled down the S flank and produced a steam-and-ash plume to a height of ~ 800 m upon contact with dammed water. Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH) reported that this collapse, like those that occurred on previous days and weeks, was associated with a new cycle of magmatic injection. The Washington VAAC reported that hot spots and plumes possibly containing ash were occasionally visible on satellite imagery on 21 October; imagery on 31 October showed a possible ash-bearing plume at ~ 4.5 km altitude.

Activity during November 2004. During November, weak-to-moderate explosions produced gas-and-ash plumes to ~ 1 km above the volcano. Many explosions were accompanied by block-and-ash avalanches from the NE and SW edges of Caliente dome. The Washington VAAC reported that satellite imagery on 3 November showed a possible ash-bearing plume at a height of ~ 5 km altitude. On 12 November, the collapse of a small sector of the SW edge of the Caliente dome produced a pyroclastic flow. On 14 November at 2012, a tectonic earthquake caused a lava-flow collapse SW of the Caliente dome, triggering a pyroclastic flow that descended to the head of San Isidro ravine, an area of abundant accumulation of pyroclastic material and a known area for lahar initiation. During December, weak-to-moderate explosions produced plumes to a maximum height of 1.3 km above the crater. Frequent block-lava avalanches traveled down the SW flank of Caliente dome. A moderate explosion on 4 December caused a partial lava-dome collapse and a pyroclastic flow that traveled SW. On 22 December small collapses occurred from lava-flow fronts on the SW side of Caliente dome. According to the Washington VAAC, ash plumes were visible on satellite imagery on several days during 22-27 December.

Activity during January-October 2005.During January 2005, frequent explosions (table 2) produced columns of gray and white ash up to 2 km in height, ash fall in towns near the volcano and frequent blocky avalanches. Early in the month, avalanches of incandescent blocks were released from lava flow fronts towards the NE and SE flanks of Santiaguito.

Table 2. Explosions recorded at the Santiaguito cone of Santa María in January 2005. Missing dates were not reported. Courtesy of INSIVUMEH.

During February 2005, frequent explosions and avalanches continued. On 10 February 2005 the Washington VAAC reported that satellite imagery showed a plume of ash and steam moving SW from the summit and ash extending 55 km after an eruption around 0645. A continuous plume of ash and steam was emitted after an eruption around 0745 and ash extended around 230 km from the summit moving at 2-50 km/hour.

During March 2005, several weak-to-moderate explosions produced ash plumes to a maximum height of ~ 1.3 km above the dome. Avalanches of volcanic blocks traveled down the E and SW flanks of Caliente dome. On 16 March, small amounts of fine ash fell in Xepax, Xecavioc, Llanos de Pinal, Las Majadas, and Quetzaltenango. During 19-20 March, ash fell to the E in the town of Zunil.

During 21-25 April several explosions at Santiaguito produced ash plumes that rose to ~ 1.2 km above the dome. Lava avalanches occurred down the SW flank of Caliente dome. Explosions on 25 April produced pyroclastic flows that traveled S down Caliente.

Continuing explosive activity from Santiaguito during 4-9 May sent ash columns as high as 1.3 km above the vent. Small collapses at the Caliente dome generated pyroclastic flows 500-3,000 m long. Constant avalanches were reported on 10 May from the lava-flow front and the Caliente dome, along with one small ash explosion. Minor explosions on 13 May sent gray ash plumes 400-600 m high. Avalanches from the SW-flank lava flow continued. Explosions during 17-20 May produced ash clouds to ~ 1 km above the volcano; ash fell 7-10 km from Caliente dome.

During the first week of June 2005, moderate explosions produced plumes that rose to ~ 1.2 km above the volcano. On 2 June, the partial collapse of the lava dome in the crater of Caliente dome generated a pyroclastic flow that traveled ~ 4 km SW. On 22-24 June explosion columns reached ~ 900 m above the crater and extended several kilometers to the SSW and W. On 27 June, in the region of Palajunoj on the SW flank, constant avalanches of lava blocks were observed. During 6-18 July, weak-to-moderate explosions continued , with plumes rising to ~ 1.3 km above the volcano. Throughout July avalanches of volcanic material were produced at the front of an active lava flow, and from the SW edge of Caliente dome.

August and early September reports were unavailable, but during 7-11 September, small-to-moderate explosions at Santiaguito produced plumes that rose to a maximum height of ~ 1.5 km above the volcano on 8 September. On 7 September, a moderate lahar traveled down the volcano's flank. About a dozen pyroclastic flows, and avalanches of volcanic material occurred from the SW edge of the lava dome, and from the front of lava deposits on the SW flank of Caliente dome.

On 26 October 2005 a small eruption produced an ash plume that drifted SW to the Pacific and was recorded on MODIS satellite imagery (figure 33). The Washington VAAC reported a hot spot that lasted for about 6 hours with an estimated plume height of 4.5 km. On 28 October a plume rose to an altitude of ~ 4.9 km.

Figure 33. MODIS (Moderate Resolution Imaging Spectroradiometer) image showing a Santa María eruption plume on 26 October 2005. The volcano's summit is identifiable by a small red outline indicating an area hotter than its surroundings. Wafting away from the summit is a thin, faint ash plume that heads SW toward the Pacific. NASA image courtesy the MODIS Rapid Response Team at NASA GSFC.

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

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); 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/); NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/).