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/).

In 1979-1980, an eruption at Chirinkotan included a series of ash explosions and a lava flow (SEAN 05:06). In October and November 1986, airborne observers saw a column of thick gas and ash, and then fumarolic activity (SEAN 12:04). This report discusses events during 2013 through April 2014. The location of Chirinkotan in the Kuril Islands is shown in figure 1.

Figure 1. Map showing location of Chirinkotan. Courtesy of Google Earth.

According to the Sakhalin Volcanic Eruption Response Team (SVERT), gas-and-steam emissions occurred frequently in 2013-2014 (table 1). The Aviation Color Code was Green on 24-25 May 2013, when emissions were first reported, but raised to Yellow during early June 2013, where it has remained through April 2014, the end of this report. The volcano was often obscured by clouds.

According to the U.S. Geological Survey, an M 8.3 earthquake occurred on 24 May 2013 beneath the Sea of Okhotsk, at a point is 656 km N of the volcano. The focal depth of the earthquake was ~ 600 km. The first reported gas-and-steam emission from Chirinkotan, which is in the Sea of Okhotsk, was on 24-25 May, suggesting a possible link between the two events.

Table 1. SVERT-reported dates on which gas-and-steam emissions were observed from 24 May 2013 through 30 April 2014, based on analysis of satellite images. Thermal alerts detected by SVERT and the MODVOLC satellite thermal alert system are also noted.

Geologic Background. The small, mostly unvegetated 3-km-wide island of Chirinkotan occupies the far end of an E-W volcanic chain that extends nearly 50 km W of the central part of the main Kuril Islands arc. It is the emergent summit of a volcano that rises 3000 m from the floor of the Kuril Basin. A small 1-km-wide caldera about 300-400 m deep is open to the SW. Lava flows from a cone within the breached crater reached the shore of the island. Historical eruptions have been recorded since the 18th century. Lava flows were observed by the English fur trader Captain Snow in the 1880s.

Information Contacts: Sakhalin Volcanic Eruption Response Team (SVERT) (URL in English: http://www.imgg.ru/?id_d=659); 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/); and Earthquake Hazards Program, US Geological Survey (URL: http://earthquake.usgs.gov/).

On 6 November 1986, weak fumarolic activity was observed during an aerial survey (SEAN 12:04). The Sakhalin Volcanic Eruption Response Team (SVERT) noted that emissions were again observed in November 2012. This report covers steam-and-gas plumes and emissions and thermal alerts between 20 November 2012 and 30 April 2014.

SVERT's monitoring of Chirpoi is hampered by the lack of surface instruments or seismic network. The volcano is primarily monitored by satellites; cloud cover, however, often prevents space-borne observations. The location of Chirpoi in the Kuril Islands is shown in figure 1.

Figure 1. Map showing location of Chirpoi. Courtesy of Google Earth.

SVERT reported thermal anomalies at a volcano of Chirpoi called Snow, starting on 17 November 2012. Periods of steam-and-gas began on 15 December 2012. This activity continued through at least April 2014, based upon analysis of satellite images (table 1). Cloud cover often obscured views of the volcano.

Table 1. Steam-and-gas plumes and emissions from Snow, a Chirpoi volcano, between 21 November 2012 and 30 April 2014, based on analysis of satellite images. Cloud cover frequently prevented observations. Courtesy of SVERT.

A search of MODVOLC thermal alerts at Chirpoi since 1980 found no such alerts until a they began at Snow on 11 November 2012. Between that date and 24 December 2012, many thermal alerts were reported. According to SVERT, this may have indicated a lava flow on the SE flank. No further alerts were reported until 8 July 2013; between 8 July and October 2013, thermal alerts were issued on six days. The only alerts between November 2013 and 30 April 2014 were on 10 March, 27-28 March, and 14, 16, 18, 21, 27, 29-30 April 2014.

Based on SVERT weekly reports on 12 and 19 November 2012, the Aviation Color Code increased from Green to Yellow between 5 and 19 November 2012, and remained Yellow through at least April 2014. (Green indicates a normal, non-eruptive state; Yellow indicates elevated unrest above background level.)

Geologic Background. Chirpoi, a small island lying between the larger islands of Simushir and Urup, contains a half dozen volcanic edifices constructed within an 8-9 km wide, partially submerged caldera. The southern rim of the caldera is exposed on nearby Brat Chirpoev Island. The symmetrical Cherny volcano, which forms the central cone of the island, erupted twice during the 18th and 19th centuries. The youngest volcano, Snow, originated between 1770 and 1810. It is composed almost entirely of lava flows, many of which have reached the sea on the southern coast. No recorded eruptions are known from Brat Chirpoev, but its youthful morphology suggests recent Strombolian activity.

Information Contacts: Sakhalin Volcanic Eruption Response Team (SVERT) (URL in English: http://www.imgg.ru/?id_d=659); and 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/).

[Following 18-months of calm at Volcán de Colima (BGVN 38:04), a sequence of intermediate-to-small size Vulcanian explosions began in January 2013.] This sequence of explosions excavated a 250,000 m³ crater in the 2007-2011 lava dome (figure 105). Episodes of effusive activity within the new crater were recorded between the explosive events. An infrared image shows fresh magma at the crater base (figure 106).

Figure 105. The new crater at Colima that was formed during the January 2013 explosive sequence. Photo was taken on 31 January 2013 during a flight of Civil Protection of Jalisco State. Courtesy of Colima Volcano Observatory.

Figure 106. Thermal image taken during a flight over Colima on 11 January showing the emergence of fresh high temperature lava. Courtesy of Facultad de Ciencias, University of Colima.

Activity during 2013. [There were three stages of activity at Colima during 2013, defined based on data from seismic and video monitoring (figure 107).] The first stage (St. 1) refers to the sequence of explosions described in (BGVN 38:04). On 15 February and the end of March (St. 2), video observations indicated continued gradual lava dome growth in the new crater. The dome increased in height at the rate of ~1 m/day. As a result, during this interval the [summit elevation] increased from 3,843 to 3,874 m. The dome continued to fill the crater through the end of March (figure 108). During April-November 2013 the third stage (St. 3) of significant dome growth stopped. The February-March lava dome growth was accompanied by an increase in the frequency and energy of the small explosions. Once the dome filled the crater a small lava flow traveled toward the W. Due to the steepness of this flank, much of the fresh material descended as rockfalls, whose frequency increased from April.

Figure 107. Plots A-C describe the development of the 2013 eruption at VolcÁn de Colima., showing three stages of development: Stage One (St. 1), involving explosions; Stage Two (St. 2), involving dome growth and extra-crater lava flow; and Stage Three (St. 3), involving lack of measurable dome growth but with ongoing explosions. (A) Daily variations in the number of small explosions and rockfalls identified from a seismometer 4 km from the crater. (B) Variations in the radiated seismic energy of explosive events recorded at a distance of 4 km. The four largest explosions of the St.1 are shown with diamonds. (C) Variations in the maximum elevation of the growing lava dome based on continuous video monitoring. Courtesy of Colima Volcano Observatory.

Figure 108. The filled crater and the lava flow that was formed during the second stage of activity on Colima's western slope. Photo was taken on 19 [March] 2013 during a flight of Civil Protection of Jalisco State. Courtesy of Colima Volcano Observatory.

During the third stage, the daily number of small explosions and rockfalls was quite stable. This stage was associated with the occurrence of 14 lahars that began with the rainy season being registered between 11 June and 8 October 2013 descending the flanks of the volcano (figure 109). The largest, lasting around 6 hours, occurred on 16 September 2013, when the Pacific coast was affected by tropical cyclone Manuel.

Figure 109. Block-rich front of the 11 June 2013 lahar recorded along the Montegrande ravine by the lahar monitoring station located 5.8 km S of the crater. Courtesy of Centro de Geociencias, UNAM.

Activity during 2014. On 21 January 2014 the Washington VAAC first reported scattered ash emissions drifting S at 4.9 km altitude followed by a second and third emission that drifted SSW and S, respectively. Smaller ash emissions were noted throughout the following weeks. For example, Washington VAAC reported that on 7 February a small emission rose and drifted E then SE, followed by a later one the same day that drifted SE. From data provided by the Mexico Meteorological Watch Office, on 28 February an ash emission drifted 15 km SE at altitudes up to 4.6 km, and the following day, on 1 March, two emissions were reported drifting NNW, followed by three other plumes later the same day. The Washington VACC continued to report on activity as seen from satellite imaging, noting another emission on 6 March that drifted NE before dissipating and ; an emission on 12 March that drifted 25 km NNE before similarly dissipating; and a 19 March emission, which rose to 4.6 km and drifted E before dissipating 30 km from the source. A separate later plume followed on 22 March and drifted N.

Geologic Background. The Colima complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the high point of the complex) on the north and the historically active Volcán de Colima at the south. A group of late-Pleistocene cinder cones is located on the floor of the Colima graben west and east of the complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide scarp, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, producing thick debris-avalanche deposits on three sides of the complex. Frequent recorded eruptions date back to the 16th century. Occasional major explosive eruptions have destroyed the summit (most recently in 1913) and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.

Information Contacts: Observatorio Vulcanologico de la Universidad de Colima (Colima Volcanological Observatory), Calle Manuel Payno, 209 Colima, Col., 28045 Mexico (URL: http://www.ucol.mex/volc/); Facultad de Ciencias, Universidad de Colima; and Washington Volcanic Ash Advisory Center (VAAC), NOAA Science Center Room 401, 5200 Auth road, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/).

A large eruption occurred at Cerro Hudson on 8 August 1991 (BGVN 16:07-18:02), which was followed by minor non-eruptive activity that caused sulfurous odors, increased river flows and turbidity, and noise at least through early 1995 (BGVN 20:02). This report describes a minor eruption during 25-26 October 2011. Cerro Hudson is located in Patagonia in the Aysén Region of Chile (figure 1).

Figure 8. Map of Chile (a), the Aysén region in red (b), and a detail marking the region's capital, Coyhaique, and Cerro Hudson (c). Original image courtesy of Wikipedia.

According to the Southern Andes Volcanological Observatory-National Geology and Mining Service (OVDAS-SERNAGEOMIN), seismicity increased during 25-26 October 2011. On 25 October, an M 4.6 volcano-tectonic earthquake occurred at a depth of 19 km, followed by a seismic swarm. More than 100 events, with depths ranging from 15 to 25 km, were recorded through the next day; twelve were M 3, and three were M 4. Most of the earthquakes were volcano-tectonic events with magnitudes below 3.6 and located W of the caldera at depths between 3 and 25 km. The earthquake hypocenters became shallower over time. OVDAS-SERNAGEOMIN did not detect any explosive event or episodes of high intensity harmonic tremor (as reported on 28 October).

During a 24-hour period beginning at 1600 on 27 October, an average of one earthquake per hour was recorded. Most were long-period with magnitudes less than 2.2. On 27 October, an M 3.6 VT earthquake occurred on the SW edge of the crater.

On 26 and 27 October, OVDAS-SERNAGEOMIN and local authorities flew over the caldera and observed three new craters along the SSE edge of the caldera, with approximate diameters of 200, 300, and 500 m. Mostly white plumes rose above the two smaller craters. The largest, southern-most crater emitted a plume with more ash that rose more than 5 km above the crater. Satellite imagery showed a plume drifting 12 km SE. The scientists also observed lahars in the Huemules river, to the W. In response, OVDAS-SERNAGEOMIN raised the Alert Level to 5 (Red), the highest level. According to the Oficina Nacional de Emergencia - Ministerio del Interior (ONEMI), 140 people were evacuated from areas within a 45-km radius of the volcano, defined as a high-risk zone. The hazard lay not only with earthquakes and eruption, but also with the possibility of flooding resulting from to glacier melt.

During another overflight on 28 October scientists observed a gas plume with a very low ash content rising 3-4 km above the craters. Seismicity continued to decrease during 28-29 October. Plumes were observed on 29 October (figure 9). Scientists conducting an overflight noted that one ash plume rose 1 km above the craters and drifted 5-8 km NE. They also confirmed that a large lahar descended the volcano and flowed into the drainage system including the Huemules river during the initial phase of the eruption. During another observation flight on 30 October, scientists saw ash plumes rising 0.8 km from two of the three craters.

Figure 9. The three vents at Cerro Hudson observed on 29 October 2011. Dark gray ash can be seen at the base of at least one vent. Courtesy of, and copyrighted by, El Mercurio and SERNAGEOMIN, Chile.

On 31 October, scientists observed gas plumes rising 0.5 km above the craters and drifting SE. Around 31 October, they also noted subsequent minor explosions and ash emissions. On 1 November, scientists observed an explosion and an accompanying ash plume that rose 1.5 km above the active craters.

On 2 November, OVDAS-SERNAGEOMIN reported that the Alert Level for Cerro Hudson had been lowered to 4 (Yellow), noting that the eruption that began on 26 October had ceased. ONEMI reported that the 140 evacuees were permitted to return home. Analysis of ash deposited on the edge of the crater during the eruption indicated the presence of juvenile basalt. During 1-6 November between 16 and 110 earthquakes per day were recorded, and satellite images showed drifting plumes daily.

According to OVDAS-SERNAGEOMIN, satellite imagery and an area web camera showed no plumes during 7-15 November. Seismic activity decreased significantly, reaching no more than four earthquakes per hour.

The NASA Earth Observatory photographed Cerro Hudson on 17 November 2011 (figure 10) and weeks later (figure 11).

Figure 10. Image of Cerro Hudson taken in natural color on 17 November 2011 by the Advanced Land Imager (ALI) on NASA's Earth Observing-1 (EO-1) satellite. The image shows extensive fresh ash on the snowy surface. The apparent vent rests on the image's left-center, at the apex of the darkest funnel-shaped area. Courtesy of NASA Earth Observatory (Image by Jesse Allen; caption by Michon Scott).

Figure 11. This post-eruptive image of Cerro Hudson, taken two weeks after figure 10, shows the volcano covered with snow. The label "apparent vent site" sits directly above the oval shaped vent site, a spot at left located below the gap between the words "apparent" and "vent" (also see previous figure). Courtesy of NASA Earth Observatory.

Geologic Background. The ice-filled, 10-km-wide caldera of Cerro Hudson volcano was not recognized until its first 20th-century eruption in 1971. It is the southernmost volcano in the Chilean Andes, related to subduction of the Nazca plate beneath the South American plate. The massive volcano covers an area of 300 km2. The compound caldera is drained through a breach on its NW rim, which has been the source of mudflows down the Río de Los Huemeles. Two cinder cones occur N of the volcano and others occupy the SW and SE flanks. This volcano has been the source of several major Holocene explosive eruptions. An eruption about 6,700 years ago was one of the largest known in the southern Andes during the Holocene; another eruption about 3,600 years ago also produced more than 10 km3 of tephra. An eruption in 1991 formed a new 800-m-wide crater in the SW portion of the caldera.

Information Contacts: SERNAGEOMIN (Southern Andes Volcanological Observatory-National Geology and Mining Service), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); Oficina Nacional de Emergencia - Ministerio del Interior (ONEMI), Beaucheff 1637 / 1671, Santiago, Chile (URL: http://www.onemi.cl/); and El Mercurio (URL: http://www.elmercurio.cl/).

Our last report on activity at Karthala, located in the Comoros Islands, covered elevated seismicity and a subsequent eruption in January 2007 (BGVN 32:01). The volcano was then quiet until May 2012.

U.S. Embassy Comoros Officer, Michael Zorick informed us that residents on Karthala's W flank, in the villages of Mde and Mkazi (each ~12 km from the summit), reported observing intensified red glow toward the volcano summit during the night of 9-10 May 2012. He further indicated that there was no perceptible seismic activity.

A search for thermal alerts on the MODVOLC website revealed an absence of alerts after those associated with the 2007 eruption.

Geologic Background. The southernmost and largest of the two shield volcanoes forming Grand Comore Island (also known as Ngazidja Island), Karthala contains a 3 x 4 km summit caldera generated by repeated collapse. Elongated rift zones extend to the NNW and SE from the summit of the Hawaiian-style basaltic shield, which has an asymmetrical profile that is steeper to the S. The lower SE rift zone forms the Massif du Badjini, a peninsula at the SE tip of the island. Historical eruptions have modified the morphology of the compound, irregular summit caldera. More than twenty eruptions have been recorded since the 19th century from the summit caldera and vents on the N and S flanks. Many lava flows have reached the sea on both sides of the island. An 1860 lava flow from the summit caldera traveled ~13 km to the NW, reaching the W coast to the N of the capital city of Moroni.

Information Contacts: Michael P. Zorick, Comoros Officer, Embassy of the United States of America, Antananarivo, Madagascar; and 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/).

This is the first Bulletin report for Mauna Kea, the tallest volcano on the Island of Hawai`i (figures 1, 2, and 3). Although the most recent eruption occurred ~4,500 years ago, this volcano has the potential to reawaken. This report presents early observations by Western explorers; discussions from Hawaiian Volcano Observatory (HVO) scientists focusing on the potential for future eruptions; seismicity during 2000-2013; and a recent report by HVO scientists highlighting drastic changes at an alpine lake, Lake Waiau.

Figure 1. Mauna Kea is one of five volcanoes comprising the Island of Hawai`i, the others being Kohala, Hualalai, Mauna Loa, and Kīlauea. The archipelago of Hawai`i includes the eight islands: Ni`ihau, Kaua`i, O`ahu, Moloka`i, Lana`i, Maui, Kaho`olawe, and Hawai`i (from W-to-E). Courtesy of Holt and others (2006) and Google Earth.

Figure 2. This view of Mauna Kea is from the Keaukaha area, the S edge of Hilo Bay. Seasonal snowfall covers the summit area which is also dotted with cinder cones. The highest point, indicated with the arrow, is located at the highest point on the rim of the cinder cone Pu`u Wekiu. The small white points to the right of the arrow are several of the astronomical telescopes belonging to the Mauna Kea Observatories, part of the University of Hawai`i's Institute for Astronomy. Photo by Valerie Veriato Victorine; courtesy of Hawaii News Now.

Figure 3. An aerial view of Mauna Kea's summit and S flank was acquired in 1995 from a NASA C-130 aircraft. The Mauna Kea Access Road reaches the summit after numerous switchbacks that cross through fields of cinder cones (note the gray line above the propeller) on the S flank. This view is approximately centered on the cinder cone Pu`u Kole, which is one of the features remaining from the Holocene Laupahoehoe eruption. A forest reserve boundary encloses the upper flanks of Mauna Kea and appears in this photo as a line that makes a sharp corner as it includes the lower edge of Pu`u Kole. Courtesy of Scott Rowland (University of Hawaii at Manoa).

Eruptive style and activity status. Mauna Kea is presently considered a volcano exhibiting quiescence that has, according to the known geologic record, an extensive history of lapsed activity. Between 6,000 and 4,000 years ago, eruptions occurred at at least seven separate vents. The record indicates that compared with Mauna Loa, which erupted every few years to few tens of years, and Hualalai, which erupted every few hundred years, Mauna Kea has exhibited long breaks in activity (USGS, 2002).

Based on the occurrence of 12 eruptions within a 10,000 year period, Mauna Kea's recurrence interval is ~1,000 years (Geohazards Consultants International, Inc., 2000). According to the Mauna Kea Science Reserve Master Plan released by the Geohazards Consultants International, Inc. in March 2000:

"Mauna Kea's post-glacial eruptions have been episodic rather than periodic, however, with a particular concentration of eruptive activity between 4,400-5,600 years ago. The 1,000 year recurrence interval of the past 10,000 years does not thus indicate that an eruption is 'overdue', but does reinforce the likelihood that eruptions will occur sporadically in the future."

This pattern of activity might also imply that the next eruption of Mauna Kea could be followed by others at much shorter intervals, representing a potential clustering of events in the given time interval (Jim Kauahikaua, personal communication, 30 May 2014).

Mauna Kea's most recent eruption occurred ~4,500 years ago, generating both lava flows and cinder cones. This activity is considered characteristic of a volcanic system that had evolved past the shield-building stage to the post-shield stage (Hoover and Fodor, 1997). The above-stated age determinations were made based on radiocarbon dating of charcoal collected within the Humu`ula soil (Porter, 1971; Wolfe and others, 1997); this soil lies directly beneath the S flank lava flows of Pu`ukole and Pu`u Loa Loa (figure 4).

Figure 4. (Index map) The Island of Hawai`i encompasses five volcanic centers. Note Hilo Bay (HB), the location where the photo in figure 2 was taken. The shaded box shows the area of the main map. (Main Map) Holocene cinder cones and lava flows are located on Mauna Kea's lower S flank, the lower extent of which have been covered by Mauna Loa lava flows. The two sets of isopachs indicate tephra units vented from the cinder cones Pu`ukole and Pu`u Loa Loa. State Highway 200 (the Saddle Road) is indicated in red, located at the lower margin. The point marked as Hale Pohaku is the location of the Visitor Information Station and the Onizuka Center for International Astronomy. Map modified from Porter (1971).

The designations of shield-building and post-shield stages come from a system of structural development that represents the current understanding of Hawaiian volcanism. Significant cinder cone eruptions are a hallmark of the post-shield stage as well as: "(1) the absence of a summit caldera and elongated fissure vents that radiate across its summit; (2) steeper and more irregular topography (for example, the upper flanks of Mauna Kea are twice as steep as those of Mauna Loa; [figure 5]); and (3) different chemical compositions of the lava" (Clague and Dalrymple, 1987; USGS, 2002).

Figure 5.Two profile photos of Mauna Kea (top) and Mauna Loa (bottom). Mauna Kea (top) displays an irregular profile due to the abundance of steep-sided cinder cones formed by hawaiite, a less fluid and more explosive lava composition compared with the tholeiitic basalt that characterizes shield-stage volcanism. Mauna Loa (bottom) exhibits the classic, shield-stage morphology that results due to numerous tholeiitic basalt eruptions (and known to be particularly voluminous). This morphology is relatively smooth and shallow compared with Mauna Kea. USGS photos taken by Taeko Jane Takahashi in 1991 with caption details from Wright and others (1992b).

Gravity model. Investigations by Kauahikaua and others (2000) determined a three-dimensional gravity model for the Island of Hawai`i distinguished the five volcanic centers comprising the island: Kohala, Mauna Kea, Hualalai, Mauna Loa, and Kīlauea (figure 6). The base data for that map came from more than 3,300 gravity measurements made above sea level. Positive gravity anomalies define gravitationally dense zones caused by intrusions and cumulates beneath the summit and known rift zones of each of the five volcanoes composing the island. Figure 6 maps the 3-dimensional structure as modeled from the gravity data and expresses the gravity anomalies in terms of elevation from the overlying ground surface.

Figure 6. The Island of Hawai`i, including Mauna Kea, in a map showing the distance from the ground surface to the modeled upper surface of dense volcanic cores. Near the center of the island, the edifice of Mauna Kea appears covered with alkali basalt vents (gray diamonds). The contour interval represents 1 km. The authors plot known vents and other features such as slumps in order to compare them to the model. The subaerial features were taken from Wolfe and Morris (1996) and the submarine geologic features, from Holcomb (1996). Rift zones are marked by linear distributions of vents; alternative locations for the summit of Mahukona volcano are shown by "a" and "b." Modified from Kauahikaua and others, 2000.

"Mauna Kea has an elliptical-shaped core, slightly elongated east-west, with a broad, linear feature trending southeast. This linear feature may be a buried rift zone of Mauna Kea, although no surface expressions of those rift zones have been mapped (Kauahikaua and others, 2000)."

The submarine feature known as the Hilo Ridge was also included in the density study with data contributed by GLORIA (a side-scan sonar) as well as satellites ERS-1, Geosat, and Seasat. Prior to this investigation, the Hilo Ridge had been attributed to Mauna Kea as its possible rift zone; however, the authors determined a stronger connection with Kohala due to multiple factors including the strongly NW-trending linear zone that extends ~80 km from the modelled core of Kohala.

Early European observations. An early survey of Hawai`i was conducted by Archibald Menzies, a botanist who accompanied Captain George Vancouver during the cruises of 1792-1794. Menzies successfully ascended Mauna Loa in February 1794 (a team from Captain Cook's crew had unsuccessfully attempted the summit in 1779; see figure 7). Menzies estimated the heights of Mauna Loa and Mauna Kea to within 31 m of the currently accepted value, "a remarkable surveying feat for that time" (Wright and others, 1992b).

Figure 7. This map of the Hawaiian Islands has been cropped and centered on the area of the Big Island. Mauna Kea and other major landmarks were annotated with the early spelling conventions. According to Wright and others, 1992b, "This was the first map of the island of Hawai`i, made in 1779 by Henry Roberts, a member of Captain Cook's crew. Four volcanoes are shown, and only the two largest ones are named. Kīlauea is conspicuously absent from this map and from a similar one made following Vancouver's voyages of 1792-1794. Neither Cook nor Vancouver visited the eastern side of Hawai`i or saw any volcanic activity." Modified from Wright and others (1992b) and Fitzpatrick (1986).

The first petrologist to study Mauna Kea, R.A. Daly, determined not only that Mauna Kea's upper flanks were dominated by lava flows more rich in silica (he called them "andesite" although current classifications label them "hawaiite"), but also that the edifice had been modified by glaciers (Wolfe and others, 1997; Daly, 1911). Stearns and Macdonald (1946) and Washington (1923) expanded the knowledge base of Mauna Kea's geochemistry, and Gregory and Wentworth (1937) established that the glacial features from the most recent glacial episode (40,000 to 13,000 years ago) were interspersed with primary volcanic material. Wolfe and others (1997) determined that "eruptive activity of Mauna Kea was partly contemporaneous with that at Kohala, Hualalai, and Mauna Loa, and the volcano boundaries are undoubtedly complex."

HVO Volcano Watch article highlights a Mauna Kea forecast. The potential for a future eruption from Mauna Kea was addressed in a Volcano Watch article posted in June 2000 by then Scientist-in-Charge, Don Swanson, from the Hawaiian Volcano Observatory (HVO) (Swanson, 2000ab). The article addresses not only eruption frequency but also trends in eruption style, the potential response of the telescope installation at Mauna Kea's summit, and a general forecast for a likely scenario in the future.

"The next eruption of Mauna Kea."

"Mauna Kea's peaceful appearance is misleading. The volcano is not dead. It erupted many times between 60,000 and 4,000 years ago, and some periods of quiet during that time apparently lasted longer than 4,000 years. Given that record, future eruptions seem almost certain.

"Before the next one, we should have ample warning provided by our current seismic and geodetic monitoring systems. A number of earthquakes occur beneath Mauna Kea each year, and you can bet that we pay close attention to them. However, they all appear to be associated with tectonic faulting rather than movement of magma.

"The telescopes on top of the volcano may be the first to indicate that something is amiss. The coordinates used for tracking their observations will begin to drift unexpectedly as the volcano is swelling. In a sense, the telescopes will serve as very expensive tiltmeters.

"We cannot now say when the next eruption will take place, except that it is unlikely to be in the next several months, given the current lack of any precursory signs. Whether the timing is years, centuries, or millennia is entirely unclear.

"But we can say something about the probable nature of the next eruption, because we know what the most recent ones were like, thanks to recently published research by Ed Wolfe [see Wolfe and others, 1997], former staff member of HVO, and colleagues.

"The next eruption could take place anywhere on the upper flanks of the volcano. As Mauna Kea evolved from its early shield stage (equivalent to Kīlauea and Mauna Loa today) to its present postshield stage, the volcano lost its rift zones. Consequently, the postshield eruptions are not concentrated along narrow zones but instead are scattered across the mountain. [See figure 6.]

"For example, the most recent eruptive period, 6,000-4,000 years ago, involved eight vents on the south flank of the volcano between Kala`i`eha cone (near Humu`ula) and Pu`ukole (east of Hale Pohaku). During this same period, eruptions took place on the northeast flank at Pu`u Lehu and Pu`u Kanakaleonui. Lava from Pu`u Kanakaleonui flowed more than 20 km (12 miles) northeastward, entering the sea to form Laupahoehoe Point.

"The next eruption will likely produce a lava flow, because each eruption in the past 60,000 years has done so. The longest flows will reach 15-25 km (9-15 miles) downslope. Most of each flow will be `a`a, but pahoehoe may form near vents.

"A prominent cinder cone will probably be constructed at each vent. The cinder cones responsible for the "bumpy" appearance of Mauna Kea's surface formed during the 60,000-4,000-year interval. The cones mentioned by name above, and several others, were built during the latest eruptive period 6,000-4,000 years ago. The next eruption will likely produce a similar cone.

"Cinder cones form at vents that are point sources, not elongate fissures. All activity is concentrated at one place, so that fountaining and spattering build a high cone rather than a long rampart. Past eruptions-and hence future ones--probably lasted months to several years, providing enough time to construct a substantial cone. Those eruptions spread voluminous ash deposits far beyond the cinder cones themselves, and the next eruption will probably do so, too.

"Possibly, however, there will not be enough spattering to build a lasting cone. Such an eruption happened about 1 km (0.6 miles) southeast of Hale Pohaku, when a vent put out a moderate volume of lava without building a spatter or cinder cone.

"The next eruption of Mauna Kea is unlikely to occur in our lifetimes, but it could. There is no reason to fear such an eruption. It would not threaten human life, provided due care were taken, though it could prove devastating to property and infrastructure, particularly if a lava flow traveled to the Hamakua coast or the Waimea area."

Mauna Kea's seismicity. HVO has monitored and maintained the record of seismicity for the entire region of Hawai`i. The seismicity detected beneath Mauna Kea has been characterized as "infrequent and sparse." Notable seismicity occurred in 1994, 2001, and 2011, when earthquakes were large enough to be felt by the general public. Island-wide instrumentation allowed excellent location data for the local seismicity (figure 8).

Figure 8. The seismic network that monitors Mauna Kea and the other volcanoes of Hawai`i spans six islands. This map appeared in the USGS Fact Sheet released in 2011.

HVO reported that, several times each year, earthquakes from Mauna Kea cause shaking that is noted by local populations - especially the operators of the Mauna Kea astronomical observatory, who rely on stable instrumentation in order to make precise observations. Reports of felt earthquakes from Mauna Kea correlated with magnitude 2.1-4.9 earthquakes during 1973-2012.

Elevated seismicity during October-December 2011 resulted in 30 felt earthquakes. Approximately 570 people reported the M 4.5 earthquake that occurred on 20 October 2011 and also 10 of the aftershocks that followed (figure 9). HVO reported that, like many of Mauna Kea's earthquakes, these earthquakes were "most likely caused by structural adjustments within the Earth's crust due to the heavy load of Mauna Kea." With an estimated volume of >30,000 km³, Mauna Kea rises ~10,000 m above the seafloor, causing stress to accumulate from the mass of the volcano (Lockwood and Hazlett, 2010).

Figure 9. This map includes the located seismicity from Mauna Kea's seismic sequence between 19 October and 31 December 2011. Within 10 km of the summit, an M 4.5 earthquake (20 October 2011) and aftershocks occurred. Courtesy of HVO.

Earthquake swarms at Mauna Kea. HVO reported that earthquake swarms occasionally occur at Mauna Kea. On 23 February 2001, a swarm of ~15 events was detected within a 21-hour period. These earthquakes were mainly located ~15 km S of Pa`auilo (~3 km NW of Kuka`iau, figure 10), at a depth of 8-11 km.

Figure 10. Geographic features of Mauna Kea included in this map are discussed in this text. Topographic contours are from U.S. Geological Survey, Hawaii County, Sheets 1 and 2, 1980; 4,000-m contour omitted. The following abbreviations are included: ag, the aqueduct gulch; HS, Hopukani Springs; HSS, Humu`ula Sheep Station; LS, Liloe Spring; WS, Waihu Spring. Map modified from Wolfe and others (1997).

Lake Waiau recedes. The cinder cone Pu`uwaiau, located within 2 km of the summit, has contained a freshwater lake that was considered permanent by Wolfe and others (1997) (figures 11 and 12). Lake Waiau has likely persisted due to the once-glassy cinders and bombs that have weathered to smectite with zeolites within the void spaces. These alteration products may serve as a weak cement between the pyroclasts and reduce the permeability of the cinder cone's base. Sporadic winter storms have provided most, if not all, of the water captured in this considerably arid region (Patrick and Delparte, 2014). Contributions from permafrost were also proposed by Woodcock (1980), but the presence of permafrost has not been confirmed near Lake Waiau.

Figure 11. An aerial view of Mauna Kea's summit was acquired in 1995 from a NASA C-130 aircraft. The highest cinder cone, Pu`u Wekiu, is centered in this view with several astronomical telescopes in view on the left-hand side. The small oval Lake Waiau is on upper the right-hand side of this photo. Courtesy of Scott Rowland (School of Ocean and Earth Science and Technology, University of Hawaii at Manoa).

Figure 12. This aerial photo includes Mauna Kea's Pu`uwaiau where Lake Waiau is indicated with the yellow arrow. The view is approximately SW. A large cinder cone, Pu`uhaukea, is in the foreground. A dark lava flow from Mauna Loa is in the far distance. Courtesy of Richard Wainscoat (Institute for Astronomy, University of Hawai`i).

Patrick and Delparte (2014) reported that the lake size before 2010 was 5,000-7,000 m² with a depth of ~3 m, but recently, the size has been decreasing rapidly. In the recent past, the lake was known to overflow through the Pohakuloa Gulch when water levels exceeded the rim (as recently as February 2002) (Ehlmann and others, 2005).

Researchers have determined that Lake Waiau is sensitive to precipitation levels (Woodcock, 1980) and that ongoing drought conditions could be driving the lake's change (Patrick and Delparte, 2014). Based on the National Drought Mitigation Center's data, since 2008, and notably in March 2010, precipitation has been sparse at the summit of Mauna Kea.

In December 2013, scientists visited the lake and observed an unprecedented sight (figure 13). Lake Waiau measured a mere 115 m² and was roughly 10-20 cm deep (Patrick and Delparte, 2014). While the lake size was known to fluctuate over time, this dramatic reduction has caused concern, given the possibility of losing a specialized ecosystem as well as a prominent feature of Hawaiian ethnogeography. Mauna Kea's summit is considered "one of the most sacred spots in the Hawaiian Islands. Archaeological sites near the summit attest to its prolonged spiritual importance...(Patrick and Delparte, 2014)."

Figure 13. The rapid drop in Mauna Kea's Lake Waiau water level began in 2010. Prior to 2010, the lake area was typically 5,000-7,000 m2, with the maximum size outlined in yellow in the top left image (depth was ~3 m). By late 2013, the lake was just 100-200 m2 in area. Photographs courtesy of Office of Mauna Kea Management and modified from Patrick and Delparte (2014)..

USGS scientists at HVO as well as collaborators, including Idaho State University, continued to study the conditions at Lake Waiau after the significant survey was conducted in December 2013. As of May 2014, strong winter rains had partially restored the lake, providing stronger evidence that the multi-year shrinkage was due to the ongoing drought as opposed to changes in the volcanic system.

A note regarding the name Mauna Kea. The popular translation of the Hawaiian name Mauna Kea is frequently "White Mountain," however, significant discussions have focused on the source of the name. There has been growing consensus that Mauna Kea is a shortened form of Mauna a Wakea, which refers to the sky father Wakea.

According to testaments presented in the Final Environmental Impact Statement of the Federal Highway Administration Project No. A-AD-6(1) which included potential cultural impacts on the island by expanding State Routes 190 and 200, "The mountain is the sacred child of Wakea, and it is the source for the land. The mountains and land were genealogically connected to native Hawaiians through the original ancestor, Wakea [sky father] and Papa [earth mother]."

Ethnographic research conducted prior to 1999 and released in the impact statement concluded that the summit area of Mauna Kea was eligible for the National Register of Historic Places due to traditional cultural property.

A note regarding Hawaiian names and nomenclature. As previously noted in other Bulletin reports, according to Runyon (2006), "The U.S. Board on Geographic Names (BGN) is responsible for establishing and maintaining uniform geographical name usage throughout all departments and agencies of the United States government. As such, the Board collects and promulgates every name that is considered official for Federal use. The official vehicle for promulgating these names and their locative attributes is the Geographic Names Information System (GNIS).

"Until the 1990's, it was also Federal policy to omit most diacritics and writing marks from placenames on Federal maps and documents. The few exceptions included the Spanish tilde and the French accent marks, but otherwise the special characters found in indigenous names were always dropped. In more recent years, however, the BGN has amended its policy to permit the inclusion of such marks, thus more accurately reflecting the true representation of the native language. An example of this has been the addition of the glottal stop (okina) and macron (kahako) to placenames of Hawaiian origin, which prior to 1995 had always been omitted. The BGN staff, under the direction and guidance of the Hawaii State Geographic Names Authority, has been restoring systemically these marks to each Hawaiian name listed in GNIS."

GVP will strive to conform to GNIS nomenclature. It remains a technological challenge, but a goal.

References: Clague, D.A., and Dalrymple, G.B., 1987, The Hawaiian-Emperor volcanic chain. Part I. Geologic evolution, chap. 1 of Decker, R.W, Wright, T.L., and Stauffer, PH., eds., Volcanism in Hawaii: U.S. Geological Survey Professional Paper 1350, v. 1, p. 5-54.

Daly, R.A., 1911, Magmatic differentiation in Hawaii: Journal of Geology, v. 19, no. 4, p. 289-316.

Federal Highway Administration, 1999, Final Environmental Impact Statement Part 1: Hawaii State Route 200, Mamalahoa Highway (SR 190) to Milepost 6 Saddle Road, County of Hawai`i, State of Hawai`i, FHWA Project No. A-AD-6(1).

Ehlmann, B.L., Arvidson, R.E., Jolliff, B.L., Johnson, S.S., Ebel, B., Lovenduski, N., Morris, J.D., Beyers, J.A., Snider, N.O., and Criss, R.E., 2005. Hydrologic and isotopic modeling of Alpine Lake Waiau, Mauna Kea, Hawai`i. University of Hawaii Press, p. 1-15.

Fitzpatrick, G.L, 1986. The early mapping of Hawaii. Honolulu: Editions Limited, vol. 1, 160 pp.

Geohazards Consultants International, Inc., Mauna Kea Science Reserve Master Plan, Volcano, HI, March 2000, 22 p.

Gregory, H.E., and Wentworth, C.K., 1937, General features and glacial geology of Mauna Kea, Hawaii: Geological Society of America Bulletin, v. 48, no. 12, p. 1719-1742.

Holt, Rinehart, and Winston (2006), Hawaii. Retrieved from http://go.hrw.com/atlas/norm_htm/hawaii.htm.

Hoover, S.R. and Fodor, R.V., 1997, Magma-reservoir crystallization processes: small-scale dikes in cumulate gabbros, Mauna Kea Volcano, Hawaii, Bulletin of Volcanology, 59, p. 186-197.

Kauahikaua, J., Hildenbrand, T., & Webring, M., 2000. Deep magmatic structures of Hawaiian volcanoes, imaged by three-dimensional gravity models. Geology, 28, 10, p. 883.

Lockwood, J.P., and Hazlett, R.W., 2010. Volcanoes: Global Perspectives, Wiley-Blackwell, Hoboken, NJ, ix, 539 p.

Okubo, P.G. and Nakata, J.S., 2011, Earthquakes in Hawai`i-An Underappreciated but Serious Hazard, Fact Sheet 2011-3013, USGS Fact Sheet, September 2011. (http://pubs.usgs.gov/fs/2011/3013/)

Patrick, M. R. and Delparte, D., 2014, Tracking Dramatic Changes at Hawaii's Only Alpine Lake: EOS (Transactions, American Geophysical Union), Vol. 95, No. 14, p. 117-118.

Porter, S.C., 1971, Holocene Eruptions of Mauna Kea Volcano, Hawaii, Science, Vol. 172 no. 3981 p. 375-377.

Stearns, H.T., and Macdonald, G.A., 1946, Geology and ground-water resources of the Island of Hawaii: Hawaii Division of Hydrography Bulletin 9, 363 p.

Swanson, D.A., (June 2000a). The next eruption of Mauna Kea. Volcano Watch. Retrieved from http://hvo.wr.usgs.gov/volcanowatch/archive/2000/00_06_01.html.

Swanson, D.A., 2000b, Don't be fooled by seemingly peaceful Mauna Kea Volcano--it could erupt again: Hawaii Tribune-Herald, June 4, p. 2.

USGS-HVO (May 2002). Mauna Kea Hawai`i's Tallest Volcano. Other Volcanoes. Retrieved from http://hvo.wr.usgs.gov/volcanoes/maunakea/.

Washington, H.S., 1923, Petrology of the Hawaiian Islands; I, Kohala and Mauna Kea, Hawaii: American Journal of Science, ser. 5, v. 5, no. 30, p. 465-502.

Wolfe, E.W., Wise, W.S., and Dalrymple, G.B., 1997, The geology and petrology of Mauna Kea volcano, Hawaii: a study of postshield volcanism. U.S. Geological Survey Professional Paper 1557, Washington, D.C.: U.S. G.P.O.

Woodcock, A., 1980. Hawaiian alpine lake level, rainfall trends, and spring flow, Pacific Science, 34, p. 195–209.

Wright, T.L., Chu, J.Y., Esposo, J., Heliker, C., Hodge, J., Lockwood, J.P., and Vogt, S.M., 1992a, Map showing lava-flow hazard zones, island of Hawaii: U.S. Geological Survey Miscellaneous Field Studies Map MF-2193, scale 1:250,000.

Wright, T.L., Takahashi, T.J., and Griggs, J.D., 1992b, Hawai`i Volcano Watch: A Pictorial History, 1779-1991, University of Hawaii Press, Honolulu, 162 p.

Geologic Background. Mauna Kea, Hawaii's highest volcano, reaches 4205 m, only 35 m above its neighbor, Mauna Loa. In contrast to Mauna Loa, Mauna Kea lacks a summit caldera and is capped by a profusion of cinder cones and pyroclastic deposits. It's rift zones are less pronounced than on neighboring volcanoes, and the eruption of voluminous, late-stage pyroclastic material has buried much of the early basaltic shield volcano, creating a steeper and more irregular profile. This transition took place about 200,000 to 250,000 years ago, and much of Mauna Kea, whose Hawaiian name means "White Mountain," was constructed during the Pleistocene. Its age and high altitude make it the only Hawaiian volcano with glacial moraines. A road that reaches a cluster of astronomical observatories on the summit also provides access to seasonal tropical skiing. The latest eruptions produced a series of cinder cones and lava flows from vents on the northern and southern flanks during the early- to mid-Holocene.

Information Contacts: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawai`i National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/observatories/hvo/); Richard Wainscoat, University of Hawaii at Manoa, Institute for Astronomy (URL: http://www.ifa.hawaii.edu/, http://www.ifa.hawaii.edu/images/aerial-tour-95/); Scott Rowland, University of Hawaii at Manoa, School of Ocean and Earth Science and Technology (URL: http://www.soest.hawaii.edu/); and Hawaii News Now (URL: http://www.hawaiinewsnow.com/).

Our last Bulletin report covered seismicity and explosions at San Cristóbal through 31 December 2012 (BGVN 38:01).

2013. The Instituto Nicaragüense de Estudios Territoriales (INETER) reported that on 7 June 2013 seven explosions at San Cristóbal, that ejected gas and ash, were detected by the seismic station located on the W flank. The explosions occurred at 0615, 0645, 0653, 0911, 1137, 1139, and 1143, and were observed by civil defense and INETER staff. The largest explosion, at 1139, generated a plume that rose 100 m. Sulfur dioxide (SO₂) emissions, which had been low, increased. A report later that afternoon stated that gas-and-ash explosions decreased, but RSAM values almost tripled to between 80 and 100 units due to increased tremor. INETER noted that tremor is frequently detected at San Cristóbal, and for the public not to be alarmed. A small mud flow, producing no damage, occurred at 1710.

2014. INETER reported that seismic tremor increased at 0340 on 17 January; RSAM values increased to 460 units from a baseline of 70 units. Twelve gas emissions were observed between 1259 and 1315, and RSAM climbed to 649 units. A report at 1700 noted that RSAM values decreased to 100 and no additional gas emissions were observed. The next day RSAM values fluctuated between 90 and 190 units.

INETER reported that a gas emission with small amounts of ash rose from San Cristóbal between 0641 and 0850 on 4 February. Although there was no increase noted, the report stated that seismicity decreased to background levels. By the afternoon SO₂ emission values were 2,000-3,000 tons per day, the normal levels, and on 7 February, they were 1,000 tons per day. RSAM fluctuated between 20 and 140 units, which is considered normal.

Based on analysis of satellite images, the Washington VAAC reported that on 11 April a gas plume from San Cristóbal that possibly contained small amounts of ash drifted 20 km W. A thermal anomaly was present in short wave infrared satellite images. Periods of elevated seismicity were also detected.

Geologic Background. The San Cristóbal volcanic complex, consisting of five principal volcanic edifices, forms the NW end of the Marrabios Range. The symmetrical 1745-m-high youngest cone, named San Cristóbal (also known as El Viejo), is Nicaragua's highest volcano and is capped by a 500 x 600 m wide crater. El Chonco, with several flank lava domes, is located 4 km W of San Cristóbal; it and the eroded Moyotepe volcano, 4 km NE of San Cristóbal, are of Pleistocene age. Volcán Casita, containing an elongated summit crater, lies immediately east of San Cristóbal and was the site of a catastrophic landslide and lahar in 1998. The Plio-Pleistocene La Pelona caldera is located at the eastern end of the complex. Historical eruptions from San Cristóbal, consisting of small-to-moderate explosive activity, have been reported since the 16th century. Some other 16th-century eruptions attributed to Casita volcano are uncertain and may pertain to other Marrabios Range volcanoes.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); and Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/).

Our last report, (BGVN 36:09), covered activity at Stromboli through 11 October 2011, characterized by explosions, spattering, rockslides, and occasional lava flows. Similar activity persisted through February 2013. Stromboli (volcano and island) sits N of Sicily in the Tyrrhenian sea along the N side of the Aeolian archipelago.

Activity during 2011. The activity documented in October 2011 continued into November, December, and January 2012, and was concentrated at the two active vent areas in the northern and southern portions of the crater terrace. The wide array of activity noted above fluctuated. There were, along with frequent episodes of spattering, in particular on 10 December 2011. The spattering episodes occurred in the southern area and did not lead to the formation of any lava flows.

Activity during 2012. Stromboli exhibited two periods of isolated activity early in 2012, discussed next. On 16 February there were two sequences of up to 6 explosion earthquakes of medium-high amplitude, and ~9 Very Long Period (VLP) events per hour.

On 6 March, instruments detected both tremor coupled with a strong explosion and at least three major explosions. The first event, at 0643 UTC, presented a VLP component with amplitude ~10-times higher than the daily average. The last event, at 0645, was also of very high amplitude. The VLP events occurred at a rate of ~12 per hour, at a low level with a single event of high amplitude, corresponding to the first event in the sequence at 0643. The VLP sequence was followed by an increase in tremor lasting ~30 minutes. The tremor amplitude was medium-low with its peak corresponding to the earlier events seen around 0643.

On 22 November 2012, the persistent explosive activity at Stromboli showed a clear increase, with episodes of spattering and low lava fountains from two vents in the northern and central portions of the crater terrace.

Beginning on 23 December 2012, repeated lava overflows from the crater terrace generated small lava flows down the northern and northwestern sectors of the Sciara del Fuoco (see images below), and were accompanied by numerous landslides.

Major lava flows occurred on the evening of 23 December 2012 (to the N), during 25-27 December 2012 (to the NW), and on the morning of 7 January 2013 (to the NW). Lava vented from points just below the rim of the northernmost explosive vent on the crater terrace. During the intervals between the main effusive episodes, lava vented at extremely low, releasing numerous incandescent blocks down the Sciara del Fuoco (the area within the sector collapse). At times, small lava flows advanced for a few tens of meters before disintegrating into blocks, such as on the morning of 10 January 2013 (see the last photo in the sequence below in figure 82).

Figure 82. Frames extracted from video recorded by the visible surveillance camera at 400 m elevation on Stromboli (SQV) during the effusive episodes between 23 December 2012 and 10 January 2013. (Note date format: DD-MM-YY.) The first frame (upper left) shows the sliding of material caused by the emplacement of a lava flow onto unstable material on the slope of the Sciara del Fuoco. Courtesy INGV.

Around this time, in all cases, the effusion of lava was preceded, and often accompanied, by intense explosive activity on the crater terrace.

More insight into behavior at Stromboli during this December 2012-March 2013 eruptive phase can be found in Di Traglia and others (2014). They applied the ground-based InSAR monitoring system at Stromboli volcano, linking changes in displacement and other field-monitored observations to volcanism.

Activity during January-February 2013. A new phase of intermittent effusive activity at Stromboli consisting of small overflows of lava from the crater terrace began on 8 February 2013 and continued with significant fluctuations until the morning of 17 February. During this interval, several episodes of effusive activity occurred, which produced lava flows reaching several tens to a few hundred meters in length in the northern and northwestern sectors of the Sciara del Fuoco.

Spattering from vent N2, which lies at the top of a hornito perched on the NW rim of the crater terrace, continued for a few hours, and then diminished during the late afternoon of 14 February. See Figure 83. Subsequently, effusive activity diminished considerably, producing only very small lava overflows that extended a few tens of meters downslope to the NW. On the morning of 17 February, all effusive activity ceased and mild Strombolian activity resumed.

Figure 83. Frames extracted from video recorded by the thermal monitoring camera at 400 m elevation on Stromboli (SQT), showing effusive activity on 11 February (top) and 14 February 2013 (bottom).

After an interval of 10 days of normal Strombolian activity, Stromboli again produced small lava overflows from the crater terrace from the afternoon of 27 February 2013 through the following night. A second episode of lava overflow started on the evening of 1 March and ceased the next afternoon. Both overflows were fed by continuous spattering from vent N2.

Reference. Di Traglia, F., Intrieri, E., Nolesini, T., Bardi, F., Del Ventisette, C., Ferrigno, F., Frangioni, S., Frodella, W., Gigli, G., Lotti, A., Tacconi Stefanelli, C., Tanteri, L., Leva, D., Casagli, N., 2014, The ground-based InSAR monitoring system at Stromboli volcano: linking changes in displacement rate and intensity of persistent volcanic activity, Bulletin of Volcanology 76:786DOI 10.1007/s00445-013-0786-2.

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

Information Contacts: Boris Behncke and Mauro Coltelli, Istituto Nazionale di Geofisica e Vulcanologia (INGV) Osservatorio Etneo (Catania), 95125 Catania (URL: http://www.ct.ingv.it/).