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/).

Aira caldera encompasses the northern half of Kagoshima Bay in Kyushu, Japan. During the Holocene activity has been focused at Sakurajima volcano along the southern rim of the caldera, and more recent activity has occurred at the Minamidake and Showa summit craters (figure 59). Minamidake crater has been persistently active since 1955, and activity at Showa crater resumed in 2006. Sakurajima is one of Japan's most active volcanoes and frequently deposits ash over the nearby Kagoshima city. This report covers activity that occurred through 2017 and is based on reports issued by the Japan Meteorological Agency (JMA).

Figure 59. The active Minamidake and Showa craters of Sakurajima volcano at Aira. Three incandescent vents within the craters are visible in this Sentinel-2 false color thermal image (bands 12, 11, 4) that was acquired on 13 December 2017. Courtesy of Sentinel Hub Playground.

Typical activity largely consists of Vulcanian explosions that produce ash plumes and small pyroclastic flows. Prior to a decrease in activity in August 2016, the volcano typically produced tens of explosions per month. The last recorded explosion in 2016 was a low-level ash plume on 22 August at 1.2 km altitude, reported by the Tokyo Volcanic Ash Advisory Center (VAAC). Sakurajima has remained on Activity Alert Level 3 (do not approach) on an alert level scale of 1 (little to no activity) to 5 (eruption or imminent eruption causing significant damage to residential areas).

Activity has been low since August 2016. No eruptions were observed through January and February 2017, and both seismicity and SO₂ emission levels remained low.

Eruptive activity resumed on 25 March 2017 at 1803 local time, when the Minamidake crater produced an ash plume to 500 m above the crater and a pyroclastic flow travelled approximately 1,100 m to the south (figure 60). Several additional small ash emission events were noted after this event.

Figure 60. Eruption at the Minamidake crater of Sakurajima (Aira caldera) on 25 March 2017 at 1803 local time. The ash plume reached 500 m above the crater and a pyroclastic flow traveled 1,100 m to the south. Image taken by the Kaigata surveillance camera, courtesy of JMA (March 2017 Monthly Sakurajima report).

Showa crater resumed activity at 0511 on 26 April 2017; 19 more events occurred through the month, including two larger explosive events. One explosive event produced an ash plume to 3,200 m above the crater on 28 April at 1101 local time. Two events occurred at the Minamidake crater through April.

Activity continued at the Showa crater in May, with 47 ash emission events, with nine of these being explosive events. One event on 2 May produced a 4,000-m-high plume that deposited ash on nearby communities (figure 61). Several larger explosions ejected blocks out to 500-800 m from the Showa crater. Activity continued at Minamidake crater, with ash reaching 2,500 m above the crater during an event on 5 May.

Figure 61. Eruption of Sakurajima in the Aira caldera on 2 May 2017 at 0320 local time. The ash plume reached 4,000 m above the crater. Image taken by the Tarumi Ararazaki surveillance camera, courtesy of JMA (May 2017 Monthly Sakurajima report).

Through June, the Showa crater produced 14 events, including two explosive events. An explosion on 6 June produced an ash plume up to 3,200 m above the crater and blocks were deposited out to 800 m from the crater. One small event occurred at Minamidake. Activity was reduced in July, with seven events at Showa crater and none at Minamidake.

During August no events took place at Minamidake. However, Showa crater remained active with 98 events, including 20 that were explosive. Activity through September was similar with no activity in Minamidake crater and 170 events at Showa, including 38 explosive events.

Activity declined again from October through December. During October there were 37 events from Showa crater, with five being explosive (figure 62). One event at Minamidake crater on 31 October produced an ash plume up to 1,000 m above the crater. During November, five events occurred at Minamidake crater, and one at Showa crater that produced an ash plume to 1,300 m above the crater. In December, one event occurred at the Showa crater and Minamidake produced one small event.

Figure 62. An explosive event is seen in this webcam image from the Sakurajima volcano Showa crater (Aira caldera) on 1 October, 2135 local time. Incandescent blocks were deposited out to 1,300 m from the crater. Image taken by the Tarumi Arasaki surveillance camera, courtesy of JMA (October 2017 Monthly Sakurajima report).

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

Information Contacts: Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Ambae (Aoba) is a large basaltic shield volcano in the New Hebrides arc that has generated periodic phreatic and pyroclastic explosions originating in the summit crater lakes Manaro Lakua and Voui during the last 25 years; the central edifice with the active summit craters is often referred to as Manaro Voui. A pyroclastic cone appeared in Lake Voui during November 2005-February 2006 (figure 30, BGVN 31:12). The volcano remained mostly quiet until an explosive eruption from a new pyroclastic cone in the lake began in mid-September 2017 and lasted through mid-November (BGVN 43:02). Activity included high-altitude ash emissions (9.1 km), lava flows, and Strombolian activity. After a quieter December, ash emissions resumed during January-April 2018. This report summarizes activity from January to June 2018, with information provided by the Vanuatu Geohazards Observatory of the Vanuatu Meteorology and Geo-Hazards Department (VMGD), the Wellington Volcanic Ash Advisory Center (VAAC), satellite data from several sources, and social media photographs.

Ongoing steam and intermittent ash emissions were observed during January and February 2018; incandescent ejecta continued from the pyroclastic cone at the summit. An increase in the frequency and volume of ash emissions in March led VMGD to raise the Alert Level to 3 (on a 0-5 level scale) by the middle of the month. Ash plume heights ranged from 3-5 km altitude. Heavy rains on 30 March caused a large lahar that significantly damaged a village on the N side of the island. A high-altitude plume on 31 March was measured at 13.7 km altitude. Significant ashfall around the island caused infrastructure damage and health hazards to humans, livestock, and plants. An explosion in early April produced another high-altitude ash plume observed in satellite imagery at 12.2 km altitude and one of the largest SO₂ plumes measured in several years. A major ash plume on 11 April rose to 9.1 km altitude and enveloped much of the island in ash-laden meteoric clouds. The pyroclastic cone growing in Lake Voui had bisected the lake by March, and continued to fill it in. By late May, only two remnants of the lake remained, and a nearby smaller lake was dry. A low-level ash emission in late June signaled the beginning of a new, larger eruptive episode that began on 1 July 2018.

Activity during January-February 2018. The Wellington VAAC reported an ash plume at Ambae on 2 January 2018 drifting E at 3.1 km altitude that dissipated after a few hours. A plume on 8 January estimated at the same altitude resulted in reports of ashfall on the N and NE areas of the island; meteoric clouds prevented observations of the plume. Ongoing steam emissions were reported for the rest of January. On 7 February a continuous ash plume was observed in satellite data at 2.7 km altitude moving N. The following day, it was visible spreading E from the summit. A pilot confirmed observation of the plume continuing to spread to the E at 3.1 km altitude late on 8 February. Another low-level emission on 10 February extended NE at 2.1 km for a few hours. An ash plume on 13 February was clearly visible drifting N in satellite imagery; its altitude was estimated at 3.1 km.

A larger eruption on 16 February generated an ash plume that rose to 4.6 km altitude and initially drifted NE. Continuous ash emission extended as high as 5.5 km through 17 February and drifted SE and then S. By the next day, the constant emissions were still visible in satellite imagery, estimated at 4.6 km altitude; the main plume was drifting E with a remnant moving to the SW, finally dissipating on 19 February (figure 54). Ash emissions were visible in infrared imagery at about 3.9 km altitude on 23 February. Ongoing explosions were observed in the webcam on 23 and 24 February; ash was visible in satellite imagery until the end of the day on 24 February. A brief explosion observed in the webcam around sunrise on 27 February generated a small ash plume that rose to 3.1 km altitude and drifted SE. Moderate sulfur dioxide emissions were recorded a number of times during January and February (figure 55).

Figure 54. On 18 February 2018, the pyroclastic cone at Ambae had grown significantly since 1 October 2017 (see figure 46 BGVN 43:02) (upper image) and actively ejected pyroclastic material along with magmatic gas and steam (lower image). Courtesy of pilot David Sarginson, Facebook.

Figure 55. SO2 plumes from Vanuatu's Ambae, Ambrym, and Gaua volcanoes were all substantial enough sometime during January and February 2018 to be recorded by the OMI instrument on NASA's Aura satellite. Emissions on 2 January 2018 (top left) were drifting slowly SW from Ambae (upper plume) and Ambrym (lower plume); only Ambae had a plume drifting W on 11 January (top right); both Ambae and Ambrym SO2 plumes drifted NE on 17 February (bottom left); on 19 February (bottom right) Gaua (top plume) produced an emission that drifted E while Ambae and Ambrym generated SO2 that drifted SW. Courtesy of NASA Goddard Space Flight Center.

Activity during March 2018. The frequency and volume of ash emissions increased significantly during March 2018. Ash plumes were visible in satellite imagery during 3-6 March 2018. The initial plume rose to 3.7 km altitude and drifted NE, rising to 3.9 on 4 March and drifting N. The following day plumes rose to 4.6 km. By 6 March the plume was lower, drifting NW at 2.4 km altitude. A series of continuous low-level ash emissions were visible in satellite and webcam imagery every day from 11-19 March (figure 56). They initially drifted SE and SW and then moved to the W on 15 March at altitudes of generally 2.4-3.1 km, occasionally higher. The plumes drifted N and W during 17-19 March. This increase in ash emissions affecting local villages led VMGD to raise the alert level from 2 to 3 on 18 March 2018. They noted that activity was similar to the previous October but with more sustained ash emissions.

Figure 56. Continuous ash emissions from Ambae beginning on 11 March 2018 (10 March UTC shown here) were visible in satellite imagery for over a week. Courtesy of European Space Agency, Copernicus EMS.

Local observers reported an explosion on 21 March that rose to 3.4 km altitude and drifted SW (figures 57-59). Continuous emissions through the end of the month were discernible in either satellite imagery or the webcam each day. Plume altitudes ranged from 3.1 to 4.9 km altitude, drifting in several directions. Significant ashfall began affecting local villages, destroying crops and livestock, and collapsing structures during the second half of March.

Figure 57. A strong explosion on 21 March 2018 at Ambae produced an ash plume that rose several kilometers above the crater. Ashfall affected villagers in many communities on the island. Image courtesy VMGD Saratamata webcam located 22 km NE on the NE tip of Ambae Island, annotations by Cultur Volcan.

Figure 58. A major ash plume rose from the crater of the pyroclastic cone in Lake Voui on Ambae on 21 March 2018. Photo courtesy of Robson S Tigona (VMGD), posted on Facebook.

Figure 59. The dense ash plume from the explosion on 21 March 2018 at Ambae caused significant localized ashfall on the SW of the island as seen from Nduidui wharf in W Ambae. Courtesy of Dan McGarry, Vanuatu Daily Post.

Local news reports on 25 March noted that ejecta from the previous evening was visible over 70 km away to the SW by residents on Espiritu Santo Island, and small amounts of ash fell on Pentecost Island, 60 km SE (figure 60). According to the Vanuatu Independent, Virgin Australia cancelled flights to Vanuatu on 25 March. The New Zealand Defence Force did an aerial survey on 26 March and observed a large ash plume rising several kilometers (figure 61). Radio New Zealand reported on 30 March that large amounts of ashfall and acid rain had damaged crops, water supplies and buildings on Ambae (figures 62). A New Zealand GNS Science volcanologist reported that gardens were covered by ash and limbs on trees were broken. Some of the roofs over buildings and water supplies had collapsed due to the weight of the volcanic ash. Heavy ashfall in the S and NW parts of the island at the end of the month resulted in evacuations of several villages in the affected areas.

Figure 60. Ashfall was observed on Pentecost Island, 60 km SE of Ambae after significant explosions overnight during 24-25 March 2018. Courtesy of Dan McGarry, Vanuatu Daily Post via twitter.

Figure 61. The New Zealand Defence Force photographed this large ash plume rising from the summit of Ambae during an aerial survey on 26 March 2018. Courtesy of the New Zealand Defence Force (NZDF).

Figure 62. Dense volcanic ash fell at the Penama Adventist College (PAC) in Red Cliff on Ambae in late March 2018. The upper image was taken on 14 April 2017, the lower image on 27 March 2018. Photos by John Metojoe, Vanuatu Police Force, and PAC. Courtesy of Philipson Bani (IRD/LMV).

The village of Waluebue on the N side of Ambae was badly damaged by a lahar during the night of 30-31 March. Homes and churches were destroyed from the mud and large boulders in the debris flow. All residents were safely evacuated (figures 63-67).

Figure 63. A large lahar deposited boulders and damaged many buildings in the village of Waluebue on the N side of Ambae during the night of 30-31 March 2018. Photo courtesy of Clifford Tarisimbi.

Figure 64. As seen in this example of a building undercut on one side and partially buried on the other, a large lahar damaged many buildings in the village of Waluebue on the N side of Ambae during the night of 30-31 March 2018. Photos courtesy of Clifford Tarisimbi.

Figure 65. Mud and boulders buried some buildings to the roofline when a large lahar damaged passed through the village of Waluebue on the N side of Ambae during the night of 30-31 March 2018. Photos courtesy of Clifford Tarisimbi.

Figure 66. Boulders a meter or more in diameter destroyed buildings when large lahar traveled through the village of Waluebue on the N side of Ambae during the night of 30-31 March 2018. Photo courtesy of Clifford Tarisimbi.

Figure 67. Boulders a meter or more in diameter destroyed buildings when large lahar traveled through the village of Waluebue on the N side of Ambae during the night of 30-31 March 2018. Photo courtesy of Clifford Tarisimbi.

A new series of high-altitude ash emissions were reported by the Washington VAAC beginning on 30 March (figure 68). Early reports from satellite images and webcams indicated an ash plume at 6.1 km altitude. This was followed within the hour of confirmation from satellite imagery of the plume at 13.7 km altitude moving NW. By the following morning, two plumes were visible, one drifting S at 6.1 km and a second drifting NW at 13.7 km altitude. Meteoric clouds prevented observations later that day, but by 1 April, intermittent explosions were producing plumes moving E at an estimated altitude of 3.0 km, and SE estimated at 6.1 km altitude.

Figure 68. A 13.7-km-high ash plume was visible from the VMGD Webcam at Ambae on 31 March 2018. Satellite imagery showed plumes drifting in multiple directions. Courtesy of VMGD.

Activity during April-June 2018. New eruptions occurred overnight during 5-6 April 2018 that generated an ash plume and a large distinct SO₂ plume. Meteoric clouds and darkness prevented observation of the ash plume, but the SO₂ signal was clearly visible on false-color satellite imagery. The plume initially rose to 7.3 km altitude and drifted W; a few hours later, it rose to 12.2 km. With a Dobson Unit measurement of 52.55 units, it was one of the strongest SO₂ plumes measured on the planet since 2015, according to Simon Carn of Michigan Technological University (figure 69). An ongoing eruption was visible in the webcam on 6 April, but meteoric clouds again prevented observation in satellite data. A cluster of lightning strikes was detected by the World Wide Lightning Location Network (WWLLN) around the reported time of the eruption, according to Simon Carn. Intermittent low-level ash emissions were confirmed in the webcam on 8 April, estimated to be moving NE and E at 3.0-4.9 km altitude.

Figure 69. The largest SO2 plume recorded since 2015 erupted from Ambae during 5-6 April 2018. Courtesy of NASA Goddard Space Flight Center.

Ash from a continuous low-level eruption during 9-10 April 2018 was clearly visible in the webcam and partly visible in satellite imagery drifting E and NE at 4.3-4.9 km altitude. The SO₂ plume from the eruption stretched across most of the South Pacific (figure 70). Ashfall from the plume spread across a large area of the island causing substantial damage in local communities (figures 71 and 72).

Figure 70. A sulfur dioxide plume from Ambae in Vanuatu stretched across the South Pacific in this 9 April 2018 image from the OMI instrument on the Aura satellite. Courtesy of NASA Goddard Space Science Center and Simon Carn.

Figure 71. Ashfall from continuous emissions at Ambae during 9-10 April 2018 spread across much of the island, damaging local communities. Image posted on 10 April 2018. Courtesy of Wilfred Woodrow, Facebook.

Figure 72. Ashfall from continuous emissions during 9-10 April 2018 at Ambae spread across much of the island, damaging local communities. Photo from Ghevin Banga, posted by Bani Philipson (IRD/LMV).

The ash plume height increased significantly on 11 April to 9.1 km altitude and drifted SE according to the Wellington VAAC. Planet Lab images showed the plume covering the N half of the island a short time later (figure 73). The following day, the plume altitude gradually lowered from 4.6 to 1.8 km and drifted N, then NW. Local communities reported intermittent low-level ash emissions and localized ashfall late on 12 April; this was the last report of ash emissions for April. Thick meteoric and ash clouds enveloped much of the island as seen in social media video on 12 April.

Figure 73. Three satellite images from Planet Labs Inc. show the changes at Ambae between September 2017 and April 2018. On 30 September 2017 (top), the pyroclastic cone in Lake Voui was still an island within the lake. By 10 March 2018 (middle), the lake had been divided in two by the growth of the cone, the lake was discolored, and ashfall covered a large area several kilometers in diameter around the lake. A major ash emission on 11 April 2018 (bottom) rose to 9.1 km altitude and covered the N half of the island. Courtesy of Planet Labs Inc. posted on Twitter at Planet@planetlabs.

According to the Vanuatu Daily Post on 16 April 2018, the Council of Ministers for Vanuatu declared their intent to seek help from International Relief Organizations to evacuate the island's population after the latest episodes of extensive ashfall destroyed much of the infrastructure. Photographs from an overflight by VGMD on 21 April 2018 showed the increased size of the pyroclastic cone inside Lake Voui dividing the lake into two segments, one nearly consumed by the cone (figure 74). They reported small eruptions on 23 and 27 April; these were the last ash emissions until the end of June 2018.

Figure 74. Aerial images of the active pyroclastic cone at Ambae were captured by VMGD during an overflight on 21 April 2018. Only dense steam emissions were observed in the view to the E across the summit, and the original Lake Voui was in two segments split by the pyroclastic cone. Courtesy of VMGD.

The thermal activity recorded by the MODVOLC and MIROVA systems corresponded with the observations of explosions and ash emissions. There were MODVOLC thermal alerts issued each month from January through 10 April 2018, with strong, multi-alert periods in February and March; these data were similar to the MIROVA signal for the period, which also showed increased activity during the same time (figure 75).

Figure 75. Data from the MIROVA project show significant pulses of heat flow from Ambae during February-April 2018. Inset photo shows the large ash plume of 9 April as viewed from the VMGD webcam, which corresponds to the largest heat flow in April shown on the graph. Courtesy of MIROVA and VMGD.

By the end of May 2018, Manaro Ngoru, the small water body on the W side of the summit was dry; Lake Voui, divided into two segments by the pyroclastic cone, had a small amount of orange-brown water in the W half, and muddy brown water in the E half (figures 76 and 77). Steam plumes rose continuously from the cone, but no ash emissions were observed.

Figure 76. The summit of Ambae on 22 May 2018 was covered with ash over a large area; former Lake Voui was divided in two by the pyroclastic cone, and only a modest steam plume rose from the top of the cone. Manaro Ngoru, the former lake on the W side of the summit, was completely dry. Courtesy of Planet Labs.

Figure 77. The W side of Lake Voui on Ambae on 29 May 2018 was a small area of dark reddish brown water around the pyroclastic cone. View is to the S. Courtesy of Bani Philipson (IRD/LMV). =

VMGB issued a volcano alert on 7 June 2018, announcing that they had lowered the Alert Level from 3 to 2, due to the reduced activity at Ambae during late April and May. Radio New Zealand reported that on 9 June, the Vanuatu government announced plans to move its Penama Province capital due to the ongoing eruption. The Penama Council agreed to relocate its headquarters from Saatamaa in Eastern Ambae to Loltong in North Pentacost. The Penama Province is one of six in Vanuatu and includes the three islands of Ambae, Maewo, and Pentecost.

The Wellington VAAC issued an ash advisory from a low-level ash emission on 21 June 2018. It was clearly visible in satellite imagery, and rose to 3 km altitude, drifting SE. That was the last activity reported until a large new ash plume was recorded in the webcam on 1 July 2018.

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); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); European Space Agency (ESA), Copernicus (URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus; 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/); New Zealand Defence Force (NZDF), Wellington, New Zealand (URL: http://www.nzdf.mil.nz/, Twitter: @NZDefenceForce); Vanuatu Daily Post (URL: http://dailypost.vu/news/flash-appeal/article_7c929c1e-dda3-5eab-925b-c814e04eeacb.html); Dan McGarry, Vanuatu Daily Post (Twitter: @dailypostdan); Vanuatu Independent News Magazine, Port Vila, Vanuatu (URL: https://vanuatuindependent.com/2018/03/26/flight-cancelled-due-to-volcanic-ash/); Simon Carn, Dept of Geological and Mining Engineering and Sciences, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931, USA (URL: http://www.volcarno.com/, http://so2.umbc.edu/omi/); Radio New Zealand, 155 The Terrace, Wellington 6011, New Zealand (URL: https://www.radionz.co.nz/international/pacific-news/359231/vanuatu-provincial-capital-moves-due-to-volcano); Bani Philipson, Observatoire de Physique du Globe de Clermont-Ferrand (OPGC) and Institut de Recherche pour le Developpement (IRD), Laboratoire Magmas et Volcans (LMV), University Campus of Cézeaux, 6 Blaise Pascal Avenue, TSA 60026 - CS 60026, 63178 AUBIERE Cedex, France (URL: http://lmv.univ-bpclermont.fr/bani-philipson/, Twitter: @philipsonbani); David Sarginson (Facebook: URL: https://www.facebook.com/david.sarginson.16); Clifford Tarisimbi (Facebook: https://www.facebook.com/profile.php?id=100009930510696); Wilfred Woodrow (Facebook: https://www.facebook.com/groups/558036627684741/permalink/974980079323725); Planet Labs Inc. (URL: http://www.planet.com/).

Ambrym volcano, located in Vanuatu along the New Hebrides Island Arc, consists of a large 12-km-diameter caldera with two active craters, Marum and Benbow. Historical activity has occurred at summit and flank vents, producing moderate explosive eruptions and lava flows that reach the coast. Historically important eruptions date back two centuries, including extra-caldera W-flank lava flows that caused destruction in coastal areas in 1820, 1894, 1913, and 1929. Since then, there have not been extra-caldera lava eruptions, although the areas around Marum and Benbow craters remain hazardous. The Vanuatu Meteorology and Geo-Hazards Department (VMGD) located in Port Vila, Vanuatu, is responsible for monitoring ongoing activity at Ambrym.

During January through June 2018, volcanic activity was confined to the eruptive vents of Benbow and Marum craters, including ongoing lava lake activity inside the active vents, substantial degassing, and emission of steam clouds. The Volcanic Alert Level remained at Level 2 on a scale from 0 to 5 with five being the highest (figure 30). At Level 2 ('Major Unrest') the danger is restricted to the active craters and the Permanent Exclusion Zones, which are located within a 1 km radius around Benbow crater and about a 2.7 km radius around Marum crater (figure 38).

Figure 38. A "Safety Map" showing Benbow and Marum craters at Ambrym with the locations of both designated permanent exclusion zones and danger zones. Courtesy of Vanuatu Meteorology and Geo-Hazards Department.

VMGD reported that the lava lakes in Benbow and Marum craters continued to be active and produced gas and steam emissions on 30 January, 19 March, and 25 April 2018. More sustained and substantial emissions were reported on 7 June.

During the reporting period, numerous thermal anomalies were detected by the MODIS satellite instruments and subsequently analyzed using the MODVOLC algorithm, possibly reflecting lava lake activity in Benbow and Marum craters (figures 39 and 40). The MIROVA (Middle InfraRed Observation of Volcanic Activity) system also detected numerous hotspots almost every day (figure 41).

Figure 39. Showing two active craters of Ambrym, Benbow and Marum. Red areas indicate approximate locations of Thermal Anomaly detections with the number of detections from MODVOLC Thermal Alert System from the period January through June 2018. Courtesy of HIGP - MODVOLC Thermal Alerts System.

Figure 40. MODVOLC thermal alerts detected during the reporting period from January to June 2018 showing hot spots located at Benbow and Marum craters. Courtesy of HIGP - MODVOLC Thermal Alerts System.

Figure 41. Plot of MODIS thermal infrared data analyzed by MIROVA showing the log radiative power of thermal anomalies at Ambrym for the year ending on 29 August 2018. Courtesy of MIROVA.

Geologic Background. Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides Arc. A thick, almost exclusively pyroclastic sequence, initially dacitic then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major Plinian eruption with dacitic pyroclastic flows about 1,900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.

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/); 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/).

Activity at Bezymianny has been frequent over the past 60 years, and almost continuous since May 2010. The Kamchatka Volcanic Eruptions Response Team (KVERT) reported that ash plumes from the 20 December 2017 explosive eruption (BGVN 43:01) rose as high as 15 km and drifted 320 km NE (figure 24). On 29 December activity included moderate gas-and-steam emissions; a lava flow likely continued to effuse onto the N flank of the lava dome. A thermal anomaly over the volcano was identified in satellite images in late December 2017.

Figure 24. Explosions from Bezymianny sent ash plumes up to 15 km altitude on 20 December 2017. Photo by Yu. Demyanchuk; courtesy of IVS FEB RAS, KVERT.

KVERT reported on 5 April 2018 that moderate gas-and-steam activity was continuing. Satellite data showed a thermal anomaly over the volcano on 29-30 March and 2-3 April, but the volcano was obscured by clouds in the other days of week. Fumarolic plumes were also seen on 13 April (figure 25). No MODVOLC thermal alerts were measured during the first half of 2018, and MIROVA analysis shows only low level radiative power anomalies for the same period (figure 26).

Figure 25. Thermal anomalies at Bezymianny recorded by the MIROVA system (log radiative power) for the year ending 2 February 2018 (top) and 28 June 2018 (bottom). Courtesy of MIROVA.

Figure 26. Thermal anomalies at Bezymianny recorded by the MIROVA system (log radiative power) for the year ending 28 June 2018. Courtesy of MIROVA.

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/); 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/); 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/).

Cleveland, at the western end of the isolated Chuginadak Island in the Aleutian Islands, is characterized by frequent small explosions that are monitored using local seismic and infrasound sensors, and by elevated surface temperatures that are monitored by satellite-based infrared sensors. The current eruptive period began in April 2016 and has continued through at least July 2018. The Alaska Volcano Observatory (AVO) is responsible for monitoring, and issues regular reports describing activity.

Small explosions in mid-December 2017 were followed by elevated surface temperatures later in the month and a lava flow in the summit crater that began effusing on 5 January 2018 (table 9). Thermal anomalies and other signs of unrest continued through 24 February, when a small explosion was detected. Another explosion was reported on 2 March with a plume rising to 4.6 km altitude and drifting ENE. Satellite data continued to identify elevated temperatures in early March. Small explosions were identified using seismic and infrasound data on 14 March and 4 April. The ash cloud on 4 April rose to 4.6 km altitude and drifted SW; hot material was ejected onto the W flank.

Thermal anomalies were ongoing in June. A small circular lava flow (~80 m in diameter) in the summit crater was reported on 25 June; a thermal anomaly noted during 29 June-2 July extending SW downslope within the crater was consistent with a lava flow, according to AVO. Weakly elevated surface temperatures were reported on many days during 7-23 July, along with some small steam plumes (figure 25). A small deposit of blocks, within the summit crater and just below the E crater rim, seen using satellite imagery during 18-23 July suggested to AVO that there had been a very small explosion not recorded using seismic or pressure sensor monitors.

Table 9. Observations of dome growth and other crater activity at Cleveland, December 2017-July 2018. Note that the absence of observable activity from satellites is often due to cloud cover. Data courtesy of Alaska Volcano Observatory (AVO).

Figure 25. Worldwide-3 satellite image of the summit crater of Cleveland volcano on 10 July 2018. The 80-m-diameter circular lava flow extruded in late June 2018 can be seen as well as minor steam emissions. Courtesy of Alaska Volcano Observatory / U.S. Geological Survey (Image 117311, color adjusted).

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

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 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://www.dggs.alaska.gov/); Anchorage Volcanic Ash Advisory Center (VAAC), Alaska Aviation Weather Unit, NWS NOAA US Dept of Commerce, 6930 Sand Lake Road, Anchorage, AK 99502-1845 USA (URL: http://vaac.arh.noaa.gov/).

The most recent activity from Copahue originates in the El Agrio crater, which has permanent fumarolic activity and an acidic lake. During 2017, ash emissions began in early June, but decreased after July, although tremor and degassing with occasional ash continued for the remainder of the year (BGVN 43:01). The volcano is monitored by the Servicio Nacional de Geología y Minería (SERNAGEOMIN). This report discusses activity during January-June 2018.

According to the Oficina Nacional de Emergencia-Ministerio del Interior (ONEMI), SERNAGEOMIN reported that a hydrothermal explosion was recorded on 24 March 2018, along with increased tremor. The Alert Level was raised to Yellow (second highest level on a four-color scale); SERNAGEOMIN recommended no entry into a restricted area within 1 km of the crater. ONEMI maintained its own Alert Level of Yellow (the middle level on a three-color scale) for the municipality of Alto Biobío (25 km SW).

Based on SERNAGEOMIN information, ONEMI reported that during 1-31 March 2018 there were 83 volcano-tectonic events recorded and 204 earthquakes indicting fluid movement. Tremor levels increased on 24 March, the same day as a phreatic explosion, though by the next day it had decreased to baseline levels. Webcams recorded gas plumes rising from El Agrio crater as high as 1 km. During an overflight on 3 April, scientists observed continuous white gas plumes rising almost 400 m.

The Buenos Aires Volcanic Ash Advisory Center (VAAC) reported that on 24 June diffuse steam emissions possibly containing ash were visible in webcam views rising to an altitude of 3.6 km.

Geologic Background. Volcán Copahue is an elongated composite cone constructed along the Chile-Argentina border within the 6.5 x 8.5 km wide Trapa-Trapa caldera that formed between 0.6 and 0.4 million years ago near the NW margin of the 20 x 15 km Pliocene Caviahue (Del Agrio) caldera. The eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains a briny, acidic 300-m-wide crater lake (also referred to as El Agrio or Del Agrio) and displays intense fumarolic activity. Acidic hot springs occur below the eastern outlet of the crater lake, contributing to the acidity of the Río Agrio, and another geothermal zone is located within Caviahue caldera about 7 km NE of the summit. Infrequent mild-to-moderate explosive eruptions have been recorded since the 18th century. Twentieth-century eruptions from the crater lake have ejected pyroclastic rocks and chilled liquid sulfur fragments.

Information Contacts: Oficina Nacional de Emergencia - Ministerio del Interior (ONEMI), Beaucheff 1637/1671, Santiago, Chile (URL: http://www.onemi.cl/); Servicio Nacional de Geología y Minería (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); 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).

Kerinci has produced intermittent ash explosions in recent years, including December 2011, June 2013, March-June 2016, and November 2016 (BGVN 42:04). The Darwin Volcanic Ash Advisory Centre (VAAC) has issued the only reports on activity between December 2016 and July 2018, and these have been based on satellite data. The Indonesia volcano monitoring agency, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), has kept the Alert Level at 2 (on a scale of 1-4) since 9 September 2007.

According to the Darwin VAAC, on 13 August 2017, an ash plume rose to an altitude of 4.3 km and drifted WSW.

Sentinel-2 satellite imagery showed what appeared to be a small ash plume rising from the crater on 21 April 2018 (figure 4). The Darwin VAAC also reported that on 5 June 2018 a minor ash emission rose to an altitude of 4.3 km and drifted W (figure 5). On 10 June an ash plume rose to an altitude of 4 km and drifted W.

Figure 4. Natural color satellite image from Sentinel-2 on 21 April 2018 showing a small light-brown ash plume rising from the Kerinci summit crater. Courtesy of Sentinel Hub.

Figure 5. A brown ash plume is visible in this natural color Sentinel-2 satellite image of the Kerinci crater on 5 June 2018. Courtesy of Sentinel Hub.

During the reporting period, no significant sulfur dioxide levels near the volcano were recorded by NASA's satellite-borne ozone instruments, and no thermal anomalies were detected.

Geologic Background. Gunung Kerinci in central Sumatra forms Indonesia's highest volcano and is one of the most active in Sumatra. It is capped by an unvegetated young summit cone that was constructed NE of an older crater remnant. There is a deep 600-m-wide summit crater often partially filled by a small crater lake that lies on the NE crater floor, opposite the SW-rim summit. The massive 13 x 25 km wide volcano towers 2400-3300 m above surrounding plains and is elongated in a N-S direction. Frequently active, Kerinci has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838.

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/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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 Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

Open lava lakes at the Kīlauea summit caldera along with a lava lake and flows from the East Rift Zone (ERZ) have been almost continuous since the current eruption began in 1983, and the rift zone has been intermittently active for at least two thousand years. The period from January-April 2018 included the ending of activity in one part of the ERZ and the beginning of a new episode. March 2018 marked the tenth year of the active lava lake inside the Overlook vent at Halema'uma'u. Information for this report comes primarily from the US Geological Survey's (USGS) Hawaiian Volcano Observatory (HVO) which provides daily reports, volcanic activity notices, and photo and video data.

At the end of 2017, the lava lake inside the Overlook vent at Halema'uma'u crater maintained the typical activity it had exhibited throughout the year, with a consistent lava circulation pattern, and occasional spattering events from hardened lava falling into the lake from the pit walls. The lake level rose and fell by a few meters over periods of hours to days, ending the year about 30 m below its level at the beginning of the year. Longer-term subsidence of the Pu'u 'O'o cone on the East Rift Zone was also apparent during 2017, although there was little change in the elevation of the lava pond inside the west pit area of the crater; occasional rockfalls triggered minor spattering. At the end of 2017 the East Rift Zone episode 61g surface lava flow activity persisted on the upper portions of the flow field near Pu'u 'O'o, on the pali, and in scattered areas along the coastal plain. Changes in the subsurface flow in lava tubes contributed to frequent changes to surface breakout locations. The lava flowing into the ocean at Kamokuna slowed and finally ended in November 2017.

During January-April 2018, the lava lake level inside the Overlook vent of Halema'uma'u crater rose and fell daily with alternating periods of inflation and deflation, with a gradual overall inflationary trend. Inflation intensified at the end of April, and the lake overflowed onto the floor of the crater during 21-27 April. The lake level had dropped several meters below the rim of the vent by the last day of the month. Activity of the episode 61g lava flow decreased gradually throughout the period. The flow remained active at the base of the pali and on the upper flow field through February, but activity tapered off on the coastal plain. By the end of March, only the upper flow field was still active. Notable inflationary tilt began at Pu'u 'O'o on 12 March 2018. Lava flowed out of vents on the main crater floor and also created a perched lava pond in the west pit. In mid-April HVO noted that the inflation resulted from increased pressurization of the magma under Pu'u 'O'o and in the past this had led to the formation of new vents and lava flows along the East Rift Zone. A marked increase in seismicity and ground deformation at Pu'u 'O'o on the afternoon of 30 April was followed by the collapse of the crater floor, dispersing red ash a significant distance around the cone. Following the collapse, HVO seismometers and tiltmeters recorded a substantial increase in seismic activity and deformation from Kīlauea's summit to an area about 10-16 km downrift (east) of Pu'u 'O'o which propagated eastward overnight along the Lower East Rift Zone (LERZ), marking the beginning of a major new eruptive phase.

Activity during January 2018. Consistent activity continued into January 2018 with few notable changes. The lava lake inside the Overlook vent at Halema'uma'u crater rose and fell by a few meters over hours and days; on the East Rift Zone the lava pond persisted at Pu'u 'O'o cone, and scattered breakouts from the episode 61g lava flow continued. Early on 19 January two earthquakes of magnitude 2.4 and 2.5 occurred on the lower East Rift Zone near Leilani Estates. Also on 19 January, a rockfall from the wall of Halema?uma?u crater plunged into the lava lake producing a short-lived explosion of spatter and wallrock that blanketed an area around the former visitor overlook. Debris fell as far as the Halema'uma'u parking lot (figure 312).

Figure 312. Spatter up to about 30 cm in size was thrown onto the rim of Halema'uma'u crater at Kīlauea during explosive events on 19 January 2018. Some fragments were thrown or blown farther downwind, reaching as far as the closed section of Crater Rim Drive in Hawai'i Volcanoes National Park. The boot of an HVO scientist, who entered the area to check on HVO's webcameras, is shown here for scale. Courtesy of HVO.

HVO noted that spattering from the lava lake at Halema'uma'u was visible from the visitor overlook overnight during 25-26 January. Spatter appeared again briefly the next day, and overnight during 29-30 January. Four spattering sites were visible on a clear 30 January day (figure 313). Webcam views overnight on 30-31 January showed that incandescence persisted from the small lava pond on the W side of the Pu'u 'O'o crater. On the morning of 26 January a new breakout from the episode 61g flow appeared on the pali. By the end of January, most of the breakouts from the episode 61g flow field were concentrated at the base of the pali and on the upper flow field, with little activity on the coastal plain.

Figure 313. Clear views at the summit of Kīlauea on 30 January 2018 revealed four spattering sites visible on the surface of the Halema'uma'u lava lake inside the Overlook vent. Through the gas plume, a visible scar (light-colored wall rock) from the 19 January rockfall that triggered an explosive event, could be seen on the southern Overlook vent wall. Another, smaller scar on the northeastern lake wall (left), resulted from two small rock falls on 24 January. Courtesy of HVO.

Activity during February 2018. The lake level inside the Overlook vent continued with daily fluctuations of several meters, between 31 and 42 m below the Halema'uma'u crater floor, during February 2018. A small veneer collapse (rockfall) into the lava lake on 23 February was visible in lava lake webcam images. Throughout the month, persistent incandescence was observed in the webcam at the Pu'u 'O'o west pit lava pond (figure 314). On 10 February a large portion of the NE rim of the west pit collapsed. Prior to and during the rim collapse, the adjacent ground also subsided. The episode 61g flow remained active at the base of the pali (figure 315) and in the upper flow field. A new breakout on the upper flow field, 1-2 km from the vent, appeared early on 26 February. A small swarm of earthquakes occurred in the upper East Rift Zone on 21 February; the largest event was a M 2.3. Seismicity throughout the volcano was otherwise at normal rates throughout the month.

Figure 314. Incandescence from the west pit at Kīlauea's Pu'u 'O'o cone on 19 February 2018 was typical of that observed during clear weather throughout the month. Courtesy of HVO.

Figure 315. 'A'a flows at the base of Pulama pali at Kīlauea on 20 February 2018 produced shimmers of heat (top center) and incandescent fragments. Rubble from the flow rolled downhill, as the molten center slowly pushed forward. Courtesy of HVO.

Activity during March 2018. A brief swarm of small earthquakes occurred in the upper East Rift Zone on 2 March 2018. An ongoing long-period earthquake swarm at 5-10 km depth beneath the caldera began late on 6 March and continued into the next day. At the Halema'uma'u crater, the lava lake fluctuated daily, with levels ranging from a low of 40.5 m below the crater floor to a high of 20 m below it. Changes in levels of up to 10 m in a 24-hour period were common. Vigorous spattering was observed on 6 March (figure 316). On 16 March, the lava lake rose high enough (26 m below the crater floor) for active spattering to be visible in webcams mounted in the HVO tower, located across the crater from the vent. The 10th anniversary of the eruption within Halema'uma'u crater was marked on 19 March. When the vent first opened on 19 March 2008, it formed a small pit about 35 m wide. Over the following decade, the pit (informally called the "Overlook crater") grew to about 280 x 200 m in size (see figure 313).

Figure 316. Within Kīlauea volcano's summit lava lake at the Halema'uma'u crater, vigorous spattering on 6 March 2018 was occurring on the southern margin where a ledge of solidified lava had built out from the vent wall. Courtesy of HVO.

Notable inflationary tilt at Pu'u 'O'o cone began on 12 March 2018; GPS stations also started recording extension across the cone on that date. A small increase in seismic events was observed at Pu'u 'O'o on the evening of 21 March. Increased views of spattering from the west pit lava pond were visible beginning the following day, likely due to subsidence over the previous months as reported by HVO. During the evening of 25 March lava flowed out of a vent in the SE part of the crater floor and continued to expand for the rest of the month (figure 317). Inflationary tilt slowed significantly on 27 March. Cracks along the ridge between the main crater and the west pit continued to grow throughout the month as the ridge continued to subside (figure 318).

Figure 317. On 25 March 2018 a small lava flow began erupting onto the Pu'u 'O'o crater floor at Kīlauea for the first time since May 2016. In this thermal image, taken by the PTcam on 26 March 2018 at 1318, the flow (bright color) appears to be supplied by one of the small spatter cones in the crater's south embayment. The lava flow did not extend beyond the crater. This type of activity is not unusual for Pu'u 'O'o. Courtesy of HVO.

Figure 318. At Pu'u 'O'o on Kīlauea's East Rift Zone, the ridge separating the main crater (top) from the west pit (bottom) had been subsiding over the previous several months due to small rockfalls and unstable ground when this image was taken on 27 March 2018. As the ground shifted, cracks along the ridge and on both sides of it continued to open. The lava pond within the west pit rose several meters during March and produced overflows (darker lava) onto the floor of the pit as it rose. A small lava flow also erupted onto the floor of the main crater on 25 March and remained active through 27 March, visible as the lava darker in color in the foreground of the main crater floor. Courtesy of HVO.

By 20 March surface lava flow activity from the episode 61g flow near the base of the pali appeared to have diminished, and only sparse lava flow activity on the coastal plains was noted after 23 March. Activity on the upper flow field, closer to Pu'u 'O'o, continued (figure 319). A 30 March overflight by HVO confirmed no flow activity on the coastal plain or the pali.

Figure 319. Active lava breakouts were scarce across the episode 61g flow field on Kīlauea's East Rift Zone, with active flows confined to an area approximately 1-2 km from Pu'u 'O'o during March 2018. This breakout from the lava tube consisted of fluid pahoehoe and was photographed on 27 March 2018 during an overflight. The incandescent area is several meters across. Courtesy of HVO.

Activity during 1-16 April 2018. Constant spattering at the Overlook vent lava lake (figure 320) was intermittently visible from HVO and the Jagger Museum during April 2018 as the lake level rose and fell several meters on a daily basis. Its lowest level of the month was 32 m below the crater floor, and a general inflationary trend throughout the month resulted in significant overflows onto the floor of Halema'uma'u crater at the end of the month. A rockfall in the morning of 6 April triggered an explosion at the summit lava lake that damaged the power system to the Halema'uma'u crater rim webcams (figure 321). A moderate swarm of over 200 earthquakes occurred on 11 April at depths of 7-9 km below the summit; the largest event in the sequence was M 2.4. Seismicity returned to its background rate in the early morning of 12 April. Three minor ledge collapses, common while the lava lake level is lowering, occurred on 12 April.

Figure 320. A clear view of Kīlauea's summit lava lake in the Overlook vent on 4 April 2018 revealed spattering on the N side and center of the lake surface, a departure from its more common location on the SE side of the lake; this occasionally happened when the surface flow direction reversed. Spattering is caused by gas bubbles bursting within the lava lake. Courtesy of HVO.

Figure 321. On 6 April 2018 at 1028 HST a partial collapse of the southern Overlook crater wall triggered an explosive event at Kīlauea's summit lava lake. A large plume of gas, ash, and lava fragments rose from the lava lake and was visible from the Jaggar overlook. The explosion threw debris onto the Halema'uma'u crater rim at the old visitor overlook, which has been closed due to ongoing volcanic hazards such as this explosive event. Courtesy of HVO.

For the first half of April 2018, steady minor inflation continued at Pu'u 'O'o, interrupted by brief episodes of sharp deflation that appeared related to small lava flows on the crater floor. During an overflight on 13 April HVO geologists viewed a perched lava pond inside the west pit (figure 322). A slight increase in seismicity in the Upper East Rift Zone began overnight during 15-16 April; the largest event was a M 2.9 earthquake.

Figure 322. During an overflight of Kīlauea on 13 April 2018 geologists from HVO observed that lava within the west pit at Pu'u 'O'o had formed a perched lava pond (center) contained within a levee. This levee, formed by an accumulation of hardened lava, confined molten lava to the perched pond, which allowed the lava surface to rise higher than the west pit floor. If the pond rises high enough, lava can spill over the levee, forming small flows around the margin of the perched pond. Courtesy of HVO.

At the beginning of April 2018 the episode 61g lava flow was active only above the Pulama pali. The areas of the upper flow field with active lava flows were located within the Kahauale'a Natural Area Reserve, which has been closed to the public since 2007 due to volcanic hazards. On 13 April 2018, geologists observed scattered breakouts from the 61g flow within about 2.2 km from Pu'u 'O'o and another sluggish breakout about 5 km from Pu'u 'O'o (figure 323).

Figure 323. An HVO geologist photographed an active pahoehoe breakout on 13 April 2018 at Kīlauea after taking a lava sample nearby. This breakout was located approximately 0.4 km from the episode 61g vent. As the flow inflated, internal pressure cracked the rigid crust of the flow allowing molten lava to ooze out. Courtesy of HVO.

Activity during 17-30 April 2018. Beginning in mid-April 2018 seismometers recorded an increase in the number of small earthquakes beneath the summit and upper East Rift Zone reflecting increased pressurization. Kīlauea's summit and East Rift Zone magma systems are connected, with changes at one sometimes leading to changes at the other. Tiltmeters, GPS, web cameras, and field observations, continued to record inflation at the Halema'uma'u crater, at Pu'u 'O'o, and at the upper portion of the episode 61g lava tube system. HVO noted that this inflation could lead to the opening of a new vent on or near Pu'u 'O'o that could cause a significant drop in the summit lake level.

At the Halema'uma'u crater, inflation significantly outpaced deflation for the second half of April. In the afternoon of 18 April the lake level was at 25 m below the crater floor. A lengthy episode of inflation brought the lava to within 6 m of the floor on the afternoon of 21 April. As the level continued to rise, a small overflow along the S crater rim occurred about midnight overnight on 21-22 April (figure 324). The lava lake was below the rim again the next morning but spilled out several times over the next several days to the N, S, and SW. The flows, similar to those produced during the last significant overflow event in April-May 2015, consisted of lobate sheets of shelly pahoehoe traveling as far as 375 m across the floor of Halema'uma'u. A small overflow had also occurred in October 2016.

Figure 324. The rising summit lava lake levels first peaked overnight on 21-22 April 2018, producing small overflows onto the floor of Halema'uma'u Crater at Kīlauea. The largest overflow, on the N side of the Overlook vent (shown here), reached about 80 m from the lake margin. Image taken on 22 April 2018, courtesy of HVO.

The summit lava lake spilled out of the Overlook crater rim multiple times during 22-27 April, caused by repeated inflation-deflation cycles (figures 325-327). Between overflows, the lava column receded below the crater rim. An overflight during the afternoon of 23 April showed that the overflows covered about 30% of the Halema'uma'u crater floor, approximately 16 ha. The height of the lava lake, on the floor of Halema'uma'u crater, was 79 m below the rim of the crater on 25 April. HVO estimated that only about one quarter of the floor of the crater remained uncovered by new flows as of 26 April. Summit tiltmeters continued to record an overall inflationary trend with brief periods of deflation until turning to more sustained deflation around midnight overnight on 26-27 April. A magnitude 3.2 earthquake occurred around 1308 HST on 26 April but did not cause any eruptive changes. Seismometers recorded a few small earthquakes in the upper East Rift Zone and south part of the caldera during 25-29 April.

Figure 325. On 24 April 2018 between around 2030 and 2300, Kīlauea's summit lava lake overflowed again. The large overflow spread W (to the right) from the lava lake onto the floor of Halema'uma'u around 2230 in this image. The bright (yellow-white) spot is spattering along the S margin of the lava lake. USGS photo by M. Patrick, courtesy of HVO.

Figure 326. Beginning at approximately 0615 on 26 April 2018 a new overflow began covering about 36 hectares (90 acres) of Kīlauea's Halema'uma'u crater floor with lava, continuing for about four hours and covering about two-thirds of crater floor. This was the largest overflow since the summit eruption began in 2008. In this view to the S taken later in the day, the gas plume was being produced by the lava lake in the SE crater floor (upper left). Courtesy of HVO.

Figure 327. This thermal image (looking S) taken on 26 April 2018 at Kīlauea shows the active overflows from the lava lake (upper left) onto the Halema'uma'u crater floor. View is toward the south. Courtesy of HVO.

The summit lake level dropped 16 m during 27-28 April, ending the period of inflation that produced the overflows onto the crater floor. The lake level remained about 15 m below the floor when skies cleared on 30 April and permitted a view from the webcam (figure 328). Slight inflation returned later in the day and the lake level rose to just beneath the vent rim.

Figure 328. A break in the weather on the morning of 30 April 2018 allowed HVO's webcam to capture this image of the lava lake within Halema'uma'u at the summit of Kīlauea. Following multiple overflows of the lava lake the previous week, the lake level dropped after summit deflation. Early that morning, the lava lake level was estimated to be about 15 m below the vent rim, but shortly thereafter, the summit switched to inflation, and the lake level rose to just below the vent rim. Courtesy of HVO.

HVO released a Volcanic Activity Notice, in addition to their regular daily report, midday on 17 April 2018. They noted that observations and measurements at Pu'u 'O'o during the previous month suggested that the magma system had become increasingly pressurized, raising the possibility that a new vent could form at any time, either on the Pu'u 'O'o cone or along adjacent areas. Since mid-March there had been uplift of the Pu'u 'O'o crater floor by several meters. Similar episodes of inflation and uplift at Pu'u 'O'o occurred in May-June 2014, prior to the start of the June 27th flow (active 2014-2016) and May 2016 before the start of the ongoing episode 61g flow.

When measured during a site visit on 18 April the pond level in the west pit at Pu'u 'O'o was 7 m higher than it had been in late March as a result of lava overflows building up the surrounding levee. An overflight on 23 April showed the perched lava pond with overflows slowly filling the pit (figure 329), and significant cracks on the NE part of the crater rim (figure 330). The pond had another overflow that remained in the pit on 24 April, and the floor continued to rise. Inflationary tilt continued at Pu'u 'O'o until it leveled off around midnight during 26-27 April, but the crater floor continued to rise for the next four days.

Figure 329. On the East Rift Zone of Kīlauea, the perched lava pond in Pu'u 'O'o's west pit persisted during the second half of April, seen here on 23 April 2018. Overflows of the pond levees were slowly filling the bottom of the west pit and raising the floor. Courtesy of HVO.

Figure 330. Ongoing uplift of the crater floor of Pu'u 'O'o at Kīlauea beginning in mid-March 2018 generated numerous cracks on the crater floor and around the rim. These cracks cut through both recent lava flows (darker color) and older flows on the crater floor. Image taken on 23 April 2018, courtesy of HVO.

Just after 1400 on 30 April 2018, a marked increase in seismicity and ground deformation began at Pu'u 'O'o. A few minutes later, a thermal webcam (PTcam) located on the crater rim showed the first of two episodes of floor collapse; the second collapse began at 1520 and lasted about an hour. Webcam views into the crater and surrounding area were frequently obscured by poor weather conditions. However, shortly after 1600 the PTcam recorded images that were likely the signature of small explosions from the western side of the crater as the floor collapsed.

Following the collapse there was an increase in seismicity and deformation from the summit to an area about 10-16 km downrift (east) of Pu'u 'O'o. Overnight, this activity continued to propagate eastward along the rift zone. The largest earthquake of this sequence was a magnitude 4.0 just offshore south of Pu'u 'O'o at 0239 on the morning of 1 May. HVO field crews were turned back the next morning by ash in the air above Pu'u 'O'o, likely due to continuing collapse within the crater and vigorous gas emissions. Reddish ash was also noted in abundance on the ground around Pu'u 'O'o.

Lava flow activity in the episode 61g flow continued on the upper flow field through the end of April 2018. Activity was focused above the pali and closer to Pu'u 'O'o, within 2 km of the vent. After the explosion and collapse of the crater floor at Pu'u 'O'o on 30 April, a large amount of red ash was deposited around the cone and covered over some of the active breakouts of the 61g flow (figure 331).

Figure 331. The collapse of the Pu'u 'O'o crater floor at Kīlauea on 30 April 2018 produced a large amount of red ash that was deposited around Pu'u 'O'o, as well as blown farther downwind, with a thin dusting of ash reaching uprift (west) as far as Mauna Ulu. On 1 May 2018, a layer of red ash covered active 61g lava flow surface breakouts in an area between 1-2 km from the 61g vent. Courtesy of HVO.

Geologic Background. Kilauea overlaps the E flank of the massive Mauna Loa shield volcano in the island of Hawaii. Eruptions are prominent in Polynesian legends; written documentation since 1820 records frequent summit and flank lava flow eruptions interspersed with periods of long-term lava lake activity at Halemaumau crater in the summit caldera until 1924. The 3 x 5 km caldera was formed in several stages about 1,500 years ago and during the 18th century; eruptions have also originated from the lengthy East and Southwest rift zones, which extend to the ocean in both directions. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1,100 years old; 70% of the surface is younger than 600 years. The long-term eruption from the East rift zone between 1983 and 2018 produced lava flows covering more than 100 km2, destroyed hundreds of houses, and added new coastline.

Information Contacts: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawai'i National Park, HI 96718, USA (URL: http://hvo.wr.usgs.gov/).

Three volcanoes in the Kirishimayama volcanic complex experienced heightened activity during late 2017 and early 2018. There were explosions at Shinmoedake during September-October 2017 and March-May 2018, an explosion at Iwo-yama in April 2018, and heightened seismicity at Ohachi in February 2018 (BGVN 43:06). Activity weakened afterwards, and by the beginning of July the three volcanoes were relatively quiet except for some fumarolic activity and seismic activity. This report documents activity between June and November 2018. Most of the information was provided in Japan Meteorological Agency (JMA) monthly reports.

Activity at Shinmoedake during June 2018. JMA reported that an explosion at 0909 on 22 June generated an ash plume that rose 2.6 km above the crater rim and drifted E. Tephra was ejected 1.1 km away, and shock waves were felt in the Miyazaki region. Minor amounts of ash fell in Kirishima prefecture and Kagoshima prefecture to the S, Miyakonojo city (Miyazaki prefecture) to the E, and Takahara Town. Another explosion at 1534 on 27 June generated a plume that rose 2.2 km above the crater rim.

According to JMA, since the beginning of May the rate of deformation had slowed, and tiltmeter data showed no change. In addition, sulfur dioxide emissions had decreased from 1,000 tons/day on mid-March to 80 tons/day on 1 June. Based on the data, JMA believed the magma supply had declined, decreasing the possibility of an eruption affecting an area outside a radius of 2 km. Thus, on 28 June, JMA lowered the Alert Level from 3 to 2.

Activity at Iwo-yama during June-July 2018. Activity weakened in May, and no volcanic explosions occurred after 27 April. However, active fumarolic activity and ejection of mud continued through November from the vent on the S side. During 23-30 July, white plumes rose 300-500 m above the vent. Also on the S side, the hot lake, which was muddy in May, became transparent in June, but was cloudy again in July. Fumarolic activity also occurred at a vent 500 W of the crater.

Volcanic earthquakes slightly increased in late May. According to measurements by the Global Navigation Satellite System (GNSS), the volcano, which had been contracting, began to expand slowly at the beginning of June. The Alert Level remained at 2.

Geologic Background. Kirishimayama is a large group of more than 20 Quaternary volcanoes located north of Kagoshima Bay. The late-Pleistocene to Holocene dominantly andesitic group consists of stratovolcanoes, pyroclastic cones, maars, and underlying shield volcanoes located over an area of 20 x 30 km. The larger stratovolcanoes are scattered throughout the field, with the centrally located Karakunidake being the highest. Onamiike and Miike, the two largest maars, are located SW of Karakunidake and at its far eastern end, respectively. Holocene eruptions have been concentrated along an E-W line of vents from Miike to Ohachi, and at Shinmoedake to the NE. Frequent small-to-moderate explosive eruptions have been recorded since the 8th century.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html).

After a major eruption on 26 October 2010 that subsided in early December of that year, Merapi erupted regularly amid elevated seismicity between 13 June 2011 and April 2014; seismicity returned to normal levels in May 2014 (BGVN 39:10). Renewed activity in the form of phreatic explosions took place during May-June 2018.

Lahar in October 2016. According to the Badan Nasional Penanggulangan Bencana (BNPB) (National Disaster Management Agency), a lahar on 27 October 2016 induced by moderate to heavy rain swept nine sand mining trucks down the Bebeng River on the SW flank; at least one truck was buried and six were severely damaged. There were no fatalities as the miners and other people at the scene escaped. Material at the summit and on the flanks produced during the October-November 2010 eruption was an estimated 20-25 million cubic meters, contributing to the continuing high potential of lahars during heavy rain. BNPB recommended that the public remain vigilant during rainy weather because a lahar formed on the upper flanks of Merapi can reach the bottom in less than 30 minutes. The Alert Level remained at 1 (on a scale of 1-4).

Phreatic explosions during May-June 2018. The volcano was apparently quiet between November 2016 and April 2018. According to the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), an explosion occurred at 0740 on 11 May 2018. The eruption began with a small roar and vibrations that were felt at the observation post for 10 minutes. A plume rose to 5.5 km above the summit. There was no seismic precursor and no subsequent seismic activity. According to a news account (The Jakarta Post) on 11 May, the increased activity caused Yogyakarta's Adisutjipto International Airport (27 km S) to close, resulting in the cancellation of eight Garuda Indonesia flights. PVMBG did not increase the alert level from Green/Normal; they interpreted the explosion as being a minor event triggered by the accumulation of volcanic gases, and unlikely to result in subsequent explosions. High levels of sulfur dioxide in the vicinity of the volcano were detected by the satellite-based Ozone Monitoring Instrument (OMI) on 11 May; concentrations reached as high as 2.0 Dobson Units.

On 21 May a phreatic explosion began at 0125 and lasted for 19 minutes, generating an ash plume that rose 700 m above the crater and drifted W. At 0938, another phreatic explosion began that lasted six minutes and produced an ash plume that rose 1.2 km above the crater. Ashfall from both events was reported in areas 15 km downwind. A third event, detected at 1750, lasted three minutes and produced a plume of unknown height. After these events, one volcano-tectonic (VT) earthquake and one tremor event were recorded. The seismicity along with increased phreatic events prompted PVMBG to raise the Alert Level to 2.

According to PVMBG, on 23 May, at 1349 the Babadan observation post heard a two-minute-long phreatic explosion. A plume was not visible due to inclement weather, though minor ashfall was reported at the Ngepos observation post. On 24 May an event at 0256 generated an ash plume that rose 6 km above the crater rim and drifted W. Roaring was heard at all the Merapi observation posts. A two-minute-long event at 1048 produced an ash plume that rose 1.5 km and drifted W. PVMBG recommended the evacuation of everyone within 3 km of the summit.

PVMBG reported that on 1 June, at 0820, an event generated an ash plume that rose at least 6 km above the crater rim and drifted NW, then SW (figure 68). Ashfall was reported at the Selo observation post. Observers noted white smoke rising from a forested area 1.5 km NW, possibly indicating burning vegetation. PVMBG indicated that VT events were occurring at about 3 km below the crater. Later that day at 2024, an ash plume from a 1.5-minute-long event rose 2.5 km above the crater rim and drifted NE and W. At 2100, an ash plume rose 1 km and drifted NW. The Alert Level remained at 2.

Figure 68. Photo of an explosion at Merapi on 1 June 2018. Courtesy of Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency.

Geologic Background. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities.

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/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); The Jakarta Post (URL: http://www.thejakartapost.com/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).