8-8-8-8-8-8-8-8-8-8-8-8-8 From: "Marlow, JoAnna" <MarlowJ@xxxxxx> Smithsonian / USGS Weekly Volcanic Activity Report 21-27 May 2025 Sally Sennert - Weekly Report Editor (kuhns@xxxxxx) URL: https://volcano.si.edu/reports_weekly.cfm <https://urldefense.com/v3/__https://volcano.si.edu/reports_weekly.cfm__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6YBOcXyZA$> New Activity/Unrest: Kanlaon, Philippines | Lewotobi, Indonesia Ongoing Activity: Ahyi, United States | Aira, Japan | Great Sitkin, United States | Home Reef, Tonga | Karymsky, Russia | Kilauea, United States | Kirishimayama, Japan | Lewotolok, Indonesia | Marapi, Indonesia | Merapi, Indonesia | Poas, Costa Rica | Semeru, Indonesia | Sheveluch, Russia The Weekly Volcanic Activity Report is a cooperative project between the Smithsonian's Global Volcanism Program and the US Geological Survey's Volcano Hazards Program. Updated by 2300 UTC every Wednesday, these reports are preliminary and subject to change as events are studied in more detail. This is not a comprehensive list of all of Earth's volcanoes erupting during the week, but rather a summary of activity at volcanoes that meet criteria discussed in detail in the "Criteria and Disclaimers" section. Carefully reviewed, detailed reports about recent activity are published in issues of the Bulletin of the Global Volcanism Network. Note that many news agencies do not archive the articles they post on the Internet, and therefore the links to some sources may not be active. To obtain information about the cited articles that are no longer available on the Internet contact the source. New Activity/Unrest Kanlaon | Philippines | 10.4096°N, 123.13°E | Summit elev. 2422 m The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported continuing unrest at Kanlaon during 20-26 May. The seismic network recorded 1-31 daily volcanic earthquakes. Daily sulfur dioxide emissions ranged from 653 to 1,836 tonnes per day. Gas-and-steam emissions generally rose 75-700 m above the crater rim and drifted NW, W, SW, and SSW. According to Civil Defense PH, heavy rain on 22 May generated lahars that overflowed the Tamburong creek at the Tamburong Bridge in Barangay Biaknabato. The lahar deposits, consisting of mud and volcanic debris, blocked the Biaknabato Bridge and a portion of the Biaknabato Highway in La Castellana. The Alert Level remained at 3 (on a scale of 0-5); the public was warned to stay 6 km away from the summit and pilots were warned not to fly close to the volcano. Geologic Summary. Kanlaon volcano (also spelled Canlaon) forms the highest point on the Philippine island of Negros. The massive andesitic stratovolcano is covered with fissure-controlled pyroclastic cones and craters, many of which are filled by lakes. The largest debris avalanche known in the Philippines traveled 33 km SW from Kanlaon. The summit contains a 2-km-wide, elongated northern caldera with a crater lake and a smaller but higher active vent, Lugud crater, to the south. Eruptions recorded since 1866 have typically consisted of phreatic explosions of small-to-moderate size that produce minor local ashfall. Sources: Philippine Institute of Volcanology and Seismology (PHIVOLCS) http://www.phivolcs.dost.gov.ph/ <https://urldefense.com/v3/__http://www.phivolcs.dost.gov.ph/__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6aIDBBixg$> ; Office of Civil Defense, Republic of the Philippines https://www.ocd.gov.ph/index.php <https://urldefense.com/v3/__https://www.ocd.gov.ph/index.php__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6aUBpSLPQ$> Lewotobi | Indonesia | 8.542°S, 122.775°E | Summit elev. 1703 m In a special 25 May report the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) stated that eruptive activity at Lewotobi Laki-laki had decreased after the larger 18 May eruption and subsequent ash plumes and crater incandescence observed during 19-20 May. Seismicity indicated decreasing surface activity and magmatic recharge at depth during 20-25 May, and tiltmeter data indicated deflation. No rumbling was heard and no incandescence was visible at the summit. An eruptive event at 0649 on 23 May produced a dense gray ash plume that rose around 300 m above the summit and drifted SW and W. Later that day a drone flight over the summit revealed that dark lava had filled the crater, covering about 87,000 square meters. At 0900 on 25 May the Alert Level was lowered to 3 on a scale of 1-4) and the public was warned to stay 6 km away from the center of Laki-laki. White steam-and-gas plumes rose as high as 800 m above the crater rim and drifted in various directions during 25-28 May. Geologic Summary. The Lewotobi edifice in eastern Flores Island is composed of the two adjacent Lewotobi Laki-laki and Lewotobi Perempuan stratovolcanoes (the "husband and wife"). Their summits are less than 2 km apart along a NW-SE line. The conical Laki-laki to the NW has been frequently active during the 19th and 20th centuries, while the taller and broader Perempuan has had observed eruptions in 1921 and 1935. Small lava domes have grown during the 20th century in both of the summit craters, which are open to the north. A prominent cone, Iliwokar, occurs on the E flank of Perampuan. Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM) http://vsi.esdm.go.id/ <https://urldefense.com/v3/__http://vsi.esdm.go.id/__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6ZY8T4Htw$> Ongoing Activity Ahyi | United States | 20.42°N, 145.03°E | Summit elev. -75 m No activity at the Ahyi Seamount was detected in either satellite or acoustic data from underwater pressure sensors near Wake Island (about 2,270 km E) during 17-23 May, though unrest continued. The Exploration Vessel Nautilus visited the area and deployed a remotely operated vehicle (ROV) on 19 May. The observations confirmed that lava had erupted over the past few years, building the summit to within 50-60 m of the ocean surface. Ahyi remained active with vigorous degassing of bubbles observed across a broad area of the summit. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level remained at Advisory (the second lowest level on a four-level scale). Geologic Summary. Ahyi seamount is a large conical submarine volcano that rises to within 75 m of the ocean surface ~18 km SE of the island of Farallon de Pajaros in the northern Marianas. Water discoloration has been observed there, and in 1979 the crew of a fishing boat felt shocks over the summit area, followed by upwelling of sulfur-bearing water. On 24-25 April 2001 an explosive eruption was detected seismically by a station on Rangiroa Atoll, Tuamotu Archipelago. The event was well constrained (+/- 15 km) at a location near the southern base of Ahyi. An eruption in April-May 2014 was detected by NOAA divers, hydroacoustic sensors, and seismic stations. Source: US Geological Survey https://www.usgs.gov/ <https://urldefense.com/v3/__https://www.usgs.gov/__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6Ztr9Tihw$> Aira | Japan | 31.5772°N, 130.6589°E | Summit elev. 1117 m The Japan Meteorological Agency (JMA) reported ongoing eruptive activity at Minamidake Crater (Aira Calderaâ??s Sakurajima volcano) during 19-28 May. The seismic network recorded 44 eruptive events and 38 explosions during 19-23 May that produced ash plumes rising up to 3 km above the crater rim and drifting N; the tallest plume followed an explosion at 1500 on 20 May. Large blocks from the explosions were ejected as far as 1.2 km from the crater rim. Sulfur dioxide emissions were extremely high, averaging 11,200 tons per day (t/d) on 20 May and 4,300 t/d on 22 May. Deformation data indicated continuing inflation. Only very small eruptive events were recorded during 26-28 May. The Alert Level remained at 3 (on a 5-level scale), and the public was warned to be cautious within 2 km of both the Minimadake and Showa craters. Geologic Summary. 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. Source: Japan Meteorological Agency (JMA) http://www.jma.go.jp/jma/ <https://urldefense.com/v3/__http://www.jma.go.jp/jma/__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6YhQtesIQ$> Great Sitkin | United States | 52.076°N, 176.13°W | Summit elev. 1740 m The Alaska Volcano Observatory (AVO) reported that slow lava effusion continued to feed a thick flow in Great Sitkinâ??s summit crater during 21-27 May; a 22 May radar image confirmed that lava was slowly advancing. Small daily earthquakes were detected by the seismic network. Weather clouds sometimes obscured views of the volcano. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale). Geologic Summary. The Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger volcano capped by a small, 0.8 x 1.2 km ice-filled summit caldera was constructed within a large late-Pleistocene or early Holocene scarp formed by massive edifice failure that truncated an older edifice and produced a submarine debris avalanche. Deposits from this and an even older debris avalanche from a source to the south cover a broad area of the ocean floor north of the volcano. The summit lies along the eastern rim of the younger collapse scarp. Deposits from an earlier caldera-forming eruption of unknown age cover the flanks of the island to a depth up to 6 m. The small younger caldera was partially filled by lava domes emplaced in 1945 and 1974, and five small older flank lava domes, two of which lie on the coastline, were constructed along northwest- and NNW-trending lines. Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano. Eruptions have been recorded since the late-19th century. Source: US Geological Survey Alaska Volcano Observatory (AVO) https://avo.alaska.edu/ <https://urldefense.com/v3/__https://avo.alaska.edu/__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6YP6yYyBw$> Home Reef | Tonga | 18.992°S, 174.775°W | Summit elev. -10 m The Tonga Geological Services reported that the eruption at Home Reef continued during 11-24 May, though satellite observations suggested decreasing activity. Thermal anomalies were last detected on 4 May and no visible ash emissions were identified in a 15 May image, though discolored water surrounding the island suggested submarine activity. Evidence for explosive activity during 20-21 May included new tephra deposits on the coneâ??s flanks and low-level ash plumes. Weather clouds often obscured views. Infrasound instruments did not detect any signals. The Aviation Color Code remained at Yellow (the second lowest level on a four-level scale, the Maritime Alert Level remained at Orange (the third level on a four-level scale) with advice to stay at least 2 nautical miles (3.7 km) from the island, and the Alert Level for residents of Vavaâ??u and Haâ??apai remained at Green (the first level on a four-level scale). Geologic Summary. Home Reef, a submarine volcano midway between Metis Shoal and Late Island in the central Tonga islands, was first reported active in the mid-19th century, when an ephemeral island formed. An eruption in 1984 produced a 12-km-high eruption plume, large amounts of floating pumice, and an ephemeral 500 x 1,500 m island, with cliffs 30-50 m high that enclosed a water-filled crater. In 2006 an island-forming eruption produced widespread dacitic pumice rafts that drifted as far as Australia. Another island was built during a September-October 2022 eruption. Source: Tonga Geological Services, Government of Tonga https://www.facebook.com/tongageologicalservice <https://urldefense.com/v3/__https://www.facebook.com/tongageologicalservice__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6aFqTnx5w$> Karymsky | Russia | 54.049°N, 159.443°E | Summit elev. 1513 m The Kamchatkan Volcanic Eruption Response Team (KVERT) reported that, in general, moderate explosive activity continued at Karymsky during 15-22 May. A thermal anomaly over the volcano was identified in satellite images during 16-18, 20, and 22 May; weather clouds obscured views on other days. The Aviation Color Code remained at Orange (the third level on a four-color scale). Dates are based on UTC; specific events are in local time where noted. Geologic Summary. Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater. Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php <https://urldefense.com/v3/__http://www.kscnet.ru/ivs/kvert/index_eng.php__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6a2Q-Prcw$> Kilauea | United States | 19.421°N, 155.287°W | Summit elev. 1222 m The Hawaiian Volcano Observatory (HVO) reported that the eruption within Kilaueaâ??s Kaluapele summit caldera, characterized by episodic fountaining from two vents along the SW margin of Halemaâ??umaâ??u Crater, continued at variable levels during 21-27 May. Incandescence at both the N and S vents was visible during 20-25 May, along with intermittent spattering at both vents and occasional dome fountaining at the N vent. Large yellow flames from burning hydrogen gas sometimes rose from the N vent. The sulfur dioxide emission rate averaged around 1,200 tonnes per day (t/d), similar to rates recorded during prior pauses between high fountaining events. After midday on 24 May minor fountaining at the N vent as high as 65 m was accompanied by lava overflowing the cone onto the crater floor. Strong incandescence and periodic vigorous spattering at both vents was visible in the afternoon of 24 May and overnight during 24-25 May. Lava fountaining at the N vent and an overspill of lava onto the crater floor also occurred overnight. Narrow lava jets rose from the N vent on 25 May and became sustained fountains at 1615 which quickly began to cover the crater floor with lava flows. The activity escalated to fountains over 300 m tall within 30 minutes. Fountaining at the S vent began at 1720 and grew rapidly, reaching sustained heights of about 250 m. The fountains produced an eruptive plume heavily laden with tephra (ash, scoria, and Pele's hair) that reached at least 4.3 km in height. Sulfur dioxide emission rates were estimated to be 50,000-75,000 t/d based on webcam images from the Mauna Loa summit. Both vents produced lava flows that covered about half of the crater floor. After about six hours of sustained fountaining, the N vent stopped erupting at 2148, and the S vent stopped erupting at approximately 2225 on 25 May. Strands of Peleâ??s hair were present throughout the summit area of Hawaiâ??i Volcanoes National Park and surrounding communities. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale). Geologic Summary. 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. Source: US Geological Survey Hawaiian Volcano Observatory (HVO) https://volcanoes.usgs.gov/observatories/hvo/ <https://urldefense.com/v3/__https://volcanoes.usgs.gov/observatories/hvo/__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6ZReb1PdQ$> Kirishimayama | Japan | 31.934°N, 130.862°E | Summit elev. 1700 m The Japan Meteorological Agency (JMA) reported that increased unrest at Shinmoedake (Shinmoe peak, a stratovolcano of the Kirishimayama volcano group) during March through early May had stabilized. Volcanic earthquakes with epicenters beneath Shinmoedake began to increase on 28 March and tiltmeter data indicated inflation on 30 March. During 22-26 April minor NW tilt was observed in inclinometer data and the number of earthquakes further increased. Volcanic tremor was detected on 27 April and during 1-2 May. During the first half of May seismicity remained high but did not significantly increase, and there were no changes detected in tiltmeter data. At 1100 on 27 May the Alert Level was lowered to 2 (on a 5-level scale) and the public was warned to exercise caution within 2 km from Shinmoedake Crater. Geologic Summary. 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. Source: Japan Meteorological Agency (JMA) http://www.jma.go.jp/jma/ <https://urldefense.com/v3/__http://www.jma.go.jp/jma/__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6YhQtesIQ$> Lewotolok | Indonesia | 8.274°S, 123.508°E | Summit elev. 1431 m The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that an eruption at Lewotolok was ongoing during 21-27 May. Daily white steam-and-gas plumes rose as high as 700 m above the summit of the cone and drifted NW and W. Gray ash plumes rose 100-500 m above the summit and drifted SE, NW, and W during 23 and 25-27 May. Clear nighttime webcam images showed incandescent material at the summit cone and on the upper S flank. The Alert Level remained at 2 (on a scale of 1-4) and the public was warned to stay 2 km away from the vent and 2.5 km away on the S, SE, and W flanks. Geologic Summary. The Lewotolok (or Lewotolo) stratovolcano occupies the eastern end of an elongated peninsula extending north into the Flores Sea, connected to Lembata (formerly Lomblen) Island by a narrow isthmus. It is symmetrical when viewed from the north and east. A small cone with a 130-m-wide crater constructed at the SE side of a larger crater forms the volcano's high point. Many lava flows have reached the coastline. Eruptions recorded since 1660 have consisted of explosive activity from the summit crater. Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM) http://vsi.esdm.go.id/ <https://urldefense.com/v3/__http://vsi.esdm.go.id/__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6ZY8T4Htw$> Marapi | Indonesia | 0.38°S, 100.474°E | Summit elev. 2885 m The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that eruptive activity at Marapi (on Sumatra) continued during 21-27 May, characterized by occasional dense ash plumes. White plumes rose 100-200 m above the summit and drifted in multiple directions during 21-22 and 24 May. Eruptive events were recorded at 1227 on 23 May and at 1457 on 26 May, though weather conditions prevented visual confirmation. On 25 May white-and-brown plumes rose 100-250 m above the summit and drifted E and SE. At 0822 on 27 May a dense white-and-gray ash plume rose 1.2 km above the summit and drifted SE. The Alert Level remained at 2 (on a scale of 1-4) and the public was warned to stay 3 km away from the active crater. Geologic Summary. Gunung Marapi, not to be confused with the better-known Merapi volcano on Java, is Sumatra's most active volcano. This massive complex stratovolcano rises 2,000 m above the Bukittinggi Plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide Bancah caldera. The summit craters are located along an ENE-WSW line, with volcanism migrating to the west. More than 50 eruptions, typically consisting of small-to-moderate explosive activity, have been recorded since the end of the 18th century; no lava flows outside the summit craters have been reported in historical time. Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM) http://vsi.esdm.go.id/ <https://urldefense.com/v3/__http://vsi.esdm.go.id/__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6ZY8T4Htw$> Merapi | Indonesia | 7.54°S, 110.446°E | Summit elev. 2910 m The Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG) reported that the eruption at Merapi (on Java) continued during 16-22 May. Seismicity remained at high levels. The SW lava dome produced 41 lava avalanches that traveled as far as 2 km SW down the Bebeng drainage, 10 that traveled as far as 1.8 km SW down the Krasak drainage, and 73 that traveled as far as 2 km W down the Sat/Putih drainage. Small morphological changes to the SW lava dome resulted from continuing effusion and minor collapses. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-7 km away from the summit, based on location. Geologic Summary. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities. Source: Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG) http://www.merapi.bgl.esdm.go.id/ <https://urldefense.com/v3/__http://www.merapi.bgl.esdm.go.id/__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6Z_AYGNGw$> Poas | Costa Rica | 10.2°N, 84.233°W | Summit elev. 2697 m The Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional (OVSICORI-UNA) reported continuing gas-and-steam emissions at Poás during 21-27 May; ash content of the plumes was either very low or not present. Sulfur dioxide gas emissions remained at high levels, though they had decreased compared to the previous week. The emissions detected in satellite data drifting SW on 20 May were estimated to be 598 tonnes per day (t/d). The fixed Differential Optical Absorption Spectroscopy (DOAS) station recorded slightly lower averages compared to the previous week, averaging around 309 t/d during 17-23 May, and a transect using a mobile DOAS instrument recorded 3,000 t/d on 22 May, similar to the previous week. Intense incandescence continued to be visible at both Boca A and Boca C vents. On 21 May the temperature at Boca A was measured with an infrared sensor mounted on a drone, revealing a maximum temperature of 470 degrees Celsius. Water continued pooling at Boca C. Pulses in acoustic data during 26-27 May likely originated from bubbling at Boca C. The volcanoâ??s Alert Level remained at 3 (the second highest level on a four-level scale). Geologic Summary. The broad vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the complex stratovolcano extends to the lower N flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, last erupted about 7,500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since an eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water. Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA) http://www.ovsicori.una.ac.cr/ <https://urldefense.com/v3/__http://www.ovsicori.una.ac.cr/__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6bnWQNnXw$> Semeru | Indonesia | 8.108°S, 112.922°E | Summit elev. 3657 m The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that activity continued at Semeru during 21-27 May, with multiple daily eruptive events recorded by the seismic network. Daily white-and-gray ash plumes rose 400-1,200 m above the summit and drifted in multiple directions. The Alert Level remained at 2 (the second lowest level on a scale of 1-4). The public was warned to stay at least 3 km away from the summit in all directions, 8 km from the summit to the SE, 500 m from the banks of the Kobokan drainage as far as 13 km from the summit, and to avoid other drainages including the Bang, Kembar, and Sat, due to lahar, avalanche, and pyroclastic flow hazards. Geologic Summary. Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano. Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM) http://vsi.esdm.go.id/ <https://urldefense.com/v3/__http://vsi.esdm.go.id/__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6ZY8T4Htw$> Sheveluch | Russia | 56.653°N, 161.36°E | Summit elev. 3283 m The Kamchatkan Volcanic Eruption Response Team (KVERT) reported that lava extrusion may have continued at Sheveluchâ??s â??300 years of RASâ?? dome on the SW flank of Old Sheveluch and at the Young Sheveluch dome during 15-22 May. Thermal anomalies over the domes were identified almost daily in satellite images; weather clouds sometimes obscured views, especially during the second half of the week. The Far Eastern Branch of the Russian Academy of Sciences (FEB RAS) reported that explosive activity was recorded by infrasound instruments on 16 May, with ash plumes that rose as high as 4.7 km above the summit and drifted NE. KVERT noted that ash plumes drifted 835 km NE and 185 km SE during 16-18 May. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Dates are based on UTC; specific events are in local time where noted. Geologic Summary. 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. Sources: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php <https://urldefense.com/v3/__http://www.kscnet.ru/ivs/kvert/index_eng.php__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6a2Q-Prcw$> ; Institute of Volcanology and Seismology (IVS) of the Far Eastern Branch of the Russian Academy of Sciences (FEB RAS) http://www.kscnet.ru/ivs/ <https://urldefense.com/v3/__http://www.kscnet.ru/ivs/__;!!IKRxdwAv5BmarQ!bTexbiROETUj09J0ThV5gBQb6rLZ7icFt1CUUUggRw-S2D4GFdTqmeRE6T3HVG0P11A3iRr3i4F4EkpCX6aEKsLAbg$> 8-8-8-8-8-8-8-8-8-8-8-8-8 ============================================================== Volcano Listserv is a collaborative venture among Arizona State University (ASU), Portland State University (PSU), the Global Volcanism Program (GVP) of the Smithsonian Institution's National Museum of Natural History, and the International Association for Volcanology and Chemistry of the Earth's Interior (IAVCEI). ASU - http://www.asu.edu/ PSU - http://pdx.edu/ GVP - https://volcano.si.edu/ IAVCEI - https://www.iavceivolcano.org/ To subscribe to the volcano list, send the message: subscribe volcano to: listserv@xxxxxxx, or write to: volcano-request@xxxxxxx To unsubscribe from the volcano list, send the message: signoff volcano to: listserv@xxxxxxx, or write to: volcano-request@xxxxxxx. To contribute to the volcano list, send your message to: volcano@xxxxxxx. Please do not send attachments. ============================================================== ------------------------------ End of Volcano Digest - 23 May 2025 to 28 May 2025 (#2025-48) *************************************************************
