The Weekly Volcanic Activity Report: May 19 – 25, 2021

New activity/unrest was reported for 3 volcanoes from May 19 – 25, 2021. During the same period, ongoing activity was reported for 18 volcanoes.

New activity/unrest: Great Sitkin, Andreanof Islands (USA) | Manam, Papua New Guinea | Nyiragongo, DR Congo.

Ongoing activity: Aira, Kyushu (Japan) | Dukono, Halmahera (Indonesia) | Ebeko, Paramushir Island (Russia) | Etna, Sicily (Italy) | Karymsky, Eastern Kamchatka (Russia) | Kilauea, Hawaiian Islands (USA) | Krysuvik-Trolladyngja, Iceland | Lewotolok, Lembata Island (Indonesia) | Merapi, Central Java (Indonesia) | Pacaya, Guatemala | Piton de la Fournaise, Reunion Island (France) | Semeru, Eastern Java (Indonesia) | Semisopochnoi, Aleutian Islands (USA) | Sheveluch, Central Kamchatka (Russia) | Sinabung, Indonesia | Soufriere St. Vincent, St. Vincent | Suwanosejima, Ryukyu Islands (Japan) | Taal, Luzon (Philippines).

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 23:00 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.

New activity/unrest

Great Sitkin, Andreanof Islands (USA)

52.076°N, 176.13°W, Summit elev. 1740 m

An increase in local earthquake activity at Great Sitkin during 24-25 May prompted AVO to raise the Aviation Color Code to Orange and the Volcano Alert Level to Watch on 25 May. An explosive eruption began later that day at 2104; the Aviation Color Code and the Volcano Alert Level were raised to Red/Warning, respectively. The explosions lasted for 1-2 minutes and produced an ash plume rising to 4.6 km (15,000 ft) a.s.l. that was observed by local mariners. Witnesses 42 km away heard “a very loud explosion.” After the explosive period seismicity decreased and satellite image images showed a detached plume drifting E. Around mid-morning on 26 May AVO lowered the Aviation Color Code and the Volcano Alert Level to Orange/ Watch, respectively.

Geological summary: The Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger parasitic 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 ancestral volcano and produced a submarine debris avalanche. Deposits from this and an 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. Historical eruptions have been recorded since the late-19th century.

Manam, Papua New Guinea

4.08°S, 145.037°E, Summit elev. 1807 m

The Darwin VAAC reported that during 20-21 May ash plumes from Manam rose to 2.1 km (7,000 ft) a.s.l. and drifted NW.

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

Nyiragongo, DR Congo

1.52°S, 29.25°E, Summit elev. 3470 m

At around 1815 on 22 May seismicity at Nyiragongo spiked, around the same time observers reported at least two fissures opening on the lower S flanks, NW of Kibati (8 km SSE) and Rukoko (10 km S). Lava from the first fissure, originating near the Shaheru crater, flowed E over a major road (N2) and then S. The second fissure produced lava flows that traveled S, overtaking and setting fire to many houses and structures in communities north of Goma, just W of Monigi (12 km S). Video posted on social media showed lava fountaining from the fissures, a glowing red sky, and residents running through the streets. About 1,000 homes and buildings were destroyed and about 25,000 people were displaced. The lava cut off electricity and water supplies to some areas. The flow may have been as wide as 1 km and stopped 1.25 km from the Goma International Airport, in the SE part of the city, during 22-23 May. According to the Toulouse VAAC ash plumes may have initially rose to 13.7 km (45,000 ft) a.s.l., though subsequent estimates put the ash plumes mostly at 6.1-9.1 km (20,000-30,000 ft) a.s.l. during 22-23 May. Satellite images and local scientists indicated that the summit lava lake had drained before the flank fissures had opened, but began refilling afterward; collapses in the summit crater were the likely cause of the ash plumes.

Initial reports indicated that about 32 people had died: about 12 from lava and gas asphyxiation while crossing lava flows, and most of the rest from accidents while fleeing. Several people, including many children, remained missing, though families were continuing to be reunited.

Seismic data during 22-24 May showed events seemingly propagating from the summit area to the S into Lake Kivu. Several strong earthquakes shook buildings in Goma, causing some to collapse and injure people; a news article noted that tremor was felt about every 30 minutes beginning around noon on 23 May. Both airports in Goma closed for security reasons. A M 5.1 earthquake with a hypocenter beneath Lake Kivu was recorded at 1037 on 24 May. The VAAC noted that ashfall around the volcano and in surrounding towns was visible in satellite data. Cracks a few 10s of centimeters wide opened in different parts of the city on 25 May. The cracks stretched for several hundred meters from the northern city limit down to the lake, and were nearly 100 m long near the airport. Some cracks were hot and emitting gasses, and some were flaming. Ash plumes rose to 6.1 km (20,000 ft) a.s.l. and drifted S; ground-based reports indicated ash in the atmosphere above Goma. Seismicity remained intense on 25 May with more than 130 earthquakes between M 2 and 5 recorded in a 24-hour period. News reports indicated hundreds of damaged buildings in neighboring Rwanda.

Geological summary: One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes of a stratovolcano contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

Ongoing activity

Aira, Kyushu (Japan)

31.593°N, 130.657°E, Summit elev. 1117 m

JMA reported that during 21-24 May incandescence from Minamidake Crater (at Aira Caldera’s Sakurajima volcano) was visible nightly. A very small eruptive event was recorded on 23 May. The Alert Level remained at 3 (on a 5-level scale), and residents were warned to stay 2 km away from the crater.

Geological 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 Aira caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim of Aira caldera and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4850 years ago, after which eruptions took place at Minamidake. Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu's largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.

Dukono, Halmahera (Indonesia)

1.693°N, 127.894°E, Summit elev. 1229 m

Based on satellite and wind model data, the Darwin VAAC reported that during 18-23 and 25 May ash plumes from Dukono rose to 2.1-2.4 km (7,000-8,000 ft) a.s.l. and drifted in multiple directions. 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.

Geological summary: 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, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. 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.

Ebeko, Paramushir Island (Russia)

50.686°N, 156.014°E, Summit elev. 1103 m

Volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, observed explosions during 14-20 May that sent ash plumes to 3.5 km (11,500 ft) a.s.l. and drifted N, NE, E, and SE. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geological summary: 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.

Etna, Sicily (Italy)

37.748°N, 14.999°E, Summit elev. 3320 m

INGV reported episodes of lava fountaining at Etna’s Southeast Crater (SEC) on 19 and 22 May that continued the recent pattern of Strombolian explosions followed by lava fountaining and lava flows. Strombolian activity began at 2340 on 19 May and produced ash plumes that drifted E. Activity intensified and lava fountains formed at 0234 on 20 May. At the same time lava overflowed the SEC and traveled SW, and within a few hours had reached 2,800 m elevation. The activity lasted about three and a half hours and then abruptly ended. The next episode during 0134-0454 on 22 May included Strombolian explosions and ash plumes that drifted SE; lava fountaining began at 0302 and flows traveled SW, overlapping the flows from 19 May. Explosions produced ash plumes that drifted SE around 0830 and 1014. Strombolian explosions intensified around 2031, producing dense ash plumes that drifted E. Lava fountains formed about two hours later, sending flows down the E and SW flanks; fountaining was over by 0038 on 23 May. A series of explosions were visible during 0351-0403, producing dense ash plumes that drifted E. Two ash plumes were observed rising from SEC’s E crater during the night and the day on 23 May. Intense explosive activity at SEC began at 1820 on 25 May, producing ash plumes that rose to 3.5 km (11,500 ft) a.s.l. and drifted E. Strombolian activity commenced at 1845 and lava fountains were visible around 2023. Lava flows were visible at 2244 and ash plumes drifted E at an altitude of 6 km (19,700 ft) a.s.l. Activity ceased by 0026 on 26 May.

Geological summary: Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Karymsky, Eastern Kamchatka (Russia)

54.049°N, 159.443°E, Summit elev. 1513 m

KVERT reported that a weak thermal anomaly over Karymsky was visible in satellite images on 13-14 and 19 May. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geological 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.

Kilauea, Hawaiian Islands (USA)

19.421°N, 155.287°W, Summit elev. 1222 m

HVO reported that lava at Kilauea's Halema`uma`u Crater lava lake circulated in a 20-m-diameter area on 19 May but was stagnant and crusted over on other days through 25 May. A few minor oozes of lava between the W vent and main island were occasionally visible. The depth of the lava lake was 229 m and had remained unchanged since 11 May. Sulfur dioxide emissions were 100-150 tons per day during 19-23 May, close to the less than 50 tonnes per day measured during the non-eruptive period from late 2018 to late 2020. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Geological summary: Kilauea, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 km2, destroying nearly 200 houses and adding new coastline to the island.

Krysuvik-Trolladyngja, Iceland

63.917°N, 22.067°W, Summit elev. 360 m

The fissure eruption in the W part of the Krýsuvík-Trölladyngja volcanic system, close to Fagradalsfjall on the Reykjanes Peninsula, continued during 19-25 May. Lava fountains rose from the fifth vent and continued to feed the lava flows. According to news sources, lava during 20-21 May overtook the eastern earthen dam that had been constructed at the head of Nátthaga valley in an attempt to prevent flows from descending towards Highway 427 (Suðurstrandarvegur) to the S, and burying fiber optic cables. By 22 May the lava was about 2.5 km from the road. The Aviation Color Code remained at Orange due to the lack of ash and tephra emissions. Authorities warned of increased gas emissions hazards.

Geological summary: The Krýsuvík-Trölladyngja volcanic system is described by the Catalogue of Icelandic Volcanoes as an approximately 50-km-long composite fissure swarm trending about N38°E, including a 30-km-long swarm of fissures, with no central volcano. It is one of the volcanic systems arranged en-echelon along the Reykjanes Peninsula west of Kleifarvatn lake. The Fagradalsfjall and Krýsuvík fissure swarms are considered splits or secondary swarms of the Krýsuvík–Trölladyngja volcanic system. Small shield volcanoes have produced a large portion of the erupted volume within the system. Several eruptions have taken place since the settlement of Iceland, including the eruption of a large basaltic lava flow from the Ogmundargigar crater row around the 12th century. The latest eruption, identified through tephrochronology, took place during the 14th century.

Lewotolok, Lembata Island (Indonesia)

8.274°S, 123.508°E, Summit elev. 1431 m

PVMBG reported that white-and-gray plumes from Lewotolok rose as high as 800 m and drifted W and E during 18-24 May. Rumbling was heard almost daily. Crater incandescent was visible on 18 May and on 22 May incandescent material was ejected 400-700 m to the SE. The Alert Level remained at 3 (on a scale of 1-4) and the public was warned to stay 3 km away from the summit crater.

Geological 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.

Merapi, Central Java (Indonesia)

7.54°S, 110.446°E, Summit elev. 2910 m

BPPTKG reported that the lava dome just below Merapi’s SW rim and the lava dome in the summit crater both continued to extrude lava during 14-20 May. The SW rim lava-dome volume was an estimated 1.284 million cubic meters, with a growth rate of about 11,700 cubic meters per day, and continued to shed material down the flank. A total of seven pyroclastic flows traveled a maximum of 2 km down the SW flank. Incandescent avalanches, recorded 58 times, traveled as far as 2 km down the SW flank and once went 800 m SE. The summit lava dome had not changed since the previous week. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 5 km away from the summit.

Geological 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.

Pacaya, Guatemala

14.382°N, 90.601°W, Summit elev. 2569 m

In a special 15 May bulletin INSIVUMEH noted that lava effusion at Pacaya ceased and activity instead was characterized by explosive activity at the summit crater. Ash-and-gas plumes rose 1 km and drifted downwind, causing ashfall in San Francisco de Sales, Concepción El Cedro, Aldea El Patrocinio, and San Miguel Petapa. Explosions ejected material up to 100 m above the summit. Ash plumes rose around 500 m above the summit and drifted 5-10 km N, NW, SW, and S during 18-21 and 24-25 May. Some explosions were recorded by the seismic network during 22-23 May; white-and-blue gas plumes rose 300-700 m and drifted 5 km W during 23-24 May.

Geological summary: Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.

Piton de la Fournaise, Reunion Island (France)

21.244°S, 55.708°E, Summit elev. 2632 m

OVPF reported that gas emissions rose from the cones at Piton de la Fournaise during 18-19 and 22-23 May; inclement weather conditions prevented visual observations on days in between. The eruption likely ceased around 0200 on 24 May, when tremor subsided, though inclement weather again prevented visual confirmation. The Alert Level remained at 2-2.

Geological summary: The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.

Semeru, Eastern Java (Indonesia)

8.108°S, 112.922°E, Summit elev. 3657 m

PVMBG reported that Semeru continued to erupt during 18-25 May. Gray-and-white plumes rose 100-700 m above the summit and drifted S, SW, and N during 18-23 May. Avalanches of material occurred four times on 18 May, traveling as far as 500 m down the Kobokan drainage. Ash plumes rose 600 and 400 m and drifted N on 21 and 22 May, respectively. The Alert Level remained at 2 (on a scale of 1-4), with a general exclusion zone of 1 km and extensions to 5 km in the SSE sector.

Geological 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.

Semisopochnoi, Aleutian Islands (USA)

51.93°N, 179.58°E, Summit elev. 1221 m

AVO reported that sulfur dioxide and steam plumes from Semisopochnoi were possibly visible in satellite images during 19-20 May. Satellite images on 21 May showed a sulfur dioxide gas plume drifting 160 km SE. Steam plumes rose from Cerberus on 24 May. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Geological summary: 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 was constructed within the caldera during the Holocene. Each of the peaks contains a summit crater; lava flows on the N flank of Cerberus 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 Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone could have been recently active.

Sheveluch, Central Kamchatka (Russia)

56.653°N, 161.36°E, Summit elev. 3283 m

KVERT reported that a thermal anomaly over Sheveluch was identified in satellite images during 14-21 May. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geological summary: The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. 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 dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. 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.

Sinabung, Indonesia

3.17°N, 98.392°E, Summit elev. 2460 m

PVMBG reported that the eruption at Sinabung continued during 19-25 May. Pyroclastic flows traveled 3 km down the E and SE flanks at 0448 on 19 May. A dense gray ash plume rose as high as 3.5 km above the summit and drifted E and S. White-and-gray plumes rose 100-400 m and drifted NE, E, SE, and S on 20 May. The Alert Level remained at 3 (on a scale of 1-4), with a general exclusion zone of 3 km and extensions to 5 km in the SE sector and 4 km in the NE sector.

Geological summary: Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. The youngest deposit is a SE-flank pyroclastic flow 14C dated by Hendrasto et al. (2012) at 740-880 CE. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

Soufriere St. Vincent, St. Vincent

13.33°N, 61.18°W, Summit elev. 1220 m

University of the West Indies Seismic Research Centre (UWI-SRC) and National Emergency Management Organisation (NEMO) reported that seismicity at Soufrière St. Vincent (often simply referred to as “La Soufriere”) remained low during 17-24 May, with a few long-period and volcano-tectonic earthquakes occasionally recorded. Persistent steaming from the crater was visible on days when weather permitted views, and thermal anomalies continued to be identified in satellite data. Sulfur dioxide emissions were 461 tons per day on 20 May. NEMO noted that the total number of displaced people was 22,759 on 15 May though the number continued to fluctuate as people arrived at shelters while others returned home or changed locations. The Alert Level remained at Orange.

Geological summary: Soufrière St. Vincent is the northernmost and youngest volcano on St. Vincent Island. The NE rim of the 1.6-km wide summit crater is cut by a crater formed in 1812. The crater itself lies on the SW margin of a larger 2.2-km-wide caldera, which is breached widely to the SW as a result of slope failure. Frequent explosive eruptions after about 4,300 years ago produced pyroclastic deposits of the Yellow Tephra Formation, which cover much of the island. The first historical eruption took place in 1718; it and the 1812 eruption produced major explosions. Much of the northern end of the island was devastated by a major eruption in 1902 that coincided with the catastrophic Mont Pelée eruption on Martinique. A lava dome was emplaced in the summit crater in 1971 during a strictly effusive eruption, forming an island within a lake that filled the crater. A series of explosive eruptions in 1979 destroyed the 1971 dome and ejected the lake; a new dome was then built.

Suwanosejima, Ryukyu Islands (Japan)

29.638°N, 129.714°E, Summit elev. 796 m

JMA reported that intermittent eruptive activity at Suwanosejima's Ontake Crater produced plumes that rose as high as 1.6 km above the crater rim during 14-21 May. Large volcanic bombs were ejected 300 m from the crater. Crater incandescence was visible overnight during 18-19 May. The Alert Level remained at 2 and the public was warned to stay 1 km away from the crater.

Geological summary: The 8-km-long, spindle-shaped island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit is truncated by a large breached crater extending to the sea on the east flank that was formed by edifice collapse. Suwanosejima, one of Japan's most frequently active volcanoes, was in a state of intermittent strombolian activity from Otake, the NE summit crater, that began in 1949 and lasted until 1996, after which periods of inactivity lengthened. The largest historical eruption took place in 1813-14, when thick scoria deposits blanketed residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed forming a large debris avalanche and creating the horseshoe-shaped Sakuchi caldera, which extends to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

Taal, Luzon (Philippines)

14.002°N, 120.993°E, Summit elev. 311 m

PHIVOLCS reported that unrest at Taal continued during 19-25 May. Low-level background tremor that had begun at 0905 on 8 April continued. During 19-21 May there were 2-30 daily low-frequency events, 10-169 daily volcanic earthquakes, and 8-139 periods of volcanic tremor with variable durations (1-37 minutes); no earthquakes were recorded during 22-25 May. Most of the earthquakes were very shallow (less than 5 km deep) beneath Taal Volcano Island (TVI) and the NE part of Taal Lake. Daily upwelling of hot volcanic fluids in the crater lake was accompanied by sometimes voluminous steam plumes that were as tall as 2 km. Sulfur dioxide emissions were 2,811-3,611 tonnes/day. Slow and steady inflation of the Taal region was recorded by multiple instruments after the January 2020 eruption. PHIVOLCS noted the continuing state of elevated unrest, reminding the public that the Alert Level for Taal remained at 2 (on a scale of 0-5). PHIVOLCS strongly recommended no entry onto the island, and access to the Main Crater, Daang Kastila fissure (along the walking trail), and boating on Taal Lake was strictly prohibited.

Geological summary: Taal is one of the most active volcanoes in the Philippines and has produced some of its most powerful historical eruptions. Though not topographically prominent, its prehistorical eruptions have greatly changed the landscape of SW Luzon. The 15 x 20 km Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2 surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, and several eruptive centers lie submerged beneath the lake. The 5-km-wide Volcano Island in north-central Lake Taal is the location of all historical eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones that have grown about 25% in area during historical time. Powerful pyroclastic flows and surges from historical eruptions have caused many fatalities.

Source: GVP