The Weekly Volcanic Activity Report: May 5 - 11, 2021

The Weekly Volcanic Activity Report: May 5 - 11, 2021

New activity/unrest was reported for 3 volcanoes from May 5 to 11, 2021. During the same period, ongoing activity was reported for 17 volcanoes.

New activity/unrest: Bulusan, Luzon (Philippines) | Nevados de Chillan, Chile | Piton de la Fournaise, Reunion Island (France).

Ongoing activity: Aira, Kyushu (Japan) | Ebeko, Paramushir Island (Russia) | Fuego, Guatemala | Karymsky, Eastern Kamchatka (Russia) | Kilauea, Hawaiian Islands (USA) | Krysuvik-Trolladyngja, Iceland | Lewotolok, Lembata Island (Indonesia) | Merapi, Central Java (Indonesia) | Pacaya, Guatemala | Sangay, Ecuador | Santa Maria, Guatemala | Semeru, Eastern Java (Indonesia) | Semisopochnoi, Aleutian Islands (USA) | Sheveluch, Central Kamchatka (Russia) | Sinabung, Indonesia | Soufriere St. Vincent, St. Vincent | Suwanosejima, Ryukyu Islands (Japan).

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

Bulusan, Luzon (Philippines)

12.769°N, 124.056°E, Summit elev. 1535 m

PHIVOLCS stated that unrest at Bulusan had increased, noting that 62 volcanic earthquakes were recorded during 7-10 May and 124 were recorded during 10-11 May. Inflation of the upper flanks first recorded on 6 March in tilt data was sustained. GPS data indicated short-term inflation starting in late February, though the long-term pattern since July 2019 showed deflation. The data suggested shallow hydrothermal processes. The Alert Level for Bulusan was raised to 1 on 11 May, reflecting abnormal conditions, and the public was reminded not to enter the 4-km-radius Permanent Danger Zone (PDZ).

Geological summary: Luzon's southernmost volcano, Bulusan, was constructed along the rim of the 11-km-diameter dacitic-to-rhyolitic Irosin caldera, which was formed about 36,000 years ago. It lies at the SE end of the Bicol volcanic arc occupying the peninsula of the same name that forms the elongated SE tip of Luzon. A broad, flat moat is located below the topographically prominent SW rim of Irosin caldera; the NE rim is buried by the andesitic complex. Bulusan is flanked by several other large intracaldera lava domes and cones, including the prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the NE. The summit is unvegetated and contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Many moderate explosive eruptions have been recorded since the mid-19th century.

Nevados de Chillan, Chile

36.868°S, 71.378°W, Summit elev. 3180 m

SERNAGEOMIN noted that sulfur dioxide emissions and thermal anomalies at Nevados de Chillán’s Nicanor Crater had both increased in March, and inflation began on 27 March. During the second half of April the dome grew at a higher rate, with growth concentrated on the W part. The dome was 66 m high at the center. The L5 lava flow advanced and was about 940 m long, and 50 m thick near the flow front. The effusion rate increased on 28 April. During 2-5 May activity was characterized by increased crater incandescence and a series of intense explosions that destroyed part of the summit lava dome. Dense ash plumes rose above the crater. Block-and-ash flows traveled less than 400 m down the NE flank and pyroclastic flows traveled short distances SW. During 4-5 May the effusion rate increased and the L5 lava flow advanced. A new lava flow (L6) emerged on 5 May from the summit crater and descended 100 m down the NE flank. A high-temperature elongated deposit in between the L5 and L6 flows was visible in infrared images. The Alert Level remained at Yellow, the second lowest level on a four-color scale. ONEMI stated that Alert Level Yellow (the middle level on a three-color scale) remained in place for the communities of Pinto and Coihueco, noting that the public should stay at least 2 km away from the crater.

Geological summary: The compound volcano of Nevados de Chillán is one of the most active of the Central Andes. Three late-Pleistocene to Holocene stratovolcanoes were constructed along a NNW-SSE line within three nested Pleistocene calderas, which produced ignimbrite sheets extending more than 100 km into the Central Depression of Chile. The largest stratovolcano, dominantly andesitic, Cerro Blanco (Volcán Nevado), is located at the NW end of the group. Volcán Viejo (Volcán Chillán), which was the main active vent during the 17th-19th centuries, occupies the SE end. The new Volcán Nuevo lava-dome complex formed between 1906 and 1945 between the two volcanoes and grew to exceed Volcán Viejo in elevation. The Volcán Arrau dome complex was constructed SE of Volcán Nuevo between 1973 and 1986 and eventually exceeded its height.

Piton de la Fournaise, Reunion Island (France)

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

OVPF reported that the eruption at Piton de la Fournaise continued during 4-11 May. Both craters were active, producing lava flows that mainly traveled though lava tubes. Lava emerged from the end of the flow field, advancing E to 1,200 m elevation by 8 May, and setting fire to local vegetation. Minor inflation of the summit area was recorded. Lava fountaining was weak at the smaller vent to the SE and a small lava pond continued to occupy the crater of the larger cone, just NW a higher elevation. Gas plumes rose from both craters, though the plumes from the smaller crater were denser. An 11 May report stated that the larger cone was 35 m tall and 226 m in diameter at its base. 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.

Ongoing activity

Aira, Kyushu (Japan)

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

JMA reported that during 3-10 May incandescence from Minamidake Crater (at Aira Caldera’s Sakurajima volcano) was visible nightly. There were four explosions and four non-explosive events during 3-7 May, producing ash plumes that rose as high has 2.5 km above the summit and ejecting bombs 0.8-1.1 km away from the crater. Very small eruptive events were recorded during 7-10 May. The sulfur dioxide emission rate was 1,300 tons per day on 19 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.

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 4-6 May that sent ash plumes to 2.5 km (8,200 ft) a.s.l. and drifted N and SE. A thermal anomaly was identified in satellite data on 5 May. 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.

Fuego, Guatemala

14.473°N, 90.88°W, Summit elev. 3763 m

INSIVUMEH reported that 5-12 explosions per hour were recorded during 4-11 May at Fuego, generating ash plumes as high as 1.1 km above the crater rim. Shock waves sometimes rattled buildings around the volcano. Ashfall was reported daily in several areas downwind, including Morelia (9 km SW), Panimaché I and II (8 km SW), Santa Sofía (12 km SW), El Porvenir (8 km ENE), Sangre de Cristo (8 km WSW), and San Pedro Yepocapa (8 km NW). Block avalanches descended the Ceniza (SSW), Seca (W), Trinidad (S), Taniluyá (SW), Las Lajas (SE), and Honda drainages, often reaching vegetated areas. Explosions ejected incandescent material 100-450 m above the summit during 4-8 May.

Geological summary: Volcán Fuego, one of Central America's most active volcanoes, is also one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between Fuego and Acatenango to the north. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at the mostly andesitic Acatenango. Eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

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 during 29-30 April and 1 May; weather clouds prevented observations during 2-7 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 the W vent on the inner NW wall of Kilauea's Halema`uma`u Crater continued to supply the lava lake at a low rate during 5-11 May through a submerged inlet. The depth of the lake was 229 m by 11 May. Lava continued to circulate in the W part, though the active area continued to shrink. The E half of the lake remained solidified and comprised about 93 percent of the total area, based on thermal measurements acquired on 16 April. The sulfur dioxide emission rate was 200-300 tons per day during 5-7 May, and 150 tons per day on 10 May, continuing a downward trend that began in mid-April. 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

IMO reported that the fissure eruption in the W part of the Krýsuvík-Trölladyngja volcanic system, close to Fagradalsfjall on the Reykjanes Peninsula, continued during 5-11 May. On 2 May pulsating high jets of lava from crater 5 prompted authorities to widen the restricted zone because; ash and lava could be deposited several hundred of meters away. Cycles of lava jetting and effusion periodically continued during 3-7 May, with lava steadily enlarging the flow field. By 4 May the area of the flow field had grown to 1.41 square kilometers, and the total volume erupted was 23 million cubic meters. Activity was quiet for a period of time during 8-9 May, though IMO noted that fountaining quickly resumed during the morning of 9 May. High jets of lava occurred every 10 minutes, sometimes with jets rising as high as 300 m. Tephra (a few centimeters in diameter) was deposited as far as 1 km from the vent and small amounts of tephra were reported in Gríndavík. Hot deposits have caused small vegetation fires within a few hundreds of meters around the eruption site. On 10 May gas plumes rose higher than 2 km a.s.l. The eruption area was closed due to local wildfires and unfavorable wind conditions. Very high fountains were visible in Reykjavik. On 11 May lava fountains again rose up to 300 m tall and were seen from the capital. The cone had grown to about 50 m high. The Aviation Color Code remained at Orange due to the lack of ash and tephra emissions.

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 mostly white plumes from Lewotolok rose as high as 600 m and drifted SE, W, and NW during 4-11 May. Gray-and-white plumes rose 500 m and drifted W, NW, and SE on 6 and 8 May. 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 30 April-6 May. The SW rim lava-dome volume was an estimated 1.1 million cubic meters on 2 May, with a growth rate of about 17,000 cubic meters per day, and continued to shed material down the flank. A total of 12 pyroclastic flows traveled a maximum of 2 km down the SW flank. Incandescent avalanches, recorded 74 times, traveled as far as 2 km down the SW flank and twice went 600 m SE. The volume of the summit lava dome was 1.7 million cubic meters on 2 May, with a growth rate of about 14,000 cubic meters per day. Electronic Distance Measurement (EDM) data showed a distance shortening between points in the NW at a rate of 0.6 cm per day, indicating minor inflation. 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

INSIVUMEH reported that during 4-11 May the lava flow on Pacaya’s N flank continued to advance, lengthening from 2.1 to 2.4 km, and spreading laterally in some areas. Incandescent blocks detached from the flow, especially along the flow margins and steep slopes. Occasional explosions at the vent (near Cerro Chino) ejected incandescent material as high as 100 m. Around 0600 on 6 May explosions at the summit produced ash plumes that drifted S. Dense ash plumes were visible drifting W and SW during 7-9 May. On 11 May an advancing lava flow on the SW flank was 2.3 km long.

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.

Sangay, Ecuador

2.005°S, 78.341°W, Summit elev. 5286 m

IG reported a high level of activity at Sangay during 5-11 May. Seismicity was characterized by 3-28 daily explosions, long-period earthquakes, lahar events, and signals indicating emissions. Weather clouds and rain sometimes prevented visual observations of the volcano, especially during 8-9 May. Based on the Washington VAAC and occasional webcam images, ash plumes were visible during 4-8 and 10 May rising as high as 2 km above the summit and drifting mainly NW, W, and SW. Eruptions during midmorning and again around noon on 7 May produced ash plumes that rose 2.3 km and drifted WSW; higher plumes rose 5.4 km and drifted NW. Notable ashfall was reported in multiple places in the afternoon; in Guamote (40 km WNW), in Riobamba, and Alusí. A lava flow descended the SE flank. Minor amounts of ash fell in parts of the Guayas province in the morning of 8 May. The seismic network recorded lahar signals during 7-10 May.

Geological summary: The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador's volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within horseshoe-shaped calderas of two previous edifices, which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been sculpted by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of a historical eruption was in 1628. More or less continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

Santa Maria, Guatemala

14.757°N, 91.552°W, Summit elev. 3745 m

INSIVUMEH reported that during 4-11 May daily explosions at Santa María’s Santiaguito lava-dome complex generated ash plumes that rose as high as 1.1 km above the summit and drifted W, SW, and S. Collapses of blocky lava from Caliente dome sent avalanches down the SE, S, SW, and W flanks, sometimes reaching the base, and causing minor ashfall around the volcano. Ashfall was also reported in San Marcos (8 km SW) and Loma Linda Palajunoj (6 km WSW) during 5-6 and 10-11 May.

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

Semeru, Eastern Java (Indonesia)

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

PVMBG reported that Semeru continued to erupt during 4-11 May. Avalanches of material traveled 200-300 m SE down the Kobokan drainage on 6 May. Gray-and-white plumes rose 200-500 m above the summit and drifted S during 8-9 May. Avalanches of material traveled as far as 700 m down the Kobokan drainage. 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 lowered the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory for Semisopochnoi on 7 May, noting that no ash emissions had been observed nor explosions recorded since 26 April. Sulfur dioxide emissions were recorded on 1 and 5 May, signifying continued unrest. Steam plumes were visible rising from the N crater of Mt. Cerberus on 7 May.

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 30 April-7 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 4-11 May. Weather conditions sometimes prevented visual observations of the volcano, though white fumarolic plumes were visible almost daily rising as high as 500 m above the summit and drifting in multiple directions. Daily avalanches descended 500-1,500 m down the E and SE flanks. At 1119 on 6 May an ash plume rose 2 km above the summit and drifted E. At 0908 and 1519 on 7 May ash plumes rose 3 km and drifted E. Ash plumes rose 1-2.8 km and drifted E, WNW, and W at 1044, 1656, and 1841 on 8 May; plumes were also seen on 9 May. At 0747 on 10 May an ash plume rose 2.5 km and drifted SW. Ash plumes on 11 May rose 700 m and drifted W at 0712, and rose 1.5 km and drifted E at 1428. 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

On 6 May government authorities lowered the Alert Level to Orange for Soufrière St. Vincent (often simply referred to as “La Soufriere”) based on recommendations from University of the West Indies Seismic Research Centre (UWI-SRC). The public was allowed to return to their homes in the Yellow and Orange zones, though access to the Red Zone remained restricted. UWI-SRC noted that over the previous few days continuing lahars had mobilized boulders 5 m in diameter and were steamy in areas where they contacted hot deposits. A small lahar signal was recorded at 0740 on 7 May. Sulfur dioxide emissions were measured from a boat near the W coast, yielding a flux of 208 tons per day on 9 May. Seismicity remained low through 11 May with only a few long-period earthquakes recorded by the seismic network.

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 35 explosions at Suwanosejima's Ontake Crater produced eruption plumes that rose as high as 2.4 km above the crater rim during 30 April-7 May. Large volcanic bombs were ejected 700 m from the crater. Crater incandescence was visible nightly. 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.

Source: GVP

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