The Weekly Volcanic Activity Report: September 15 - 21, 2021

The Weekly Volcanic Activity Report: September 15 - 21, 2021

New activity/unrest was reported for 2 volcanoes from September 15 to 21, 2021. During the same period, ongoing activity was reported for 15 volcanoes.

New activity/unrest: La Palma, Spain | Semisopochnoi, Aleutian Islands (USA).

Ongoing activity: Agung, Bali (Indonesia) | Aira, Kyushu (Japan) | Chirinkotan, Kuril Islands (Russia) | Ebeko, Paramushir Island (Russia) | Etna, Sicily (Italy) | Great Sitkin, Andreanof Islands (USA) | Karymsky, Eastern Kamchatka (Russia) | Katmai, United States | Krysuvik-Trolladyngja, Iceland | Merapi, Central Java (Indonesia) | Pavlof, United States | Popocatepetl, Mexico | Sheveluch, Central Kamchatka (Russia) | 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.

New activity/unrest

La Palma, Spain

28.57°N, 17.83°W, Summit elev. 2426 m

An eruption began at La Palma after about a week of intensifying seismicity that showed hypocenters becoming shallower and moving NW, and significant related inflation. During 17-18 September the PEVOLCA (Plan de Emergencias Volcánicas de Canarias) steering committee (comprised of representatives from multiple agencies, local authorities, and institutions) reviewed mitigation, evacuation, and emergency plans. Helicopter and drone overflights were conducted in areas thought to be at risk from an eruption. IGN reported that during 17-18 September seismicity decreased, though an M 2 felt by local residents was located at 100 m depth, and vertical deformation occurred near the earthquake epicenters.

IGN noted that seismicity intensified during the morning of 19 September, with earthquakes located at 0-6 km depth; a M 4.2 event was recorded at 1116 and vertical deformation increased. Authorities evacuated about 50 residents with reduced mobility and their companions from Las Manchas de Abajo, Jedey, San Nicolás and El Paraíso (El Paso and Los Llanos de Aridane), El Charco (Fuencaliente), La Bombilla (Los Llanos de Aridane and Tazacorte), and El Remo and Puerto Naos (Los Llanos de Aridane). Residents in an area prone to landslides were also evacuated. Other preparations continued at the hospital, in neighborhoods, and at evacuation centers.

At 1510 on 19 September an eruption began in the area of Cabeza de Vaca, in the municipality of El Paso. Observers near the eruption site observed a large explosion that ejected material and produced a gas-and-ash plume; volcanic tremor was recorded by the seismic network. Two 200-m-long fissures aligned N-S opened about 200 m apart. INVOLCAN scientists observed seven vents along the fissures during the initial stage of the eruption. Multiple tall lava fountains fed flows downslope to the W, igniting forest fires. Photos and video posted by IGN showed multiple pulsating fountains fanning out from parts of the fissure. Ash plumes rose about 1.5 km and gas plumes rose 3 km and drifted ESE. The PEVOLCA steering committee briefly raised the Alert Level to Orange, and then to Red (the highest level on a four-color scale) by 1700 for high-risk municipalities directly affected by the eruption. About 5,500 people evacuated with no injuries reported, and authorities recommended that residents stay at least 2 km from the vents. The La Palma airport briefly closed, livestock were evacuated, and education centers were closed along with sections of multiple highways. Later that day INVOLCAN scientists who measured an area of the flows determined an average flow rate of 700 m per hour and temperatures around 1,075 degrees Celsius. By the next day a main cone had formed.

The sulfur dioxide gas emission rate was 6,000-11,500 tons per day during 19-20 September. Satellite data showed a plume of sulfur dioxide drifting 475 km SE and reaching the coastline of Africa by 20 September. A map produced on 20 September by IGN in partnership with Copernicus Emergency Management Service (EMS) showed that the main part of the lava flow had traveled more than 3 km W and another branch extended about 1.5 km WSW. The flows had covered about 1 square kilometer and destroyed an estimated 166 buildings. A news article noted that activity was concentrated at four main vents, the last (and ninth) of which opened at 1956 on 20 September about 900 m from the main vents. Strong lava fountaining continued during 20-21 September and ash fell in the vicinity of the vents. Ash plumes rose 2.4-4.6 km (8,000-15,000 ft) a.s.l. and drifted as far as 55 km SW and S according to the Toulouse VAAC. Sulfur dioxide gas plumes drifted W and E at an altitude of 3 km (10,000 ft) a.s.l. By 0814 on 21 September an updated Copernicus EMS map showed that 350 homes had been covered by lava and the flow field had expanded to 1.54 square kilometers. According to a news report lava up to 12 m thick was advancing at a rate of 200 m per hour. A few hundred more residents evacuated as lava advanced towards Tacande; bringing the number of evacuees to about 5,700. The S lava branch was advancing slowly, at a rate of 2 m per hour. Later that day INVOLCAN stated that increased volcanic tremor amplitude reflected greater intensity of Strombolian explosions at the vents.

Geological summary: The 47-km-long wedge-shaped island of La Palma, the NW-most of the Canary Islands, is composed of two large volcanic centers. The older northern one is cut by the massive steep-walled Caldera Taburiente, one of several massive collapse scarps produced by edifice failure to the SW. The younger Cumbre Vieja, the southern volcano, is one of the most active in the Canaries. The elongated volcano dates back to about 125,000 years ago and is oriented N-S. Eruptions during the past 7,000 years have formed abundant cinder cones and craters along the axis of Cumbre Vieja, producing fissure-fed lava flows that descend steeply to the sea. Eruptions recorded since the 15th century have produced mild explosive activity and lava flows that damaged populated areas. The southern tip of the island is mantled by a broad lava field emplaced during the 1677-1678 eruption. Lava flows also reached the sea in 1585, 1646, 1712, 1949, and 1971.

Semisopochnoi, Aleutian Islands (USA)

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

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 15-21 September. Weather clouds obscured views of the volcano on most days. Several small daily explosions were recorded by local seismic stations; ash plumes were not visible in satellite images suggesting that they remained below 3 km (10,000 ft) a.s.l. and did not rise above the cloud deck. Overnight during 18-19 September small, discontinuous, low-level ash plumes were visible drifting 100 km SE. Ash emissions increased in frequency and intensity on 19 September. Ash clouds rose as high as 4.6 km (15,000 ft) a.s.l. and continued to drift 100 km SE. Sulfur dioxide emissions increased in the afternoon. AVO raised the Aviation Color Code to Red and the Volcano Alert Level to Warning at 2158. Explosions continued overnight and the next day, and ash plumes rose up to 4.6 km a.s.l. Plumes drifted 100 km NW. At 2012 on 20 September AVO lowered the Aviation Color Code to Orange noting the frequency of discrete explosions had decreased to a rate of about one per hour, though ash plumes from these events were still rising to 4.6 km a.s.l. and drifting NW. Sulfur dioxide plumes drifted N during 20-21 September.

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.

Ongoing activity

Agung, Bali (Indonesia)

8.343°S, 115.508°E, Summit elev. 2997 m

PVMBG reported that activity at Agung was last observed on 13 June 2019 and a thermal anomaly over the crater was last identified in satellite images in October 2019. During the previous year deformation data indicated no changes at the volcano and seismicity decreased. During 1 Janaury-13 September white gas-and-steam plumes rose 20-50 m above the summit. On 13 September the Alert Level was lowered to 1 (on a scale of 1-4).

Geological summary: Symmetrical Agung stratovolcano, Bali's highest and most sacred mountain, towers over the eastern end of the island. The volcano, whose name means "Paramount," rises above the SE rim of the Batur caldera, and the northern and southern flanks extend to the coast. The summit area extends 1.5 km E-W, with the high point on the W and a steep-walled 800-m-wide crater on the E. The Pawon cone is located low on the SE flank. Only a few eruptions dating back to the early 19th century have been recorded in historical time. The 1963-64 eruption, one of the largest in the 20th century, produced voluminous ashfall along with devastating pyroclastic flows and lahars that caused extensive damage and many fatalities.

Aira, Kyushu (Japan)

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

JMA reported that an explosion at Minamidake Crater (at Aira Caldera's Sakurajima volcano) at 1617 on 19 September produced an eruption plume that rose 1 km above the crater rim. Crater incandescence was visible at night during 20-21 September. The report noted that inflation around the summit continued to be recorded. 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.

Chirinkotan, Kuril Islands (Russia)

48.98°N, 153.48°E, Summit elev. 724 m

SVERT and KVERT reported that volcanic activity at Chirinkotan was last observed during 23-24 August. The Aviation Color Code was lowered to Green in mid to late September.

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

Ebeko, Paramushir Island (Russia)

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

According to volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, explosions during 10-11 September produced ash plumes that rose as high as 2 km (6,600 ft) a.s.l. and drifted S 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 that tremor amplitude at Etna began gradually increasing at 0420 on 21 September and then suddenly increased at 0440. Ash emissions rose from the Southeast Crater (SEC) at 0815 and by 0855 Strombolian activity was visible. An eruption plume rose 4.5 km above the summit and drifted ENE. Within an hour lava fountaining began and the plume rose 9 km and drifted ENE. Lava overflowed the crater and traveled SW. Lava fountaining had ceased by 1130, though Strombolian activity within the crater continued. Tremor amplitude decreased at 1250 and explosive activity ceased.

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.

Great Sitkin, Andreanof Islands (USA)

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

AVO reported that lava effusion continued at Great Sitkin during 15-21 September, though weather clouds often prevented webcam and satellite views. Seismicity remained elevated and was characterized by small earthquakes consistent with lava effusion. A radar image from 16 September indicated that the lava dome had grown to 1,130 m E-W and 910 m N-S, and was about 30 m thick. The edges of the dome touched the S and W rims of the crater. Elevated surface temperatures were identified in satellite data during 20-21 September. The Aviation Color Code and the Volcano Alert Level remained at Orange and 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.

Karymsky, Eastern Kamchatka (Russia)

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

KVERT reported that a thermal anomaly over Karymsky was identified in satellite images during 10-17 September. Ash plumes rose as high as 7 km (23,000 ft) a.s.l. and drifted 180 km E and SE during 10 and 15-16 September. 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.

Katmai, United States

58.28°N, 154.963°W, Summit elev. 2047 m

AVO reported that on 21 September strong winds in the vicinity of Katmai and the Valley of Ten Thousand Smokes blew unconsolidated ash SE towards Kodiak Island at an altitude up to 2.4 km (8,000 ft) a.s.l. The ash was originally deposited during the Novarupta eruption in 1912. The Volcano Alert Level remained at Normal and the Aviation Color Code remained at Green.

Geological summary: Prior to 1912, Mount Katmai was a compound stratovolcano with four NE-SW-trending summits, most of which were truncated by caldera collapse in that year. Two or more large explosive eruptions took place from Mount Katmai during the late Pleistocene. Most of the two overlapping pre-1912 Katmai volcanoes are Pleistocene in age, but Holocene lava flows from a flank vent descend the SE flank of the SW stratovolcano into the Katmai River canyon. Katmai was initially considered to be the source of the Valley of Ten Thousand Smokes ash flow in 1912. However, the 3 x 4 km wide caldera of 1912 is now known to have formed as a result of the voluminous eruption at nearby Novarupta volcano. The steep walled young caldera has a jagged rim that rises 500-1000 m above the caldera floor and contains a 250-m-deep, still-rising lake. Lake waters have covered a small post-collapse lava dome (Horseshoe Island) that was seen on the caldera floor at the time of the initial ascent to the caldera rim in 1916. Post-1912 glaciers have formed on a bench within Katmai caldera.

Krysuvik-Trolladyngja, Iceland

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

The eruption from the fifth vent in the W part of the Krýsuvík-Trölladyngja volcanic system, close to Fagradalsfjall on the Reykjanes Peninsula, continued during 15-18 September. According to a news article lava ponded for a few days in Geldingadalur, and during 14-15 September the crust ruptured and sent a larger lava flow rapidly into the S part of the valley; the flow then turned E into the Nàtthagi valley. Authorities temporarily closed the area due to the activity and the large number of tourists; the Coast Guard rescued two people whose exit route had been cut off by the flow. Lava continued to flow on this path during 16-17 September and overtook the "A" hiking trail. Later that day at around 1800 the flow rate decreased or paused, and only minor incandescence from the vent was visible.

The Institute of Earth Sciences reported that based on aerial photography acquired on 17 September the area of the flow field had grown to 4.8 square kilometers, and the total volume erupted was 151 million cubic meters. The lava-flow rate during 11-17 September averaged 16 cubic meters per second. IMO noted that 19 September marked six months since the eruption started.

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.

Merapi, Central Java (Indonesia)

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

BPPTKG reported that no morphological changes to Merapi's two lava domes, situated just below the SW rim and in the summit crater, were detected during 10-16 September. As many as 144 lava avalanches traveled a maximum of 2 km SW. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-5 km away from the summit based on location.

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.

Pavlof, United States

55.417°N, 161.894°W, Summit elev. 2493 m

AVO reported that periods of elevated seismic tremor with no clear explosion signals were recorded at Pavlof during 14-18 September. Webcam images were mostly obscured by weather clouds. Minor ash deposits on the upper flanks and at least one minor ash emission was visible in a clear webcam view on 18 September. Small low-level ash emissions that dissipated quickly were noted by observers and visible in webcam images at 1500 on 19 September and at 0900 on 20 September. Ash deposits on the mid-flanks were identified in satellite data. Seismicity remained elevated during 2021 September; an explosion was recorded early on the 21 September. The vent in the crater continued to migrate N based on satellite data. The Volcano Alert Level and Aviation Color Code remained at Watch and Orange, respectively.

Geological summary: The most active volcano of the Aleutian arc, Pavlof is a 2519-m-high Holocene stratovolcano that was constructed along a line of vents extending NE from the Emmons Lake caldera. Pavlof and its twin volcano to the NE, 2142-m-high Pavlof Sister, form a dramatic pair of symmetrical, glacier-covered stratovolcanoes that tower above Pavlof and Volcano bays. A third cone, Little Pavlof, is a smaller volcano on the SW flank of Pavlof volcano, near the rim of Emmons Lake caldera. Unlike Pavlof Sister, Pavlof has been frequently active in historical time, typically producing Strombolian to Vulcanian explosive eruptions from the summit vents and occasional lava flows. The active vents lie near the summit on the north and east sides. The largest historical eruption took place in 1911, at the end of a 5-year-long eruptive episode, when a fissure opened on the N flank, ejecting large blocks and issuing lava flows.

Popocatepetl, Mexico

19.023°N, 98.622°W, Summit elev. 5393 m

CENAPRED reported that each day during 14-21 September there were 89-152 steam-and-gas emissions from Popocatépetl. The plumes drifted mainly NW and some contained ash. As many as five daily explosions were recorded during 14-19 September and some ejected incandescent material onto the flanks. Explosions at 1818, 1839, and 2350 on 14 September produced ash plumes that rose 1.2-1.5 km above the crater rim. Explosions at 1015 and 1441 on 15 September produced ash plumes that rose 1.8-2.2 km. During 15-17 September minor ashfall was reported in the municipalities of Cuernavaca, Valle de Chalco, Chiautla, Ixtapaluca, Nezahualcóyotl, La Paz, Ecatepec, Ayapango, Temamatla, Tenango del Aire, Tlalmanalco, Amecameca, Tepetlixpa, Tlalnepantla, and Acolman in the México State, and in Iztapalapa, Xochimilco, and Tlahuac in México City. The Alert Level remained at Yellow, Phase Two (middle level on a three-color scale).

Geological summary: Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

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 10-17 September. 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.

Soufriere St. Vincent, St. Vincent

13.33°N, 61.18°W, Summit elev. 1220 m

National Emergency Management Organisation (NEMO) reported that activity at Soufrière St. Vincent had been low over the previous few months. On 15 September the Alert Level was lowered to Yellow and remaining evacuees were allowed to return home.

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 the number of daily explosions at Suwanosejima's Ontake Crater increased on 16 September and remained elevated through 20 September. Eruption plumes rose as high as 2.4 km above the crater rim and material was generally ejected 300 m away from the crater. Notably, explosions at 2014 on 16 September and at 0212 on 17 September ejected material almost 1 km S and SE, respectively. 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: Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 15 September-21 September 2021. Managing editor: Sally Kuhn Sennert


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