The Weekly Volcanic Activity Report: October 27 – November 2, 2021

the-weekly-volcanic-activity-report-october-27-november-2-2021

New activity/unrest was reported for 2 volcanoes from October 27 to November 2, 2021. During the same period, ongoing activity was reported for 19 volcanoes.

New activity/unrest: Kilauea, Hawaiian Islands (USA) | Ulawun, New Britain (Papua New Guinea).

Ongoing activity: Aira, Kyushu (Japan) | Ebeko, Paramushir Island (Russia) | Fuego, Guatemala | Fukutoku-Oka-no-Ba, Volcano Islands (Japan) | Great Sitkin, Andreanof Islands (USA) | Ibu, Halmahera (Indonesia) | Karymsky, Eastern Kamchatka (Russia) | La Palma, Spain | Lewotolok, Lembata Island (Indonesia) | Merapi, Central Java (Indonesia) | Pavlof, United States | Popocatepetl, Mexico | Reventador, Ecuador | Sangay, Ecuador | Santa Maria, Guatemala | Semeru, Eastern Java (Indonesia) | Semisopochnoi, Aleutian Islands (USA) | Sheveluch, Central Kamchatka (Russia) | 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

Kilauea, Hawaiian Islands (USA)

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

HVO reported that the summit eruption at Kilauea continued during 26 October-2 November at a vent in the lower W wall of Halema`uma`u Crater. Lava entered the lake through a breach in the E part of the W wall cone, feeding the lake which had risen 52 m since 29 September. The lava lake was not level; the W end was 8 m higher than the stagnant E part on 27 October. The sulfur dioxide emission rate was high at 3,600 tonnes per day on 28 October. Lava fountains rose less than 10 m from the W vent, though by 29 October low roiling and spatter bursts were also observed. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

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.

Ulawun, New Britain (Papua New Guinea)

5.05°S, 151.33°E, Summit elev. 2334 m

RVO reported increased unrest at Ulawun. Very small discrete seismic events had been recorded for the past several months by the seismometer located on the SW flank, 5 km from the summit. A small thermal anomaly was identified in satellite images at around 0500 on 3 November. At approximately 0800 RSAM values increased to 100, and by 1115, had risen to 1,400. The values fluctuated between 100 and 1,000 units at least through 1300 when the data was summarized. Tremor was detected on a seismometer at Ulamona, 11-12 km NW from the summit, during periods with higher RSAM values. Steam emissions rose from the crater.

Geological summary: The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Ongoing activity

Aira, Kyushu (Japan)

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

JMA reported that incandescence from Minamidake Crater (at Aira Caldera’s Sakurajima volcano) was visible at night during 25 October-1 November. Two very small eruptions were detected on 28 and 31 October. 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

On 31 October an explosion at Ebeko produced an ash plume that rose to 1.8 km (5,900 ft) a.s.l. and drifted 5 km NE. KVERT raised the Aviation Color Code to 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 3-14 explosions per hour were recorded at Fuego during 26 October-2 November, generating ash plumes as high as 1.1 km above the crater rim and shock waves felt in communities around the volcano. Ash plumes mostly drifted as far as 50 km SW, W, and NW and 20 km N and S, causing almost daily ashfall in several areas downwind, including Morelia (9 km SW), Panimaché I and II (8 km SW), Santa Sofía (12 km SW), Yucales (12 km SW), El Porvenir (8 km ENE), Finca Palo Verde, La Rochela, 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), and Las Lajas (SE) drainages, often reaching vegetated areas. Explosions ejected incandescent material 100-400 m above the summit each day.

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.

Fukutoku-Oka-no-Ba, Volcano Islands (Japan)

24.285°N, 141.481°E, Summit elev. -29 m

The Japan Coast Guard reported that floating pumice from the mid-August Fukutoku-Oka-no-Ba eruption had arrived at coastlines more than 1,000 kilometers away in early October. The pumice first arrived at Kitadaito Island (1,035 km W) on 8 October. In late October pumice circled Okinawa and Maejima islands (1,422 km W) and several ports in the Kagoshima prefecture (1,322 NW). The pumice damaged hundreds of boats and ships, clogged harbors, and impacted the fishing and tourism industries in several areas. Several local governments began the process of removing the pumice from the water.

Geological summary: Fukutoku-Oka-no-ba is a submarine volcano located 5 km NE of the pyramidal island of Minami-Ioto. Water discoloration is frequently observed from the volcano, and several ephemeral islands have formed in the 20th century. The first of these formed Shin-Ioto ("New Sulfur Island") in 1904, and the most recent island was formed in 1986. The volcano is part of an elongated edifice with two major topographic highs trending NNW-SSE, and is a trachyandesitic volcano geochemically similar to Ioto.

Great Sitkin, Andreanof Islands (USA)

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

AVO reported that lava flows on Great Sitkin’s S and W flanks were 600 m long by 27 October based on satellite images, and lava effusion likely continued during 27 October-2 November. Seismicity remained elevated and was characterized by small earthquakes consistent with ongoing lava flows. Elevated surface temperatures were occasionally detected in satellite images. 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.

Ibu, Halmahera (Indonesia)

1.488°N, 127.63°E, Summit elev. 1325 m

PVMBG reported that during 26 October-2 November gray-and-white ash plumes from Ibu rose 200-800 m above the summit and drifted N, W, and S. There were at least 151 eruptive events observed during 28-30 October. The Alert Level remained at a 2 (on a scale of 1-4), and the public was warned to stay at least 2 km away from the active crater and 3.5 km away on the N side.

Geological summary: The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, has contained several small crater lakes. The 1.2-km-wide outer crater is breached on the N, creating a steep-walled valley. A large cone grew ENE of the summit, and a smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. The first observed and recorded eruption was a small explosion from the summit crater in 1911. Eruptive activity began again in December 1998, producing a lava dome that eventually covered much of the floor of the inner summit crater along with ongoing explosive ash emissions.

Karymsky, Eastern Kamchatka (Russia)

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

KVERT reported that during 22 and 26-28 October explosions at Karymsky generated ash plumes that rose as high as 4 km (13,100 ft) a.s.l. and drifted 65 km E and SE. A thermal anomaly was visible on 22 and 28 October. 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.

La Palma, Spain

28.57°N, 17.83°W, Summit elev. 2426 m

The eruption at La Palma continued during 26 October-2 November, characterized by Strombolian explosions, lava fountaining from multiple vents, advancing and branching lava flows, and daily ash emissions. Eruption details are based on official sources including PEVOLCA (Plan de Emergencias Volcánicas de Canarias) steering committee summaries issued daily. Seismicity remained elevated, with most earthquakes located 10-15 km deep (though some were as deep as 38 km); dozens of events were felt by local residents and some were felt across the entire island. A M 5 earthquake was recorded at 0724 on 30 October at a depth of 35 km and was the largest earthquake recorded since the beginning of the eruption. A second M 5 earthquake was recorded at 1852 on 1 November and had a depth of 38 km. Both of these events, as well as some of the other notable earthquakes, were felt across La Palma Island and in some areas of La Gomera and Tenerife islands.

The vents in the main cone continued to effuse lava, eject tephra, and produce sometimes dense and billowing ash-and-gas plumes that rose 2.2-5 km (7,200-16,400 ft) a.s.l. Several vents in the main cone were active, though the activity levels varied in intensity throughout the week. A small collapse of the upper part of the main cone on 26 October caused lava to flow W over previous flows that filled in some small gaps where they had not previously covered. Beginning around noon on 29 October a series of intense and audible explosions occurred for several hours, generating a large amount of ash that was distributed across the valley. The tallest ash plumes were observed during 30-31 October. Audible explosions and significant ash emissions continued intermittently through 2 November, with ashfall affecting the entire W and NW parts of the island. Authorities issued multiple air quality alerts warning residents of some affected areas (Los Llanos de Aridane in particular), to stay indoors and, if going outside, to wear a filtering mask. For a period of time on 31 October the larger explosions were accompanied by shock waves and concurrently, the effusion rate at the NW flank vent notably increased. Sulfur dioxide emissions fluctuated at high levels between 4,990 and 22,000 tons per day during 27 October-2 November and showed an overall downward trend during the last week in October; no estimates were made on 29 October due to technical difficulties.

Lava effused at a high rate from a vent on the NW flank of the main cone, flowing through pre-existing lava channels and tubes, and occasionally breaking out and forming new flows. The lava-flow field was characterized by three main areas: the initial main flow that traveled W, flowing around the S part of Montaña de Todoque, toward the sea and creating a lava delta, a flow that had branched off of the main flow to the S, and the flows that traveled W along the N margins of the main flow. Lava flows sometimes overflowed their channels, forming ephemeral flows that spread laterally, descended short distances, and were also transported downslope in lava tubes. The initial flow that reached the sea and formed the delta was not notably fed and was 30 m thick in some areas. The lava flows that had advanced W along the S side of Montaña de La Laguna was 86 m from the coast of Tazacorte, near the beach of El Perdido. The southern flow had advanced at a low rate and by 28 October was 400 m from the sea by 27 October. Lava that travelled SW over older flows emplaced along the S margins of the flow field overflowed the channel, bifurcated, and quickly advanced 1.5 km W and SW over new ground during 28-30 October. This lava flow continued to advance and by 2 November it was 150 m from the LP-211 road, though the advancement rate had slowed considerably to 1 meter per hour. Overall, the flow field widened to 3.1 km, with most of the expansion occurring along the S margins, and covered an estimated 9.77 square kilometers by 2 November.

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.

Lewotolok, Lembata Island (Indonesia)

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

PVMBG reported that the eruption at Lewotolok continued during 26 October-2 November. White-and-gray plumes rose as high as 1 km above the summit and drifted in multiple directions. Rumbling and banging noises were heard daily. Crater incandescence was visible on 28 October and incandescent material was ejected 100-200 m from the vent on 29 October and 1 November. 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 no morphological changes to Merapi’s SW lava dome, located just below the SW rim, and in the summit crater during 22-28 October. As many as 30 lava avalanches traveled a maximum of 1.8 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 the eruption at Pavlof continued during 27 October-2 November and was focused at a vent on the upper SE flank, near the location of the 2007 vent. Seismicity remained elevated with tremor and daily small explosion signals. The explosions likely produced low-level ash plumes that rose no higher than 3 km (10,000 ft) a.s.l., though weather clouds often prevented confirmation by satellite and webcam images. Elevated surface temperatures were visible in satellite images during 25-26 October. A small plume and discolored snow at the summit were visible in mostly clear satellite images during 27-28 October. Slightly elevated temperatures were identified in satellite images during 31 October-2 November. Minor steaming at the vent was seen in webcam images on 1 November, as well as a small ash plume that rose to a low height and dissipated quickly. 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 26 October-2 November there were 9-118 steam-and-gas emissions from Popocatépetl. Some of the emissions contained ash during 26-28 October and 31 October-1 November. 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.

Reventador, Ecuador

0.077°S, 77.656°W, Summit elev. 3562 m

IG reported that a high level of activity continued to be recorded at Reventador during 26 October-2 November; cloudy weather conditions sometimes prevented webcam and satellite views. Gas-and-ash plumes, often observed multiple times a day with the webcam or reported by the Washington VAAC, rose as high as 1.4 km above the summit crater and drifted mainly W, NW, N, and NE. Ashfall was reported in El Reventador village on 27 October. At night during 26 and 30-31 October and 1 November incandescent blocks were observed rolling 500-700 m down the flanks in all directions.

Geological summary: Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic Volcán El Reventador stratovolcano rises to 3562 m above the jungles of the western Amazon basin. A 4-km-wide caldera widely breached to the east was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1300 m above the caldera floor to a height comparable to the caldera rim. It has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. The largest historical eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

Sangay, Ecuador

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

IG reported a high level of activity at Sangay during 27 October-2 November. Seismicity was characterized by 120-175 daily explosions, long-period earthquakes, lahar events, and signals indicating emissions. Weather clouds and rain often prevented visual and webcam observations of the volcano, though almost daily ash-and-gas plumes were identified in satellite images by the Washington VAAC or in webcam views; plumes rose 570-2,000 m above the volcano and drifted N, NW, W, and SW. Thermal anomalies over the volcano were often visible in satellite data. Incandescent material was observed descending the SE flank on 31 October.

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 almost daily ash plumes from Santa Maria’s Santiaguito lava-dome complex rose 500-900 m during 26 October-2 November, depositing ash on the flanks and in Monte Claro during 1-2 November. Extrusion continued at the summit dome complex and generated block-and-ash flows that traveled down the dome’s flanks in several directions, often reaching the base. Incandescence from the crater was visible at night.

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 on 31 October two ash plumes from Semeru were observed rising 400-500 m above the summit and drifting SW. Eruptive activity was recorded the next day, though plumes were not visually observed. 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 eruptive activity at Semisopochnoi's North Cerberus crater continued during 26 October-2 November. Daily tremor and minor explosions were detected in seismic and infrasound data. Although weather clouds often prevented webcam and satellite views, intermittent, low-level ash emissions were visible during clear views, rising as high as 3.7 km (12,000 ft) a.s.l. and dissipating quickly. Sulfur dioxide emissions were detected during 26-27 and 30-31 October. 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 22-29 October. 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.

Suwanosejima, Ryukyu Islands (Japan)

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

JMA reported that an explosion at 1317 on 26 October at Suwanosejima's Ontake Crater produced an eruption plume that rose as high as 3.3 km above the crater rim and ejected material 1.9 km away from the crater. Ashfall was reported in Toshima village (4 km SSW). No explosions were recorded during 29 October-1 November, though eruption plumes rose as high as 2.4 km and tephra was ejected 400 m from crater. The Alert Level remained at 3 and the public was warned to stay 2 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.

Reference:

Global Volcanism Program, 2021. Report on Kilauea (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 27 October-2 November 2021. Smithsonian Institution and US Geological Survey.

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