The Weekly Volcanic Activity Report: October 11 – 17, 2023

the weekly volcanic activity report

New activity/unrest was reported for 3 volcanoes from October 11 to 17, 2023. During the same period, ongoing activity was reported for 18 volcanoes.

New activity/unrest: Bezymianny, Central Kamchatka (Russia) | Home Reef, Tonga Ridge | Klyuchevskoy, Central Kamchatka (Russia).

Ongoing activity: Aira, Kyushu (Japan) | Colima, Mexico | Fuego, South-Central Guatemala | Great Sitkin, Andreanof Islands (USA) | Lewotolok, Lembata Island | Mayon, Luzon (Philippines) | Merapi, Central Java | Popocatepetl, Mexico | Reventador, Ecuador | Sangay, Ecuador | Santa Maria, Southwestern Guatemala | Semeru, Eastern Java | Sheveluch, Central Kamchatka (Russia) | Shishaldin, Fox Islands (USA) | Suwanosejima, Ryukyu Islands (Japan) | Taal, Luzon (Philippines) | Villarrica, Central Chile | Wrangell, Eastern Alaska.

New activity/unrest

Bezymianny, Central Kamchatka (Russia)

55.972°N, 160.595°E | Summit elev. 2882 m

KVERT reported that activity at Bezymianny was significantly elevated during 0700-0830 on 17 October and was characterized by large collapses on the E flanks of the lava dome based on satellite and webcam images. These collapses generated hot avalanches of material and produced ash-and-gas plumes that rose as high as 3.5 km a.s.l. and drifted 15 km NE. At 1419 the Aviation Color Code was raised to Orange (the third level on a four-color scale). Lava extrusion continued at least through 1727 and ash plumes had drifted as far as 86 km NE. All times are local.

Geological summary: The modern Bezymianny, much smaller than its massive neighbors Kamen and Kliuchevskoi on the Kamchatka Peninsula, was formed about 4,700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7,000 years ago. Three periods of intensified activity have occurred during the past 3,000 years. The latest period, which was preceded by a 1,000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large open crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Home Reef, Tonga Ridge

18.992°S, 174.775°W | Summit elev. -10 m

The Tonga Geological Services reported that Home Reef was erupting with a total of 11 eruptive events detected in satellite data during 12-17 October. On 14 October the Aviation Color Code was Yellow and the Hazard Alert was Orange; on 17 October the Aviation Color Code was lowered to Green and the Hazard Alert was lowered to Yellow, though mariners continued to be advised to stay 4 km away from the island. According to the Wellington VAAC a pilot observed an ash plume below 300 m (1,000 ft) a.s.l. in the vicinity of the volcano on 17 October, though the Tonga Meteorological Services stated that the emissions were mainly composed of steam. The most recent dimensions of the island were estimated to be about 424 m N-S and 223 m E-W, with an approximate total surface area of 17 acres, based on a 10 October satellite image. The island had steep headlands on the E half and a more gradual slope on the W half.

Geological summary: Home Reef, a submarine volcano midway between Metis Shoal and Late Island in the central Tonga islands, was first reported active in the mid-19th century, when an ephemeral island formed. An eruption in 1984 produced a 12-km-high eruption plume, large amounts of floating pumice, and an ephemeral 500 x 1,500 m island, with cliffs 30-50 m high that enclosed a water-filled crater. In 2006 an island-forming eruption produced widespread dacitic pumice rafts that drifted as far as Australia. Another island was built during a September-October 2022 eruption.

Klyuchevskoy, Central Kamchatka (Russia)

56.056°N, 160.642°E | Summit elev. 4754 m

KVERT reported that the Strombolian eruption at Klyuchevskoy continued during 11-16 October and fed lava flows the descended the Apakhonchichsky drainage on the SE flank. Activity was notable during 11-12 October, characterized by the presence of ash in gas-and-steam plumes and an increase in the lava effusion rate. KVERT raised the Aviation Color Code to Orange (the third level on a four-color scale) as a result. According to observers at the Kamchatka Volcanological Station, lava effusion was almost continuous and incandescent material was ejected as high as 300 m above the crater rim. On 16 October lava on the SE flank melted snow and ice, causing phreatic explosions and large collapses of material from the margins of the flow. Dates and times are in UTC; specific events are in local time where noted.

Geological summary: Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka’s highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Ongoing activity

Aira, Kyushu (Japan)

31.5772°N, 130.6589°E | Summit elev. 1117 m

JMA reported ongoing activity at Minamidake Crater (Aira Caldera’s Sakurajima volcano) during 9-16 October, with incandescence at the crater observed nightly. During the week there were a total of 18 eruptive events and 18 explosions. Ash plumes rose as high as 2.6 km above the crater rim and large blocks were ejected 800-900 m from the vent. The Alert Level remained at 3 (on a 5-level scale), and the public was warned to stay 2 km away from both craters.

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 caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim and built an island that was joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4,850 years ago, after which eruptions took place at Minamidake. Frequent eruptions since the 8th century have deposited ash on the city of Kagoshima, located across Kagoshima Bay only 8 km from the summit. The largest recorded eruption took place during 1471-76.

Colima, Mexico

19.514°N, 103.62°W | Summit elev. 3850 m

On 13 October the Centro Universitario de Estudios Vulcanológicos (CUEV) – Universidad de Colima reported that during the previous week three lahars descended the Zarco (WSW), Montegrande (S), and La Arena drainages, triggered by Hurricane Lidia. In general, steam-and-gas emissions were low and rose from the NE part of the crater.

Geological summary: The Colima complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the high point of the complex) on the north and the historically active Volcán de Colima at the south. A group of late-Pleistocene cinder cones is located on the floor of the Colima graben west and east of the complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide scarp, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, producing thick debris-avalanche deposits on three sides of the complex. Frequent recorded eruptions date back to the 16th century. Occasional major explosive eruptions have destroyed the summit (most recently in 1913) and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.

Fuego, South-Central Guatemala

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

INSIVUMEH reported that, in general, 3-9 explosions per hour were recorded at Fuego during 10-17 October, though the rate of explosions was not noted on some of the days. The explosions generated ash-and-gas plumes that rose as high as 1.1 km above the crater rim and drifted as far as 30 km mainly SW, W, NW, and N. Minor ashfall was reported on a few of the days in areas downwind including Morelia (9 km SW), Panimaché I and II (8 km SW), Santa Sofía (12 km SW), Sangre de Cristo (8 km W), Acatenango (8 km E), San Pedro Yepocapa (8 km NW), La Soledad (7 km N), La Rochela (8 km SSW), and Las Palmas. Weak rumbling was heard daily, and shock waves were occasionally detected. Explosions caused daily block avalanches to descend various drainages including the Ceniza (SSW), Seca (W), Trinidad (S), Taniluyá (SW), Honda (E), and El Jute (ESE), and Las Lajas (SE). The explosions ejected incandescent material as high as 300 m above the summit on some of the days. In the afternoon of 11 October lahars descended the Las Lajas, El Jute, and Ceniza drainages, carrying tree branches, trunks, and blocks as large as 1.5 m in diameter.

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.

Great Sitkin, Andreanof Islands (USA)

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

AVO reported that slow lava effusion likely continued at Great Sitkin during 10-17 October and was confirmed by radar data on 15 October. A thick flow in the summit crater mainly expanded E. Weakly elevated surface temperatures were identified in satellite data during 10-11 October. Seismicity was low and only a couple of earthquakes were detected during 15-16 October. Weather clouds often obscured satellite and webcam views. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

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.

Lewotolok, Lembata Island

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

PVMBG reported that the eruption at Lewotolok continued during 11-17 October. White-and-gray ash plumes rose as high as 400 m above the summit and W, NW, and E during 11-12 and 14 October. On the other days during the week white steam-and-gas plumes rose as high as 500 m and drifted NW. At 2047 on 14 October a webcam image captured incandescent material that was ejected above the summit. The Alert Level remained at 2 (on a scale of 1-4) and the public was warned to stay at least 2 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.

Mayon, Luzon (Philippines)

13.257°N, 123.685°E | Summit elev. 2462 m

PHIVOLCS reported that slow lava effusion at Mayon’s summit crater continued during 11-17 October. The lengths of the lava flow in the Mi-Isi (S), Bonga (SE), and Basud (E) drainages remained at 2.8 km, 3.4 km, and 1.1 km, respectively. Collapses at the lava dome and from the margins of the lava flows produced incandescent rockfalls and occasional pyroclastic density currents (PDCs, or pyroclastic flows) that descended the flanks as far as 4 km. Each day seismic stations recorded 100-126 rockfall events and 1-3 PDC events. There were 1-2 daily volcanic earthquakes during 10-14 October, and 26-37 daily volcanic earthquakes during 15-17 October that also included 24-32 tremor events that lasted 1-32 minutes each. Sulfur dioxide emissions measured almost daily averaged between 797 and 1,255 tonnes per day, with the highest value recorded on 12 October. The Alert Level remained at 3 (on a 0-5 scale) and residents were reminded to stay away from the 6-km-radius Permanent Danger Zone (PDZ). PHIVOLCS recommended that civil aviation authorities advise pilots to avoid flying close to the summit.

Geological summary: Symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the most active volcano of the Philippines. The steep upper slopes are capped by a small summit crater. Recorded eruptions since 1616 CE range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often damaged populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

Merapi, Central Java

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

BPPTKG reported that the eruption at Merapi (on Java) continued during 6-12 October and seismicity remained at elevated levels. The SW lava dome produced a total of 163 lava avalanches that descended the S and SW flanks; 18 traveled as far as 1.6 km down the upper part of the Boyong drainage and 145 traveled as far as 2 km down the upper Bebeng drainage. Morphological changes to the SW lava dome were due to continuous collapses of material. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-7 km away from the summit based on location.

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.

Popocatepetl, Mexico

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

CENAPRED reported that eruptive activity continued at Popocatépetl during 10-17 October. Long-period events totaling 87-402 per day were accompanied by steam-and-gas plumes that sometimes contained minor amounts of ash. Some of the plumes drifted NW and W, though cloudy weather conditions sometimes prevented visual observations. Periods of low-amplitude and high-frequency volcanic tremor were recorded daily, each lasting 23-462 minutes. According to the Washington VAAC, a large, discrete ash plume was identified in a satellite image at 1026 on 12 October rising to 6.7 km (22,000 ft) a.s.l. and drifting NE. A thermal anomaly was also visible. A minor explosion was recorded at 0405 on 13 October by the seismic network; the VAAC reported that an ash plume was seen in satellite and webcam images at 0421 drifting almost 30 km N at an altitude of 6.1 km (20,000 ft) a.s.l. A satellite image from 0101 on 14 October showed ash fanning out to the NW at 6.7 km a.s.l. and an image from 0701 showed a continuously emitted ash plume drifting WNW and NW at the same altitude; the VAAC noted that the webcam was not operational. CENAPRED stated that a moderate explosion was recorded at 1419 on 14 October. Video taken by observers and posted on social media showed a dark ash plume rising from the volcano. At 1831 on 14 October ash emissions were ongoing and visible in webcam and satellite images drifting WNW and NW according to the VAAC. At 0626 on 15 October an ash plume was visible in satellite and webcam images slowly drifting W at an altitude of 6.4 km (21,000 ft) a.s.l. The Alert Level remained at Yellow, Phase Two (the second level on a three-color scale) and the public was warned to stay 12 km away from the crater.

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-EPN reported that the eruption at Reventador was ongoing during 10-17 October. Seismicity was characterized by 15-43 daily explosions, long-period earthquakes, harmonic tremor, and tremor associated with emissions. Several daily ash-and-gas plumes rose as high as 1.3 km above the crater rim and drifted in multiple directions. Daily crater incandescence was visible during both overnight and morning hours. Incandescent material was ejected as high as 600 m above the crater rim several times during 10-11 October. Avalanches of incandescent material descended the flanks, concentrating down the SE flank during the beginning of the week, and traveling as far as 800 m from the summit. Weather conditions sometimes prevented views of the volcano. Secretaría de Gestión de Riesgos maintained the Alert Level at Orange (the second highest level on a four-color scale).

Geological summary: Volcán El 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 stratovolcano has 4-km-wide avalanche scarp open to the E formed by edifice collapse. A young, unvegetated, cone rises from the amphitheater floor to a height comparable to the rim. It has been the source of numerous lava flows as well as explosive eruptions visible from Quito, about 90 km ESE. Frequent lahars in this region of heavy rainfall have left extensive deposits on the scarp slope. The largest recorded 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-EPN reported a high level of eruptive activity at Sangay during 10-17 October, with seismic stations recording 292-802 daily explosions. Several daily ash-and-gas plumes rose as high as 1.5 km above the crater rim and drifted N, NW, W, and SW. During overnight and morning hours webcam images showed incandescent material descending the SE flank as far as 1.8 km from the crater several times daily during overnight and early morning hours. Incandescence at the crater was often visible; incandescent material was ejected 500 m above the crater rim during 10-11 October. Secretaría de Gestión de Riesgos maintained the Alert Level at Yellow (the second highest level on a four-color scale).

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 the open 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 eroded by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of an eruption was in 1628. Almost 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, Southwestern Guatemala

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

INSIVUMEH reported that eruptive activity continued at Santa Maria’s Santiaguito lava dome complex during 11-17 October with lava extrusion at Caliente dome. Incandescence from the dome was visible during most nights and early mornings, and occasionally from the lava flow on the WSW flank. Explosions triggered incandescent avalanches that descended the dome’s flanks in all directions. Block avalanches descended drainages on the SW, S, SE, and E flanks; during 12-13 and 16-17 October the avalanches were occasionally accompanied by small pyroclastic flows. Daily weak-to-moderate explosions generated gas-and-ash plumes that rose 800-1,000 m above the dome and drifted in multiple directions. During 13-14 October explosions occurred at a rate of 1-2 per hour and produced block-and-ash flows that descended the SW, S, and SE flanks and left gray ash deposits.

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

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

PVMBG reported that eruptive activity continued at Semeru during 11-17 October, though weather conditions sometimes prevented visual observations. White-and-gray ash plumes rose 200-700 m above the summit and drifted N, SE, S, and SW during 11-12 and 14-17 October. The Alert Level remained at 3 (third highest on a scale of 1-4). The public was warned to stay at least 5 km away from the summit in all directions, 13 km from the summit to the SE, 500 m from the banks of the Kobokan drainage as far as 17 km from the summit, and to avoid other drainages including the Bang, Kembar, and Sat, due to lahar, avalanche, and pyroclastic flow hazards.

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.

Sheveluch, Central Kamchatka (Russia)

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

KVERT reported that the eruption at Sheveluch continued during 5-12 October. A daily thermal anomaly was identified in satellite images and a plume of resuspended ash drifted 90 km ESE on 11 October. The Aviation Color Code remained at Orange (the third level on a four-color scale). Dates are based on UTC times; specific events are in local time where noted.

Geological summary: The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1,300 km3 andesitic volcano is one of Kamchatka’s largest and most active volcanic structures, with at least 60 large eruptions during the Holocene. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes occur on its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large open caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Shishaldin, Fox Islands (USA)

54.756°N, 163.97°W | Summit elev. 2857 m

AVO reported that activity at Shishaldin during 10-17 October was characterized by daily sulfur dioxide gas emissions (except on 12 October) and frequent small earthquakes. Daily elevated surface temperatures were identified in satellite images. Steam-and-gas plumes observed in webcam images were reported each day, though weather conditions occasionally prevented views. The emissions were robust during 14-16 October, likely generated by the interaction of hot material and snow and ice. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Geological summary: The symmetrical glacier-covered Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. It is the westernmost of three large stratovolcanoes in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning “mountain which points the way when I am lost.” Constructed atop an older glacially dissected edifice, it is largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the W and NE sides at 1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of Strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century. A steam plume often rises from the summit crater.

Suwanosejima, Ryukyu Islands (Japan)

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

JMA reported that the eruption at Suwanosejima’s Ontake Crater continued during 9-16 October and crater incandescence was visible nightly. During 11-12 and 16 October eruptive events generated plumes that rose as high as 1.5 km above the crater rim and drifted W, SW, and SE, and ejected large blocks as far as 400 m from the vent. A total of eight explosions were recorded by the seismic network at 1522 on 14 October, at 0337, 0433, 0555, 1008, and 1539 on 15 October, and at 0454 and 0517 on 16 October. Ash plumes from the explosions rose as high as 900 m and drifted SE. Ash fell in Toshima village (3.5 km SSW). The Alert Level remained at 2 (on a 5-level scale) and the public was warned to stay at least 1 km away from the crater.

Geological summary: The 8-km-long 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. One of Japan’s most frequently active volcanoes, it was in a state of intermittent Strombolian activity from Otake, the NE summit crater, between 1949 and 1996, after which periods of inactivity lengthened. The largest recorded 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 open Sakuchi caldera, which extends to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

Taal, Luzon (Philippines)

14.0106°N, 120.9975°E | Summit elev. 311 m

PHIVOLCS reported increased and continuous gas emissions at Taal in a special report issued on 12 October. Pronounced upwelling of gasses and hot fluids in the lake produced short plumes that drifted SW. Sulfur dioxide emissions were as high as 9,762 tonnes per day (t/d), the highest measurement recorded in 2023; emissions in September and October averaged 3,781 t/d. These upwellings in the lake continued during 14-16 October and sulfur dioxide emissions averaged 4,878 t/d on 14 October. The Alert Level remained at 1 (on a scale of 0-5), and PHIVOLCS reminded the public that the entire Taal Volcano Island was a Permanent Danger Zone (PDZ).

Geological summary: Taal is one of the most active volcanoes in the Philippines and has produced some powerful eruptions. The 15 x 20 km Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2 surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, with several submerged eruptive centers. The 5-km-wide Volcano Island in north-central Lake Taal is the location of all observed eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones. Powerful pyroclastic flows and surges have caused many fatalities.

Villarrica, Central Chile

39.42°S, 71.93°W | Summit elev. 2847 m

POVI reported that Strombolian activity at Villarrica continued to be observed in webcam images during 11-16 October. Lava fountains were observed during 11-12 October; incandescent material was ejected as high as 125 m above the crater rim and incandescent bombs were ejected onto the upper flanks. Strombolian explosions were less vigorous during 12-16 October with ballistics rising no higher than 100 m above the crater rim. Some incandescent material was ejected onto the upper N flank during 15-16 October. According to SERNAGEOMIN, the Alert Level remained at Yellow (the third level on a four-level scale) and the public was warned to stay 2 km away from the crater. SENAPRED maintained the Alert Level at Yellow (the middle level on a three-color scale) for the communities of Villarrica, Pucón (16 km N), Curarrehue, and Panguipulli.

Geological summary: The glacier-covered Villarrica stratovolcano, in the northern Lakes District of central Chile, is ~15 km south of the city of Pucon. A 2-km-wide caldera that formed about 3,500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesite cone at the NW margin of a 6-km-wide Pleistocene caldera. More than 30 scoria cones and fissure vents are present on the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Eruptions documented since 1558 CE have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

Wrangell, Eastern Alaska

62.006°N, 144.017°W | Summit elev. 4278 m

On 13 October AVO changed both the Aviation Color Code and the Volcano Alert Level for Wrangell to Unassigned because of a station outage and the inability to reliably detect unrest at the volcano. AVO will continue using satellite, regional infrasound, and lightning data, and reports from pilots and ground observers to detect signs of eruptive activity.

Geological summary: With a diameter of 30 km at 2000 m elevation, Mount Wrangell is one of the world’s largest continental-margin volcanoes. The massive andesitic shield volcano has produced fluid lava flows as long as 58 km and contains an ice-filled caldera 4-6 km in diameter and 1 km deep, located within an ancestral 15-km-wide caldera. Most of the edifice was constructed during eruptions between about 600,000 and 200,000 years ago. Formation of the summit caldera followed sometime between about 200,000 and 50,000 years ago. Three post-caldera craters are located at the broad summit, along the northern and western caldera rim. A steep-sided flank cinder cone, Mount Zanetti, is located 6 km NW of the summit. The westernmost cone has been the source of infrequent historical eruptions beginning in the 18th century. Increased heat flux in recent years has melted large volumes of ice in the northern crater.

References:

Smithsonian Institution / US Geological Survey – Weekly Volcanic Activity Report – October 11 – 17, 2023 – Managing Editor: Sally Sennert.

Featured image credit: The Watchers

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