The Weekly Volcanic Activity Report: November 1 – 7, 2023

New activity/unrest was reported for 3 volcanoes from November 1 to 7, 2023. During the same period, ongoing activity was reported for 16 volcanoes.

New activity/unrest: Ioto, Volcano Islands | Klyuchevskoy, Central Kamchatka (Russia) | Reykjanes, Reykjanes Peninsula.

Ongoing activity: Aira, Kyushu (Japan) | Dukono, Halmahera | Ebeko, Paramushir Island (Russia) | Great Sitkin, Andreanof Islands (USA) | Lewotolok, Lembata Island | Mayon, Luzon (Philippines) | Merapi, Central Java | Reventador, Ecuador | Sabancaya, Peru | Sangay, Ecuador | Sheveluch, Central Kamchatka (Russia) | Shishaldin, Fox Islands (USA) | Suwanosejima, Ryukyu Islands (Japan) | Ubinas, Peru | Ulawun, New Britain (Papua New Guinea) | Villarrica, Central Chile.

New activity/unrest

Ioto, Volcano Islands

24.751°N, 141.289°E | Summit elev. 169 m

The eruption at Ioto (Iwo-jima), at a vent located about 1 km off the SE coast of Okinahama, continued during 1-3 November. A 2 November Sentinel satellite images showed a thermal anomaly at the SE end of the island which was elongated to the NNW-SSE. A white plume drifted about 400 m WSW. During an overflight on 3 November observers photographed the island and noted that a 169-m-high cone had formed at the SSE end according to news sources. Explosions occurred about every one minute that ejected dark material and incandescent material about 800 m above the vent. Floating, brown-colored pumice was present in the water around the island.

Geological summary: Ioto in the central Volcano Islands portion of the Izu-Bonin-Mariana arc lies within a 9-km-wide submarine caldera. Ioto, Iwojima, and Iojima are among many transliterations of the name. The volcano is also known as Ogasawara-Iojima to distinguish it from several other “Sulfur Island” volcanoes in Japan. The triangular, low-elevation, 8-km-long island narrows toward its SW tip and has produced trachyandesitic and trachytic rocks that are more alkalic than those of other volcanoes in this arc. The island has undergone uplift for at least the past 700 years, accompanying resurgent doming of the caldera; a shoreline landed upon by Captain Cook’s surveying crew in 1779 is now 40 m above sea level. The Motoyama plateau on the NE half of the island consists of submarine tuffs overlain by coral deposits and forms the island’s high point. Many fumaroles are oriented along a NE-SW zone cutting through Motoyama. Numerous recorded phreatic eruptions, many from vents on the W and NW sides of the island, have accompanied the uplift.

Klyuchevskoy, Central Kamchatka (Russia)

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

An intense eruption at Klyuchevskoy began on 31 October, prompting KVERT to raise the Aviation Color Code to Red (the highest level on a four-color scale). Ash plumes rose as high as 14 km (45,900 ft) a.s.l. and drifted as far as 2,255 km ESE during 31 October-1 November. Lava fountains rose as high has 1 km above the summit and fed lava flows that descended the Apakhonchichsky, Krestovsky, and Kozyrevsky drainages on the SE, S, and W flanks. According to Kamchatka Volcanological Station observers pyroclastic flows descended the flanks. Lahars descended the Studenoy River, blocking the Kozyrevsk-Petropavlovsk federal highway, and descended the Krutenkaya River, blocking the road E of Klyuchi. According to news articles the ash plumes caused some flight cancellations and disruptions in the Aleutians, British Columbia, and along flight paths connecting the Unites States to Japan and South Korea.

Activity began to wane at around 2300 on 1 November and by 2000 on 2 November ash plumes were rising only as high as 6.5 km (21,300 ft) a.s.l. and drifting NNE. The Aviation Color Code was lowered to Orange. The main plume from the most intense phase of the eruption had drifted more than 3,000 km E and SE and contained about 0.1 teragram (100,000 tonnes) of sulfur dioxide based on satellite data. Eruptive activity at the summit continued during 3-4 November, producing ash plumes that rose as high as 5.5 km (18,000 ft) a.s.l. and drifted 125 km ENE. The eruption had ceased by 5 November. Collapses of material and phreatic explosions from hot lava interacting with ice and snow along the Apakhonchichsky drainage generated ash plumes that rose 5.5-8.2 km (18,000-26,900 ft) a.s.l. and drifted almost 260 km E and ENE during 3 and 5-6 November.

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.

Reykjanes, Reykjanes Peninsula

63.817°N, 22.717°W | Summit elev. 140 m

IMO reported that increased seismicity and deformation at the Reykjanes Peninsula were ongoing during 1-7 November and indicated magma accumulation at depths of 4-5 km in an area NW of Mt. Thorbjorn. A total of 7 cm of uplift was recorded in satellite data and by the Global Navigation Satellite System (GNSS) station near Mt. Thorbjorn during 27 October-6 November. The rate of inflation was fairly constant though it began to accelerate on 3 November. Data models indicated that the volume change associated with the uplift was double that of the four previous inflation events recorded during 2020-2022; the inflow of magma was estimated at 7 cubic meters per second, or four times greater than the highest inflow rate recorded during the previous events.

Intense seismicity continued. Over 10,500 earthquakes were detected during 25 October-1 November, out of which more than 26 exceeded M 3 and the largest was a M 4.5 recorded at 0818 on 25 October. Seismicity increased for early on 3 November, and then notably decreased around 1730. The signals were located along previously known faults, aligned in a N-S direction W of Mt. Thorbjorn. There was no indication of magma migrating to the surface. During 4-7 November there were around 2,200 earthquakes, which were located between Mt. Thorbjorn and Sýlingafell during 6-7 November.

Geological summary: The Reykjanes volcanic system at the SW tip of the Reykjanes Peninsula, where the Mid-Atlantic Ridge rises above sea level, comprises a broad area of postglacial basaltic crater rows and small shield volcanoes. The submarine Reykjaneshryggur volcanic system is contiguous with and is considered part of the Reykjanes volcanic system, which is the westernmost of a series of four closely-spaced en-echelon fissure systems that extend diagonally across the Reykjanes Peninsula. Most of the subaerial part of the system (also known as the Reykjanes/Svartsengi volcanic system) is covered by Holocene lavas. Subaerial eruptions have occurred in historical time during the 13th century at several locations on the NE-SW-trending fissure system, and numerous submarine eruptions dating back to the 12th century have been observed during historical time, some of which have formed ephemeral islands. Basaltic rocks of probable Holocene age have been recovered during dredging operations, and tephra deposits from earlier Holocene eruptions are preserved on the nearby Reykjanes Peninsula.

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 30 October-6 November, with incandescence at the crater observed nightly. Sulfur dioxide emissions averaged 1,300 tons per day on 2 November. There was a total of 10 eruptive events recorded during 30-31 October and 1-2 November. Ash plumes rose as high as 1.8 km above the crater rim and drifted N, E, and SE. 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.

Dukono, Halmahera

1.6992°N, 127.8783°E | Summit elev. 1273 m

PVMBG reported that the eruption at Dukono was ongoing during 1-7 November. Daily dense white-and-gray or gray-to-black ash plumes rose as high as 1.2 km above the summit and drifted in multiple directions. Ashfall up to 0.5 mm thick fell in several areas downwind including Mede, Popilo, Gorua, Waro ino-Weri, Buwaele, Gura, Cina, Gamsungi, and Tobelo (15 km ENE). Banging noises were also heard several times in the same villages. The Alert Level remained at Level 2 (on a scale of 1-4), and the public was warned to remain outside of the 2-km exclusion zone.

Geological summary: Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia’s most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, have occurred since 1933. During a major eruption in 1550 CE, a lava flow filled in the strait between Halmahera and the N-flank Gunung Mamuya cone. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

Ebeko, Paramushir Island (Russia)

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

KVERT reported that moderate explosive activity at Ebeko was ongoing during 26 October-2 November. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E), explosions generated ash plumes that rose as high as 2.6 km (8,500 ft) a.s.l and drifted NE. A thermal anomaly was identified in satellite images on 28 October; weather clouds obscured views on other days. The Aviation Color Code remained at Orange (the third level on a four-color scale). Dates are UTC; specific events are in local time where noted.

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.

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 1-7 November, producing a thick flow in the summit crater that mainly expanded E. Seismicity was low with only a few earthquakes recorded by the seismic network during the week. Weakly elevated surface temperatures were identified in satellite data during 3-4 November. Weather clouds sometimes obscured 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 1-7 November. White-and-gray ash plumes rose 100-400 m above the summit and drifted W and NW on 1 November. White steam-and-gas plumes rose 50-400 m and drifted W, NW, and E on the other days during the week. Webcam images captured at 1853 on 1 November and 0350 on 3 November showed incandescent material being ejected above the summit. Incandescence at the summit was visible in a webcam image at 2128 on 4 November. 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 1-7 November. 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 produced rockfalls and occasional pyroclastic density currents (PDCs, or pyroclastic flows) that descended the flanks as far as 4 km. Each day, seismic stations recorded 84-175 rockfall events and 66-187 daily volcanic earthquakes including 62-179 tremor events that each lasted 1-49 minutes. There were 0-4 daily PDC events. Sulfur dioxide emissions, measured almost daily, averaged between 920 and 1,539 tonnes per day, with the highest value recorded on 1 November. 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 27 October-2 November. The SW lava dome produced a total of 135 lava avalanches that descended the S and SW flanks; 16 traveled as far as 1.6 km down the upper part of the Boyong drainage and 119 traveled as far as 1.9 km down the upper Bebeng drainage. Morphological changes to the SW lava dome were due to continuous collapses of material. Seismicity remained at elevated levels. 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.

Reventador, Ecuador

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

IG-EPN reported that the eruption at Reventador was ongoing during 31 October-7 November. Seismicity was characterized by 37-52 daily explosions, long-period earthquakes, harmonic tremor, and tremor associated with emissions. Several daily ash-and-gas plumes rose as high as 1.2 km above the crater rim and drifted mainly N, NW, N, and NE. Daily crater incandescence was visible during both overnight and morning hours. Avalanches of incandescent material descended the flanks, traveling as far as 800 m from the summit. Incandescent material was ejected as high as 300 m above the crater rim several times during 4-7 November. 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.

Sabancaya, Peru

15.787°S, 71.857°W | Summit elev. 5960 m

Instituto Geofísico del Perú (IGP) reported that the eruption at Sabancaya continued at moderate levels during 30 October-5 November with a daily average of five explosions. Gas-and-ash plumes rose as high as 2.2 km above the summit and drifted W, SW, and SE. A total of 12 thermal anomalies from the lava dome in the summit crater were detected using satellite data. Minor inflation was detected near the Hualca Hualca sector (4 km N). The Alert Level remained at Orange (the second highest level on a four-color scale) and the public were warned to stay outside of a 12 km radius.

Geological summary: Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning “tongue of fire” in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions date back to 1750.

Sangay, Ecuador

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

IG-EPN reported a high level of eruptive activity at Sangay during 31 October-7 November, with seismic stations recording 436-1,122 daily explosions. Several ash-and-gas plumes per day during 1-4 and 6 November rose as high as 2.5 km above the crater rim and drifted NE, N, NW, and SW. Webcam images showed incandescent material descending the SE flank as far as 1.8 km from the crater each day during overnight and early morning hours. Incandescence at the crater was often visible; incandescent material was ejected as high as 1 km above the crater rim during 4-5 November. 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.

Sheveluch, Central Kamchatka (Russia)

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

KVERT reported that the eruption at Sheveluch continued during 26 October-2 November. A daily thermal anomaly was identified in satellite images. 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 the thirteenth significant explosive event since 12 July was recorded at Shishaldin on 2 November. An increase in seismic and infrasound tremor amplitudes began at 1940 on 2 November, indicating a likely eruption. The Volcano Alert Level was raised to Watch (the third level on a four-level scale) and the Aviation Color Code was raised to Orange (the third color on a four-color scale), though ash was not identified in satellite data. At 2000 a sustained ash cloud drifting W was identified in satellite data at an altitude of 6.1 km (20,000 ft) a.s.l. By 0831 on 3 November ash emissions were no longer visible in satellite images and seismic and infrasound data indicated a decline in activity. During 4-7 November seismic activity remained elevated with ongoing tremor and small, low-frequency earthquakes. Minor emissions of steam and sulfur dioxide were visible in webcam and satellite images. Elevated surface temperatures were identified in satellite images on a few occasions. Infrasound signals consistent with small explosions were recorded during 5-7 November.

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 30 October-6 November. Eruptive events during 30-31 October and 2 and 4 November generated ash plumes that rose as high as 1.5 km above the crater rim and drifted NW, S, and W; on 30 October and 4 November the ash plumes rose into weather clouds and may have gone higher than observed. The eruptive events ejected large blocks as far as 300 m from the vent. 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.

Ubinas, Peru

16.355°S, 70.903°W | Summit elev. 5672 m

Instituto Geofísico del Perú (IGP) reported that activity at Ubinas was at low levels during 30 October-5 November. Seismicity was low with daily averages of 95 volcano-tectonic earthquakes indicating rock fracturing and 24 long-period earthquakes signifying the movement of gas and magma. Gas-and-steam plumes rose as high as 900 m above the crater rim and drifted E and SE; no explosions nor ash emissions were recorded. The Alert Level was lowered to Yellow (the second level on a four-color scale) and the public was warned to stay 2 km away from the crater.

Geological summary: A small, 1.4-km-wide caldera cuts the top of Ubinas, Perú’s most active volcano, giving it a truncated appearance. It is the northernmost of three young volcanoes located along a regional structural lineament about 50 km behind the main volcanic front. The growth and destruction of Ubinas I was followed by construction of Ubinas II beginning in the mid-Pleistocene. The upper slopes of the andesitic-to-rhyolitic Ubinas II stratovolcano are composed primarily of andesitic and trachyandesitic lava flows and steepen to nearly 45 degrees. The steep-walled, 150-m-deep summit caldera contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits from the collapse of the SE flank about 3,700 years ago extend 10 km from the volcano. Widespread Plinian pumice-fall deposits include one of Holocene age about 1,000 years ago. Holocene lava flows are visible on the flanks, but historical activity, documented since the 16th century, has consisted of intermittent minor-to-moderate explosive eruptions.

Ulawun, New Britain (Papua New Guinea)

5.05°S, 151.33°E | Summit elev. 2334 m

Rabaul Volcano Observatory (RVO) reported that diffuse white plumes rose from Ulawun’s summit crater on 1 November. A low booming noise was heard at 1945. Minor crater incandescence began to be visible later that day at around 2100 and was observed until sunrise. White emissions were visible early on 2 November but by the afternoon clouds of gray-to-brown ash were occasionally observed when weather permitted observations. Crater incandescence was again visible at nightfall but was more intense than the previous night and remained visible until sunrise. Seismicity was dominated by low-level volcanic tremor. Small, low-frequency earthquakes occurring at long intervals began to be recorded at some point before 2300 on 1 November; an increase in both magnitude and frequency occurred after 2300 and the signal again intensified after 0800 on 2 November. Seismicity slightly declined around 0800 on 3 November and remained at those levels at least through noon. The Alert Level remained at Stage 2 (on the four-level scale).

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.

Villarrica, Central Chile

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

According to the Buenos Aires VAAC a diffuse ash-and-gas plume from Villarrica was observed in satellite and webcam images at 0900 on 2 November rising to 3.7 km (12,000 ft) a.s.l. and dissipating near the summit. POVI reported that lava fountaining above the crater rim was visible in webcam images for more than 15 seconds on 3 November. Incandescence from the summit was visible during the early morning hours of 6 November. The Volcanic Alert level remained at Yellow (the third level on a four-level scale) according to SERNAGEOMIN 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.

References:

Smithsonian Institution / US Geological Survey Weekly Volcanic Activity Report – November 1 – 7, 2023 -Managing Editor: Sally Sennert.

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