The Weekly Volcanic Activity Report: October 18 – 24, 2023

New activity/unrest was reported for 5 volcanoes from October 18 to 24, 2023. During the same period, ongoing activity was reported for 16 volcanoes.

New activity/unrest: Bezymianny, Central Kamchatka (Russia) | Bogoslof, Fox Islands (USA) | Home Reef, Tonga Ridge | Klyuchevskoy, Central Kamchatka (Russia) | Slamet, Central, Java.

Ongoing activity: Aira, Kyushu (Japan) | Bulusan, Luzon (Philippines) | Ebeko, Paramushir Island (Russia) | Erta Ale, Ethiopia | Great Sitkin, Andreanof Islands (USA) | Lewotolok, Lembata Island | Mayon, Luzon (Philippines) | Merapi, Central Java | Nevado del Ruiz, Colombia | Sabancaya, Peru | Semeru, Eastern Java | Sheveluch, Central Kamchatka (Russia) | Shishaldin, Fox Islands (USA) | Suwanosejima, Ryukyu Islands (Japan) | Ubinas, Peru | Villarrica, Central Chile.

New activity/unrest

Bezymianny, Central Kamchatka (Russia)

55.972°N, 160.595°E; summit elev. 2882 m

KVERT reported that eruptive activity at Bezymianny continued during 18-23 October. Large collapses on the E flanks of the lava dome that began on 17 October continued the next day. A VONA issued at 1616 on 18 October described continuing large collapses and subsequent ash plumes that rose 4.5-5 km (14,800-16,400 ft) a.s.l. and drifted 32 km NW. A large explosion at 1630 produced ash plumes that rose 10-11 km (32,800-36,100 ft) a.s.l. and drifted 50 km NNE, prompting KVERT to raise the Aviation Color Code to Red (the highest level on a four-color scale). According to the Kamchatka Volcanological Station, inclement weather clouds hindered views of the volcano but a roar was heard at about 1650 and a dark ash cloud was visible. KVERT noted that by 2030 the ash cloud had detached and was 250 m long and 70 km wide; the cloud continued to drift NNE at an altitude of 8 km (26,200 ft) a.s.l. At 2117 the Aviation Color Code was lowered to Orange. Within two days, the ash cloud drifted NE and then NW as far as 850 km. Minor ashfall was reported in Kozyrevsk, 45 km W. At 0820 on 20 October an ash plume was identified in satellite images drifting 100 km ENE at altitudes of 4-4.5 km (13,100-14,800 ft) a.s.l. At 0903 the Aviation Color Code was lowered to Yellow. Lava effusion continued; fumarolic activity and dome incandescence were visible.

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.

Bogoslof, Fox Islands (USA)

53.93°N, 168.03°W; summit elev. 150 m

AVO raised the Volcano Alert Level for Bogoslof to Advisory (the second level on a four-level scale) and the Aviation Color Code to Yellow (the second color on a four-color scale) on 24 October due to increased seismicity. Over 90 earthquakes were detected in the vicinity of the volcano during the previous three days. No signs of unrest had been recorded in satellite data over the past several days.

Geological summary: Bogoslof is the emergent summit of a submarine volcano that lies 40 km N of the main Aleutian arc. It rises 1,500 m above the Bering Sea floor. Repeated construction and destruction of lava domes at different locations during historical time has greatly modified the appearance of this “Jack-in-the-Box” volcano and has introduced a confusing nomenclature applied during frequent visits by exploring expeditions. The present triangular-shaped, 0.75 x 2 km island consists of remnants of lava domes emplaced from 1796 to 1992. Castle Rock (Old Bogoslof) is a steep-sided pinnacle that is a remnant of a spine from the 1796 eruption. The small Fire Island (New Bogoslof), about 600 m NW of Bogoslof Island, is a remnant of a lava dome formed in 1883.

Home Reef, Tonga Ridge

18.992°S, 174.775°W; summit elev. -10 m

The Tonga Geological Services reported that the eruption at Home Reef was ongoing. A total of 11 eruptive events were detected in satellite data during 16-19 October. A pilot observed an ash plume rising to 300 m at 1150 on 18 October. The Aviation Color Code remained at Yellow (the second level on a four-color scale) and mariners were advised to stay 4 km away from the island.

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 13-20 October and fed lava flows that descended the Apakhonchichsky drainage on the SE flank. Lava descended the Kozyrevsky drainage on 17 October. A daily bright thermal anomaly was identified in satellite images and plumes of resuspended ash rose to 6 km (19,700 ft) a.s.l. and drifted 430 km E. The Aviation Color Code remained at Orange (the third level on a four-color scale). 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.

Slamet, Central, Java

7.242°S, 109.208°E; summit elev. 3428 m

PVMBG reported continuing inflation and increased seismicity at Slamet in a 19 October press release. An increase in the amplitude of a continuous tremor signal was recorded by the seismic network on 1 October and a period of harmonic tremor that lasted one hour and 18 minutes was recorded on 18 October. Tiltmeter and Electronic Distance Measurement data from the Cilik station located at an elevation of 1,500 m showed inflation while another station (Buncis) showed deflation; the Jurangmangu station located at a lower elevation than Cilik showed no significant deformation pattern. Inflation was recorded in tilt data at the Bambangan station (at 2,000 m elevation) during 11-18 October. Gas emissions rose 50-300 m above the summit. The Alert Level was raised to 2 (on a scale of 1-4) due to increasing activity and the public was warned to stay outside a 2 km radius.

Geological summary: Slamet, Java’s second highest volcano at 3428 m and one of its most active, has a cluster of about three dozen cinder cones on its lower SE-NE flanks and a single cinder cone on the western flank. It is composed of two overlapping edifices, an older basaltic-andesite to andesitic volcano on the west and a younger basaltic to basaltic-andesite one on the east. Gunung Malang II cinder cone on the upper E flank on the younger edifice fed a lava flow that extends 6 km E. Four craters occur at the summit of Gunung Slamet, with activity migrating to the SW over time. Historical eruptions, recorded since the 18th century, have originated from a 150-m-deep, 450-m-wide, steep-walled crater at the western part of the summit and have consisted of explosive eruptions generally lasting a few days to a few weeks.

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 16-23 October, with incandescence at the crater observed nightly. Sulfur dioxide emissions were extremely high, averaging 4,200 tons per day on 16 October. During the week, there were a total of 11 eruptive events and 20 explosions, with a daily average of 1-5 explosions recorded during 16-21 October. Ash plumes rose as high as 3.6 km above the crater rim and drifted E, SE, and S, and large blocks were ejected as far as 1.2 km from the crater rim. A period of inflation began at around 0600 on 21 October, but ceased following an eruptive event during 0346-0430 on 24 October; the event produced an ash plume that rose 2.3 km above the crater rim and ejected large blocks 1.2 km. 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.

Bulusan, Luzon (Philippines)

12.769°N, 124.056°E; summit elev. 1535 m

In a special advisory, PHIVOLCS reported that from 0500 on 14 October to 2100 on 22 October the seismic network at Bulusan recorded a total of 87 volcanic earthquakes. Out of those, 29 were volcano-tectonic events associated with rock fracturing, located at depths of 1-8 km beneath the S and W flanks of the volcano. Gas emissions from the summit crater were at weak-to-moderate levels; sulfur dioxide emissions averaged 241 tonnes per day on 19 October, near background levels. Ground deformation data from electronic tiltmeter stations continued to record inflation at the S flank since February 2023. The Alert Level remained at 0 (the lowest level on a scale of 0-5) and PHIVOLCS reminded the public not to enter the 4-km-radius Permanent Danger Zone (PDZ).

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

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 13-20 October. A thermal anomaly was identified in satellite images on 14 October; weather clouds obscured views on other days. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E), explosions on 14 and 19 October generated ash plumes that rose as high as 4 km (13,100 ft) a.s.l and drifted to the E. 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 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.

Erta Ale, Ethiopia

13.601°N, 40.666°E; summit elev. 585 m

An eruption at Erta Ale continued during 5-20 October based on satellite data. Four thermal anomalies were located in the N and S pit craters, aligned in a NW-SE direction, based on a 5 October image. The northernmost anomaly in the N pit crater, was relatively weak. The other three, one located at the SE rim of the N pit crater and two in the S pit crater, were brighter and likely represented spatter cones. These three anomalies were more intense in a 10 October image. An image on 15 October showed lava flows likely coming from the two cones in the S pit crater traveling SE, SSE, NE, and SW. Minor, linear anomalies to the N of the cone on the SE rim of the N pit crater likely represented lava flows. The flows had cooled by 20 October.

Geological summary: The Erta Ale basaltic shield volcano in Ethiopia has a 50-km-wide edifice that rises more than 600 m from below sea level in the Danakil depression. The volcano includes a 0.7 x 1.6 km summit crater hosting steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located SE of the summit and is bounded by curvilinear fault scarps on the SE side. Basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera usually also holds at least one long-term lava lake that has been active since at least 1967, and possibly since 1906. Recent fissure eruptions have occurred on the N flank.

Great Sitkin, Andreanof Islands (USA)

52.076°N, 176.13°W; summit elev. 1740 m

AVO reported that slow lava effusion at Great Sitkin was confirmed in satellite radar data on 17 October and likely continued during 18-24 October. A thick lava flow in the summit crater mainly expanded E. Seismicity was low and only a couple of earthquakes were detected during 17-19 October. Weather clouds sometimes 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 18-24 October. White-and-gray ash plumes rose 400-600 m above the summit and W and NW during 19-21 and 23-24 October. White steam-and-gas plumes rose 200-300 m and drifted W and NW on the other days during the week. 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 43-175 rockfall events and 9-70 daily volcanic earthquakes including 2-67 tremor events that lasted as short as one minute to as long as about four and a half hours. Sulfur dioxide emissions measured near-daily averages between 727 and 1,521 tonnes per day, with the highest value recorded on 17 October. Short-lived bursts of gas were recorded in seismic and infrasound data at 1836 on 20 October and 0006 on 21 October. A period of increased lava effusion that started at 2210 on 21 October was characterized by more intense incandescence at the summit crater, followed by rockfalls and lava flows in the Mi-Isi and Bonga drainages. One PDC per day was recorded on 19, 21, and 22 October and two were recorded during 23-24 October; 53 were recorded during 24-25 October, accompanying a second period of increased effusion on 24 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 13-19 October. The SW lava dome produced a total of 207 lava avalanches that descended the S and SW flanks; 54 traveled as far as 1.6 km down the upper part of the Boyong drainage, 151 traveled as far as 1.8 km down the upper Bebeng drainage, one traveled 1.5 km down the Sat/Putih drainage, and one traveled 800 m down the Senowo drainage. Morphological changes to the SW lava dome were due to continuous collapses of material. Seismicity remained at elevated levels and indicated increased magmatic activity at depths of less than 1.5 km below the summit. 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.

Nevado del Ruiz, Colombia

4.892°N, 75.324°W; summit elev. 5279 m

Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that the eruption at Nevado del Ruiz continued at low-to-moderate levels during 17-23 October. Seismic events indicating the movement of fluids increased in number and intensity compared to the previous week. The number of signals indicating rock fracturing increased in intensity, though decreased in number. These events were located in areas as far as 13 km ESE and SW of Arenas Crater, at depths less than one to 7 km. Earthquakes recorded at 2214 on 21 October (M 3) and at 0837 on 22 October (M 3.2) were felt by residents in the municipality of Murillo. Thermal anomalies on the crater floor were identified in satellite images, though they were less intense than the previous week. Several ash-and-gas emissions were visible during the week, with the highest plumes rising to 1.6 km above the crater rim on 17 October. Plumes drifted SW, NW, and NNE. The Alert Level remained at Yellow, Level III (the second level on a four-level scale).

Geological summary: Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America’s deadliest eruption.

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 16-22 October with a daily average of six explosions. Gas-and-ash plumes rose as high as 2 km above the summit and drifted SE and S. A total of two 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.

Semeru, Eastern Java

8.108°S, 112.922°E; summit elev. 3657 m

PVMBG reported that eruptive activity continued at Semeru during 18-24 October, though weather conditions sometimes prevented visual observations. Daily white-and-gray ash plumes rose 100-800 m above the summit and drifted in multiple directions. 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 13-20 October and 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 activity at Shishaldin through 24 October had remained elevated since the last explosive event which occurred on 3 October. Sulfur dioxide emissions were elevated with daily averages of more than 1,000 tons per day based on satellite data; during periods in between previous explosive events, sulfur dioxide emissions were either low or were not detected. Abundant amounts of steam rose from the summit as well as from a liner feature that extended about 400 m from the summit down the NE flank. Seismicity remained elevated and was characterized by nearly constant seismic tremor and frequent, small, long-period, or low-frequency earthquakes. The seismicity was indicative of the movement of volcanic fluids and gases within the volcano and had been typically low in between previous explosive events. Daily elevated surface temperatures were identified in satellite data, though temperatures were inconsistent with lava at the surface. Pilots reported a prominent steam plume drifting 40 km WSW at altitudes of 3-4.6 km (10,000-15,000 ft) a.s.l. during the afternoon of 21 October. Minor steam emissions were visible in webcam images during 22-24 October. 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 16-23 October and crater incandescence was visible nightly. Eruptive events generated plumes that rose as high as 1.6 km above the crater rim and drifted S and SE and ejected large blocks as far as 400 m from the vent. Ash fell in Toshima village (3.5 km SSW). Explosions recorded at 0454 and 0517 on 16 October produced ash plumes that rose 500-600 m above the crater rim and drifted SE. During an overflight on 17 October scientists observed no notable changes in the crater and surrounding areas. 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.

Ubinas, Peru

16.355°S, 70.903°W; summit elev. 5672 m

Instituto Geofísico del Perú (IGP) reported that the eruption at Ubinas continued during 16-22 October at low-to-moderate levels. There were daily averages of 204 volcano-tectonic earthquakes indicating rock fracturing and 25 long-period earthquakes signifying the movement of gas and magma. Steam-and-gas emissions rose as high as 1 km above the crater rim and drifted E and SE. The Alert Level remained at Orange (the third level on a four-color scale) and the public was warned to stay 4 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.

Villarrica, Central Chile

39.42°S, 71.93°W; summit elev. 2847 m

POVI reported that Strombolian activity and crater incandescence at Villarrica was observed in webcam images during 22-23 October, coinciding with the highest thermal radiance identified in Sentinel satellite data since July 2018. 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.


Smithsonian Institution / US Geological Survey – Weekly Volcanic Activity Report – October 18 – 24, 2023 – Managing Editor: Sally Sennert.


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