The Weekly Volcanic Activity Report: October 25 - 31, 2023

New activity/unrest was reported for 8 volcanoes from October 25 to 31, 2023. During the same period, ongoing activity was reported for 20 volcanoes.

New activity/unrest

Bezymianny, Central Kamchatka (Russia)

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

KVERT reported that a daily thermal anomaly over Bezymianny was identified in satellite images during 20-26 October. Dates are UTC; specific events are in local time where noted.

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

Unrest continued at Bogoslof during 25-31 October with numerous daily earthquakes recorded in seismic data. No additional signs of unrest were recorded in satellite data. The Volcano Alert Level remained at Advisory (the second level on a four-level scale) and the Aviation Color Code remained at Yellow (the second color on a four-color scale).

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.

Bulusan, Luzon (Philippines)

12.769°N, 124.056°E | Summit elev. 1535 m

PHIVOLCS reported that increased seismicity at Bulusan that began on 14 October continued. The seismic network recorded a total of 121 volcanic earthquakes from 0500 on 14 October to 1500 on 25 October. Out of those, 37 were volcano-tectonic events associated with rock fracturing and were located at depths of 1-9 km beneath the NW and SE flanks of the volcano. Ground deformation data from electronic tiltmeter stations continued to record inflation at the S flank, first detected in February, and at the NE flank since September. The Alert Level was raised to 1 (the second level on a scale of 0-5) and PHIVOLCS reminded the public not to enter the 4-km-radius Permanent Danger Zone (PDZ) and to be vigilant within the 2-km Extended Danger Zone (EDZ) on the SE flank.

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.

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 nine eruptive events were detected in satellite data during 21-30 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.

Ioto, Volcano Islands

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

According to a news source, an eruption at Ioto (Iwo-jima) occurred at a vent located about 1 km off the coast of Okinahama, on the SE side the island. During an overflight on 30 October observers recorded explosions every few minutes that ejected dark material about 20 m above the ocean. Ejecta from the vent built a black-colored island and floating pumice was present 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

KVERT reported that the Strombolian eruption at Klyuchevskoy continued during 20-29 October and a daily bright thermal anomaly was identified in satellite images. Lava fountains sometimes rose as high as 500 m above the summit and fed lava flows that descended the Apakhonchichsky and Kozyrevsky drainages on the SE and S flanks. Phreatic explosions were sometimes generated from the interaction with lava and glaciers on the flanks and caused collapses of older deposits in the drainages. Plumes of the previously deposited ash generally rose as high as 7 km (23,000 ft) a.s.l. and drifted 280 km NE, E, and SE during 22-29 October, though on 23 and 29 October plumes rose as high as 8 km (26,200 ft) a.s.l. Scientists at the Kamchatka Volcanological Station visited the volcano on 28 October and noted that the cinder cone at the summit had grown. They also observed advancing lava on the E flank that extended about 2 km from the summit to 2,700 m elevation, incandescent material being ejected 500 m above the crater, and avalanches in the Apakhonchichsky drainage. Ash plumes rose more than 2 km.

Activity intensified on 31 October. Ash plumes were identified in satellite images rising as high as 10 km (32,800 ft) a.s.l., prompting KVERT to raise the Aviation Color Code to Red (the highest level on a four-color scale). Ash plumes had drifted as far as 1,300 km SSE. 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.

Reykjanes, Reykjanes Peninsula

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

IMO reported that an intense earthquake swarm on the Reykjanes Peninsula began on 24 October. By 1700 on 26 October more than 4,000 earthquakes had been located at depths of 2-6 km. A total of 14 earthquakes had a magnitude over M 3; the largest event, a M 4.5, was recorded at 0818 on 25 October. Most of the activity occurred between Stóra-Skogafell and an area NE of Eldvörp. No ground deformation was recorded, though a single GPS station (FEFC), E of Festarfjall, recorded localized movement to the SE. During 25-26 October the displacement recorded by the FEFC station totaled about 2 cm and movement was also detected at a station in Selatangar. The swarm continued and by 1400 on 27 October more than 5,800 earthquakes had been recorded; a M 4 earthquake occurred at 0402 on 27 October and was located about 2 km N of Grindavík.

Seismicity decreased considerably by 1330 on 28 October, though the swarm was ongoing with a total of more than 7,000 earthquakes. Uplift centered around Svartsengi, 1.5 km NW of Mt. Thorbjorn, was clearly evident in satellite radar and GPS data. The uplift had begun at some point the previous day and likely signified a magmatic intrusion at depth. IMO raised the Aviation Color Code for Reykjanes to Yellow (the second level on a four-color scale) at 1518 on 28 October. During 1130 on 29 October to 1130 on 30 October about 1,300 earthquakes occurred at depths of 2-4 km. The largest event was a M 2.7 at 1140 on 29 October. Uplift continued during 28-31 October, though the rates began to decrease. Modeling suggested that magma was accumulating at a depth of about 4 km. An earthquake swarm began at 0840 on 31 October and lasted about two hours. The events were located at depths of 1.5-5 km and indicted that magma was moving.

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.

Slamet, Central Java

7.242°S, 109.208°E | Summit elev. 3428 m

PVMBG reported that daily white emissions rose 50-100 m above Slamet’s summit and drifted S and W during 25-30 October. The Alert Level was lowered to 1 (on a scale of 1-4) on 30 October and the public was warned to stay 2 km away from the summit crater.

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 23-30 October, with incandescence at the crater observed nightly. An eruptive period was recorded during 0346-0430 on 24 October; at 0346 a notable ash plume rose as high as 3.4 km above the crater rim and drifted E and ejected large blocks 1-1.3 km from the crater rim. At 0416 an ash plume rose 2.1 km above the crater rim and drifted E. A large amount of ashfall, likely from those events, was observed in Kurokami Town during a field survey later that day. Sulfur dioxide emissions were high on 25 October, averaging 2,200 tons per day. During an aerial observation on 25 October scientists noted that the N side of Showa Crater had slightly enlarged compared to the previous observations on 8 March. A high-temperature geothermal area on the Minamidake Crater floor was also visible. Periods of inflation were recorded in deformation data during 0000-1400 on 26 October and 0100-1600 on 28 October. An eruptive event at 0116 on 30 October produced an ash plume that rose 1 km above the crater rim and drifted N. 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.

Ambrym, Vanuatu

16.25°S, 168.12°E | Summit elev. 1334 m

The Vanuatu Meteorology and Geo-Hazards Department (VMGD) reported ongoing volcanic earthquakes and tremors at Ambrym during October. Volcanic activity increased for a few hours during 22-23 October and diffuse gas emissions were detected in satellite data on 23 October. The Alert Level was lowered to 1 (on a scale of 0-5) on 28 April. VMGD warned the public to stay outside of Permanent Danger Zone A, defined as a 1-km radius around Benbow Crater and a 2-km radius around Marum Crater, and additionally to stay 500 m away from the ground cracks created by the December 2018 eruption.

Geological summary: Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides Arc. A thick, almost exclusively pyroclastic sequence, initially dacitic then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major Plinian eruption with dacitic pyroclastic flows about 1,900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.

Aniakchak, Alaska Peninsula, Alaska

56.88°N, 158.17°W | Summit elev. 1341 m

AVO reported that on 26 October strong winds in areas NW of Aniakchak and E of Port Heiden dispersed unconsolidated ash up to 0.9 km (3,000 ft) a.s.l. to the NW. The ash cloud was visible in satellite images and in Port Heiden webcam views. The Volcano Alert Level remained at Normal (the lowest level on a four-level scale) and the Aviation Color Code remained at Green (the lowest level on a four-color scale). Equipment failed on 30 October, so AVO could no longer seismically monitor the volcano at an adequate level and determine if activity was at a typical background level. Both the Volcano Alert Level and the Aviation Color Code were changed to Unassigned.

Geological summary: One of the most dramatic calderas of the Aleutian arc, the 10-km-wide Aniakchak caldera formed around 3,400 years ago during a voluminous eruption in which pyroclastic flows traveled more than 50 km N to the Bering Sea and also reached the Pacific Ocean to the south. At least 40 explosive eruptions have been documented during the past 10,000 years, making it the most active volcano of the eastern Aleutian arc. A dominantly andesitic pre-caldera volcano was constructed above basement Mesozoic and Tertiary sedimentary rocks that are exposed in the caldera walls to elevations of about 610 m. The ice-free caldera floor contains many pyroclastic cones, tuff cones, maars, and lava domes. Surprise Lake on the NE side drains through The Gates, a steep-walled breach on the east side of the 1-km-high caldera rim that was the site of catastrophic draining of a once larger lake about 1850 years BP. Vent Mountain and Half Cone are two long-lived vents on the south-central and NW caldera floor, respectively. The first and only confirmed historical eruption took place in 1931 from vents on the west and SW caldera floor.

East Epi, Vanuatu

16.6797°S, 168.3893°E | Summit elev. 833 m

The Vanuatu Meteorology and Geo-Hazards Department (VMGD) reported that minor unrest continued at Epi during October. Volcanic seismicity was sustained, though no surficial activity was observed. The Alert Level remained at 1 (on a scale of 0-5) and the public was warned to stay outside of the Danger Zone, defined as a 2-km radius around the active submarine vent.

Geological summary: The submarine East Epi group of basaltic and dacitic cones are located within a possible 10-km-diameter caldera off the NE coast of southern Epi Island in Vanuatu. Three cones (1-1.5 basal diameter), known as Epi A, Epi B (or Cioan), and Epi C, are located along the northern rim of the inferred caldera, though Beier et al. (2018) suggest an alternate to the post-caldera formation model. A few smaller cones are south of Epi B. Ephemeral islands were formed during eruptions at Epi B in 1920 and 1953, and the summit was at 34 m below sea level at the time of a 2001 survey. Epi Island is largely volcanic, with Mount Allombei on the west, Pomare (also known as Tavani Kutali or Nikalo) on the east, and Tavani Ruro forming the SE peninsula. Pomare volcano is the highest point on the island and has three subsidiary cones to the east.

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 19-26 October. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E), explosions generated ash plumes that rose as high as 2.5 km (8,200 ft) a.s.l and drifted NE. 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.

Erta Ale, Ethiopia

13.601°N, 40.666°E | Summit elev. 585 m

Eruptive activity at Erta Ale continued during 20-25 October based on satellite data. The four thermal anomalies, located in the N and S pit craters and aligned in a NW-SE direction, were less bright on 25 October relative to the 20 October image.

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.

Fuego, South-Central Guatemala

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

INSIVUMEH reported that, in general, 2-7 explosions per hour were recorded at Fuego during 24-31 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 and W. Ashfall was reported on most 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), San Pedro Yepocapa (8 km NW), and Palo Verde (10 km WSW). Weak rumbling and shock waves were recorded daily. Explosions caused daily block avalanches that descended various drainages including the Ceniza (SSW), Seca (W), Taniluyá (SW), El Jute (ESE), and Las Lajas (SE), sometimes reaching vegetated areas. The explosions ejected incandescent material 100-300 m above the summit on most of the days.

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 25-31 October, producing a thick flow in the summit crater that mainly expanded E. Seismicity was characterized as low with only a few daily earthquakes recorded by the seismic network. Weakly elevated surface temperatures were identified in satellite data during 24-27 October, indicative of the eruption of lava. 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.

Ibu, Halmahera

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

PVMBG reported that Ibu continued to erupt during 25-31 October. Daily white-and-gray ash emissions rose 200-1,000 m above the summit and drifted NW, NE, E, and SE. The Alert Level remained at a 2 (the second highest level on a four-level scale), with the public advised to stay outside of the 2 km hazard zone and 3.5 km away from the N area of the active crater.

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

Krakatau, Sunda Strait

6.1009°S, 105.4233°E | Summit elev. 285 m

In a press release PVMBG reported that there was a significant increase in seismicity at Krakatau on 28 October, indicating the movement of magma towards the surface. Deformation measurements showed inflation at two of the stations since April and at one of the stations since September. White gas-and-steam plumes rose as high as 300 m above the summit. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to stay at least 5 km away from the crater.

Geological summary: The renowned Krakatau (frequently mis-named as Krakatoa) volcano lies in the Sunda Strait between Java and Sumatra. Collapse of an older edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of that volcano are preserved in Verlaten and Lang Islands; subsequently the Rakata, Danan, and Perbuwatan cones were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption caused more than 36,000 fatalities, most as a result of tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former Danan and Perbuwatan cones. Anak Krakatau has been the site of frequent eruptions since 1927.

Lewotolok, Lembata Island

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

PVMBG reported that the eruption at Lewotolok continued during 25-31 October. White-and-gray ash plumes rose 350-500 m above the summit and W and NW during 26-27 and 29 October. White steam-and-gas plumes rose 300-400 m and drifted W and NW on the other days during the week. Webcam images captured at 2102 on 25 October and 2224 on 26 October showed incandescent material being 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 produced incandescent rockfalls and occasional pyroclastic density currents (PDCs, or pyroclastic flows) that descended the flanks as far as 4 km. Each day the seismic network recorded 97-226 rockfall events and 40-137 volcanic earthquakes mostly characterized as tremor events that each lasted 1-72 minutes. There were 48-53 daily PDC events during 25-26 October and 1-4 daily PDC events during the rest of the week. Sulfur dioxide emissions, measured almost daily, averaged between 600 and 1,257 tonnes per day, with the highest value recorded on 29 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.

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 24-31 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 upper WSW flank. Daily weak-to-moderate explosions occurring at a rate of 1-4 per hour generated gas-and-ash plumes that rose 700-1,000 m above the dome and drifted W and SW. Explosions produced block-and-ash flows that descended the SW, S, SE, and E flanks of Caliente dome and were occasionally accompanied by small pyroclastic flows.

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.

Sheveluch, Central Kamchatka (Russia)

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

KVERT reported that the eruption at Sheveluch continued during 19-26 October. A thermal anomaly was identified in satellite images during 20, 23-24, and 26 October; weather clouds obscured views on the other days. 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 unrest at Shishaldin continued during 25-31 October with observations suggesting ongoing degassing of magma at shallow levels beneath the summit. Seismicity was elevated, consisting of seismic tremor and small, low-frequency earthquakes, though activity had begun to slowly decline after the last explosive event on 3 October. Minor steam emissions were visible in webcam images during 24-25 October. Elevated surface temperatures were identified in satellite data during 28-29 October, though they did not indicate lava at the surface. On 31 October the Volcano Alert Level was lowered to Advisory (the second level on a four-level scale) and the Aviation Color Code was lowered to Yellow (the second 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 23-30 October. Eruptive events during 25-27 and 29-30 October generated plumes that rose as high as 1.9 km above the crater rim and drifted SE, S, and SW and ejected large blocks as far as 400 m from the vent. 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.

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 23-29 October at low-to-moderate levels. There were daily averages of 175 volcano-tectonic earthquakes indicating rock fracturing and 17 long-period earthquakes signifying the movement of gas and magma. Daily gas-and-steam plumes rose as high as 500 m above the crater rim and drifted in multiple directions. At 0043 on 27 October an ash, gas, and steam emission rose 500 m above the crater rim and drifted SE and E. A minor thermal anomaly on the crater floor was visible. 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.

Ulawun, New Britain (Papua New Guinea)

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

Rabaul Volcano Observatory (RVO) reported that variable amounts of white steam emissions rose from Ulawun’s summit crater during 1-28 October and drifted SE; small volumes of blue vapor were visible on 18 October. Low-level seismicity, characterized by small continuous volcanic tremors recorded during the last week of September, continued through the first week of October. Small, discrete, low-frequency volcanic earthquakes and short-duration sub-continuous volcanic tremors emerged on 8 October and fluctuated at low-to-moderate levels through 28 October. The pattern of seismicity again changed on 28 October when both low-frequency and high-frequency earthquakes were detected. Though activity was forecasted to remain low, RVO noted that some of the seismic patterns were similar to those observed before the 14 and 25 September eruptions; RVO recommended that the Alert Level be raised to 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

SERNAGEOMIN reported that at 0700 on 31 October an ash-and-gas plume rose 260 m above Villarrica’s crater rim. 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.

Yasur, Vanuatu

19.532°S, 169.447°E | Summit elev. 361 m

The Vanuatu Meteorology and Geohazards Department (VMGD) reported that activity at Yasur continued at a high level of “major unrest,” as defined by the Alert Level 2 status (the middle level on a scale of 0-4) during October. Recent satellite observations indicated an increase in steam, gas, and ash emissions from the summit crater. Explosions continued, with some ejecting bombs that landed back in and around the crater. A significant landslide occurred inside the vent on 10 October. The public was reminded to not enter the restricted area within 600 m around the boundaries of the Permanent Exclusion Zone, defined by Danger Zone A on the hazard map.

Geological summary: Yasur has exhibited essentially continuous Strombolian and Vulcanian activity at least since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island in Vanuatu, this pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide open feature associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

References:

Smithsonian Institution / US Geological Survey – Weekly Volcanic Activity Report – October 25 – 31, 2023 – Managing Editor: Sally Sennert.

Featured image credit: The Watchers

Related by tag and category
Related by tag
Related by category