The Weekly Volcanic Activity Report: October 1-7, 2026

New activity/unrest

Ambrym, Vanuatu

16.25°S, 168.12°E; Elev. 1,334 m

The Vanuatu Meteorology and Geo-Hazards Department (VMGD) reported that the eruption at Ambrym was continuing and that seismicity had increased into October. Persistent thermal anomalies identified in satellite images varied between moderate and very high levels. Ongoing sulfur dioxide gas emissions were characterized as moderate to high. Residents observed gas emissions on 2 October, along with incandescence at the summit and ashfall. On 8 October the Alert Level was raised to 3 (on a scale of 0-5) and the exclusion zone was modified; the public was warned to stay outside of Permanent Danger Zone B, defined as a 2-km radius around Benbow Crater, a 2.5-km radius around Marum Crater (including Maben-Mbwelesu, Niri-Mbwelesu, and Mbwelesu craters), and a 1.5-km radius around the 2018 fissures.

Geological summary: Ambrym is a large basaltic volcano with a 12-km-wide caldera formed during a major Plinian eruption with dacitic pyroclastic flows about 1,900 years ago. A thick, almost exclusively pyroclastic sequence, initially dacitic then basaltic, overlies lava flows of a pre-caldera shield volcano. 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 been frequently reported since 1774, though mostly limited to extra-caldera eruptions that would have affected local populations. Since 1950 observations of eruptive activity from cones within the caldera or from flank vents have occurred almost yearly.

Gareloi, United States

51.79°N, 178.794°W; Elev. 1,573 m

A single brief (less than one minute) explosion was detected at Gareloi in geophysical data at 0727 on 1 October, prompting the Alaska Volcano Observatory (AVO) to raise the Volcano Alert Level to Advisory (the second lowest level on a four-level scale) and the Aviation Color Code to Yellow (the second lowest color on a four-color scale) over an hour later. Infrasound data suggested that the explosion originated at the S crater. It was unknown if ash was produced by the explosion due to weather clouds obscuring views up to 6.1 km (20,000 ft) a.s.l.; any ash would likely be minor due to the short duration of the explosion. Later that day a small crater like feature near the fumarole field on the S flank was visible in radar data. No additional signs of unrest were detected through 6 October. The Volcano Alert Level was lowered to Normal and the Aviation Color Code was lowered to Green at 1037 on 6 October.

Geological summary: The 8 x 10 km Gareloi Island, the northernmost volcano of the Delarof Group at the western end of the Andreanof Islands, consists of a stratovolcano with two summits and a prominent SE-trending fissure. The fissure was formed during an eruption in 1929 and extends from the southern summit to the sea. Steep sea cliffs that are cut into rocks of an older, eroded center are found on the SW coast, and submarine deposits of three debris avalanches produced by edifice collapse are found offshore. Young lava flows cover the older volcano from the summit to the coast along three broad axes trending NW, ENE, and S. The 1929 eruption originated from 13 craters along a 4-km-long fissure. Phreatic explosions were followed by the ejection of glassy pumice, lapilli, scoria, and older blocks, as well as by the emission of four short, steep lava flows, one of which reached the SE coast.

Hokkaido-Komagatake, Japan

42.063°N, 140.677°E; Elev. 1,131 m

The Japan Meteorological Agency (JMA) reported increased unrest at Hokkaido-Komagatake starting in late September. A slight increase in the number of volcanic earthquakes located about 1 km below sea level beneath the summit crater was detected during 23-24 September. The number of earthquakes at shallow depths increased on 26 September and seismicity continued to intensify. At 1300 that same day tiltmeters recorded uplift around the crater floor. A relatively large earthquake (M 1.4) was recorded at 2030 on 28 September. No surficial changes were observed. At 0730 on 2 October the Alert Level was raised to 2 (the second lowest level on a 5-level scale) and the public was warned that ballistics could be ejected as far as 4 km. Inflation slightly accelerated on 2 October and there was an increase in small-amplitude volcanic earthquakes mainly originating at shallow depths beneath the summit crater floor. Both seismicity and inflation slowed later that day. No earthquakes were recorded during 4-7 October, though inflation continued.

Geological summary: Much of the truncated Hokkaido-Komagatake andesitic volcano on the Oshima Peninsula of southern Hokkaido is Pleistocene in age. The sharp-topped summit lies at the western side of a large breached crater that formed as a result of edifice collapse in 1640 CE. Hummocky debris avalanche material occurs at the base of the volcano on three sides. Two late-Pleistocene and two Holocene Plinian eruptions occurred prior to the first historical eruption in 1640, which began a period of more frequent explosive activity. The 1640 eruption, one of the largest in Japan during historical time, deposited ash as far away as central Honshu and produced a debris avalanche that reached the sea. The resulting tsunami caused 700 fatalities. Three Plinian eruptions have occurred since 1640; in 1694, 1856, and 1929.

Krakatau, Indonesia

6.1009°S, 105.4233°E; Elev. 285 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported continuing eruptive activity at Krakatau during 1-7 October. White plumes were visible during 1-4 October rising as high as 50 m above the summit. The seismic network detected four eruptive events on 5 October. No eruption plumes were observed, possibly due to weather conditions or darkness, though incandescent material being ejected above the summit was visible in webcam images at 2022 and 2037. The Alert Level remained at 2 (on a scale of 1-4) and the public was advised to stay 2 km away from summit.

Geological summary: The renowned Krakatau (frequently misnamed 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.

Manam, Papua New Guinea

4.08°S, 145.037°E; Elev. 1,807 m

The Darwin Volcanic Ash Advisory Centre (VAAC) reported that an ash plume from Manam was identified in satellite images drifting WNW at 2.1 km (7,000 ft) a.s.l. on 3 October. During 5-7 October ash plumes rose to 1.8-2.1 km (6,000-7,000 ft) a.s.l. and drifted NW, N, and NE.

Geological summary: The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country’s most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical basaltic-andesitic stratovolcano to its lower flanks. These valleys channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island’s shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most observed eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Marapi, Indonesia

0.38°S, 100.474°E; Elev. 2,885 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that eruptive activity at Marapi (on Sumatra) continued during 1-7 October. Seismicity increased during the week. Eruptive events were recorded at 1000 on 1 October, at 2239 on 4 October, and at 0107 on 7 October, but not visually confirmed due to weather conditions or darkness. The Alert Level remained at 2 (on a scale of 1-4) and the public was warned to stay 3 km away from the active crater.

Geological summary: Gunung Marapi, not to be confused with the better-known Merapi volcano on Java, is Sumatra’s most active volcano. This massive complex stratovolcano rises 2 km above the Bukittinggi Plain in the Padang Highlands. A broad summit contains multiple partially overlapping craters constructed within the 1.4 km Bancah caldera. The summit craters are located along an ENE-WSW line, with volcanism migrating to the west. More than 50 eruptions, typically consisting of small-to-moderate explosive activity, have been recorded since the end of the 18th century; no lava flows outside the summit craters have been observed.

Nevados de Chillan, Chile

36.868°S, 71.378°W; Elev. 3,180 m

The Servicio Nacional de Geología y Minería (SERNAGEOMIN) and the Servicio Geológico Minero Argentino (SEGEMAR) reported that a new lava flow at Nevados de Chillán was first visible on 29 September. Seismicity intensified on 27 September. Thermal anomalies coinciding with the area where explosive activity has been reported just SW of Nicanor Crater were identified in satellite images in recent days but intensified on 29 September. A lava flow on the W flank of the summit crater complex was visible in webcam images that same day. During the early hours on 1 October there was persistent incandescence at the vent along with several explosive events producing ash plumes that rose as high as 500 m above the summit and drifted NE and SE. Increased surface temperatures were identified in satellite data on 4 October. Explosive activity increased during the early hours of 5 October, characterized by persistent incandescence in the area of the active craters and ejection of ballistics to greater distances than previously recorded. The Alert Level remained at Yellow (the second lowest level on a four-color scale) and the public was warned that an eruption may impact areas within 2 km of the active crater. The Sistema y Servicio Nacional de Prevención y Repuesta Ante Desastres (SENAPRED) maintained an “Preventive Early Alert” for Pinto and Coihueco and warned the public to stay 2 km away from Emission Center 3 (EC3).

Geological summary: The compound volcano of Nevados de Chillán is one of the most active of the Central Andes. Three late-Pleistocene to Holocene stratovolcanoes were constructed along a NNW-SSE line within three nested Pleistocene calderas, which produced ignimbrite sheets extending more than 100 km into the Central Depression of Chile. The dominantly andesitic Cerro Blanco (Volcán Nevado) stratovolcano is located at the NW end of the massif. Volcán Viejo (Volcán Chillán), which was the main active vent during the 17th-19th centuries, occupies the SE end. The Volcán Nuevo lava-dome complex formed during 1906-1945 on the NW flank of Viejo. The Volcán Arrau dome complex was then constructed on the SE side of Volcán Nuevo between 1973 and 1986, and eventually exceeded its height. Smaller domes or cones are present in the 5-km valley between the two major edifices.

Telica, Nicaragua

12.606°N, 86.84°W; Elev. 1,036 m

The Washington Volcanic Ash Advisory Center (VAAC) reported that an ash plume at Telica was identified in webcam images on 30 September rising to 1.2 km (4,000 ft) a.s.l. and drifting SW and NE. On 1 October frequent ash emissions visible in both satellite and webcam images rose as high as 1.5 km (5,000 ft) a.s.l. and drifted NW and NE. A diffuse ash plume was seen in webcam images on 3 October rising to 1.5 km a.s.l. and drifting NW.

Geological summary: Telica, one of Nicaragua’s most active volcanoes, has erupted frequently since the beginning of the Spanish era. This volcano group consists of several interlocking cones and vents with a general NW alignment. Sixteenth-century eruptions were reported at symmetrical Santa Clara volcano at the SW end of the group. However, its eroded and breached crater has been covered by forests throughout historical time, and these eruptions may have originated from Telica, whose upper slopes in contrast are unvegetated. The steep-sided cone of Telica is truncated by a 700-m-wide double crater; the southern crater, the source of recent eruptions, is 120 m deep. El Liston, immediately E, has several nested craters. The fumaroles and boiling mudpots of Hervideros de San Jacinto, SE of Telica, form a prominent geothermal area frequented by tourists, and geothermal exploration has occurred nearby.

Ongoing activity

Aira, Japan

31.5772°N, 130.6589°E; Elev. 1,117 m

The Japan Meteorological Agency (JMA) reported ongoing eruptive activity at Minamidake Crater (Aira Caldera’s Sakurajima volcano) during 28 September-5 October. Volcanologists conducted a field survey on 28 September and measured slightly high sulfur dioxide emissions, averaging 1,300 tons per day. A total of 16 eruptive events during 28-30 September, on 1 October, and on 6 October produced ash plumes that rose as high as 1.8 km above the crater and drifted in various directions. Crater incandescence was visible in nighttime webcam images during 2-5 October. An explosion at 0123 on 5 October generated an ash plume that rose 2 km above the crater rim and ejected large blocks 600-900 above the rim. The Alert Level remained at 3 (on a 5-level scale), and the public was warned to be cautious within 1 km of both the Minimadake and Showa 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.

Chikurachki, Russia

50.324°N, 155.461°E; Elev. 1,781 m

The Kamchatkan Volcanic Eruption Response Team (KVERT) reported that no further unrest at Chikurachki was detected after explosions on 20 September. The Aviation Color Code was lowered to Green (the lowest level on a four-color scale) at 2220 on 5 October. Dates are based on UTC; specific events are in local time where noted.

Geological summary: Chikurachki, the highest volcano on Paramushir Island in the northern Kuriles, is a relatively small cone constructed on a high Pleistocene edifice. Oxidized basaltic-to-andesitic scoria deposits covering the upper part of the cone give it a distinctive red color. Frequent basaltic Plinian eruptions have occurred during the Holocene. Lava flows have reached the sea and formed capes on the NW coast; several young lava flows are also present on the E flank beneath a scoria deposit. The Tatarinov group of six volcanic centers is located immediately to the south, and the Lomonosov cinder cone group, the source of an early Holocene lava flow that reached the saddle between it and Fuss Peak to the west, lies at the southern end of the N-S-trending Chikurachki-Tatarinov complex. The Tatarinov centers are extensively modified by erosion and have a more complex structure. Tephrochronology gives evidence of an eruption around 1690 CE from Tatarinov, although its southern cone contains a sulfur-encrusted crater with fumaroles that were active along the margin of a crater lake until 1959.

Etna, Italy

37.748°N, 14.999°E; Elev. 3,357 m

The Sezione di Catania – Osservatorio Etneo (INGV) reported that eruptive activity at Etna’s summit craters during 28 September-4 October was characterized by gas emissions at the summit craters and periodic minor ash emissions at Northeast Crater (NEC). Ash emissions at NEC were characterized as very short in duration with variable frequency and intensity, and overall lower than the activity observed during the previous week. The volcano Alert Level remained at Yellow (the second lowest level on a four-level scale) according to the Dipartimento della Protezione Civile.

Geological summary: Mount Etna, on the island of Sicily, has one of the world’s longest documented records of volcanism, dating back to 1500 BCE. Basaltic lava flows cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend down the flanks in all directions and have reached the sea over a broad area on the SE side.

Great Sitkin, United States

52.076°N, 176.13°W; Elev. 1,740 m

The Alaska Volcano Observatory (AVO) reported that slow lava effusion continued to feed a thick flow in Great Sitkin’s summit crater that advanced E during 28 September-7 October based on webcam and satellite images. Satellite data from 28 September revealed a small collapse on the S side of the lava dome and minor steaming from the summit area. Minor earthquakes consistent with the growth of the lava dome and occasional rockfalls were detected by the seismic network during the week. Weather clouds obscured webcam and satellite views during most of the week, though steaming at the summit area was visible in satellite images during 2-3 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 Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger 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 older edifice and produced a submarine debris avalanche. Deposits from this and an even 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. Eruptions have been recorded since the late-19th century.

Ibu, Indonesia

1.4941°N, 127.6324°E; Elev. 1,357 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that activity at Ibu continued during 1-7 October, with daily eruptive events recorded by the seismic network. Gray or white-to-gray ash plumes rose 200-700 m above the summit and drifted in multiple directions on most days; only white plumes were visible on 2 October. Incandescence at the summit and on the flanks was visible in a few webcam images. The Alert Level remained at 2 (the second lowest level on a four-level scale) and the public was advised to stay 2 km away from the active crater and 3.5 km away from the N crater wall opening.

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.

Karangetang, Indonesia

2.781°N, 125.407°E; Elev. 1,797 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that the eruption at Karangetang’s North Crater (Kawah Dua) continued during 1-7 October. White plumes rose as high as 200 m above the summit and drifted in various directions on most days. On 1 and 6 October white, gray, and brown ash plumes rose 700 m above the summit and drifted N. Incandescence at the North Crater and from lava flows and/or incandescent avalanches on the flanks was visible in some webcam images throughout the week. Rumbling sounds were occasionally reported. The Alert Level remained at 2 (on a scale of 1-4) and the public was advised to stay 1.5 km away from both craters, with an extension to 2.5 km on the NW and SW flanks of North Crater.

Geological summary: Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia’s most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented (Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.

Kilauea, United States

19.421°N, 155.287°W; Elev. 1,222 m

The Hawaiian Volcano Observatory (HVO) reported that the eruption within Kīlauea’s Kaluapele summit caldera, characterized by incandescence, intermittent spatter, and lava flows from vents along the SW and W margins of Halemaʻumʻʻu Crater, continued at variable levels during 30 September-7 October. An earthquake swarm located about 1.5 km beneath the active vents began at around 1400 on 30 September and persisted for about six hours. Seismic activity stayed at the same depth but migrated NE of the active vents around 2000, near an area where ground changes were observed in satellite data between 11 and 27 September. A second swarm continued at a high rate for nearly eight hours, with more than 50 earthquakes detected before activity subsided around 0400 on 1 October, although seismicity in the region was ongoing. At around the time the seismicity migrated NE, tiltmeters in the summit region began to show extremely rapid changes consistent with crack growth in an E-W orientation near the active vents. Elevated rates of ground deformation continued along with the earthquakes until about 0300 on 1 October. In total, the tiltmeter recorded about 40 microradians of inflation over a period of 18 hours. The seismicity and inflation indicated that a magmatic dike intrusion had occurred. Seismicity decreased over the next day; a total of around 130 earthquakes were recorded. An interferogram comparing satellite data from 24 September and 2 October showed that the dike extended from the established vent area in Halemaʻumaʻu and cut across the NW part of Kaluapele, at a depth of 300 m or less. The path of the dike followed fractures in the caldera floor that formed in 2018 and created a series of new, small fractures that were identified in satellite images.

Overflows from the vent complex stopped just prior to the onset of the intrusive activity during the afternoon of 30 September. Overflows resumed once the seismicity migrated away from the current vents and continued, even after the intrusive activity slowed and stopped. In total, there were at least 10 overflows during and after the main intrusive event. Both the N and S vents also spattered overnight and had persistent strong incandescence, and W vent had occasional incandescence. Incandescence and flaming continued to be visible at the N and S vents during 2-7 October. Periodic spattering occurred at both vents during 4-7 October. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code at Orange (the second highest color on a four-color scale).

Geological summary: Kilauea overlaps the E flank of the massive Mauna Loa shield volcano in the Island of Hawai`i. Eruptions are prominent in Polynesian legends; written documentation since 1820 records frequent summit and flank lava flow eruptions interspersed with periods of long-term lava lake activity at Halema`uma`u crater in the summit caldera until 1924. The 3 x 5 km caldera was formed in several stages about 1,500 years ago and during the 18th century; eruptions have also originated from the lengthy East and Southwest rift zones, which extend to the ocean in both directions. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1,100 years old; 70% of the surface is younger than 600 years. The long-term eruption from the East Rift Zone between 1983 and 2018 produced lava flows covering more than 100 km2, destroyed hundreds of houses, and added new coastline.

Lewotolok, Indonesia

8.274°S, 123.508°E; Elev. 1,431 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported continuing eruptive activity at Lewotolok during 1-7 October. Gray ash plumes rose 100-600 m above the summit and drifted NW and W during 2-3 and 5-6 October. An active lava flow on the SE flank was 500 m long. Several webcam images showed incandescent material being ejected above the summit and onto the flanks. The Alert Level remained at 2 (on a scale of 1-4). The public was warned to stay 2 km away from the summit with an extension to 3 km on the S and SE flanks.

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, Philippines

13.257°N, 123.685°E; Elev. 2,462 m

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported ongoing activity at Mayon during 30 September- 7 October. The seismic network recorded 8-19 daily volcanic earthquakes. Sulfur dioxide emissions generally averaged 457-1,468 tonnes per day. Daily emissions rose 100-900 m above the crater and drifted in multiple directions. One ash emission lasting one minute was recorded on 2 October. At 0804 on 3 October a grayish ash plume rose 200 m above the summit and drifted SW. Minor Strombolian activity was observed that same day. The Alert Level remained at 2 (on a 0-5 scale) and the public was 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 periods of andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic density currents 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, Indonesia

7.54°S, 110.446°E; Elev. 2,910 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that the eruption at Merapi (on Java) continued during 1-7 October with avalanches produced by the active lava dome on the upper SW flank. The seismic network recorded multiple lava avalanches per day that traveled as far as 2.5 km down the Sat/Putih and Krasak drainages on the SW flank and the Boyong drainage on the S flank. On 1 October a pyroclastic flows traveled 1.6 km down the Boyong drainage. 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.

Purace, Colombia

2.3095°N, 76.3948°W; Elev. 4,650 m

The Washington Volcanic Ash Advisory Center (VAAC) reported that during 30 September-7 October daily ash plumes from Puracé rose to 5.1-6.4 km (17,000-21,000 ft) a.s.l., or as high as 1.8 km above the summit, and drifted in multiple directions based on webcam images, satellite images, weather models, and Volcano Observatory Notices to Aviation issued by the Servicio Geológico Colombiano (SGC). The Alert Level remained at Yellow (the second lowest level on a four-color scale).

Geological summary: Puracé is an active andesitic volcano with a 600-m-diameter summit crater at the NW end of the Los Coconucos Volcanic Chain. This volcanic complex includes nine composite and five monogenetic volcanoes, extending from the Puracé crater more than 6 km SE to the summit of Pan de Azúcar stratovolcano. The dacitic massif which the complex is built on extends about 13 km NW-SE and 10 km NE-SW. Frequent small to moderate explosive eruptions reported since 1816 CE have modified the morphology of the summit crater, with the largest eruptions in 1849, 1869, and 1885.

Rincon de la Vieja, Costa Rica

10.8314°N, 85.3364°W; Elev. 1,729 m

The Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional (OVSICORI-UNA) reported that small phreatic eruptions at Rincón de la Vieja had become more frequent since July. The Comisión Nacional de Prevención de Riesgos y Atención de Emergencias (CNE) raised the Alert Level to Yellow (second level on a four-color scale) for the districts of Dos Ríos (13 km N) and Aguas Claras (3 km NW) in the canton of Upala (22 km ENE), as well as the districts of Cañas Dulces (24 km ESE), Curubandé (18 km SW), and Mayorga (15 km W) in the canton of Liberia (21 km SW). CNE noted that there were more than 170 phreatic eruptions during the previous week. Daily phreatic eruptions were recorded during 4-7 October. The Alert Level remained at 3 (Caution) and the Aviation Color Code remained Orange.

Geological summary: Rincón de la Vieja is a volcanic complex in the Guanacaste Range of NW Costa Rica. Sometimes referred to as the Rincon de la Vieja-Santa María Volcanic Complex, it consists of a slightly arcuate 20-km-long ridge of 12 craters and pyroclastic cones constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the “Colossus of Guanacaste,” it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. The Santa María cone, the highest peak of the complex, is located on the E side of the ridge and has a lake within the 400-m-diameter crater. A Plinian eruption producing the 0.25 km3 Río Blanca tephra about 3,500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous reported eruptions possibly dating back to the 16th century, have been from the active crater, near the center of the complex, with an acidic 300-m-diameter lake.

Sabancaya, Peru

15.787°S, 71.857°W; Elev. 5,960 m

The Instituto Geofísico del Perú’s (IGP) Centro Vulcanológico Nacional (CENVUL) reported continuing eruptive activity at Sabancaya during 28 September-4 October. The seismic network detected 52 seismic events associated with the movement of magmatic fluids, along with earthquakes indicating internal rock fracturing; no volcanic explosions occurred during the period. Gas, steam, and ash emissions periodically rose as high as 900 m above the summit and drifted less than 10 km W. Moderate sulfur dioxide (SO₂) emissions averaged 1,910 tons per day, and seven thermal anomalies (each 1 MW or less) associated with the lava dome were identified. The Alert Level remained at Orange (the third level on a four-color scale) and the public was warned to stay outside of a 12 km radius from the summit.

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 observed eruptions date back to 1750 CE.

Semeru, Indonesia

8.108°S, 112.922°E; Elev. 3,657 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that activity continued at Semeru during 1-7 October, with daily eruptive events recorded by the seismic network. Daily white-to-gray or gray ash plumes rose 400-1,300 m above the summit and drifted in multiple directions. The Alert Level remained at 3 (the second highest level on a scale of 1-4) and the public was warned to stay at least 5 km away from the Jonggring Saloko Crater in all directions, 13 km from the summit on the SE flank along the Kobokan drainage, and 500 m from the banks of the Kobokan drainage as far as 17 km SE of the summit.

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, Russia

56.653°N, 161.36°E; Elev. 3,283 m

The Kamchatkan Volcanic Eruption Response Team (KVERT) reported continuing lava effusion and explosive activity at the lava domes along the N crater floor of Young Sheveluch (on the SW flank of Old Sheveluch) during 1-7 October. A thermal anomaly was identified in satellite images on a few of the days; weather clouds occasionally obscured views. Explosive activity during 2240-2245 on 4 October generated ash plumes that rose 6.5 km (21,300 ft) a.s.l. and drifted 87 km NE by 5 October. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Dates are based on UTC; 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.

Stromboli, Italy

38.789°N, 15.213°E; Elev. 924 m

The Sezione di Catania – Osservatorio Etneo (INGV) reported that eruptive activity continued at Stromboli during 28 September-4 October. Webcam images showed Strombolian activity from vents in Area N within the upper part of the Sciara del Fuoco, and vents in Area C-S (South-Central Crater) on the crater terrace. Explosions at Area N ejected lapilli and bombs above the vents and explosions at Area C-S ejected both fine and coarse tephra above the vents. The daily frequency of explosions at both vents was at medium-to-low levels and the intensity of the explosions was generally at medium levels. Lava overflowed Area N during the early morning hours on 1 October and ended at 0952. The lava flow split into two branches and stopped in the upper part of the Sciara del Fuoco. The Alert Level remained at Yellow (the second lowest level on a four-level scale) according to the Dipartimento della Protezione Civile.

Geological summary: Spectacular incandescent nighttime explosions at Stromboli have long attracted visitors to the “Lighthouse of the Mediterranean” in the NE Aeolian Islands. This volcano has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent scarp that formed about 5,000 years ago due to a series of slope failures which extends to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

References:

¹ Smithsonian Institution / US Geological Survey Weekly Volcanic Activity Report – GVP – October 1-7, 2026 – Managing Editor: Sally Sennert

Teo Blašković

Teo Blašković founded The Watchers in 2011 and edited it until 2026, covering seismic and volcanic activity, extreme weather, space weather and near-Earth objects. Articles on this page are his archive.

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