The Weekly Volcanic Activity Report: September 24-30, 2026

New eruptive activity/unrest: Ambrym, Vanuatu | Chikurachki, Russia | Krakatau, Indonesia | Marapi, Indonesia | Masaya, Nicaragua | Nevados de Chillan, Chile | Sangay, Ecuador.

Continuing eruptive activity, unrest, or other observations: Aira, Japan | Etna, Italy | Fuego, Guatemala | Great Sitkin, United States | Ibu, Indonesia | Karangetang, Indonesia | Kilauea, United States | Lewotolok, Indonesia | Mayon, Philippines | Merapi, Indonesia | Papandayan, Indonesia | Purace, Colombia | Reventador, Ecuador | Sabancaya, Peru | Santa Maria, Guatemala | Semeru, Indonesia | Sheveluch, Russia | Stromboli, Italy.

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 continued during 21-29 September. A thermal anomaly continued to be identified in satellite images, though it was gradually decreasing in intensity. During an overflight on 28 September observers saw an intense glow through weather clouds and from within the volcanic plume in Marum Crater. Closer observations revealed explosive activity ejecting incandescent material high above a vent. The Alert Level remained at 2 (on a scale of 0-5). 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 (including Maben-Mbwelesu, Niri-Mbwelesu, and Mbwelesu craters).

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.

Chikurachki, Russia

50.324°N, 155.461°E; Elev. 1,781 m

The Kamchatkan Volcanic Eruption Response Team (KVERT) reported ongoing activity at Chikurachki during 24-30 September. A thermal anomaly was identified in satellite images during 26-27 September; weather clouds obscured views on a few of the days. KVERT noted that explosions had not been detected since 20 September. At 2204 on 28 September the Aviation Color Code was lowered to Yellow (the second lowest level on a four-color scale). 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.

Krakatau, Indonesia

6.1009°S, 105.4233°E; Elev. 285 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that two small islands near Krakatau were newly visible after the larger eruption in early September. The continuous eruption during 4-6 September produced lava fountains, widespread ashfall, and lava flows that advanced NW, W, and SW. The deposits changed the W and SW coastlines and increased the size of the island by 32.8 hectares, making the total size of the island 341.5 hectares. Small new islands were observed on 22 September by people visiting and photographing the area. The islands were located approximately 760 m from the NW coast and approximately 495 m from the SE coast; the new islands and the central part of the main island are aligned on a NW-SE trend. The emergence of the islands is thought to be linked to the 4-6 September eruption, though PVMBG noted that further data, observations, and analysis were needed to confirm if they were new eruption centers or not. The public was advised to stay 2 km away from summit, and on 24 September the public was warned to stay 1 km away from the new islands. The Alert Level remained at 2 (on a scale of 1-4).

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.

Marapi, Indonesia

0.38°S, 100.474°E; Elev. 2,885 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that an eruptive event at Marapi (on Sumatra) was recorded at 2140 on 26 September. Webcam views were obscured by weather conditions. According to news reports the event was accompanied by loud booms and rumbling sounds, generated an ash plume that rose 1 km above the summit, and ejected incandescent material onto the upper flanks based on video and eye-witness accounts posted on social media by residents. Ashfall was reported in Bukittinggi City; a resident posted a video of ashfall at 2257 on attendees at an outdoor concert. An eruptive event recorded at 1735 on 29 September was not visually confirmed due to weather conditions. 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.

Masaya, Nicaragua

11.9844°N, 86.1688°W; Elev. 594 m

The Washington Volcanic Ash Advisory Center (VAAC) reported that during 1230-1400 on 28 September diffuse ash plumes from Masaya were visible in satellite and webcam images rising to 2.1-2.4 km (7,000-8,000 ft) a.s.l. and drifting over 22 km W and NW.

Geological summary: Masaya volcano in Nicaragua has erupted frequently since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano’s molten “gold” until it was found to be basalt rock upon cooling. It lies within the massive Pleistocene Las Sierras caldera and is itself a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The Nindirí and Masaya cones, the source of observed eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6,500 years ago. Recent lava flows cover much of the caldera floor and there is a lake at the far eastern end. A lava flow from the 1670 eruption overtopped the north caldera rim. Periods of long-term vigorous gas emission at roughly quarter-century intervals have caused health hazards and crop damage.

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 increasing activity at Nevados de Chillán in late September, particularly at Emission Center 3 (EC3) on the W margin of the summit complex. Seismicity indicated 1-3 daily explosions and possible ash plumes during 23-26 September, but weather conditions prevented visual confirmation on most days; an explosion at 2320 on 25 September produced an ash plume that rose 700 m above the summit and drifted SE. On 23 September the Sistema y Servicio Nacional de Prevención y Repuesta Ante Desastres (SENAPRED) warned the public to stay 2 km away from EC3.

Explosions at both 0517 and 0625 on 27 September ejected ballistics towards the NW and generated ash plumes that rose 900 m above the summit and drifted SSE. Crater incandescence associated with the events was visible. An ash plume from an explosion at 0942 on 28 September rose 500 m above the summit and drifted SSE. Similar explosions were observed throughout the day. At 0652 on 29 September an explosion generated an ash plume that rose 600 m above the summit and drifted SSE as well as a pyroclastic flow. Similar explosions were detected throughout the rest of the day. 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 “Early Preventive Alert” for Pinto and Coihueco.

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.

Sangay, Ecuador

2.005°S, 78.341°W; Elev. 5,286 m

The Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN) reported that volcanic activity at Sangay continued during 23-30 September. The seismic network recorded 1-14 daily explosions, a few long-period earthquakes, a period of harmonic tremor, and 0-6 daily signals indicating emissions. Daily ash-and-gas plumes visible in webcam views and satellite images, and those reported by the Washington Volcanic Ash Advisory Center, rose as high as 1.5 km above the crater rim and drifted in multiple directions, though mainly NW and W. During dark hours incandescence at the summit was visible along with the occasional descent of incandescent material as far as 400 m down the flank; weather clouds sometimes prevented visual observations. Several ejections of incandescent material at the summit were visible in webcam images during 29-30 September. The Secretaría de Gestión de Riesgos (SGR) maintained the Alert Level at Yellow (the second highest level on a four-color scale).

Geological summary: The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador’s volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within the open calderas of two previous edifices which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been eroded by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of an eruption was in 1628. Almost continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

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 14-21 September. Crater incandescence was visible in nighttime webcam images during 14-18 September. Volcanologists conducted a field survey on 15 September and measured high sulfur dioxide emissions, averaging 2,600 tons per day. A total of 32 eruptive events during the week produced ash plumes that rose as high as 2.5 km above the crater and ejected large blocks 600 m from the vent. 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.

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 21-27 September was characterized by gas emissions at the summit craters and periodic ash emissions at Northeast Crater (NEC). Ash emissions at NEC increased on 24 September and were reddish-brown in color. The plume rose about 4 km (13,000 ft) a.s.l., or about 650 m above the summit, and caused minor ashfall downwind on the SE flank as far as the coast (around 20 km). During the late afternoon of 28 September ash emissions were variable and at times very diffuse. 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.

Fuego, Guatemala

14.4748°N, 90.8806°W; Elev. 3,799 m

The Instituto Nacional de Sismología, Vulcanologia, Meteorologia e Hidrología (INSIVUMEH) reported that eruptive activity at Fuego continued during 23-30 September. Daily explosions recorded by the seismic network, at rates of 1-7 per hour, generated gas-and-ash plumes that rose as high as 1.2 km above the summit and mainly drifted as far as 40 km W, NW, and N, and occasionally to the SE. Explosions produced shock waves and rumbling sounds that were reported daily. Explosions often ejected incandescent material, sometimes as high as 300 m above the summit, and onto the flanks causing incandescent block avalanches; notable avalanches descended the Seca (W), Taniluyá (SSW), Ceniza (SSW), Honda, and Las Lajas (SE) drainages, sometimes reaching vegetated areas. Occasional collapses at the summit also caused incandescent block avalanches. Ashfall was reported in Panimaché II (8 km SW), Yepocapa (8 km NW), and surrounding areas during 25-26 September, and in communities on the NW flank during 27-28 September.

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 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, 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 16-23 September based on webcam and satellite images. Minor earthquakes consistent with the growth of the lava dome and occasional rockfalls were detected by the seismic network on a few of the days. Weather clouds obscured webcam and satellite views during most of the week, though steaming at the summit area was visible in satellite images during 27-28 September. 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 24-30 September, with daily eruptive events recorded by the seismic network. Gray ash plumes rose 200-600 m above the summit and drifted N and NE on most days; weather conditions obscured views on 27 September. 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 24-30 September. White plumes rose as high as 700 m above the summit and drifted in various directions on most days; white-and-gray plumes rose 20 m and drifted in different directions on 25 and 27 September. 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 noted on most days. At 1807 on 30 September a dense white-and-gray ash plume rose 1 km above the summit and drifted N. 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 craters and vents along the SW and W margins of Halemaʻumaʻu Crater, continued at variable levels during 24-30 September. Incandescence and flaming continued at the N, W, and S vents, with intermittent spatter bursts from all of the vents. After about 10 days of quiescence at the vent complex overflows at the N vent began at 2210 on 22 September; by evening on 28 September the vent had overflowed 85 times. Many of the overflows were fed by vigorous fountains that rose 5-10 m above the 10-15 m cone that had built up at the north vent. Most of the overflows lasted about 10-35 minutes and produced lava flows that traveled a few hundred meters from the vent. Starting at 1944 on 28 September through 0900 on 29 September the N vent produced a series of 80 short, rapid cycles of overflows and lava drainbacks. Each overflow lasted about 2-5 minutes, with most pauses between each cycle lasting about 5-7 minutes. During 27-29 September the S vent produced several small lava flows. 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 24-30 September. Gray ash plumes rose 400-700 m above the summit and drifted NW and W almost daily; white plumes rose 300 m above the summit on 28 September. 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 23-29 September. The seismic network recorded 8-22 daily volcanic earthquakes; one rockfall was recorded on both 23 and 24 September. Sulfur dioxide emissions generally averaged 692-1,249 tonnes per day. Daily emissions rose 500-900 m above the crater and drifted in different directions. One ash emission lasting one minute was recorded on 23 September. Minor Strombolian activity was observed on 26 September. 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 24-30 September with lava avalanches produced by the active lava dome on the upper SW flank. The seismic network recorded up to three lava avalanches per day that traveled as far as 2.5 km down the Sat/Putih drainage on the SW flank and the Boyong drainage on the S flank. 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.

Papandayan, Indonesia

7.3175°S, 107.7306°E; Elev. 2,643 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that blue flames at the Manifestasi Panas Baru site at Papandayan’s Manuk Crater were visible during the early hours of 24 September. The blue flames suggested intense temperatures and combustion of surface materials; a powdery residue resembling combustion ash was observed near the site. Thermal activity at the site had been decreasing. There were no significant changes to gas emission ratios, though significant volcanic gas emissions continued to be detected. A strong sulfur odor was detected in areas downwind. Blue flames were last observed in July 2025 at Baru Crater. The Alert Level remained at 1 (on a scale of 1-4) and tourists were advised to stay 500 m away from the active craters.

Geological summary: Papandayan is a complex stratovolcano at the S end of a curved volcanic massif with Kendang volcano ~9 km away at the N end, Gunung Puntang ~3.5 km NNE, and Gunung Jaya ~6 km NNE. Several episodes of collapse have created an irregular profile and produced debris avalanches that have affected lowland areas. The summit area includes four large craters, including the 1.1-km-wide, flat-floored Alun-Alun crater. A sulfur-encrusted fumarole field occupies the active Kawah Mas (“Golden Crater”). The first reported eruption, in 1772 CE, included a collapse of the NE flank and a debris avalanche that destroyed 40 villages and killed almost 3,000 people. Smaller phreatic eruptions occurred during 1923-25, 1942, and 2002.

Purace, Colombia

2.3095°N, 76.3948°W; Elev. 4,650 m

The Servicio Geologico Colombiano (SGC) reported decreasing eruptive activity at Puracé by the end of September. Thermal anomalies generated by high-temperature gas emissions had decreased to low levels. Sulfur dioxide emissions did not significantly increase nor show abrupt variations, and carbon dioxide emission levels significantly decreased during the past two weeks. Starting on 15 September there was a notable decrease in the frequency and energy of ash emissions; 2-3 daily ash emissions rose as high as 600 m above the summit when seen during 26-28 September. Seismic energy associated with fluid movements within the volcano had decreased over the previous few days. On 29 September the Alert Level was lowered to 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.

Reventador, Ecuador

0.077°S, 77.656°W; Elev. 3,562 m

The Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN) reported that eruptive activity at Reventador continued at a high level during 23-30 September. Seismicity included 74-97 daily explosions, long-period earthquakes, harmonic tremor, and tremor associated with emissions. Daily ash-and-gas plumes were visible in webcam images and reported by the Washington Volcanic Ash Advisory Center rising as high as 1.3 km above the crater rim and drifting NW, WNW, and W. Incandescent blocks were visible during dark hours each day rolling as far as 1.1 km down the flanks. Secretaría de Gestión de Riesgos (SGR) maintained the Alert Level at Orange (the second highest level on a four-color scale).

Geological summary: Volcán El Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic stratovolcano has 4-km-wide avalanche scarp open to the E formed by edifice collapse. A young, unvegetated, cone rises from the amphitheater floor to a height comparable to the rim. It has been the source of numerous lava flows as well as explosive eruptions visible from Quito, about 90 km ESE. Frequent lahars in this region of heavy rainfall have left extensive deposits on the scarp slope. The largest recorded eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

Sabancaya, Peru

15.787°S, 71.857°W; Elev. 5,960 m

The Instituto Geofísico del Perú’s (IGP) Centro Vulcanológico Nacional (CENVUL) reported continuing eruptive activity at Sabancaya during 21-27 September. The seismic network detected 42 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 1.5 km above the summit and drifted less than 10 km W. Moderate sulfur dioxide (SO₂) emissions averaged 581 tons per day, and 13 thermal anomalies (each 2 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.

Santa Maria, Guatemala

14.757°N, 91.552°W; Elev. 3,745 m

The Instituto Nacional de Sismología, Vulcanología, Meteorología e Hidrología (INSIVUMEH) reported ongoing eruptive activity at Santa Maria’s Santiaguito dome complex during 23-30 September, with continuing lava extrusion at Caliente dome. Incandescence at the summit was observed during dark hours. Effusion of blocky lava and collapses of material produced daily incandescent block avalanches that descended the flanks, particularly the W, SW, and S flanks. Daily explosions, 0-3 per hour when reported, generated gas-and-ash plumes that rose as high as 1.3 km above the dome and drifted SW, W, and NW. Ashfall was reported in the mountainous area of the Monteclaro settlement and its surroundings during 25-26 September, along with farms and communities on the SE flank during 28-29 September.

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 E towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

Semeru, 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 24-30 September, with daily eruptive events recorded by the seismic network. Daily white-to-gray ash plumes rose 300-1,300 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 24-30 September. A thermal anomaly was identified in satellite images on most days; weather clouds occasionally obscured views. An explosion at 1750 on 25 September generated ash plumes that rose 10.5 km (34,400 ft) a.s.l. and drifted 300 km W. Minor ashfall was reported in Klyuchi (50 km SW) according to the Institute of Volcanology and Seismology (IVS) of the Far Eastern Branch of the Russian Academy of Sciences (FEB RAS). An ash plume from an explosion at 2120 on 27 September rose around 10 km (32,800 ft) a.s.l. and drifted 850 km W. 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 21-27 September. 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-high levels and the intensity of the explosions was generally at low levels. 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 – September 24-30, 2026 – Managing Editor: Sally Sennert