The Weekly Volcanic Activity Report: December 17-23, 2025

New activity/unrest: Home Reef, Tonga | Purace, Colombia | Sabancaya, Peru | Yellowstone, United States.

New activity/unrest

Home Reef, Tonga

18.992°S, 174.775°W | Summit elev. -10 m

Satellite images of Home Reef showed that between 17-22 December new lobes of lava advanced in multiple directions from a crater the center of the island. Flows to the E and SE each entered the ocean and extended the coastline by about 100 m. Near infrared data on 17 and 22 December showed thermal anomalies over the summit; the 22 December image showed brighter areas over the at least six lava flows in all sectors except the SW.

Geologic 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.

Purace, Colombia

2.3095°N, 76.3948°W | Summit elev. 4650 m

The Servicio Geologico Colombiano (SGC) reported continuing eruptive activity at Puracé during 17-23 December. Seismicity was characterized by pulses of tremor, long-period signals indicating fluid movement, and periods of continuous tremor. The seismicity was located at depths of less than 2 km and was related to internal movement of gases as well as emissions. Low-magnitude earthquakes indicating rock fracturing were located beneath Puracé and Piocollo volcanoes, within 3 km of the craters, at depths of 1-3 km. Gas-and-ash emissions, 2-7 per day, were associated with some seismic signals and visible in webcam images rising 600-1,700 m above the summit and drifting NW, W, and SW. Significant sulfur dioxide emissions detected in satellite data dispersed within 250 m of the crater. Elevated temperatures in the crater area continued to be detected and were possibly associated with the emissions of hot gases. White gas-and-steam emissions, first observed on 18 November, continued to rise from the fissure on the inner N wall. Ashfall was reported in Cristales (NW) and in the area of the Puracé Indigenous Reserve Cabildo (NW) during 16-17 December and in Coconuco (12 km WNW) and in Chapa (28 km SW) of the municipality of Sotará (23 km W) during 17-18 December. A gas odor was reported in Chapa and ashfall was noted in the Río Negro sector and at the Paletará Indigenous Council House (16 km SW) during 18-19 December. The Alert Level remained at Orange (the second highest level on a four-color scale) and the public was warned to stay away from the crater.

Geologic 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.

Sabancaya, Peru

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

The Instituto Geofísico del Perú’s (IGP) Centro Vulcanológico Nacional (CENVUL) reported eruptive activity at Sabancaya during 15-22 December. The seismic network detected 8-14 daily earthquakes indicating the movement of magma and gases. An explosion on 16 December generated a gas, steam, and ash plume that rose 1.3 km above the crater rim. Six thermal anomalies at the bottom of the crater were identified in satellite images. The next day, on 17 December, an explosion produced a gas, steam, and ash plume that rose 1.2 km above the crater rim. Three thermal anomalies at the bottom of the crater were identified in satellite images. Daily gas-and-steam plumes rose as high as 1.3 km above the crater rim during the rest of the week and drifted in various directions within 10 km. There were 1-2 thermal anomalies identified in satellite images each day during 20-22 December. 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.

Geologic 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.

Yellowstone, United States

44.43°N, 110.67°W | Summit elev. 2805 m

The Yellowstone Volcano Observatory (YVO) reported that a small hydrothermal explosion occurred at Black Diamond Pool, in Yellowstone’s Biscuit Basin thermal area, at 0923 on 20 December based on webcam images. 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 color on a four-color scale).

Geologic summary: The Yellowstone Plateau volcanic field developed through three volcanic cycles spanning two million years that included some of the world’s largest known eruptions. Eruption of the over 2,450 km3 Huckleberry Ridge Tuff about 2.1 million years ago created the more than 75-km-long Island Park caldera. The second cycle concluded with the eruption of the Mesa Falls Tuff around 1.3 million years ago, forming the 16-km-wide Henrys Fork caldera at the western end of the first caldera. Activity subsequently shifted to the present Yellowstone Plateau and culminated 640,000 years ago with the eruption of the over 1,000 km3 Lava Creek Tuff and the formation of the present 45 x 85 km caldera. Resurgent doming subsequently occurred at both the NE and SW sides of the caldera and voluminous (1000 km3) intracaldera rhyolitic lava flows were erupted between 150,000 and 70,000 years ago. No magmatic eruptions have occurred since the late Pleistocene, but large hydrothermal events took place near Yellowstone Lake during the Holocene. Yellowstone is presently the site of one of the world’s largest hydrothermal systems, including Earth’s largest concentration of geysers.

Ongoing activity

Ahyi, United States

20.437°N, 145.03°E | Summit elev. -50 m

On 19 December the US Geological Survey reported that there were no definitive signs of unrest at Ahyi Seamount during the previous week. One low-confidence detection from Ahyi’s direction was observed in data from underwater pressure sensors near Wake Island (about 2,270 km E of Ahyi) on 17 December. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level remained at Advisory (the second lowest level on a four-level scale).

Geologic summary: Ahyi seamount is a large conical submarine volcano ~18 km SE of the island of Farallon de Pajaros in the northern Marianas. Water discoloration has been observed there, and in 1979 the crew of a fishing boat felt shocks over the summit area, followed by upwelling of sulfur-bearing water. On 24-25 April 2001 an explosive eruption was detected seismically by a station on Rangiroa Atoll, Tuamotu Archipelago. The event was well constrained (+/- 15 km) at a location near the southern base of Ahyi. An eruption in April-May 2014 was detected by NOAA divers, hydroacoustic sensors, and seismic stations.

Aira, Japan

31.5772°N, 130.6589°E | Summit elev. 1117 m

The Japan Meteorological Agency (JMA) reported ongoing eruptive activity at Minamidake Crater (Aira Caldera’s Sakurajima volcano) during 15-22 December. Nightly crater incandescence was visible in webcam images and small eruptive events were occasionally detected. Sulfur dioxide emissions were characterized as high, averaging 2,800 tons per day on 19 December. The Alert Level remained at 3 (on a 5-level scale), and the public was warned to be cautious within 2 km of both the Minimadake and Showa craters.

Geologic summary: The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan’s most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim and built an island that was joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4,850 years ago, after which eruptions took place at Minamidake. Frequent eruptions since the 8th century have deposited ash on the city of Kagoshima, located across Kagoshima Bay only 8 km from the summit. The largest recorded eruption took place during 1471-76.

Dukono, Indonesia

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

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that eruptive activity at Dukono continued during 17-23 December. Daily white-and-gray gas-and-ash plumes rose as high as 800 m above the summit and drifted E. The Alert Level remained at Level 2 (on a scale of 1-4) and the public was warned to stay 4 km away from the Malupang Warirang Crater.

Geologic summary: The Dukono complex in northern Halmahera is on an edifice with a broad, low profile containing multiple peaks and overlapping craters. Almost continuous explosive eruptions, sometimes accompanied by lava flows, have occurred since 1933. During a major eruption in 1550 CE, a lava flow filled in the strait between Halmahera and the Gunung Mamuya cone, 10 km NE. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also had reported eruptions.

Fuego, Guatemala

14.4748°N, 90.8806°W | Summit elev. 3799 m

The Instituto Nacional de Sismología, Vulcanologia, Meteorologia e Hidrología (INSIVUMEH) reported that eruptive activity at Fuego continued during 16-23 December. Daily Strombolian explosions recorded by the seismic network, at rates of 4-12 per hour, generated gas-and-ash plumes that rose as high as 1.1 km above the summit and drifted as far as 30 km in multiple directions. Occasional rumbling sounds, shock waves, and/or sounds associated with gas emissions were reported. Explosions occasionally ejected incandescent material as high as 300 m above the summit and showered the upper flanks with incandescent material. Incandescent block avalanches descended the Las Lajas (SE), Santa Teresa (W), Taniluya (SSW), and Ceniza (SSW) drainages, sometimes reaching vegetated areas. Ashfall was reported in areas downwind including Panimaché I and II (8 km SW), Morelia (10 km SW), and Yepocapa (8 km NW) during 16-17 December, in Panimaché I and II and Finca Paloverde (10 km SW) during 17-18 December, and in San Pedro Yepocapa and other areas on the SW flank during 20-21 December. During the early afternoon on 18 December lahars descended the Ceniza, Zarco, and Mazate drainages, carrying tree branches, trunks, volcanic material, and blocks as large as 3 m in diameter.

Geologic 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 | Summit elev. 1740 m

The Alaska Volcano Observatory (AVO) reported that slow lava effusion continued to feed a thick flow in Great Sitkin’s summit crater during 16-22 December. The dome continued to slowly inflate and there was minor advancement at the margins of the flow. Seismicity was low, though a data outage that began on 20 December degraded seismic monitoring. Elevated surface temperatures consistent with lava effusion were identified in satellite data daily or almost daily. 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).

Geologic 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 | Summit elev. 1357 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that the eruption at Ibu continued during 17-23 December. Daily white-to-gray or gray ash plumes rose 200-900 m above the summit and drifted in multiple directions; weather conditions occasionally prevented visual confirmation. Incandescence at the summit was visible in several nighttime 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.

Geologic 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.

Kanlaon, Philippines

10.4096°N, 123.13°E | Summit elev. 2422 m

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported continuing eruptive activity at Kanlaon during 16-23 December. The seismic network recorded 1-7 daily volcanic earthquakes. Gas-and-steam emissions of variable densities rose as high as 100 m above the crater rim and drifted NW, W, and SW; weather clouds obscured views on 18 December. Daily sulfur dioxide emissions ranged from 1,787 to 2,763 tonnes per day. Diffuse ash emissions rose 300 m above the summit and drifted NW during 0901-0929 and 1029-1107. Later that day a period of ash emissions began at 1605 and persisted for about two hours, sending plumes as high as 900 m above the summit that drifted NW. By the end of the day there had been four periods of ash emissions. The Alert Level remained at 2 (on a scale of 0-5); the public was warned to stay out of the 4-km-radius Permanent Danger Zone (PDZ) and pilots were advised to avoid flying close to the summit.

Geologic summary: Kanlaon volcano (also spelled Canlaon) forms the highest point on the Philippine island of Negros. The massive andesitic stratovolcano is covered with fissure-controlled pyroclastic cones and craters, many of which are filled by lakes. The largest debris avalanche known in the Philippines traveled 33 km SW from Kanlaon. The summit contains a 2-km-wide, elongated northern caldera with a crater lake and a smaller but higher active vent, Lugud crater, to the south. Eruptions recorded since 1866 have typically consisted of phreatic explosions of small-to-moderate size that produce minor local ashfall.

Katmai, United States

58.279°N, 154.9533°W | Summit elev. 2047 m

The Anchorage Volcanic Ash Advisory Center (VAAC) reported that during 16-17 and 20 December plumes of unconsolidated ash in the vicinity of Katmai and the Valley of Ten Thousand Smokes were visible in satellite images rising to 1.8 km (6,000 ft) a.s.l. Plumes drifted SE on 20 December. The ash was originally deposited during the Novarupta-Katmai eruption in 1912. 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).

Geologic summary: Katmai was initially considered to be the source of the Valley of Ten Thousand Smokes ash flow in 1912. However, the 3 x 4 km caldera of 1912 is now known to have formed as a result of the voluminous eruption at nearby Novarupta volcano. The edifice had four NE-SW-trending summits, most of which were truncated by the 1912 collapse. Two or more large explosive eruptions took place during the late Pleistocene. Most of the two overlapping pre-1912 Katmai volcanoes are Pleistocene, but Holocene lava flows from a flank vent descend the SE flank of the SW edifice into the Katmai River canyon. The steep walled young caldera has a jagged rim that rises 500-1,000 m above the caldera floor and contains a deep lake. Lake waters have covered a small post-collapse lava dome (Horseshoe Island) that was seen on the caldera floor at the time of the initial ascent to the caldera rim in 1916.

Kilauea, United States

19.421°N, 155.287°W | Summit elev. 1222 m

The Hawaiian Volcano Observatory (HVO) reported that the eruption within Kilauea’s Kaluapele summit caldera, characterized by episodic fountaining, incandescence, and intermittent spatter from craters along the SW margin of Halema’uma’u Crater, continued at variable levels during 16-22 December. Incandescence at both the S and N vents was visible during dark hours on most nights, though sometimes weather conditions prevented clear views. Seismic signals showed pronounced tremor bursts every 3-12 minutes during 16-17 December, possibly related to gas pistoning. Continuous, low level volcanic tremor signals were recorded during the rest of the week. Sulfur dioxide emission rates averaged 3,400 tonnes per day (t/d) on 17 December; the rate was somewhat elevated relative to emission rates of 1,200-1,500 t/d typically observed during non-fountaining periods. Incandescence was continuous at both vents during 21-22 December; nearly-continuous spattering occurred at one side of the N vent and the S vent produced intermittent spatter. 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).

Geologic summary: Kilauea overlaps the E flank of the massive Mauna Loa shield volcano in the island of Hawaii. 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 Halemaumau 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.

Krasheninnikov, Russia

54.596°N, 160.27°E | Summit elev. 1816 m

The Kamchatkan Volcanic Eruption Response Team (KVERT) reported that eruptive activity at Krasheninnikov continued during 11-18 December. A large thermal anomaly over the volcano was identified in satellite images during 12, 15, and 17-18 December; weather clouds obscured views on the other days. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Dates and times are provided in Coordinated Universal Time (UTC); specific events are indicated in local time where specified.

Geologic summary: The late Pleistocene to Holocene Krasheninnikov volcano is comprised of two overlapping stratovolcanoes within a 9 x 10 km Pleistocene caldera. Young lava flows from summit and flank vents descend both into the caldera and down its outer flanks, and older flows that covered much of the SE caldera rim extended downslope at least 7 km. Tephra deposits from the caldera-forming eruption directly overlie a 39,000 years before present (BP) tephra thought to be associated with the formation of Uzon caldera (Florenskii, 1988). The intra-caldera stratovolcanoes are situated along a NE-SW-trending fissure that has also produced zones of Holocene cinder cones extending 15-20 km beyond the caldera. Construction of the southern edifice began about 11,000 years BP and lasted for about 4,500 years; it has a summit crater about 800-900 m wide. The northern edifice was constructed during a cycle of similar length that began about 6,500 years ago; it has a summit crater about 1.5 km wide, within which is low cone with an 800-m-wide crater containing another small cone. An eruptive cycle during about 600-400 years BP (1350-1550 CE) produced the Pauk lava cone in the crater of the northern cone and the Yuzhny lava flow on SW flank outside the caldera, followed by the Molodoy flow from the upper SW flank (Ponomareva, 1987; Ponomareva and Tsyurupa, 1985; Ponomareva and Braitseva, 1990).

Marapi, Indonesia

0.38°S, 100.474°E | Summit elev. 2885 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that eruptive activity at Marapi (on Sumatra) continued during 17-23 December. White emissions rose as high as 150 m above the summit and drifted E and SE during 17 and 20-21 December; weather conditions sometimes prevented visual observations. Eruptive events were recorded at 2115 on 18 December and at 1247 on 19 December though weather conditions prevented visual confirmation. 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.

Geologic 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 2,000 m above the Bukittinggi Plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide 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 reported in historical time.

Merapi, Indonesia

7.54°S, 110.446°E | Summit elev. 2910 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that the eruption at Merapi continued during 10-16 December. The SW lava dome produced 3-36 daily lava avalanches that traveled as far as 1.5 km SW down the Bebeng drainage, 1.8 km down the Sat/Putih drainage, and as far as 1.8 km SW down the Krasak drainage. A pyroclastic flow traveled 1.5 km down the flanks on 20 December. 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.

Geologic 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.

Popocatepetl, Mexico

19.023°N, 98.622°W | Summit elev. 5393 m

The Centro Nacional de Prevención de Desastres (CENAPRED) reported that eruptive activity continued at Popocatépetl during 16-23 December. The seismic network recorded 4-32 long-period events per day, accompanied by steam-and-gas emissions with occasional minor ash content that drifted NNE, NE, and E. In addition, the seismic network recorded 0-76 minutes of low-amplitude tremor daily; during 18-19 December there was a 70-minute sequence of low-amplitude signals indicting emissions. According to the Washington Volcanic Ash Advisory Center (VAAC) ash plumes visible in webcam and satellite images during 17-18 and 21 December rose 5.8-7 km (19,000-23,000 ft) a.s.l. (as high as 1.6 km above the summit) and drifted NE and NNE. The 21 December ash plume was characterized as large. The Alert Level remained at Yellow, Phase Two (the middle level on a three-color scale) and the public was warned to stay 12 km away from the crater.

Geologic summary: Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America’s 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Reventador, Ecuador

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

The Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN) reported that eruptive activity continued at Reventador during 16-23 December. Seismic data was not available due to transmission problems. Ash-and-gas plumes visible in webcam and/or satellite images were reported daily rising as high as 1.3 km above the crater rim and drifting in multiple directions. Minor amounts of ash fell in Santa Rosa (30 km SSW), Linares, and El Chaco (35 km SSW) during 19-20 December. Secretaría de Gestión de Riesgos (SGR) maintained the Alert Level at Orange (the second highest level on a four-color scale).

Geologic 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.

Sangay, Ecuador

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

The Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN) reported that the eruption continued at Sangay during 16-23 December. The seismic network recorded 110-328 daily explosions. Ash-and-gas plumes were observed in satellite images on a few days during the beginning of the week rising 800-900 m above the summit and drifting mainly S, SW, and W. Weather clouds often obscured views, especially during the second part of the week. The Secretaría de Gestión de Riesgos (SGR) maintained the Alert Level at Yellow (the second highest level on a four-color scale).

Geologic 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.

Semeru, Indonesia

8.108°S, 112.922°E | Summit elev. 3657 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that activity continued at Semeru during 17-23 December, with daily eruptive events recorded by the seismic network. White-and-gray or gray ash plumes were observed daily rising 300-1,200 m above the summit and drifting in multiple directions; some eruptive events were not observed due to weather conditions. Minor incandescence at the summit on the upper SE flank was visible in several nighttime webcam images. According to a news article lahars were detected for three hours on 21 December. There were no reports of damage to villages caused by the lahars but a photo showed a truck that got stuck in the deposits as it crossed the Bondeli River. The Alert Level remained at 3 (the second lowest level on a scale of 1-4) and the public was warned to stay at least 5 km away from the summit 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.

Geologic 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 | Summit elev. 3283 m

The Kamchatkan Volcanic Eruption Response Team (KVERT) reported continuing eruptive activity at Sheveluch’s “300 years of RAS” dome on the SW flank of Old Sheveluch and at the Young Sheveluch dome during 11-18 December. A thermal anomaly was identified in satellite images during 14-15 and 17-18 December; the volcano was obscured by weather clouds on the other days. 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.

Geologic 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.

Suwanosejima, Japan

29.638°N, 129.714°E | Summit elev. 796 m

The Japan Meteorological Agency (JMA) reported that eruptive activity at Suwanosejima’s Ontake Crater continued during 12-19 December. Incandescence was observed nightly in webcam images, and eruption plumes rose as high as 800 m above the crater rim. Ashfall was reported in Toshima Village (3.5 km SSW). The Alert Level remained at 2 (the second level on a five-level scale) and the public was warned to be cautious within 1.5 km of the crater.

Geologic summary: The 8-km-long island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two active summit craters. The summit is truncated by a large breached crater extending to the sea on the E 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 covered 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 an open collapse scarp extending 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.

Whakaari/White Island, New Zealand

37.52°S, 177.18°E | Summit elev. 294 m

According to the Wellington Volcanic Ash Advisory Center (VAAC) a low-level ash plume at Whakaari/White Island was observed by a pilot and identified in satellite and webcam images rising more than 900 m above the summit. The Volcanic Alert Level remained at 2 (on a scale of 0-5) and the Aviation Color Code remained at Yellow (the second lowest level on a four-color scale).

Geologic summary: The uninhabited Whakaari/White Island is the 2 x 2.4 km emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes. The SE side of the crater is open at sea level, with the recent activity centered about 1 km from the shore close to the rear crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. The formation of many new vents during the 19th and 20th centuries caused rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities. The official government name Whakaari/White Island is a combination of the full Maori name of Te Puia o Whakaari (“The Dramatic Volcano”) and White Island (referencing the constant steam plume) given by Captain James Cook in 1769.

References:

¹ Smithsonian Institution / US Geological Survey Weekly Volcanic Activity Report – GVP – December 17-23, 2025 – Managing Editor: Sally Sennert

Teo Blašković

I'm a dedicated researcher, journalist, and editor at The Watchers. With over 20 years of experience in the media industry, I specialize in hard science news, focusing on extreme weather, seismic and volcanic activity, space weather, and astronomy, including near-Earth objects and planetary defense strategies. You can reach me at teo /at/ watchers.news.

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