The Weekly Volcanic Activity Report: December 3-9, 2025

New activity/unrest

Ambae, Vanuatu

15.389°S, 167.835°E | Summit elev. 1496 m

The Vanuatu Meteorology and Geohazards Department (VMGD) reported eruptive activity at Ambae during the last week of November and the first week of December based on seismic signals, satellite data, and webcam images. Steam, gas, and ash plumes were visible in satellite and webcam observations during 24-30 November and 1-5 December. A low-level thermal anomaly was also detected in satellite images during 30 November and 1-2 December. Ashfall was reported in surrounding communities downwind in late November and during 1-7 December. A webcam image from 8 December showed a plume that may have contained ash rising from the crater. According to the Wellington Volcanic Ash Advisory Center (VAAC) low-level ash plumes rose 1.8-2.4 km (6,000-8,000 ft) a.s.l. and drifted NW during 3-5 December, then rose as high as 3.7 km (12,000 ft) a.s.l. and drifted E during 7-8 December. The Alert Level remained at 2 (on a scale of 0-5), and the public was warned to stay outside of Danger Zone A, defined as a 2-km radius around the active vents in Lake Voui, and to stay away from drainages during heavy rains.

Geologic summary: The island of Ambae, also known as Aoba, is a massive 2,500 km3 basaltic shield that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW-trending rift zone with numerous scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. That large central edifice is also called Manaro Voui or Lombenben volcano. Post-caldera explosive eruptions formed the summit craters about 360 years ago. A tuff cone was constructed within Lake Voui (or Vui) about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast.

Bezymianny, Russia

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

The Kamchatkan Volcanic Eruption Response Team (KVERT) reported that a large thermal anomaly over Bezymianny was identified in satellite images during 28 November-4 December. The Aviation Color Code remained at Yellow (the second lowest level on a four-level scale). Dates are reported in UTC; specific events are in local time where noted.

Geologic summary: The modern Bezymianny, much smaller than its massive neighbors Kamen and Kliuchevskoi on the Kamchatka Peninsula, was formed about 4,700 years ago over a late-Pleistocene lava-dome complex and an edifice built about 11,000-7,000 years ago. Three periods of intensified activity have occurred during the past 3,000 years. The latest period, which was preceded by a 1,000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large open crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Bur ni Telong, Indonesia

4.769°N, 96.821°E | Summit elev. 2617 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported increased seismicity at Bur ni Telong. The seismic network detected an increase in the number of deep volcanic events, with 87 events recorded during 1-3 December. Additionally, the network recorded 19 local tectonic earthquakes. During 0000-1317 on 4 December there were 39 shallow volcanic earthquakes, one deep volcanic earthquake, and two local tectonic earthquakes. No emissions were observed. The Alert Level remained at 2 (the second lowest level on a scale of 1-4), though at 1500 on 4 December the exclusion zone was increased to a radius of 3 km from the crater area. The public was reminded to avoid the fumarole and solfatara regions, especially during cloudy or rainy weather.

Geologic summary: The conical Bur ni Telong volcano was constructed at the southern base of the massive Bur ni Geureudong volcanic complex, one of the largest in northern Sumatra. The historically active volcano lies 4.5 km from the summit of Geureudong, and its summit crater has migrated to the ESE, leaving arcuate crater rims. Lava flows are exposed on the southern flank. Explosive eruptions were recorded during the 19th and 20th centuries.

Mayon, Philippines

13.257°N, 123.685°E | Summit elev. 2462 m

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported increased seismic activity at Mayon and new lava at the summit in December. Photos of the summit dome on 8 and 10 December revealed that dark lava spines had been recently extruded. The seismic network detected an increase in rockfalls from an average of three events per day in 2025 to an average of 16 events per day in December, coincident with the extrusion. The Alert Level remained at 1 (on a 0-5 scale); the public was warned to stay out of the 6-km-radius Permanent Danger Zone (PDZ) and pilots were advised to avoid flying close to the summit.

Geologic 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.

Piton de la Fournaise, France

21.244°S, 55.708°E | Summit elev. 2632 m

The Observatoire Volcanologique du Piton de la Fournaise (OVPF) reported that a magmatic intrusion was detected beneath the E rim of Dolomieu Crater at Piton de la Fournaise during 2225-2330 on 5 December based on seismic data. The seismic network recorded 227 shallow volcano-tectonic earthquakes with magnitudes less than 1 at depths of 1.8-2.3 km. Some of the located earthquakes showed that magma migrated less than 500 m from an area below the SE rim to an area below the NE rim. The seismicity was accompanied by rapid, low-magnitude deformations at the summit area that lasted less than an hour. Seismicity continued after the intrusion ceased, with a decreasing rate through the next day. The Alert Level was raised to 1 (or an Orange Alert). During 7-8 December seismicity had returned to a rate of 1-3 earthquakes per hour, comparable to before the intrusion. The Alert Level was lowered back to “Vigilance” (or a Yellow Alert) was initiated on 28 November and described as “a possible eruption in medium term (a few days or weeks) or presence of risks on the sector (rockfalls, increase of gas emissions, still hot lava flows)”.

Geologic summary: Piton de la Fournaise is a massive basaltic shield volcano on the French island of Réunion in the western Indian Ocean. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three scarps formed at about 250,000, 65,000, and less than 5,000 years ago by progressive eastward slumping, leaving caldera-sized embayments open to the E and SE. Numerous pyroclastic cones are present on the floor of the scarps and their outer flanks. Most recorded eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest scarp, which is about 9 km wide and about 13 km from the western wall to the ocean on the E side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures outside the scarps.

Purace, Colombia

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

The Servicio Geologico Colombiano (SGC) reported continuing eruptive activity at Puracé during 2-9 December. Seismicity was characterized by tremor and long-period signals indicating fluid movement, periods of continuous tremor, and earthquakes indicating rock fracturing located at depths of 1-3 km. Daily gas-and-ash emissions rose 100-900 m above the summit and drifted downwind. On 3 December a temperature increase within the crater was identified in satellite data. During 2-3 December minor ashfall was reported in areas to the SE including Cristales and Agua Hirviendo. Ashfall on 3 December was reported in the Cristales area and Casa de Cabildo of Puracé (N), in Río Negro and Paletará council (16 km SW), in the Agua Hirviendo hot springs (11 km WNW), and in San Juan (NE). 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.

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 3-9 December, with daily eruptive events recorded by the seismic network. Daily white-and-gray or gray ash plumes rose 400-1,100 m above the summit and drifted in multiple directions. Incandescence at the summit on the upper SE flank was visible in several nighttime webcam images. 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.

Ongoing activity

Ahyi, United States

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

On 5 December the US Geological Survey reported that signs of unrest at Ahyi Seamount were observed during the previous week. Single detections from Ahyi’s direction were detected at underwater pressure sensors near Wake Island (about 2,270 km E of Ahyi) on 29 and 30 November. Slightly discolored water was seen a few hundred meters E of the seamount in high-resolution satellite images on 30 November. 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 2-8 December with 11 eruptive events and nine explosions. Ash plumes rose as high as 2.2 km above the crater rim and large blocks were ejected as far as 700 m from the vent. Nightly crater incandescence was visible in webcam images. Sulfur dioxide emissions were characterized as high, averaging 2,300 tons per day on 5 December. Daily eruptive events produced ash plumes that rose 1-2.2 km above the crater rim and drifted NE and SE. Explosions at 1107, at 2046, at 2212, and at 2338 on 4 December, at 0654 and at 2229 on 5 December, at 0213 on 6 December, and at 2053 and at 184 on 8 December generated ash plumes that rose 600-1,700 m above the crater rim and drifted E and SE. 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.

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 2-9 December. Small earthquakes were detected by the seismic network along with occasional rockfall signals. Elevated surface temperatures were identified in satellite views during 4-7 December. Weather clouds obscured satellite and webcam views. AVO noted that the rate of lava effusion appeared to be declining gradually. 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 3-8 December. Daily white-to-gray or gray ash plumes rose 200-600 m above the summit and drifted NE, E, and SE; weather conditions occasionally prevented visual confirmation. Incandescence at the summit was visible in a few 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.

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 2-9 December. During a helicopter overflight on 2 December volcanologists observed a spattering lava surface deep within the N vent. Incandescence at both the N and S vents was visible overnight during 2-5 December, and was accompanied by flames from burning gas (likely hydrogen gas) and occasional weak spattering. Persistent low-to-moderate tremor was punctuated by minor seismic tremor bursts suggestive of irregular gas pistoning at depth. Periods of gas pistoning became more frequent overnight during 4-5 December and incandescence at the N vent intensified. Spattering at the N vent increased by 0330 on 5 December. Large flames arose from the S vent and from a crack adjacent to the N vent.

During the episode of lava fountaining that ended on 25 November a new vent opened within the N vent; the original vent (the right vent) and a new vent to the left, separated by a septum of rock. Lava erupted from the N vent at 1250 on 5 December and lasted for about two minutes. Three more lava overflows, each lasting 10-20 minutes, occurred later that day during 1700-2000. A short lava overflow was recorded at 0235 on 6 December and was followed by continuous overflows at 0337. Most of the overflows came from the left vent, but by around 0700 the right vent also began overflowing, increasing the effusion rate and producing fountains. Lava fountains rose 5-20 m and produced ribbon-like flows onto the Halema’uma’u Crater floor. The S vent continued to glow and spatter intermittently but produced no overflows. Activity escalated and by 0845 sustained lava fountains at both the right and left vents of the N vent were 15-30 m high. Lava fountains rose from the S vent at 0849 and quickly reached 370 m high while the fountains at the N vent dropped to 150 m. All three vents were producing lava fountains, which was an extremely rare event. By 0940 the S vent fountains were about twice as high as the N vent fountains. The S vent became enlarged and produced fountains over 300 m tall that arced towards the S wall of the crater. Molten spatter and pumice from the S vent destroyed the “V3” streaming camera site, located within the closed area, just before 1000.

The eruption was sustained for about 12 hours with lava fountains rising as high as 370 m. The dual fountains at the N vent ceased at 1150 and the S vent ceased erupting at 2052. The fountains produced an estimated 12 million cubic meters of lava that covered 50-60% of the crater floor. The combined average eruption rate was an estimated 190 cubic meters per second with a peak of 1,000 cubic meters per second just before 1000 when fountains at the S vent rose to high levels. The associated eruption plume, composed of water vapor, sulfur dioxide gas, Pele’s hair, reticulite and fine ash, rose 6.1 km (about 20,000 ft) above ground level. Tephra including Pele’s hair and fine ash carried in lower levels of the plume fell in Pahala and other communities SW of the vents. Satellite imagery showed that the upper regions of the gas-and-ash cloud drifted E across lower Puna and reached an area well out to sea before turning S. Reticulite pieces up to about 75 mm fell along Chain of Craters Road E of the summit.

Both vents and the crack adjacent to the N vent were intermittently incandescent overnight during 6-9 December. Incandescent lava on the crater floor gradually cooled and went dark during 6-7 December, though spatter-fed flows on the slopes S of both vents remained partially incandescent and moved downslope through 9 December. 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 the eruption at Krasheninnikov continued during 28 November-4 December. A large thermal anomaly over the volcano was identified in satellite images during 28 November-2 December. Gas-and-steam plumes drifted 60 km NW on 30 November and 1 December. Satellite images showed active lava and continuing advancement of flows on the ENE flank during 22 November-6 December. 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).

Lewotobi, Indonesia

8.542°S, 122.775°E | Summit elev. 1703 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that activity at Lewotobi Laki-laki had significantly declined during the previous few weeks. Seismic data showed decreased activity; specifically, signals indicated fluid movement at depth and not magma migration towards the surface. There was also a lack of shallow volcanic earthquakes indicating no significant pressures higher in the conduit. The intensity of surficial activity decreased during 1-7 December, with fluctuating avalanche earthquake signals due to instability of material on the flanks. Deformation data showed a decreasing trend during October-December. On 8 December the Alert Level was lowered to 3 (the second highest level on a scale of 1-4) and the public was warned to stay 6 km away from the center of Laki-laki.

Geologic summary: The Lewotobi edifice in eastern Flores Island is composed of the two adjacent Lewotobi Laki-laki and Lewotobi Perempuan stratovolcanoes (the “husband and wife”). Their summits are less than 2 km apart along a NW-SE line. The conical Laki-laki to the NW has been frequently active during the 19th and 20th centuries, while the taller and broader Perempuan has had observed eruptions in 1921 and 1935. Small lava domes have grown during the 20th century in both of the summit craters, which are open to the north. A prominent cone, Iliwokar, occurs on the E flank of Perampuan.

Manam, Papua New Guinea

4.08°S, 145.037°E | Summit elev. 1807 m

The Darwin Volcanic Ash Advisory Centre (VAAC) reported that ash plumes from Manam were identified in satellite images and reported by the Rabaul Volcano Observatory drifting SE and SW at an altitude of 2.4 km (8,000 ft) a.s.l. during 5-6 December.

Geologic 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 | Summit elev. 2885 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that an eruptive event at Marapi (on Sumatra) was recorded at 1616 on 4 December. Emissions were not observed due to weather clouds. 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.

Nevado del Ruiz, Colombia

4.892°N, 75.324°W | Summit elev. 5279 m

The Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued during 2-8 December, though weather conditions sometimes obscured visual observations. Seismic data indicated that events associated with fluid movement decreased in both number and intensity compared to the previous week. There were no confirmed ash emissions associated with the signals; gas-and-steam emissions rose as high as 1 km above the summit and drifted in various directions. Seismicity associated with rock fracturing was similar in number and intensity compared to the previous week. The earthquakes were low magnitude (up to M1) and mainly located at depths of 2-9 km below Arenas Crater and below the flanks within 12 km. Seismicity associated with activity at the lava dome was recorded on 4 December. Daily sulfur dioxide emissions fluctuated at low levels. Low-level thermal anomalies at the bottom of the crater were periodically identified in satellite images. The Alert Level remained at Yellow (the second level on a four-level scale).

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

Nyamulagira, DR Congo

1.408°S, 29.2°E | Summit elev. 3058 m

The eruption at Nyamulagira continued in December based on observations using satellite images. Incandescence on the floor of the summit caldera and from active lava flows on the NW flanks was visible in a 7 December satellite image. The distal end of the farthest lava flow was about 6.5 km from the crater rim.

Geologic summary: Africa’s most active volcano, Nyamulagira (also known as Nyamuragira), is a massive high-potassium basaltic shield about 25 km N of Lake Kivu and 13 km NNW of the steep-sided Nyiragongo volcano. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Documented eruptions have occurred within the summit caldera, as well as from the numerous flank fissures and cinder cones. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Recent lava flows extend down the flanks more than 30 km from the summit as far as Lake Kivu; extensive lava flows from this volcano have covered 1,500 km2 of the western branch of the East African Rift.

Planchon-Peteroa, Chile

35.223°S, 70.568°W | Summit elev. 3977 m

The Servicio Geológico Minero Argentino (SEGEMAR) reported that at 0944 on 4 December a gas-and-ash plume at Planchón-Peteroa rose 850 m above the crater rim and drifted NE. The plume dissipated near the summit. The Alert Level remained at Yellow (the middle level on a three-color scale). According to the Sistema y Servicio Nacional de Prevención y Repuesta Ante Desastres (SENAPRED) the communities of Molina (66 WNW), Curicó (68 km NW), Romeral (75 km NW), and Teno (68 km NW) continued to be under a “Preventive Early Warning” (since 18 July 2025) and that a security perimeter 4 km from the craters was in effect.

Geologic summary: Planchón-Peteroa is an elongated complex volcano along the Chile-Argentina border with several overlapping calderas. Activity began in the Pleistocene with construction of the basaltic andesite to dacitic Volcán Azufre, followed by formation of the basaltic and basaltic andesite Volcán Planchón, 6 km N. About 11,500 years ago much of Azufre and part of Planchón collapsed, forming the massive Río Teno debris avalanche, which traveled 95 km to reach Chile’s Central Valley. Subsequently, Volcán Planchón II was formed. The youngest volcano, andesitic and basaltic andesite Volcán Peteroa, consists of scattered vents between Azufre and Planchón, and and contains a small steaming crater lake. Reported eruptions from the complex have been dominantly explosive, although lava flows were emplaced in 1837 and 1937.

Poas, Costa Rica

10.2°N, 84.233°W | Summit elev. 2697 m

The Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional (OVSICORI-UNA) reported that an explosive eruption at Poás occurred at 2234 on 6 December, generated an eruption plume that rose around 400 m above the crater rim, and ejected incandescent ballistics. The eruption lasted about five minutes. The Volcanic Alert Level remained at 2 (the second lowest level on a four-level scale).

Geologic summary: The broad vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the complex stratovolcano extends to the lower N flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, last erupted about 7,500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world’s most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since an eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

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 2-9 December. The seismic network recorded 3-70 long-period events per day, accompanied by steam-and-gas emissions with occasional minor ash content that drifted in various directions. In addition, the seismic network recorded 96 minutes of low-amplitude tremor during 7-8 December and 201 minutes of low-amplitude tremor consisting of 78 minutes of high-frequency tremor and 123 minutes of harmonic tremor during 8-9 December. According to the Washington Volcanic Ash Advisory Center (VAAC) ash plumes visible in webcam and satellite images on 3, 5, 7, and 9 December rose 5.6-6.1 km (18,500-20,000 ft) a.s.l. (about 400 m above the crater rim) and drifted in multiple directions. 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 2-9 December. Seismicity included 57-88 daily explosions, long-period earthquakes, harmonic tremor, and tremor associated with emissions, though transmission of the data was interrupted during 7-9 December. Daily ash-and-gas plumes visible in webcam and/or satellite images rose as high as 1.6 km above the crater rim and drifted in multiple directions. Minor ashfall was reported in the El Reventador sector of Sucumbíos Province (N and NE) during the morning of 3 December and in various areas of Napo province, including San Luis (8 km SE), Manuel Galindo (8 km SE), and the El Reventador parish during 5-9 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 2-9 December. The seismic network recorded 89-165 explosions each day. Ash-and-gas plumes were observed on most days in webcam and/or satellite images rising 300-900 m above the summit and drifting NE, E, and SE, though weather clouds often obscured views. Crater incandescence was visible during the morning of 5 December. 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.

Santa Maria, Guatemala

14.757°N, 91.552°W | Summit elev. 3745 m

The Instituto Nacional de Sismología, Vulcanología, Meteorología e Hidrología (INSIVUMEH) reported high levels of ongoing eruptive activity at Santa Maria’s Santiaguito dome complex during 2-10 December, with continuing lava extrusion at Caliente dome. Daily explosions, 1-7 per hour when reported, generated gas-and-ash plumes that rose 800-900 m above the dome and drifted W and SW. Effusion of blocky lava and collapses of incandescent material produced incandescent block avalanches that descended the flanks. Ashfall was reported in areas downwind including San Marcos Palajunoj (8 km SW) and Loma Linda (7 km W) during 4-5 December.

Geologic 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.

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 27 November-4 December. Explosions on 27 November generated ash plumes that rose as high as 10 km (32,800 ft) a.s.l. and drifted as far as 655 km E. A thermal anomaly was identified in satellite images during 28 November-2 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 28 November-5 December. Incandescence was observed nightly in webcam images. Eruption plumes rose as high as 700 m above the crater rim. 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.

Taal, Philippines

14.0106°N, 120.9975°E | Summit elev. 311 m

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported eruptive activity at Taal during 3-9 December. The seismic network recorded 3-9 daily volcanic earthquakes along with periods of volcanic tremor lasting one minute long to over 13 hours long. Daily gas-and-steam emissions with variable densities generally rose as high as 600 m above the crater rim and drifted mainly SW and NE. Minor phreatic and phreatomagmatic events at 0058 and 0104 on 4 December produced plumes that rose 1.2 km above the crater rim and drifted SW. Both events lasted two minutes. The second event ejected incandescent ballistics 300 m above the lake. Sulfur dioxide emissions averaged 466 tonnes per day on 5 December. The Alert Level remained at 1 (on a scale of 0-5); PHIVOLCS reminded the public that the entire Taal Volcano Island (TVI) was a Permanent Danger Zone (PDZ) and recommended that the Main Crater and areas along the Daang Kastila fissure should remain prohibited. Pilots were warned to avoid flying over TVI.

Geologic summary: Taal is one of the most active volcanoes in the Philippines and has produced some powerful eruptions. The 15 x 20 km Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2 surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, with several submerged eruptive centers. The 5-km-wide Volcano Island in north-central Lake Taal is the location of all observed eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones. Powerful pyroclastic flows and surges have caused many fatalities.

Whakaari/White Island, New Zealand

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

On 8 December GeoNet reported that eruptive activity at Whakaari/White Island had declined and that no ash emissions had been detected during the previous week. Sources of recent observations included an overflight, ongoing satellite monitoring, and images from the Whakatane and Te Kaha webcams along the Bay of Plenty coast. Gas sampling during the overflight revealed lower levels of sulfur dioxide than previous measurements. The Volcanic Alert Level was lowered to 2 (on a scale of 0-5) and the Aviation Color Code was lowered to 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 3-9, 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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