The Weekly Volcanic Activity Report: May 14–20, 2025

New activity/unrest: Bezymianny, Russia | Kanlaon, Philippines | Klyuchevskoy, Russia | Lewotobi, Indonesia | Raung, Indonesia.

New activity/unrest

Bezymianny, Russia

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

The Kamchatkan Volcanic Eruption Response Team (KVERT) reported that a thermal anomaly over Bezymianny was detected in satellite imagery from May 8 to 15. According to the Institute of Volcanology and Seismology (IVS) of the Far Eastern Branch of the Russian Academy of Sciences (FEB RAS), crater incandescence was visible during dark hours on several days when not obscured by weather clouds. On May 12, hot avalanches of material descended the flanks. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale). Dates are in UTC unless otherwise noted.

Geological summary: The modern Bezymianny, much smaller than its massive neighbors Kamen and Kliuchevskoi on the Kamchatka Peninsula, was formed about 4 700 years ago over a late Pleistocene lava-dome complex and an edifice built between 11 000 and 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 1955–56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large open crater that was formed by the 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.

Kanlaon, Philippines

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

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported that a five-minute-long eruption at Kanlaon on May 13, involved two successive ejections of incandescent material and an ash plume that possibly rose as high as 8 000 m (26 247 feet) above the crater rim. Pyroclastic density currents traveled up to 2 km (1.2 miles) down the southern flanks. Ashfall affected 51 barangays across nine municipalities in four provinces. On the same day, sulfur dioxide emissions averaged 5 241 tonnes per day. Satellite data showed that the resulting sulfur dioxide plume drifted extensively across the Philippines, Palawan Island, and northern Borneo.

From May 14 to 20, gas-and-steam emissions continued, with occasional ash observed drifting west and southwest on May 14. During the remainder of the week, diffuse gas-and-steam plumes rose up to 100 m (328 feet) above the summit and drifted northwest, west, and southwest. The seismic network detected between 2 and 16 volcanic earthquakes daily. Daily sulfur dioxide emissions ranged from 852 to 2 533 tonnes. The Alert Level remained at Level 3 (on a scale of 0–5). Authorities advised the public to remain at least 6 km (3.7 miles) away from the summit and warned aviation operators to avoid flying near the volcano.

Geological summary: Kanlaon volcano (also spelled Canlaon) is the highest point on the Philippine island of Negros. This massive andesitic stratovolcano is dotted with fissure-controlled pyroclastic cones and craters, several of which are filled by lakes. The largest known volcanic debris avalanche in the Philippines extended 33 km (20.5 miles) southwest from the volcano. The summit area features a 2 km (1.2 miles) wide, elongated northern caldera with a crater lake and a smaller, elevated active vent called Lugud crater to the south. Since 1866, eruptions have typically consisted of small-to-moderate phreatic explosions that produce minor ashfall in surrounding areas.

Klyuchevskoy, Russia

56.056°N, 160.642°E | Summit elev. 4754 m

The Kamchatkan Volcanic Eruption Response Team (KVERT) reported that a thermal anomaly at Klyuchevskoy was intermittently detected in satellite imagery from May 8 to 15. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale). Dates are given in UTC unless otherwise noted.

Geological summary: Klyuchevskoy is the highest and most active volcano on the Kamchatka Peninsula. Since its formation about 6 000 years ago, this symmetrical basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without extended periods of inactivity. It rises above a saddle northeast of Kamen volcano and lies southeast of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past 3 000 years, with most lateral craters and cones forming along radial fissures on the volcano’s northeast-to-southeast flanks between 500 m (1 640 feet) and 3 600 m (11 811 feet) elevation. Eruptions recorded since the late 17^th century have frequently altered the morphology of the 700 m (2 297 feet) wide summit crater. Over the past 400 years, most eruptions have originated from the summit crater, though several major explosive and effusive events have occurred from flank vents as well.

Lewotobi, Indonesia

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

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported continued eruptive activity at Lewotobi Laki-laki from May 12 to 20, with a significant eruption on May 18. On May 14 and from May 16 to 17, white steam-and-gas plumes rose between 50 and 800 m (164 to 2 625 feet) above the crater rim and drifted in various directions. On May 15, white-and-gray plumes rose as high as 300 m (984 feet) above the summit and drifted southwest and west. At 01:20 on May 18, a gray ash plume rose 900 m (2 953 feet) above the summit and drifted southwest and south.

At approximately 11:49, a period of continuous emissions of ash, steam, and gas began with a dense gray ash plume that rose 800 m (2 625 feet) above the summit and drifted north. Dense ash emissions persisted throughout the day, accompanied by rumbling and banging sounds audible at the nearest observation post. The ash plume rose to 2 km (6 562 feet) by 12:09 and reached 3 km (9 843 feet) by 12:18, drifting north and northeast. Between 12:46 and 13:23, the plume rose as high as 3.5 km (11 483 feet) above the summit and began drifting northwest as well. By 14:05, the plume had reached 6 km (19 685 feet) above the summit and expanded in multiple directions: northeast, north, northwest, west, and southwest. By 14:30, the plume had decreased to 4 km (13 123 feet) and drifted north, northwest, and west. Visual observations were hindered at 15:27 and 16:14 due to hazy conditions caused by ash in the air, possibly mixed with weather clouds. At 16:37, a dense ash plume rose to 2 km (6 562 feet) above the summit and drifted northwest.

At 20:00 local time, PVMBG raised the Alert Level to Level 4 (on a scale of 1–4). The public was advised to stay at least 6 km (3.7 miles) away from the center of Laki-laki and 7 km (4.3 miles) in a semicircular area extending clockwise from the west to the northeast.

Geological summary: Lewotobi comprises two stratovolcanoes, Lewotobi Perempuan (female) to the north and Lewotobi Laki-laki (male) to the south. They are located in eastern Flores Island and have produced numerous historical eruptions, primarily from Laki-laki. The volcanoes are composed of andesitic to basaltic lava, and the complex is part of a larger volcanic zone associated with subduction along the Sunda Arc

Raung, Indonesia

8.119°S, 114.056°E | Summit elev. 3260 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported increased volcanic activity at Raung on May 16. At 05:51 local time, an observer recorded an ash plume rising approximately 1 250 m (4 101 feet) above the summit, drifting south to southwest. According to the Darwin Volcanic Ash Advisory Center (VAAC), the plume had dissipated by 11:40 the same day. The Alert Level remained at Level 2 (on a scale of 1–4), and the public was advised to stay at least 3 km (1.9 miles) away from the summit crater.

Geological summary: Raung, one of Java’s most active volcanoes, is a massive stratovolcano located in easternmost Java, constructed southwest of the rim of Ijen caldera. The barren summit is marked by a dramatic, steep-walled caldera measuring 2 km (1.2 miles) wide, which has been the site of frequent historical eruptions. A prehistoric collapse of Gunung Gadung on the western flank produced a large debris avalanche that traveled 79 km (49.1 miles), nearly reaching the Indian Ocean. Raung includes several volcanic centers aligned along a northeast-southwest trend, including Gunung Suket to the northeast and Gunung Gadung to the west.

Ongoing activity

Aira, Japan

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

The Japan Meteorological Agency (JMA) reported ongoing eruptive activity at Minamidake Crater of Sakurajima, within Aira Caldera. No eruptions were recorded from May 5 to 15; however, inflation was detected in deformation data, especially beginning at 20:00 on May 12. Sulfur dioxide emissions were slightly low, averaging 300 tonnes per day, with the most recent higher measurement being 900 tonnes per day on May 2.

A phase of continuous eruptive activity, including seven explosions, began around 10:45 on May 15 and lasted until about 04:00 on May 16. Ash plumes rose as high as 3 km (9 843 feet) above the summit and drifted in multiple directions. Large volcanic blocks were ejected as far as 1.2 km (0.75 miles) from the vent. Field observations confirmed significant ashfall on the eastern part of the island on May 15 and on the northern side on May 16. Following the explosions on May 15, deformation data indicated a brief period of deflation, after which inflation resumed.

From May 16 through at least 15:00 on May 19, intermittent eruptive activity persisted. A total of 86 eruptive events and 44 explosions were detected. Ash plumes generally rose as high as 2.9 km (9 514 feet) above the crater, and blocks were ejected as far as 900 m (2 953 feet) from the crater rim. A notable explosion at 18:54 on May 18 generated an ash plume that rose 3.2 km (10 499 feet) above the crater rim and drifted southeast. Blocks from that event also reached as far as 1.2 km (0.75 miles) from the rim.

The Alert Level remained at Level 3 (on a 5-level scale). The public was advised to remain at least 2 km (1.2 miles) away from both the Minamidake and Showa craters.

Geological summary: The Aira caldera, located in the northern half of Kagoshima Bay, contains the active post-caldera Sakurajima volcano. Formation of the 17 by 23 km (10.6 by 14.3 miles) caldera occurred about 22 000 years ago during the eruption of the voluminous Ito pyroclastic flow. The smaller Wakamiko caldera formed in the northeastern part of Aira during the early Holocene, along with several post-caldera cones. Sakurajima began forming about 13 000 years ago on the southern rim of the caldera and initially formed an island, which was later joined to the Osumi Peninsula during the major eruption of 1914. Activity at the Kitadake summit cone ceased about 4 850 years ago, after which eruptions shifted to Minamidake. Frequent explosive eruptions since the 8th century have deposited ash on Kagoshima City, located only 8 km (5 miles) across the bay. The largest known historical eruption occurred between 1471 and 1476.

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 from May 14 to 20. Daily gas-and-ash plumes—white, gray, or black in color—rose between 600 and 1 500 m (1 969 to 4 921 feet) above the summit and drifted north, northeast, east, and southeast. Emissions were continuous for most of the day on May 14, from approximately 05:17 to 17:03 on May 15, from about 08:03 on May 16 until around 22:17 on May 19, and during the morning of May 20. The Alert Level remained at Level 2 (on a scale of 1–4), and the public was advised to stay at least 4 km (2.5 miles) away from the Malupang Warirang Crater.

Geological summary: The Dukono volcanic complex in northern Halmahera sits on a broad, low-profile edifice with multiple overlapping craters and peaks. It has exhibited nearly continuous explosive activity, occasionally accompanied by lava flows, since 1933. A major eruption in 1550 CE produced a lava flow that filled the strait between Halmahera and the Gunung Mamuya cone, located 10 km (6.2 miles) to the northeast. Malupang Warirang, located 1 km (0.6 miles) southwest of the summit crater complex, contains a 700 by 570 m (2 297 by 1 870 feet) crater and has also been the site of reported eruptions.

Etna, Italy

37.748°N, 14.999°E | Summit elev. 3357 m

The Sezione di Catania – Osservatorio Etneo (INGV) reported continuing eruptive activity at Etna’s Southeast Crater and gas emissions from the Bocca Nuova Crater, Northeast Crater, and Voragine between May 12 and 18, 2025. Strombolian activity at the Southeast Crater began in the late afternoon of May 12, though visual observations were initially obscured by weather clouds.

The activity was visually confirmed at 20:30 during a break in the clouds. An eruption cloud drifted downwind and caused minor tephra fall along the southeastern flank of the volcano, reaching the towns of Petrulli and Zafferana Etnea. Two small lava flows were observed descending the southern and eastern flanks of the Southeast Crater, traveling distances of approximately 0.8 km (0.5 miles) and 1.8 km (1.1 miles), respectively.

Geological summary: Mount Etna, located above the city of Catania on the island of Sicily, has one of the world’s longest documented records of volcanism, dating back to 1500 BCE. Basaltic lava flows from historical eruptions cover much of the volcano’s surface. Etna is Italy’s highest and most voluminous volcano, with the Mongibello stratovolcano—truncated by several small calderas—having been built during the late Pleistocene and Holocene atop an older shield volcano. The Valle del Bove, a prominent 5 by 10 km (3.1 by 6.2 miles) caldera, opens to the east and defines much of the volcano’s eastern profile. Etna’s activity typically includes two eruptive styles, often occurring simultaneously: persistent explosive eruptions (sometimes accompanied by minor lava flows) from one or more summit craters, and less frequent but higher-effusion flank eruptions that originate from fissures descending from the summit area. These flank events often produce cinder cones and long lava flows that can reach the foot of the volcano on all sides and have occasionally reached the sea on the southeastern flank.

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 at Great Sitkin’s summit crater from May 14 to 20, feeding a thick lava flow. Small daily earthquakes were detected by the seismic network throughout the week. Satellite imagery from May 16 to 19 showed weakly elevated surface temperatures consistent with ongoing lava effusion.

Steaming from the active vent was observed on May 17 and 18. At times, weather clouds obscured visual observations of the volcano. A radar image acquired on May 20 confirmed that the lava was slowly advancing to the northeast. 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 most of the northern part of Great Sitkin Island in the central Aleutians. A younger cone, capped by a small ice-filled summit caldera measuring 0.8 by 1.2 km (0.5 by 0.75 miles), was built within a larger late-Pleistocene or early Holocene collapse scarp. That collapse event truncated an older volcanic edifice and generated a large submarine debris avalanche, with deposits extending across the ocean floor to the north. The summit lies along the eastern rim of the younger scarp. Deposits from an earlier caldera-forming eruption of unknown age reach up to 6 m (19.7 feet) thick on the flanks of the island. The younger caldera was partially filled by lava domes formed in 1945 and 1974. Additionally, five older flank lava domes—two of which are located along the coast—were built along northwest- and north-northwest-trending alignments. Hydrothermal activity near the head of Big Fox Creek, to the south of the volcano, includes hot springs, mud pots, and fumaroles. Eruptions have been documented since the late 19th century.

Ibu, Indonesia

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

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that the eruption at Ibu continued from May 14 to 20, 2025. Daily ash emissions, ranging in color from gray to white-to-gray or white-to-brown, rose as high as 1 km (3 281 feet) above the summit and drifted in multiple directions. Incandescence at the crater was visible in some nighttime webcam images. The Alert Level remained at Level 3 (the second highest level on a four-level scale). The public was advised to remain at least 4 km (2.5 miles) from the active crater and 5 km (3.1 miles) from the northern opening of the crater wall.

Geological summary: The truncated summit of the Gunung Ibu stratovolcano, located along the northwest coast of Halmahera Island, contains large nested summit craters. The inner crater measures 1 km (0.6 miles) wide and 400 m (1 312 feet) deep and has occasionally held small crater lakes. The 1.2 km (0.75 miles) wide outer crater is breached to the north, forming a steep-walled valley. A large cone has grown to the east-northeast of the summit, and a smaller cone to the west-southwest has fed a lava flow down the western flank. A group of maars lies below the northern and western flanks. The first observed eruption occurred in 1911 as a small explosion from the summit crater. Renewed eruptive activity began in December 1998, producing a lava dome that eventually covered most of the inner crater floor, accompanied by ongoing explosive ash emissions.

Karymsky, Russia

54.049°N, 159.443°E | Summit elev. 1513 m

The Kamchatkan Volcanic Eruption Response Team (KVERT) reported that moderate explosive activity generally continued at Karymsky from May 8 to 15. Satellite images detected ash clouds drifting up to 250 km (155.3 miles) to the southeast and northeast during May 10 and 11. A thermal anomaly over the volcano was observed from May 11 to 15, though views were obscured by weather clouds on other days. The Aviation Color Code remained at Orange (the third level on a four-color scale). Dates are reported in UTC; specific events are in local time where noted.

Geological summary: Karymsky, the most active volcano in Kamchatka’s eastern volcanic zone, is a symmetrical stratovolcano built within a 5 km (3.1 miles) wide caldera that formed during the early Holocene. This caldera cuts into the southern side of the older Pleistocene Dvor volcano and lies just north of the mid-Pleistocene Polovinka caldera, which itself contains the smaller Akademia Nauk and Odnoboky calderas. Seismic activity preceding eruptions at Karymsky often originates beneath Akademia Nauk caldera, located immediately to the south. The Karymsky caldera formed approximately 7 600 to 7 700 radiocarbon years ago, and construction of the current stratovolcano began about 2 000 years later. The current eruptive period began roughly 500 years ago, following a 2 300-year quiescence. Much of the volcanic cone is covered by lava flows less than 200 years old. Historical eruptions have typically been vulcanian or vulcanian-strombolian in style, featuring moderate explosive activity and occasional lava flows from the summit crater.

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, from two vents along the southwestern margin of Halemaʻumaʻu Crater, continued at variable levels from May 14 to 20. Incandescence at both the northern and southern vents was visible from May 13 to 16, and occasional spattering occurred at the northern vent on the evening of May 14. At 22:45 on May 15, small, sporadic “gas-piston” events began at the northern vent, producing spatter fountains and short lava flows. Five additional gas-piston events and lava flows occurred during the early morning of May 16 at 00:30, 01:00, 01:25, 01:54, and 02:43. Dome fountains began to overflow the crater at 04:40, and sustained high fountaining activity started at 05:13.

Fountain heights peaked at 300 m (984 feet) around 06:00, then began oscillating between 100 and 150 m (328 to 492 feet). By 06:10, multiple lava flows were covering approximately 30–40 percent of the crater floor. A gas plume rose as high as 3 km (9 843 feet) and drifted west-southwest, away from populated areas. Sulfur dioxide emissions were estimated at around 50 000 tonnes per day, similar to previous moderate-to-high fountaining episodes. After over 10 hours of sustained high fountaining, the activity ended at 15:29. An estimated 3.8 million m³ (0.00091 mi³) of lava had been erupted during this event.

Incandescence from the lava flows remained visible near the active vent area and along the northern margin of the crater floor overnight from May 16 to 17. Both vents continued to show incandescence from May 16 to 20. 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: Kilauea overlaps the eastern flank of the massive Mauna Loa shield volcano on the Island of Hawaiʻi. Eruptions at Kilauea are prominent in Polynesian oral traditions, and written documentation since 1820 records frequent summit and flank eruptions, including long-term lava lake activity in Halemaʻumaʻu Crater until 1924. The 3 by 5 km (1.9 by 3.1 miles) summit caldera formed in multiple stages around 1 500 years ago and again during the 18^th century. Eruptions also occur along the lengthy East and Southwest Rift Zones, which extend to the ocean. About 90 percent of the volcano’s surface is covered by lava flows less than 1 100 years old, and approximately 70 percent is younger than 600 years. A prolonged eruption from the East Rift Zone from 1983 to 2018 produced lava flows that covered more than 100 km² (38.6 mi²), destroyed hundreds of homes, and created new coastline.

Lewotolok, Indonesia

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

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that the eruption at Lewotolok was ongoing from May 14 to 20. Daily white steam-and-gas plumes rose as high as 100 m (328 feet) above the summit and drifted northwest and west. A nighttime webcam image captured on May 15 showed incandescence at the summit. At 07:51 on May 19, a gray ash plume rose approximately 500 m (1 640 feet) above the summit and drifted northwest. The Alert Level remained at Level 2 (on a scale of 1–4), and the public was advised to stay at least 2 km (1.2 miles) away from the vent and 2.5 km (1.6 miles) away on the southern, southeastern, and western flanks.

Geological summary: Lewotolok (also known as Lewotolo) is a stratovolcano located at the eastern tip of a narrow peninsula that extends north into the Flores Sea from Lembata (formerly Lomblen) Island. The volcano appears symmetrical when viewed from the north and east. A small cone with a 130 m (427 feet) wide crater, constructed on the southeastern side of a larger crater, marks the summit. Numerous lava flows have reached the coastline. Since 1660, eruptions have been characterized by explosive activity from the summit crater.

Manam, Papua New Guinea

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

The Darwin Volcanic Ash Advisory Centre (VAAC) reported that an ash plume from Manam was observed in satellite imagery at 10:20 on May 16, drifting southeast. The plume dissipated by 12:20 the same day.

Geological summary: The 10 km (6.2 miles) wide island of Manam, located 13 km (8.1 miles) off the northern coast of mainland Papua New Guinea, is one of the country’s most active volcanoes. Four prominent radial valleys descend from the unvegetated summit of the conical basaltic-andesitic stratovolcano to its lower flanks, serving as channels for lava flows and pyroclastic avalanches that occasionally reach the coast. Five small satellitic cones are situated along the northern, southern, and western shorelines of the island. Two summit craters are present, both of which are active, though most observed eruptions have originated from the southern crater. These eruptions have primarily deposited material into the southeast valley over the past century. Since 1616, frequent mild-to-moderate explosive eruptions have been recorded. Occasionally, larger eruptions have produced pyroclastic flows and lava flows that have reached coastal plains and entered the sea, sometimes impacting nearby populated areas.

Marapi, Indonesia

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

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that eruptive activity from Verbeek Crater at Marapi, located on Sumatra, continued from May 14 to 20, and was marked by occasional dense gray ash plumes. The highest ash plume during the period rose 1.6 km (5 249 feet) above the crater rim at 09:42 on May 14 and drifted northeast.

At 19:39 on May 15, an ash plume rose 800 m (2 625 feet) and drifted east. On May 17, two ash plumes were recorded: one at 09:47 rose 1 km (3 281 feet) and drifted north, and another at 09:54 rose 600 m (1 969 feet) and drifted northeast. The Alert Level remained at Level 2 (on a scale of 1–4), and the public was advised to remain at least 3 km (1.9 miles) away from the active crater.

Geological summary: Gunung Marapi, not to be confused with the more widely known Merapi volcano on Java, is the most active volcano on the island of Sumatra. This large complex stratovolcano rises about 2 000 m (6 562 feet) above the Bukittinggi Plain in the Padang Highlands. The broad summit area contains several partially overlapping craters constructed within the 1.4 km (0.87 miles) wide Bancah caldera. The summit craters are aligned along an east-northeast to west-southwest trend, with volcanic activity having migrated westward over time. Since the late 18^th century, more than 50 eruptions—typically small-to-moderate explosive events—have been documented. No lava flows outside the summit area have been recorded in historical time.

Merapi, Indonesia

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

The Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG) reported that eruptive activity at Merapi, located on Java, continued from May 9 to 15. Seismicity remained elevated throughout the week. The southwest lava dome produced 43 lava avalanches that traveled as far as 2 km (1.2 miles) southwest down the Bebeng drainage, 18 that extended up to 2 km (1.2 miles) southwest down the Krasak drainage, and 32 that descended up to 2 km (1.2 miles) west down the Sat/Putih drainage.

Ongoing lava effusion and minor collapses caused small morphological changes to the southwest lava dome. The highest recorded temperature at the dome was 247.4°C (477.3°F). A drone survey conducted on May 12 and webcam observations indicated that the dome’s volume increased by 71 200 m³ (0.000017 mi³), bringing the total estimated volume to 3 996 800 m³ (0.00096 mi³). The size of the central dome remained unchanged, though its highest recorded temperature decreased by 3°C to 218°C (424°F).

The Alert Level remained at Level 3 (on a scale of 1–4), and the public was advised to remain 3 to 7 km (1.9 to 4.3 miles) away from the summit, depending on the sector.

Geological summary: Merapi, one of Indonesia’s most active volcanoes, rises above one of the world’s most densely populated regions and dominates the landscape immediately north of the city of Yogyakarta. It is the youngest and southernmost volcano in a chain extending north-northwest to Ungaran. The development of “Old Merapi” during the Pleistocene ended with a major edifice collapse around 2 000 years ago, leaving behind a large arcuate scarp that cuts into the older Batulawang volcano. Growth of the current, steep-sided “Young Merapi” edifice began southwest of this scarp and remains active today. Due to frequent eruptions, its summit area remains mostly unvegetated. Repeated dome growth and collapse events have generated pyroclastic flows and lahars that have devastated agricultural areas on the western and southern flanks, causing significant fatalities over 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 from May 13 to 19. Seismic data indicated a decrease in both the number and intensity of events associated with fluid movement compared to the previous week. However, seismicity related to rock fracturing increased in both number and intensity. These earthquakes were primarily located beneath Arenas Crater and along the northeastern and southwestern flanks, within a radius of 12 km (7.5 miles) and at depths between 1 and 7 km (0.6 to 4.3 miles).

Seismic signals suggesting growth of the lava dome remained at low levels. Satellite data revealed low-energy thermal anomalies on the crater floor, although weather clouds often obscured visibility. Sulfur dioxide emissions remained significant, with consistent detection in satellite observations. Gas-and-steam plumes rose as high as 500 m (1 640 feet) above the summit and drifted northwest, west-northwest, and west. The only confirmed gas-and-ash plume of the week rose approximately 700 m (2 297 feet) above the summit at 08:37 on May 17. The Alert Level remained at Yellow (the second level on a four-level scale).

Geological summary: Nevado del Ruiz is a glacier-capped stratovolcano in central Colombia, covering an area of more than 200 km² (77.2 mi²). Since the start of the Pleistocene, three major edifices composed of andesitic and dacitic lavas and pyroclastic materials have been built. The modern cone is a cluster of lava domes within the caldera of an older volcano. The summit hosts the 1 km (0.6 miles) wide and 240 m (787 feet) deep Arenas Crater. The La Olleta pyroclastic cone on the southwestern flank may also have been active in historical times. Large landslides have left steep headwalls along the flanks. Historical eruptions dating back to the 16^th century have often melted parts of the summit icecap, generating deadly lahars. The 1985 eruption, which triggered a massive lahar, remains the deadliest volcanic event in South America.

Ontakesan, Japan

35.893°N, 137.48°E | Summit elev. 3067 m

Escalating seismicity and minor inflation at Ontakesan in January 2025 prompted the Japan Meteorological Agency (JMA) to raise the Alert Level to Level 2 (on a scale of 1–5). By February, deformation had stalled and seismic activity had declined, with only a few volcanic earthquakes detected by the seismic network through May 20. At 11:00 on May 20, the Alert Level was lowered to Level 1.

Geological summary: Ontakesan, Japan’s second-highest volcano, is a massive stratovolcano located at the southern end of the Northern Japan Alps. It is a major site of religious pilgrimage in central Japan. The volcano is built within a mostly buried 4 by 5 km (2.5 by 3.1 miles) caldera and lies at the southern edge of the Norikura volcanic zone, which extends northward to Yakedake. The older volcanic complex comprised at least four major stratovolcanoes formed between about 680 000 and 420 000 years ago. Ontakesan was dormant for over 300 000 years before the construction of the younger edifice, whose broad summit is marked by a series of small explosion craters aligned along a north-northeast trend. Several phreatic eruptions occurred after the deposition of the roughly 7 300-year-old Akahoya tephra from Kikai caldera. The first historical eruption was in 1979, originating from summit fissures. A major non-eruptive landslide in 1984 triggered a debris avalanche and lahar that descended valleys on the southern and eastern flanks. Minor phreatic activity caused ashfall near the summit in 1991 and 2007. A significant phreatic explosion in September 2014 occurred during a busy hiking period, resulting in numerous fatalities.

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 gas-and-steam emissions, occasionally containing ash, continued at Poás from May 14 to 20. Overall volcanic activity decreased during the week, and deformation data indicated ongoing deflation. Vigorous emissions persisted at Boca A, where incandescence was visible at night. At Boca C, water pooling within the crater continued to bubble, and heavy rainfall at the beginning of the week contributed to further filling of the crater.

A moderate phreatic eruption occurred at 04:08 on May 18, producing a gas-and-steam plume with minor ash content that rose approximately 1 km (3 281 feet) above the crater rim and drifted southwest. Sulfur dioxide emissions detected via satellite were estimated at 650 tonnes per day on May 18, 350 tonnes per day on May 19, and 598 tonnes per day on May 20. The Alert Level remained at Level 3 (the second highest level on a four-level scale), and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geological summary: Poás, one of Costa Rica’s most active volcanoes, is a broad, heavily vegetated stratovolcano with three craters aligned along a north–south trend. Its multi-hued summit crater lakes are easily accessible from the capital city, San José. A fissure trending north–south extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost summit crater lake, Botos, last erupted approximately 7 500 years ago. The more prominent northern crater lake, Laguna Caliente, is geothermally heated and among the most acidic natural lakes on Earth, with a pH near zero. Frequent phreatic and phreatomagmatic eruptions have occurred at Laguna Caliente since the first recorded event in 1828, often producing geyser-like ejections of crater-lake water.

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 from May 13 to 20. Seismicity included 68–106 daily explosions, long-period earthquakes, harmonic tremor, and tremor associated with emissions. Multiple daily ash-and-gas plumes rose 200–2 000 m (656–6 562 feet) above the crater rim and drifted in multiple directions. Webcams recorded multiple nightly instances of incandescent material descending the flanks as far as 1.1 km (0.68 miles) below the crater rim, specifically down the east-southeast and southeast flanks during May 17–18. Weather clouds occasionally obscured views. The 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 a 4 km (2.5 miles) wide avalanche scarp open to the east 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 (56 miles) east-southeast. 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 (10.6 miles) high eruption column, pyroclastic flows that traveled up to 8 km (5 miles), 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 high levels of eruptive activity at Sangay from May 13 to 20. The seismic network recorded 98–194 daily explosions. Ash-and-gas plumes were observed in webcam and/or satellite images on most days, rising as high as 2 km (6 562 feet) above the summit and drifting in multiple directions. Weather clouds often obscured observations, especially during the first half of the week. Crater incandescence was sometimes visible during dark hours from May 17 through 20. Incandescent avalanches of material descended the southeast flank 600 m (1 969 feet) during May 18–19. 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 at least 14 000 years. It towers above the tropical jungle on the east side, while flat ash-covered plains on the other sides have been deeply incised into steep-walled canyons up to 600 m (1 969 feet) deep by heavy rains. 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. This nearly 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 May 14 to 20, 2025, with multiple daily eruptive events recorded by the seismic network. Daily white-and-gray or gray ash plumes rose 300–1 000 m (984–3 281 feet) above the summit and drifted in multiple directions. The Alert Level remained at Level 2 (the second lowest level on a scale of 1–4). The public was warned to stay at least 5 km (3.1 miles) away from the summit in all directions, 13 km (8.1 miles) from the summit to the southeast, 500 m (1 640 feet) from the banks of the Kobokan drainage as far as 17 km (10.6 miles) from the summit, and to avoid other drainages—including the Bang, Kembar, and Sat—due to hazards from lahars, avalanches, and pyroclastic flows.

Geological summary: Semeru, the highest and one of the most active volcanoes on Java, lies at the southern end of a volcanic massif that extends north to the Tengger caldera. The steep-sided volcano, also known 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 cuts along a north–south trend through the summit area, and cinder cones and lava domes are present on the eastern and northeastern flanks. The summit topography is complex due to shifting crater locations from northwest to southeast. Frequent eruptions in the 19th and 20th centuries were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive events that produced pyroclastic flows reaching the lower flanks.

Sheveluch, Russia

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

The Kamchatkan Volcanic Eruption Response Team (KVERT) and the Institute of Volcanology and Seismology (IVS) of the Far Eastern Branch of the Russian Academy of Sciences (FEB RAS) reported that lava extrusion may have continued at Sheveluch’s “300 years of RAS” dome on the southwest flank of Old Sheveluch and at the Young Sheveluch dome during May 8 to 15. Thermal anomalies over the domes were identified in satellite images on most days, though weather clouds sometimes obscured views. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Dates are reported in UTC; specific events are in local time where noted.

Geological summary: The high, isolated massif of Sheveluch (also spelled Shiveluch) rises above the lowlands north-northeast of the Kliuchevskaya volcano group. The 1 300 km³ (312 mi³) andesitic volcano is one of the largest and most active in Kamchatka, with at least 60 large eruptions during the Holocene. The summit of the roughly 65 000-year-old Stary Shiveluch is truncated by a broad 9 km (5.6 miles) wide late-Pleistocene caldera breached to the south. Many lava domes are present on the outer flanks. The Molodoy Shiveluch lava dome complex was built during the Holocene within the breached caldera, and Holocene dome extrusion has also occurred on the flanks of Stary Shiveluch. Widespread tephra deposits from these eruptions serve as important markers for dating volcanic activity in Kamchatka. Frequent dome collapses, including a major one in 1964, have produced debris avalanches that cover much of the caldera floor.

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 from May 15 to 19, 2025. Incandescence was observed nightly in webcam images. No explosions were detected, though plumes from eruptive events rose as high as 1 km (3 281 feet) above the crater rim. The Alert Level remained at Level 2 (the second level on a five-level scale), and the public was warned to remain at least 1.5 km (0.9 miles) away from the crater.

Geological summary: Suwanosejima is an 8 km (5 miles) long island in the northern Ryukyu Islands, consisting of an andesitic stratovolcano with two active summit craters. The summit is truncated by a large breached crater extending to the sea on the eastern flank, the result of a past edifice collapse. One of Japan’s most frequently active volcanoes, Suwanosejima was in a state of intermittent Strombolian activity from Otake, the northeastern summit crater, between 1949 and 1996. After 1996, periods of inactivity became more common. The largest recorded eruption occurred in 1813–14, producing thick scoria deposits.

References:

¹ Smithsonian Institution / US Geological Survey – GVP – Weekly Volcanic Activity Report May 14–20, 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.