The Weekly Volcanic Activity Report: July 23–29, 2025

New activity/unrest: Kirishimayama, Japan | Klyuchevskoy, Russia | Reykjanes, Iceland | Telica, Nicaragua.

New activity/unrest

Kirishimayama, Japan

31.934°N, 130.862°E | Summit elev. 1700 m

The Japan Meteorological Agency (JMA) reported that eruptive activity continued at Shinmoedake (Shinmoe peak, a stratovolcano of the Kirishimayama volcano group) during 22-29 July. The number of volcanic earthquakes located beneath Shinmoedake, first detected in late October 2024, continued to fluctuate; volcanic tremor was also occasionally detected. Diffuse grayish-white plumes rose 100-200 m above the crater rim and drifted W during 22-24 July. Eruptive events were detected on 27 July but weather conditions obscured views. The Alert Level remained at 3 (on a 5-level scale) and the public was warned to exercise caution within 3 km from Shinmoedake Crater.

Geological summary: Kirishimayama is a large group of more than 20 Quaternary volcanoes located north of Kagoshima Bay. The late-Pleistocene to Holocene dominantly andesitic group consists of stratovolcanoes, pyroclastic cones, maars, and underlying shield volcanoes located over an area of 20 x 30 km. The larger stratovolcanoes are scattered throughout the field, with the centrally located Karakunidake being the highest. Onamiike and Miike, the two largest maars, are located SW of Karakunidake and at its far eastern end, respectively. Holocene eruptions have been concentrated along an E-W line of vents from Miike to Ohachi, and at Shinmoedake to the NE. Frequent small-to-moderate explosive eruptions have been recorded since the 8th century.

Klyuchevskoy, Russia

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

The Kamchatkan Volcanic Eruption Response Team (KVERT) reported that eruptive activity at Klyuchevskoy’s summit crater continued during 17-30 July. A strong thermal anomaly was identified in satellite images. Lava had been slowly filling up the crater since 20 April; according to Kamchatka Volcanological Station (Volkstat), bright crater incandescence observed on 19 July by scientists visiting the area confirmed that a significant amount of new lava was present in the summit crater. At 2324 on 29 July a M 8.8 tectonic earthquake occurred about 400 km S and was unrelated to the ongoing eruption. At 2350 on 29 July an ash plume was identified in a satellite image extended 58 km E. A satellite image captured at around 0036 on 30 July showed a large lava flow had already descended the WSW flank. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Dates are based on UTC times; specific events are in local time where noted.

Geological summary: Klyuchevskoy is the highest and most active volcano on the Kamchatka Peninsula. Since its origin about 6,000 years ago, this symmetrical, basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during approximately the past 3,000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 and 3,600 m elevation. Eruptions recorded since the late 17th century have resulted in frequent changes to the morphology of the 700-m-wide summit crater. These eruptions over the past 400 years have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Reykjanes, Iceland

63.817°N, 22.717°W | Summit elev. 140 m

The Icelandic Meteorological Office (IMO) reported that a fissure within the Reykjanes volcanic system that began erupting on 16 July in an area NE of Stóra Skógfell, along the Sundhnúkur crater row, continued to erupt during 23-29 July. Measurements of the flow field taken on 23 July indicated that the total volume of new lava in the Sundhnúkur area was estimated to be 26.8 million cubic meters and covered an estimated 3.3 square kilometers. One crater continued to produce lava flows and periodic spatter; activity at the crater declined during the mornings of 23 and 24 July and then remained stable during the rest of the week. A small vent opened on the W flank of the crater’s cone on 28 July but was inactive by 29 July. During 28-29 July a new crater formed inside the main crater and became the center of the activity. Lava flowed E and SE. The flow thickened with only minor changes to the flow margins; a small breakout at the SE part of the flow traveled a short distance S. Sulfur dioxide emissions significantly decreased during 23-24 July, though on 24 July volcanic smog (vog) was widely reported, including in Ísafjörður (about 240 km N) and Strandir (about 200 km NNE). A small amount of vog was detected in some areas overnight during 24-25 July. Gas emissions during 28-29 July drifted over populated areas in SW Iceland.

Geological summary: The Reykjanes volcanic system at the SW tip of the Reykjanes Peninsula, where the Mid-Atlantic Ridge rises above sea level, comprises a broad area of postglacial basaltic crater rows and small shield volcanoes. The submarine Reykjaneshryggur volcanic system is contiguous with and is considered part of the Reykjanes volcanic system, which is the westernmost of a series of four closely-spaced en-echelon fissure systems that extend diagonally across the Reykjanes Peninsula. Most of the subaerial part of the system (also known as the Reykjanes/Svartsengi volcanic system) is covered by Holocene lavas. Subaerial eruptions have occurred in historical time during the 13th century at several locations on the NE-SW-trending fissure system, and numerous submarine eruptions dating back to the 12th century have been observed during historical time, some of which have formed ephemeral islands. Basaltic rocks of probable Holocene age have been recovered during dredging operations, and tephra deposits from earlier Holocene eruptions are preserved on the nearby Reykjanes Peninsula.

Telica, Nicaragua

12.606°N, 86.84°W | Summit elev. 1036 m

The Washington Volcanic Ash Advisory Center (VAAC) reported that during 21-22 July diffuse ash plumes from Telica were identified in satellite images and/or webcam images drifting as far as 10 km SW at an altitude of 1.5 km (5,000 ft) a.s.l. A plume with possible ash was visible in webcam images drifting W on 25 July.

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

Ongoing activity

Ahyi, United States

20.42°N, 145.03°E | Summit elev. -75 m

At 1047 on 24 July both the Aviation Color Code and the Volcano Alert Level for Ahyi Seamount were lowered to Unassigned because signs of unrest had declined, and discolored seawater over the seamount was last observed on 28 May. The latest phase of activity began in August 2024 and was characterized by visible plumes of discolored seawater observed sporadically in satellite images.

Geological summary: Ahyi seamount is a large conical submarine volcano that rises to within 75 m of the ocean surface ~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 21-28 July. Occasional very small eruptive events occurred during 21-25 July. Crater incandescence was visible during 22-23 and 27 July. An explosion at 1243 on 27 July generated a small ash plume that rose 800 m above the crater rim and drifted NW. Another small ash plume from an explosion at 0716 on 28 July rose 500 m above the crater rim and drifted W. 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.

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

Asosan, Japan

32.8849°N, 131.085°E | Summit elev. 1592 m

The Japan Meteorological Agency (JMA) reported that unrest at Asosan had decreased. The amplitude of volcanic tremors had increased during 4-7 July but then returned to low levels afterward. During field surveys on 16 and 23 July scientists observed no changes compared to field surveys conducted before the increased tremor amplitude. Sulfur dioxide gas emissions were low in July, averaging 200-500 tons per day. At 1100 on 25 July the Alert Level was lowered to 1 (on a scale of 1-5).

Geological summary: The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan’s most active volcanoes. It was the location of Japan’s first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu’s most popular tourist destinations.

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 23-29 July. White-and-gray gas-and-ash plumes rose 700-3,500 m above the summit and drifted in multiple directions on most days; weather conditions obscured views on 26 July. Ashfall was reported from Ruko (11 km NW) to Tobelo City (15 km ENE) on 24 July, and in Mamuya Village (8 km N) and surrounding areas on 26 and 28 July. 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.

Geological 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.

Etna, Italy

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

The Sezione di Catania – Osservatorio Etneo (INGV) reported various gas emissions from Etna’s summit craters during 21-27 July. Sporadic ash emissions rose from SE Crater during the week. On 25 July notably intense gas emissions rose from a vent on the NE Crater floor on and gas emissions rose from several fumarolic vents along the SE Crater flanks and near the summit

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

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 22-29 July. Incandescence at the summit was occasionally observed in overnight webcam images. Pulses of gas and ash were visible during 22-23 and 26-27 July; the plumes drifted W and SE during 26-27 July. A lahar descended the Ceniza (SSW) drainages on 25 July. Avalanches of material that descended the Seca (W) drainage during 26-27 July.

Geological summary: Volcán Fuego, one of Central America’s most active volcanoes, is also one of three large stratovolcanoes overlooking Guatemala’s former capital, Antigua. The scarp of an older edifice, Meseta, lies between Fuego and Acatenango to the north. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at the mostly andesitic Acatenango. Eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

Great Sitkin, United States

52.076°N, 176.13°W | 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 23-29 July. Lava flow advancement was concentrated at the SW lobe, which advanced 5 m during 20-23 July and continued to inflate. Small daily earthquakes were detected by the seismic network, including signals probably caused by small rockfalls from the steep flanks. Elevated surface temperatures consistent with lava effusion were observed in clear satellite views during 22-23 and 25-28 July. Minor steaming at the flow was visible in both webcam and satellite images during 28-29 July. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Geological summary: The Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger volcano capped by a small, 0.8 x 1.2 km ice-filled summit caldera was constructed within a large late-Pleistocene or early Holocene scarp formed by massive edifice failure that truncated an older edifice and produced a submarine debris avalanche. Deposits from this and an even older debris avalanche from a source to the south cover a broad area of the ocean floor north of the volcano. The summit lies along the eastern rim of the younger collapse scarp. Deposits from an earlier caldera-forming eruption of unknown age cover the flanks of the island to a depth up to 6 m. The small younger caldera was partially filled by lava domes emplaced in 1945 and 1974, and five small older flank lava domes, two of which lie on the coastline, were constructed along northwest- and NNW-trending lines. Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano. Eruptions have been recorded since the late-19th century.

Ibu, Indonesia

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

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that the eruption at Ibu continued during 23-29 July. Daily dense gray or white-to-gray ash plumes rose 200-800 m above the summit and drifted NW, NE, and SE. Crater incandescence was visible in nighttime webcam images. The Alert Level remained at 3 (the second highest level on a four-level scale) and the public was advised to stay 4 km away from the active crater and 5 km away from the N crater wall opening.

Geological summary: The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, has contained several small crater lakes. The 1.2-km-wide outer crater is breached on the N, creating a steep-walled valley. A large cone grew ENE of the summit, and a smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. The first observed and recorded eruption was a small explosion from the summit crater in 1911. Eruptive activity began again in December 1998, producing a lava dome that eventually covered much of the floor of the inner summit crater along with ongoing explosive ash emissions.

Kanlaon, Philippines

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

At 1830 on 29 July the Philippine Institute of Volcanology and Seismology (PHIVOLCS) lowered the Alert Level for Kanlaon to 2 on a scale of 0-5) noting declining activity after the 13 May eruption. Volcanic earthquakes recorded by the seismic network averaged eight events per day during 14 May-29 July, fewer than the average of 14 events per day during 3 June 2024-13 May 2025. Volcano-tectonic earthquakes continued to be detected and were located mostly 0-15 km below the surface along a NW-SE transect though the edifice. Despite the decline in average events per day, overall seismic energy represented by RSAM values had not significantly decreased. An ash plume was observed on 5 June, but afterwards only gas-and-steam plumes were seen rising from the summit crater. Sulfur dioxide emissions had decreased to an average of 1,857 tonnes per day during 14 May-29 July. A low rate of inflation had been detected by continuous Global Positioning System (GPS) and Electronic Distance Measurement (EDM) data since 2022, though deflation was detected during the last week of June and the first week of July. PHIVOLCS urged communities to remain evacuated from the 4-km-radius Permanent Danger Zone (PDZ).

Geological 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.

Karymsky, Russia

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

The Kamchatkan Volcanic Eruption Response Team (KVERT) reported that moderate steam-and-gas activity continued at Karymsky during 18-24 July. A weak thermal anomaly over the volcano was identified in satellite images during 19-21 July; the volcano was quiet or weather conditions prevented views on the other days of the week. At 1100 on 25 July the Aviation Color Code was lowered to Yellow (the second level on a four-color scale). Dates are based on UTC; specific events are in local time where noted.

Geological summary: Karymsky, the most active volcano of Kamchatka’s eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with 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, characterized by episodic fountaining and intermittent spatter at two vents along the SW margin of Halema’uma’u Crater, continued at variable levels during 23-29 July. Intermittent incandescence at the N vent was visible during the first half of the week and absent starting overnight during 26-27 July. Incandescence at two areas higher up on the eruptive cone was intermittent and became less intense through the week. Seismic and gas data indicated that gas pistoning occurred as often as every 3-5 minutes; however, no lava or spatter was visible at the surface in association with the activity. 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 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.

Lewotolok, Indonesia

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

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that an eruption at Lewotolok was ongoing during 23-29 July. White-to-gray or gray ash plumes rose 200-500 m above the summit of the cone and drifted W, NW, and SE; weather conditions obscured views on 29 July. Clear nighttime webcam images showed incandescent material being ejected above the cone. The Alert Level remained at 3 (on a scale of 1-4) and the public was warned to stay 3 km away from the summit.

Geological summary: The Lewotolok (or Lewotolo) stratovolcano occupies the eastern end of an elongated peninsula extending north into the Flores Sea, connected to Lembata (formerly Lomblen) Island by a narrow isthmus. It is symmetrical when viewed from the north and east. A small cone with a 130-m-wide crater constructed at the SE side of a larger crater forms the volcano’s high point. Many lava flows have reached the coastline. Eruptions recorded since 1660 have consisted of explosive activity from the summit crater.

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 23-29 July. An explosion at 0723 on 23 July produced a dense white-and-gray ash plume that rose around 1.6 km and drifted SE. According to a news report residents in the Ampek Angkek District (12 km NNW) heard a loud explosion and felt their houses shake. Eruptive events were recorded by the seismic network at 1730 on 25 July and at 1344 on 27 July, but weather clouds obscured 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.

Geological summary: Gunung Marapi, not to be confused with the better-known Merapi volcano on Java, is Sumatra’s most active volcano. This massive complex stratovolcano rises 2,000 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 Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG) reported that the eruption at Merapi (on Java) continued during 18-24 July. Earthquakes were more intense compared to the previous week. The SW lava dome produced 15 lava avalanches that traveled as far as 1.8 km SW down the Bebeng drainage, 24 that traveled as far as 2 km SW down the Krasak drainage, 70 that traveled as far as 2 km W down the Sat/Putih drainage, and one that descended the Boyong drainage on the S flank as far as 1.5 km. Small morphological changes to the SW lava dome resulted from minor collapses. The volume of the SW dome decreased by 66,700 cubic meters to an estimated 4,011,000 cubic meters, based on webcam images and a 17 July drone survey and webcam images. The temperature of the dome had increased by 2.8 degrees Celsius (degrees C) to 244.9 degrees C. The volume of the central dome increased by about 1,600 cubic meters to an estimated 2,368,900 cubic meters, though no morphological changes were observed. The temperature increased by 3.5 degrees C to 218.6 degrees C. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-7 km away from the summit, based on location.

Geological summary: Merapi, one of Indonesia’s most active volcanoes, lies in one of the world’s most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities.

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 continuing gas-and-steam emissions with occasional minor amounts of ash at Poás during 23-29 July. Strong incandescence at Boca A vent was observed and the level of the hyperacid lake over Boca C remained at stable levels. Dense gas-and-steam emissions continued to be emitted from both Boca A and Boca C vents. On 24 July the Comisión Nacional de Emergencias (CNE) conducted an overflight of the crater using a drone with an infrared camera and measured a maximum temperature of 819 degrees Celsius over Boca A and 74-87 degrees Celsius at the lake over Boca C. They observed highly altered pinkish-yellow rocks at the rim of Boca A and down in the crater. Sulfur dioxide emissions measured by satellite averaged 37 tons per day (t/d) during 20-24 July and 520 t/d on 26 July. A moderate eruption that began at 0244 on 27 July lasted for three minutes, producing ash emissions and ejecting incandescent blocks 1 km above the crater floor. The Comisión Nacional de Emergencias (CNE) lowered the Alert Level to Green for Parque Nacional Volcán Poás and district of Toro Amarillo in the Canton of Sarchí (including the Desagüe, Agrio, Anonos, and Gorrión river basins) on 2 July due to decreasing activity and then lifted the Green Alert for the park and surrounding areas on 23 July. The volcanic Alert Level remained at 2 (the second lowest level on a four-level scale) and the Aviation Color Code remained at Yellow (the second lowest color on a four-color scale).

Geological 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.

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 22-29 July with continuing lava extrusion at Caliente dome. Daily explosions, 1-5 per hour when reported, generated gas-and-ash plumes that rose as high as 1 km above the dome and drifted as far as 20 km W and SW. Effusion of blocky lava and collapses of previous deposits produced block avalanches that descended multiple flanks; the collapsed material sometimes produced pyroclastic flows that reached the base of the volcano. Incandescence was visible at Caliente dome mostly during dark hours. On 25 July a minor lahar descended the Cabello de Ángel river, a tributary of the Nimá I, on the E flank, carrying tree trunks, branches, and volcanic blocks up to 3 m in diameter. The lahar was hot and has a sulfur odor. Minor ashfall was reported in communities to the S and SW during 25-26 July.

Geological summary: Symmetrical, forest-covered Santa María volcano is part of a chain of large stratovolcanoes that rise above the Pacific coastal plain of Guatemala. The sharp-topped, conical profile is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank, and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four vents, with activity progressing E towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

Semeru, Indonesia

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

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that activity continued at Semeru during 23-29 July, often with multiple daily eruptive events recorded by the seismic network. Dense white-and-gray or gray ash plumes rose 500-1,000 m above the summit and drifted in multiple directions; weather clouds occasionally obscured views, particularly during 25 and 28-29 July. Incandescence at the summit was visible in a few webcam images; incandescent material traveling down the flank was visible at 2049 on 26 July in a webcam image. The Alert Level remained at 2 (the second lowest level on a scale of 1-4). The public was warned to stay at least 3 km away from the summit in all directions, 8 km from the summit to the SE, 500 m from the banks of the Kobokan drainage as far as 13 km from the summit, and to avoid other drainages including the Bang, Kembar, and Sat, due to lahar, avalanche, and pyroclastic flow hazards.

Geological summary: Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.

Sheveluch, Russia

56.653°N, 161.36°E | 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 17-24 July. Thermal anomalies over the domes were identified in satellite images all week. According to the Kamchatka Volcanological Station (Volkstat) minor ash plumes were visible on 22 July; no dome growth was observed. Explosions on 23 July produced ash plumes that rose as high as 3 km (10,000 ft) a.s.l. and drifted 70 km E. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Dates are based on UTC; specific events are in local time where noted.

Geological summary: The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1,300 km3 andesitic volcano is one of Kamchatka’s largest and most active volcanic structures, with at least 60 large eruptions during the Holocene. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes occur on its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large open caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

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 21-28 July. Incandescence was observed nightly in webcam images. An explosion at 0452 on 21 July generated an ash plume that rose 900 m above the crater rim and drifted W. Another explosion was recorded at 1209 on 24 July, though conditions prevented visual confirmation. 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.

Geological 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.

References:

¹ Smithsonian Institution / US Geological Survey – GVP – Weekly Volcanic Activity Report – July 23–29, 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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