The Weekly Volcanic Activity Report: April 23-29, 2026

New activity/unrest: Masaya, Nicaragua | Poas, Costa Rica | Rincon de la Vieja, Costa Rica.

New activity/unrest

Masaya, Nicaragua

11.9844°N, 86.1688°W; Elev. 594 m

The Washington Volcanic Ash Advisory Center (VAAC) reported that on 26 April a diffuse ash plume from Masaya was visible in satellite and webcam images rising to 1.5 km (5,000 ft) a.s.l. and drifting less than 20 km E.

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

Poas, Costa Rica

10.2°N, 84.233°W; Elev. 2,697 m

The Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional (OVSICORI-UNA) reported eruptive activity at Poás during 22-29 April. Gas emissions across the lake and from the new fumarolic field along the inner W wall were visible during 22-23 April. A phreatic/Surtseyan eruption at Boca A at 1524 on 27 April ejected jets of dark material above the lake’s surface and produced a steam plume that rose around 100 m. A second eruptive event the next day, on 28 April, lasted around one minute and consisted of three explosive pulses based on acoustic data. The event produced an eruption plume that rose 400 m and ejected ballistics to the SE that landed on the upper crater terrace. The Volcanic Alert Level remained at 2 (the second lowest level on a four-level 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.

Rincon de la Vieja, Costa Rica

10.8314°N, 85.3364°W; Elev. 1,729 m

The Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA) reported minor eruptive events at Rincón de la Vieja during 23-29 April. A phreatic eruption at 1140 on 23 April produced a steam-and-gas plume that rose 100 m above the crater rim. Gas-and-steam plumes rose 500 m vertically above the crater rim due to lack of wind throughout the day on 24 April. A moderate ash eruption recorded at 0302 on 27 April was the most energetic event so far in 2026. The Alert Level remained at Level 2, Yellow, the second lowest level on a four-level scale.

Geological summary: Rincón de la Vieja is a volcanic complex in the Guanacaste Range of NW Costa Rica. Sometimes referred to as the Rincon de la Vieja-Santa María Volcanic Complex, it consists of a slightly arcuate 20-km-long ridge of 12 craters and pyroclastic cones constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the “Colossus of Guanacaste,” it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. The Santa María cone, the highest peak of the complex, is located on the E side of the ridge and has a lake within the 400-m-diameter crater. A Plinian eruption producing the 0.25 km3 Río Blanca tephra about 3,500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous reported eruptions possibly dating back to the 16th century, have been from the active crater, near the center of the complex, with an acidic 300-m-diameter lake.

Ongoing activity

Aira, Japan

31.5772°N, 130.6589°E; Elev. 1,117 m

The Japan Meteorological Agency (JMA) reported ongoing eruptive activity at Minamidake Crater (Aira Caldera’s Sakurajima volcano) during 24-27 April. Crater incandescence was visible in nighttime webcam images. Very small eruptive events were periodically detected. 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.

Ambae, Vanuatu

15.389°S, 167.835°E; Elev. 1,496 m

The eruption at Ambae continued during 24-25 April based on reports from the Wellington Volcanic Ash Advisory Center (VAAC). On 24 April sulfur dioxide emissions were identified in satellite images alongside a plume visible in webcam images; weather clouds prevented confirmation of ash. Weather clouds continued to obscure views for a few subsequent images. A diffuse ash plume was identified in a satellite image at 0915 on 25 April drifting SE at an altitude at or below 2.4 km (8,000 ft) a.s.l. The Alert Level remained at 3 (on a scale of 0-5), and the public was warned to stay outside of Danger Zone B, defined as a 3-km radius around the active vents in Lake Voui, and to stay away from drainages during heavy rains.

Geological 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.

Dukono, Indonesia

1.6992°N, 127.8783°E; Elev. 1,273 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that eruptive activity at Dukono continued during 23-29 April. Daily white-and-gray ash plumes rose 400-1,400 m above the summit and drifted in multiple directions. 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.

Fuego, Guatemala

14.4748°N, 90.8806°W; Elev. 3,799 m

The Instituto Nacional de Sismología, Vulcanologia, Meteorologia e Hidrología (INSIVUMEH) reported that eruptive activity at Fuego continued during 22-29 April. Daily Strombolian explosions recorded by the seismic network, at rates of 5-13 per hour when reported, generated gas-and-ash plumes that rose as high as 1.1 km above the summit and drifted as far as 40 km in different directions. Rumbling sounds, shock waves, and/or sounds associated with gas emissions were reported daily. Explosions occasionally ejected incandescent material as high as 300 m above the summit. Incandescent block avalanches descended the Seca (W), Taniluyá (SSW), Ceniza (SSW), Las Lajas (SE), Santa Teresa (W), and Trinidad (SSW) drainages, sometimes reaching vegetated areas. Ashfall was reported in areas downwind including in El Rodeo (10 km SSE), El Zapote (10 km SSE), La Reunión (7 km SE), and Alotenango (8 km ENE) during 22-23 April, on the W and SW flanks during 27-28 April, and in Panimaché I and II (8 km SW), Finca La Asunción (12 km SW), Morelia (10 km SW), El Porvenir (11 km SW), and their surrounding areas.

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

Great Sitkin, United States

52.076°N, 176.13°W; Elev. 1,740 m

The Alaska Volcano Observatory (AVO) reported that slow lava effusion continued to feed a thick flow in Great Sitkin’s summit crater during 22-29 April. Lava-dome growth and rockfalls were concentrated on the E and S parts of the flow. The rockfalls were recorded daily by the seismic network. Weather clouds often prevented webcam and satellite observations. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

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

Ibu, Indonesia

1.4941°N, 127.6324°E; Elev. 1,357 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that activity at Ibu continued during 23-29 April, with daily eruptive events recorded by the seismic network. Daily gray or white-to-gray ash plumes rose 300-700 m above the summit and drifted in multiple directions. The Alert Level remained at 2 (the second lowest level on a four-level scale) and the public was advised to stay 2 km away from the active crater and 3.5 km away from the N crater wall opening.

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

Kanlaon, Philippines

10.4096°N, 123.13°E; Elev. 2,422 m

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported continuing eruptive activity at Kanlaon during 22-29 April. The seismic network recorded 7-54 daily volcanic earthquakes, including 2-5 daily periods of tremor lasting three minutes to just over one hour. Sulfur dioxide emissions ranged from 1,162 to 2,098 tonnes per day. Emissions were visible daily that generally rose 300-1,800 m above the summit and drifted in multiple directions. There were 2-11 daily periods of ash emissions, each lasting for three minutes to just over one hour. At 1723 on 24 April, at 0832 on 25 April, and at 1830 on 26 April ash plumes visible in webcam images rose 800 m, 300 m, and 1,200 m above the summit, respectively, and drifted W and SW. The Alert Level remained at 2 (on a scale of 0-5); the public was warned to stay out of the 4-km-radius Permanent Danger Zone (PDZ) and pilots were advised to avoid flying close to the summit.

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.

Kilauea, United States

19.421°N, 155.287°W; Elev. 1,222 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 22-29 April. Three lava overflows at the N vent were recorded during 20-21 April. Overflows at the S vent on 22 April were followed by low dome fountaining. Low fountaining at the N vent began at 0100 on 23 April; over the following 30 minutes activity decreased at the S vent and increased at the N vent. At 0134 a sharp increase in seismic tremor and deflation detected by summit tiltmeters marked the start of the high fountaining at the N vent. The fountains grew steadily until peak heights were reached at 0300; the main part of the fountains rose to at least 220 m, with diffuse areas of tephra at the top of the fountain occasionally going above 300 m. An eruption plume rose to 6 km (20,000 ft) a.s.l. and drifted S and SW. No significant tephra fallout was reported at visitor areas of Hawai’i Volcanoes National Park or on county roads, but Pele’s hair and fine ash was reported falling in communities at the S end of the island. After their peak, fountain height gradually decreased and were about 100 m high just before abruptly ending at 1001, after 8.5 hours in total of continuous lava fountaining. At 1013 the Volcano Alert Level was lowered to Advisory and the Aviation Color Code was lowered to Yellow due to reduced ground and aviation hazards. The average effusion rate was 170 cubic meters per second; the highest peak was just over 300 cubic meters per second, occurring at around 0300. An estimated 5.2 million cubic meters of lava erupted and covered about 50 percent of the Halema’uma’u Crater floor. Gas jetting and flames at the S vent were periodically visible during the fountaining episode at the N vent.

Variable incandescence and occasional flaming at both vents were visible during 24-29 April. The lava flows on the crater floor were incandescent and spread E during 24-25 April; only a few glowing spots on the flow field were visible during the rest of the week as the lava cooled. Seismic tremor with bursts of tremor every 1-10 minutes likely associated with gas pistoning cycles in the eruptive vents persisted. Earthquake activity at the summit was low.

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.

Krasheninnikov, Russia

54.596°N, 160.27°E; Elev. 1,816 m

The Kamchatkan Volcanic Eruption Response Team (KVERT) reported that lava flows at Krasheninnikov continued to effuse onto the ENE and E flanks of the Northern Cone during 22-29 April. A large daily thermal anomaly was identified in satellite images. Satellite images showed small thermal anomalies along the active lava flow on the ENE flank on 23 and 26 April; the flows were obscured by either volcanic or weather clouds on 28 April. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale). Dates and times are provided in Coordinated Universal Time (UTC); events are in local time only where specified.

Geological 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; Elev. 1,703 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported periodic ash plumes at Lewotobi Laki-laki during 23-29 April. Periodic ash plumes were visible in webcam images and detected by the seismic network. Daily dense gray ash plumes during 23-26 April rose as high as 1.8 km above the crater rim and drifted SW, W, N, and NE. A few eruptive events were recorded but not visually observed. Minor incandescence at the summit was visible in a webcam image at 2322 on 24 April. The Alert Level remained at 2 (the second lowest level on a scale of 1-4) and the exclusion zone was a radius of 4 km from the center of Laki-laki.

Geological 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.

Lewotolok, Indonesia

8.274°S, 123.508°E; Elev. 1,431 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported ongoing eruptive activity at Lewotolok during 24-29 April. An eruptive event at 0209 on 23 April generated an ash plume that rose around 300 m above the summit and rifted SW and W. Incandescent material at the summit and on the upper flanks was visible in a webcam image one minute later. Minor incandescence at the summit was visible in a few webcam images on 24, 26, and 29 April. White-and-gray ash plumes rose 100 m above the summit and drifted W and SW on 29 April and rumbling was heard. The Alert Level remained at 2 (on a scale of 1-4) and the public was warned to stay 2 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; Elev. 2,885 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that eruptive activity at Marapi (on Sumatra) continued during 23-29 April. White plumes rose as high as 100 m above the summit on a few of the days and drifted in multiple directions. An eruptive event was recorded at 0510 on 23 April by the seismic network but not visually observed. 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.

Mayon, Philippines

13.257°N, 123.685°E; Elev. 2,462 m

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported that the eruption at Mayon continued during 21-29 April, characterized by lava effusion, pyroclastic density currents (PDCs), incandescent rockfalls, ash-and-gas plumes, and occasional minor Strombolian activity. Emissions were visible daily, rising as high as 1.5 km above the summit and drifting in multiple directions. Each day the seismic network recorded 195-281 rockfalls, 0-2 PDCs, and 12-62 volcanic earthquakes. The earthquake counts included 8-35 daily periods of volcanic tremor, each lasting between one minute to two hours and 39 minutes. Near daily measurements of sulfur dioxide emissions averaged 815-3,434 tonnes per day. The lava flows did not advance in the Basud (E) and Bonga (SE) drainages, remaining 3.8 and 3.2 km long, respectively. The lava flow in the Mi-isi (S) drainage advanced 300 m during 24-25 April to a total length of 1.6 km. Minor Strombolian activity and short periods of lava fountaining were recorded daily. The Alert Level remained at 3 (on a 0-5 scale) and residents were reminded to stay away from the 6-km-radius Permanent Danger Zone (PDZ). PHIVOLCS recommended that civil aviation authorities advise pilots to avoid flying close to the summit.

Geological summary: Symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the most active volcano of the Philippines. The steep upper slopes are capped by a small summit crater. Recorded eruptions since 1616 CE range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer periods of andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic density currents and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often damaged populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

Merapi, Indonesia

7.54°S, 110.446°E; Elev. 2,910 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that the eruption at Merapi (on Java) continued during 23-29 April with occasional lava avalanches produced by the active lava dome on the upper SW flank. Daily white plumes rose as high as 600 m above the summit on most days and drifted in different directions. On 23 April two lava avalanches descended the Sat/Putih drainage (W flank) as far as 2 km. The next day, on 24 April, four lava avalanches descended the Sat/Putih drainage and one pyroclastic flow traveled 1.5 km down the SW flank. On 25 April a total of 21 lava avalanches descended the Sat/Putih and Krasak (W flank) drainages as far as 2 km. There were 23 lava avalanches that descended the Sat/Putih drainage as far as 2 km on 26 April; the next day, 27 April, there were 33 lava avalanches that reached as far as 2 km down the Sat/Putih and Bebeng (SW flank) drainages. 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.

Nevado del Ruiz, Colombia

4.892°N, 75.324°W; Elev. 5,279 m

The Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued during 21-27 April. Seismic data indicated that events associated with fluid movement remained at overall low levels and similar intensity compared to the previous week, though they slightly increased in number. There were no long-duration signals recorded, seismic events associated with pulsating ash emissions, or ejection of hot material. Events associated with rock fracturing decreased in number and increased in intensity. The earthquakes were mainly located beneath the Arenas Crater and the SSW flanks at distances of less than 4 km from the crater; additional earthquakes were scattered in multiple directions within 10 km. The depths of these events ranged from 1-7 km. The largest earthquake was an M 1.5 that occurred at 0127 on 23 April at a depth of 4 km in an area 3 km SSW of the Arenas Crater. Daily sulfur dioxide emissions fluctuated at low levels. Gas-and-steam emissions rose as high as 1 km above the summit and generally drifted mainly SE and NE. 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).

Geological 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.

Reventador, Ecuador

0.077°S, 77.656°W; Elev. 3,562 m

The Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN) reported that eruptive activity at Reventador continued at a high level during 22-29 April. Seismicity included 70-87 daily explosions, long-period earthquakes, harmonic tremor, and tremor associated with emissions. Ash-and-gas plumes, sometimes multiple per day, were visible in webcam and satellite images and reported by the Washington Volcanic Ash Advisory Center (VAAC). The ash plumes rose 600-1,900 m above the crater rim and drifted in multiple directions. Crater incandescence was visible nearly nightly and incandescent blocks were also visible nightly rolling as far as 1.3 km down the flanks. Thermal anomalies were often identified in satellite images. At around 0300 on 27 April a moderate-sized, secondary lahar descended the Marker River on the S flank. A pyroclastic flow descended the SW flank during the morning of 29 April. Weather clouds sometimes obscured views. Secretaría de Gestión de Riesgos (SGR) maintained the Alert Level at Orange (the second highest level on a four-color scale).

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

Sabancaya, Peru

15.787°S, 71.857°W; Elev. 5,960 m

The Instituto Geofísico del Perú’s (IGP) Centro Vulcanológico Nacional (CENVUL) reported continuing eruptive activity at Sabancaya during 22-28 April. The seismic network detected 4-14 daily earthquakes indicating the movement of magma and gases. As many as five thermal anomalies were identified in satellite images. Gas-and-steam emissions rose as high as 100 m above the summit and drifted in multiple directions on 22 April. Gas, steam, and ash plumes rose 300-2,200 m above the summit and drifted NW, W, SW, and W during 24-28 April. The Alert Level remained at Orange (the third level on a four-color scale) and the public was warned to stay outside of a 12 km radius from the summit.

Geological summary: Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning “tongue of fire” in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of observed eruptions date back to 1750 CE.

Sangay, Ecuador

2.005°S, 78.341°W; Elev. 5,286 m

The Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN) reported that the eruption continued at Sangay during 22-29 April. The seismic network recorded 190-473 daily explosions. Daily or near-daily ash-and-gas plumes visible in webcam views, satellite images, and reported by the Washington Volcanic Ash Advisory Center rose 300-2,800 m above the crater rim and drifted in multiple directions. Almost nightly there were several observations of incandescent material descending the flanks as far as 1.4 km, particularly to the NW and N; weather conditions sometimes prevented views. The Secretaría de Gestión de Riesgos (SGR) maintained the Alert Level at Yellow (the second highest level on a four-color scale).

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

Santa Maria, Guatemala

14.757°N, 91.552°W; Elev. 3,745 m

The Instituto Nacional de Sismología, Vulcanología, Meteorología e Hidrología (INSIVUMEH) reported ongoing eruptive activity at Santa Maria’s Santiaguito dome complex during 22-29 April, with continuing lava extrusion at Caliente dome. Incandescence at the summit was sometimes observed during dark hours. Daily explosions, 1-3 per hour when reported, generated gas-and-ash plumes that rose as high as 900 m above the dome and drifted as far as 20 km SW and W. Effusion of blocky lava and collapses of material produced daily incandescent block avalanches that descended the flanks, mainly to the W, SW, and S. The block avalanches were sometimes accompanied by short pyroclastic flows during 22-23 and 27-28 April; the latter pyroclastic flows generated ash plumes that rose 900 m above the dome and drifted W and SW. Lahars in the Nimá I and Tambor drainages on the S and SE flanks on 22 April and in the Nimá I drainage on 24 April carried tree trunks, branches, and volcanic blocks up to 1 m in diameter. The lahar in the Tambor drainage was hot and had a sulfur odor due to the remobilization of pyroclastic flow deposits. Minor ashfall was reported in Las Marias (10 km S), Calaguaché (9 km S), Belén (10 km S), and other nearby areas during 22-23 April, and in La Tranquilidad (7 km SW), San Marcos Palajunoj (10 km SW), and the surrounding areas during 26-27 April. Several pyroclastic flows descended the S and SW flanks 2-4 km during 0240-0600 on 28 April, though weather clouds obscured visual confirmation. The pyroclastic flows were detected by the seismic network as peaks in Real-time Seismic Amplitude Measurement (RSAM) data. Moderate amounts of ashfall were reported in local farms and communities on the S and SW flanks, and minor amounts fell in areas as far as 100 km W and SW. During 28-29 April block avalanches descended the flanks at a rate of 2-4 per hour. Minor ashfall was reported in Finca El Faro (7 km S), La Florida (6 km S), San Marcos Palajunoj, and surrounding areas.

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

Semeru, Indonesia

8.108°S, 112.922°E; Elev. 3,657 m

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that activity continued at Semeru during 23-29 April, with daily eruptive events recorded by the seismic network. Daily white-to-gray and gray ash plumes were visible rising 300-1,000 m above the summit that were mainly drifting S, SW, and W, and occasionally NE. An eruptive event at 1959 on 24 April generated an ash plume that rose around 700 m above the summit; a news report stated that an accompanying pyroclastic flow traveled 4.5 km down the Kobokan drainage on the SE flank. 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.

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

Sheveluch, Russia

56.653°N, 161.36°E; Elev. 3,283 m

The Kamchatkan Volcanic Eruption Response Team (KVERT) reported continuing eruptive activity at the lava domes along the N crater floor of Young Sheveluch (on the SW flank of Old Sheveluch) during 23-29 April. Growth continued along the N part of the main lava dome. A daily thermal anomaly was identified in satellite images. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Dates are based on UTC; specific events are in local time where noted.

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

Stromboli, Italy

38.789°N, 15.213°E; Elev. 924 m

The Sezione di Catania – Osservatorio Etneo (INGV) reported that eruptive activity continued at Stromboli during 20-26 April. Webcam images showed Strombolian activity from five vents in Area N within the upper part of the Sciara del Fuoco, and from at least two vents in Area C-S (South-Central Crater) on the crater terrace. The vents in Area N (two in sector N1 and three in sector N2) continued to produce low- to medium-intensity explosions at a rate of 3-14 per hour, ejecting lapilli and bombs less than 150 m above the vents. Spattering at N2 was observed. Low- to medium-intensity explosions ejected tephra from two vents in Area C-S at a rate of 4-9 times per hour.

INGV scientists conducted a field survey during 1300-1700 on 21 April, observing eruptive activity, taking measurements, and collecting samples. They noted that the South-Central Crater appeared as a deep and wide depression with at least three vents. The main vent, S1, was a scoria cone producing sustained Strombolian activity that ejected clasts higher than 150 m; the clast fell within the crater terrace. The scientists collected samples of scoriaceous lapilli in the vicinity of Pizzo (S3). Activity at two other vents was characterized as intermittent, including weak explosions associated with ash emissions or prolonged jets of pressurized gas. At Area N a small cone active in sector N2 alternated between weak spattering activity and Strombolian explosions. In sector N1, a vent that initially produced an intense ash emission associated with forceful jets of magma fragments progressively produced effusive activity over the observation period. A lava flow emerged from a fissure located at the base of the cone and rapidly advanced to the mid-to-upper section of the Sciara del Fuoco, with subsequent flows forming multiple overlapping layers. Two days later a lava overflow occurred at the same area; large incandescent blocks from the S vent of N2 began to roll down the upper part of the Sciara del Fuoco at 1812 on 23 April and were followed by advancing lava. The flow was cooling by the early hours of 24 April. The Alert Level remained at Yellow (the second lowest level on a four-level scale) according to the Dipartimento della Protezione Civile.

Geological summary: Spectacular incandescent nighttime explosions at Stromboli have long attracted visitors to the “Lighthouse of the Mediterranean” in the NE Aeolian Islands. This volcano has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent scarp that formed about 5,000 years ago due to a series of slope failures which extends to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Suwanosejima, Japan

29.638°N, 129.714°E; Elev. 796 m

The Japan Meteorological Agency (JMA) reported that eruptive activity at Suwanosejima’s Ontake Crater continued during 17-24 April. Incandescence was observed nightly in webcam images. An eruptive event on 21 April produced an ash plume that rose 500 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.

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.

Taal, Philippines

14.0106°N, 120.9975°E; Elev. 311 m

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported eruptive activity at Taal during 22-29 April. The seismic network generally recorded 0-6 daily volcanic earthquakes; additionally, there were two periods of tremor lasting 1-3 minutes on 22 April, three periods on 28 April lasting two minutes to three hours and 14 minutes, and five periods on 29 April lasting 14 minutes to two hours and 10 minutes. Daily diffuse gas-and-steam emissions rose as high as 500 m above the crater rim and drifted SW. Minor phreatic eruptions during 0157-0207 on 25 April generated eruption plumes that rose 150-200 m above the crater rim. That same day there were 25 volcanic earthquakes and 23 periods of tremor each lasting 1-29 minutes. Two minor phreatomagmatic events, each around two minutes long, occurred during 2052-2103 on 29 April and produced plumes that rose 400-600 m above the crater rim. One phreatic eruption that was four minutes long was also recorded that same day. 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.

Geological 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.

References:

¹ Smithsonian Institution / US Geological Survey Weekly Volcanic Activity Report – GVP – April 23-29, 2026 – 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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