The Weekly Volcanic Activity Report: April 24 – 30, 2024


New activity/unrest was reported for 6 volcanoes from April 24 – 30, 2024. During the same period, ongoing activity was reported for 22 volcanoes.

New activity/unrest: Poas, Costa Rica | Puyehue-Cordon Caulle, Central Chile | Rincon de la Vieja, Costa Rica | Ruang, Sangihe Islands | Taal, Luzon (Philippines) | Tofua, Tonga Ridge.

Ongoing activity: Aira, Kyushu (Japan) | Ambrym, Vanuatu | Dukono, Halmahera | Ebeko, Paramushir Island (Russia) | Fernandina, Isla Fernandina (Galapagos) | Great Sitkin, Andreanof Islands (USA) | Ibu, Halmahera | Kanlaon, Philippines | Kavachi, Solomon Islands | Lateiki, Tonga Ridge | Lewotobi, Flores Island | Lewotolok, Lembata Island | Marapi, Central Sumatra | Masaya, Nicaragua | Merapi, Central Java | Reventador, Ecuador | Reykjanes, Reykjanes Peninsula | Sangay, Ecuador | Semeru, Eastern Java | Sheveluch, Central Kamchatka (Russia) | Suwanosejima, Ryukyu Islands (Japan) | Yasur, Vanuatu.

New activity/unrest

Poas, Costa Rica

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

OVSICORI-UNA reported continuing gas-and-steam emissions from vents Boca A and Boca C on the crater floor of Poás during 24-30 April. Although emissions from Boca C often contained low ash content, no ash was present for a period of time during 25-27 April. Plumes intensified on 28 April and rose several hundred meters high. A sulfur odor was reported in Sarchí and Grecia (both about 17 km SW) on 25 April. Incandescence from Boca A was visible at night during 27-28 April and from both Boca A and Boca C at night during 29-30 April.

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.

Puyehue-Cordon Caulle, Central Chile

40.59°S, 72.117°W | Summit elev. 2236 m

SERNAGEOMIN reported that inflation had been detected at the Puyehue-Cordón Caulle volcanic complex since 2011 based on GNSS satellite and radar data. The inflation is centered about 6 km WNW of the 2011 eruption vents. The rate of inflation had increased during the first few months of 2024, reaching a maximum average of 2.4 cm per month, which was the highest rate detected since GNSS equipment was installed in 2017. Seismicity began to slightly increase in mid-2020 and was characterized by volcano-tectonic and hybrid events from a shallow source near the 2011 vents. Gas emissions rose from the 2011 vents and were nearly 90 degrees Celsius. The Alert Level was raised to Yellow (the second lowest color on a four-color scale) on 26 April based on the high deformation rates.

Geological summary: The Puyehue-Cordón Caulle volcanic complex (PCCVC) is a large NW-SE-trending late-Pleistocene to Holocene basaltic-to-rhyolitic transverse volcanic chain SE of Lago Ranco. The 1799-m-high Pleistocene Cordillera Nevada caldera lies at the NW end, separated from Puyehue stratovolcano at the SE end by the Cordón Caulle fissure complex. The Pleistocene Mencheca volcano with Holocene flank cones lies NE of Puyehue. The basaltic-to-rhyolitic Puyehue volcano is the most geochemically diverse of the PCCVC. The flat-topped, 2236-m-high volcano was constructed above a 5-km-wide caldera and is capped by a 2.4-km-wide Holocene summit caldera. Lava flows and domes of mostly rhyolitic composition are found on the E flank. Historical eruptions originally attributed to Puyehue, including major eruptions in 1921-22 and 1960, are now known to be from the Cordón Caulle rift zone. The Cordón Caulle geothermal area, occupying a 6 x 13 km wide volcano-tectonic depression, is the largest active geothermal area of the southern Andes volcanic zone.

Rincon de la Vieja, Costa Rica

10.83°N, 85.324°W | Summit elev. 1916 m

OVSICORI-UNA reported that the amplitude of seismic tremor at Rincón de la Vieja intensified on 17 April and then increased again on 25 April. The tremor signals were accompanied by long-period events occurring at a rate of sometimes hundreds per day. The intensities of the earthquakes were the highest recorded within the last five years. A total of 19 small eruptive events were recorded during 17-25 April and produced steam-and-gas plumes that rose as high as 2 km. Sulfur dioxide emissions began to increase on 21 April and increased more notably during 24-25 April, rising from around 77 tonnes per day (t/d) to around 493 t/d. Tremor amplitude fluctuated at high levels during 26-29 April, reaching a new peak at around 0200 on 28 April. Gas-and-steam emissions were continuous. The Alert Level remained at Level 3, Orange, the third highest level on a four-level scale.

Geological summary: Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge 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. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide 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 historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Ruang, Sangihe Islands

2.3°N, 125.37°E | Summit elev. 725 m

PVMBG reported that seismicity significantly increased at Ruang on 29 April and the signals indicated magma moving towards the surface. Earthquakes began to be felt at 0015 on 30 April. At 0115 the earthquakes intensified; residents in neighboring Tagulandang Island reportedly felt continuous shaking, heard loud roaring, and saw an ash plume rising about 2 km above the summit. Activity continued to escalate and at 0130 the Alert Level was raised to 4 (the highest level on a scale of 1-4). The public was warned to stay 7 km away from the active crater and residents on Tagulandang within 6 km were instructed to evacuate. A webcam photo from 0232 on 30 April showed lava being ejected above the summit; an eruptive event was recorded in seismic data at 0235. According to the Darwin VAAC ash plumes had risen to 15.2 km (50,000 ft) a.s.l. by 0300 and to 19.2 km (63,000 ft) a.s.l. by 0320, and by 0620 were expanding radially; the plumes may have risen to 23 km (75,400 ft) a.s.l. or more based on other expert analysis.

PVMBG noted that at 0835 dense gray-to-black ash plumes rose at least 5 km and drifted E and S. A webcam photo from 0827 showed multiple pyroclastic density currents descending the flanks. According to a characterization by BNPB the eruption ejected incandescent lava high above the summit and lightning was frequently seen in the plumes. Tephra fell over a more extensive area compared the 16-18 April eruption phase; gravel-sized tephra fell in Apengsala, about 8 km NNE from Ruang’s central vent, and outside of the exclusion zone. According to a news report residents felt shock waves from the explosions. At least three eruptive events were recorded during 1200-1800 that produced gray-and-black ash plumes at least as high as 1.5 km. The VAAC noted that by 1510 the high-level plume had detached from the summit and was drifting W and SW, and ash between 13.7-19.2 km (45,000-63,000 ft) a.s.l. continued to be identified drifting WNW at least through 0940 on 1 May. Ash plumes continued to be identified in satellite images, rising to 3 km (10,000 ft) a.s.l. and drifting N and SE at least through 1240 on 1 May.

According to a news report the eruption and the presence of ash and ashfall caused the closure of seven airports, scheduled to reopen on 1 May: the Sam Ratulangi International Airport (98 km SW in Manado, North Sulawesi), the Gorontalo Airport (371 km SW), the Siau/Sitaro Airport (40 km N), the Bolaang Mongondow Airport (215 km SW), the Tahuna/Naha Airport (150 km N), the Pohuwato Airport (445 SW), and the Pogogul Airport (460 km WSW). On 1 May about 123 residents were evacuated to Bitung City by boat. Ashfall was notable at the Sam Ratulangi International Airport with delays affecting about 7,000 passengers.

Geological summary: Ruang volcano is the southernmost volcano in the Sangihe Island arc, north of Sulawesi Island; it is not the better known Raung volcano on Java. The 4 x 5 km island volcano is across a narrow strait SW of the larger Tagulandang Island. The summit contains a crater partially filled by a lava dome initially emplaced in 1904. Explosive eruptions recorded since 1808 have often been accompanied by lava dome formation and pyroclastic flows that have damaged inhabited areas.

Taal, Luzon (Philippines)

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

PHIVOLCS reported ongoing unrest at Taal during 23-30 April. Upwelling gasses and hot fluids in the lake were visible during daily observations. Daily emissions of gas-and-steam rose from Main Crater Lake as high as 1.8 km, were sometimes voluminous, and drifted generally NW and SW. There were 0-14 daily earthquakes recorded by the seismic network including a few periods of volcanic tremor lasting 2-4 minutes. One phreatic event lasting two minutes long was recorded during 28-29 April. The Alert Level remained at 1 (on a scale of 0-5), and PHIVOLCS reminded the public that the entire Taal Volcano Island was a Permanent Danger Zone (PDZ) and to take extra precautions around Main Crater, when boating on Taal Lake, and along the Daang Kastila fissure.

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.

Tofua, Tonga Ridge

19.75°S, 175.07°W | Summit elev. 515 m

Tonga Geological Services reported that activity at Tofua increased on 26 April and was characterized as having an unusual pattern of activity. A total of 45 eruptive events were identified in data from 0956 on 26 April to 0246 on 28 April. An intensifying thermal anomaly was also identified in satellite images. At 2200 on 28 April an ash plume was identified in a satellite image rising 4-6 km above the summit and drifting NW; it was no longer visible 4 hours later. A SW-drifting plume of sulfur dioxide was also identified in a few satellite images. The number of thermal anomalies over the volcano decreased during 28-30 April, and though sulfur dioxide emissions continued to be detected, the flux had decreased. Mariners were advised to stay 2 km away from the island.

Geological summary: The low, forested Tofua Island in the central part of the Tonga Islands group is the emergent summit of a large stratovolcano that was seen in eruption by Captain Cook in 1774. The summit contains a 5-km-wide caldera whose walls drop steeply about 500 m. Three post-caldera cones were constructed at the northern end of a cold fresh-water caldera lake, whose surface lies only 30 m above sea level. The easternmost cone has three craters and produced young basaltic-andesite lava flows, some of which traveled into the caldera lake. The largest and northernmost of the cones, Lofia, has a steep-sided crater that is 70 m wide and 120 m deep and has been the source of historical eruptions, first reported in the 18th century. The fumarolically active crater of Lofia has a flat floor formed by a ponded lava flow.

Ongoing activity

Aira, Kyushu (Japan)

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

JMA reported ongoing eruptive activity at Minamidake Crater (Aira Caldera’s Sakurajima volcano) during 22-29 April with nighttime crater incandescence. Sulfur dioxide emissions averaged 1,800 tons per day on 22 April. Very small eruptive events were occasionally recorded during 22-26 April. The Alert Level remained at 3 (on a 5-level scale), and the public was warned to stay 2 km away from both 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.

Ambrym, Vanuatu

16.25°S, 168.12°E | Summit elev. 1334 m

On 25 April the Vanuatu Meteorology and Geo-Hazards Department (VMGD) reported that small fumarolic steam emissions were ongoing in both of Ambrym’s Benbow and Marum craters. A satellite image from 20 April showed minor amounts of gas emissions. Incandescence at Marum was visible at night during 20-21 April and a low- to moderate-intensity thermal anomaly was identified in a satellite image on 23 April. Seismic data also confirmed ongoing unrest. The Alert Level remained at 2 (on a scale of 0-5). VMGD warned the public to stay outside of Permanent Danger Zone A, defined as a 1-km radius around Benbow Crater and a 2-km radius around Marum Crater, and to stay 500 m away from the ground cracks created by the December 2018 eruption.

Geological summary: Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides Arc. A thick, almost exclusively pyroclastic sequence, initially dacitic then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major Plinian eruption with dacitic pyroclastic flows about 1,900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.

Dukono, Halmahera

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

PVMBG reported that the eruption at Dukono was ongoing during 24-30 April. Gray-and-white ash plumes rose 100-1,500 m above the summit and drifted NW, W, and SW almost daily; emissions were not observed on 26 April. The Alert Level remained at Level 2 (on a scale of 1-4), and the public was warned to remain outside of the 3-km exclusion zone.

Geological summary: Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia’s most active volcanoes. More-or-less 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 N-flank Gunung Mamuya cone. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

Ebeko, Paramushir Island (Russia)

50.686°N, 156.014°E | Summit elev. 1103 m

KVERT reported that moderate explosive activity was ongoing at Ebeko during 18-25 April. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E), explosions during 22-25 April generated ash plumes that rose as high as 3 km (11,500 ft) a.s.l. and drifted S, SE, and NE. A thermal anomaly was identified in satellite images during 22-24 April; on other days either no activity was observed or weather conditions prevented views. The Aviation Color Code remained at Orange (the third level on a four-color scale). Dates are UTC; specific events are in local time where noted.

Geological summary: The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.

Fernandina, Isla Fernandina (Galapagos)

0.37°S, 91.55°W | Summit elev. 1476 m

Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN) reported that the eruption at Fernandina continued during 24-30 April. Daily thermal anomalies along the lava flow were identified in satellite images and gas-and-steam emissions rose from the area where lava entered the ocean. Sulfur dioxide emissions, measured using satellite data, fluctuated between about 343 and 1,362 tons per day.

Geological summary: Fernandina, the most active of Galápagos volcanoes and the one closest to the Galápagos mantle plume, is a basaltic shield volcano with a deep 5 x 6.5 km summit caldera. The volcano displays the classic “overturned soup bowl” profile of Galápagos shield volcanoes. Its caldera is elongated in a NW-SE direction and formed during several episodes of collapse. Circumferential fissures surround the caldera and were instrumental in growth of the volcano. Reporting has been poor in this uninhabited western end of the archipelago, and even a 1981 eruption was not witnessed at the time. In 1968 the caldera floor dropped 350 m following a major explosive eruption. Subsequent eruptions, mostly from vents located on or near the caldera boundary faults, have produced lava flows inside the caldera as well as those in 1995 that reached the coast from a SW-flank vent. Collapse of a nearly 1 km3 section of the east caldera wall during an eruption in 1988 produced a debris-avalanche deposit that covered much of the caldera floor and absorbed the caldera lake.

Great Sitkin, Andreanof Islands (USA)

52.076°N, 176.13°W | Summit elev. 1740 m

AVO reported that slow lava effusion in Great Sitkin’s summit crater was last confirmed in a 21 April radar satellite image with continuing inflation over the vent and advancement of the NW lava lobe. Effusion likely continued during 24-30 April. Seismicity was low. Weather clouds fully or partly obscured satellite and webcam views, though weakly elevated surface temperatures were observed in satellite images during 26-27 April. 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, Halmahera

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

PVMBG reported that Ibu continued to erupt during 24-30 April. Daily white-and-gray ash plumes generally rose as high as 2 km above the summit and drifted in multiple directions. According to a social media post a loud boom followed by a roar accompanied the eruptive event on 26 April. Ash plumes rose as high as 2 km and incandescence emanated in the plume up to 700 m. At 0037 on 28 April a dense gray-to-black plume rose as high as 3.5 km and drifted W. Incandescence emanated from the summit was visible in a webcam image from 29 April. The Alert Level remained at 2 (the second highest level on a four-level scale), with the public advised to stay outside of the 2 km hazard zone and 3.5 km away from the N area of the active crater.

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

10.412°N, 123.132°E | Summit elev. 2435 m

PHIVOLCS issued a special notice for Kanlaon at 1530 on 30 April noting increased sulfur dioxide emissions. On 30 April a Flyspec instrument measured an average of 2,707 tonnes per day (t/d) of sulfur dioxide emissions at the summit crater, the second highest value recorded in 2024; sulfur dioxide emissions average 3,098 t/d on 19 January. The report noted that higher sulfur dioxide gas fluxes had been recorded for a year with an overall average of 1,300 t/d. The rate of volcanic earthquakes remained at baseline levels of three events per day, though episodes of increased activity had occurred several times during the previous year. Ground deformation data from continuous GPS and electronic tilt data indicated inflation of the volcano since March 2022 and specifically at the E flank starting in 2023. The Alert Level remained at 1 (on a scale of 0-5) and PHIVOLCS reminded the public to remain outside of the 4-km-radius Permanent Danger Zone.

Geological summary: Kanlaon volcano (also spelled Canlaon) forms the highest point on the island of Negros, Philippines. 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.

Kavachi, Solomon Islands

8.991°S, 157.979°E | Summit elev. -20 m

Satellite data showed an area of yellow-green discolored water in the vicinity of the submarine Kavachi volcano that extended about 5.3 km SSW, became diffuse and curved NE, extending for another 6.5 km.

Geological summary: Named for a sea-god of the Gatokae and Vangunu peoples, Kavachi is located in the Solomon Islands south of Vangunu Island. Sometimes referred to as Rejo te Kvachi (“Kavachi’s Oven”), this shallow submarine basaltic-to-andesitic volcano has produced ephemeral islands up to 1 km long many times since its first recorded eruption during 1939. Residents of the nearby islands of Vanguna and Nggatokae (Gatokae) reported “fire on the water” prior to 1939, a possible reference to earlier eruptions. The roughly conical edifice rises from water depths of 1.1-1.2 km on the north and greater depths to the SE. Frequent shallow submarine and occasional subaerial eruptions produce phreatomagmatic explosions that eject steam, ash, and incandescent bombs. On a number of occasions lava flows were observed on the ephemeral islands.

Lateiki, Tonga Ridge

19.18°S, 174.87°W | Summit elev. 43 m

Satellite data showed an area of yellowish-green discolored water in the vicinity of the submarine Lateiki volcano on 26 April. The area of discolored water was narrow and drifted about 2 km SE and curved to the W, becoming more diffuse, and extending another 8.5 km before dissipating.

Geological summary: Lateiki, previously known as Metis Shoal, is a submarine volcano midway between the islands of Kao and Late that has produced a series of ephemeral islands since the first confirmed activity in the mid-19th century. An island, perhaps not in eruption, was reported in 1781 and subsequently eroded away. During periods of inactivity following 20th-century eruptions, waves have been observed to break on rocky reefs or sandy banks with depths of 10 m or less. Dacitic tuff cones formed during the eruptions in 1967 and 1979 were soon eroded beneath the ocean surface. An eruption in 1995 produced an island with a diameter of 280 m and a height of 43 m following growth of a lava dome above the surface.

Lewotobi, Flores Island

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

PVMBG reported that during 24-25 and 27 April white steam-and-gas plumes rose as high as 100 m above the summit of Lewotobi’s Laki-laki volcano and drifted W and SW. On 28 April white-and-gray ash plumes rose 100-300 m and drifted SW and W. Emissions were not observed on 26 April. The Alert Level remained at 2 (the second lowest level on a scale of 1-4) and the public was warned to stay outside of the exclusion zone, defined as a 2-km radius around Laki-laki crater, 3 km to the NNE, and 5 km on the NE flanks.

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, Lembata Island

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

PVMBG reported that the eruption at Lewotolok continued during 24-30 April. White-and-gray ash plumes rose as high as 400 m above the summit and drifted W and NW during 25-26 April. White emissions rose up to 500 m above the summit and drifted W and NW on the other days. The Alert Level remained at 3 (on a scale of 1-4) and visitors and residents of Lamawolo, Lamatokan, and Jontona were warned to stay 2 km away from the vent and 3 km away from the vent on the S and SE flanks.

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, Central Sumatra

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

PVMBG reported that eruptive activity at Marapi (on Sumatra) was ongoing during 24-30 April. White-and-gray ash plumes rose 300-1,000 m above the summit and drifted N, NW, and W on 24, 27, and 29 April. White steam-and-gas plumes rose 300 m above the summit and drifted NW on 26 April; emissions were not visible on the other days, though an eruptive event was recorded on 25 April. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 4.5 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.

Masaya, Nicaragua

11.9844°N, 86.1688°W | Summit elev. 594 m

On 18 April INETER reported that there continued to be no signs of lava-lake activity at the bottom of Masaya’s Santiago Crater after material from a landslide had covered the lake on 2 March. Small landslides continued to occur periodically, and one was shown in a webcam photo from 17 April. Continuous diffuse gas emissions rose from a vent on the crater floor and from a new vent located on the inner SW wall.

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.

Merapi, Central Java

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

BPPTKG reported that the eruption at Merapi (on Java) continued during 19-25 April. Seismicity remained at high levels. The SW lava dome produced 152 lava avalanches that traveled as far as 2 km down the SW flank. Morphological changes to the SW lava dome were due to continuing effusion and collapses of material. 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.

Reventador, Ecuador

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

IG-EPN reported that a moderate eruption at Reventador was ongoing during 23-30 April. Seismicity was unknown due to data transmission problems. Even though cloudy weather conditions often prevented webcam and satellite observations, daily ash-and-gas plumes were visible rising as high as 1.4 km above the crater rim and drifting NW, W, and SW. Secretaría de Gestión de Riesgos 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.

Reykjanes, Reykjanes Peninsula

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

IMO reported that the cone just E of Sundhnúk and along the fissure within the Reykanes volcanic system continued to erupt lava. The average effusion rate was 0.9 (± 0.4) cubic meters per second during 15-25 April, whereas during the first half of April the rate was an estimated 3-4 cubic meters per second. By 25 April the lava-flow field was an estimated 6.16 square kilometers with an approximate volume of 34 (± 1.9) million cubic meters. The average thickness of the flows was 5.5 (± 0.3) m.

During 24-30 April lava flowed S through an open channel near the cone and, more distally, through lava tubes. The tubes transported lava to the area NE of Grindavík, inflating the flow field along the constructed barriers there; on 27 April a small flow overtopped the barrier and flowed down to its base. Gas emissions continued to drift downwind and residents were advised to monitor air quality. Inflation from magma accumulation beneath Svartsengi was first detected at the beginning of April and has continued based on modeling of GPS and satellite data, though on 30 April IMO noted that the rate had slowed during the previous few days.

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.

Sangay, Ecuador

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

IG-EPN reported that high levels of eruptive activity continued at Sangay during 23-30 April. The seismic network recorded 388-1,167 daily explosions during the week. Daily gas-and-ash plumes visible in webcam and/or satellite images generally rose as high as 2 km above the summit and drifted NW, W, and SW; weather conditions often hindered views during the week. Incandescent material was visible daily during dark hours descending the SE flank as far as 1.8 km. Several episodes of explosions were visible in webcam images during 25-28 April and pyroclastic density currents descended the SE flank during 27-29 April. Ash plumes possibly rose as high as 7 km above the summit and drifted W and SW during 28-29 April. 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.

Semeru, Eastern Java

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

PVMBG reported that eruptive activity continued at Semeru during 24-30 April. Almost daily white-and-gray ash plumes rose 100-1,000 m above the summit and drifted in multiple directions; an eruptive event was recorded on 30 April though no emissions were observed. The Alert Level remained at 3 (the third highest level on a scale of 1-4). The public was warned to stay at least 5 km away from the summit in all directions, 13 km from the summit to the SE, 500 m from the banks of the Kobokan drainage as far as 17 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, Central Kamchatka (Russia)

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

KVERT reported that eruptive activity at Sheveluch continued during 18-26 April with a daily thermal anomaly identified in satellite images. A plume of resuspended ash drifted 195 km S and SE during 22-24 April. The Aviation Color Code remained at Orange (the third level on a four-color scale). Dates are based on UTC times; 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, Ryukyu Islands (Japan)

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

JMA reported that eruptive activity at Suwanosejima’s Ontake Crater continued during 22-29 April. Crater incandescence was observed in webcam images nightly. Emissions rose as high as 800 m above the crater rim; no explosions were detected. The Alert Level remained at 2 (on a 5-level scale) and the public was warned to stay at least 1.5 km away from 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.

Yasur, Vanuatu

19.532°S, 169.447°E | Summit elev. 361 m

On 25 April the Vanuatu Meteorology and Geohazards Department (VMGD) reported that activity at Yasur continued at a level of “major unrest,” as defined by the Alert Level 2 status (on a scale of 0-5). Recent visual observations and photos taken in the field indicated that explosions continued, producing emissions of gas, steam, and/or ash. Gas emissions were identified in satellite images during the previous few days. The report warned that some of the explosions may eject material that falls in and around the crater. The public was reminded to not enter the restricted area within 600 m around the boundaries of the Permanent Exclusion Zone, defined by Danger Zone A on the hazard map.

Geological summary: Yasur has exhibited essentially continuous Strombolian and Vulcanian activity at least since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island in Vanuatu, this pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide open feature associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.


1 Smithsonian Institution / US Geological Survey – Weekly Volcanic Activity Report – April 24 – 30, 2024 – Managing Editor: Sally Sennert.


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