The Weekly Volcanic Activity Report: May 15 - 21, 2024

New activity/unrest was reported for 11 volcanoes from May 15 to 21, 2024. During the same period, ongoing activity was reported for 16 volcanoes.

New activity/unrest

Asosan, Kyushu (Japan)

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

JMA reported continuing unrest at Asosan. Sulfur dioxide gas emissions were somewhat high, averaging 1,600 tons per day (t/d), when measured during a field survey on 9 May. The amplitude of volcanic tremors began to increase at around 0600 on 15 May and increased again round 0900. At 0920 the Alert Level was raised to 2 (on a scale of 1-5) and the public was warned to stay at least 1 km away from the crater. During a field visit later that morning scientists observed a hot spring within the pool on the Nakadake Crater floor and measured sulfur dioxide emissions of 800 t/d. Volcanic tremor amplitude was variable and decreased to low levels by 0700 on 16 May. White steam-and-gas plumes rose 100-300 m above the crater rim during 16-17 May and crater incandescence was occasionally visible in webcam images at night. Sulfur dioxide emissions had decreased to 500 t/d on 17 May.

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

Concepcion, Nicaragua

11.538°N, 85.622°W | Summit elev. 1700 m

Instituto Nicaragüense de Estudios Territoriales (INETER) reported that a small-to-moderate explosion at Concepción occurred at 1420 on 16 May. An ash-and-gas plume rose at least 2 km above the crater rim and caused ashfall up to 1 mm deep in Los Ramos (SE), La Unión (SE), Los Angeles, La Flor (5 km NW), Urbaite, and Las Pilas. According to the Washington VAAC the ash plume was identified in satellite images at 1520 drifting NW at an altitude of about 5.5 km (18,000 ft) a.s.l., or at around 3.8 km above the summit.

Geological summary: Volcán Concepción is one of Nicaragua’s highest and most active volcanoes. The symmetrical basaltic-to-dacitic stratovolcano forms the NW half of the dumbbell-shaped island of Ometepe in Lake Nicaragua and is connected to neighboring Madera volcano by a narrow isthmus. A steep-walled summit crater is 250 m deep and has a higher western rim. N-S-trending fractures on the flanks have produced chains of spatter cones, cinder cones, lava domes, and maars located on the NW, NE, SE, and southern sides extending in some cases down to Lake Nicaragua. Concepción was constructed above a basement of lake sediments, and the modern cone grew above a largely buried caldera, a small remnant of which forms a break in slope about halfway up the N flank. Frequent explosive eruptions during the past half century have increased the height of the summit significantly above that shown on current topographic maps and have kept the upper part of the volcano unvegetated.

Ibu, Halmahera

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

PVMBG reported that the eruption at Ibu continued to intensify during 11-21 May, with ash plumes rising higher and having denser ash content. Seismicity was also high and increasing. Beginning on 11 May the ash plumes began rising 4-5 km above the summit; the plumes were dense and gray and drifted N and NW, and incandescent ejecta was visible. Eruptive events were recorded on 12 and 14 May, though weather conditions prevented visual observations. During 13-16 May gray-to-black ash plumes rose as high as 5 km and drifted multiple directions. Roaring and banging noises were heard in areas as far away as the Ibu observation post (9 km W). At 1500 on 16 May the Alert Level was raised to 4 (the highest level on a four-level scale) and the public was advised to stay 4 km away from the active crater and 7 km away from the N crater wall opening. BNPB reported that 263 residents evacuated from three villages, Gam Ici, Goin, and Sangaji Nyeku.

White-and-gray ash plumes with variable densities rose 4-5 km above the summit and drifted multiple directions during 17-18 and 20-21 May. Photos from just after 2000 on 18 May showed lightning in the dense ash plumes. Only white steam-and-gas plumes were visible on 19 May, rising 200-300 m above the summit and drifting N, NE, and E. According to a news report the total number of evacuees rose to more than 400 by 19 May; the residents were from seven villages in the West Halmahera District.

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.

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 15-21 May. White gas-and-steam plumes rose 200-300 m above the summit and drifted in multiple directions on most days; no emissions were visible on 16 and 20 May. White-and-gray ash plumes rose 400-550 above the summit and drifted NW on 18 May.

The 11 May lahars that caused several fatalities, evacuations, and widespread damage in the Agam Regency continued to impact the area. As of 1700 on 16 May BNBP reported that the death toll had reached 67 people, while 20 remained missing and 40-44 had been injured; overall 989 families were impacted by the lahars. 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.

Purace, Colombia

2.32°N, 76.4°W | Summit elev. 4650 m

Observatorio Vulcanológico y Sismológico de Popayán, Servicio Geologico Colombiano (SGC) reported that the daily number of both volcanic tremor (VT) and long-period (LP) seismic events at Puracé trended downward during 14-21 May, and by the end of the week had reached pre-29 April levels. The VT events had low magnitudes and were located at depths up to 2.4 km beneath the volcano and its E flank. The largest VT events, M 1.5, were recorded at 1821 on 14 May and at 0711 on 16 May. LP earthquakes were located at depths less than 3 km beneath the volcano and its N flank. Inclement weather often prevented visual observations of emissions, though during 15-16 May a gas plume rose as high as 650 m above the summit and drifted W. Both carbon dioxide and sulfur dioxide emissions remained above baseline levels. The Alert Level remained at Orange (the second highest level on a four-color scale).

Geological summary: Puracé in Colombia consists of an andesitic stratovolcano with a 500-m-wide summit crater constructed over a dacitic shield volcano. It lies at the NW end of a volcanic massif opposite Pan de Azúcar stratovolcano, 6 km SE. A NW-SE-trending group of seven cones and craters, Los Coconucos, lies between the two larger edifices. Frequent explosive eruptions in the 19th and 20th centuries have modified the morphology of the summit crater. The largest eruptions occurred in 1849, 1869, and 1885.

Ruang, Sangihe Islands

2.3°N, 125.37°E | Summit elev. 725 m

On 15 May BNPB reported that a total of 9,343 residents of Tagulandang and Ruang islands remained in evacuation centers because of eruptions from Ruang. According to PVMBG daily white steam-and-gas plumes that were sometimes dense rose as high as 700 m above the summit and drifted in multiple directions during 15-21 May. The Alert Level was lowered to 2 (the second lowest level on a scale of 1-4) at 0900 on 18 May and the public was warned to stay 2 km away from the active crater.

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.

Sheveluch, Central Kamchatka (Russia)

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

KVERT reported that the Karan-1 lava dome on Sheveluch’s SW flank continued to grow during 9-16 May. An intense and large thermal anomaly over the dome was identified in satellite images during 9-12 May; the dome was obscured by weather clouds on the other days. 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.

Slamet, Central Java

7.242°S, 109.208°E | Summit elev. 3428 m

PVMBG reported that daily white emissions rose 50-500 m above Slamet’s summit and drifted W during 15-21 May. The Alert Level remained at 2 (on a scale of 1-4). On 16 May the exclusion zone was increased from 2 km to 3 km based on monitoring data.

Geological summary: Slamet is one of Java’s most active volcanoes. It has a cluster of about three dozen cinder cones on its lower SE-NE flanks and a single cinder cone on the W flank. It is composed of two overlapping edifices, an older basaltic-andesite to andesitic volcano on the west and a younger basaltic to basaltic-andesite one on the east. Gunung Malang II cinder cone on the upper E flank on the younger edifice fed a lava flow that extends 6 km E. Four craters occur at the summit of Gunung Slamet, with activity migrating to the SW over time. Eruptions recorded since the 18th century have originated from a 150-m-deep, 450-m-wide, steep-walled crater at the western part of the summit and have consisted of explosive eruptions generally lasting a few days to a few weeks.

Spurr, Alaska Peninsula

61.299°N, 152.251°W | Summit elev. 3374 m

On 15 May AVO reported that elevated seismicity at Spurr was consistent with an intrusion of magma deep beneath the volcano. An extended outage of the seismic network occurred during February-April; elevated seismicity was already occurring when the network returned on 3 April. An average of four earthquakes per day were located after that time, with a maximum of 33 earthquakes detected on 26 April. They were typically smaller than M 1 and were located near the summit and as deep as 30 km below sea level. This activity represents an increase in earthquake rate and occurrence of deeper (>20 km) low-frequency earthquakes compared to recent years. Minor uplift of the ground surface at the volcano of about 1 cm was detected in local GPS data beginning in November 2023, which was a deviation from the long-term trend and may be related to the seismicity. Minor steaming from fumaroles in the summit crater area was sometimes visible; no notable changes to the ice-and-snow cover or gas-and-steam emissions were observed in association with these geophysical observations. A short observational flight was conducted on 14 May. The Volcano Alert Level remained at Normal (the lowest level on a four-level scale) and the Aviation Color Code remained at Green (the lowest color on a four-color scale).

Geological summary: Mount Spurr is the closest volcano to Anchorage, Alaska (130 km W) and just NE of Chakachamna Lake. The summit is a large lava dome at the center of a roughly 5-km-wide amphitheater open to the south formed by a late-Pleistocene or early Holocene debris avalanche and associated pyroclastic flows that destroyed an older edifice. The debris avalanche traveled more than 25 km SE, and the resulting deposit contains blocks as large as 100 m in diameter. Several ice-carved post-collapse cones or lava domes are present. The youngest vent, Crater Peak, formed at the southern end of the amphitheater and has been the source of about 40 identified Holocene tephra layers. Eruptions from Crater Peak in 1953 and 1992 deposited ash in Anchorage.

Taal, Luzon (Philippines)

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

PHIVOLCS reported ongoing unrest at Taal during 13-21 May. Daily upwelling of gases and hot fluids in the lake generated steam-and-gas plumes that rose as high as 2.4 km above the crater rim and drifted WNW. Sulfur dioxide emissions increased to 5,094 tonnes per day (t/d) on 13 May. A phreatic event began at 1345 on 15 May, lasted about five minutes, and produced a steam plume that rose 500 m above Main Crater rim and drifted W and NW. On 16 May a series of short phreatic events were visible in webcam images and detected by the seismic network during 0854-0857, 1107-1110, 1348-1350, 1737-1738, and a fifth that ended at 2303. The events produced steam plumes that rose 50-300 m and drifted WNW. Sulfur dioxide emissions decreased to 3,823 t/d on 20 May. 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.

Ubinas, Peru

16.345°S, 70.8972°W | Summit elev. 5608 m

Instituto Geofísico del Perú (IGP) reported that thermal anomalies from the main crater floor at Ubinas were identified daily during 15-21 May, except for on 15 May. Daily gas-and-steam plumes rose as high as to 1.6 km above the crater rim. The Alert Level remained at Yellow (the second level on a four-color scale) and the public was warned to stay 2 km away from the crater.

Geological summary: The truncated appearance of Ubinas, Perú’s most active volcano, is a result of a 1.4-km-wide crater at the summit. It is the northernmost of three young volcanoes located along a regional structural lineament about 50 km behind the main volcanic front. The growth and destruction of Ubinas I was followed by construction of Ubinas II beginning in the mid-Pleistocene. The upper slopes of the andesitic-to-rhyolitic Ubinas II stratovolcano are composed primarily of andesitic and trachyandesitic lava flows and steepen to nearly 45°. The steep-walled, 150-m-deep summit crater contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits from the collapse of the SE flank about 3,700 years ago extend 10 km from the volcano. Widespread Plinian pumice-fall deposits include one from about 1,000 years ago. Holocene lava flows are visible on the flanks, but activity documented since the 16th century has consisted of intermittent minor-to-moderate explosive eruptions.

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 13-20 May with nighttime crater incandescence. An explosion at 1442 on 15 May generated an ash plume that rose 2 km above the crater rim and drifted SE and ejected blocks as far as 1.1 km from the crater. Sulfur dioxide emissions were elevated, averaging 700 tons per day on 17 May. Explosions at 1928 on 18 May and 0121 on 20 May produced ash plumes that rose 1.2 and 2.3 km, respectively, above the crater rim and drifted W. The explosions ejected blocks 0.5-1.1 km from the crater. An eruptive event at 1442 on 20 May generated an ash plume that rose 1.2 km and drifted S. The Alert Level remained at 3 (on a 5-level scale), and the public was warned to stay 1 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.

Campi Flegrei, Italy

40.827°N, 14.139°E | Summit elev. 458 m

INGV reported that a seismic swarm at Campi Flegrei consisted of about 150 earthquakes recorded from 1951 on 20 May to 0031 on 21 May. The largest event in the swarm, a M 4.4 located at a depth of 2.6 km beneath the Solfatara, was the largest recorded since the current cycle of seismicity associated with uplift began in 2005. A total of 450 earthquake events were recorded the previous month. The rate of inflation was 2 cm per month and remained unchanged. The report noted that during a 1982-84 seismic crisis there were more than 1,300 monthly events recorded, with associated uplift as high as 9 cm per month.

Geological summary: Campi Flegrei is a 13-km-wide caldera that encompasses part of Naples and extends to the south beneath the Gulf of Pozzuoli. Episodes of significant uplift and subsidence within the dominantly trachytic caldera have occurred since Roman times. The earliest known eruptive products are dated 47,000 years BP. The caldera formed following two large explosive eruptions, the massive Campanian ignimbrite about 36,000 BP, and the over 40 km3 Neapolitan Yellow Tuff (NYT) about 15,000 BP. Following eruption of the NYT a large number of eruptions originated from widely scattered subaerial and submarine vents. Most activity occurred during three intervals: 15,000-9,500, 8,600-8,200, and 4,800-3,800 BP. The latest eruption were in 1158 CE at Solfatara and activity in 1538 CE that formed the Monte Nuovo cinder cone.

Dukono, Halmahera

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

PVMBG reported that the eruption at Dukono was ongoing during 15-21 May. Dense white steam-and-gas plumes rose 500-600 m and drifted N on 15 May. Gray-and-white ash plumes rose 400-1,300 m above the summit and drifted E on most of the other days; weather conditions prevented views on 21 May. 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 10-17 May According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E), explosions during 13-14 and 16 May generated ash plumes that rose as high as 2.5 km (8,200 ft) a.s.l. and drifted NE. A thermal anomaly was identified in satellite images on 16 May; 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 likely ended on 8 May. Daily thermal anomalies from the cooling lava flows on the SSE flank were identified in satellite images during 14-21 May. The number and intensity of the thermal anomalies were variable but decreased overall and were low by the end of the week. Sulfur dioxide emissions were 13 tons per day at 1356 on 15 May.

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 likely continued during 15-21 May. Seismicity was low with daily, small, occasional earthquakes. The active portion of the lava flow was warm and snow-free, and steaming was visible in occasional clear satellite and webcam views; weather clouds sometimes prevented such views. 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.

Lewotobi, Flores Island

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

PVMBG reported that eruptive activity at Lewotobi’s Laki-laki volcano continued during 15-21 May. White steam-and-gas plumes rose as high as 100 m above the summit and drifted NW, W, and SW during 15, 17-18, and 21 May. Gray-and-white ash plumes rose 100 m above the summit and drifted W, SW, and NE during 16 and 19-20 May. 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 11-21 May. A lava flow breached the W crater rim on 11 May and traveled 1.2 km down the W flank by 12 May. White-and-gray ash plumes rose as high as 600 m and drifted W and NW during 13, 15, and 17-20 May. White steam-and-gas plumes rose 300-500 m above the summit and drifted NW, W, and SW on the other days during 11-21 May. The lava flow on the W flank had not advanced by 20 May. 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.

Merapi, Central Java

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

BPPTKG reported that the eruption at Merapi (on Java) continued during 10-16 May. Seismicity had decreased compared to the previous week. The SW lava dome produced 68 lava avalanches that traveled as far as 2.1 km down the Bebeng drainage on 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.

Popocatepetl, Mexico

19.023°N, 98.622°W | Summit elev. 5393 m

CENAPRED reported that eruptive activity continued at Popocatépetl during 14-21 May. The seismic network recorded long-period events totaling 30-85 per day that were sometimes accompanies by steam-and-gas emissions; steam, gas, and ash emissions were visible during 18-19 May. The seismic network also recorded 98 minutes to more than 8.5 hours of tremor each day and a few volcano-tectonic earthquakes. According to the Washington VAAC daily ash plumes visible in webcam and satellite images rose to 5.5-6.1 km (18,000-20,000 ft) a.s.l. (or as high as 700 m above the crater rim) and drifted SW, SW, and WSW. Thermal anomalies in the crater were detected during 16-17 May. The Alert Level remained at Yellow, Phase Two (the middle level on a three-color scale) and the public was warned to stay 12 km away from the crater.

Geological summary: Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America’s 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Reventador, Ecuador

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

IG-EPN reported that an eruption at Reventador was ongoing during 14-21 May. Seismicity was characterized by 46-78 daily explosions, long-period earthquakes, harmonic tremor, volcano-tectonic events, and tremor associated with emissions. Ash-and-gas plumes rose as high as 1.1 km above the crater rim and drifted NW, W, and SW during 14-18 and 21 May. Weather conditions sometimes prevented views, especially during 19-20 May. Incandescence at the crater was visible during most nights and avalanches of incandescent material descended the flanks as far as 500 m from the summit on a few of the nights. 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.

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 14-21 May. The seismic network recorded 99-1,212 daily explosions during the week. Gas-and-ash plumes visible in webcam and/or satellite images on most days rose as high as 1 km above the summit and drifted NW and SW; weather conditions often hindered views during the week. Incandescent material at the crater was visible during dark hours on most nights and incandescent avalanches descending the SE flank as far as 1.8 km during 15-16 May. 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 15-21 May. Daily white-and-gray ash plumes rose 300-900 m above the summit and drifted in multiple directions. Several additional eruptive events were recorded during the week by the seismic network, though plumes were not visually confirmed. According to news articles pyroclastic flows descended the SE flank as far as 3 km on 18 May. Pyroclastic flows descended the SE flank during 20-21 May, though the distances were unknown due to weather conditions. 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.

Stromboli, Aeolian Islands (Italy)

38.789°N, 15.213°E | Summit elev. 924 m

INGV reported that eruptive activity continued at Stromboli during 13-19 May. Webcam images showed Strombolian activity at two vents in Area N (one at N1 and one at N2), within the upper part of the Sciara del Fuoco, and from two vents at S2 in Area C-S (South-Central Crater) on the crater terrace. At Area N, low- to medium-intensity explosive activity ejected coarse material (bombs and lapilli) less than 80 m and 150 m from vents in the N1 and N2 sectors, respectively. The average frequency of explosions from this area was 10-18 events per hour. Spattering at N1 was almost continuous and intense at times. At Area C-S, explosive activity at two vents in sector S2 ejected both coarse and fine material higher than 150 m above the vent. The average explosion rate was 5-8 events per hour.

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, 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 13-20 May. Crater incandescence was observed nightly in webcam images. Emissions rose as high as 800 m above the crater rim and blocks were ejected as far as 200 m from the crater’s center; 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.

Villarrica, Central Chile

39.42°S, 71.93°W | Summit elev. 2847 m

SERNAGEOMIN reported that the eruption at Villarrica continued. A volcano-tectonic evet was recorded by the seismic network at 0428 on 18 May. At 0911 on that same day a gas-and-ash plume rose 340 m above the crater rim and drifted ESE. The Volcanic Alert Level remained at Yellow (the second lowest level on a four-level scale) and the public was warned to stay 500 m away from the active crater.

Geological summary: The glacier-covered Villarrica stratovolcano, in the northern Lakes District of central Chile, is ~15 km south of the city of Pucon. A 2-km-wide caldera that formed about 3,500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesite cone at the NW margin of a 6-km-wide Pleistocene caldera. More than 30 scoria cones and fissure vents are present on the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Eruptions documented since 1558 CE have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

References:

¹ Smithsonian Institution / US Geological Survey – Weekly Volcanic Activity Report – May 15 – 21, 2024 – Managing Editor: Sally Sennert

Featured image credit: TW

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