The Weekly Volcanic Activity Report: January 10 - 16, 2024

New activity/unrest was reported for 6 volcanoes from January 10 – 16, 2024. During the same period, ongoing activity was reported for 14 volcanoes.

New activity/unrest

Ahyi, Mariana Islands (USA)

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

Signs of unrest at Ahyi Seamount were observed during the previous few weeks. Plumes of discolored water drifting as far as 10 km from the vent were identified in satellite data on 24 December 2023 and again on 4 and 10 January 2024. Hydroacoustic arrays located on Wake Island did not record any significant signals, though submarine plumes have been observed in the past without clear hydroacoustic evidence. The Aviation Color Code was raised to Yellow (the second level on a four-color scale) and the Volcano Alert Level was raised to Advisory (the second level on a four-level scale) on 14 January because the likelihood of an eruption had increased. No unusual activity was observed in satellite data during 15-17 January.

Geological summary: Ahyi seamount is a large conical submarine volcano that rises to within 75 m of the ocean surface ~18 km SE of the island of Farallon de Pajaros in the northern Marianas. Water discoloration has been observed there, and in 1979 the crew of a fishing boat felt shocks over the summit area, followed by upwelling of sulfur-bearing water. On 24-25 April 2001 an explosive eruption was detected seismically by a station on Rangiroa Atoll, Tuamotu Archipelago. The event was well constrained (+/- 15 km) at a location near the southern base of Ahyi. An eruption in April-May 2014 was detected by NOAA divers, hydroacoustic sensors, and seismic stations.

Ambrym, Vanuatu

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

The Vanuatu Meteorology and Geo-Hazards Department (VMGD) reported that at 2217 on 13 January an eruption began at Ambrym’s Benbow Crater based on webcam and seismic data. The eruption was characterized by a loud explosion, intense incandescence at the crater, and gas-and-steam emissions. The Alert Level was raised from 1 to 3 (on a scale of 0-5) and the public to stay 2 km away from Benbow Crater and 4 km away from Marum Crater, and additionally to stay 500 m away from the ground cracks created by the December 2018 eruption. Sulfur dioxide emissions measured using satellite data were 1,116 tons per day on 14 January. Activity decreased during 15-17 January based on webcam images, seismic data, and field observations. Gas, steam, and ash emissions had decreased, and crater incandescence was dim or not visible at all. The Alert Level was lowered to 2 on 17 January.

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.

Grimsvotn, Iceland

64.416°N, 17.316°W | Summit elev. 1719 m

IMO reported that at 0653 on 11 January a M 4.3 earthquake occurred at Grímsvötn and was the largest earthquake recorded at the volcano since measurements started in 1991. A gradual increase in tremor was recorded at Mt. Grímsfjall, which rises about 300 m above the flat ice shelf over the subglacial lake, since 7 January and the water level in the Gígjukvísl River began to rise on 10 January. IMO noted that a jökulhlaup had likely begun and that the earthquake was in response to pressure release from the flood. The Aviation Color Code was raised to Yellow (the second level on a four-color scale) reflecting the slight increase in the likelihood of an eruption being triggered by the flood. IMO noted that the last eruption was in 2004; since then, 12 jökulhlaups have occurred with no eruptions.

Water levels in the Gígjukvísl River steadily and significantly increased during 11-12 January and the river widened; the river rose 70 cm based on data from a stream gauge at the bridge crossing Highway 1. The water level stabilized during 13-14 January, signifying that it had reached peak flow, and was then expected to subside. Around midnight on 15 January the seismometer at Grímsfjall began recording increased tremor, which was likely due to increased geothermal activity and is commonly observed at the end of a jökulhlaup.

Geological summary: Grímsvötn, Iceland’s most frequently active volcano in recent history, lies largely beneath the vast Vatnajökull icecap. The caldera lake is covered by a 200-m-thick ice shelf, and only the southern rim of the 6 x 8 km caldera is exposed. The geothermal area in the caldera causes frequent jökulhlaups (glacier outburst floods) when melting raises the water level high enough to lift its ice dam. Long NE-SW-trending fissure systems extend from the central volcano. The most prominent of these is the noted Laki (Skaftar) fissure, which extends to the SW and produced the world’s largest known historical lava flow in 1783. The 15 km3 basaltic Laki lavas were erupted over 7 months from a 27-km-long fissure system. Extensive crop damage and livestock losses caused a severe famine that resulted in the loss of one-fifth of the population of Iceland.

Lewotobi, Flores Island

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

PVMBG reported that the eruption at Lewotobi’s Laki-laki volcano was ongoing during 10-16 January. Dense white-and-gray or white, gray, and brown ash plumes rose as high as 2 km above the summit and drifted N and NE. Lava flows from the summit crater continued to advance down the N flank and were about 2 km long by 11 January. Rumbling was reported on 13 January. On 14 January as many as four pyroclastic flows traveled up to 1 km down the NE, N, and NNW flanks and lava avalanches traveled 1.5-2 km down the NE flank, according to news articles. Incandescent avalanches of material and accompanying pyroclastic flows traveled as far as 1.5 km N on 15 January. Incandescent avalanches also traveled 2-3 km NE and 1 km NNE. The exclusion zone was increased to 5 km from the Laki-laki Crater and 6 km from the crater on the N and NE flanks during the evening of 16 January. The Alert Level remained at 4 (the highest level on a scale of 1-4).

Geological summary: The Lewotobi “husband and wife” twin volcano (also known as Lewetobi) in eastern Flores Island is composed of the Lewotobi Lakilaki and Lewotobi Perempuan stratovolcanoes. Their summits are less than 2 km apart along a NW-SE line. The conical Lakilaki has been frequently active during the 19th and 20th centuries, while the taller and broader Perempuan has erupted only twice in historical time. Small lava domes have grown during the 20th century in both of the crescentic summit craters, which are open to the north. A prominent flank cone, Iliwokar, occurs on the E flank of Perampuan.

Marapi, Central Sumatra

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

PVMBG reported that eruptive activity at Marapi (on Sumatra) was ongoing at Verbeek Crater during 10-16 January. Dense, white-and-gray ash plumes rose as high as 1.5 km above the summit and drifted NW, W, and SW during 11-15 January. Weather conditions sometimes prevented views of the volcano. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 4.5 km away from Verbeek 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.

Reykjanes, Reykjanes Peninsula

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

IMO reported that a seismic swarm began near the older Sundhnúkagígar crater row on the Reykjanes peninsula around 0230 on 14 January. Both GPS data and borehole pressure readings indicated that magma was moving. IMO raised the Aviation Color Code to Orange (the third level on a four-color scale), noting an increased likelihood of an eruption. The locations of the earthquakes shifted towards the town of Grindavík where, according to Almannavarnadeild ríkislögreglustjóra (National Commissioner of the Icelandic Police and Department of Civil Protection and Emergency Management), evacuations started around 0300.

A fissure eruption began at around 0757 just N of Grindavík, SE of Hagafell, and was visible on webcams. The Aviation Color Code was raised to Red, but then lowered back to Orange at 0826 because no ash was detected in radar data. A Coast Guard helicopter was dispatched to investigate the eruption site. A NE-SW-trending fissure was visible and notably lengthened within about 10 minutes according to a news article. The fissure grew to about 900 m long and crossed through the eastern part of a curving E-W-oriented earthen berm built to deflect lava flows away from the town. Lava fountaining occurred along the length of the fissure. Lava spread perpendicular from the fissure and to the SW, covering the E half of the berm, though the longest flow traveled WSW along the berm and away from the town. Construction workers managed to reach their heavy equipment that was being used to build the berm and drive them to safety away from the lava flows. Lava covered part of Grindavíkurvegur road and overtopped a small area of the berm at the road, flowing S.

A shorter second fissure that was about 100 m long opened at 1210 on 14 January to the SW of the first and S of the berm, about 200 m from the Efrahópi neighborhood in Grindavík. Lava flows traveled S, entering the town and setting at least three houses on fire. This fissure was no longer active by 1640 on 15 January and the effusion rate at the larger, main fissure had decreased. Seismicity and the rate of deformation had also decreased, though deformation near the S part of the magmatic dike near Grindavík continued to be detected. Displacement within the town was as high as 1.4 m during 14-15 January; ground cracks had developed, and existing ones had expanded. Thermal images from a 15 January drone flight indicated that previously mapped fissures SW of Grindavík had significantly enlarged. Lava effusion at the longer fissure was concentrated at two of four main vents. Lava effusion at the main fissure ceased around 0100 on 16 January. Seismicity continued to decrease, though event locations indicated that magma movement continued. Most of the seismic activity was concentrated near Hagafell, close to the main fissure. IMO lowered the Aviation Color Code to Yellow at 2105, noting the ongoing decline of seismicity.

A man working on filling cracks in Grindavík fell into one of the cracks on 10 January and was unable to be located. Hundreds of rescue workers searched for the man but due to unsafe conditions and landslides occurring inside the crack the search was stopped on 12 January.

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.

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 8-15 January with incandescence at the crater observed nightly. An explosion at 1552 on 9 January produced an ash plume that rose as high as 1.2 km above the crater rim and drifted E and SE. Small eruptive events were occasionally recorded during 12-15 January. 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.

Bulusan, Luzon (Philippines)

12.769°N, 124.056°E | Summit elev. 1535 m

PHIVOLCS reported increased seismicity at Bulusan in a special advisory. From 0500 on 11 January to 1000 on 11 January the seismic network recorded a total of 71 volcanic-tectonic earthquakes associated with rock fracturing. The earthquakes were located at depths of 1-6 km beneath the S flank. The largest event was a M 2.2. Diffuse gas plumes rose from the summit crater and drifted W and SE. The Alert Level remained at 1 (the second level on a scale of 0-5) and PHIVOLCS reminded the public not to enter the 4-km-radius Permanent Danger Zone (PDZ) and to be vigilant within the 2-km Extended Danger Zone (EDZ) on the SE flank.

Geological summary: Luzon’s southernmost volcano, Bulusan, was constructed along the rim of the 11-km-diameter dacitic-to-rhyolitic Irosin caldera, which was formed about 36,000 years ago. It lies at the SE end of the Bicol volcanic arc occupying the peninsula of the same name that forms the elongated SE tip of Luzon. A broad, flat moat is located below the topographically prominent SW rim of Irosin caldera; the NE rim is buried by the andesitic complex. Bulusan is flanked by several other large intracaldera lava domes and cones, including the prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the NE. The summit is unvegetated and contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Many moderate explosive eruptions have been recorded since the mid-19th century.

Dukono, Halmahera

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

PVMBG reported that the eruption at Dukono was ongoing during 10-16 January. Gray-and-white ash plumes generally rose 100-700 m above the summit and drifted S during 10-15 January; emissions were not observed on 11 January. White-and-gray ash plumes rose to 1.7 km above the summit and drifted SW on 16 January. The Alert Level remained at Level 2 (on a scale of 1-4), and the public was warned to remain outside of the 2-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 4-11 January. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E), explosions on 6, 8, and 9 January generated ash plumes that rose as high as 2.5 km (8,200 ft) a.s.l and drifted SE and NW. 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.

Great Sitkin, Andreanof Islands (USA)

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

On 11 January AVO reported that a radar image of Great Sitkin showed that the thick flow in the summit crater continued to expand to the E and reached the N margin of an earlier flow; effusion likely continued during 12-16 January. Local webcams and seismic data communications were offline due to a storm-related power failure. No unusual activity was visible in mostly cloudy satellite images. Weakly elevated surface temperatures were identified in satellite data during 15-16 January. 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 parasitic 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 ancestral volcano and produced a submarine debris avalanche. Deposits from this and an 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. Historical eruptions have been recorded since the late-19th century.

Lewotolok, Lembata Island

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

PVMBG reported that the eruption at Lewotolok continued during 10-16 January. White-and-gray ash plumes rose 150 m above the summit and drifted E on 12 January. White steam-and-gas plumes rose as high as 200 m above the summit and drifted NE, E, and SE on the other days, though no emissions were visible on 12 January. Incandescent lava was occasionally ejected about the vent. The Alert Level remained at 2 (on a scale of 1-4) and the public was warned to stay at least 2 km away from the summit crater.

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 5-11 January. The SW lava dome produced a total of 189 lava avalanches that descended the S, SW, and W flanks; eight traveled S as far as 1.5 km down the upper part of the Boyong drainage, 178 traveled SW as far as 1.8 km down the upper part of the Bebeng drainage, and three traveled as far as 1.5 km down the Sat/Putih drainage. Four pyroclastic flows descended the Boyong and Bebeng drainages as far as 1.5 km. Morphological changes to the SW lava dome identified in webcam images were due to continuing 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.

Poas, Costa Rica

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

OVSICORI-UNA reported that small phreatic eruptions at Poás continued to be observed during 8-16 January. Phreatic eruptions were recorded daily, ejecting sediment no more than 200 m above the lake’s surface and producing steam-and-gas plumes that rose no higher than 500 m. In a special report OVSICORI-UNA noted that both gas-and-steam emissions and seismicity began to increase during the second half of 2023. The lake level had been decreasing since October 2023 and eruptive events became more frequent and energetic in December; a phreatic eruption at 2051 on 11 January was the largest event recorded during December 2023-January 2024.

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.

Popocatepetl, Mexico

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

CENAPRED reported that eruptive activity continued at Popocatépetl during 9-16 January. Long-period events totaling 6-64 per day were accompanied by steam-and-gas plumes that occasionally contained minor amounts of ash. The plumes mainly drifted ENE and NE. The seismic network recorded 14.5-23 daily hours of tremor, including both low- and high-frequency events. Minor amounts of ash fell in Nealtican (21 km E) during 11-12 January. Ashfall was also reported in Nativitas (40 km NE), Tetlatlahuaca (42 km NE), Zacatelco (45 km NE), Xicohtinco (45 km NE), Ayometla (46 km ENE), Papalotla (62 km NNW), Tenancingo, San Pablo del Monte (49 km E), Mazatecochco (50 km ENE), Tlaxcala (50 km NW), and Tepeyanco (47 km NW) in the state of Tlaxcala on 15 January and in Nealtican, Juan C. Bonilla (32 km ENE), and Tlaltenango in the state of Puebla on 16 January. 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.

Rincon de la Vieja, Costa Rica

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

OVSICORI-UNA reported continued unrest at Rincón de la Vieja during 8-16 January. Small phreatic eruptions were recorded almost daily, sometimes producing gas-and-steam plumes that rose as high as 3 km above the crater rim. Almost continuous gas-and-steam emissions were visible during 10-11 January. The Alert Level remained at Level 3, Orange, the third 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.

Sangay, Ecuador

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

IG-EPN reported a high level of eruptive activity at Sangay during 9-16 January, with seismic stations recording 232-626 daily explosions. Ash-and-gas plumes were visible in both webcam and satellite images during 9-14 January, rising as high as 1.5 km above the crater rim and drifting W, WSW, and SW. On 12 January an explosion deposited incandescent material on all flanks as far as 1 km from the summit crater. At 1810 that same day a pyroclastic density current descended the SE drainage and an ash plume rose 1 km above the summit and drifted SW. Crater incandescence was sometimes visible at night, and during 11-12 and 13-14 January incandescent material was observed descending the SE drainage as far as 1 km. Cloudy weather prevented views during 15-16 January, though crater incandescence was observed overnight. Secretaría de Gestión de Riesgos 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 10-16 January. Daily white-and-gray ash plumes that were sometimes dense rose 500-1,000 m above the summit and drifted in multiple directions. The Alert Level remained at 3 (third highest 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 the eruption at Sheveluch continued during 4-11 January with a daily thermal anomaly identified in satellite images. 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 the eruption at Suwanosejima’s Ontake Crater continued during 8-15 January. Eruptive events on 11 January produced ash plumes that rose as high as 1.1 km above the crater rim and drifted SE. An explosion at 0548 on 13 January produced an ash plume that rose 800 m and drifted SE. At 0022 on 14 January an explosion ejected large blocks 1.1 km to the N and 1 km to the S of the vent and produced an ash plume that rose 500 m above the crater rim. The Alert Level was raised to 3 (on a 5-level scale) and the public was warned to stay 2 km away from the crater. Another eruptive event at 2313 on 15 January generated an ash plume that rose more than 1 km above the crater rim and drifted S.

Geological summary: The 8-km-long island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit is truncated by a large breached crater extending to the sea on the east 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 blanketed 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 the open Sakuchi caldera, which extends to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

References:

Smithsonian Institution / US Geological Survey – Weekly Volcanic Activity Report, 10 January-16 January 2024 – Managing Editor: Sally Sennert

Featured image credit: TW

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