The Weekly Volcanic Activity Report: December 27, 2023 - January 2, 2024

New activity/unrest was reported for 2 volcanoes from December 27, 2023, to January 2, 2024. During the same period, ongoing activity was reported for 23 volcanoes.

New activity/unrest: Lewotobi, Flores Island | Marapi, Central Sumatra.

New activity/unrest

Lewotobi, Flores Island

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

PVMBG reported that seismicity at Lewotobi had increased on 12 December and was followed by the emergence of “tornillo” earthquakes indicating fluid movement at depth. An eruption occurred on 23 December at Laki-laki and lasted about 24 minutes. A 160-m-long fissure on the upper NW flank was visible afterwards and it emitted dense white plumes that rose 300 m. At 0253 on 28 December an observer noted a dense white-and-gray ash plume that rose 1 km above the summit and drifted NW. On 1 January the amplitude of continuous tremors increased. A new vent opened along a fissure located on the upper SSE flank and produced a white, gray, and black ash plume that rose 1-1.5 km above the summit. The Alert Level was raised to 3 (on a scale of 1-4) at 1600 and the public was warned to stay 3 km away from the Perempuan and Laki-laki craters and an additional 4 km from the NNW and SSE flanks of Laki-laki. At 0454 on 2 January a gray-to-brown ash plume rose 1.5 km above the summit and drifted SW and W.

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.

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 27 December 2023-2 January 2024, though fog and rain occasionally prevented visual observations of the summit. At 1205 on 27 December a dense gray ash plume rose 1.5 km above the summit and drifted SW and W. Ash plumes rose 500-700 m above the summit and drifted S, SW, and W during 31 December 2023-1 January 2024. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to stay 3 km away from the summit 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.

Ongoing activity

Ahyi, Mariana Islands (USA)

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

A plume of discolored water in the vicinity of Ahyi Seamount was observed in satellite images on 1 January. The plume possibly signified underwater volcanic activity but that interpretation could not be confirmed because pressure sensors at Wake Island were not operational; more distant sensors did not record any activity. Both the Aviation Color Code and the Volcano Alert Level remained at Unassigned.

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

Aira, Kyushu (Japan)

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

JMA reported ongoing activity at Minamidake Crater (Aira Caldera’s Sakurajima volcano) during 25 December 2023-1 January 2024, with incandescence at the crater observed nightly. Small eruptive events were occasionally recorded during the week. 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.

Ambae, Vanuatu

15.389°S, 167.835°E | Summit elev. 1496 m

On 28 December the Vanuatu Meteorology and Geohazards Department (VMGD) reported that steam-and-gas emissions at Ambae were ongoing based on satellite images. Ashfall was reported in the N parts of the island during 19-21 December, coincident with strong SE trade winds. The Alert Level remained at 2 (on a scale of 0-5) and the public was warned to stay outside of the Danger Zone, defined as a 2-km radius around the active vents in Lake Voui, and away from drainages during heavy rains.

Geological summary: The island of Ambae, also known as Aoba, is a massive 2,500 km3 basaltic shield that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW-trending rift zone with numerous scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. That large central edifice is also called Manaro Voui or Lombenben volcano. Post-caldera explosive eruptions formed the summit craters about 360 years ago. A tuff cone was constructed within Lake Voui (or Vui) about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast.

Bulusan, Luzon (Philippines)

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

In a special advisory, PHIVOLCS reported that from 2100 on 29 December 2023 to 2100 on 2 January 2024 the seismic network at Bulusan recorded a total of 116 volcanic earthquakes. Out of those, 110 were volcano-tectonic events associated with rock fracturing at depths of 2-6 km beneath the S flank of the volcano; the other six were low-frequency events associated with fluid movement. Gas emissions from the summit crater were at weak-to-moderate levels. Ground deformation data from electronic tiltmeter stations continued to record inflation at the S flank since February 2023. 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 27 December 2023-2 January 2024. Daily, dense, white-and-gray ash-and-gas plumes rose 700-2,800 m above the summit and drifted N, W, and SW. 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 21-28 December. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E), explosions during 22-23 and 25-26 December generated ash plumes that rose as high as 4 km (13,100 ft) a.s.l and drifted E. 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.

Fuego, South-Central Guatemala

14.473°N, 90.88°W | Summit elev. 3763 m

INSIVUMEH reported that eruptive activity continued at Fuego during 27 December 2023-2 January 2024. Explosions were recorded daily, averaging 5-20 per hour on most days where counts were reported. The explosions generated ash-and-gas plumes that rose as high as 1.2 km above the crater rim and drifted as far as 30 km NW, N, NE, and E. Ashfall was reported on most of the days in areas downwind including Alotenango (8 km ENE), Ciudad Vieja (14 km NE), Parramos (18 km NNE), Sumpango (25 km NE), San Lucas (28 km NE), Sacatepéquez (18 km ENE), La Reunión (7 km SE), Alotenango (8 km ENE), La Antigua (18 km NE), San Miguel Dueñas (10 km NE), El Rodeo (10 km SSE), El Porvenir (8 km ENE), and San Cayetano. Weak rumbling sounds and shock waves were recorded daily and shook structures within a 10-km radius. Explosions caused daily block avalanches that descended various drainages including the Ceniza (SSW), Seca (W), Taniluyá (SW), and Las Lajas (SE). The explosions ejected incandescent material 200-300 m above the summit on most of the days.

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

Great Sitkin, Andreanof Islands (USA)

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

AVO reported that a 24 December radar image of Great Sitkin showed continuing growth of a thick flow in the summit crater; effusion likely continued during 27 December 2023-2 January 2024. Weather clouds often obscured views of the volcano. Minor steaming from the active flow field was identified in a webcam images during a break in cloud cover during 31 December-1 January. Seismicity was low. 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.

Heard, Kerguelen Plateau

53.106°S, 73.513°E | Summit elev. 2745 m

A 29 December satellite image of Heard Island’s Big Ben volcano showed a thermal anomaly at the summit that was elongated to the SW. The anomaly narrowed and terminated at an area that was about 1 km from the summit, suggesting the presence of a lava flow.

Geological summary: Heard Island on the Kerguelen Plateau in the southern Indian Ocean consists primarily of the emergent portion of two volcanic structures. The large glacier-covered composite basaltic-to-trachytic cone of Big Ben comprises most of the island, and the smaller Mt. Dixon lies at the NW tip of the island across a narrow isthmus. Little is known about the structure of Big Ben because of its extensive ice cover. The active Mawson Peak forms the island’s high point and lies within a 5-6 km wide caldera breached to the SW side of Big Ben. Small satellitic scoria cones are mostly located on the northern coast. Several subglacial eruptions have been reported at this isolated volcano, but observations are infrequent and additional activity may have occurred.

Ibu, Halmahera

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

PVMBG reported that Ibu continued to erupt during 27-31 December. Daily white-and-gray ash emissions that were sometimes dense rose 200-800 m above the summit and drifted SE and S. The Alert Level remained at a 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.

Klyuchevskoy, Central Kamchatka (Russia)

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

An explosive Strombolian eruption began at Klyuchevskoy on 27 December and a bright thermal anomaly was identified in satellite images. On 30 December an ash plume rose as high as 6 km (19,700 ft) a.s.l. and drifted 195 km NW based on satellite and webcam images. KVERT raised the Aviation Color Code to Orange (the third level on a four-color scale). On 31 December explosions generated ash plumes that rose to 6.5 km (21,300 ft) a.s.l. and drifted 230 km WNW. A thermal anomaly persisted through 1 January, though explosions were not detected; the Aviation Color Code was lowered to Yellow. Dates are based on UTC times; specific events are in local time where noted.

Geological summary: Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka’s highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Lewotolok, Lembata Island

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

PVMBG reported that the eruption at Lewotolok continued during 27 December 2023-2 January 2024. White-and-gray ash plumes rose 250-400 m during 27-28 December, 31 December, and 1 January, and drifted NW, E, NW, and SE. White steam-and-gas plumes rose 100-600 m above the summit on the other days and drifted W, NW, NE, and E. 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 22-28 December. The SW lava dome produced a total of 102 lava avalanches that descended the S and SW flanks; 16 traveled S as far as 1.5 km down the upper part of the Boyong drainage and the other 86 traveled SW as far as 1.9 km down the upper part of the Bebeng drainage. Morphological changes to the SW lava dome identified in webcam images were due to continuing collapses of material. The volume of the SW dome was an estimated 2,948,100 cubic meters and the dome in the main crater was an estimated 2,358,400 cubic meters based on 20 December aerial photos. 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. Phreatic eruptions at 1922 and 1926 on 25 December and at 0235 on 26 December ejected material 50 m above the lake surface. At 1535 on 27 December a small phreatic event ejected a plume of water and sediment 100 m above the lake and produced a steam-and-gas plume that rose 500 m. Events recorded at 0117 on 29 December, as well as at 0500, 1034, and 1530 on 30 December, ejected sediment, water, and gas no higher than 200 m above the lake.

Geological summary: The broad vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the complex stratovolcano extends to the lower N flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, last erupted about 7,500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world’s most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since an eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Rincon de la Vieja, Costa Rica

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

OVSICORI-UNA reported continued unrest at Rincón de la Vieja during 8-14 September. Small phreatic eruptions were detected at 1113 on 7 November and 0722 on 8 November. The previous week a total of 10 steam-and-gas exhalations were recorded, and the average SO2 flux was 334 tonnes/day, which is the highest value measured in recent years. At 0136 on 12 November and 0415 on 14 November small gas emissions were detected. 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.

Santa Maria, Southwestern Guatemala

14.757°N, 91.552°W | Summit elev. 3745 m

INSIVUMEH reported that eruptive activity continued at Santa Maria’s Santiaguito lava dome complex during 26 December 2023-2 January 2024 with lava extrusion at Caliente dome. Incandescence from the dome was visible during most nights and early mornings. Explosions occurring at a rate of 1-4 per hour on most days generated gas-and-ash plumes that rose as high as 1 km above the dome and drifted as far as 25 km in multiple directions. The explosions produced block avalanches on the dome’s S, SE, and E flanks in addition to generating short-range pyroclastic flows on the W, SW, and S flanks. Ashfall was reported in areas downwind including Llanos del Pinal (6 km NNE), Santa María de Jesús (5 km SE), Calaguaché (9 km S), Loma Linda (7 km W), and Quetzaltenango (18 km WNW) on a few of the days. During 31 December-1 January block-and-ash or pyroclastic flows traveled as far as 3 km down the flank.

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

Semeru, Eastern Java

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

PVMBG reported that eruptive activity continued at Semeru during 27 December 2023-2 January 2024. White-and-gray ash plumes that were sometimes dense rose 700-800 m above the summit and drifted S and SW during 27-28 December, 31 December, and 1 January. 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 21-29 December. A daily thermal anomaly was 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.

Shishaldin, Fox Islands (USA)

54.756°N, 163.97°W | Summit elev. 2857 m

On 2 January AVO lowered the Volcano Alert Level for Shishaldin to Advisory (the second level on a four-level scale) and the Aviation Color Code to Yellow (the second color on a four-color scale), noting that activity had declined over the past two months since the last significant explosive event on 3 November. Small explosions continued to be periodically detected in infrasound data, though no new deposits inside or outside the crater had recently been observed. Surface temperatures detected in satellite data were low, suggesting that no fresh lava was present in the summit crater. Steaming from the crater continued to be observed in webcam images.

Geological summary: The symmetrical glacier-covered Shishaldin in the Aleutian Islands is the westernmost of three large stratovolcanoes in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning “mountain which points the way when I am lost.” Constructed atop an older glacially dissected edifice, it is largely basaltic in composition. Remnants of an older edifice are exposed on the W and NE sides at 1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is covered by massive aa lava flows. Frequent explosive activity, primarily consisting of Strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century. A steam plume often rises from the summit crater.

Stromboli, Aeolian Islands (Italy)

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

INGV reported that eruptive activity continued at Stromboli during 25-31 December. Webcam images showed Strombolian activity at three vents in Area N (one at N1 and two at N2), within the upper part of the Sciara del Fuoco, and from two vents at S2 in Area C-S (South-Central Crater) in the crater terrace. The average daily totals of explosions at both Area N and Area C-S vents were at normal levels with explosions ejecting mixtures of ash, bombs, and lapilli. Spattering occurred at S2, and at N2 during 27-30 December. A series of six explosions and a brief period of lava fountaining were recorded during 2252-2257 on 30 December. The first explosion was very large and ejected pyroclastic material onto the Sciara del Fuoco. The following five explosions were smaller than the first, but still larger than average. The Dipartimento della Protezione Civile maintained the Alert Level at Yellow (the second highest level on a four-level scale).

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 the eruption at Suwanosejima’s Ontake Crater continued during 25 December 2023-1 January 2024. No explosions were detected, though large blocks were ejected as far as 300 m from the vent. Eruption plumes rose 1-1.6 km above the crater rim during 27-28 December, 30 December, and 1 January, and drifted SW, S, SE, and E. Ashfall was reported in Toshima village (3.5 km SSW), though dates were not specified. The Alert Level remained at 2 (on a 5-level scale) and the public was warned to stay at least 1 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.

Ulawun, New Britain (Papua New Guinea)

5.05°S, 151.33°E | Summit elev. 2334 m

According to the Darwin VAAC a webcam image at Ulawun showed a pyroclastic flow descending a flank at 1230 on 31 December. An ash plume possibly rose to 2.7 km (9,000 ft) a.s.l. and drifted NE based on similar previous plumes and weather models; weather clouds prevented satellite views.

Geological summary: The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea’s most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Yasur, Vanuatu

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

On 28 December the Vanuatu Meteorology and Geohazards Department (VMGD) reported that activity at Yasur continued during December at a level of “major unrest,” as defined by the Alert Level 2 status (the middle level on a scale of 0-4). Recent satellite observations indicated an increase in steam, gas, and ash emissions from the summit crater. Explosions continued, with some ejecting bombs that landed back 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.

References:

Smithsonian Institution / US Geological Survey – Weekly Volcanic Activity Report – December 27, 2023 – January 2, 2024 – Managing Editor: Sally Sennert.

Featured image credit: The Watchers

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