The Weekly Volcanic Activity Report: January 3 - 9, 2024

New activity/unrest was reported for 4 volcanoes from January 3 to 9, 2024. During the same period, ongoing activity was reported for 17 volcanoes.

New activity/unrest: Grimsvotn, Iceland | Kanaga, Andreanof Islands (USA) | Lewotobi, Flores Island | Marapi, Central Sumatra.

New activity/unrest

Grimsvotn, Iceland

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

A brief seismic swarm at Grímsvötn was recorded by the seismic network beginning at 1600 on 4 January, prompting Icelandic Meteorological Office (IMO) to raise the Aviation Color Code to Yellow (the second level on a four-color scale). The swarm consisted of seven earthquakes with magnitudes above 1, which was considered unusual. Since the beginning of December there had been evidence of water drainage from the lake; the earthquakes may have been related to the drainage, but it was not confirmed. Activity did not escalate on 5 January and only one M 0.6 earthquake was detected. The Aviation Color Code was lowered to Green. The report noted that seismic activity at the volcano had been above background levels during the previous four months.

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.

Kanaga, Andreanof Islands (USA)

51.923°N, 177.168°W | Summit elev. 1307 m

AVO reported that unrest at Kanaga continued during 3-9 January; no new eruptive activity was evident in satellite and webcam images. Small daily earthquakes were detected until 2 January when a storm-related power failure took local monitoring data offline. Satellite radar images showed that large NW-SE-trending fractures intersecting the summit crater had likely formed around the time of the 18 December explosive event. The Volcano Alert Level remained at Advisory (the second level on a four-level scale) and the Aviation Color Code remained at Yellow (the second color on a four-color scale).

Geological summary: Symmetrical Kanaga stratovolcano is situated within the Kanaton caldera at the northern tip of Kanaga Island. The caldera rim forms a 760-m-high arcuate ridge south and east of Kanaga; a lake occupies part of the SE caldera floor. The volume of subaerial dacitic tuff is smaller than would typically be associated with caldera collapse, and deposits of a massive submarine debris avalanche associated with edifice collapse extend nearly 30 km to the NNW. Several fresh lava flows from historical or late prehistorical time descend the flanks of Kanaga, in some cases to the sea. Historical eruptions, most of which are poorly documented, have been recorded since 1763. Kanaga is also noted petrologically for ultramafic inclusions within an outcrop of alkaline basalt SW of the volcano. Fumarolic activity occurs in a circular, 200-m-wide, 60-m-deep summit crater and produces vapor plumes sometimes seen on clear days from Adak, 50 km to the east.

Lewotobi, Flores Island

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

PVMBG reported that the eruption at Lewotobi’s Laki-laki volcano from a fissure on the upper NNW flank and from a vent on the upper SSE flank was ongoing during 3-9 January. White plumes rose 300-1,000 m above the summit and drifted SW and W during 3-5 December. During the rest of the week white-and-gray or gray-to-brown ash plumes rose 1-1.5 km above the summit and drifted NW, N, and NE. The ash plumes were sometimes dense.

Masks had been distributed in Hokeng Jaya, Pululera, Klatanlo, and Nawakote in the district of Wulanggitan and the village of Dulempari in the district of Bura after the eruption began in late December and residents were encouraged to wear them when outside to minimize ash inhalation. On 1 January as many as 1,185 residents of Boru Village and 328 residents in the Konga Village area self-evacuated to several other locations including relatives’ homes and evacuation posts. Ash fell in several areas in the Wulanggitan and Bura districts. Badan Penanggulangan Bencana Daerah (BPBD) East Flores Regency mobilized and provided residents with essentials including mobile kitchens, food, tents, and cleaned ash off roadways. By 4 January a total of 3,898 people had evacuated. The Frans Xavier Seda Airport in Sikka District closed on 1 January due to thick ash deposits on the runways; it remained closed as of 9 January.

Activity intensified during the evening of 9 January. Incandescent material was ejected from the summit and lava flows from the NNW-flank fissure descended the NW flank. At 2300 the Alert Level was raised to 4 (on a scale of 1-4) and the public was warned to stay 4 km away from the Perempuan and Laki-laki craters and an additional 5 km from the NNW flanks of Laki-laki.

Geological summary: The Lewotobi edifice in eastern Flores Island is composed of the two adjacent Lewotobi Laki-laki and Lewotobi Perempuan stratovolcanoes (the “husband and wife”). Their summits are less than 2 km apart along a NW-SE line. The conical Laki-laki to the NW has been frequently active during the 19th and 20th centuries, while the taller and broader Perempuan has had observed eruptions in 1921 and 1935. Small lava domes have grown during the 20th century in both of the summit craters, which are open to the north. A prominent cone, Iliwokar, occurs on the E flank of Perampuan.

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 3-9 January. White plumes rose 300-350 m above the summit and drifted S and SW on 4 January. White-and-gray ash plumes rose 150-600 m above the summit and drifted S, SW, N, and NE during 5-8 January.

PVMBG reevaluated instrumental data and visual observations at Marapi and concluded that activity was continuing at high levels; at 1800 on 9 January they raised the Alert Level to 3 (on a scale of 1-4) and warned the public to stay 4.5 km away from Verbeek Crater. They noted that ongoing high seismicity and increasing numbers of low-frequency and deep volcanic earthquakes indicated that magma continued to be supplied at depth. Incandescence at the crater and the ejection of incandescent material after the 3 December eruption indicated that the eruption style had change from phreatic to magmatic; sulfur dioxide emissions measured from satellite were at high levels.

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

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 1-8 January 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.

Dukono, Halmahera

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

PVMBG reported that the eruption at Dukono was ongoing during 3-9 January. Gray-and-white ash plumes rose as high as 4 km above the summit and drifted SW on 3 January. White-and-gray ash plumes rose 100-1,900 m above the summit and drifted W and SW during 4 and 6-8 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 28 December 2023-4 January 2024. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E), explosions during 30-31 December generated ash plumes that rose as high as 3.5 km (11,500 ft) a.s.l and drifted SE. 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.

Gamalama, Halmahera

0.81°N, 127.3322°E | Summit elev. 1714 m

Although there was no eruptive activity reported at Gamalama, in a 4 January press release PVMBG noted that the number of daily deep volcanic earthquakes had significantly increased. The seismic network recorded a total of 45 deep volcanic earthquakes during 0000-0600 on 4 January; an average of 2-3 events per day had been recorded since January 2023. Diffuse white plumes only rose as high as 120 m above the summit during the previous month whereas typically they can rise as high as 300 m. PVMBG noted that the most likely hazard would be a phreatic event that could ejected material within the 1.5-km radius, though ash may be carried farther by wind. The Alert Level remained at 2 (on a scale of 1-4); visitors and residents were warned not to approach the crater within a 1.5-km radius.

Geological summary: Gamalama is a near-conical stratovolcano that comprises the entire island of Ternate off the western coast of Halmahera, and is one of Indonesia’s most active volcanoes. The island was a major regional center in the Portuguese and Dutch spice trade for several centuries, which contributed to the extensive documentation of activity. Three cones, progressively younger to the north, form the summit. Several maars and vents define a rift zone, parallel to the Halmahera island arc, that cuts the volcano; the S-flank Ngade maar formed after about 14,500–13,000 cal. BP (Faral et al., 2022). Eruptions, recorded frequently since the 16th century, typically originated from the summit craters, although flank eruptions have occurred in 1763, 1770, 1775, and 1962-63.

Great Sitkin, Andreanof Islands (USA)

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

AVO reported that a radar image of Great Sitkin showed continuing growth of a thick flow in the summit crater with expansion to the E; effusion likely continued during 3-9 January. Radial cracks around the central vent widened and pushed material 15 m N. Weather clouds often obscured views of the volcano. Seismicity was low, though beginning during 2-4 January web cameras and seismic data were offline due to a power failure. 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.

Iya, Flores Island

8.891°S, 121.641°E | Summit elev. 618 m

PVMBG reported that during 1-31 December diffuse white plumes rose as high as 80 m above Iya’s summit. During most of that period seismicity was at normal levels and characterized by both deep and shallow volcanic earthquakes. A total of 55 deep volcanic earthquakes were recorded during the month with 12 of them recorded during 30-31 December, signifying a significant increase during that period. The Alert Level was remained at 1 (on a scale of 1-4), and the public was warned to limit activity near the active crater area.

Geological summary: Gunung Iya is the southernmost of a group of three volcanoes comprising a small peninsula south of the city of Ende on central Flores Island. The cones to the north, Rooja and Pui, appear to be slightly older and have not shown historical activity, although Pui has a youthful profile (a reported 1671 eruption of Pui was considered to have originated from Iya volcano). Iya, whose truncated southern side drops steeply to the sea, has had numerous moderate explosive eruptions during historical time.

Lewotolok, Lembata Island

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

PVMBG reported that the eruption at Lewotolok continued during 3-9 January. White-and-gray ash plumes rose 300-350 m above the summit and drifted NW on 3 and 6 January. White steam-and-gas plumes rose 400-500 m above the summit and drifted NW on the other days. 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 29 December 2023-4 January 2024. The SW lava dome produced a total of 83 lava avalanches that descended the S and SW flanks; six traveled S as far as 1.4 km down the upper part of the Boyong drainage and the other 77 traveled SW as far as 2 km down the upper part of the Bebeng drainage. Two pyroclastic flows descended the Bebeng, traveling as far as 1.8 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.

Nevado del Ruiz, Colombia

4.892°N, 75.324°W | Summit elev. 5279 m

Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that eruptive activity at Nevado del Ruiz continued at moderate levels during 2-8 January. Seismic events indicating rock fracturing increased in both number an intensity. These events were located in areas up to 4 km in various directions from Arenas Crater at depths of 1-7 km. The seismic activity was most notable on 3 and 5 January; the largest earthquake, a M 3.9, was recorded at 1103 on 3 January and felt by officials of the Parque Nacional Natural Los Nevados, SGC personnel in the field, and residents in Manizales (27 km NW). Seismicity associated with ash-and-gas emissions decreased in both size and number. The maximum height of the ash-and-gas emissions was 1.8 km above the summit, recorded on 6 January. Emissions during the week drifted NW, W, and SW, causing ashfall near the volcano and occasionally in Manizales. The Alert Level remained at Yellow, Level III (the second level on a four-level scale), and the public was warned to stay out of the restricted areas around Arenas Crater.

Geological summary: Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America’s deadliest eruption.

Purace, Colombia

2.32°N, 76.4°W | Summit elev. 4650 m

Observatorio Vulcanológico y Sismológico de Popayán, Servicio Geologico Colombiano (SGC) reported increased unrest at Puracé on 5 January. A sudden increase in carbon dioxide emissions was detected during the morning and decreased through the day; increased gas emissions were visible in webcam images during the afternoon. Seismicity increased at 1450 and continued at high levels at least through 1715, the time the report was issued. The earthquake signals indicated fluid movement, had low magnitudes, and were located less than 2 km below the summit. The Alert Level remained at Yellow (the second 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.

Reventador, Ecuador

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

IG-EPN reported that a moderate eruption at Reventador was ongoing during 2-9 January. Seismicity was characterized by 37-58 daily explosions, long-period earthquakes, harmonic tremor, and tremor associated with emissions. Several ash-and-gas plumes rose as high as 1.3 km above the crater rim and drifted S, SW, W, and NW, though cloudy conditions often prevented views. Crater incandescence was occasionally visible during both overnight and morning hours; incandescent material was ejected 200-300 m above the crater and avalanches of incandescent material descended the flanks as far as 600 m from the summit during 6-9 January. A small lahar was recorded on 6 January. 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.

Sabancaya, Peru

15.787°S, 71.857°W | Summit elev. 5960 m

Instituto Geofísico del Perú (IGP) reported that the eruption at Sabancaya continued at moderate levels during 3-7 January with a daily average of 61 explosions. Gas-and-ash plumes rose as high as 1.7 km above the summit and drifted less than 10 km NW, W, and SW. Thermal anomalies over the lava dome in the summit crater were identified in satellite data. Slight inflation was detected near the Hualca Hualca sector (4 km N). The Alert Level remained at Orange (the third level on a four-color scale) and the public were warned to stay outside of a 12 km radius.

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

Sangay, Ecuador

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

IG-EPN reported a high level of eruptive activity at Sangay during 1-9 January, with seismic stations recording 173-583 daily explosions. Ash-and-gas plumes were visible, in both webcam and satellite images, rising as high as 1.5 km above the crater rim and drifting SW during 1-5 January. Webcam images showed incandescence at the summit vent and incandescent material descending the SE flank as far as 1.8 km from the crater. Beginning at 1536 on 6 January a series of explosions and ash emissions were visible in webcam images with ash-and-gas plumes rising 3 km above the summit and drifting NW. The activity continued into the late afternoon and intensified; ash plumes rose as high as 8 km above the summit and drifted W, NW, and N. Ashfall was reported in several towns downwind, including San Antonio, Pancún, Cebadas (35 km WNW), Gualiñag, Guargallá Chico, Guamote (40 km WNW), Pungalá (25 km NW), and Chunchi (73 km SW) in the province of Chimborazo, Chillanes (80 km W) in the province of Bolívar, Montalvo (106 km WNW), Babahoyo (135 km WNW), Ventanas, Pueblo Viejo (141 km NW), Vinces (165 km WNW), and Baba (152 km WNW) in the province of El Oro, and Palestina (185 km WNW) in the province of Guayas. Several pyroclastic flows descended the SE drainage during 6-7 January. Ash-and-gas plumes rose 400-800 m above the summit during 7-8 January. During the morning of 8 January, a pyroclastic flow descended the SE drainage and minor ashfall was reported in the Guamote-Chimborazo canton. Cloudy weather prevented views during 8-9 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 3-9 January. Daily white-and-gray ash plumes that were sometimes dense rose 400-1,200 m above the summit and drifted S, SW, and W. 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 28 December 2023-4 January 2024 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 1-8 January. No explosions were detected, though large blocks were ejected as far as 400 m from the vent. Ash plumes rose 1-2 km above the crater rim during 1-2, 6, and 8 January and drifted in multiple directions. Ash emissions were continuous during 0157-0620 and 0834-2235 on 2 January. 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

Rabaul Volcano Observatory (RVO) reported that activity at Ulawun was low during 6 December 2023-9 January 2024. During periods of good visibility white steam plumes of variable densities were seen rising from the summit crater. On 19 December visibility was poor, though during a brief clear period, observers noted brown-tinged steam plumes. On 31 December residents of Noau Village photographed dense brown ash plumes rising a few hundred meters above the summit and drifting W, and a small pyroclastic flow descending the NNE flank. The Alert Level remained at Stage 1 (on the four-level scale).

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.

References:

Smithsonian Institution / US Geological Survey – Weekly Volcanic Activity Report – January 3 – 9, 2024 – Managing Editor: Sally Sennert.

Featured image credit: TW

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