The Weekly Volcanic Activity Report: January 11 – 17, 2023

New activity/unrest was reported for 5 volcanoes from January 11 – 17, 2023. During the same period, ongoing activity was reported for 15 volcanoes.

New activity/unrest: Dieng Volcanic Complex, Central Java | Ijen, Eastern Java | Kilauea, Hawaiian Islands (USA) | Marapi, Central Sumatra | Semisopochnoi, Aleutian Islands (USA).

Ongoing activity: Ahyi, Mariana Islands (USA) | Aira, Kyushu (Japan) | Cotopaxi, Ecuador | Ebeko, Paramushir Island (Russia) | Great Sitkin, Andreanof Islands (USA) | Karymsky, Eastern Kamchatka (Russia) | Kerinci, Central Sumatra | Krakatau, Sunda Strait | Lewotolok, Lembata Island | Merapi, Central Java | San Miguel, Eastern El Salvador | Semeru, Eastern Java | Sheveluch, Central Kamchatka (Russia) | Suwanosejima, Ryukyu Islands (Japan) | Villarrica, Central Chile.

New activity/unrest

Dieng Volcanic Complex, Central Java

7.2°S, 109.879°E | Summit elev. 2565 m

PVMBG reported increasing activity at Dieng Volcanic Complex in a press release posted on 14 January. The number of deep volcanic earthquakes and local tectonic earthquakes had been increasing starting on 9 January. Carbon dioxide gas concentrations at Timbang Crater also intensified, averaging 0.09-0.11 percent during 1-13 January. Primary hazards at Dieng included phreatic eruptions at Sileri Crater and flows of carbon dioxide gas that can impact residents and tourists. Based on the data and potential hazards at the complex, PVMBG raised the Alert Level to 2 (on a scale of 1-4) and warned the public to stay 1 km away from Sileri Crater and to stay out of Timbang Crater, and to take caution when digging in the ground as gasses could be released.

At 2116 on 15 January carbon dioxide emissions significantly increased. The carbon dioxide gas concentration at 0027 on 16 January was 5,600 parts per million (ppm), rising to 7,300 ppm by 0130. The mobile instrument measuring the gas was located 170 m from the midpoint of Timbang Crater. At 0540 the gas concentration was as high as 10,000 ppm, measured from 130 m away from the crater’s midpoint. In a second press release, PVMBG warned the public to stay 500 m away from the SE, S, and SW sectors of Timbang Crater.

Geological summary: The Dieng plateau in the highlands of central Java is renowned both for the variety of its volcanic scenery and as a sacred area housing Java’s oldest Hindu temples, dating back to the 9th century CE. The Dieng Volcanic Complex consists of multiple stratovolcanoes and more than 20 small Pleistocene-to-Holocene craters and cones over a 6 x 14 km area. Prahu stratovolcano was truncated by a large Pleistocene caldera, which was subsequently filled by a series of cones, lava domes, and craters, many containing lakes. Lava flows cover much of the plateau, but observed activity has been restricted to minor phreatic eruptions. Gas emissions are a hazard at several craters and have caused fatalities. There are abundant thermal features and high heat flow across the area.

Ijen, Eastern Java

8.058°S, 114.242°E | Summit elev. 2769 m

PVMBG reported that unrest continued at Ijen during 10-17 January. There were 2-30 daily earthquakes indicating emissions and 2-19 daily shallow volcanic earthquakes. One tornillo earthquake was recorded on 10 January. Diffuse white gas plumes were visible rising as high as 400 m above the summit during 10-14 January. The Alert Level remained at 2 (on a scale of 1-4) and residents, visitors, and sulfur miners were advised to not approach the crater within 1.5 km.

Geological summary: The Ijen volcano complex at the eastern end of Java consists of a group of small stratovolcanoes constructed within the 20-km-wide Ijen (Kendeng) caldera. The north caldera wall forms a prominent arcuate ridge, but elsewhere the rim was buried by post-caldera volcanoes, including Gunung Merapi, which forms the high point of the complex. Immediately west of the Gunung Merapi stratovolcano is the historically active Kawah Ijen crater, which contains a nearly 1-km-wide, turquoise-colored, acid lake. Kawah Ijen is the site of a labor-intensive mining operation in which baskets of sulfur are hand-carried from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of cones forms an E-W zone across the southern side of the caldera. Coffee plantations cover much of the caldera floor; nearby waterfalls and hot springs are tourist destinations.

Kilauea, Hawaiian Islands (USA)

19.421°N, 155.287°W | Summit elev. 1222 m

HVO reported that lava continued to erupt from vents on the central E portion of Kilauea’s Halema’uma’u Crater floor during 10-17 January. Activity was concentrated in a large lava lake, covering about 12 hectares in the E half of the crater on 10 January. One dominant lava fountain, 6-7 m high, was active within this area. Lava flows built up the margins of the lake, causing the lake to be perched; small overflows along the margins were visible during 13-16 January. A smaller area of lava was active within the basin in the W half of the crater that had been the focus of activity during 2021-2022. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geological summary: Kilauea overlaps the E flank of the massive Mauna Loa shield volcano in the island of Hawaii. Eruptions are prominent in Polynesian legends; written documentation since 1820 records frequent summit and flank lava flow eruptions interspersed with periods of long-term lava lake activity at Halemaumau crater in the summit caldera until 1924. The 3 x 5 km caldera was formed in several stages about 1,500 years ago and during the 18th century; eruptions have also originated from the lengthy East and Southwest rift zones, which extend to the ocean in both directions. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1,100 years old; 70% of the surface is younger than 600 years. The long-term eruption from the East rift zone between 1983 and 2018 produced lava flows covering more than 100 km2, destroyed hundreds of houses, and added new coastline.

Marapi, Central Sumatra

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

PVMBG reported that the explosive eruption at Marapi continued during 10-17 January with daily dense ash plumes rising above the crater rim and drifting in various directions. White-and-gray ash plumes at 0900 and 0912 on 10 January rose 200-300 m and drifted NE and SE. Gray ash plumes rose 400-800 m at 0825, 0941, and 1133 on 11 January and drifted N, NE, E, and SE. Multiple gray ash plumes visible on 12 January (0640, 0936, 1042, 1058, 1217, 1824) rose as high as 1 km and drifted NE, E, and SE. White-and-gray ash plumes rose 200-600 m and drifted NE, SE, and SW during 13-15 January; rainy weather conditions prevented visual observations on 16 January. The Alert Level remained at 2 (on a scale of 1-4) and the public was warned to stay 3 km away from the 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.

Semisopochnoi, Aleutian Islands (USA)

51.93°N, 179.58°E | Summit elev. 1221 m

AVO reported that eruptive activity at Semisopochnoi’s Mount Young was ongoing during 10-17 January. Seismicity was elevated with small local earthquakes and weak tremor. Minor steam emissions were visible in webcam images during 11 and 16-17 January. Several small explosion signals were detected by local seismic and infrasound sensors during 16-17 January; no activity was identified in cloudy satellite views. The Aviation Color Code remained at Orange (the second highest level on a four-color scale) and the Volcano Alert Level remained at Watch (the second highest level on a four-level scale).

Geological summary: Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island’s northern part. The three-peaked Mount Cerberus (renamed Mount Young in 2023) was constructed within the caldera during the Holocene. Each of the peaks contains a summit crater; lava flows on the N flank appear younger than those on the south side. Other post-caldera volcanoes include the symmetrical Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented eruptions have originated from Young, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone could have been recently active.

Ongoing activity

Ahyi, Mariana Islands (USA)

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

Unrest at Ahyi Seamount was occasionally detected during 11-17 January. Pressure sensors on Wake Island (2,270 km E of Ahyi) were back online and recorded possible explosions during 11-12 and 15-16 January. One weak signal, possibly from the seamount, was recorded during 16-17 January. No activity was visible in clear or partly cloudy satellite images. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level remained at Advisory (the second lowest level on a four-level scale).

Geological summary: Ahyi seamount is a large conical submarine volcano that rises to within 75 m of the sea surface about 18 km SE of the island of Farallon de Pajaros (Uracas) 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 of the seamount, 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)

31.593°N, 130.657°E | Summit elev. 1117 m

JMA reported ongoing eruptive activity at Minamidake Crater (at Aira Caldera’s Sakurajima volcano) during 9-16 January. Crater incandescence was visible nightly. Eruptive events at 0210 on 9 January and 1837 on 14 January produced plumes that rose 1 km above the crater rim. Sulfur dioxide emissions were high at 2,100 tons per day on 13 January. The Alert Level remained at 3 (on a 5-level scale), and residents were warned to stay 2 km away from the crater.

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 Aira caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim of Aira caldera and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4850 years ago, after which eruptions took place at Minamidake. Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu’s largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.

Cotopaxi, Ecuador

0.677°S, 78.436°W | Summit elev. 5911 m

IG reported that the eruption at Cotopaxi continued during 11-17 January, characterized by daily steam-and-gas emissions often with variable content. On 11 January ash plumes rose as high as 200 m above the crater rim and drifted W and SW. Minor ashfall was noted in areas of Mulaló, Macaló Grande, San Antonio, San Ramón (127 km W), Ticatilín (15 km SW), and MAE Norte (18 km N), and a sulfur odor was noted in Ticatilín and Control Caspi (20 km WSW) of the Parque Nacional Cotopaxi. On 12 January steam, gas, and ash plumes rose as high as 1 km and drifted SE, SW, and W. On 13 January a dense ash plume rose 2 km and drifted NE, causing ashfall in Ticatilín; other ash plumes rose 1 km and drifted W and N that same day. Steam-and-gas emissions rose 300-700 m during 14-17 January and drifted E, SE, and SW. Ash-and-gas plumes rose 1 km on 17 January and drifted W and SW; minor ashfall was reported in Mulaló and San Juan de Pastocalle (20 km WSW). Servicio Nacional de Gestión de Riesgos y Emergencias (SNGRE) maintained the Alert Level at Yellow (the second lowest level on a four-color scale).

Geological summary: The symmetrical, glacier-covered, Cotopaxi stratovolcano is Ecuador’s most well-known volcano and one of its most active. The steep-sided cone is capped by nested summit craters, the largest of which is about 550 x 800 m in diameter. Deep valleys scoured by lahars radiate from the summit of the andesitic volcano, and large andesitic lava flows extend to its base. The modern edifice has been constructed since a major collapse sometime prior to about 5,000 years ago. Pyroclastic flows (often confused in historical accounts with lava flows) have accompanied many explosive eruptions, and lahars have frequently devastated adjacent valleys. Strong eruptions took place in 1744, 1768, and 1877. Pyroclastic flows descended all sides of the volcano in 1877, and lahars traveled more than 100 km into the Pacific Ocean and western Amazon basin. Smaller eruptions have been frequent since that time.

Ebeko, Paramushir Island (Russia)

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

KVERT reported that moderate activity at Ebeko was ongoing during 5-12 January. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E) explosions during 6 and 9-11 January generated ash plumes that rose as high as 4.5 km (14,800 ft) a.s.l. and drifted W and ESE. A thermal anomaly was identified in satellite images on 10 January. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Dates are based on UTC times; 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

AVO reported that radar images acquired on 13 and 15 January confirmed ongoing slow lava effusion at Great Sitkin; effusion likely continued through 17 January. Slightly elevated surface temperatures were identified in satellite images during 10-11 January and a few small earthquakes were detected on most days during 10-17 January. Weather clouds sometimes obscured satellite and webcam views. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level 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.

Karymsky, Eastern Kamchatka (Russia)

54.049°N, 159.443°E | Summit elev. 1513 m

KVERT lowered the Aviation Color Code for Karymsky to Green (the lowest level on a four-color scale) on 12 January, noting that ash explosions were last detected on 7 August 2022. A minor thermal anomaly visible in satellite images and moderate levels of gas-and-steam emissions persisted. Dates are based on UTC times; specific events are in local time where noted.

Geological summary: Karymsky, the most active volcano of Kamchatka’s eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Kerinci, Central Sumatra

1.697°S, 101.264°E | Summit elev. 3800 m

The eruption at Kerinci was ongoing during 10-17 January. Daily ash plumes that were brown or gray and mostly dense rose generally 400-900 m above the summit and drifted N, NE, and W during 10-14 January. At 1810 on 12 January a dense gray ash plume rose 1.2 km above the summit and drifted NW. Only white plumes were occasionally visible rising from the summit during 15-17 January. The Alert Level remained at 2 (on a scale of 1-4) and the public was reminded to stay 3 km away from the crater.

Geological summary: Gunung Kerinci in central Sumatra forms Indonesia’s highest volcano and is one of the most active in Sumatra. It is capped by an unvegetated young summit cone that was constructed NE of an older crater remnant. There is a deep 600-m-wide summit crater often partially filled by a small crater lake that lies on the NE crater floor, opposite the SW-rim summit. The massive 13 x 25 km wide volcano towers 2400-3300 m above surrounding plains and is elongated in a N-S direction. Frequently active, Kerinci has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838.

Krakatau, Sunda Strait

6.102°S, 105.423°E | Summit elev. 155 m

PVMBG reported that the eruption at Anak Krakatau continued. At 1754 on 11 January a dense gray ash plume rose around 200 m above the summit and drifted NE, followed by dense black ash plumes at 2241 and 2325 on 11 January and at 0046 on 12 January that rose 200-300 m and drifted NE. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay at least 5 km away from the crater.

Geological summary: The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of that volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption caused more than 36,000 fatalities, most as a result of tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

Lewotolok, Lembata Island

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

PVMBG reported that at 0747 on 14 January an eruption at Lewotolok produced a white-and-gray ash plume that rose around 400 m above the summit and drifted E. At 2055 on 16 January a white-and-gray ash plume of variable density rose around 400 m above the summit and drifted SE. A photo posted with the report showed incandescence emanating from the summit, possibly from ejected material. The Alert Level remained at 2 (on a scale of 1-4) and the public was warned to stay 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 continued during 6-12 January and seismicity remained at high levels. The SW lava dome produced three lava avalanches that traveled as far as 1.2 km down the SW flank (upstream in the Kali Bebeng drainage). Avalanche sounds were heard on six occasions. No significant morphological changes to the central and SW lava domes were evident in webcam images. 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.

San Miguel, Eastern El Salvador

13.434°N, 88.269°W | Summit elev. 2130 m

On 14 January MARN reported that a gradual decrease in activity to low levels had been recorded at San Miguel since 1 December 2022. Sulfur dioxide emissions were below the baseline of 300 tons per day and no deformation was detected. Minor emissions and occasional explosions of gas and ash continued to be recorded by the seismic network and were occasionally visible. At 0817 on 14 January a gas-and-ash emission was seen in webcam images rising just over the crater rim.

Geological summary: The symmetrical cone of San Miguel, one of the most active volcanoes in El Salvador, rises from near sea level to form one of the country’s most prominent landmarks. A broad, deep, crater complex that has been frequently modified by eruptions recorded since the early 16th century caps the truncated unvegetated summit, also known locally as Chaparrastique. Flanks eruptions of the basaltic-andesitic volcano have produced many lava flows, including several during the 17th-19th centuries that extended to the N, NE, and SE. The SE-flank flows are the largest and form broad, sparsely vegetated lava fields crossed by highways and a railroad skirting the base of the volcano. Flank vent locations have migrated higher on the edifice during historical time, and the most recent activity has consisted of minor ash eruptions from the summit crater.

Semeru, Eastern Java

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

PVMBG reported that the eruption at Semeru continued during 3-10 January with daily ash plumes of variable densities rising above the summit. At 0737 on 10 January white-and-brown ash plumes rose 500 m above the summit and drifted N. A gray-to-brown ash plume at 0532 on 11 January rose 200 m and drifted N. White-to-gray ash plumes were visible at 0552, 0621, and 0710 on 11 January, and at 0629 and 0723 on 12 January rising 200-500 m above the summit and drifting N, W, and SW. At 0525 on 13 January a white-and-brown ash plume rose 700 m and drifted S. A white-to-gray ash plume rose 500 m and drifted SW at 0627 and a dense ash plume rose 1 km and drifted SW at 0802. At 0502 on 14 January a dense white-and-gray ash plume rose 700 m and drifted SW. Multiple white, gray, and brown ash plumes on 15 January rose as high as 400 m and drifted N, NE, and SW. Four gray ash plumes visible on 16 January (at 0558, 1613, 1627, and 1655) rose as high as 700 m and drifted NW, N, and NE. The Alert Level remained at 3 (on a scale of 1-4). The public was warned to stay at least 5 km away from the summit, and 500 m from Kobokan drainages within 17 km of the summit, along with other drainages originating on Semeru, 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 ongoing eruption at Sheveluch during 5-12 January was generally characterized by explosions, hot avalanches, lava-dome extrusion, and strong fumarolic activity. A daily thermal anomaly was identified in satellite images, and minor ash plumes from explosions and lava-dome collapses drifted 92 km W on 7 January. The Aviation Color Code remained at Orange (the second highest 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 9-16 January. No explosions were recorded, though during 9-13 January eruption plumes rose as high as 1.1 km above the crater rim and blocks were ejected as far as 300 m from the vent. Ashfall was occasionally reported in Toshima village (3.5 km SSW). Eruption plumes rose as high has 700 m during 13-16 January. The Alert Level remained at 3 (on a 5-level scale), and residents were warned to stay 2 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 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.

Villarrica, Central Chile

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

SERNAGEOMIN reported that the eruption at Villarrica was ongoing during 11-17 January. Strombolian explosions and lava fountaining from the vent on the crater floor were frequently visible in webcam images. Explosions during 11-12 January ejected material 80 m high and as far as 250 m onto the NE flank. The number of explosions increased during 14-15 January, some ejecting material up to 150 m above the crater rim. POVI scientists counted about 70 instances of lava fountaining from 2130 on 14 January to 0600 on 15 January. Material ejected by the explosions stayed within or near the crater during 16-17 January. The Alert Level remained at Yellow (the second lowest level on a four-color scale). ONEMI maintained the Alert Level at Yellow (the middle level on a three-color scale) for the municipalities of Villarrica, Pucón (16 km N), Curarrehue, and the commune of Panguipulli.

Geological summary: Glacier-clad Villarrica, one of Chile’s most active volcanoes, rises above the lake and town of the same name. It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. A 6-km-wide caldera formed during the late Pleistocene. A 2-km-wide caldera that formed about 3500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesitic cone at the NW margin of the Pleistocene caldera. More than 30 scoria cones and fissure vents dot the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Historical eruptions, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

References:

Smithsonian / US Geological Survey Weekly Volcanic Activity Report – January 11 – 17, 2023 – Managing Editor: Sally Kuhn Sennert