The Weekly Volcanic Activity Report: February 8 – 14, 2023
New activity/unrest was reported for 5 volcanoes from February 8 to 14, 2023. During the same period, ongoing activity was reported for 18 volcanoes.
New activity/unrest: Aira, Kyushu (Japan) | Chikurachki, Paramushir Island (Russia) | Karangetang, Sangihe Islands | Lascar, Northern Chile | Tengger Caldera, Eastern Java.
Ongoing activity: Ahyi, Mariana Islands (USA) | Cotopaxi, Ecuador | Dukono, Halmahera | Ebeko, Paramushir Island (Russia) | Great Sitkin, Andreanof Islands (USA) | Huaynaputina, Peru | Ibu, Halmahera | Kerinci, Central Sumatra | Kilauea, Hawaiian Islands (USA) | Lewotolok, Lembata Island | Marapi, Central Sumatra | Merapi, Central Java | Semeru, Eastern Java | Semisopochnoi, Aleutian Islands (USA) | Sheveluch, Central Kamchatka (Russia) | Suwanosejima, Ryukyu Islands (Japan) | Tangkuban, Parahu Western Java | Villarrica, Central Chile.
Aira, Kyushu (Japan)
JMA reported ongoing eruptive activity at Aira Caldera’s Sakurajima volcano during 6-12 February and nightly crater incandescence. Three eruptive events and two explosions were recorded at Minamidake Crater. The first explosion, at 1815 on 9 November, generated an ash plume that rose 2 km above the crater rim and drifted N and ejected large blocks 600-900 m from the crater rim. The second explosion, at 1007 on 11 February, produced an ash plume that rose 1.7 km and ejected large blocks 600-900 m from the crater rim. An ash plume from an eruptive event at 1323 on 12 February rose 1.7 km and drifted E.
A very small eruption at Showa Crater at 1052 on 8 February produced an ash plume that rose 800 m above the crater rim. This was the first eruption at Showa Crater since 3 April 2018. Ash plumes from events recorded at 1110 and 1425 rose as high as 1 km and drifted SE and SW, respectively, and blocks were ejected 200-300 m from the crater. Ashfall was reported in an area from Arimura-cho (4.5 km SE) to Furusato-cho (3 km S). 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.
Chikurachki, Paramushir Island (Russia)
KVERT reported that a moderate explosive eruption at Chikurachki continued during 2-9 February. A thermal anomaly was identified in satellite images during 5-6 February and ash plumes drifted 125 km SE, E, and NE. 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: Chikurachki, the highest volcano on Paramushir Island in the northern Kuriles, is a relatively small cone constructed on a high Pleistocene edifice. Oxidized basaltic-to-andesitic scoria deposits covering the upper part of the young cone give it a distinctive red color. Frequent basaltic Plinian eruptions have occurred during the Holocene. Lava flows have reached the sea and formed capes on the NW coast; several young lava flows are also present on the E flank beneath a scoria deposit. The Tatarinov group of six volcanic centers is located immediately to the south, and the Lomonosov cinder cone group, the source of an early Holocene lava flow that reached the saddle between it and Fuss Peak to the west, lies at the southern end of the N-S-trending Chikurachki-Tatarinov complex. In contrast to the frequently active Chikurachki, the Tatarinov centers are extensively modified by erosion and have a more complex structure. Tephrochronology gives evidence of an eruption around 1690 CE from Tatarinov, although its southern cone contains a sulfur-encrusted crater with fumaroles that were active along the margin of a crater lake until 1959.
Karangetang, Sangihe Islands
According to PVMBG the eruption at Karangetang’s Main Crater (S crater) continued during 8-14 February. Multiple nighttime webcam images posted with daily reports showed three main incandescent lava flows of different lengths descending the S, SW, and W flanks. Incandescent rocks dotted the upper flanks, possibly from ejected or collapsed material from the crater; the incandescence was most intense at the summit. The Alert Level remained at 3 (on a scale of 1-4) and the public was advised to stay 2.5 km away from Main Crater with an extension to 3.5 km on the S and SE flanks.
Geological summary: Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia’s most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented (Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.
Lascar, Northern Chile
SERNAGEOMIN reported that seismicity at Láscar was dominated by volcano-tectonic signals with smaller numbers of both long-period and tornillo-type events during 7-14 February. Seismicity increased during the week, associated with continuing effusion of the dome-like structure that had emerged on the crater floor on 30 January. Daily whitish gas emissions were mostly diffuse and rose around 400 m above the crater rim, though emissions rose as high as 700 m during 11-12 February. Sulfur dioxide emissions were low, no deformation was detected, and no thermal anomalies were identified in satellite images. The Alert Level remained at Orange (the second highest level on a four-color scale) and SENAPRED warned the public to stay at least 10 km away from the crater. ONEMI maintained an Alert Level Yellow (the middle level on a three-color scale) for San Pedro de Atacama (70 km NW).
Geological summary: Láscar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters. Prominent lava flows descend its NW flanks. An older, higher stratovolcano 5 km E, Volcán Aguas Calientes, displays a well-developed summit crater and a probable Holocene lava flow near its summit (de Silva and Francis, 1991). Láscar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires.
Tengger Caldera, Eastern Java
PVMBG sent a team of scientists to investigate Tengger Caldera’s Bromo cone after an increase in activity was detected on 3 February, characterized by crater incandescence, rumbling sounds, and a strong sulfur dioxide odor. They observed somewhat dense white emissions rising as high as 300 m during 9-12 February and heard moderate-to-strong rumbling noises. A sulfur dioxide odor was strong near the crater and measurements indicated that levels were above the healthy (non-hazardous) threshold of 5 parts per million; differential optical absorption spectroscopy (DOAS) measurements indicated an average flux of 190 tons per day on 11 February. During clear periods the largest solfatara on the NNW part of the crater floor was visible and ranged in temperature from 46 to 66 degrees Celsius based on handheld instruments. Crater incandescence, originating from the solfatara, was visible at night. The Alert Level remained at 2 (on a scale of 1-4), and visitors were warned to stay outside of a 1-km radius of the crater.
Geological summary: The 16-km-wide Tengger caldera is located at the northern end of a volcanic massif extending from Semeru volcano. The massive volcanic complex dates back to about 820,000 years ago and consists of five overlapping stratovolcanoes, each truncated by a caldera. Lava domes, pyroclastic cones, and a maar occupy the flanks of the massif. The Ngadisari caldera at the NE end of the complex formed about 150,000 years ago and is now drained through the Sapikerep valley. The most recent of the calderas is the 9 x 10 km wide Sandsea caldera at the SW end of the complex, which formed incrementally during the late Pleistocene and early Holocene. An overlapping cluster of post-caldera cones was constructed on the floor of the Sandsea caldera within the past several thousand years. The youngest of these is Bromo, one of Java’s most active and most frequently visited volcanoes. This volcano is located within the Bromo Tengger Semeru-Arjuno, a UNESCO Biosphere Reserve property.
Ahyi, Mariana Islands (USA)
Unrest at Ahyi Seamount continued during 7-14 February. Pressure sensors on Wake Island, 2,270 km E of Ahyi Seamount, occasionally detected possible activity including possible explosions during 13-14 February. No activity was identified in satellite images, though the image resolutions were too low to detect water discoloration. 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.
IG reported that the eruption at Cotopaxi continued during 7-14 February, characterized by daily or almost daily emissions of gas, steam, and ash; inclement weather conditions occasionally prevented views. Gas-and-ash emissions rose as high as 2 km above the crater rim and drifted NW, W, and E during 7-10 February. Minor ashfall was reported in the parish of Tambillo (32 km NNW), Mejia region, on 10 February. Steam-and-gas emissions rose to 1 km and drifted W and SW on 11 February. Gas-and-ash plumes rose around 500 m on 12 February and drifted SW. Minor amounts of ash fell in El Chasqui (17 km W), Mulaló (19 km SW), and San Juan de Pastocalle (20 km WSW). During 13-14 February several steam-and-ash emissions rose as high as 1 km and drifted W and SW. Minor ashfall was reported in Mulaló, San Agustín (11 km W), Ticatilín (15 km WSW), San Ramón (17 km SW), Control Caspi (20 km WSW), and in Pastocalle (22 km W). 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.
PVMBG reported that white-and-gray plumes of variable densities rose from Dukono as high as 150 m above the summit and drifted S and E on 8 and 10 February. Inclement weather conditions sometimes prevented visual observations. The Alert Level remained at 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, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. 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)
KVERT reported that moderate activity at Ebeko was ongoing during 2-9 February. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E) explosions during 4-5 and 7-8 February generated ash plumes that rose as high as 4.5 km (14,800 ft) a.s.l. and drifted NE and E. Ashfall was reported in Severo-Kurilsk on 5 and 8 February. A thermal anomaly was identified in satellite images on 8 February. 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)
AVO reported that a 6 February satellite image confirmed continuing lava effusion at Great Sitkin and growth of the flow field to the E; effusion likely continued during 7-14 February. Weather clouds often obscured satellite and webcam views, though steam emissions were observed during 8 and 11-12 February. Seismicity was low most of the week; a network outage began at 2120 on 12 February and prevented transmission of seismic data. 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. This volcano is located within the Aleutian Islands, a UNESCO Biosphere Reserve property.
IGP reported that on 4 February a small-to-medium lahar descended the El Volcán drainage, on the S flank of Huaynaputina, and traveled to within 500 m of Quinistaquillas, in the province of Sánchez Cerro, Moquegua region.
Geological summary: Huaynaputina (whose name means “new volcano”) is a relatively inconspicuous volcano that was the source of the largest historical eruption of South America in 1600 CE. It has no prominent topographic expression and lies within a 2.5-km-wide depression formed by edifice collapse and further excavated by glaciers within an older edifice of Tertiary-to-Pleistocene age. Three overlapping ash cones with craters up to 100 m deep were constructed during the 1600 CE eruption on the floor of the ancestral crater, whose outer flanks are heavily mantled by ash deposits from the 1600 eruption. This powerful fissure-fed eruption may have produced nearly 30 km3 of dacitic tephra, including pyroclastic flows and surges that traveled 13 km to the east and SE. Lahars reached the Pacific Ocean, 120 km away. The eruption caused substantial damage to the major cities of Arequipa and Moquengua, and regional economies took 150 years to fully recover.
PVMBG reported that the eruption at Ibu continued during 7-14 February. White-and-gray plumes of variable densities rose as high as 800 m above the summit and drifted NE and NW during 6-7 February. The Alert Level remained at a 2 (on a scale of 1-4), and the public was warned to stay at least 2 km away from the active crater and 3.5 km away on the N side.
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.
Kerinci, Central Sumatra
PVMBG reported that the eruption at Kerinci was ongoing during 8-14 February. Ash plumes were visible on most days, though weather conditions prevented views towards the end of the week. At 0724 on 8 February a gray ash plum rose 150 m above the summit and drifted E. Gray-to-brown ash plumes rose 150 m and drifted NE that same day. White-and-gray ash plumes rose 150 m and drifted NE during 9-10 February. At 1740 on 10 February a dense gray ash plume rose around 100 m and drifted E, and on 14 February white-and-brown ash plumes rose 200 m and drifted NE. 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. This volcano is located within the Tropical Rainforest Heritage of Sumatra, a UNESCO World Heritage property.
Kilauea, Hawaiian Islands (USA)
HVO reported that lava continued to erupt from three locations on Kilauea’s Halema’uma’u Crater floor during 7-14 February. The lava lake in E half of the crater was active and remained at about 10 hectares in size. A small 3-6 m high lava fountain in the S part of the E lake was active during the first few days but had diminished during 10-11 February and remained at lower levels during the rest of the week. The smaller western lake in the basin of the 2021–2022 lava lake as well as the smaller lava pond in the central portion of the crater floor remained active and overflowed frequently each day. Activity in the southern small lava pond had decreased. During 12-14 February a small lava fountain was visible in the smaller central lava pond and was active along with the fountain in the S part of the E lake. Lava continued to overflow the pond and possibly connected to the larger E lava lake. 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: Kīlauea 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. This volcano is located within the Hawaiian Islands, a UNESCO World Heritage property.
Lewotolok, Lembata Island
PVMBG reported that the eruption at Lewotolok was ongoing during 7-14 February. Minor crater incandescence at the summit was visible in most of the daily webcam images posted with the daily PVMBG reports. A webcam image captured at 2140 on 11 February showed Strombolian activity. White-and-gray plumes rose as high as 300 m above the crater rim and drifted NE, E, and SE on each day except 9-10 and 14 February due to weather clouds. 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.
Marapi, Central Sumatra
PVMBG reported that the eruption at Marapi continued during 8-14 February. White, gray, and black plumes rose as high as 400 m and drifted SW and S on 10 February. At 1827 a dense black ash plume rose 400 m and drifted NE and E. White-and-gray plumes that were sometimes dense rose as high as 200 m and drifted E and SE on 12 February. Diffuse white-and-gray plumes rose 100 m and drifted N and S on 13 February. 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.
Merapi, Central Java
BPPTKG reported that the eruption at Merapi continued during 3-9 February and seismicity remained at high levels. The SW lava dome produced five lava avalanches that traveled as far as 1.8 km down the SW flank (upstream in the Kali Bebeng drainage) and one pyroclastic flow traveled 1.5 km SW (on 8 February). 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.
Semeru, Eastern Java
PVMBG reported that the eruption at Semeru continued during 6-12 February. Somewhat dense to dense white-and-gray ash plumes rose 300-500 m above the summit and drifted N and NE, though weather conditions often prevented visual observations. At 0623 on 11 February a white-and-brown ash plume rose 600 m above the summit, and at 0754 a dense white-to-gray ash plume rose 600 m and drifted E. At 0527 on 14 February a somewhat-dense, white-to-gray ash plume rose around 800 m. Avalanches of material were detected during the week and sometimes roaring was heard, but they were rarely seen due to weather. Deformation fluctuated and was characterized by overall inflation. The number of earthquakes increased. 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 in all directions, 13 km from the summit to the SE, 100 m away from the banks of the Kobokan drainage as far as 17 km from the summit, and to avoid 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. This volcano is located within the Bromo Tengger Semeru-Arjuno, a UNESCO Biosphere Reserve property.
Semisopochnoi, Aleutian Islands (USA)
AVO reported that eruptive activity at Semisopochnoi’s Mount Young continued during 7-14 February. Seismicity was low, and a few local earthquakes were recorded during 7-8 February. Steam emissions were visible in webcam images almost daily though views were often cloudy. 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. This volcano is located within the Aleutian Islands, a UNESCO Biosphere Reserve property.
Sheveluch, Central Kamchatka (Russia)
KVERT reported that the ongoing eruption at Sheveluch during 2-9 February 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 lava-dome collapses drifted 110 km NE on 6 February. 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)
JMA reported that the eruption at Suwanosejima’s Ontake Crater continued during 6-13 February with a total of 10 explosions recorded by the seismic network. The explosions produced eruption plumes that rose as high as 1.5 km above the crater rim and ejected large blocks as far as 400 m from the vent. Crater incandescence was observed nightly. Occasional ashfall was reported in Toshima village (3.5 km SSW). The Alert Level remained at 2 (on a 5-level scale) and residents were warned to stay 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 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.
Tangkuban, Parahu Western Java
PVMBG issued a special report based on recent observations of Tangkuban Parahu. Webcam images captured from 1830 on 9 February to 0300 on 10 February showed incandescence emanating from Ecoma Crater. A team of PVMBG scientists inspected the crater during 1900-2000 on 10 February to identify the source of the incandescence. They observed intense emissions rising from Ecoma Crater, heard roaring and rumbling, and detected a strong sulfur odor, but did not see incandescence. Remote measurements of solfatara temperatures in Ecoma Crater using thermal cameras show varying temperatures, with a maximum of 105 degrees Celsius, and were influenced by airflow conditions at the crater. A multi-gas detector did not record high concentrations of volcanic gases. Seismic data from June 2022 to February 2023 suggested variable rates of fluid movement and increased heating of the subsurface to the surface. Data from monitoring instruments and visual observations indicated that the incandescent was not caused by rising magma and instead by reactions of sulfur deposits around the vents; the Alert Level remained at 1 (on a scale of 1-4) and tourists were advised to avoid descending into the craters.
Geological summary: Gunung Tangkuban Parahu is a broad stratovolcano overlooking Indonesia’s former capital city of Bandung. The volcano was constructed within the 6 x 8 km Pleistocene Sunda caldera, which formed about 190,000 years ago. The volcano’s low profile is the subject of legends referring to the mountain of the “upturned boat.” The Sunda caldera rim forms a prominent ridge on the western side; elsewhere the rim is largely buried by deposits of the current volcano. The dominantly small phreatic eruptions recorded since the 19th century have originated from several nested craters within an elliptical 1 x 1.5 km summit depression.
Villarrica, Central Chile
The eruption at Villarrica was ongoing during 6-12 February. POVI reported that three explosions were heard during 1940-1942 on 6 February, and then hours later spatter was seen rising 30 m above the crater rim. On 9 February lava fountains were seen rising around 50 m above the crater rim. SERNAGEOMIN noted that in the early part of the week small Strombolian explosions and gas emissions were recorded and observed in webcam images. A period of increased seismicity was recorded on 12 February, after several weeks of stable levels. The seismicity and recent visual observations (especially ash emissions observed on 27 January) indicated that activity was localized at shallow levels, without a clear indication of deep magmatic contribution. 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.
Smithsonian / US Geological Survey Weekly Volcanic Activity Report – February 8 – 14, 2023 – Managing Editor: Sally Kuhn Sennert
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