The Weekly Volcanic Activity Report: February 1 – 7, 2023

the weekly volcanic activity report

New activity/unrest was reported for 5 volcanoes from February 1 to 7, 2023. During the same period, ongoing activity was reported for 17 volcanoes.

New activity/unrest: Chikurachki, Paramushir Island (Russia) | Epi, Vanuatu | Karangetang, Sangihe Islands | Lascar, Northern Chile | Tengger Caldera, Eastern Java.

Ongoing activity: Ahyi, Mariana Islands (USA) | Aira, Kyushu (Japan) | Cotopaxi, Ecuador | Ebeko, Paramushir Island (Russia) | Etna, Sicily (Italy) | Fuego, South-Central Guatemala | Great Sitkin, Andreanof Islands (USA) | Kerinci, Central Sumatra | Kilauea, Hawaiian Islands (USA) | Lewotolok, Lembata Island | Marapi, Central Sumatra | Merapi, Central Java | Santa Maria, Southwestern Guatemala | Semeru, Eastern Java | Semisopochnoi, Aleutian Islands (USA) | Sheveluch, Central Kamchatka (Russia) | Suwanosejima, Ryukyu Islands (Japan).

New activity/unrest

Chikurachki, Paramushir Island (Russia)

50.324°N, 155.461°E | Summit elev. 1781 m

KVERT reported that the moderate explosive eruption at Chikurachki that began on 28 January continued through 2 February. Explosions during 28-29 and 31 January and 1-2 February produced ash plumes that rose to as high as 4 km (13,100 ft) a.s.l. and drifted 125 km SE, E, and NE based on satellite data. A thermal anomaly was identified in satellite images on 31 January. The Aviation Color Code remined at Orange (the second highest level on a four-color scale).

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.

Epi, Vanuatu

16.68°S, 168.37°E | Summit elev. 833 m

According to the Vanuatu Meteorology and Geo-Hazards Department (VMGD) an overflight of Epi was conducted during the afternoon of 31 January. Steam was observed rising from the ocean’s surface above Epi B, water around the eruption site was discolored, and rafts of pumice were floating on the surface following the currents. Several strands of pumice rafts to the SW, NW, and N of Epi B were visible in 2 February Sentinel B satellite images. During 0700-1030 on 7 February residents observed minor, low-level steaming above Epi B. The intensity of steam emissions varied, increasing and decreasing as new lava was erupted from Epi B. Steaming was again reported by residents starting around 0600 on 8 February. The seismic network recorded elevated seismicity during the previous few days.

Geological summary: A large caldera, with submarine post-caldera cones active in historical time, lies off the eastern coast of Epi Island. Epi Island itself, located slightly west of the main New Hebrides volcanic arc, largely consists of two Quaternary volcanoes, Mount Allombei on the west and Pomare (Tavani Kutali) on the east. Tavani Ruro, which forms an elongated eastern extension of Epi Island across a narrow isthmus, is related to Kuwae caldera to the east. Pomare volcano is the highest point on the island and has three well-preserved subsidiary cones to the east with youthful summit craters. Pomare volcano is truncated on its eastern side by the largely submarine East Epi caldera, which has been the source of all historical eruptions. Three small submarine basaltic and dacitic cones, known as Epi A, Epi B, and Epi C, are located along the northern rim of the breached caldera. Ephemeral islands were formed during eruptions in 1920 and 1953, and the summit of the shallowest cone, Epi B, was at 34 m below sea level at the time of a 2001 survey.

Karangetang, Sangihe Islands

2.781°N, 125.407°E | Summit elev. 1797 m

PVMBG reported a recent increase in activity at Karangetang. During 1-31 January white-and-gray plumes were occasionally seen rising as high as 150 m from Main Crater (the south crater) and incandescence emanated from the lava dome in Crater II (also called North Crater); weather conditions often prevented visual observations. The number of seismic signals indicating avalanches of material began increasing on 18 January, and then increased again in early February. The number of avalanches from Main Crater increased on 4 February, with material traveling as far as 800 m down the Batuawang (S) and Batang (W) drainages and as far as 1 km W down the Beha (W) drainage. During 1-7 February white plumes rose 50-100 m above both craters.

An eruption began during the evening on 8 February at around 1700. PVMBG raised the Alert Level to 3 (on a scale of 1-4) and advised the public to generally stay 2.5 km away from Main Crater with an extension to 3.5 km on the S and SE flanks. Photos showed incandescent material at Main Crater and possible lava fountaining. Incandescent material had also descended the flank in at least two directions, and ash plumes rose along their paths. Eruption plumes rose from the summit.

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

23.37°S, 67.73°W | Summit elev. 5592 m

SERNAGEOMIN reported that a dome-like structure was first visible on the floor of Láscar’s summit crater in 30 January satellite images, after a period of increased seismicity recorded during the previous few days. The structure was 81 m by 93 m in dimension and covered an area of about 5,332 square meters. Seismicity was low during 1-7 February, though levels increased towards the end of the week. The dome was bigger in a 2 February satellite image and covered an area of 6,290 square meters, suggesting an estimated extrusion rate of 308 square meters per day during 30 January-2 February. At 2053 on 4 February a low-level, reddish-colored gas emission rose 200-340 m above the crater rim and drifted SW. 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

7.942°S, 112.95°E | Summit elev. 2329 m

PVMBG reported that activity at Tengger Caldera’s Bromo cone increased at 2114 on 3 February and was characterized by crater incandescence, rumbling sounds, and a strong sulfur dioxide odor. The report noted that sometimes-dense white plumes rose as high as 900 m above the summit during the previous week and through 7 February, and that vegetation on the E caldera wall was yellow and withered. The seismic network recorded continuous tremor and deep and shallow volcanic earthquakes. 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.

Ongoing activity

Ahyi, Mariana Islands (USA)

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

Unrest at Ahyi Seamount continued during 31 January-7 February. Pressure sensors on Wake Island, 2,270 km E of Ahyi Seamount, detected activity during 31 January-1 February and possible activity during 4-6 February. Plumes of discolored water were not identified satellite images, though the image resolutions were too low to detect it. 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 30 January-6 February and crater incandescence was visible nightly. Sulfur dioxide emissions were high at 2,000 tons per day on 30 January. An explosion at 1951 on 3 February produced an ash plume that rose 1.2 km above the crater rim and ejected large blocks as far as 500 m from the crater. 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 1-7 February, characterized by daily emissions of gas, steam, and ash emissions; inclement weather conditions occasionally prevented views. Gas-and-steam emissions were visible rising from the crater on 1 February. Seismicity increased at 0100 on 2 February and was associated with an ash plume that rose 1.3 km above the summit and drifted NW. Later that day emissions containing ash rose as high as 2.5 km and drifted N, NE, and SE. Ashfall was reported in the N part of Parque Nacional Cotopaxi, and in the area of the Tesalia (47 km NNW) and Güitig factories. Ashfall was also reported in the Quito and Mejía regions including in Amaguaña (35 km NNW), Quitumbe (43 km NNW), Conocoto (41 km N), Guamaní, La Ecuatoriana (44 km NNW), Turubamba (43 km NNW), Chillogallo (47 km NNW), La Magdalena, Machachi (24 km NW), Tambillo (32 km NNW), Alóag (28 km NW), and Cutuglahua (35 km NNW). On 3 February ash plumes rose as high as 2.5 km and drifted in multiple directions, and ash fell in Amaguaña, La Armenia, Quitumbe, Conocoto, Guamaní, La Ecuatoriana, Turubamba, Chillogallo, La Magdalena, Machachi, Tambillo, Alóag, Cutuglahua, Uyumbicho (30 km NNW), Aloasí (24 km NW), and El Chaupi (24 km WNW). On 4 February ash plumes rose 1.5 km and drifted NNE and SE. Ashfall was noted in Guamaní, Turubamba, Chillogallo, La Ecuatoriana, Quitumbe, Tambillo, Machachi, Aloasí, Aloag, and Conocoto. On 5 February steam-and-gas emissions with low ash content drifted NW. In the afternoon ash emissions rose 200 m and drifted S. Minor gas emissions were visible during 6-7 February. 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 26 January-2 February. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E) explosions during 28-29 and 31 January and 1 February generated ash plumes that rose as high as 4 km (13,100 ft) a.s.l. and drifted NE. A thermal anomaly was identified in satellite images on 31 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.

Etna, Sicily (Italy)

37.748°N, 14.999°E | Summit elev. 3357 m

INGV reported that the vents at the NE base of Etna’s SE Crater, in the Valle del Leone at about 2,800 m elevation, continued to feed lava flows during 30 January-5 February. The flow rate was highly variable with an increase on 1 February, a gradual decrease overnight during 1-2 February, and a complete cessation on the morning of 2 February. Later, during the afternoon of 2 February, lava again effused from the vent and traveled over pre-existing flows. The effusion rate started to decrease in the afternoon of 4 February and progressively decreased overnight into 5 February. By the afternoon of 5 February, the flows appeared to be cooling.

Intense gas emissions rose from Bocca Nuova Crater while gas emissions at Northeast Crater (NEC) and Voragine were minimal. Activity at Southeast Crater was characterized by fumarolic activity localized along the crater rim and from the May-June 2022 eruptive vent which also occasionally produced flashes of incandescence at night. Occasional diffuse ash emissions were also visible and rapidly dispersed with the wind.

Geological summary: Mount Etna, towering above Catania on the island of Sicily, has one of the world’s longest documented records of volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Fuego, South-Central Guatemala

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

INSIVUMEH reported that 4-12 explosions per hour were recorded at Fuego during 31 January-6 February, generating ash plumes that rose as high as 1.1 km above the crater rim and drifted as far as 20 km SW, WSW, and W. Ashfall was recorded during 2-4 February in areas downwind including Morelia (9 km SW), Panimaché I and II (8 km SW), Santa Sofía (12 km SW), El Porvenir (8 km ENE), San Pedro Yepocapa (8 km NW), and Finca Palo Verde. Daily block avalanches descended various drainages including the Ceniza (SSW), Seca (W), Trinidad (S), Taniluyá (SW), Honda, Las Lajas (SE), and El Jute (ESE), and often reached vegetated areas. Daily shock waves rattled structures in communities around the volcano and rumbling was often heard. Explosions ejected incandescent material 100-200 m above the summit each day. Resuspend ash deposits from high winds during 3-4 February formed “curtains” of ash on the S flank.

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

Great Sitkin, Andreanof Islands (USA)

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

AVO reported that seismicity at Great Sitkin was low during 1-7 February. No activity was observed, though weather clouds 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.

Kerinci, Central Sumatra

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

PVMBG reported that the eruption at Kerinci was ongoing during 1-7 February. An eruptive event was recorded at 0230 on 3 February but was not visually confirmed. White-and-gray ash plumes were visible later that day rising 100 m above the summit and drifting NE and E. At 0646 on 4 February a gray-to-brown ash plume rose 200 m and drifted E and SE. At 0722 on 5 February a dense brown ash plume rose 200 m and drifted NE and E. White-and-brown emissions rose as high as 150 m on 7 February. 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.

Kilauea, Hawaiian Islands (USA)

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

HVO reported that lava continued to erupt on Kilauea’s Halema’uma’u Crater floor during 1-7 February. Activity was concentrated in the E half of the crater in a large, perched lava lake with well-defined levees, covering about 10 hectares. A smaller lake to the W was active in the basin of the 2021-2022 lava lake. Part of the E lake began to crust over on 1 February, forming a crusted isthmus through the center of the lake and two smaller areas of lava on the N and S sides. The lava fountain was located on the S side. Lava in each of the two smaller areas independently circulated in opposite directions from each other. At around 2315 lava fountaining ceased but resumed about 45 minutes later, rising 1-2 m. During 0100-0400 on 2 February lava from the S side flooded across the whole E lake, covering the isthmus, and returning the E lake to the size it was (10 hectares). The W Lake, and two smaller lava ponds in the central and S portions of the crater floor, remained relatively stable, though one of the ponds overflowed. Two small floating islands in the E lake sank during 2-3 February.

During 2-7 February the E lake, the W lake, and the two small lava ponds remained active and stable. The lava fountain continued to be active, though during 4-5 February bursts of activity caused the fountain to double in height. A second small lava fountain was temporarily active near the first fountain during 0300-0700 on 5 February. Starting at around 2100 on 5 February through 0900 on 6 February a large breakout occurred on the N portion of the crater floor covering an area equal to or slightly larger than the E lava lake. A smaller breakout S of the E lake occurred around 0000 on 6 February. The large breakout continued to be active on 6 February but was only weakly active by 7 February. 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.

Lewotolok, Lembata Island

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

PVMBG reported that the eruption at Lewotolok was ongoing during 1-7 February. Incandescence above the crater was visible in a 1 February webcam image. White-and-gray plumes rose as high as 400 m above the crater rim and drifted E and SE on 1 and 5 February. White plumes of variable densities were visible on other days of the week. 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

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

PVMBG reported that the eruption at Marapi continued during 1-7 February. White-and-gray emissions rose as high as 200 m and drifted in various directions during 1-2 and 4 February; white steam plumes were visible on 3 February. White-and-brown plumes rose as high as 400 m on 6 February. Weather clouds sometimes prevented views of the volcano. 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

7.54°S, 110.446°E | Summit elev. 2910 m

BPPTKG reported that the eruption at Merapi continued during 27 January-2 February and seismicity remained at high levels. The SW lava dome produced six lava avalanches that traveled as far as 1.8 km down the SW flank (upstream in the Kali Bebeng drainage); occasional avalanche sounds were recorded. No significant morphological changes to the central and SW lava domes were evident in webcam images. At 0710 on 8 February a pyroclastic flow traveled 1.5 km down the Boyong drainage on the SW flank. Ashfall was reported in areas downwind including Sangup, Musuk, and Mriyan. 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.

Santa Maria, Southwestern Guatemala

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

INSIVUMEH reported that the eruption at Santa María’s Santiaguito lava-dome complex continued during 31 January-6 February. Effusion from Caliente cone fed lava flows that descended the San Isidro and Zanjón Seco drainages on the W and SW flanks; the longest part of the lava flow was 4.4 km on 15 January. Incandescence from the dome and the lava flows was visible nightly. Block-and-ash flows from the dome, and from both the ends and sides of the flows, descended the S, SW, and W flanks almost daily. “Curtains” of ash sometimes rose several hundred meters along their paths. Explosions were generally weak-to-moderate in size and produced gas-and-steam plumes with minor amounts of ash that rose several hundred meters above the complex. Explosions and accompanying rumbling were heard in El Palmar (12 km SSW) during 3-4 February. Ashfall from both explosions and block-and-ash flows was reported in the Monte Claro (S), El Faro, and La Florida (6 km S), Santa Marta, and El Viejo Palmar (11 km S) ranches during 3-4 February.

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

Semeru, Eastern Java

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

PVMBG reported that the eruption at Semeru continued during 1-7 February. White-and-gray ash plumes that were somewhat dense rose 300-700 m above the summit and drifted N, NE, S, and SW. One of the ash plumes, recorded at 0729 on 1 February, was a dense white-and-gray plume that rose 700 m and drifted NE. At 0700 on 2 February an ash plume rose 600 m and drifted NE. On 3 February white-and-gray plumes rose 100-300 m and drifted S, SW, W, and N. An eruptive event at 1242 on 5 February produced a white, gray, and brown ash plume that rose around 1.5 km and drifted N. Webcam images showed a pyroclastic flow descending the SE flank and ash plumes rising its path. 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.

Semisopochnoi, Aleutian Islands (USA)

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

AVO reported that eruptive activity at Semisopochnoi’s Mount Young continued during 1-7 February. Seismicity was elevated and daily weak tremor was recorded. Minor steam emissions were visible in webcam images during 3-7 February. 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.

Sheveluch, Central Kamchatka (Russia)

56.653°N, 161.36°E | Summit elev. 3283 m

KVERT reported that the ongoing eruption at Sheveluch during 26 January-2 February was generally characterized by explosions, hot avalanches, lava-dome extrusion, and strong fumarolic activity. A persistent thermal anomaly was identified daily in satellite images, and minor ash plumes from explosions and lava-dome collapses drifted 70 km NE on 27 and 31 January and 2 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)

29.638°N, 129.714°E | Summit elev. 796 m

JMA reported that the eruption at Suwanosejima’s Ontake Crater continued during 30 January-6 February with a total of seven 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 and rumbling noises were 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.


Smithsonian / US Geological Survey Weekly Volcanic Activity Report – February 1 – 7, 2023 – Managing Editor: Sally Kuhn Sennert


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