The Weekly Volcanic Activity Report: February 22 - 28, 2023

New activity/unrest was reported for 5 volcanoes from February 22 to 28, 2023. During the same period, ongoing activity was reported for 18 volcanoes.

New activity/unrest: Aira, Kyushu (Japan) | Aniakchak, Alaska Peninsula, Alaska | Epi, Vanuatu | Karangetang, Sangihe Islands | Trident, Alaska.

New activity/unrest

Aira, Kyushu (Japan)

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

JMA reported ongoing eruptive activity at Minamidake Crater and Showa Crater (at Aira Caldera’s Sakurajima volcano) during 13-20 February and incandescence at both craters was visible nightly. Very small eruptive events occurred at Showa Crater. Three explosions and three or four eruptive events were recorded at Minamidake Crater during the week. Volcanic plumes rose as high as 1.5 km above the Minamidake Crater rim and large blocks were ejected 600-900 m from the vent. During an overflight on 21 February scientists observed white plumes rising from a vent on the N inner crater wall at Showa Crater and they noted more voluminous emissions compared to the 12 October 2022 overflight. No notable changes at Minamidake Crater were observed. At 1230 on 26 February an eruptive event at Minamidake Crater produced a plume that rose 1.2 km above the crater rim. The Alert Level remained at 3 (on a 5-level scale), and residents were warned to stay 2 km away from both craters.

Geological summary: The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan’s most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the 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.

Aniakchak, Alaska Peninsula, Alaska

56.88°N, 158.17°W | Summit elev. 1341 m

On 22 February AVO raised the Aviation Color Code for Aniakchak to Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level to Advisory (the second lowest level on a four-level scale) due to a recent increase in the number of earthquakes and a shallowing of those events. Background seismicity was generally characterized as deep (more than 15 km below sea level) long-period events occurring at a rate of about four events per month. Beginning in October 2022 the rate increased, and the earthquakes were located at depths less than 9 km below sea level. The earthquake rate further increased on 31 January and was sustained with dozens of earthquakes detected per day, including a M 3.7 earthquake recorded on 17 February.

Elevated seismicity continued during 23-27 February at a variable rate. Dozens of earthquakes were recorded daily during 22-26 February, though more than one hundred small earthquakes (not all locatable) were detected during 24-25 February. Small earthquakes occurred at the rate of about 10 per hour during 26-28 February. AVO noted that there was no indication that an eruption of Aniakchak was imminent, or that one will occur. Increases in seismic activity have been detected previously at other similar volcanoes, with no subsequent eruptions.

Geological summary: One of the most dramatic calderas of the Aleutian arc, the 10-km-wide Aniakchak caldera formed around 3,400 years ago during a voluminous eruption in which pyroclastic flows traveled more than 50 km N to the Bering Sea and also reached the Pacific Ocean to the south. At least 40 explosive eruptions have been documented during the past 10,000 years, making it the most active volcano of the eastern Aleutian arc. A dominantly andesitic pre-caldera volcano was constructed above basement Mesozoic and Tertiary sedimentary rocks that are exposed in the caldera walls to elevations of about 610 m. The ice-free caldera floor contains many pyroclastic cones, tuff cones, maars, and lava domes. Surprise Lake on the NE side drains through The Gates, a steep-walled breach on the east side of the 1-km-high caldera rim that was the site of catastrophic draining of a once larger lake about 1850 years BP. Vent Mountain and Half Cone are two long-lived vents on the south-central and NW caldera floor, respectively. The first and only confirmed historical eruption took place in 1931 from vents on the west and SW caldera floor.

Epi, Vanuatu

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

On 23 February the Vanuatu Meteorology and Geo-Hazards Department (VMGD) reported that minor unrest continued at Epi. Seismicity was sustained though there was only minor manifestation at the water’s surface; steaming at the surface lasting only a few hours at most was occasionally observed. The Alert Level remained at 1 (on a scale of 0-5) and the public was warned to stay outside of the Danger Zone, defined as a 2-km radius around the active vent.

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

According to PVMBG the eruption at Karangetang’s Main Crater (S crater) continued during 22-28 February. Nighttime webcam images posted with daily reports showed incandescent lava flows descending the flanks, though images from 0054 on 26 February and 0026 on 1 March showed only minor incandescence near the summit. The Darwin VAAC reported that during 22-23 February ash plume rose to an altitude of 2.1 km (7,000 ft) a.s.l. and drifted SE based on analyses of satellite imagery and weather models. The Alert Level remained at 3 (on a scale of 1-4) and the public were 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.

Trident, Alaska

58.236°N, 155.1°W | Summit elev. 1864 m

An earthquake swarm at Trident began on 24 August 2022 and within about four days the seismic network began detecting episodes of weak seismic tremor and low frequency earthquakes. The events were initially located at depths around 25 km, but then they progressively shallowed to around 5 km by 28 August. AVO raised the Aviation Color Code for Trident to Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level to Advisory (the second lowest level on a four-level scale) on 29 September due to an ongoing seismic swarm. AVO attributed the swarm to moving magma or magmatic fluids and noted that seismic swarms had previously been recorded with no subsequent eruptions. The swarm subsided and on 19 October 2022 AVO lowered both the Aviation Color Code and the Volcano Alert Level were lowered to Green and Normal, respectively, and noted that tremor had been absent since 30 September.

Beginning on 1 January 2023 seismicity again increased with earthquakes occurring at an average rate of about ten per day at depths less than 6 km. The elevated seismicity was sustained, prompting AVO raised the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory on 22 February. Dozens of small earthquakes were recorded daily during 23-28 February; the largest event, a M4, was recorded during the morning of 24 February. Trident last erupted during 1953-1974.

Geological summary: The Trident stratovolcano cluster was named for the three prominent peaks that were the most visible features at the summit prior to 1953. The andesitic-dacitic group consists of four overlapping stratovolcanoes and numerous flank lava domes, including Falling Mountain and Mt. Cerberus on the far west flank. The summit complex is located 3-5 km SE of Novarupta volcano, and merges along a ridge to the NE with Katmai. The three oldest Trident volcanoes are glaciated and Pleistocene in age, while the youngest, Southwest Trident, was formed during historical time. Eruptions migrated through time from the NE to the SW. In 1953 a new lava dome began growing on the SW flank of Trident I volcano. A series of thick andesitic lava flows were erupted between 1953 and 1968, forming a cone with 400-800 m of local relief. Periodic explosions took place until 1974, and the current summit contains a 350-m-wide crater. Some of the distal lava flows from West Trident stratovolcano collapsed into the Novarupta vent during its 1912 eruption.

Ongoing activity

Ambae, Vanuatu

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

On 23 February the Vanuatu Meteorology and Geo-Hazards Department (VMGD) reported that the cone in Ambae’s Lake Voui continued to produce emissions consisting of steam, volcanic gases, and possibly occasional ash that drifted downwind. Volcanic earthquakes were recorded by the seismic network. The Alert Level remained at 2 (on a scale of 0-5) and the public was warned to stay outside of the Danger Zone, defined as a 2-km radius around the active vents in Lake Voui, and away from drainages during heavy rains.

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

Bezymianny, Central Kamchatka (Russia)

55.972°N, 160.595°E | Summit elev. 2882 m

KVERT reported that during 17-23 February a daily thermal anomaly over Bezymianny was identified in satellite images. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale). Dates are based on UTC times; specific events are in local time where noted.

Geological summary: The modern Bezymianny, much smaller than its massive neighbors Kamen and Kliuchevskoi on the Kamchatka Peninsula, was formed about 4,700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7,000 years ago. Three periods of intensified activity have occurred during the past 3,000 years. The latest period, which was preceded by a 1,000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large open crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Cotopaxi, Ecuador

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

IG reported that the eruption at Cotopaxi continued during 22-28 February, characterized by almost daily emissions of gas, steam, and ash; inclement weather conditions occasionally prevented views. Gas-and-steam emissions rose 500 m above the crater rim and drifted W during 21-22 February. Weather clouds prevented visual observations of the volcano during most of 23 February, though by the late afternoon and into the next morning steam emissions with low ash content were seen rising 500 m and drifted SW. Gas-and-steam plumes rose 500 m and drifted W on 25 February. Several emissions of gas, steam, and ash rose as high as 2.4 km and drifted SE on 26 February. During periodic breaks in weather clouds, continuous emissions of gas, steam, and ash sere seen rising as high as 1.5 km and drifting E and SE. Minor amounts of ash fell in the province of Pichincha in Rumiñahui (61 km N), Rumipamba Vallecito, Conocoto (41 km N), El Pedregal (60 km N), Guamaní (42 km NNW), Quitumbe (41 km NNW), La Ecuatoriana (44 km NNW), Chillogallo (47 km NNW), Urubamba (Santo Tomas, 40 km NNW), La Magdalena (Barrio Nuevo, Villaflora, 48 km NNW) and San Bartolo. At 1430 on 28 February an ash plume rose 500 m and drifted SW. 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 16-23 February. A thermal anomaly was identified in satellite images on 21 February. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E) explosions on 22 February generated ash plumes that rose as high as 3 km (10,000 ft) a.s.l. and drifted E. 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.

Fuego, South-Central Guatemala

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

INSIVUMEH reported that 4-10 explosions per hour were recorded at Fuego during 22-28 February, generating ash plumes that rose as high as 1.1 km above the crater rim and drifted as far as 30 km NW, W, and SW. Weather clouds often prevented visual observations on 22 February. Explosions ejected incandescent material 100-400 m above the summit each day, and daily shock waves rattled structures in communities around the volcano. 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. Ashfall was recorded almost daily in areas downwind including Morelia (9 km SW), Panimaché I and II (8 km SW), Santa Sofía (12 km SW), Sangre de Cristo (8 km WSW), El Porvenir (8 km ENE), San Pedro Yepocapa (8 km NW), Finca la Asunción, Finca Palo Verde, and La Soledad (11 km N).

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 slow lava effusion at Great Sitkin was confirmed by recent satellite images. A radar image from 19 February showed advancement of the E lobe of the flow field. Additionally, a smaller lobe to the S was advancing towards the crater rim where lava previously spilled down the SW flank in 2021-2022. Lava effusion in the summit crater was visible in 24 and 26 February satellite images. Seismicity was very low 22-28 February with a few local earthquakes detected during 22-23 and 24-25 February. Weather cloud cover sometimes prevented webcam and satellite views. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

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 22-28 February. Weather clouds often prevented visual observations of the volcano. White-and-gray ash plumes rose 50-150 m above the crater rim and drifted W and E on 26 February. The next day white-and-brown ash plumes rose as high as 150 m and drifted W. 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 the eruption on the floor of Kilauea’s Halema’uma’u Crater continued during 22-28 February but at a decreased rate. The E and central vents were not erupting. The western lake in the basin of the 2021-2022 lava lake remained active but with weak lava flows. A small amount of lava is circulating within the lake with intermittent crustal overturns; the lake is mostly crusted over. 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.

Merapi, Central Java

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

BPPTKG reported that the eruption at Merapi (on Java) continued during 17-23 February and seismicity remained at high levels. The SW lava dome produced 11 lava avalanches that traveled as far as 1.7 km down the SW flank (upstream in the Bebeng and Boyong drainages). No significant morphological changes to the central and SW lava domes were evident in webcam images. An avalanche from the weathered and altered 1998 lava wall was visible in webcam images on 10 February. 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.

Nyamulagira, DR Congo

1.408°S, 29.2°E | Summit elev. 3058 m

The Observatoire Volcanologique de Goma (OVG) reported that the lava lake on Nyamulagira’s crater floor continued to be active during 13-19 February. Seismicity was generally low, characterized by a few long-period earthquakes located up to 15 km deep along the large fracture connecting the Nyamuragira and Nyiragongo. High concentrations of carbon dioxide were measured in the Mazuku areas, and in an area to the W of a camp in the Lac Vert district in Bulengo; OVG warned residents to stay away from those areas.

Geological summary: Africa’s most active volcano, Nyamulagira (also known as Nyamuragira), is a massive high-potassium basaltic shield about 25 km N of Lake Kivu and 15 km NE of the steep-sided Nyiragongo volcano. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Documented eruptions have occurred within the summit caldera, as well as from the numerous flank fissures and cinder cones. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Recent lava flows extend down the flanks more than 30 km from the summit as far as Lake Kivu; extensive lava flows from this volcano have covered 1,500 km2 of the western branch of the East African Rift.

Nyiragongo, DR Congo

1.52°S, 29.25°E | Summit elev. 3470 m

The Observatoire Volcanologique de Goma (OVG) reported that the lava lake on Nyiragongo’s crater floor continued to be active during 13-19 February; faint glow emanated from the crater on 15 February. Seismicity was generally low, characterized by a few long-period earthquakes located up to 15 km deep along the large fracture connecting the Nyamuragira and Nyiragongo. A seismic station near the volcano registered a minor increase in the intensity of signals on 17 February. High concentrations of carbon dioxide were measured in the Mazuku areas, and in an area to the W of a camp in the Lac Vert district in Bulengo; OVG warned residents to stay away from those areas. The Alert Level remained at Yellow.

Geological summary: One of Africa’s most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes of a stratovolcano contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

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 22-28 February. Effusion from Caliente dome fed lava flows that slowly descended the San Isidro and Zanjón Seco drainages on the W and SW flanks. 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. Ash plumes from the avalanches and from occasional explosions at the summit rose a few hundred meters high; during 22-23 February ash plumes rose 700 m above the summit and drifted WNW.

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 22-28 February. Dense white-and-gray ash plumes rose 300-1,000 m above the summit and drifted N, NE, and E on 22 February. Weather conditions mostly prevented visual observations during the rest of the week, though at 0705 on 23 February a dense white-and-gray ash plume was seen rising to 1 km and drifting SE. The seismic network recorded an eruptive event at 0404 on 26 February; no emissions were observed. 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.

Sheveluch, Central Kamchatka (Russia)

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

KVERT reported that the ongoing eruption at Sheveluch was generally characterized by explosions, hot avalanches, lava-dome extrusion, and strong fumarolic activity. A daily thermal anomaly was identified in satellite images during 16-23 February. During a field visit to the volcano on 25 February Kamchatka Volcano Station scientists observed and photographed the dome and saw incandescent debris avalanches on the originating at the dome’s summit. 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.

Stromboli, Aeolian Islands (Italy)

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

INGV reported that both explosive and effusive activity at Stromboli occurred during 20-26 February at two vents in Area N, within the upper part of the Sciara del Fuoco, and at least two vents in the Area C-S (South-Central Crater area) in the crater terrace area. Explosions at vents N1 and N2 in Area N were variable in intensity and ejected coarse material (bombs and lapilli) 80-150 m at a rate of 2-7 explosions per hour. Spattering occasionally occurred at N2 vents during 20-24 February and was sometimes intense. Explosive activity at S2 in the Central-South area (CS) ejected fine-to-coarse material as high as 150 m above the vent at a rate of 1-7 explosions per hour. At around 0700 on 27 February lava overflowed vents in Area N and produced lava flows and at around midnight intense spattering in the same area was visible. Spattering continued at least through 2100 on 28 February; the lava flows were cooling, though some areas were hot due to accumulated material.

Geological summary: Spectacular incandescent nighttime explosions at Stromboli have long attracted visitors to the “Lighthouse of the Mediterranean” in the NE Aeolian Islands. This volcano has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent scarp that formed about 5,000 years ago due to a series of slope failures which extends to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Suwanosejima, Ryukyu Islands (Japan)

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

JMA reported that the eruption at Suwanosejima’s Ontake Crater continued during 20-27 February. A total of 20 explosions were recorded, sending ash plumes as high as 2 km above the crater rim and ejecting large blocks as far as 400 m from the vent. Crater incandescence was visible at night. 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.

Villarrica, Central Chile

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

The eruption at Villarrica was ongoing during 22-28 February. Low-intensity gas emissions rose from the crater on 22 February. Long-period earthquakes recorded at 1056 and 1301 on 27 February were associated with ash plumes that rose 300 m above the crater rim. Several additional minor ash emissions were visible during 1056-1320. The Alert Level remained at Yellow (the second lowest level on a four-color scale) according to SERNAGEOMIN. 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.

Yasur, Vanuatu

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

On 23 February the Vanuatu Meteorology and Geohazards Department (VMGD) reported that activity at Yasur continued at a high level of “major unrest,” as defined by the Alert Level 2 status (the middle level on a scale of 0-4). Recent observations confirmed that low-to-moderate explosions continued, ejecting bombs that landed back into the crater and producing ash, gas, and steam emissions. The larger explosions occasionally ejected material outside of the crater. The public was reminded to not enter the restricted area within 600 m around the cone, defined by Danger Zone A on the hazard map.

Geological summary: Yasur has exhibited essentially continuous Strombolian and Vulcanian activity at least since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island in Vanuatu, this pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide open feature associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

References:

Smithsonian / US Geological Survey Weekly Volcanic Activity Report, February 22 – 28, 2023 – Managing Editor: Sally Kuhn Sennert

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