The Weekly Volcanic Activity Report: March 22 – 28, 2023

the weekly volcanic activity report

New activity/unrest was reported for 4 volcanoes from March 222 – 28, 2023. During the same period, ongoing activity was reported for 18.

New activity/unrest: Asamayama, Honshu (Japan) | Bezymianny, Central Kamchatka (Russia) | Kita-Ioto, Volcano Islands | Ulawun, New Britain (Papua New Guinea).

Ongoing activity: Ahyi, Mariana Islands (USA) | Aira, Kyushu (Japan) | Asosan, Kyushu (Japan) | Cotopaxi, Ecuador | Ebeko, Paramushir Island (Russia) | Fuego, South-Central Guatemala | Great Sitkin, Andreanof Islands (USA) | Karangetang, Sangihe Islands | Krakatau, Sunda Strait | Lewotolok, Lembata Island | Merapi, Central Java | Santa Maria, Southwestern Guatemala | Semeru, Eastern Java | Semisopochnoi, Aleutian Islands (USA) | Sheveluch, Central Kamchatka (Russia) | Stromboli, Aeolian Islands (Italy) | Suwanosejima, Ryukyu Islands (Japan) | Villarrica, Central Chile.

New activity/unrest

Asamayama, Honshu (Japan)

36.406°N, 138.523°E | Summit elev. 2568 m

JMA reported that inflation on Asamayama’s W flank began to be detected on 15 March, and the number of shallow volcanic earthquakes increased on 21 March. On 22 March JMA raised the Alert Level to 2 (on a scale of 1-5) and warned the public that very small eruptions may impact areas within 500 m of the crater.

Geological summary: Asamayama, Honshu’s most active volcano, overlooks the resort town of Karuizawa, 140 km NW of Tokyo. The volcano is located at the junction of the Izu-Marianas and NE Japan volcanic arcs. The modern Maekake cone forms the summit and is situated east of the remnant of an older andesitic volcano, Kurofuyama, which was destroyed by a late-Pleistocene landslide about 20,000 years before present (BP). Growth of a dacitic shield volcano was accompanied by pumiceous pyroclastic flows, the largest of which occurred about 14,000-11,000 BP, and by growth of the Ko-Asamayama lava dome on the east flank. Maekake, capped by the Kamayama pyroclastic cone that forms the present summit, is probably only a few thousand years old and has observed activity dating back at least to the 11th century CE. Maekake has had several major Plinian eruptions, the last two of which occurred in 1108 (Asamayama’s largest Holocene eruption) and 1783 CE.

Bezymianny, Central Kamchatka (Russia)

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

KVERT reported that at 1825 on 29 March an ash plume from Bezymianny rose as high as 6 km (19,700 ft) a.s.l. and drifted NE. The Aviation Color Code was raised to Orange (the second highest level on a four-color scale).

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.

Kita-Ioto, Volcano Islands

25.424°N, 141.284°E | Summit elev. 792 m

JMA reported that a submarine eruption occurred at Funka Asane, a submarine vent 4-5 km NW of Kita-Ioto, at around 1800 on 27 March based on satellite images.

Geological summary: No historical eruptions have occurred from the deeply eroded Kita-Ioto stratovolcano, which forms a steep-sided basaltic cone rising about 800 m above the sea. However, eruptions have been recorded since the 18th century from Funka Asane, a submarine vent 4-5 km NW of the island. Kita-Ioto is the northernmost of the Kazan Retto (Volcano Islands), located in the middle of the Izu-Marianas arc.

Ulawun, New Britain (Papua New Guinea)

5.05°S, 151.33°E | Summit elev. 2334 m

RVO reported a short eruption at Ulawun, during 0408-0425 on 28 March, based on seismic data. A local volcano observer reported minor ashfall in areas to the NW including Ubili village, and the Ulamona Mission, Saltamana, and Ibana Village Oil Palm areas. According to the Darwin VAAC at 0600 an ash plume was visible in a satellite image drifting W at 3.4 km (11,000 ft) a.s.l.; the plume had dissipated by 1000.

Geological summary: The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea’s most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Ongoing activity

Ahyi, Mariana Islands (USA)

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

Unrest at Ahyi Seamount continued during 21-28 March. A plume of discolored water was observed in high-resolution satellite images acquired on 21 and 22 March. No observations indicated that activity has breached the ocean surface. One possible underwater explosion was detected by pressure sensors on Wake Island, 2,270 km E, during 26-27 March. 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 20-27 March, with crater incandescence visible nightly. Two explosions recorded on 21 and 22 March produced ash plumes that rose 1.2 km above the crater rim and ejected large blocks 1-1.3 km from the vent. Two eruptive events during 24-27 March produced volcanic plumes that rose 1.1 km. 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.

Asosan, Kyushu (Japan)

32.884°N, 131.104°E | Summit elev. 1592 m

The amplitude of volcanic tremor signals at Asosan increased in December 2022, and then further intensified on 30 January, prompting JMA to raise the Alert Level to 2 (on a scale of 1-5) and warn the public to stay at least 1 km away from the crater. The amplitude fluctuated at high levels for a few weeks, and then decreased on 19 February and again on 14 March. Daily sulfur dioxide emissions had exceeded 1,000 tons per day starting in December 2022; emissions declined to below that threshold by mid-January and remained at lower levels. At 1100 on 23 March the Alert Level was lowered to 1.

Geological summary: The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan’s most active volcanoes. It was the location of Japan’s first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu’s most popular tourist destinations.

Cotopaxi, Ecuador

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

IG reported that eruptive activity at Cotopaxi was ongoing during 22-28 March. Gas-and-steam emissions were visible during 21-24 March rising as high as 1 km above the crater rim and drifting E; weather clouds prevented views of the volcano on 23 March. Ash emissions rose 500-800 m above the crater rim and drifted SW and SE during 25-26 March. Ash plumes rose 1.1 km above the crater rim and rifted SE, NE, and NW on 27 March. Ash plumes rose as high as 2 km above the crater rim on 28 March and drifted NW, causing minor ashfall in the Machachi parish on the N flank, in Parque Nacional Cotopaxi. 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 March. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E) explosions during 18 and 21-22 March generated ash plumes that rose as high as 2.8 km (9,200 ft) a.s.l. and drifted NE and E. Ash plumes were identified in satellite images drifting 76 km E during 22-23 March. 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 recorded at Fuego during 22-28 March generated ash plumes that rose as high as 1.1 km above the crater rim and drifted at least 25 km in multiple directions. Ashfall was reported almost daily in areas downwind including Morelia (9 km SW), Panimaché I and II (8 km SW), Santa Sofía (12 km SW), Finca Palo Verde, La Rochela, Sangre de Cristo (8 km WSW), El Porvenir (8 km ENE), Finca Asunción, Aldeas, and San Pedro Yepocapa (8 km NW). Ashfall was not confirmed during 23-24 March Explosions ejected incandescent material up to 200 m above the crater. Daily block avalanches descended the flanks in various directions towards the Ceniza (SSW), Santa Teresa, Seca (W), Taniluya (SW), Trinidad (S), Las Lajas (SE), Honda (E), and El Jute (ESE) ravines, sometimes reaching vegetated areas. Shockwaves caused structures to shake in communities around the volcano.

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 a 23 March satellite image confirmed that lava continued to slowly erupt at the summit of Great Sitkin, producing a thick lava flow. The flow advanced to the E and likely continued to be fed through 28 March. 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 color 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.

Karangetang, Sangihe Islands

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

Webcam images of Karangetang posted in PVMBG daily reports during 23-28 March showed incandescent material at the summit Main Crater (S crater) and on the flanks. 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.

Krakatau, Sunda Strait

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

PVMBG reported that the eruption at Anak Krakatau continued during 22-29 March and multiple ash plumes were visible rising from the vent during 28-29 March. Ash plumes recorded at 0412, 0743, 1221, 1513, and 1935 on 28 March were dense and dark gray and rose as high has 2.5 km above the summit. The ash plumes drifted NE and W. Webcam images captured incandescent material being ejected above the vent at 0415 and around the summit area at 2003. At 0041 on 29 March a dense dark ash plume rose 600 m and drifted W. A webcam image from 0047 showed incandescent material at the vent. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay at least 5 km away from the crater.

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

Lewotolok, Lembata Island

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

PVMBG reported that the eruption at Lewotolok was ongoing during 22-28 March. Daily ash plumes, sometimes dense, were visible rising as high as 800 m above the summit and drifting mainly W and NW. VONAs issued on most days described dense gray or gray-to-white ash plumes at 0517, 1623, and 2016 on 22 March, at 1744 on 24 March, at 0103 on 26 March, at 0845 and 1604 on 27 March, and at 0538 on 28 March. A webcam image at 2220 on 22 March showed incandescent material around the summit area and being ejected above the summit. Another webcam images at 0103 on 26 March captured a Strombolian explosion at the summit. The Alert Level remained at 2 (on a scale of 1-4) and the public was warned to stay 2 km away from the summit crater.

Geological summary: The Lewotolok (or Lewotolo) stratovolcano occupies the eastern end of an elongated peninsula extending north into the Flores Sea, connected to Lembata (formerly Lomblen) Island by a narrow isthmus. It is symmetrical when viewed from the north and east. A small cone with a 130-m-wide crater constructed at the SE side of a larger crater forms the volcano’s high point. Many lava flows have reached the coastline. Eruptions recorded since 1660 have consisted of explosive activity from the summit crater.

Merapi, Central Java

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

BPPTKG reported that the eruption at Merapi (on Java) continued during 17-23 March and seismicity remained at high levels. The SW lava dome produced 160 lava avalanches that traveled as far as 1.8 km down the SW flank (upstream in the Bebeng and Boyong drainages). Two pyroclastic flows traveled 1.3 km down the SW flank, upstream of the Bebeng/Krasak drainage. Morphological changes to the SW lava dome were evident in webcam images due to continuing collapses of material, though the volume remained unchanged at 1,686,200 cubic meters. 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 Santa Maria-Santiaguito lava dome complex remained highly active during 22-28 March. On most days steady degassing from the dome produced gas plumes that drifted S and SW. Incandescence from the dome and along lava flow margins was visible most nights or early mornings. The lava flow that extended 4.3 km down the SW flank in the San Isidro and Zanjón Seco drainages was active. Activity from the lava dome included explosions and avalanches, and small pyroclastic flows during 22-23 March. Daily weak to moderate explosions generated ash plumes up to 1 km above the crater that drifted SW and W, and avalanches traveled down multiple flanks.

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 March, with daily emissions of dense ash plumes. At 0605 and 0810 on 23 March gray and white-to-gray ash plumes rose 800 m above the summit and drifted NW and SW. At 0548 on 24 March a white-to-gray ash plume rose 1 km and drifted S. On 25 March at 0600 a white-to-gray ash plume rose 500 m and drifted S and SW, at 0705 a gray ash plume rose 700 m and drifted SE and S, and at 0738 a gray-to-brown ash plume rose 1.2 km and drifted SE. At 0619 and 0659 on 26 March dense white-to-gray ash plumes rose 1 km and drifted SE. At 0756 on 27 March a white-to-gray ash plume rose 800 m and drifted S. At 0130 on 28 March a dense gray ash plume drifted NE and at 0759 a somewhat dense white-to-gray plume rose 800 m and drifted N. 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.

Semisopochnoi, Aleutian Islands (USA)

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

AVO reported that low-level unrest continued at Semisopochnoi during 22-28 March. Steam emissions from the N crater of Mount Young were visible during 22 and 26-27 March. No explosive activity was detected in seismic or infrasound 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 color on a four-color 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 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 March. 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 March, though inclement weather conditions prevented views on most days. Activity was centered at three vents in Area N within the upper part of the Sciara del Fuoco, and from four vents in Area C-S (South-Central Crater) on the crater terrace. Explosions at two vents in the N1 crater and one vent in the N2 crater in Area N were low to medium intensity and ejected coarse material (bombs and lapilli) 80-150 m at a rate of 6-12 explosions per hour. Explosive activity at three active vents at the S2 sector in Area C-S ejected coarse material generally as high as 150 m above the vent at a rate of 5-7 explosions per hour; material was ejected as high as 300 m on 23 March. Sector C was characterized by occasional low-intensity explosive activity through the week and intense spattering on 22 March. No activity was recorded at sector S1. A strong explosion at 1549 on 25 March at Area C-S and was followed by two minor explosions; the sequence lasted about three minutes.

A lava overflow event at one of the N1 vents began at 2242 on 23 March and was preceded by spattering activity in Area N. After about an hour lava flowed along the Sciara del Fuoco in the ravine that had formed in October 2022. The flow rate notably increased during 0200-0400 on 26 March and caused avalanches of material from collapses at the advancing flow front. By that afternoon the flow was cooling down and no longer being fed. It was unknown due to weather conditions if material reached the coastline.

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 March. Eruptive activity including three explosions sent ash plumes as high as 2 km above the rim and ejecting large blocks as far as 300 m from the vent. Crater incandescence was visible 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.

Villarrica, Central Chile

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

The eruption at Villarrica was ongoing during 21-28 March. POVI reported that on 21 March Strombolian explosions ejected material 100 m above the crater rim. SERNAGEOMIN reported that at 0551 on 24 March a long-period earthquake was associated with low-intensity crater incandescence. According to POVI a cone with a vent that was about 13 m in diameter had formed on the crater floor and was visible during a recent overflight. Sometimes lava fountains rose over 100 m. At 2249 on 26 March Strombolian explosions ejected incandescent material more than 110 m above the crater rim. The Volcanic Alert level remained at Yellow (the second highest on a four-level scale) according to SERNAGEOMIN. SENAPRED maintained the Alert Level at Yellow (the middle level on a three-color scale) for the communities of Villarrica, Pucón (16 km N), Curarrehue, and Panguipulli, and SINAPRED maintained an exclusion zone of 1 km from the crater.

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

References:

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

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