The Weekly Volcanic Activity Report: March 15 - 21, 2023

New activity/unrest was reported for 5 volcanoes from March 15 – 21, 2023. During the same period, ongoing activity was reported for 21 volcanoes.

New activity/unrest: Merapi, Central Java | Nyamulagira, DR Congo | Semisopochnoi, Aleutian Islands (USA) | Takawangha, Andreanof Islands (USA) | Tanaga, Andreanof Islands (USA).

New activity/unrest

Merapi, Central Java

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

BPPTKG summarized the eruption at Merapi (on Java) during 10-16 March, including the collapses at the SW lava dome that began on 11 March and continued through the week. A total of 68 pyroclastic flows traveled as far as 4 km down the Bebeng and Krasak drainages on the SW flank. The largest pyroclastic flows were recorded during 11-12 March, which caused ashfall of varying intensity in areas to the W, NW, and N including in Dukun District, Sawangan, Magelang Regency; Magelang City; Selo District, Boyolali Regency; Ambarawa, Jambu, Sumowono, Pringapus, Banyubiru, Bawen Districts, Semarang Regency. Morphological changes to the SW lava domes were evident in webcam and drone images. The volume of the dome before 11 March was 2,759,100 cubic meters and by 13 March the dome volume had decreased to 1,686,200 cubic meters, with an estimate volume loss of 1,072,800 cubic meters. The volume of the summit dome remained unchanged and was estimated at 2,312,100 cubic meters.

According to the Darwin VAAC ash plumes were visible in webcam images on 15 and 17 March rising as high as 1.2 km above the summit and drifting S and W, respectively. On both days weather conditions prevented satellite image views. During 16-20 March BPPTKG reported 14-38 daily counts of lava avalanches with material descending the SW flank as far as 1.8 km. Daily counts were not available for 17 March, though incandescent avalanches were visible in webcam footage; rainy weather sometimes prevented visual observations. 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

An 18 March satellite image of Nyamulagira showed a large thermal anomaly, possibly 600 m wide, in the summit crater, indicating that the eruption that had begun on 14 March was continuing.

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 13 km NNW 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.

Semisopochnoi, Aleutian Islands (USA)

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

AVO reported that low-level ash emissions from the N crater of Semisopochnoi’s Mount Young were observed in several web camera images during 18-19 March. Small explosions and volcanic tremor had also resumed. Ash emissions were not detected in satellite images, though on 18 March a robust steam-and-gas plume was visible drifting 150 km from the N crater. AVO raised the Volcano Alert Level to Watch (the second highest level on a four-level scale) and the Aviation Color Code to Orange (the second highest color on a four-color scale) on 19 March. Low-level seismicity continued during 20-21 March and one small explosion was detected in seismic and infrasound data. Clouds obscured webcam and satellite views.

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.

Takawangha, Andreanof Islands (USA)

51.873°N, 178.006°W | Summit elev. 1449 m

AVO reported that earthquake activity near Takawangha had decreased in both rate and magnitude from the peak of the swarm recorded during 9-11 March. More than 800 earthquakes, including multiple M2 and above events, were detected beneath Tanaga Island at depths less than 9 km below sea level during 11-17 March. The decline in activity decreased the potential for an eruption, so AVO lowered the Volcano Alert Level to Advisory (the second lowest level on a four-level scale) and the Aviation Color Code to Yellow (the second lowest color on a four-color scale) on 16 March. The Volcano Alert Level and Aviation Color Code for Tanaga (8 km W) were also lowered to the same level. Several M 2 and higher earthquakes were detected during 17-18 March, in addition to numerous smaller events. Earthquake activity persisted through 20 March.

Geological summary: Takawangha is a youthful volcano with an ice-filled caldera on northern Tanaga Island, near the western end of the Andreanof Islands. It lies across a saddle from historically active Tanaga volcano to the west; older, deeply eroded volcanoes lie adjacent to the east. The summit of the dominantly basaltic to basaltic-andesite volcano is largely ice covered, with the exception of five Holocene craters that during the last few thousand years produced explosive eruptions and lava flows that reached the lower flanks. No historical eruptions are known, although radiocarbon dating indicates explosive eruptions have occurred within the past several hundred years.

Tanaga, Andreanof Islands (USA)

51.885°N, 178.146°W | Summit elev. 1806 m

AVO reported that earthquake activity near Tanaga had decreased in both rate and magnitude from the peak of the swarm recorded during 9-11 March. More than 800 earthquakes, including multiple M2 and above events, were detected beneath Tanaga Island at depths less than 9 km below sea level during 11-17 March. The decline in activity decreased the potential for an eruption, so AVO lowered the Volcano Alert Level to Advisory (the second lowest level on a four-level scale) and the Aviation Color Code to Yellow (the second lowest color on a four-color scale) on 16 March. The Volcano Alert Level and Aviation Color Code for Takawangha (8 km E) were also lowered to the same level. Several M 2 and higher earthquakes were detected during 17-18 March, in addition to numerous smaller events. Earthquake activity persisted through 20 March.

Geological summary: Tanaga volcano, the second largest volcanic center of the central Aleutians, is the central and highest of three youthful stratovolcanoes oriented along a roughly E-W line at the NW tip of Tanaga Island. Ridges to the east and south represent the rim of an arcuate caldera formed by collapse of an ancestral edifice during the Pleistocene. Most Holocene eruptions originated from Tanaga volcano itself, which consists of two large cones, the western of which is the highest, constructed within a caldera whose 400-m-high rim is prominent to the SE. At the westernmost end of the complex is conical Sajaka, a double cone that may be the youngest of the three volcanoes. Sajaka One volcano collapsed during the late Holocene, producing a debris avalanche that swept into the sea, after which the Sajaka Two cone was constructed within the collapse scarp.

Ongoing activity

Ahyi, Mariana Islands (USA)

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

Unrest at Ahyi Seamount continued during 15-21 March. A total of three short (~30 seconds) hydroacoustic detections from the direction of Ahyi were detected by pressure sensors on Wake Island, 2,270 km E, during 17-19 March. Weather clouds often prevented satellite views. Data was not available during 20-21 March due to an outage, though a plume of discolored water was visible in satellite images. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level remained at Advisory (the second lowest level on a four-level scale).

Geological summary: Ahyi seamount is a large conical submarine volcano that rises to within 75 m of the sea surface about 18 km SE of the island of Farallon de Pajaros (Uracas) in the northern Marianas. Water discoloration has been observed there, and in 1979 the crew of a fishing boat felt shocks over the summit area of the seamount, followed by upwelling of sulfur-bearing water. On 24-25 April 2001 an explosive eruption was detected seismically by a station on Rangiroa Atoll, Tuamotu Archipelago. The event was well constrained (+/- 15 km) at a location near the southern base of Ahyi. An eruption in April-May 2014 was detected by NOAA divers, hydroacoustic sensors, and seismic stations.

Aira, Kyushu (Japan)

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

JMA reported ongoing eruptive activity at Minamidake Crater (at Aira Caldera’s Sakurajima volcano) during 13-20 March, with crater Incandescence visible nightly. Sulfur dioxide emissions were high at 2,100 tons per day on 13 March. On 14 March an explosion produced an ash plume that rose 1 km above the crater rim. Three eruptive events were recorded during 17-20 February, producing volcanic plumes that rose as high as 1 km. No activity or crater incandescence was detected at Showa Crater. 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.

Cotopaxi, Ecuador

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

IG reported that eruptive activity at Cotopaxi was ongoing during 15-21 March. Gas-and-steam emissions were visible on most days rising as high as 1 km above the crater rim and drifting in multiple directions. On 16 March several gas emissions containing minor amounts of ash rose as high as 1.5 km and drifted SE. During 19-20 March ash-and-gas plumes rose 1-1.5 km and drifted E and SE. 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.

Dukono, Halmahera

1.693°N, 127.894°E | Summit elev. 1229 m

PVMBG reported that white-and-gray plumes of variable densities rose from Dukono as high as 450 m above the summit and drifted N and W during 15-16, 18, and 20 March. No plumes were observed on 17 March, but white steam-and-gas plumes rose 150 m and drifted W on 19 March. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to remain outside of the 2-km exclusion zone.

Geological summary: Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia’s most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

Ebeko, Paramushir Island (Russia)

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

KVERT reported that moderate activity at Ebeko was ongoing during 9-16 March. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E) explosions during 10-12 March generated ash plumes that rose as high as 3.5 km (11,500 ft) a.s.l. and drifted NE and NW. A thermal anomaly was identified in satellite images on 10 and 13 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 were recorded at Fuego during 15-21 March, ejecting incandescent material up to 400 m above the crater and generating ash plumes that rose as high as 1.3 km above the crater rim. The ash plumes drifted as far as 20 km in multiple directions. Ashfall was reported on a few of the days 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), Finca Palo Verde, La Rochela, Finca Asunción, Ceilán, San Andrés Osuna, Aldeas, and San Pedro Yepocapa (8 km NW). 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 immediately surrounding the volcano. A lahar notice issued at 1530 on 15 March described lahars in the Ceniza ravine that carried branches, tree trunks, and blocks 30 cm to 1.5 m in diameter. Lahars on 18 March descended the El Jute and Las Lahas drainages, carrying branches, tree trunks, and blocks 30 cm to 1.5 m in diameter.

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 eruptive activity at Great Sitkin continued during 15-21 March, characterized by the eruption of lava that was confined to the summit crater. Radar data from 20 March confirmed slow growth of the lava flow. 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.

Ibu, Halmahera

1.488°N, 127.63°E | Summit elev. 1325 m

PVMBG reported that the eruption at Ibu continued during 15-18 March. White-and-gray plumes of variable densities rose as high as 800 m above the summit and drifted N, SE, SW, and W. The Darwin VAAC reported that on 20 March ash plumes rose to 2.1 km (7,000 ft) a.s.l., or about 800 m above the summit, and drifted SW based on satellite images. The Alert Level remained at a 2 (on a scale of 1-4), and the public was warned to stay at least 2 km away from the active crater and 3.5 km away on the N side.

Geological summary: The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, has contained several small crater lakes. The 1.2-km-wide outer crater is breached on the N, creating a steep-walled valley. A large cone grew ENE of the summit, and a smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. The first observed and recorded eruption was a small explosion from the summit crater in 1911. Eruptive activity began again in December 1998, producing a lava dome that eventually covered much of the floor of the inner summit crater along with ongoing explosive ash emissions.

Karangetang, Sangihe Islands

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

PVMBG reported that the summit Main Crater (S crater) on Karangetang continued to erupt during 15-21 March. Incandescent material at the summit and on the flanks was evident in webcam images captured at 0007 and 2345 on 16 March,1828 on 17 March, 1940 on 18 March, 2311 on 19 March, and 2351 on 20 March. The incandescence was most intense on 18 and 20 March, with webcam images possibly capturing Strombolian explosions. Based on satellite images, the Darwin VAAC reported that on 18 March an ash plume rose to 2.4 km (6,000 ft) a.s.l. and drifted SW and a thermal anomaly was visible. The Alert Level remained at 3 (the third highest on a scale on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

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.

Kilauea, Hawaiian Islands (USA)

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

On 21 March HVO reported that Kilauea was no longer erupting. The lava lake in Halema’uma’u Crater was no longer being supplied as of 7 March based on lava lake levels and crater floor observations. Sulfur dioxide emissions had decreased to near pre-eruption background levels. The Volcano Alert Level was lowered to Advisory (the second lowest level on a four-level scale) and the Aviation Color Code was lowered to Yellow (the second lowest color 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.

Krakatau, Sunda Strait

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

The Darwin VAAC reported that at 1446 on 18 March white-and-gray ash plumes at Anak Krakatau rose about 500 m above the summit and drifted SW. At 1846 on that same day a gray ash plume rose 300 m and drifted SW. An eruptive event was recorded at 2143, though it was not visible due to darkness. 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 15-21 March. White gas-and-steam plumes rose as high as 500 m above the summit and drifted in multiple directions during 15-19 March. White-and-gray ash plumes rose 400-600 m above the summit and drifted W and NW during 20-21 March. 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 on 17 March a white-and-gray plume from Marapi (on Sumatra) rose as high as 400 m above the summit and drifted N and E. Emissions were not observed on other days during 15-19 March, though some of the days were cloudy. White gas plumes rose 50 m above the summit on 20 March. 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.

Mauna Loa, Hawaiian Islands (USA)

19.475°N, 155.608°W | Summit elev. 4170 m

HVO reported that Mauna Loa had been quiet since the eruption ended on 13 December 2022 and the number of earthquakes beneath the summit had returned to background levels. Inflation continued as magma replenished the summit reservoir. On 16 March HVO lowered the Volcano Alert Level to Normal (the lowest level on a four-level scale) and the Aviation Color Code to Green (the lowest level on a four-color scale).

Geological summary: Massive Mauna Loa is a basaltic shield volcano that rises almost 9 km from the ocean floor to form the world’s largest Holocene volcano. Flank eruptions typically occur from the lengthy NE and SW rift zones, and from the Moku’aweoweo summit is caldera, which is within an older and larger 6 x 8 km caldera. Two of the youngest large debris avalanches documented in Hawaii traveled nearly 100 km from Mauna Loa; the second of the Alika avalanches was emplaced about 105,000 years ago (Moore et al., 1989). Almost 90% of the surface of the volcano is covered by lavas less than 4,000 years old (Lockwood and Lipman, 1987). Beginning about 1,500 years ago, a series of voluminous overflows from a summit lava lake covered about 25% of the volcano’s surface. Over the last 750 years, from shortly after the formation of Moku’aweoweo caldera until the present, an additional 25% of the volcano has been covered with lava flows, mainly from summit and NW rift zone vents.

Nevado del Ruiz, Colombia

4.892°N, 75.324°W | Summit elev. 5279 m

Servicio Geológico Colombiano (SGC) reported that several ash emissions at Nevado del Ruiz were visible in webcam images and reported by residents during 18-20 March. The emissions were associated with seismic signals indicating fluid movement in the conduit. An ash emission at 0902 on 20 March rose 2.7 km above the summit and drifted SW. It was one of the tallest plumes recorded in recent days and was visible from the municipalities of Caldas, Tolima, and Risaralda. The Alert Level remained at 3 (Yellow; the second lowest level on a four-color scale).

Geological summary: Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America’s deadliest eruption.

Popocatepetl, Mexico

19.023°N, 98.622°W | Summit elev. 5393 m

CENAPRED reported that there were 110-236 steam-and-gas emissions, sometimes containing minor amounts of ash, rising from Popocatépetl each day during 14-21 March; explosions also occurred almost daily. On 15 March a moderately-sized explosion recorded at 0009 was followed by minor explosions at 0058, 0220, 0641, 1215, 1509, and 2105, with another moderate explosion at 1848. On 16 March minor explosions were recorded at 0155 and 2215, and on 17 March they were recorded at 1441, 2105, and 2349. On 19 March multiple minor explosions were recorded, at 0003, 0220, 0926, and 2023, and moderate explosions occurred at 0501, 1300, and 1315. Minor explosions on 20 March were recorded at 0013, 0200, 0226, and 2112, and a moderate one occurred at 1404. A minor explosion occurred at 1712 on 21 March. According to the Washington VAAC daily ash plumes rose to 6.1-8.2 (20,000-27,000 ft) a.s.l., or around as high as 2.8 km above the summit, and drifted mainly N, NE, and S. The Alert Level remained at Yellow, Phase Two (the middle level on a three-color scale).

Geological summary: Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America’s 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

San Miguel, Eastern El Salvador

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

On 16 March MARN reported that gas emissions at San Miguel had decreased in the past few days and noted that gas-and-ash plumes were last observed on 9 March.

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

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 15-21 March. Emissions of gas and steam rose up to 800 m above the crater and drifted S, SW, and SE. Almost daily explosions produced ash plumes that rose as high as 800 m above the summit and often drifted SW. 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 during the nights and early mornings. Block-and-ash flows originated from Caliente, and the middle and front of the lava flow. Lahars descended the Cabello de Ángel drainage (a tributary of Nimá I on the SE flank) on 19 March and consisted of a cement-like mixture of volcanic material, branches, and tree trunks.

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 15-21 March. Dense ash plumes were visible almost daily. At 0737 and 0748 on 15 March white-and-gray ash plumes rose 600-800 m above the summit and drifted S and SE. At 0601 on 16 March a white-and-gray ash plume rose 600 m and drifted S, and at 0748 a gray-to-brown ash plume rose 500 m and drifted SW and W. At 0534 on 18 March a white-and-gray ash plume rose 500 m and drifted SW. Just over an hour later, at 0655, a white-and-gray ash plume rose 1 km and drifted S. At 0713 on 20 March white-and-gray ash plume rose 600 m and drifted SW and W, and at 0811 a gray-to-brown ash plume rose 1 km and drifted S. 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 9-16 March. Ash plumes drifted as far as 62 km E on 11 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.

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 13-20 March. A total of 20 explosions were recorded, sending ash plumes as high as 2.4 km above the crater rim and ejecting large blocks as far as 500 m from the vent. Crater incandescence was visible at night. 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.

References:

Smithsonian / US Geological Survey Weekly Volcanic Activity Report – March 15 – 21, 2023 – Managing Editor: Sally Kuhn Sennert

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