The Weekly Volcanic Activity Report: May 24 – 30, 2023

the weekly volcanic activity report

New activity/unrest was reported for 6 volcanoes from May 24 to 30, 2023. During the same period, ongoing activity was reported for 17 volcanoes.

New activity/unrest: Ahyi, Mariana Islands (USA) | Etna, Sicily (Italy) | Karangetang, Sangihe Islands | Nyamulagira, DR Congo | Popocatepetl, Mexico | Rincon de la Vieja, Costa Rica.

Ongoing activity: Aira, Kyushu (Japan) | Bezymianny, Central Kamchatka (Russia) | Cotopaxi, Ecuador | Dukono, Halmahera | Ebeko, Paramushir Island (Russia) | Fuego, South-Central Guatemala | Great Sitkin, Andreanof Islands (USA) | Lewotolok, Lembata Island | Merapi, Central Java | Reventador, Ecuador | San Miguel, Eastern El Salvador | Sangay, Ecuador | Semeru, Eastern Java | Sheveluch, Central Kamchatka (Russia) | Stromboli, Aeolian Islands (Italy) | Suwanosejima, Ryukyu Islands (Japan) | Taupo, North Island (New Zealand).

New activity/unrest

Ahyi, Mariana Islands (USA)

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

Unrest at Ahyi Seamount continued during 21-30 May. Underwater events were detected by pressure sensors on Wake Island (2,270 km E) at least during 24-25 and 28-30 May. The events were possibly related to underwater explosions or earthquakes at the volcano. No activity was visible in cloudy or partly cloudy 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.

Etna, Sicily (Italy)

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

INGV reported that during 23-24 May activity at Etna was characterized by weak intra-crater explosive activity at the SE Crater and minor incandescence at Bocca Nuova Crater based on webcam images. A drone survey of the lava flows and tephra deposits emplaced during the 21 May paroxysmal eruption was conducted on 27 May. Lava flows had traveled 2.3 km, reaching 2,650 m elevation. During a field inspection on 28 May volcanologists observed gas emissions rising from Bocca Nuova and fumarolic activity at both Voragine Crater and NE Crater.

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

Karangetang, Sangihe Islands

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

Webcam images of Karangetang published in PVMBG daily reports periodically showed incandescence at Main Crater (S crater) and from material on the flanks of Main Crater during 23-30 May. Incandescence at the summit was most intense in the webcam images from 2332 on 26 May and 2304 on 29 May; the material on the flanks was brightest in the 29 May image. White gas-and-steam plumes were visible on most days rising as high as 150 m above the summit and rifting in various directions. 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. The Alert Level remained at 3 (on a scale of 1-4) and the public was warned to stay 2.5 km away from the craters on the S and SW flanks and 1.5 km away on the other 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.

Nyamulagira, DR Congo

1.408°S, 29.2°E | Summit elev. 3058 m

On 28 May the Observatoire Volcanologique de Goma (OVG) reported that the lava flows on Nyamulagira’s upper W flank had begun to cool and solidify. By 29 May seismicity had returned to levels similar to those recorded before the 17 May increase in activity. Lava effusion continued but was confined to the summit crater; incandescence above the crater was periodically visible.

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.

Popocatepetl, Mexico

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

CENAPRED reported that during 23-30 May activity at Popocatépetl consisted of seismic tremors, very few minor and moderate explosions, near-constant emissions of steam, gas, and sometimes ash, and ejections of incandescent material. Overall activity slightly decreased during the week. A total of approximately 140 hours of high-frequency tremors of variable duration and intensity were recorded.

A M 1.2 volcano-tectonic earthquake was recorded at 0340 on 24 May. Less than two hours later, at 0503, a minor explosion generated an ash plume that rose to 1 km above the summit and ejected incandescent material onto the flanks. A moderate explosion occurred at 1343. The Washington VAAC reported continuous ash emissions that rose 8.5-10.7 km (28,000-35,000 ft) a.s.l. and drifted SE. Ashfall was reported in Nealtican (21 km E), San Pedro Cholula (34 km E), San Andrés Cholula (36 km E), Tzicatlacoyan (65 km E), Tianguismanalco (22 km SE), Atlixco (25 km SE), Huaquechula (30 km SE), Ocoyucan (33 km SE), San Diego La Mesa Tochimiltzingo (39 km SE), San Juan Atzompa (71 km SE), Tehuitzingo (85 km SE), Tepexi de Rodríguez (88 km SE), Atzitzihuacán (23 km S), and Tilapa (48 km S).

Emissions were sometimes continuous during the night of 24 May into the early morning of 25 May; the plumes drifted SE and were occasionally visible in webcam images. According to the VAAC ash emissions rose 7.6-8.5 km (25,000-28,000 ft) a.s.l. and drifted S, SSE, and SE. Ashfall was reported at 0045 in Atlixco, San Pedro Cholula, and the capital of Puebla. Minor ashfall was reported at 0600 in the municipality of Tetela del Volcan of Estado de Morelos. Incandescent material was ejected onto the flanks close to the crater on 25 May.

The Secretary of Navy (SEMAR) conducted a drone flight during the morning of 25 May to collect information about crater activity for the Comité Científico Asesor (CCA), or Scientific Advisory Committee. During a meeting on 26 May that included the CCA, CENAPRED, CNPC, and other agencies it was shared that the drone footage of the crater showed no new lava dome, and that ash and incandescent material had significantly filled in the inner crater.

Periods of continuous or nearly continuous ash emissions were recorded during 26-30 May and incandescent material was sometimes ejected short distances from the crater rim. At 1726 on 26 May a minor explosion generated steam, gas, and ash plume and ejected incandescent material. At 1926 on 29 May a minor explosion was recorded. During 26-30 May ash, steam, and gas emissions rose 5.2-7.9 km (17,000-26,000 ft) a.s.l. and drifted SE, E, and ESE according to the VAAC. Ashfall was reported in Nopalucan (87 km NE), San Pedro Cholula (34 km E), Cuautlancingo (38 km E), Puebla Capital, Amozoc (61 km E), Chietla (56 km S), Tlapanalá (39 km SE), Nopalucan (87 km NE), Tepexco (43 km S), Chila de la Sal (104 km S), Chila de las Flores (144 km SE), Tulcingo del Valle (111 km S), Atzala (53 km S), Xochiltepec (53 km SE), Yecapixtla (30 km SW), Amecameca (18 km NW), Atlixco, Atzitzihuacán (23 km S), Ayapango (21 km NW), San Pedro Benito Juárez (10-12 km SE), Acatlán de Osorio, Tlacotepec (110 km SE), Ecatzingo (15 km SW), Tochimilco (16 km SSE), Hueyapan (17 km SW), Tetela del Volcán, Tianguismanalco (22 km SE), Atlixco, Tenango del Aire (29 km NW), Huaquechula, Chautla (36 km NE), and Zacualpan (31 km SW).

The eruption continued to impact residents. Air quality alerts were issued in Puebla on a few of the days during the first part of the week. According to the government of Puebla on 25 May the Ministry of Health warned residents to protect themselves from airborne ash with protective clothing and to stay inside when possible due to a reported increase in illnesses relating to ash exposure. By 26 May over one million students were able to return to classrooms.

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.

Rincon de la Vieja, Costa Rica

10.83°N, 85.324°W | Summit elev. 1916 m

OVSICORI-UNA reported that phreatic explosions continued at Rincón de la Vieja during 24-30 May. Moderate phreatic events at 1815 and 1830 on 24 May produced voluminous gas-and-steam plumes possibly containing some lake sediments that rose about 2.5 km above the crater rim. Aerial photos from that day showed fairly low lake water levels. The water was a milky gray color and was convecting, partly due to of subaqueous fumaroles. White deposits comprised of altered rocks blanketed the active crater from eruptive activity in recent days. A strong phreatic explosion at 1435 on 25 May produced an ash, gas, and steam plume that drifted NW. Small phreatic events were recorded at 2230 on 25 May and at 0453 and 0704 on 26 May. During a 26 May overflight the lake water level was observed to have significantly dropped compared to 24 May. Phreatic eruptions were recorded at 1357 and 2348 on 26 May and at 0221 and 0632 on 27 May. An energetic eruption at 2135 on 27 May ejected incandescent material and generated a plume mainly comprised of water vapor that rose 3.5-4 km above the crater rim. A significant lahar descended the Pénjamo River and possibly other drainages. On 29 May OVSICORI-UNA noted that the volcano was very active with frequent explosive eruptions. At 0244 an explosion ejected incandescent material and generated a lahar in the Pénjamo River.

Geological summary: Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the “Colossus of Guanacaste,” it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A Plinian eruption producing the 0.25 km3 Río Blanca tephra about 3,500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Ongoing activity

Aira, Kyushu (Japan)

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

JMA reported ongoing activity at both Minamidake Crater and Showa Crater (Aira Caldera’s Sakurajima volcano) during 22-29 May. Crater incandescence was observed nightly at Minamidake, and during 25-29 May at Showa; incandescence at Showa had not been visible since 5 March. The only eruptive event at Showa during this period was at 1125 on 22 May, when material was ejected 200-300 m from the crater and an ash plume rose 1.5 km above the crater rim. At 0610 on 24 May an explosion at Minamidake ejected material 300-500 m from the crater and generated an ash plume that rose 1.5 km above the crater and drifted to the SW. An eruptive event at 1327 on 25 May produced an ash plume that rose 2.3 km. On 26 May two explosions (at 0647 and 1441) and an eruptive event (1311) generated ash plumes that rose as high as 1.6 km and drifted N and S. The explosion at 1441 ejected blocks 500-700 m from the vent. An explosion at 1520 on 28 May ejected material 600-900 m from the crater and produced an ash plume that rose 2.3 km from the summit . 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.

Bezymianny, Central Kamchatka (Russia)

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

KVERT reported that eruptive activity at Bezymianny was generally characterized by lava effusion, gas-and-steam emissions, lava dome incandescence, and hot avalanches that traveled down the flanks during 24-30 May. A persistent thermal anomaly was identified daily in satellite data. 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 moderate eruptive activity continued at Cotopaxi during 23-30 May. Seismic activity was mainly characterized by long-period earthquakes and tremors associated with emissions that occurred almost daily; a total of three volcanic-tectonic earthquakes were recorded during the week. Weather clouds often hindered views, though gas-and-steam emissions were visible daily. During 23-24 May ash-and-gas emissions rose as high as 1 km above the summit and drifted W. On 26 May a period of continuous ash emissions was recorded with the plumes rising as high as 2 km above the summit and drifting NW and W. On 30 May ash plumes rose 1.2 km and drifted W; ashfall was reported in the Pastocalle parish of Latacunga canton (Cotopaxi Province). 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 Dukono continued to erupt during 24-30 May. Daily explosions were recorded by the seismic network. White-and-gray plumes of variable densities rose as high as 450 m above the summit and drifted E. The Alert Level remained at Level 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 18-25 May. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E) explosions during 23-25 May generated ash plumes that rose as high as 3.5 km (11,500 ft) a.s.l. and drifted S, SE, and E. A thermal anomaly was identified in satellite images on 24 May and ash plumes were visible drifting 75 km SE on 25 May. 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 1-3 weak explosions per hour were recorded at Fuego on most days during 24-30 May. The explosions generated ash plumes that rose between 450-750 m above the summit. The plumes drifted as far as 10 km SE on 26 and 30 May, 10 km SE and S on 27 May, and 6 km SE and S on 29 May. Ashfall was reported in El Zapote (10 km SSE), La Rochela (8 km SSW), and San Andrés Osuna (12 km SSW) on 26 and 30 May. Minor crater incandescence was occasionally visible during some nights and early mornings. Minor lahars descended the Ceniza drainage on 25 and 28 May and a weak-to-moderate lahar descended the Santa Teresa on 29 May. Both lahars consisted of hot volcanic material, branches, tree trunks, and volcanic blocks as large as 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 slow lava effusion continued at Great Sitkin during 23-30 May. A sequence of small low-frequency earthquakes was recorded for several hours on 23 May but did not result in any observed change in eruptive activity. Several small earthquakes were recorded daily during 24-27 May. No changes to the flow field were identified in satellite images acquired on 23, 27, or 28 May. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geological summary: The Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger parasitic volcano capped by a small, 0.8 x 1.2 km ice-filled summit caldera was constructed within a large late-Pleistocene or early Holocene scarp formed by massive edifice failure that truncated an ancestral volcano and produced a submarine debris avalanche. Deposits from this and an older debris avalanche from a source to the south cover a broad area of the ocean floor north of the volcano. The summit lies along the eastern rim of the younger collapse scarp. Deposits from an earlier caldera-forming eruption of unknown age cover the flanks of the island to a depth up to 6 m. The small younger caldera was partially filled by lava domes emplaced in 1945 and 1974, and five small older flank lava domes, two of which lie on the coastline, were constructed along northwest- and NNW-trending lines. Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano. Historical eruptions have been recorded since the late-19th century.

Lewotolok, Lembata Island

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

PVMBG reported that the eruption at Lewotolok continued during 24-30 May. Daily white-to-gray plumes of variable densities rose as high as 800 m above the summit and drifted E, NE, N, and NW. At 2037 on 27 May a webcam image showed an explosion of incandescent material above the summit. At 0613 on 29 May a dense gray-and-black ash plume rose 800 m above the summit and drifted NE and E. The Alert Level remained at 2 (on a scale of 1-4) and the public was warned to stay at least 2 km away from the summit crater in all directions.

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 19-25 May and seismicity remained at elevated levels. The SW lava dome produced 236 minor lava avalanches that traveled as far as 2 km down the SW flank (upstream in the Bebeng and Boyong drainages). Morphological changes to the SW lava dome due to continuing collapses of material were evident in webcam and drone images. Based on a 17 May drone survey, the SW dome volume was an estimated 2,372,800 cubic meters and the dome in the main crater was an estimated 2,337,300 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.

Reventador, Ecuador

0.077°S, 77.656°W | Summit elev. 3562 m

IG reported that the eruption at Reventador was ongoing during 23-30 May. Seismicity was characterized by 28-43 daily explosions, long-period earthquakes, harmonic tremors, and emission-related tremors. Daily gas-and-ash emissions rose as high has 1 km above the crater and drifted SW, W, NW, and NE. On most nights incandescent blocks were seen rolling 500-1,000 m down the flanks; incandescence at the crater and on the upper flanks was also periodically visible. Servicio Nacional de Gestión de Riesgos y Emergencias (SNGRE) maintained the Alert Level at Orange (the second highest level on a four-color scale).

Geological summary: Volcán El Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic stratovolcano has 4-km-wide avalanche scarp open to the E formed by edifice collapse. A young, unvegetated, cone rises from the amphitheater floor about 1,300 m to a height comparable to the rim. It has been the source of numerous lava flows as well as explosive eruptions visible from Quito, about 90 km ESE. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the scarp. The largest recorded eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

San Miguel, Eastern El Salvador

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

MARN reported that seismicity at San Miguel was detected on 23 May and remained elevated. At 1647 on 27 May an explosion generated a gas-and-ash plume that rose 700 m; seismicity decreased afterwards. Sulfur dioxide emissions were as high as 400 tons per day that same day based on measurements from an instrument located on the W flank, and then decreased to 268 and below 100 tons per day on 28 and 29 May, respectively. MARN warned the public to stay at least 3 km away from the crater.

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.

Sangay, Ecuador

2.005°S, 78.341°W | Summit elev. 5286 m

IG reported a high level of activity at Sangay during 23-30 May, though weather clouds sometimes prevented visual observations. There were 304-600 daily explosions recorded by the seismic network; no data was reported on 28 May. Ash plumes were seen in webcam images and reported by the Washington VAAC almost daily. On 23 May incandescent material extending 1.8 km down the SE flank was visible in webcam images. On 24 May pyroclastic flows descending 200 m were visible in between somewhat-dense weather clouds. An ash plume rose 300 m and drifted W. On 25 May ash plumes rose as high as 2 km and drifted NE and SE. Ash emissions were visible in webcam images at 1734 and were continuous for a period of time. Crater incandescence was visible overnight during 25-27 May and ash plumes that rose 500-800 m drifted SW and NW during 26-27 May. Incandescence from the lava flow on the SE flank was noted overnight during 28-29 May. The VAAC reported that at 0610 on 29 May ash plumes were visible in satellite images drifting W at 30,000 ft a.s.l., or 3.9 km above the summit, and drifting N at 40,000 ft a.s.l., or 6.9 km above the summit. Several pyroclastic flows descending the SE flank were visible in webcam images at 0615. At 1730 ashfall was reported in Cebadas Parish (Chimborazo province). 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 isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador’s volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within the open calderas of two previous edifices which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been eroded by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of an eruption was in 1628. Almost continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

Semeru, Eastern Java

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

PVMBG reported that the eruption at Semeru continued during 24-30 May. Volcano Observatory Notices for Aviation (VONAs) that described ash emissions were issued throughout the week. Daily sometimes-dense ash plumes rose as high as 1 km above the summit and drifted S, SW, W, and N. The Alert Level remained at 3 (third highest 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, 500 m from the banks of the Kobokan drainage as far as 17 km from the summit, and to avoid other drainages 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 eruption at Sheveluch was ongoing during 18-25 May. A thermal anomaly over the active crater and Karan lava dome area was identified in satellite images all week. Intense fumarolic activity at the active crater was likely associated with dome growth. 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 ongoing activity at Stromboli during 22-28 May. The Strombolian activity was centered at two vents in Area N (one each at craters N1 and N2), within the upper part of the Sciara del Fuoco, and from four vents in Area C-S (South-Central Crater) in the crater terrace. Low-intensity explosions at a rate of 3-7 per hour from Area N ejected mainly coarse material (bombs and lapilli) from N2, with mainly ash emissions from N1 as high as 80 m above the vents. Low- to medium-intensity explosions at an average rate of 2-7 per hour from the two vents in sector S2 (Area C-S) ejected a mix of coarse material and ash. During 27-28 May intense gas emissions at S1 sometimes contained coarse material. Intense spattering and occasionally weak explosions of coarse material was observed in sector C (Area C-S).

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 22-29 May and incandescence at the crater was visible nightly. Daily ash plumes from eruptive events rose as high as 1.6 km above the crater rim and drifted in multiple directions. Blocks were ejected as far as 300 m from the crater. At 2245 on 23 May an explosion generated an ash plume that rose 600 m and drifted S. The Alert Level remained at 3 (on a 5-level scale) and residents were warned to stay 2 km away from the crater.

Geological summary: The 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.

Taupo, North Island (New Zealand)

38.82°S, 176°E | Summit elev. 760 m

GeoNet reported that earthquake activity and ground deformation at Taupo declined during January-April and returned to background levels in May. The Volcanic Alert Level was lowered to 0 (the lowest level on a six-level scale) on 30 May and the Aviation Color Code remained at Green (the lowest level on a four-color scale). Unrest at the volcano started in early May 2022; during the year there were just over 1,800 earthquakes located beneath the volcano along with ground deformation both on the lake floor and around the lake.

Geological summary: Taupo, the most active rhyolitic volcano of the Taupo volcanic zone, is a large, roughly 35-km-wide caldera with poorly defined margins. It is a type example of an “inverse volcano” that slopes inward towards the most recent vent location. The caldera, now filled by Lake Taupo, largely formed as a result of the voluminous eruption of the Oruanui Tephra about 22,600 years before present (BP). This was the largest known eruption at Taupo, producing about 1,170 km3 of tephra. This eruption was preceded during the late Pleistocene by the eruption of a large number of rhyolitic lava domes north of Lake Taupo. Large explosive eruptions have occurred frequently during the Holocene from many vents within Lake Taupo and near its margins. The most recent major eruption took place about 1800 years BP from at least three vents along a NE-SW-trending fissure centered on the Horomotangi Reefs. This extremely violent eruption was New Zealand’s largest during the Holocene and produced the thin but widespread phreatoplinian Taupo Ignimbrite, which covered 20,000 km2 of North Island.


Smithsonian / US Geological Survey Weekly Volcanic Activity Report – May 24 – 30, 2023 – Managing Editor: Sally Kuhn Sennert

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