The Weekly Volcanic Activity Report: May 10 – 16, 2023

the weekly volcanic activity report

New activity/unrest was reported for 2 volcanoes from May 10 – 16, 2023. During the same period, ongoing activity was reported for 22 volcanoes.

New activity/unrest: Fuego, South-Central Guatemala | Kita-Ioto, Volcano Islands.

Ongoing activity: Aira, Kyushu (Japan) | Bezymianny, Central Kamchatka (Russia) | Cotopaxi, Ecuador | Dukono, Halmahera | Ebeko, Paramushir Island (Russia) | Etna, Sicily (Italy) | Great Sitkin, Andreanof Islands (USA) | Krakatau, Sunda Strait | Lewotolok, Lembata Island | Merapi, Central Java | Nyamulagira, DR Congo | Popocatepetl, Mexico | Reventador, Ecuador | Rincon de la Vieja, Costa Rica | Sangay, Ecuador | Santa Maria, Southwestern Guatemala | Semeru, Eastern Java | Semisopochnoi, Aleutian Islands (USA) | Sheveluch, Central Kamchatka (Russia) | St. Helens, Washington | Stromboli, Aeolian Islands (Italy) | Suwanosejima, Ryukyu Islands (Japan).

New activity/unrest

Fuego, South-Central Guatemala

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

INSIVUMEH reported that a range of 1-7 weak explosions per hour were recorded at Fuego during 10-16 May. The explosions generated ash plumes that rose to a maximum height of 850 m above the crater and drifted up to 12 km E, SE, S, and SW. Occasional weak avalanches of material were visible near the crater. During 9-10 May wind entrained loose ash that was deposited along the Ceniza, Las Lajas, and Seca drainages. On 12 May a minor lahar descended the Ceniza drainage, carrying branches, tree trunks, and volcanic blocks up to 1.5 m in diameter. Minor incandescent over the crater was visible overnight during 12-13 and 15-16 May. Wind entrained ash deposits during 15-16 May causing localized “curtains” of ash.

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.

Kita-Ioto, Volcano Islands

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

Japan Coast Guard reported that a small area of bluish-white discolored water above Funka Asane, a submarine vent 4-5 km NW of Kita-Ioto, was visible on 11 May. This was the first time discolored water was seen over the vent in about two years.

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.

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 8-15 May. Crater incandescence was observed nightly at Minamidake Crater. On 8 May sulfur dioxide emissions were extremely high at 3,900 tons per day. At 1315 on 9 May an explosion at Minamidake generated an ash plume that rose 1.2 km above the crater rim and drifted SW, and ejected blocks 1.1 km from the vent. Eruptive events at 1527, 1724, and 1817 on 11 May produced ash plumes that rose as high as 1.3 km and drifted NW and W. At Showa Crater eruptive events recorded at 1009, 1303, and 1401 on 8 May, at 0550, 0726, 2204, and 2321 on 11 May, at 1831 on 12 May, and at 0859 on 14 May produced ash plumes that rose as high as 1.7 km above the crater rim and drifted in multiple directions. Sulfur dioxide emissions were somewhat high on 12 May, averaging 1,800 tons per day. 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 activity at Bezymianny was generally characterized by gas-and-steam emissions, incandescence at the lava dome, and hot avalanches from the lava dome during 4-11 May. A daily thermal anomaly was identified daily in satellite images. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale). Dates are based on UTC times; specific events are in local time where noted.

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

Cotopaxi, Ecuador

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

IG reported that moderate eruptive activity continued at Cotopaxi during 9-16 May. Daily seismic activity was characterized by long-period earthquakes and tremors indicating emissions; a few volcano-tectonic earthquakes were recorded during the week. Emissions of steam, gas, and variable amounts of ash were observed on most days. During 9-10 May plumes with moderate amounts of ash rose 2-3 km above the crater rim and drifted SW, N, and NE. Ashfall was reported in areas to the SW, including San Joaquín and San Agustín de Callo. On 11 May gas-and-steam plumes rose 700 m above the summit and drifted to the E and SE. Emissions with moderate ash content on 12 May rose 1-2 km above the crater rim and drifted to the SE; later that day ash plumes rose 700 m. On 13 May steam-and-gas emissions with low or no ash content rose 900 m above the summit and drifted S, and gas-and-ash plumes rose 800 m and drifted SE. On 15 May steam-and-ash plumes rose 400 m and drifted W and SW. Weather clouds often prevented views during 14-16 May. 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 the eruption at Dukono was ongoing during 10-15 May. Daily dense white-and-gray ash plumes rose as high as 700 m above the summit and drifted E and N. 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 4-11 May. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E) explosions during 4, 6-7, and 9-10 May generated ash plumes that rose as high as 4 km (13,100 ft) a.s.l. and drifted E. A thermal anomaly was identified in satellite images on 9 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.

Etna, Sicily (Italy)

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

INGV reported that an explosion at Etna’s SE Crater occurred at 0839 on 14 May and produced an ash emission that rapidly dispersed around the summit area. The Aviation Color Code was raised to Yellow at 0902 and then lowered back to Green at 1830 on 14 May. No significant variations in the seismic data were associated with the explosion.

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.

Great Sitkin, Andreanof Islands (USA)

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

AVO reported that lava likely continued to erupt at the summit of Great Sitkin during 9-16 May. Satellite data acquired on 11 May showed that the thick lava continued to expand towards the E but remained confined to the summit crater. Seismicity was low. Nothing significant was seen in satellite and webcam images during most of the week due to persistent weather clouds obscuring views. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

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

Krakatau, Sunda Strait

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

During 10-13 May PVMBG reported that white-and-gray and white-and-brown ash plumes generally rose as high as 200 m above Anak Krakatau’s summit and drifted SW and NW, though a few Volcano Observatory Notices for Aviation (VONAs) described higher plumes. At 1241 on 11 May a gray ash plume rose 1 km above summit and drifted SW. At 0920 on 12 May a dense gray ash plume rose 2.5 km and drifted SW. At 2320 a dense gray ash plume rose 1.5 km and drifted SW. An accompanying webcam image showed incandescent material being ejected above the vent. At 0710 on 13 May a dense gray ash plume rose 2 km and drifted SW. 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 9-16 May. Almost daily white-and-gray ash plumes generally rose as high as 500 m above the summit and drifted in variable directions. At 0632 on 11 May a white-to-gray ash plume rose 500 m and drifted SW. At 0645 and 0957 on 11 May white-to-gray ash plumes rose 400-600 m and drifted E and SE, respectively. Nighttime webcam images of incandescent material being ejected above the summit were posted in daily reports during 10-13 May. 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 5-11 May and seismicity remained at elevated levels. The SW lava dome produced 106 lava avalanches that traveled as far as 1.8 km down the SW flank (upstream in the Bebeng drainages). Morphological changes to the SW lava dome due to continuing collapses of material were evident in webcam images. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-7 km away from the summit based on location.

Geological summary: Merapi, one of Indonesia’s most active volcanoes, lies in one of the world’s most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities.

Nyamulagira, DR Congo

1.408°S, 29.2°E | Summit elev. 3058 m

The Observatoire Volcanologique de Goma (OVG) reported that the lava lake in Nyamulagira’s summit crater continued to be active during 30 April-6 May. A Sentinel satellite image from 7 May showed active lava flows traveling towards the NW part of the crater. Another image on 12 May showed active flows along the NE margin of the dark and cooler 7 May flows. Weather clouds and possible volcanic emissions obscured parts of the crater.

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 there were 127-281 daily steam, gas, and ash emissions and minor-to-moderate explosions recorded at Popocatépetl during 9-16 May. Plumes mostly drifted SE, ESE, and ENE. On 9 May minor explosions were recorded at 1141, 2009, and 2310, and on 10 May moderate explosions were recorded at 0152 and 0316. Ashfall was reported in Tlalmanalco (30 km NW) and Tetela del Volcán (20 km SW) in Morelos during 9-10 May. On 11 May minor explosions were recorded at 0135, 0215, and 1621, while moderate explosions were recorded at 0526, 0811, 0838, 1601, and 1646. Minor explosions occurred at 1318 and 1452 on 12 May. On 13 May minor explosions occurred at 0012, 0805, and 2146, and a moderate explosion occurred at 1012. Ashfall was reported in the municipalities of Nealtican (20 km E), Huejotzingo (21 km E), and Domingo Arenas (20 km NE). On 14 May minor explosions were recorded at 0605, 0711, 0831, 1413, 1439, and 2312; moderate explosions were recorded at 1253, 1444, 1608, and 1941. On 15 May the network detected minor explosions at 0033 and 0051, and moderate explosions at 0352, 0512, 0617, 0852, 1051, 1232, and 1613. Minor amounts of ash fell in the municipalities of Puebla (43 km E) and Atlixco (24 km SE) and moderate amounts fell in municipalities near the volcano to the S. Weather clouds prevented views on 16 May. According to the Washington VAAC daily ash plumes were identified in satellite images rising 6.1-7.3 km (20,000-24,000 ft) a.s.l. (0.7-1.9 km above the crater rim) and drifting E and SE. The Alert Level remained at Yellow, Phase Two (the middle level on a three-color scale). CENAPRED urged people to respect the exclusion radius of 12 km and to not ascend the volcano.

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.

Reventador, Ecuador

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

IG reported that the eruption at Reventador was ongoing during 10-16 May. Seismicity was characterized by explosions, long-period earthquakes, harmonic tremors, and emission-related tremors. Steam, gas, and ash plumes were observed in some webcam images, though weather conditions occasionally obscured views. Ash emissions on 12 May rose 500 m above the crater rim and drifted N. On 14 May a steam-and-ash plume rose 250 m and drifted NE. On 16 May an ash plume rose as high as 1 km above the crater and drifted W and SW. Incandescence at the crater was visible at night during 10-12 and 16 May, and incandescent blocks rolled 200-700 m down the flanks. 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.

Rincon de la Vieja, Costa Rica

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

OVSICORI-UNA reported that periodic phreatic eruptions occurred at Rincón de la Vieja during 9-16 May. Phreatic events recorded at 1945 on 9 May, at 1419 on 10 May, and at 1100 on 11 May produced plumes that rose less than 1.5 km above the crater rim. Additional phreatic activity were recorded at 2232 on 11 May, and at both 2332 and 2338 on 12 May, though it was not known if emissions were generated. A short-lived explosive event at 0258 on 14 May ejected material onto the N flank and caused lahars to descend the Penjamo, Azul, and Azufrado rivers. Phreatic events at 1155 and 1748 that same day produced emissions that rose 500 m and 1.5 km above the crater rim, respectively. Gas emissions were occasionally visible during 15-16 May.

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.

Sangay, Ecuador

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

IG reported a high level of activity at Sangay during 9-16 May, though weather clouds prevented visual observations during most of the week. Ash plumes rose 500 m and drifted SW on 9 May. A webcam image from 1833 on 14 May showed lava flowing 500 m down the SE flank. 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.

Santa Maria, Southwestern Guatemala

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

INSIVUMEH reported that the eruption at Santa María’s Santiaguito lava-dome complex continued during 10-16 May. Effusion from the Caliente dome complex fed lava flows that descended the San Isidro and Zanjón Seco drainages on the W and SW flanks; the main lava flow was 4.3 km long and remained active. Daily weak-to-moderate explosions generated gas, steam, and ash plumes that generally rose up to 800 m above the crater and drifted SE, S, SW, and W. Explosions were sometimes accompanied by block-and-ash flows that descended multiple flanks of the dome. Incandescence from the dome and lava flows was visible during the nights and early mornings. An average of 40 explosions per day were recorded during 9-10 and 13-14 May, generating ash plumes that rose up to 1 km above the dome and drifted S and SW. Ashfall was reported in Fincas El Patrocinio, El Faro (7 km S), Las Marías (10 km S), and others nearby on 10 May.

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 10-16 May and a few Volcano Observatory Notices for Aviation (VONAs) describing ash emissions were issued during the week. White-to-gray ash plumes that were sometimes dense rose 500-700 m above the summit and drifted S, SW, W, and N at 1115 on 10 May, at 0725 and 0830 on 12 May, at 0858, 1010, and 1241 on 13 May, at 0523 and 1656 on 14 May, and at 0757 on 16 May. 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, 100 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.

Semisopochnoi, Aleutian Islands (USA)

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

AVO reported that low-level unrest continued at Semisopochnoi during 9-16 May. Weather clouds mostly obscured satellite and webcam views. Volcanic tremor was detected during 9-10 May; there was no evidence of explosive or earthquake activity in the geophysics data during the rest of the week. 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: 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 occasional explosions, continuing lava-dome growth, incandescence, and strong fumarolic activity during 4-11 May. A thermal anomaly over the active crater and Karan lava dome area was identified in satellite images all week. Intense fumarolic activity was likely associated with dome growth. During 8-9 May ash from pyroclastic flow deposits on the SE flank were resuspended by winds and blown 60 km W based on satellite images. 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.

St. Helens, Washington

46.2°N, 122.18°W | Summit elev. 2549 m

USGS reported that at 2045 on 14 May a debris flow in Mount St. Helens’ South Coldwater Creek destroyed a Highway SR 504 bridge, cutting off access and power to Johnston Ridge Observatory. While the loss of power interrupted a major telemetry hub, other stations remined operational and continued to provide data; the debris flow was recorded in seismic data from nearby stations. The source material in the flow originated from the climactic 1980 debris avalanche and eruption of Mount St. Helens. According to a news article at least 11 people had to spend the night at the Johnston Ridge Observatory and were airlifted out the next day. Officials noted that the highway will be closed for an indefinite amount of time.

Geological summary: Prior to 1980, Mount St. Helens formed a conical, youthful volcano sometimes known as the Fujisan of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Mount St. Helens was formed during nine eruptive periods beginning about 40-50,000 years ago and has been the most active volcano in the Cascade Range during the Holocene. Prior to 2,200 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older edifice, but few lava flows extended beyond the base of the volcano. The modern edifice consists of basaltic as well as andesitic and dacitic products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the north flank, and were witnessed by early settlers.

Stromboli, Aeolian Islands (Italy)

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

INGV reported ongoing Strombolian activity at Stromboli during 8-14 May. Activity was centered at two vents (one each at craters N1 and N2) in Area N, within the upper part of the Sciara del Fuoco, and from three vents in the Area C-S (South-Central Crater area) in the crater terrace area. Explosions at the N1 and N2 craters in Area N were low intensity and ejected coarse material (bombs and lapilli), sometimes mixed with ash at N1, as high as 80 m at a rate of 4-9 explosions per hour. Medium- to high-intensity explosions at the two vents in sector S2 (Area C-S) ejected ash sometimes mixed with coarse material at an average rate of 5-8 explosions per hour. Low-intensity gas explosions occurred at S1 in Area C-S. No significant activity was identified in Sector C in 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 8-15 May and crater incandescence was reported nightly. Explosions recorded at 0701, 1200, and 2330 on 8 May produced ash plumes that rose as high as 1 km above the crater rim and mainly drifted SE. Explosions were also recorded at 1358 and 1648, though characteristics of associated emissions were unknown. Eruptive events at 2001 on 8 May, 1753 on 9 May, 0405, 0647, and 1236 on 11 May, and 1919 on 13 May generated ash plumes that rose as high as 1.3 km and generally drifted S, SW, and N. 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.


Smithsonian / US Geological Survey Weekly Volcanic Activity Report – May 10 – 16, 2023 – Managing Editor: Sally Kuhn Sennert


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