The Weekly Volcanic Activity Report: April 26 – May 2, 2023

New activity/unrest was reported for 6 volcanoes from April 26 – May 2, 2023. During the same period, ongoing activity was reported for 16 volcanoes.

New activity/unrest: Ambae, Vanuatu | Barren Island, Andaman Islands (India) | Bezymianny, Central Kamchatka (Russia) | Kanlaon, Philippines | Rincon de la Vieja, Costa Rica | Sheveluch, Central Kamchatka (Russia). 

Ongoing activity: Aira Kyushu, (Japan) | Cotopaxi, Ecuador | Ebeko Paramushir Island, (Russia) | Fuego, South-Central Guatemala | Great Sitkin, Andreanof Islands (USA) | Lewotolok, Lembata Island | Merapi, Central Java | Popocatepetl, Mexico | Ruapehu, North Island (New Zealand) | Sangay, Ecuador | Santa Maria, Southwestern Guatemala | Semeru, Eastern Java | Semisopochnoi, Aleutian Islands (USA) | Stromboli, Aeolian Islands (Italy) | Suwanosejima, Ryukyu Islands (Japan) | Yasur, Vanuatu.

New activity/unrest

Ambae, Vanuatu

15.389°S, 167.835°E; summit elev. 1496 m

On 27 April the Vanuatu Meteorology and Geo-Hazards Department (VMGD) reported that the cone in Ambae’s Lake Voui continued to produce emissions consisting of steam, volcanic gases, and ash. Volcanic earthquakes were recorded by the seismic network. Activity intensified during 5-7 April and was characterized by higher steam, gas, and ash plumes and nighttime incandescence from the growing cone. Lava flows from the vent traveled N into a small water lake, filling it in. The Alert Level remained at 2 (on a scale of 0-5) and the public was warned to stay outside of the Danger Zone, defined as a 2-km radius around the active vents in Lake Voui, and away from drainages during heavy rains.

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

Barren Island, Andaman Islands (India)

12.278°N, 93.858°E; summit elev. 354 m

The Darwin VAAC reported that continuous ash plumes from Barren Island were identified in satellite images during 0620-1250 on 1 May rising to 4.6 km (15,000 ft) a.s.l. and drifting NW.

Geological summary: Barren Island, a possession of India in the Andaman Sea about 135 km NE of Port Blair in the Andaman Islands, is the only historically active volcano along the N-S volcanic arc extending between Sumatra and Burma (Myanmar). It is the emergent summit of a volcano that rises from a depth of about 2250 m. The small, uninhabited 3-km-wide island contains a roughly 2-km-wide caldera with walls 250-350 m high. The caldera, which is open to the sea on the west, was created during a major explosive eruption in the late Pleistocene that produced pyroclastic-flow and -surge deposits. Historical eruptions have changed the morphology of the pyroclastic cone in the center of the caldera, and lava flows that fill much of the caldera floor have reached the sea along the western coast.

Bezymianny, Central Kamchatka (Russia)

55.972°N, 160.595°E; summit elev. 2882 m

KVERT reported that the ongoing eruption at Bezymianny was characterized by gas-and-steam emissions, occasional collapses at the lava dome, and hot avalanches during 20-27 April. A daily thermal anomaly was identified in satellite images. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale). Dates are based on UTC times; specific events are in local time where noted.

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

Kanlaon, Philippines

10.412°N, 123.132°E; summit elev. 2435 m

PHIVOLCS issued a special notice for Kanlaon at 0700 on 1 May, noting increased sulfur dioxide emissions. Real-time, continuous volcanic gas monitoring of thermal springs on the N flank detected sulfur dioxide for the first time beginning in April. On 30 April a Flyspec instrument measured an average of 1,099 tonnes per day of sulfur dioxide emissions at the summit crater, a value which was significantly higher than the average of 124 tonnes per day measured since March. During the month of April, the seismic network recorded 141 volcanic earthquakes, an average of five per day, at shallow depths less than 10 km in the N and W parts of the volcano. Ground deformation data from continuous GPS and electronic tilt data indicated short-term inflation of the lower and mid-flanks of the volcano since March. The Alert Level remained at 1 (on a scale of 0-5) and PHIVOLCS reminded the public to remain outside of the 4-km-radius Permanent Danger Zone.

Geological summary: Kanlaon volcano (also spelled Canlaon), the most active of the central Philippines, forms the highest point on the island of Negros. The massive andesitic stratovolcano is dotted with fissure-controlled pyroclastic cones and craters, many of which are filled by lakes. The largest debris avalanche known in the Philippines traveled 33 km SW from Kanlaon. The summit contains a 2-km-wide, elongated northern caldera with a crater lake and a smaller, but higher, historically active vent, Lugud crater, to the south. Historical eruptions, recorded since 1866, have typically consisted of phreatic explosions of small-to-moderate size that produce minor ashfalls near the volcano.

Rincon de la Vieja, Costa Rica

10.83°N, 85.324°W; summit elev. 1916 m

OVSICORI-UNA reported that phreatic eruptions continued to periodically occur at Rincón de la Vieja during 26 April-1 May. Near-continuous and intense tremor continued along with a few low-frequency, tornillo-type earthquakes and volcanic-tectonic earthquakes. Phreatic events at 0453, 0523, and 0545 on 26 April generated gas-and-steam plumes, and an event at 0528 on 27 April produced a gas-and-steam plume that rose 800 m above the crater rim. Several phreatic events occurred during 27-28 April and generated gas-and-steam emissions that generally rose no higher than 200 m above the crater rim. A small event at 1030 on 30 April produced a gas-and-steam plume that rose 500 m. A gas-and-steam plume from a moderate phreatic eruption at 1306 on 1 May rose 1 km above the crater rim and was seen by residents N of the volcano and in images from webcams located in Sensoria and Gavilan. A small event was recorded later that day at 2032.

Field observations found that the larger eruption on 21 April ejected tephra up to 3 km around the crater, mainly to the N and S. An analysis of ash deposits under a microscope revealed gray and dark metallic, sulfur-rich spheres characteristic of the hydrothermal system as well as juvenile volcanic glass. Ballistics up to 15 cm in diameter were found around the crater.

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.

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 20-27 April. Gas-and-steam emissions obscured the volcano during 20-23 April. A thermal anomaly was identified in satellite images during 24-27 April. A photograph taken on 29 April by the Kamchatka Volcanological Station showed a lava dome which was higher than the crater rim. 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.

Ongoing activity

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 24 April-2 May, with crater incandescence visible nightly. Very small eruptive events occasionally occurred during the week. On 28 April sulfur dioxide emissions were somewhat high at 1,800 tons per day. An explosion at 0422 on 2 May ejected large blocks 500-700 m from the crater and generated an ash plume that rose 1.8 km above the crater rim and drifted SW. 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 ongoing moderate eruptive activity at Cotopaxi during 26 April-2 May. Cloudy weather sometimes prevented webcam and satellite views, but emissions of steam-and-ash were visible on most days. On 26 April a gas plume with minor amounts of ash rose 500 m above the crater rim and drifted E. On 28 April an ash plume rose 800 m and drifted SE and W; ashfall was reported in the S part of Parque Nacional Cotopaxi. Gas-and-ash plumes rose 800 m and drifted W on 29 April, and two ash emissions rose 200-800 m and drifted SW and W on 30 April. At 0130 on 1 May the seismic network began recording a high-frequency signal that corresponded to the descent of a very small secondary lahar that remained within the bounds of Parque Nacional Cotopaxi. Gas-and-ash emissions rose 300 m and drifted W during 1-2 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.

Ebeko Paramushir Island, (Russia)

50.686°N, 156.014°E; summit elev. 1103 m

KVERT reported that moderate activity at Ebeko was ongoing during 20-27 April and a thermal anomaly was identified in satellite images on 20 and 26 April. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E) and satellite data explosions during 22 and 25-26 April generated ash plumes that rose as high as 3.5 km (11,500 ft) a.s.l. and drifted E. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Dates are based on UTC times; specific events are in local time where noted.

Geological summary: The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.

Fuego, South-Central Guatemala

14.473°N, 90.88°W; summit elev. 3763 m

INSIVUMEH reported that a range of 5-14 weak and moderate explosions per hour were recorded at Fuego during 26 April-2 May. The explosions generated ash plumes, weak to moderate rumbling sounds, and shockwaves that vibrated the roofs and windows of nearby houses. Ash plumes rose 1.1 km above the crater and sometimes dispersed as far as 15 km S, SW, SE, and W. Ash fall was reported in Panimaché I and II (8 km SW), Morelia (9 km SW), Santa Sofía (12 km SW), El Porvenir (11 km SW), Finca La Asunción, La Rochela (8 km SSW), Finca Ceilán (9 km S), and San Andres Osuna. Incandescent material was ejected as high as 350 m above the crater almost daily. Weak and moderate avalanches descended multiple drainages including the Seca (W), Ceniza (SSW), Taniluyá (SW), Trinidad (S), Las Lajas (SE), Santa Teresa (ESE), and Honda (SE); sometimes reaching the edges of vegetation. In the evening on 27 April a weak-to-moderate lahar descended the Ceniza, a tributary of the Achiguate River, and consisted of fine-grain, hot material, branches, tree trunks, and blocks that ranged from 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 lava continued to slowly erupt at the summit of Great Sitkin during 26 April-2 May. Weather clouds obscured satellite and webcam views during most of the week. Seismicity was low, and during 27-28 April only a few small events were detected. Satellite data last acquired up to 24 April showed that the thick lava continued to expand toward the E and remained confined to the summit crater. 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 was ongoing during 26 April-2 May. Almost daily white-and-gray plumes rose as high as 500 m above the summit and drifted NW, W, and SW. White gas-and-steam plumes rose 300 m and drifted SW on 28 April. Crater incandescence was visible in webcam images posted with the 27 April report. 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 21-27 April and seismicity remained at elevated levels. The SW lava dome produced 148 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 were evident in webcam images due to continuing collapses of material. 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.

Popocatepetl, Mexico

19.023°N, 98.622°W; summit elev. 5393 m

CENAPRED reported that there were 65-288 daily steam-and-gas emissions, sometimes containing ash, and daily explosions at Popocatépetl during 26 April-2 May. Ash-and-gas plumes drifted ENE. On most days webcam images showed nighttime incandescence in the crater and from material that had been deposited on the upper flanks. A moderate explosion at 0109 on 26 April ejected material that landed on the N flank as far as 1 km from the crater rim. A minor explosion was recorded later that day at 1817. A moderate explosion at 0116 on 27 April ejected incandescent material onto the upper flanks. Another moderate explosion was recorded at 1147 and minor explosions were recorded at 0348, 0606, 0857, and 1059. Minor explosions continued to be detected during the rest of the week: at 0857 and 1750 on 28 April, 0150 and 2350 on 29 April, at 2205, 2220, 2256, and 2345 on 30 April, and at 0000, 0130, 0356, 0454, and 0506 on 1 May. A moderate explosion occurred at 1249 on 30 April. On 2 May minor explosions occurred at 0335 and 0942. According to the Washington VAAC ash plumes were identified in satellite images daily rising 5.8-7.3 km (19,000-24,000 ft) a.s.l. (0.4-1.9 km above the crater rim) and drifting NE, E, and SE. 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.

Ruapehu, North Island (New Zealand)

39.28°S, 175.57°E; summit elev. 2797 m

On 3 May GeoNet reported that temperatures in Ruapehu’s cater lake had declined from 32 to 21 degrees Celsius since January, and other monitoring parameters indicated that volcanic unrest remained low. Weak volcanic tremor persisted and very few earthquakes were located beneath the volcano. Gas emissions were at low-to-moderate levels during the previous three months, and only minor changes to the lake water chemistry were identified over the past several months and most recently on 6 April. The Volcanic Alert Level remained at 1 (on a scale from 0-5) and the Aviation Color Code remained at Green (the lowest level on a four-color scale).

Geological summary: On 3 May GeoNet reported that temperatures in Ruapehu’s cater lake had declined from 32 to 21 degrees Celsius since January, and other monitoring parameters indicated that volcanic unrest remained low. Weak volcanic tremor persisted and very few earthquakes were located beneath the volcano. Gas emissions were at low-to-moderate levels during the previous three months, and only minor changes to the lake water chemistry were identified over the past several months and most recently on 6 April. The Volcanic Alert Level remained at 1 (on a scale from 0-5) and the Aviation Color Code remained at Green (the lowest level on a four-color scale).

Sangay, Ecuador

2.005°S, 78.341°W; summit elev. 5286 m

IG reported a high level of activity at Sangay during 25 April-2 May. Gas, steam, and ash plumes were occasionally observed in IG webcam images or described in Washington VAAC volcanic activity notifications, though weather clouds prevented observations on most days. On 25 April an ash-and-gas plume rose as high as 6 km above the crater rim and drifted SW. That same day notifications issued by the Washington VAAC indicated that ash plumes rose to 4.7 km (22,000 ft) a.s.l. (1.4 km above the crater rim) and drifted E, SE, SW, and W. IG noted that minor amounts of ash fell in the Province of Chimborazo in the Matriz and Juan de Velasco parishes, and in the Guamote canton. The VAAC reported that ash plumes rose as high as 1.4 km above the crater rim and drifted in multiple directions during 26-27 and 29 April. IG noted that a minor ash plume was visible in satellite images drifting W on 28 April. On 1 May an ash plume rose 1 km above the crater rim and drifted W. 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 26 April-2 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 ash-and-steam plumes that rose as high as 1 km above the dome and drifted W and SW. The explosions were also accompanied by block-and-ash flows that descended multiple flanks of the dome. Avalanches of material were also generated from the lava-flow front and margins. During 28-29 April quiet rumbling sounds were barely heard on nearby farms. Incandescence from the dome and the lava flows was visible nightly. On 28 April a lahar descended the Cabello de Angel River, a tributary of the Nimá I and Samalá rivers, on the E flank and was registered by the nearby seismic stations. The lahar consisted of volcanic material, water, volcanic blocks up to 1 m in diameter, and tree trunks and branches. On 30 April at 0920 a moderate explosion generated a pyroclastic flow that traveled 5 km SW and produced an ash cloud that rose 100 m along the flow. Seismic data confirmed that the event lasted 40 minutes.

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 26 April-2 May and frequent Volcano Observatory Notices for Aviation (VONAs) describing ash emissions were issued through the week. On 28 April at 0739, 0822, and 2035 dense white-and-gray or gray-to-brown ash plumes rose 500-1,000 m above the summit and drifted S and SW. On 29 April at 0551 and 0734 dense white-and-gray ash plumes rose 800-1,000 m and drifted S. At 0624 and 0738 on 30 April white-and-gray ash plumes of variable densities rose 500-800 m and drifted NE. At 0611 on 1 May a dense white-and-gray ash plume rose 700 m and drifted S and SW, and at 0705 on 2 May a dense white-and-gray ash plume rose 500 m and drifted N. The Alert Level remained at 3 (on a scale of 1-4). The public was warned to stay at least 5 km away from the summit in all directions, 13 km from the summit to the SE, 100 m from the banks of the Kobokan drainage as far as 17 km from the summit, and to avoid other drainages originating on Semeru, including the Bang, Kembar, and Sat, due to lahar, avalanche, and pyroclastic flow hazards.

Geological summary: Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.

Semisopochnoi, Aleutian Islands (USA)

51.93°N, 179.58°E; summit elev. 1221 m

AVO reported that low-level unrest continued at Semisopochnoi during 26 April-2 May. Seismicity was at low levels, and a few small local earthquakes were recorded during 28-29 April. Daily minor steam emissions were seen rising from Mount Young, though cloudy weather sometimes prevented webcam and satellite views. Ash deposits near the crater rim were visible during 27-28 April, though it was unclear if they were recent. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest color on a four-color scale).

Geological summary: Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island’s northern part. The three-peaked Mount Cerberus (renamed Mount Young in 2023) was constructed within the caldera during the Holocene. Each of the peaks contains a summit crater; lava flows on the N flank appear younger than those on the south side. Other post-caldera volcanoes include the symmetrical Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented eruptions have originated from Young, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone could have been recently active.

Stromboli, Aeolian Islands (Italy)

38.789°N, 15.213°E; summit elev. 924 m

INGV reported ongoing Strombolian activity at Stromboli during 24-30 April. 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 two vents in the N1 crater and one vent in the N2 crater in Area N were low to medium intensity and ejected coarse material (bombs and lapilli), sometimes mixed with ash, 80-150 m high at a rate of 3-8 explosions per hour. Explosions at the three vents in sector S2 (Area C-S) ejected ash sometimes mixed with coarse material at an average rate of 4-7 explosions per hour. Sectors C and S1 in Area C-S did not show significant activity. Although thermal activity was generally low and the summit was often clouded by weather, a thermal anomaly was detected at 0150 on 29 April.

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 24 April-1 May. No explosions were recorded, but eruptive activity produced periodic ash plumes, and during 28 April-1 May blocks were ejected as far as 200 m from the vent. On 28 April at 0643 an ash-and-gas plume rose 1.5 km above the crater rim and drifted NW. 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.

Yasur, Vanuatu

19.532°S, 169.447°E; summit elev. 361 m

On 27 April the Vanuatu Meteorology and Geohazards Department (VMGD) reported that activity at Yasur continued at a high level of “major unrest,” as defined by the Alert Level 2 status (the middle level on a scale of 0-4). Recent observations confirmed that low-to-moderate explosions continued, ejecting bombs that landed back into the crater and producing gas-and-ash emissions. The larger explosions occasionally ejected material outside of the crater. The public was reminded to not enter the restricted area within 600 m around the cone, defined by Danger Zone A on the hazard map.

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

Reference:

Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 26 April-2 May 2023 Managing Editor: Sally Kuhn Sennert