The Weekly Volcanic Activity Report: May 17 – 23, 2023
New activity/unrest was reported for 5 volcanoes from May 17 – 23, 2023. During the same period, ongoing activity was reported for 18 volcanoes.
New activity/unrest: Ahyi, Mariana Islands (USA) | Etna, Sicily (Italy) | Karangetang, Sangihe Islands | Nyamulagira, DR Congo | Popocatepetl, Mexico.
Ongoing activity: Aira, Kyushu (Japan) | Bulusan, Luzon (Philippines) | Cotopaxi, Ecuador | Ebeko, Paramushir Island (Russia) | Fuego, South-Central Guatemala | Great Sitkin, Andreanof Islands (USA) | Ibu, Halmahera | Lewotolok, Lembata Island | Merapi, Central Java | Nevado del Ruiz, Colombia | Rincon de la Vieja, Costa Rica | Sabancaya, Peru | Sangay, Ecuador | Santa Maria, Southwestern Guatemala | Semeru, Eastern Java | Semisopochnoi, Aleutian Islands (USA) | Sheveluch, Central Kamchatka (Russia) | Suwanosejima, Ryukyu Islands (Japan).
Ahyi, Mariana Islands (USA)
20.42°N, 145.03°E; summit elev. -75 m
The U.S. Geological Survey reported that unrest at Ahyi Seamount was again detected, after activity paused in early April. Signals consistent with eruptive activity were recorded by underwater pressure sensors on Wake Island, 2,270 km E, beginning at about 2210 on 21 May and were continuing. A plume of discolored sea water was observed above the area of the vent in a satellite image on 22 May. On 23 May the Aviation Color Code was changed to Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level was changed to 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
Strong explosive eruptions were reported at Etna by INGV starting on 18 May after continuous degassing and moderate seismicity over the previous few days, with significant Strombolian activity and a paroxysmal event at SE Crater on 21 May. Views were often obscured by persistent weather cloud cover. Strombolian activity from SE Crater at 0456 on 18 May was seen in webcam images from the camera located at Montagnola. The Aviation Color Code was raised to Yellow (second lowest level on a four-color scale) at 1242 following a sudden increase in volcanic tremor amplitude that began at 1210. The signal amplitude decreased for a short time but then increased to an even higher level at 1330. A seismic swarm in the summit area at 1644 was immediately followed by ground deformation recorded at the Punta Lucia and Pizzi Deneri summit stations. At 1656 weak intra-crater Strombolian activity at SE Crater was observed in images taken by the INGV thermal camera at La Montagnola (3 km S). Explosive activity from Bocca Nuova crater starting at 1700 was visible in thermal images from the Bronte (13 km WNW) webcam, concurrent with infrasonic signals. The Aviation Color Code was raised to Orange at 1751. The activity likely persisted for a few hours based on satellite images; weather conditions prevented confirmation with webcams. Tremor fluctuated and by 0927 on 19 May levels had begun to decrease.
Intermittent explosive activity persisted at SE Crater during 19-20 May, with pulsating gas emissions rising from the crater. A sharp increase in volcanic tremors at 0720 on 21 May was a precursor to significant tall lava fountaining during 0730-1140, with ash plumes that rose to 10 km and drifted SW, S, and SE. At 0937 the Aviation Color Code was raised to Red after INGV field personnel observed ash and lapilli fall on the SW flank and ashfall in Adrano at 560 m elevation. Lava flows from SE Crater descended the W part of the Valle del Bove as far as 1.9 km E and the S flank as far as 2 km. Satellite data showed a large sulfur dioxide plume drifting E. Weather clouds prevented views of the activity. Tremor levels sharply decreased starting at 1135 and had stabilized by 1200. Ashfall was also reported in Catania and Aci Castello. According to news reports the ashfall caused the Catania-Fontanarossa Airport in Sicily to close until 0900 on 22 May. The runway had been covered in ash and at least 68 flights to and from the airport were cancelled.
The Aviation Color Code was lowered to Orange at 0601 on 22 May, though lava flows were still active. By 0832 on 23 May monitoring data indicated that eruptive activity had ceased, and webcam images showed that the lava flows were cooling. The Aviation Color Code was lowered to Yellow at 0840 and then to Green at 1051.
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
PVMBG reported that activity at Karangetang had intensified in May, leading to a change in the Alert Level status. During 1-17 May white gas-and-steam plumes were sometimes dense and rose as high as 250 m above the summit, slightly higher than the 200 m maximum height noted in April. Incandescence at North Crater was visible at night 10-25 m above the lava dome. Incandescence also emanated from Main Crater though the glow was less intense, reaching about 10 m above the dome. Sounds of falling rocks at Main Crater were heard on 15 May, the seismic network recorded 32 rockfall events in the crater on 17 May, and rock avalanches on 18 May traveled as far as 1.5 km down the SW and S flanks accompanied by rumbling sounds. On 19 May the Alert Level was raised to 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. A webcam image from 2025 on 19 May showed incandescent material traveling down the flanks. On 21 May white gas-and-steam plumes rose 400 m above the summit.
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
The Observatoire Volcanologique de Goma (OVG) reported that lava continued to erupt from vents in Nyamulagira’s summit crater during 17-23 May. Lava flows began moving into the N and NW parts of the crater beginning on 9 May, towards the low point of the crater rim. Intense incandescence from the summit was visible from Goma (27 km S) during the evenings of 17 and 19 May. Satellite images showed a notable sulfur dioxide plume drifting NW and W during 19-20 May. Drone footage acquired on 20 May captured images of narrow lava flows traveling about 100 m down the W flank. Intense incandescence emanating from the summit was again visible from Goma at around 1830. Data from the Rumangabo seismic station indicated a downward trend in activity during 17-20 May and a significant decrease during 20-21 May. Though weather clouds were dense over the summit, hot lava on the NW flank was visible in a 22 May Sentinel-2 infrared (SWIR) image.
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.
19.023°N, 98.622°W; summit elev. 5393 m
CENAPRED reported that activity at Popocatépetl intensified during 16-23 May after recent activity characterized by the formation of small to medium lava domes on the summit crater floor and their subsequent destruction. There were 154-168 daily steam, gas, and ash emissions and minor-to-moderate explosions during 16-19 May. Periods of high-frequency tremor lasted more than 12 hours during 16-17 May and more than 10 hours during 17-18 May. Minor ashfall was reported on 18 May in the municipalities of Atlixco (25 km SE) and Cholula (35 km E), Puebla. Six volcano-tectonic earthquakes with magnitudes as high as 1.8 were recorded along with over 2 hours of high-frequency tremor on 19 May. Residents of Tétela del Volcán (18 km SW), Morelos, noted minor ashfall. According to the Washington VAAC ash plumes rose 6.7-7 km (22,000-23,000 ft) a.s.l., or 1.3-1.6 km above the summit, during 16-19 May.
A period of high-frequency tremor that began at around 1800 on 19 May and lasted about 10 hours until about 0400 on 20 May was accompanied by steam, gas, and ash plumes that drifted NNW and continuous ejection of incandescent tephra onto the flanks as far as 1.5 km from the crater. On 20 May the Benito Juárez International Airport closed during about 0430-1000 and the Felipe Ángeles International Airport closed during 0600-1100 in order to clear ash from runways. Ash fell in multiple areas downwind including in the municipalities of Venustiano Carranza (66 km NW), Gustavo A. Madero (73 km NW), Azcapotzalco (78 km NW), Tlalpan (62 km NW), Iztapalapa (58 km NW), Amecameca (18 km NW), Ayapango (21 km NW), Ozumba (18 km W), Ecatzingo (15 km SW), Atlautla (16 km W), Valle de Chalco (44 km NW), La Paz (50 km NW), Chalco (38 km NW), Nezahualcóyotl (56 km NW), Temamatla (32 km NW), Tenango del Aire (29 km NW), Tlalmanalco (27 km NW), Juchitepec (28 km NW), Cocotitlán (34 km NW), and Tepetlixpa (21 km W). Ashfall in Puebla municipalities included Huejotzingo (28 km NE), Nealtican (21 km E), Chignahuapan (108 km NE), Puebla Capital (44 km E), San Martín Texmelucan (35 km NE), and San Felipe Teotlalcingo (26 km NE).
Additional explosions were recorded at 1047, 1247, 1454, 2136, 2238, and 2253 on 20 May. Almost 19 hours of high-frequency tremor recorded during 20-21 May was accompanied by continuous emissions of steam, gas, and ash and occasional ejections of incandescent material short distances onto the flanks. The Washington VAAC reported that activity intensified at 1453 on 20 May as a large, dense ash plume was visible in webcam images. By 1551 the ash plume was visible in satellite images rising to 8.2 km (27,000 ft) a.s.l., or 2.8 km above the summit. By 2041 the dense ash plume had risen to 9.1 km (30,000 ft) a.s.l., or 3.7 km above the summit, and drifted ENE far over the Gulf of Mexico. The plume rose as high as 9.7 km (32,000 ft) a.s.l., or 4.3 km above the summit by 2136 and remained at that altitude at least through 0341 on 21 May as it fanned out to the NE and ENE. By 0951 on 21 May ash plumes were rising to 9.1 km and at 1436 plumes were reaching 8.5 km (28,000 ft) a.s.l., or 3.1 km above the summit. Satellite images showed a large dense ash plume drifting 388 km NE over the Bay of Campeche, but emissions were most dense within 65 km of the summit. Webcam images showed that continuing dense ash emissions.
According to CENAPRED the Scientific Advisory Committee of the Popocatépetl Volcano announced on 21 May that the Alert Level was raised from Yellow, Phase 2, to Yellow, Phase 3, the highest of the three sub-phases based on the intensifying activity over the previous few days. The National Coordination of Civil Protection (CNPC) announced actions to be implemented by the state civil protection units including preparing evacuation routes and evacuation teams and shelters. Ashfall was reported in Puebla state, in the municipalities of San Andrés Cholula (36 km E), San Pedro Cholula (34 km E), Cuautlancingo (38 km E), Amozoc (61 km E), Puebla Capital (44 km E), Zacatlán (121 km NE), Tetela de Ocampo (121 km NE), and Chignahuapan (108 km NE). The Hermanos Serdán International Airport, in Puebla (30 km NE), closed at 2300 on 21 May until 0700 on 22 May according to Gobierno de Puebla.
High-frequency tremor was almost constant for over 23 hours during 21-22 May. Steam, gas, and ash emissions were continuous with occasional ejections of incandescent material short distances onto the flanks. Explosions occurred at 1355 on 21 May and 0533 on 22 May. According to the Washington VAAC satellite images acquired at 0236, 0821, 1421, and 1936 revealed continuing ash emissions to 3.7 km above the summit, drifting E and ENE. An accompanying very large sulfur dioxide plume drifted as far as Cancun, 1,295 km E. Ashfall occurred in the municipalities of San Andrés Cholula (36 km E), San Pedro Cholula (34 km E), Cuautlancingo (38 km E), Amozoc (61 km E), Zacatlán (121 km NE), Tetela de Ocampo (121 km NE), San Nicolás de los Ranchos (15 km NE), Palmar de Bravo (115 km SE), Tepeaca (76 km E), in Izúcar de Matamoros (51 km S), Epatlán (51 km SE), Teopantlán (52 km SE), Tlapacoya (144 km NE), Huatlatlauca Chignahuapan (72 km SE), and in the Puebla capital, in the state of Puebla. Ash also fell in Juchitepec (28 km W), State of Mexico, Hueyapan (17 km SW), Locality of Xochitepec (municipality of Jolalpan) (68 km SW), in Morelos, and in the capital of the state of Tlaxcala (50 km NE). At 1651 on 22 May the Hermanos Serdán International Airport suspended operations due to ash on the runway.
Tremor remained nearly continuous (more than 20 hours) during 22-23 May. Ongoing steam, gas, and ash emissions drifted NE, and occasional ejections of incandescent material short distances onto the flanks. Ash fell in the municipalities of Nealtican, Tianguismanalco, Atlixco, San Diego la Mesa, Huaquechula, and Atzizihuacán, State of Puebla. Ash plumes rose as high as 3.7 km above the summit and drifted E according to the Washington VAAC.
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.
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 15-22 May. Crater incandescence was observed nightly at Minamidake Crater. At 1429 on 17 May an eruptive event at Showa Crater produced an ash plume that rose 1.2 km above the crater rim and drifted N. An explosion from Minamidake Crater at 2027 generated an ash plume that rose 400 m and ejected large blocks 600-900 m from the crater; another eruptive event at 2051 produced an ash plume that rose as high as 1 km and drifted N. An explosion at Minamidake was recorded at 1519 on 18 May. Showa Crater sent an ash plume 1.5 km high at 1125 on 22 May. 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.
Bulusan, Luzon (Philippines)
12.769°N, 124.056°E; summit elev. 1535 m
In a special advisory, PHIVOLCS reported that from 0500 on 21 May to 1600 on 22 May the seismic network at Bulusan recorded a total of 37 volcanic earthquakes. Out of those, 34 were volcano-tectonic earthquakes associated with rock fracturing and three were low-frequency volcanic earthquakes associated with movement of volcanic gas. Minor steam emissions from an active vent on the SE flank were occasionally visible. Ground deformation data from electronic tiltmeter stations continued to record short-term inflation of the SE flanks, first detected in December 2022. The Alert Level remained at 0 (the lowest level on a scale of 0-5) and PHIVOLCS reminded the public not to enter the 4-km-radius Permanent Danger Zone (PDZ).
Geological summary: Luzon’s southernmost volcano, Bulusan, was constructed along the rim of the 11-km-diameter dacitic-to-rhyolitic Irosin caldera, which was formed about 36,000 years ago. It lies at the SE end of the Bicol volcanic arc occupying the peninsula of the same name that forms the elongated SE tip of Luzon. A broad, flat moat is located below the topographically prominent SW rim of Irosin caldera; the NE rim is buried by the andesitic complex. Bulusan is flanked by several other large intracaldera lava domes and cones, including the prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the NE. The summit is unvegetated and contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Many moderate explosive eruptions have been recorded since the mid-19th century.
12.769°N, 124.056°E; summit elev. 1535 m
IG reported that moderate eruptive activity continued at Cotopaxi during 17-23 May. Seismic activity was mainly characterized by long-period earthquakes and tremors associated with emissions that occurred almost daily; a total of six volcanic-tectonic earthquakes were recorded during the week. Emissions of steam, gas, and variable amounts of ash were observed on most days; clouds obscured views on 19 May. Weak steam-and-gas emissions that barely rose above the crater level were recorded during 17 and 20-22 May; the emissions drifted W on 22 May. Starting at 0510 on 18 May emissions of steam-and-ash rose 1-3 km above the crater and drifted N and NE; ashfall was reported in Machachi (23 km NW). During the morning of 23 May several steam-and-gas emissions with possible minor ash content were observed rising 1 km above the crater and drifting S. 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)
0.677°S, 78.436°W; summit elev. 5911 m
KVERT reported that moderate activity at Ebeko was ongoing during 11-18 May. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E) explosions during 12-16 May generated ash plumes that rose as high as 3.5 km (11,500 ft) a.s.l. and drifted in multiple directions. A thermal anomaly was identified in satellite images during 13-14 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 1-4 weak explosions per hour were recorded at Fuego on most days during 16-23 May. The explosions generated ash plumes that rose 250-750 m above the crater; the plumes drifted S and SW during 18-20 May and as far as 10 km SW during 21-22 May. Slight incandescent at the crater was occasionally visible during dark hours a few times during the week. Very minor ashfall was reported in Morelia (9 km SW) and Panimaché (8 km SW) during 20-22 May.
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 16-23 May. Satellite data acquired on 16 May showed that the thick lava continued to expand towards the E but remained confined to the summit crater. Elevated surface temperatures were identified in satellite images during 18 and 21-23 May. Seismicity was low with some variations; five small earthquakes occurred during 19-20 May and small low-frequency earthquakes that began at 1000 on 23 May were ongoing at least through 1206. 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.
1.488°N, 127.63°E; summit elev. 1325 m
PVMBG reported that Ibu continued to erupt during 18-23 May. An average of approximately 80 eruption-related earthquakes were recorded by the seismic network during 18-22 May. White-and-gray emissions of variable densities rose as high as 1 km above the summit and drifted N, E, SE, and W. At 2021 and 2140 on 21 May dense gray ash plumes rose 600 m and 1 km above the summit, respectively, and drifted W. The Alert Level remained at a 2 (the second highest level on a four-level scale), and the public was advised to stay outside of the 2 km hazard radius, and to stay 3.5 km away from the N area of the active crater.
Geological summary: The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, has contained several small crater lakes. The 1.2-km-wide outer crater is breached on the N, creating a steep-walled valley. A large cone grew ENE of the summit, and a smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. The first observed and recorded eruption was a small explosion from the summit crater in 1911. Eruptive activity began again in December 1998, producing a lava dome that eventually covered much of the floor of the inner summit crater along with ongoing explosive ash emissions.
Lewotolok, Lembata Island
8.274°S, 123.508°E; summit elev. 1431 m
PVMBG reported that the eruption at Lewotolok was ongoing during 17-23 May. Almost daily white-and-gray ash plumes rose as high as 700 m above the summit and drifted in variable directions; only white gas-and-steam plumes were visible on 19 May. A nighttime webcam image of incandescent material being ejected above the summit was captured at 1844 on 17 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 12-18 May and seismicity remained at elevated levels. The SW lava dome produced 182 minor lava avalanches that traveled as far as 1.8 km down the SW flank (upstream in the Bebeng and Boyong drainages) and one that traveled 500 m NW (upstream of the Senowo River). Morphological changes to the SW lava dome due to continuing collapses of material were evident in webcam and drone 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.
Nevado del Ruiz, Colombia
4.892°N, 75.324°W; summit elev. 5279 m
Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that the eruption at Nevado del Ruiz continued during 17-23 May and was characterized by periodic gas, steam, and ash emissions, thermal anomalies at the lava dome in Arenas Crater, and elevated seismicity. Seismic signals indicating rock-fracturing events were located 3-8 km around the Arenas Crater at depths of 1-6 km. The largest event, a M 2.1, was recorded at 0341 on 21 May and was located 2 km below the Arenas crater. Gas-and-ash emissions rose as high as 1.5 km above the crater and drifted multiple directions. A thermal anomaly was observed within the crater on 18 May. The Alert Level was remained at Orange, Level II (the second highest level on a four-level scale).
Geological summary: Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America’s deadliest eruption.
Rincon de la Vieja, Costa Rica
10.83°N, 85.324°W; summit elev. 1916 m
OVSICORI-UNA reported that small phreatic eruptions periodically occurred at Rincón de la Vieja during 16-23 May. Four small events occurred during 16-17 May; the last one, recorded at 1255 on 17 May, produced a gas-and-steam plume that rose 700 m above the crater rim. Sulfur dioxide emissions were almost as high as 5,000 tonnes per day on 17 May; emissions averaged around 132 tonnes per day during the previous week. Events were recorded at 1537 on 18 May and at 0727 and 1025 on 19 May. Vigorous gas emissions were visible in the early morning of 20 May and a phreatic event occurred at 1648 that same day. At 1349 a phreatic event generated a plume mostly comprised of steam that rose 1 km above the crater rim.
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.
15.787°S, 71.857°W; summit elev. 5960 m
Instituto Geofísico del Perú (IGP) reported moderate levels of activity at Sabancaya during 15-21 May with a daily average of 37 explosions. Gas-and-ash plumes rose as high as 2.4 km above the summit and drifted NE, E, and SE. Eight thermal anomalies originating from the lava dome in the summit crater were identified in satellite data. Seismic sensors detected 232 volcanic activity-related earthquakes, in addition to volcano-tectonic earthquakes. The Alert Level remained at Orange (the second highest level on a four-color scale) and the public were warned to stay outside of a 12-km radius.
Geological summary: Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning “tongue of fire” in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions date back to 1750.
2.005°S, 78.341°W; summit elev. 5286 m
IG reported a high level of activity at Sangay during 17-23 May, though weather clouds sometimes prevented visual observations. Incandescent material at the crater and along the lava flow extending 1 km down the SE flank was visible nightly. On 17 May steam-and-ash emissions rose 500 m above the summit and drifted SW. On 18 May an ash plume rose 1.7 km and drifted N and SW. At 2000 on 20 May ash plumes rose 2 km above the summit and drifted to the SW. Continuous ash emissions persisted during 21-22 May, drifting W and SW. Ashfall during 20-22 May was reported in Chauzan, Guamote, Tixán, Palmira, Cebadas, and Alausí cantons in the Province of Chimborazo. 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 16-23 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. Avalanches of material from the growing dome and occasional explosions descended all sides of the dome and avalanches from the lava flow descended the S and SW flanks. Explosions generated gas, steam, and ash plumes that drifted S and SW on a few days. 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 21-22 May, generating ash plumes that rose up to 1 km above the dome and drifted SW.
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 17-23 May and several Volcano Observatory Notices for Aviation (VONAs) describing ash emissions were issued during the week. Daily white-to-gray ash plumes that were sometimes dense rose 200-800 m above the summit and drifted in multiple directions. VONAs were issued as follows: 0501, 0646, and 0919 on 17 May; 0517 and 0822 on 18 May; 0547, 0911, and 0936 on 19 May; 0545, 0733, 0742, and 1054 on 20 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
On 17 May AVO reported that eruptive activity at Semisopochnoi had declined during the previous week, though seismicity remained slightly elevated and low-level steaming continued from Mount Young. Ash emissions had last occurred on 5 May leaving minor deposits on the NW flank of Mount Young’s N crater. The Aviation Color Code was lowered to Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level was lowered to Advisory (the second highest level on a four-level scale). Intense gas emissions were periodically visible in webcam images during 17-18 and 20-21 May. On 22 May a weak sulfur dioxide signal was detected, suggestive of low-level degassing.
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 eruption at Sheveluch was ongoing during 11-18 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. Plumes of ash, originally deposited during the 10-13 April eruption and resuspended by strong winds, were visible in satellite images drifting 400 km SE during 14-15 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 high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1,300 km3 andesitic volcano is one of Kamchatka’s largest and most active volcanic structures, with at least 60 large eruptions during the Holocene. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes occur on its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large open caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.
Suwanosejima, Ryukyu Islands (Japan)
29.638°N, 129.714°E; summit elev. 796 m
JMA reported that the eruption at Suwanosejima’s Ontake Crater continued during 15-22 May. Incandescence was visible nightly, and seismicity remained elevated during 15-19 May. On 16 May an ash plume rose 1.8 km above the crater rim and caused ashfall in Toshima village (3.5 km SSW). On 17 May, an ash plume rose to 1.1 km and drifted NW. Four eruptive events were observed during 21-23 May. On 21 May an eruptive event ejected volcanic blocks up to 200 m from the crater and produced an ash plume that rose 1.8 km above the crater and drifted E. On 22 May an ash plume rose to 1 km above the crater and drifted SE. Two eruptive events on 23 May generated ash plumes that rose 600 m above the crater and drifted SE and 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.
Smithsonian / US Geological Survey Weekly Volcanic Activity Report – May 17 -23, 2023 – Managing Editor: Sally Kuhn Sennert
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