The Weekly Volcanic Activity Report: June 21 – 27, 2023

the weekly volcanic activity report

New activity/unrest was reported for 5 volcanoes from June 21 – 27, 2023. During the same period, ongoing activity was reported for 17 volcanoes.

New activity/unrest: Klyuchevskoy, Central Kamchatka (Russia) | Kuchinoerabujima, Ryukyu Islands (Japan) | Lokon-Empung, Sulawesi | Mayon, Luzon (Philippines) | Ubinas, Peru.

Ongoing activity: Ahyi, Mariana Islands (USA) | Aira, Kyushu (Japan) | Cotopaxi, Ecuador | Ebeko, Paramushir Island (Russia) | Fuego, South-Central Guatemala | Great Sitkin, Andreanof Islands (USA) | Karangetang, Sangihe Islands | Lewotolok, Lembata Island | Merapi, Central Java | Nevado del Ruiz, Colombia | Popocatepetl, Mexico | Reventador, Ecuador | Rincon de la Vieja, Costa Rica | Santa Maria, Southwestern Guatemala | Semeru, Eastern Java | Sheveluch, Central Kamchatka (Russia) | Suwanosejima, Ryukyu Islands (Japan).

New activity/unrest

Klyuchevskoy, Central Kamchatka (Russia)

56.056°N, 160.642°E | Summit elev. 4754 m

KVERT reported that a minor Strombolian eruption began at Klyuchevskoy at 2323 on 22 June and a bright thermal anomaly was visible in satellite images. The Aviation Color Code was raised to Yellow (the second lowest level on a four-color scale).

Geological summary: Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka’s highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Kuchinoerabujima, Ryukyu Islands (Japan)

30.443°N, 130.217°E | Summit elev. 657 m

JMA reported that the number of volcanic earthquakes increased at Kuchinoerabujima. A total of 100 shallow volcanic earthquakes were recorded during 17-26 June with most epicenters located near Furudake Crater and some located near Shindake Crater (just N of Furudake). Sulfur dioxide emissions were low, and typical white emissions rose 100-500 m above Shindake on 13 and 25 June. No changes at the geothermal area on the W flank of Shindake were observed during a field inspection during 19-20 June. The Alert Level was raised to 2 (on a scale of 1-5) on 26 June due to the increased seismicity. The public was warned that ejected blocks and pyroclastic flows may impact areas within 2 km of Shindake.

Geological summary: A group of young stratovolcanoes forms the eastern end of the irregularly shaped island of Kuchinoerabujima in the northern Ryukyu Islands, 15 km W of Yakushima. The Furudake, Shindake, and Noikeyama cones were erupted from south to north, respectively, forming a composite cone with multiple craters. All historical eruptions have occurred from Shindake, although a lava flow from the S flank of Furudake that reached the coast has a very fresh morphology. Frequent explosive eruptions have taken place from Shindake since 1840; the largest of these was in December 1933. Several villages on the 4 x 12 km island are located within a few kilometers of the active crater and have suffered damage from eruptions.

Lokon-Empung, Sulawesi

1.358°N, 124.792°E | Summit elev. 1580 m

PVMBG reported continuing daily emissions at Lokon-Empung during 21-27 June. The plumes had variable densities, rose as high as 300 m above the crater rim, and were white on most days; plumes were described as white and gray on 21 June. The volcano Alert Level remained at 2 (on a scale of 1-4) and the public was reminded not to approach Tompaluan Crater within a radius of 1.5 km.

Geological summary: The Lokong-Empung volcanic complex, rising above the plain of Tondano in North Sulawesi, includes four peaks and an active crater. Lokon, the highest peak, has a flat craterless top. The morphologically younger Empung cone 2 km NE has a 400-m-wide, 150-m-deep crater that erupted last in the 18th century. A ridge extending 3 km WNW from Lokon includes the Tatawiran and Tetempangan peaks. All eruptions since 1829 have originated from Tompaluan, a 150 x 250 m crater in the saddle between Lokon and Empung. These eruptions have primarily produced small-to-moderate ash plumes that sometimes damaged croplands and houses, but lava-dome growth and pyroclastic flows have also occurred.

Mayon, Luzon (Philippines)

13.257°N, 123.685°E | Summit elev. 2462 m

PHIVOLCS reported that eruptive activity continued at Mayon during 20-27 June. Slow aseismic lava effusion few a growing lava dome in the summit crater and fed lava flows that advanced down the Mi-isi (S) and Bonga (SE) drainages. Previously reported maximum lava flow lengths of 2.5 km along the Mi-isi and 1.8 km along the Bonga drainages were revised on 24 June to 1.3 km and 1.2 km, respectively; by 27 June the Mi-isi flow was 1.6 km long. The dome remained unstable and produced incandescent rockfalls and pyroclastic density currents (PDCs, or pyroclastic flows). The collapse material traveled as far as 3.3 km away from the crater. Daily steam-and-gas emissions rose as high as 800 m above the crater and drifted SW, WSW, and W. Average daily measurements of sulfur dioxide emissions fluctuated between 507 and 925 tonnes per day. Each day, seismic stations recorded 241-339 rockfall events and 1-17 PDC events, each lasting up to five minutes. On 26 June PHIVOLCS released an advisory due to increased seismic activity and ground deformation, noting that the number of volcano-tectonic earthquakes increased during the week; there were two during 20-21 June, two during 23-24 June, and 107 during 26-27 June. The increased seismicity was accompanied by a sharp increase in ground tilt on the SW part of the volcano. The Disaster Response Operations Monitoring and Information Center (DROMIC) reported that as of 1600 on 27 June, the increased unrest had affected a total of 41,488 people and displaced a total of 20,138 people from 26 barangays within the province of Albay. The Alert Level remained at 3 (on a 0-5 scale). Residents were reminded to stay away from the 6-km-radius Permanent Danger Zone (PDZ), and PHIVOLCS recommended that civil aviation authorities advise pilots to avoid flying close to the summit.

Geological summary: Symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the most active volcano of the Philippines. The steep upper slopes are capped by a small summit crater. Recorded eruptions since 1616 CE range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often damaged populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

Ubinas, Peru

16.355°S, 70.903°W | Summit elev. 5672 m

Instituto Geofísico del Perú (IGP) reported that a new eruption began at Ubinas on 22 June after three days on increased seismicity. The seismic network recorded a total of 315 volcano-tectonic earthquakes with a maximum magnitude of 1.8 and 281 long-period earthquakes. The eruption began at 0011 on 22 June with a minor ash plume rising 1 km above the crater rim and drifted E based on seismicity and webcams.

During 23-25 June IGP reported a total of 402 volcano-tectonic earthquakes with a maximum magnitude of 1.9 and 865 long-period earthquakes. Sporadic diffuse ash emissions continued during this period that rose as high as 1.5 km above the crater rim. On 23 June the Buenos Aires VAAC reported that diffuse ash plumes were visible in satellite images rising to 6.4 km (21,000 ft) a.s.l., or about 700 m above the summit, and drifting NE and NW. At 1500 they noted that continuous steam emissions occasionally accompanied by diffuse ash puffs were visible in webcam images. On 24 June small diffuse ash puffs were visible in webcam and satellite images rising 6.4-7 km (21,000-23,000 ft) a.s.l., or 700-1,300 m above the summit, and drifting NW. On 25 June continuous gas emissions with sporadic diffuse ash puffs were visible in webcam images, though the ash was too diffuse to be detected in satellite images. IGP noted that no notable deformation nor thermal anomalies were detected. The Alert Level remained at Yellow (the second level on a four-color scale).

Geological summary: A small, 1.4-km-wide caldera cuts the top of Ubinas, Perú’s most active volcano, giving it a truncated appearance. It is the northernmost of three young volcanoes located along a regional structural lineament about 50 km behind the main volcanic front. The growth and destruction of Ubinas I was followed by construction of Ubinas II beginning in the mid-Pleistocene. The upper slopes of the andesitic-to-rhyolitic Ubinas II stratovolcano are composed primarily of andesitic and trachyandesitic lava flows and steepen to nearly 45 degrees. The steep-walled, 150-m-deep summit caldera contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits from the collapse of the SE flank about 3,700 years ago extend 10 km from the volcano. Widespread Plinian pumice-fall deposits include one of Holocene age about 1,000 years ago. Holocene lava flows are visible on the flanks, but historical activity, documented since the 16th century, has consisted of intermittent minor-to-moderate explosive eruptions.

Ongoing activity

Ahyi, Mariana Islands (USA)

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

Unrest at Ahyi Seamount possibly continued during 21-27 June. One small hydroacoustic signal coming from the direction of the seamount was detected by pressure sensors on Wake Island (2,270 km E) during 23-24 June. Data from the sensors on Wake Island stopped transmitting at 0414 on 24 June though no signals were detected by sensors on Saipan during the rest of the week. No surface activity was visible in satellite images. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level remained at Advisory (the second lowest level on a four-level scale).

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

Aira, Kyushu (Japan)

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

JMA reported ongoing activity at both Minamidake Crater and Showa Crater (Aira Caldera’s Sakurajima volcano) during 19-26 June. Very small eruptive events occasionally occurred at Minamidake and incandescence was observed at night. An explosion at Showa at 0438 on 22 June produced an ash plume that rose 600 m above the crater rim and drifted E and ejected blocks 500-800 m from the vent. Sulfur dioxide emissions averaged 1,400 tons per day on 22 June. The Alert Level remained at 3 (on a 5-level scale), and the public was warned to stay 2 km away from both craters.

Geological summary: The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan’s most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the Aira caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim of Aira caldera and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4850 years ago, after which eruptions took place at Minamidake. Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu’s largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.

Cotopaxi, Ecuador

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

IG reported that moderate eruptive activity continued at Cotopaxi during 20-27 June. Several gas-and-ash emissions rose as high as 900 m above the summit and drifted S, SW, and W during 21-22 June. During 22-23 June gas plumes with low amounts of ash rose less than 200 m above the summit and drifted SW. Additional gas-and-steam emissions during 23-26 June rose as high as 500 m above the summit and drifted to the S and SW. Weather clouds often prevented direct observations. 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 15-22 June. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E) explosions during 16-17, 20, and 22 June generated ash plumes that rose as high as 3.5 km (11,500 ft) a.s.l. and drifted NE and SE. A thermal anomaly was identified in satellite images on 22 June; weather clouds obscured views on the other days. 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 1-6 explosions per hour were recorded at Fuego during 21-27 June, generating daily ash plumes that rose as high as 1.1 km above the crater rim and drifted as far as 30 km S, SW, W, and NW. The ash plumes were described as dense during 22-23 June and mostly gas with diffuse ash during 24-26 June. The explosions occasionally triggered weak-to-moderate avalanches that descended multiple ravines. Minor ashfall was reported on all days, except 21 June, in areas downwind including La Soledad (7 km N), El Porvenir (8 km SE), Panimanché I and II (8 km SW), Morelia (9 km SW), Santa Sofía (12 km SW), Yucales (12 km SW), Finca Palo Verde (10 km WSW), Sangre de Cristo (8 km W), and Yepocapa (9 km WNW). Lahars descended the Ceniza (SSW) ravine on 21 June and the El Jute (ESE) ravine on 23 June.

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 likely continued at Great Sitkin during 20-26 June. Minor seismicity was ongoing, and a few small earthquakes were recorded during 25-26 June. Elevated surface temperatures were identified in satellite images during 20-21 June and minor steaming was visible in satellite and webcam views during 25-27 June; weather clouds sometimes obscured webcam and satellite views on the other days. 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.

Karangetang, Sangihe Islands

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

PVMBG reported that dense white gas-and-steam plumes from Karangetang were visible rising as high as 150 m and drifting in multiple directions during 21-27 June. Webcam images published in the reports on 21, 25, and 27 June showed incandescence at Main Crater (S crater) and from material on the flanks of Main Crater. The Alert Level remained at 3 (on a scale of 1-4) and the public were advised to stay 2.5 km away from Main Crater with an extension to 3.5 km on the S and SE flanks.

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.

Lewotolok, Lembata Island

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

PVMBG reported that the eruption at Lewotolok continued during 21-27 June. Emissions mainly consisted of white steam-and-gas plumes that rose as high as 800 m above the summit and drifted W and NW; white-and-gray ash plumes rose as high as 800 m above the main crater and drifted W and NW during 22-23 June. Incandescence was visible at the summit during 24-26 June, and a webcam image taken at 2257 on 25 June showed incandescent ejecta at the summit. The Alert Level remained at 2 (on a scale of 1-4) and the public was warned to stay at least 2 km away from the summit crater.

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 16-22 June and seismicity remained at elevated levels. The SW lava dome produced 116 lava avalanches that traveled as far as 1.8 km down the SW flank (upstream in the Bebeng and Boyong drainages). Morphological changes to the SW lava dome were 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.

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 20-27 June and was characterized by gas, steam, and ash emissions, and variable seismic activity. The number of seismic events related to fluid movement, emissions, and rock fracturing fluctuated throughout the week; seismicity was highest at the beginning of the week and notably high during 22-23 June with the most intense seismicity recorded since the current period of elevated activity began on 24 March. Earthquakes occurred at distances of 1-8 km from Arenas crater at depths of 1-6 km. A period of continuous ash emissions in the afternoon of 20 June was visible in webcam images. Ashfall was reported in Manizales. Ash emissions on 21 June rose as high as 1.3 km above the crater rim, drifted WNW, and continued to rise to as high as 4 km above the summit. Incandescence from the crater was visible coincident with pulsating ash emissions during 20-23 June. Gas, steam, and ash plumes rose as high as 1.8 km and drifted NW during 24-27 June. Minor ashfall was reported in the municipalities of Villamaría (28 km NW) and Manizales (28 km NW) on 22 and 25 June respectively. The Alert Level was lowered to Yellow, Level III (the second level on a four-level scale) on 27 June. SGC noted that monitoring data was more stable in recent weeks; earthquake magnitudes were overall lower, the locations were more random, and the patterns did not indicate magma movement. Additionally, thermal anomalies at the lava dome were less intense, ash emissions had decreased, and gas emissions remained relatively stable.

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

Popocatepetl, Mexico

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

CENAPRED reported that ongoing activity at Popocatépetl during 20-27 June included 14-66 daily steam-and-gas emissions, sometimes containing minor amounts of ash. Seismic activity was characterized as daily periods of high-frequency events and variable amplitude tremors, volcano-tectonic earthquakes (2235 and 2329 on 21 June, 1520 and 2134 on 26 June), 15 minutes of low-amplitude harmonic tremor during 21-22 June, and both minor and moderate explosions. Small bursts of incandescent ejecta from the crater were observed during the night of 20 June. Minor ashfall was reported in Cuernavaca (66 km W), state of Morelos, during 20-21 June. At 0312 on 22 June a moderate explosion ejected incandescent ballistic material as far as 1.5 km from the crater and generated an ash plume that rose 2 km above the crater. Minor amounts of fell in Hueyapan (16 km SSW), state of Morelos, during 21-22 June. Minor explosions at 0405 and 0745 on 23 June produced ash plumes that rose 500 m; the first explosion ejected incandescent material short distances from the crater. Ashfall was reported in the municipalities of Ozumba (19 km W), Tepetlixpa (21 km W), Juchitepec (29 km WNW), and Amecameca (19 km NW), all within the State of México. A minor explosion was recorded at 0809 on 27 June. The Alert Level remained at Yellow, Phase Two (the middle level on a three-color scale) and the public was warned to stay 12 km away from the crater.

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 20-27 June. Seismicity was characterized by 7-30 daily explosions, long-period earthquakes, harmonic tremor, and tremor associated with emissions. Weather clouds often hindered visual observations, though crater incandescence was visible on most nights and early mornings, and from the S-flank lava flow on 21-22 June. During 21-23 June ash emissions rose as high as 1 km above the crater and drifted to the NE, W, and NW. During 23-26 June gas-and-ash emissions rose as high as 1 km above the crater and drifted to the W and NW. 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 the level of the water lake in Rincón de la Vieja’s summit crater declined during 30 May-21 June based on drone footage. A small phreatic eruption occurred at 0607 on 22 June. Several small phreatic eruptions were recorded overnight during 25-26 June. A small event at 0547 on 26 June produced a steam-and-gas plume that rose 1.5 km above the crater rim. Another small event at 0308 on 27 June produced a gas-and-steam plume that rose more than 1 km, though weather clouds and darkness obscured views. The Alert Level remained at 3 (the second highest level on a 0-4 scale).

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.

Santa Maria, Southwestern Guatemala

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

INSIVUMEH reported that the eruption at Santa Maria’s Santiaguito lava dome complex continued during 20-27 June, with effusion of lava flows, explosions, and avalanches. Dome growth sometimes produced avalanches and short pyroclastic flows that traveled down the S, SW, and W flanks. Weak and moderate explosions were recorded daily. Explosions also triggered dome collapses, resulting in weak and moderate debris avalanches that descended the flanks in many directions. Incandescence at the crater and along lava flow margins was visible during most nights and early mornings. During 20-21 June ash-and-gas plumes rose 800 m and drifted W and SW. On 23 June a lahar descended the Río Cabello de Ángel, a tributary of the Nimá I and Samalá rivers on the E flank. The lahar consisted of a mixture of fine volcanic material, water, volcanic blocks up to 1 m in diameter, and tree trunks and branches.

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 21-27 June. White-and-gray or white-to-brown ash plumes of variable densities generally rose as high as 1 km above the summit and drifted in multiple directions; emissions were not visible on 25 June, a partly cloudy day. A webcam image showed incandescent material at the summit and on the flanks at 0145 on 23 June. According to Info Semeru (a local news source) a pyroclastic flow traveled 5 km down the SE flanks at 1910 on 26 June. PVMBG reported that at the same time a gray-to-brown ash plume rose 1.5 km above the summit and drifted NE and E, and a webcam image showed incandescent material descending the flank. The Alert Level remained at 3 (third highest on a scale of 1-4). The public was warned to stay at least 5 km away from the summit in all directions, 13 km from the summit to the SE, 500 m from the banks of the Kobokan drainage as far as 17 km from the summit, and to avoid other drainages including the Bang, Kembar, and Sat, due to lahar, avalanche, and pyroclastic flow hazards.

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

Sheveluch, Central Kamchatka (Russia)

56.653°N, 161.36°E | Summit elev. 3283 m

KVERT reported that the eruption at Sheveluch was ongoing during 15-22 June. Intense fumarolic activity at the active crater was likely associated with growth of the lava dome. A thermal anomaly over the active crater area was identified in satellite images during 16, 18-19, and 22 June. 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 at low levels during 21-27 June. At 1521 on 25 June an eruptive event produced an ash plume that rose 1.3 km above the crater rim and drifted to the N, and ejected a large block 100 m from the crater. At 0036 on 27 June an ash plume rose 1.2 km and drifted N, followed by another at 0909 that rose 1.8 km and drifted E. The Alert Level remained at 2 (on a 5-level scale) and the public was warned to stay at least 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 Institution / US Geological Survey Weekly Volcanic Activity Report – June 21 – 27, 2023 – Managing Editor: Sally Sennert.


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