The Weekly Volcanic Activity Report: January 25 – 31, 2023
New activity/unrest was reported for 7 volcanoes from January 25 – 31, 2023. During the same period, ongoing activity was reported for 18 volcanoes.
New activity/unrest: Asosan, Kyushu (Japan) | Chikurachki, Paramushir Island (Russia) | Epi, Vanuatu | Erta Ale, Ethiopia | Lascar, Northern Chile | Myojinsho, Izu Islands | Nishinoshima, Izu Islands.
Ongoing activity: Ahyi, Mariana Islands (USA) | Aira, Kyushu (Japan) | Cotopaxi, Ecuador | Ebeko, Paramushir Island (Russia) | Etna, Sicily (Italy) | Great Sitkin, Andreanof Islands (USA) | Kaitoku Seamount, Volcano Islands (Japan) | Kilauea, Hawaiian Islands (USA) | Krakatau, Sunda Strait | Lewotolok, Lembata Island | Merapi, Central Java | Popocatepetl, Mexico | Sabancaya, Peru | Semeru, Eastern Java | Semisopochnoi, Aleutian Islands (USA) | Sheveluch, Central Kamchatka (Russia) | Stromboli, Aeolian Islands (Italy) | Suwanosejima, Ryukyu Islands (Japan).
Asosan, Kyushu (Japan)
32.884°N, 131.104°E | Summit elev. 1592 m
JMA reported that the amplitude of volcanic tremor signals at Asosan increased at around 1200 on 30 January and then increased again around 1220 and remained high. At 1330 JMA raised the Alert Level to 2 (on a scale of 1-5) and warned the public to stay at least 1 km away from the crater. White plumes were visible rising 300 m above the crater rim.
Geological summary: The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan’s most active volcanoes. It was the location of Japan’s first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu’s most popular tourist destinations.
Chikurachki, Paramushir Island (Russia)
50.324°N, 155.461°E | Summit elev. 1781 m
KVERT reported that an explosive eruption at Chikurachki likely began at 0630 on 29 January. Ash plumes rose to as high as 3 km (10,000 ft) a.s.l. and drifted 75 km SE based on satellite data. The Aviation Color Code was raised to Orange (the second highest level on a four-color scale). At 1406 and 1720 ash plumes were identified in satellite images rising to 4.3 km (14,000 ft) a.s.l. and drifting 70 km E. Ash plumes had dissipated by 2320.
Geological summary: Chikurachki, the highest volcano on Paramushir Island in the northern Kuriles, is a relatively small cone constructed on a high Pleistocene edifice. Oxidized basaltic-to-andesitic scoria deposits covering the upper part of the young cone give it a distinctive red color. Frequent basaltic Plinian eruptions have occurred during the Holocene. Lava flows have reached the sea and formed capes on the NW coast; several young lava flows are also present on the E flank beneath a scoria deposit. The Tatarinov group of six volcanic centers is located immediately to the south, and the Lomonosov cinder cone group, the source of an early Holocene lava flow that reached the saddle between it and Fuss Peak to the west, lies at the southern end of the N-S-trending Chikurachki-Tatarinov complex. In contrast to the frequently active Chikurachki, the Tatarinov centers are extensively modified by erosion and have a more complex structure. Tephrochronology gives evidence of an eruption around 1690 CE from Tatarinov, although its southern cone contains a sulfur-encrusted crater with fumaroles that were active along the margin of a crater lake until 1959.
16.68°S, 168.37°E | Summit elev. 833 m
The Wellington VAAC reported that a low-level plume of ash and sulfur dioxide from a new eruption at Epi was identified in satellite data at 0730 on 31 January. According to the Vanuatu Meteorology and Geo-Hazards Department (VMGD) residents saw steaming at the ocean’s surface in the area over the vents at around 0748, and phreatic explosions that ejected steam and tephra 100 m above the water. The Alert Level was raised to 1 (on a scale of 0-5) and the public was warned to stay 10 km away from the East Epi submarine volcano. Observers reportedly saw a growing cone from ongoing ash emissions. The VAAC noted that the eruption was short-lived and had ceased by 1548; the ash had dissipated.
Three submarine cones, Epi A, Epi B, and Epi C, and smaller cones and craters, are located 10-16 km NNE from the summit of Epi Island and are aligned along the N rim of an inferred caldera. Epi B is the shallowest of the seamounts and has been historically active, most recently in February 2004. A March 2004 bathymetric survey revealed that Epi B was about 300 m tall, with a diameter of about 1.8 km at the base. The summit crater was about 150 m in diameter and the crater floor was at a depth of 90 m. The highest point was on the NW rim of the summit crater, at a depth of 34 m.
Geological summary: A large caldera, with submarine post-caldera cones active in historical time, lies off the eastern coast of Epi Island. Epi Island itself, located slightly west of the main New Hebrides volcanic arc, largely consists of two Quaternary volcanoes, Mount Allombei on the west and Pomare (Tavani Kutali) on the east. Tavani Ruro, which forms an elongated eastern extension of Epi Island across a narrow isthmus, is related to Kuwae caldera to the east. Pomare volcano is the highest point on the island and has three well-preserved subsidiary cones to the east with youthful summit craters. Pomare volcano is truncated on its eastern side by the largely submarine East Epi caldera, which has been the source of all historical eruptions. Three small submarine basaltic and dacitic cones, known as Epi A, Epi B, and Epi C, are located along the northern rim of the breached caldera. Ephemeral islands were formed during eruptions in 1920 and 1953, and the summit of the shallowest cone, Epi B, was at 34 m below sea level at the time of a 2001 survey.
Erta Ale, Ethiopia
13.6°N, 40.67°E | Summit elev. 613 m
Small thermal anomalies in both of Erta Ale’s N and S pit craters were identified in satellite images on 23 January. On 28 January the anomaly in the N pit crater was large and intense.
Geological summary: The Erta Ale basaltic shield volcano is the most active in Ethiopia, with a 50-km-wide edifice that rises more than 600 m from below sea level in the barren Danakil depression. It is the namesake and most prominent feature of the Erta Ale Range. The volcano includes a 0.7 x 1.6 km elliptical summit crater hosting steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located SE of the summit and is bounded by curvilinear fault scarps on the SE side. Fresh-looking basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera usually also holds at least one long-term lava lake that has been active since at least 1967, or possibly since 1906. Recent fissure eruptions have occurred on the N flank.
Lascar, Northern Chile
23.37°S, 67.73°W | Summit elev. 5592 m
SERNAGEOMIN reported increased seismicity at Láscar on 26 January with long-period (LP) events indicating fluid movement at shallower depths. The Alert Level was raised to Yellow (the second lowest level on a four-color scale) and SENAPRED warned the public to stay at least 3 km away from the crater. ONEMI declared an Alert Level Yellow (the middle level on a three-color scale) for San Pedro de Atacama (70 km NW). A seismic signal at 2259 corresponded to the ejection of incandescent material and the emission of a plume that likely contained tephra and rose almost 1.9 km and drifted NW.
The intensity of LP events significantly increased at 2300 on 27 January and remained at anomalous levels. A series of four LP events were recorded at 0015, 0032, 0043, and 0052 on 28 January and corresponding emissions rose 380 m above the crater rim and drifted NW. An M 3.2 volcano-tectonic earthquake was recorded at 0115 and felt by residents. LP earthquakes continued to be detected, along with tremor and volcano-tectonic events to a lesser extent. Minor crater incandescence was visible and gas plumes rose as high as 760 m. At 0430 the Alert Level was raised to Orange and the restricted zone was increased to 5 km. Elevated levels of seismicity continued to be detected during 28-30 January. Whitish-gray gas plumes possibly containing tephra rose to low heights and minor crater incandescence was occasionally observed. On 31 January SERNAGEOMIN stated that a satellite image from the day before showed a dome-like feature on the crater floor that was 81 m by 93 m in dimension and covered an area of about 5,332 square meters. The exclusion zone was increased to 10 km.
Geological summary: Láscar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters. Prominent lava flows descend its NW flanks. An older, higher stratovolcano 5 km E, Volcán Aguas Calientes, displays a well-developed summit crater and a probable Holocene lava flow near its summit (de Silva and Francis, 1991). Láscar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires.
Myojinsho, Izu Islands
31.888°N, 139.918°E | Summit elev. 11 m
According to JMA an area of pale yellow-green discolored water with a diameter of about 100 m was visible about 65 km SSE of Myojinsho on 26 January, based on an overflight conducted by the Japan Coast Guard. An eruption warning was issued to mariners. Discolored water was last observed in March 2017.
Geological summary: Beyonesu Rocks represent part of the barely exposed rim of the largely submarine Myojinsho caldera. Formation of the 8-9 km wide caldera was followed by construction of a large (2.6 km3) lava dome and/or lava flow complex on the caldera floor, originally located at a depth of 1000-1100 m. Most historical eruptions, recorded since the late-19th century, have occurred from the large post-caldera Myojinsho lava dome on the NE rim of the caldera. Deposits from submarine pyroclastic flows associated with growth of the dacitic lava dome mantle the conical dome and extend into the NE part of the caldera and down its outer slopes. An explosive submarine eruption from Myojinsho in 1952 destroyed a Japanese research vessel, killing all 31 on board. Submarine eruptions have also been observed from other points on the caldera rim and outside of the caldera. The Beyonesu Rocks were named after the French warship the Bayonnaise, which was surveying volcanic islands south of Tokyo Bay in 1850.
Nishinoshima, Izu Islands
27.247°N, 140.874°E | Summit elev. 25 m
The Japan Coast Guard reported that during an overflight of Nishinoshima on 25 January scientists observed intermittent activity and small, blackish-gray plumes rising 900 m from the central part of the crater. The fumarolic zone on the E flank and base of the cone had expanded and emissions had intensified. Dark brown discolored water was visible all around the volcanic island.
Geological summary: The small island of Nishinoshima was enlarged when several new islands coalesced during an eruption in 1973-74. Another eruption that began offshore in 2013 completely covered the previous exposed surface and enlarged the island again. Water discoloration has been observed on several occasions since. The island is the summit of a massive submarine volcano that has prominent satellitic peaks to the S, W, and NE. The summit of the southern cone rises to within 214 m of the sea surface 9 km SSE.
Ahyi, Mariana Islands (USA)
20.42°N, 145.03°E | Summit elev. -75 m
Unrest at Ahyi Seamount continued during 24-31 January. Pressure sensors on Wake Island, 2,270 km E of Ahyi Seamount, detected a possible explosion signal on 25 January. Plumes of discolored water were identified in satellite images during 27-31 January. 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 eruptive activity at Minamidake Crater (at Aira Caldera’s Sakurajima volcano) during 23-30 January and crater incandescence was visible nightly. Two explosions were recorded on 24 January, though weather clouds prevented visual confirmation. Sulfur dioxide emissions were high at 2,800 tons per day on 26 January. An explosion at 2342 on 28 January produced an ash plume that rose 2.2 km above the crater rim and ejected large blocks as far as 700 m from the crater. 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 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.
0.677°S, 78.436°W | Summit elev. 5911 m
IG reported that the eruption at Cotopaxi continued during 24-31 January, characterized by almost daily gas-and-steam and ash emissions; inclement weather conditions prevented views of the volcano on 29 January. During 24-25 January steam-and-gas plumes rose to the crater level and drifted W. During 26-27 January gas-and-ash plumes rose less than 1 km above the crater rim and drifted SW and W. Minor ashfall was reported in San Agustín de Callo (18 km WSW), Lima Villacís, Mulaló, Barrancas, Ticatilín and Caspi (20 km WSW), and San Ramon (127 km W). Steam-and-gas emissions rose 600 m and drifted S on 28 January. A significant increase in the size and density of ash emissions was evident in satellite images at 0820 on 30 January. The plumes rose as high as 2.5 km above the crater rim and drifted SW, S, and SE. Minor amounts of ash fell in Mulaló and Latacunga (18 km WSW). Ash plumes rose as high as 1.7 km and drifted S and SE on 31 January. 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 19-26 January. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E) explosions during 20-24 January generated ash plumes that rose as high as 3.7 km (12,100 ft) a.s.l. and drifted SE, NE, and N. An ash plume was identified in satellite images drifting 40 km NE on 21 January and a thermal anomaly was visible during 21-22 January. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Dates are based on UTC times; specific events are in local time where noted.
Geological summary: The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.
Etna, Sicily (Italy)
37.748°N, 14.999°E | Summit elev. 3357 m
INGV reported that the vents at the NE base of Etna’s SE Crater, in the Valle del Leone at about 2,800 m elevation, continued to feed lava flows during 23-29 January, without notable changes compared to the week before. Intense gas emissions rose from Bocca Nuova Crater while gas emissions at Northeast Crater (NEC) and Voragine were minimal. Activity at Southeast Crater was characterized by fumarolic activity localized along the crater rim and from the May-June 2022 eruptive vent which also occasionally produced flashes of incandescence at night. Diffuse ash emissions rapidly dispersed with the wind.
Geological summary: Mount Etna, towering above Catania on the island of Sicily, has one of the world’s longest documented records of volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.
Great Sitkin, Andreanof Islands (USA)
52.076°N, 176.13°W | Summit elev. 1740 m
AVO reported that slightly elevated surface temperatures at Great Sitkin were identified in satellite images during 25-26 January. Seismicity was low during 25-31 January and a few small earthquakes recorded during 27-28 January. Satellite and webcam views were mostly cloudy. A 26 January radar image confirmed growth of the flow field to the E. 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.
Kaitoku Seamount, Volcano Islands (Japan)
26.127°N, 141.102°E | Summit elev. -95 m
Discolored water around the Kaitoku Seamount was visible in a 26 January Sentinel 2 satellite image. The plume was diffuse and dispersed a few kilometers E. No discolored water was visible in a 31 January image.
Geological summary: A submarine eruption was observed in 1984 from Kaitoku Seamount (Kaitoku Kaizan), a three-peaked submarine volcano 130 km NNW of Kita-Iojima. A submarine eruption had previously been reported in 1543 from a point about 40 km to the SW, which the Japan Meteorological Agency attributes to Kaitoku.
Kilauea, Hawaiian Islands (USA)
19.421°N, 155.287°W | Summit elev. 1222 m
HVO reported that lava continued to erupt in the E portion of Kilauea’s Halema’uma’u Crater floor during 24-31 January. Activity was concentrated in the E half of the crater in a large, perched lava lake with well-defined levees, covering about 10 hectares. A smaller lake to the W was active in the basin of the 2021-2022 lava lake. One dominant lava fountain, 6-7 m high, was active in the E lake. Small daily overflows occurred along the margins of the E lake. 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: Kilauea overlaps the E flank of the massive Mauna Loa shield volcano in the island of Hawaii. Eruptions are prominent in Polynesian legends; written documentation since 1820 records frequent summit and flank lava flow eruptions interspersed with periods of long-term lava lake activity at Halemaumau crater in the summit caldera until 1924. The 3 x 5 km caldera was formed in several stages about 1,500 years ago and during the 18th century; eruptions have also originated from the lengthy East and Southwest rift zones, which extend to the ocean in both directions. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1,100 years old; 70% of the surface is younger than 600 years. The long-term eruption from the East rift zone between 1983 and 2018 produced lava flows covering more than 100 km2, destroyed hundreds of houses, and added new coastline.
Krakatau, Sunda Strait
6.102°S, 105.423°E | Summit elev. 155 m
PVMBG reported that the eruption at Anak Krakatau continued during 24-31 January. Eruptive events at 0231 and 2256 on 25 January and 0003 on 26 January ejected incandescent material from the vent, based on webcam photos. Eruptive events at 0512, 0633, and 0732 on 26 January and 1312 on 27 January produced dense gray ash plumes that rose 300-500 m above the summit and drifted NE, E, and SE. Webcam images showed incandescent ejecta at 2135, 2144, and 2328 January. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay at least 5 km away from the crater.
Geological summary: The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of that volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption caused more than 36,000 fatalities, most as a result of tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.
Lewotolok, Lembata Island
8.274°S, 123.508°E | Summit elev. 1431 m
PVMBG reported that the eruption at Lewotolok was ongoing during 24-31 January. Nighttime webcam images captured near-daily incandescent material that was ejected above the summit crater. Almost daily emissions that were white and gray and had variable densities rose as high as 600 m above the summit and drifted SE, E, and NE. 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 continued during 20-26 January and seismicity remained at high levels. The SW lava dome produced 14 lava avalanches that traveled as far as 1.8 km down the SW flank (upstream in the Kali Bebeng drainage). Avalanche sounds were heard on seven occasions. No significant morphological changes at the SW dome were observed but the central dome decreased in height based on webcam images. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-7 km away from the summit based on location.
Geological summary: Merapi, one of Indonesia’s most active volcanoes, lies in one of the world’s most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities.
19.023°N, 98.622°W | Summit elev. 5393 m
CENAPRED reported that there were 81-238 steam-and-gas emissions, often containing ash, rising from Popocatépetl each day during 24-31 January and explosions occurred almost daily. Two explosions were recorded at 1424 and 1426 on 24 January. Minor ashfall was reported on 25 January in San Nicolás de los Ranchos (15 km ENE). Later that day, at 2231, an explosion ejected incandescent material onto the flanks. An overflight was conducted by Instituto de Geofísica de la Universidad Nacional Autónoma de México (UNAM) and the Guardia Nacional on 27 January to observe the crater. They saw a small lava dome that was about 30-40 m in diameter and 5-10 m tall on the inner crater floor. The inner crater floor had remnants of the previous domes mixed with fine tephra deposits and was 160-180 m deep. The rim of the inner crater was 390-410 m in diameter, similar to previous observations. A minor explosion later that day at 2214 produced an ash plume, based on a webcam image. Minor explosions were recorded at 0451, 0521, 1828, and 2232 on 28 January. A webcam image from 0343 on 29 January showed deposits of incandescent material that was ejected onto the flanks. Another explosion occurred at 2254. Explosions were noted at 0141 and 0621 on 30 January; minor ashfall was recorded in Amecameca (19 km NW), Temamatla (32 km NW), and Tenango Del Aire (28 km NW). A moderate explosion at 0029 on 31 January produced an ash plume that rose 1.8 km above the crater rim and ejected incandescent material onto the flanks almost 2 km from the crater rim. Minor explosions occurred at 0533, 0619, and 0721. 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.
15.787°S, 71.857°W | Summit elev. 5960 m
Instituto Geofísico del Perú (IGP) reported moderate levels of activity at Sabancaya during 23-29 January with a daily average of 59 explosions. Gas-and-ash plumes rose as high as 2.1 km above the summit and drifted SW and W. Four thermal anomalies originating from the lava dome in the summit crater were identified in satellite data. Minor inflation continued to be detected near Hualca Hualca (4 km N). 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.
Semeru, Eastern Java
8.108°S, 112.922°E | Summit elev. 3657 m
PVMBG reported that the eruption at Semeru continued during 24-31 January. Dense white-and-gray ash plumes rose 500-600 m above the summit at 0450 and 0540 on 25 January and drifted N. A dense gray ash plume rose 600 m at 0534 on 27 January and drifted NW, and at 0802 a dense white-and-gray ash plume rose 500 m and drifted N. At 0602 and 0639 on 29 January dense gray ash plumes rose 500-600 m and drifted NE. 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, and 500 m from Kobokan drainages within 17 km of the summit, along with 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 eruptive activity at Semisopochnoi’s Mount Young was ongoing during 24-31 January. Seismicity was elevated and daily weak tremor was recorded. Minor steam emissions were visible in webcam images on 24 January and 29-30 January. Discolored snow observed at the summit in webcam images during 28-29 January possibly indicated minor, low-level explosive activity at the vent. The Aviation Color Code remained at Orange (the second highest level on a four-color scale) and the Volcano Alert Level remained at Watch (the second highest level on a four-level scale).
Geological summary: Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island’s northern part. The three-peaked Mount Cerberus (renamed Mount Young in 2023) was constructed within the caldera during the Holocene. Each of the peaks contains a summit crater; lava flows on the N flank appear younger than those on the south side. Other post-caldera volcanoes include the symmetrical Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented eruptions have originated from Young, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone could have been recently active.
Sheveluch, Central Kamchatka (Russia)
56.653°N, 161.36°E | Summit elev. 3283 m
KVERT reported that the ongoing eruption at Sheveluch during 19-26 January was generally characterized by explosions, hot avalanches, lava-dome extrusion, and strong fumarolic activity. A daily thermal anomaly was identified in satellite images, and minor ash plumes from explosions and lava-dome collapses drifted 25 km SW on 22 January. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Dates are based on UTC times; specific events are in local time where noted.
Geological summary: The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1,300 km3 andesitic volcano is one of Kamchatka’s largest and most active volcanic structures, with at least 60 large eruptions during the Holocene. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes occur on its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large open caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.
Stromboli, Aeolian Islands (Italy)
38.789°N, 15.213°E | Summit elev. 924 m
INGV reported that both explosive and effusive activity at Stromboli occurred during 23-29 January at four vents in Area N, within the upper part of the Sciara del Fuoco, and at two vents in the Area C-S (South-Central Crater area) in the crater terrace area. Explosions at vents N1 and N2 in Area N were variable in intensity and ejected coarse material (bombs and lapilli) 80-150 m at a rate of 4-6 explosions per hour. Intense spattering occasionally occurred at N2 vents. Explosive activity at the Central-South area (CS) ejected fine-to-coarse material as high as 150 m above the vent at a rate of 6-7 explosions per hour during 23-27 January; the rate decreased to less than one event per hour the rest of the week.
At 1419 on 24 January lava overflowed vents in the N2 area after a period of intense spattering. The lava flowed partially down the Sciara del Fuoco, and by the next morning, they were cooling. A major explosion began at 1007 on 30 January that lasted three minutes long. Coarse pyroclastic material was ejected several hundred meters high and was deposited on the crater terrace and the upper parts of the Sciara del Fuoco. An ash cloud quickly dispersed to the S.
Geological summary: Spectacular incandescent nighttime explosions at Stromboli have long attracted visitors to the “Lighthouse of the Mediterranean” in the NE Aeolian Islands. This volcano has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent scarp that formed about 5,000 years ago due to a series of slope failures which extends to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.
Suwanosejima, Ryukyu Islands (Japan)
29.638°N, 129.714°E | Summit elev. 796 m
JMA reported that the eruption at Suwanosejima’s Ontake Crater continued during 23-30 January. The number of explosions increased on 26 January; a total of 13 explosions were recorded during the week. The explosions produced eruption plumes that rose as high as 1.7 km above the crater rim and entered weather clouds. Large blocks were ejected as far as 400 m from the crater’s center. Nighttime crater incandescence was observed starting on 26 January. Ashfall was reported in Toshima village (3.5 km SSW). The Alert Level remained at 2 (on a 5-level scale) and residents were warned to stay 1 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 – January 25 – 31, 2023 – Managing Editor: Sally Kuhn Sennert
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