The Weekly Volcanic Activity Report: January 4 – 10, 2023

the weekly volcanic activity report

New activity/unrest was reported for 5 volcanoes from January 4 to 10, 2023. During the same period, ongoing activity was reported for 19 volcanoes.

New activity/unrest: Ijen, Eastern Java | Kaitoku Seamount, Volcano Islands (Japan) | Kilauea, Hawaiian Islands (USA) | Marapi, Central Sumatra | Semisopochnoi, Aleutian Islands (USA).

Ongoing activity: Ahyi, Mariana Islands (USA) | Aira, Kyushu (Japan) | Cleveland, Chuginadak Island (USA) | Cotopaxi, Ecuador | Ebeko, Paramushir Island (Russia) | Etna, Sicily (Italy) | Fuego, South-Central Guatemala | Great Sitkin, Andreanof Islands (USA) | Kerinci, Central Sumatra | Krakatau, Sunda Strait | Merapi, Central Java | Nevado del Ruiz, Colombia | Nevados de Chillan, Central Chile | Santa Maria, Southwestern Guatemala | Semeru, Eastern Java | Sheveluch, Central Kamchatka (Russia) | Stromboli, Aeolian Islands (Italy) | Suwanosejima, Ryukyu Islands (Japan) | Villarrica, Central Chile.

New activity/unrest

Ijen, Eastern Java

8.058°S, 114.242°E | Summit elev. 2769 m

PVMBG reported that beginning in July 2022 the seismic network at Ijen began detecting increasing numbers of shallow volcanic earthquakes and earthquake signals characteristic of emissions, indicating increasing pressure at shallow depths within the hydrothermal system. The number of shallow volcanic earthquakes again increased on 1 January. The temperature of the crater lake water rose from 16 degrees Celsius in December 2022 to 45.6 degrees Celsius on 5 January 2023. During a field visit on 5 January scientists noted that the color of the lake water was light green, dense white solfatara plumes were visible rising from vents, and the sulfur odor was strong. Increased activity at the volcano is often characterized by a change in the lake water color from green to whitish-green due to the resuspension of disturbed lake-bottom sediments from increased gas emissions. The elevated unrest promoted PVMBG to raise the Alert Level to 2 (on a scale of 1-4) on 7 January. Residents, visitors, and miners were advised to not approach the crater within 1.5 km.

Geological summary: The Ijen volcano complex at the eastern end of Java consists of a group of small stratovolcanoes constructed within the 20-km-wide Ijen (Kendeng) caldera. The north caldera wall forms a prominent arcuate ridge, but elsewhere the rim was buried by post-caldera volcanoes, including Gunung Merapi, which forms the high point of the complex. Immediately west of the Gunung Merapi stratovolcano is the historically active Kawah Ijen crater, which contains a nearly 1-km-wide, turquoise-colored, acid lake. Kawah Ijen is the site of a labor-intensive mining operation in which baskets of sulfur are hand-carried from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of cones forms an E-W zone across the southern side of the caldera. Coffee plantations cover much of the caldera floor; nearby waterfalls and hot springs are tourist destinations.

Kaitoku Seamount, Volcano Islands (Japan)

26.127°N, 141.102°E | Summit elev. -95 m

Discolored water around the Kaitoku Seamount was visible in 1 and 6 January Sentinel satellite images. Concentric circles of discolored water radiated out from the vent area and a plume drifted W. The plume of discolored water extended S in the 6 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

Small earthquake swarms were recorded at Kilauea on 30 December 2022 and 2 January 2023, with heightened seismicity in between those dates. Increased seismicity and changes in the pattern of deformation began to be recorded during the morning of 5 January. At around 1500 both the rate of deformation and seismicity dramatically increased indicating magma moving towards the surface; at 1520 HVO raised the Volcano Alert Level to Watch (the second highest level on a four-level scale) and the Aviation Color Code to Orange (the second highest color on a four-color scale).

Incandescence seen in webcam images at 1634 on 5 January indicated that an eruption began in Halema’uma’u Crater, prompting HVO to raise the Volcano Alert Level to Warning (the highest level on a four-level scale) and the Aviation Color Code to Red (the highest color on a four-color scale). Vents opened in the E central portion of the crater floor and produced multiple lava fountains and flows. Fountain bursts ejected lava as high as 50 m during the initial phase of activity, though in general fountaining was consistently 10 m high. By 1930 lava had covered most of the crater floor (an area of about 120 hectares) to a depth of 10 m. A higher-elevation island that formed during the initial phase of the December 2020 eruption remained exposed (and appeared darker in images) along with a ring of older lava around the lava lake that was active prior to December 2022. Overnight during 5-6 January the lava fountains became less vigorous, rising to 5 m, and lava effusion slowed. By 0815 on 6 January HVO lowered the Volcano Alert Level to Watch and the Aviation Color Code to Orange because the initial high effusion rates were declining and there was no threat of significant volcanic ash outside of the closed area within?Hawai’i Volcanoes National Park. The sulfur dioxide emission rate was about 12,500 tonnes per day. Lava continued to erupt from the vents during 6-8 January, though the footprint of the active area had shrunk, which has been common during the early stages of recent eruptions within Halema’uma’u. By 9 January only one dominant fountain was visible that continued to be active at least through 10 January.

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.

Marapi, Central Sumatra

0.38°S, 100.474°E | Summit elev. 2885 m

PVMBG reported that an explosive eruption at Marapi began at 0611 on 7 January, generating a dense white-and-gray ash plume that rose 300 m above the summit and drifted SE. Images posted with the report showed jets of dark material rising from the crater. Emissions continued to periodically rise form the crater; at 0944, 1034, and 1451 dense white or white-to-gray ash plumes rose 200-250 m above the summit and drifted SE. Seismic signals indicated that eruptive events also occurred at 1135, 1144, 1230, 1715, and 1821, but no ash emissions were visually observed. At 1250 on 8 January a dense white ash plume rose 150 m and drifted SE and at 1300 a dense white-to-gray ash plume rose 200 m and drifted E. Seismic signals indicated eruptive events at 0447, 1038, and 1145, but again no ash emissions were visually observed. At 0634 on 9 January a dense white ash plume rose around 250 m and drifted E and SE. The eruption was preceded by an increase in the number of deep volcanic earthquakes beginning on 25 December 2022 and summit inflation. The Alert Level remained at 2 (on a scale of 1-4).

Geological summary: Gunung Marapi, not to be confused with the better-known Merapi volcano on Java, is Sumatra’s most active volcano. This massive complex stratovolcano rises 2,000 m above the Bukittinggi Plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide Bancah caldera. The summit craters are located along an ENE-WSW line, with volcanism migrating to the west. More than 50 eruptions, typically consisting of small-to-moderate explosive activity, have been recorded since the end of the 18th century; no lava flows outside the summit craters have been reported in historical time.

Semisopochnoi, Aleutian Islands (USA)

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

AVO reported that eruptive activity at Semisopochnoi’s Mount Young, formerly Mount Cerberus, was ongoing during 4-10 January. Daily minor steam emissions were visible in webcam views. Seismicity was above background levels; low-level explosive activity was detected in geophysical data during 4-5 January with elevated seismicity and infrasound signals observed on local stations. Volcanic tremor was detected during 7-9 January, and very weak explosive activity was detected in seismic and infrasound data on 9 January. 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.

Ongoing activity

Ahyi, Mariana Islands (USA)

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

Unrest continued to be detected at Ahyi Seamount during 4-10 January. Daily signals possibly indicating explosions were detected by hydrophone sensors on Wake Island (2,270 km E of Ahyi), though a data outage began at 0118 on 8 January. No activity was visible in mostly cloudy satellite images, though a plume of discolored water originating from the summit region of the seamount was seen in partly cloudy satellite images on 8 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 2-9 January. Crater incandescence was visible nightly. Sulfur dioxide emissions were slightly elevated at 1,000 tons per day on 4 January. One explosion on 3 January and two explosions on 8 January were recorded by the seismic network. Eruption plumes rose as high as 2.4 km above the crater rim and blocks were ejected as far as 1.1 km from the vent. 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.

Cleveland, Chuginadak Island (USA)

52.825°N, 169.944°W | Summit elev. 1730 m

AVO lowered both the Volcano Alert Level and the Aviation Color Code for Cleveland to Unassigned (insufficient monitoring to make an assessment) on 5 January, noting that signs of unrest had declined over the previous several months. Elevated surface temperatures in the summit crater were occasionally identified in satellite images but at a reduced frequency and strength. The last eruptive activity was a short-lived explosion on the evening of 1 June 2020, and sulfur dioxide emissions were last detected on 29 July 2022.

Geological summary: The beautifully symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited Chuginadak Island. It lies SE across Carlisle Pass strait from Carlisle volcano and NE across Chuginadak Pass strait from Herbert volcano. Joined to the rest of Chuginadak Island by a low isthmus, Cleveland is the highest of the Islands of the Four Mountains group and is one of the most active of the Aleutian Islands. The native name, Chuginadak, refers to the Aleut goddess of fire, who was thought to reside on the volcano. Numerous large lava flows descend the steep-sided flanks. It is possible that some 18th-to-19th century eruptions attributed to Carlisle should be ascribed to Cleveland (Miller et al., 1998). In 1944 it produced the only known fatality from an Aleutian eruption. Recent eruptions have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks.

Cotopaxi, Ecuador

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

IG reported that the low-level eruption at Cotopaxi continued during 3-11 January, characterized by daily steam-and-gas emissions often with low ash content. Plumes of gas, steam, and minor ash content rose as high as 1.7 km above the crater rim and drifted NW, W, SW, and E, based on webcam views, satellite images, and information from the Guayaquil Meteorological Office. Minor ashfall was reported in the sectors of Colcas, San Ramon, and San Agustin de Callo (18 km WSW). 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 29 December 2022-5 January 2023. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E) explosions during 31 December and 1-5 January generated ash plumes that rose as high as 4 km (13,100 ft) a.s.l. and drifted NE and E. A thermal anomaly was identified in satellite images during 3-4 January and an ash cloud drifted 12 km NE on 4 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 2-8 January. The active flow field consisted of overlapping lava flows that expanded into the Valle del Leone and the Valle del Bove and hornitos. By 7 January the longest active lava flow had descended to 2,170 m elevation, and the area of the flow field was an estimated 0.63 square kilometers. Gas emissions rose from the summit craters, mainly at Bocca Nuova.

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.

Fuego, South-Central Guatemala

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

INSIVUMEH reported that 2-8 explosions per hour were recorded at Fuego during 3-10 January, generating ash plumes that rose more than 1.2 km above the crater rim and drifted as far as 30 km in various directions. Daily ashfall was noted in areas downwind including Morelia (9 km SW), Panimaché I and II (8 km SW), Santa Sofía (12 km SW), El Porvenir (8 km ENE), Los Yucales (12 km SW), Sangre de Cristo (8 km WSW), El Porvenir (8 km ENE), San Pedro Yepocapa (8 km NW), and Finca Palo Verde. The avalanches occasionally resuspended ash deposits that rose 100 m and drifted W and SW. Daily shock waves rattled structures in communities around the volcano. Daily block avalanches descended the Ceniza (SSW), Seca (W), Trinidad (S), Taniluyá (SW), Honda, Las Lajas (SE), El Jute (ESE), and Trinity drainages, sometimes reaching vegetated areas. Strombolian explosions ejected incandescent material as high as 300 m above the summit almost daily.

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 4-10 January, though weather clouds often obscured satellite and webcam views. A few small daily earthquakes were detected during 6-10 January and slightly elevated surface temperatures were identified in satellite images during 7-10 January. 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.

Kerinci, Central Sumatra

1.697°S, 101.264°E | Summit elev. 3800 m

The eruption at Kerinci was ongoing during 4-8 January with brown, brown-to-gray, or white-and-brown ash plumes rising as high as 200 m above the crater rim and drifting NE and E. The Alert Level remained at 2 (on a scale of 1-4).

Geological summary: Gunung Kerinci in central Sumatra forms Indonesia’s highest volcano and is one of the most active in Sumatra. It is capped by an unvegetated young summit cone that was constructed NE of an older crater remnant. There is a deep 600-m-wide summit crater often partially filled by a small crater lake that lies on the NE crater floor, opposite the SW-rim summit. The massive 13 x 25 km wide volcano towers 2400-3300 m above surrounding plains and is elongated in a N-S direction. Frequently active, Kerinci has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838.

Krakatau, Sunda Strait

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

PVMBG reported that the eruption at Anak Krakatau continued. A dense gray ash plume was seen at 1410 on 4 January rising 100 m above the summit and drifting E, followed at 1509 by a dense gray-to-black ash plume to 3 km above summit that also drifted E. Another event at 0013 on 5 January sent a dense gray ash plume 750 m above the summit that drifted NE. Although weather sometimes prevented visual observations during 6-9 January, white plumes of variable intensities rose as high as 200 m from the summit and drifted mainly NE and E. 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.

Merapi, Central Java

7.54°S, 110.446°E | Summit elev. 2910 m

BPPTKG reported that the eruption at Merapi continued during 30 December 2022-5 January 2023 and seismicity remained at high levels. The SW lava dome produced eight lava avalanches that traveled as far as 1.5 km down the SW flank (upstream in the Kali Bebeng drainage). One pyroclastic flow descended 900 m SW. No significant morphological changes to the central and SW lava domes were evident in webcam images. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-7 km away from the summit based on location.

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

Nevado del Ruiz, Colombia

4.892°N, 75.324°W | Summit elev. 5279 m

Servicio Geológico Colombiano’s (SGC) reported that at 0706 on 6 January an ash cloud rose from Nevado del Ruiz and drifted NE, causing ashfall in Villahermosa (27 km NE). The ash emission occurred simultaneously with a seismic signal indicated moving fluids within the volcano’s conduit. The Alert Level remained at 3 (Yellow; the second lowest level on a four-color 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.

Nevados de Chillan, Central Chile

36.868°S, 71.378°W | Summit elev. 3180 m

On 10 January SERNAGEOMIN lowered the Alert Level for Nevados de Chillán to Green, the lowest level on a four-color scale. No activity at the surface had been observed since mid-October 2022; other data reflected ongoing internal processes, though recently the activity had been lower and gradually returning to background levels. The report reminded residents not to approach the crater within 500 m. According to ONEMI, Sistema Nacional de Prevención y Respuesta ante Desastres (SINAPRED) declared “Preventive Early Warning” for the communities of Pinto and Coihueco.

Geological summary: The compound volcano of Nevados de Chillán is one of the most active of the Central Andes. Three late-Pleistocene to Holocene stratovolcanoes were constructed along a NNW-SSE line within three nested Pleistocene calderas, which produced ignimbrite sheets extending more than 100 km into the Central Depression of Chile. The dominantly andesitic Cerro Blanco (Volcán Nevado) stratovolcano is located at the NW end of the massif. Volcán Viejo (Volcán Chillán), which was the main active vent during the 17th-19th centuries, occupies the SE end. The Volcán Nuevo lava-dome complex formed during 1906-1945 on the NW flank of Viejo. The Volcán Arrau dome complex was then constructed on the SE side of Volcán Nuevo between 1973 and 1986, and eventually exceeded its height. Smaller domes or cones are present in the 5-km valley between the two major edifices.

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 3-10 January. Effusion from Caliente cone fed lava flows that descended the San Isidro and El Tambor drainages on the W and SW flanks. Occasional block avalanches from the dome, and from both the ends and sides of the flows, descended the S, SW, and W flanks. The avalanches sometimes generated minor ash plumes that rose along their paths. Almost daily explosions produced gas-and-steam plumes with minor amounts of ash that rose as high as 800 m above the complex and sometimes drifted 5-8 km SW. Ashfall was reported in Las Marías (10 km S) and El Viejo Palmar (11 km S) during 8-9 January.

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 3-10 January; weather clouds prevented visual observations during 4-6 January. At 0503 on 7 January a white-to-gray ash plume rose 400 m above the summit and drifted N. Ash plumes of variable densities generally rose 200-400 m above the summit and drifted N and NE on 8 January. At 0819 a white-to-brown ash plume rose 500 m and drifted N and NE. A webcam image posted on social media showed an incandescent lava flow extending 500 m from the summit crater on the SE flank. On 9 January at 0652 a white-to-brown ash plume rose 200 m and drifted N and NE. On 10 January white-and-gray ash plumes rose as high as 300 m and drifted N and 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.

Sheveluch, Central Kamchatka (Russia)

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

KVERT reported that the ongoing eruption at Sheveluch during 29 December 2022-5 January 2023 was generally characterized by explosions, hot avalanches, lava-dome extrusion, and strong fumarolic activity. A daily thermal anomaly was identified in satellite images, and ash plumes from lava-dome collapses drifted 175 km E, NE, W, and SW during 30-31 December and 4-5 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 2-8 January at four vents in Area N, within the upper part of the Sciara del Fuoco, and at one vent in the Area C-S (South-Central Crater area) in the crater terrace area. The explosions were variable in intensity and ejected coarse material (bombs and lapilli) 80-150 m at a rate of 3-10 explosions per hour. Intense spattering from all four vents occurred during the week. Explosive activity at the Central-South area (CS) ejected fine-to-coarse material as high as 250 m above the vent at a rate of 1-4 explosions per hour.

At 2136 on 2 January lava overflowed vents in the N2 area, after a period of intense spattering. The lava flowed part way down the Sciara del Fuoco, likely channeled in the ravine that had formed in October, out of view from webcams. The flow was well-fed for a couple of hours but then effusion slowed or stopped, and it began to cool. The same activity occurred again, with a lava overflow occurring at 0224 on 4 January, traveling about the same distance, and cooling within a few hours.

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 2-9 January. No explosions were recorded, though eruption plumes rose as high as 1.3 km above the crater rim. During 2-6 January blocks were ejected as far as 200 m from the vent and ashfall was occasionally reported in Toshima village (3.5 km SSW). 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.

Villarrica, Central Chile

39.42°S, 71.93°W | Summit elev. 2847 m

SERNAGEOMIN reported that activity at Villarrica had increased in recent weeks, with explosions ejecting material almost as far as 480 m, near the extent of the 500 m exclusion zone in place around the crater. On 6 January the exclusion zone was increased to 1 km as a preventative measure. The Alert Level remained at Yellow (the second lowest level on a four-color scale). ONEMI maintained the Alert Level at Yellow (the middle level on a three-color scale) for the municipalities of Villarrica, Pucón (16 km N), Curarrehue, and the commune of Panguipulli.

Geological summary: Glacier-clad Villarrica, one of Chile’s most active volcanoes, rises above the lake and town of the same name. It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. A 6-km-wide caldera formed during the late Pleistocene. A 2-km-wide caldera that formed about 3500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesitic cone at the NW margin of the Pleistocene caldera. More than 30 scoria cones and fissure vents dot the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Historical eruptions, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

References:

Smithsonian / US Geological Survey Weekly Volcanic Activity Report – January 4 – 10, 2023 – Managing Editor: Sally Kuhn Sennert

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