The Weekly Volcanic Activity Report: December 21

New activity/unrest was reported for 2 volcanoes from December 21 to 27, 2022. During the same period, ongoing activity was reported for 16 volcanoes.

New activity/unrest: Etna, Sicily (Italy) | Kaitoku Seamount, Volcano Islands (Japan).

New activity/unrest

Etna, Sicily (Italy)

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 19-25 December. The active flow field consisted of overlapping lava flows that expanded into the Valle del Leone and the Valle del Bove. By 25 December the most active lava flow had descended to 2,150 m elevation. Gas emissions rose from the summit craters.

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.

Kaitoku Seamount, Volcano Islands (Japan)

After JMA first reported new activity around the Kaitoku Seamount in August, discolored water continued to be periodically visible in Sentinel satellite images through 27 December. Though weather clouds sometimes prevented views of the vent area, and on occasion no activity was visible in clear images, plumes of discolored water drifting away from the vent area appeared to become more frequent in October. Images from 18 October, and 22 and 27 November possibly captured material at the surface or an eruption plume rising above the water. The Japan Coast Guard posted pictures of disturbed water around the vent in November. Recent Sentinel images on 17 and 27 December captured plumes of discolored water drifting as far as 10 km from the vent area.

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.

Ongoing activity

Ahyi, Mariana Islands (USA)

Unrest continued to be detected at Ahyi Seamount during 21-27 December. Wake Island hydrophone sensors detected daily signals that possibly indicated explosions. An underwater plume was visible in satellite images during 26-27 December. 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)

JMA reported ongoing eruptive activity at Minamidake Crater (at Aira Caldera’s Sakurajima volcano) during 19-26 December. Crater incandescence was visible nightly. Sulfur dioxide emissions were slightly high at 1,500 tons per day on 19 December. An explosion at 0449 on 22 December ejected blocks 600-900 m from the vent. An explosion at 1954 on 24 December produced an ash plume that rose 1.2 km above the crater rim and ejected large blocks 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.

Alaid, Kuril Islands (Russia)

KVERT reported that a thermal anomaly over Alaid was identified in satellite images on 17 and 22 December; weather clouds obscured observations on the other days during 16-21 December. 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 highest and northernmost volcano of the Kuril Islands, Alaid is a symmetrical stratovolcano when viewed from the north, but has a 1.5-km-wide summit crater that is breached open to the south. This basaltic to basaltic-andesite volcano is the northernmost of a chain constructed west of the main Kuril archipelago. Numerous pyroclastic cones are present the lower flanks, particularly on the NW and SE sides, including an offshore cone formed during the 1933-34 eruption. Strong explosive eruptions have occurred from the summit crater beginning in the 18th century. Reports of eruptions in 1770, 1789, 1821, 1829, 1843, 1848, and 1858 were considered incorrect by Gorshkov (1970). Explosive eruptions in 1790 and 1981 were among the largest reported in the Kuril Islands.

Cotopaxi, Ecuador

On 23 December IG issued a special report about increased activity at Cotopaxi. A total of 27 ash emissions had been recorded since the eruption began on 21 October; one ash emission was recorded in October, four were recorded in November, and 22 were recorded by 23 December. Based on Washington VAAC notices, ash clouds drifted the farthest, 60 km NNW, on 26 November and 20 December after rising 2.2 km (the maximum recorded height) and 1.5 km above the crater rim, respectively. Ashfall on those two days was reported in the Mejía, Rumiñahui, and Quito regions. Ash samples from 21 October and 26 November revealed a slight increase in the total percentage of juvenile material; an analysis of 20 December ash was in progress. Increases in sulfur dioxide emissions were measured both by satellite and ground-based Differential Optical Absorption Spectroscopy (DOAS) instruments. Gas measurements taken during periodic overflights showed increases in the ratio of sulfur dioxide to hydrogen sulfide. Based on these and other monitoring data, IG reiterated that the activity was caused by magma in the volcano’s conduit, though not from new magma entering the system after the 2015 eruption.

Daily emissions with ash continued to be observed in webcam images and reported by the Washington VAAC during 23-27 December; weather clouds obscured views on 26 December. Gas-and-steam plumes with low ash content rose as high as 1.5 km above the crater rim and drifted in various directions. 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.

Dukono, Halmahera

PVMBG reported that almost daily white-and-gray plumes of variable densities rose from Dukono as high as 400 m above the summit and drifted N and E during 23-27 December. Inclement weather conditions sometimes prevented visual observations. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to remain outside of the 2-km exclusion zone.

Geological summary: Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia’s most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

Ebeko, Paramushir Island (Russia)

KVERT reported that moderate activity at Ebeko was ongoing during 15-22 December. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E) explosions on 18 December generated ash plumes that rose to 2.5 km (8,200 ft) a.s.l. and drifted NE. A thermal anomaly was identified in satellite images that same day; the volcano was obscured by weather clouds on the other days of the week. 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.

Great Sitkin, Andreanof Islands

AVO reported that satellite data acquired on 22 December confirmed that the lava flow field at Great Sitkin was advancing E. Slow lava effusion likely continued during 23-27 December, though nothing significant was visible in sometimes cloudy satellite images or detected in seismic data. Elevated surface temperatures were identified in satellite images during 21-23 and 25-27 December. 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.

Klyuchevskoy, Central Kamchatka (Russia)

On 22 December KVERT lowered the Aviation Color Code for Klyuchevskoy to Green (the lowest level on a four-color scale), noting that the eruption had ended in November and the thermal anomaly that had been identified in satellite images had returned to background levels. Dates are based on UTC times; specific events are in local time where noted.

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.

Manam, Northeast of New Guinea

The Darwin VAAC reported that on 26 December an ash plume from Manam rose to 3 km (10,000 ft) and drifted S and SSE based on satellite images.

Geological summary: The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country’s most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical basaltic-andesitic stratovolcano to its lower flanks. These valleys channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island’s shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most observed eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Merapi, Central Java

BPPTKG reported that the eruption at Merapi continued during 16-22 December and seismicity remained at high levels. The SW lava dome produced three lava avalanches that traveled as far as 1.5 km down the SW flank (upstream in the Kali Bebeng drainage). Sounds of falling material were noted four times. No significant morphological changes to the central and SW lava domes were evident. 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.

Reventador, Ecuador

IG described the ongoing eruption at Reventador as moderate during 21-27 December. Daily seismicity was characterized by explosions, long-period earthquakes, periods of harmonic tremor, and signals that indicated emissions. Gas, steam, and ash plumes, observed daily with webcams or reported by the Washington VAAC, rose as high as 1.3 km above the summit and drifted in multiple directions. Weather clouds occasionally prevented webcam and satellite views of the volcano. Crater incandescence was visible nightly or during the early morning hours; incandescent blocks rolled down all flanks, descending as far as 700 m.

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.

Sangay, Ecuador

IG reported a high level of activity at Sangay during 20-27 December, which included daily explosions, volcanic tremor, and gas, steam, and ash emissions. The daily count of explosions ranged from 708-1,250, though seismic data transmission was sometimes interrupted. Almost daily ash-and-gas plumes were identified in IG webcam images and satellite images according to the Washington VAAC; weather clouds sometimes prevented observations of the summit. Gas, steam, and ash plumes rose as high as 1.2 km above the volcano and drifted mainly NW, W, SW, and S. Multiple daily thermal anomalies were identified in satellite images. Crater incandescence was visible some nights and early mornings. Incandescent material was observed rolling down the SE flank during 26-27 December.

Geological summary: The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador’s volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within the open calderas of two previous edifices which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been eroded by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of an eruption was in 1628. Almost continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex. This volcano is located within the Sangay National Park, a UNESCO World Heritage property.

Sheveluch, Central Kamchatka (Russia)

KVERT reported that the ongoing eruption at Sheveluch during 15-22 December 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 were visible drifting 110 km NNE on 16 December. 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)

INGV reported that both explosive and effusive activity at Stromboli were observed during 19-25 December at four vents in Area N, one N1 vent and three N2 vents; all were located in the upper portion of the Sciara del Fuoco. Explosions from the vents were variable in intensity and ejected coarse material (bombs and lapilli) 80-150 m high at a rate of 3-10 explosions per hour. Intense spattering from all four vents occurred during the week. Lava flows reached about halfway down the Sciara del Fuoco.

At 0942 on 19 December 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 1547 on 21 December and traveling about the same distance. On 22 December explosive activity at the Central-South area (CS) ejected fine-to-coarse material as high as 150 m above the vent.

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. This volcano is located within the Isole Eolie (Aeolian Islands), a UNESCO World Heritage property.

Suwanosejima, Ryukyu Islands (Japan)

JMA reported that the eruption at Suwanosejima’s Ontake Crater continued during 19-26 December. No explosions were recorded. Eruption plumes rose at least 1 km above the crater rim and disappeared into weather clouds, and blocks were ejected as far as 30 m from the vent. Ashfall was occasionally reported in Toshima village (3.5 km SSW) during 23-26 December. 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

SERNAGEOMIN reported that at 0845 on 24 December a volcano-tectonic earthquake at Villarrica was followed by increased Strombolian activity. Explosions ejected material generally to heights of less than 100 m, though one explosion ejected incandescent tephra as far as 400 m onto the SW flank. According to POVI, there were 11 ejections of incandescent ballistics that impacted the upper SW flank between 2225 on 25 December to 0519 on 26 December. The Alert Level remained at Yellow (the second lowest level on a four-color scale) and the public was warned that material could be ejected within 500 m of the crater. 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 – December 21 – 27, 2022 – Managing Editor: Sally Kuhn Sennert

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