The Weekly Volcanic Activity Report: December 2 - 8, 2020

The Weekly Volcanic Activity Report: December 2 - 8, 2020

New activity/unrest was reported for 5 volcanoes from December 2 to 8, 2020. During the same period, ongoing activity was reported for 14 volcanoes.

New activity/unrest: Lewotolo, Lomblen Island (Indonesia) | Manam, Papua, New Guinea | Merapi, Central Java (Indonesia) | Piton de la Fournaise, Reunion Island (France) | Telica, Nicaragua.

Ongoing activity: Aira, Kyushu (Japan) | Dukono, Halmahera (Indonesia) | Ebeko, Paramushir Island (Russia) | Ibu, Halmahera (Indonesia) | Karymsky, Eastern Kamchatka (Russia) | Klyuchevskoy, Central Kamchatka (Russia) | Korovin, Andreanof Islands (USA) | Nevado del Ruiz, Colombia | Semeru, Eastern Java (Indonesia) | Sheveluch, Central Kamchatka (Russia) | Sinabung, Indonesia | Suwanosejima, Ryukyu Islands (Japan) | Villarrica, Chile | Whakaari/White Island, North Island (New Zealand).

The Weekly Volcanic Activity Report is a cooperative project between the Smithsonian's Global Volcanism Program and the US Geological Survey's Volcano Hazards Program. Updated by 23:00 UTC every Wednesday, these reports are preliminary and subject to change as events are studied in more detail. This is not a comprehensive list of all of Earth's volcanoes erupting during the week, but rather a summary of activity at volcanoes that meet criteria discussed in detail in the "Criteria and Disclaimers" section. Carefully reviewed, detailed reports about recent activity are published in issues of the Bulletin of the Global Volcanism Network.

New/activity unrest

Lewotolo, Lomblen Island (Indonesia)

PVMBG reported that the eruption at Lewotolo continued during 1-8 December. Black-and-gray ash plumes were visible daily, rising as high as 1.5 km abo e the summit. Incandescence at the summit was visible nightly and material was sometimes ejected as high as 20 m above the summit. BNPB noted that by 5 December there were a total of 9,028 people housed in 11 evacuation centers. The Alert Level was remained at 3 (on a scale of 1-4) and the public was warned to stay 4 km away from the summit crater.

Geological summary: Anchoring the eastern end of an elongated peninsula that is connected to Lembata (formerly Lomblen) Island by a narrow isthmus and extends northward into the Flores Sea, Lewotolo rises to 1423 m. Lewotolo is a symmetrical stratovolcano as 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. Historical eruptions, recorded since 1660, have consisted of explosive activity from the summit crater.

Manam, Papua New Guinea

Based on analyses of satellite imagery and model data, the Darwin VAAC reported that on 6 December an ash emission from Manam rose to an altitude of 2.4 km (8,000 ft) a.s.l. and drifted SW.

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 (Indonesia)

BPPTKG and PVMBG reported that during 27 November-8 December white emissions from Merapi rose as high as 600 m above the summit. Rock avalanches were heard, though not visually confirmed due to weather conditions. A comparison of photos taken on 26 and 29 November showed no morphology changes in the summit area. Seismicity was higher than the previous week. Electronic Distance Measurement (EDM) data continued to measure a distance shortening between points in the NW at a rate of 11 cm per day. The Alert Level remained at 3 (on a scale of 1-4).

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.

Piton de la Fournaise, Reunion Island (France)

OVPF reported that a seismic crisis at Piton de la Fournaise was recorded during 0510-0554 on 4 December and was accompanied by minor, but rapid, deformation located just below the center and N rim of Dolomieu Crater. Seismicity declined after the crisis but inflation continued through 6 December. A second seismic crisis began at 0228 on 7 December and was again accompanied by rapid deformation. At about 0440 three fissures opened on the WSW flank of Dolomieu Crater at elevations between 2,300 and 2,190 m, spanning a 700-m-long area. Lava began erupting during 0455-0500. An overflight was conducted during 0700-0730; scientists observed lava fountains rising 15 m high from the three fissures and short lava flows. By 1700 the fissure at the highest elevation was the most active with five small vents while the other two fissures were noticeably less active. The eruption phase ended at 0715 on 8 December following a gradual drop in tremor and a three-hour phase of seismic signals indicating degassing. No surficial activity was visible.

Geological summary: The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano. This volcano is located within the Pitons, Cirques et Remparts de I'ile de la Reunion, a UNESCO World Heritage property.

Telica, Nicaragua

INETER reported that there were 598 “low energy” ash-and-gas explosions at Telica recorded during 1-3 December, making a total of 775 recorded since the activity began on 30 November. Gas-and-ash plumes rose 50-400 m above the crater rim and mainly drifted SW. Ashfall was reported in areas downwind including in Zarandaj (7 km WSW), Cristo Rey (6 km W), Las Colinas (7 km WSW), Garrobo Empinado (8 km SW), El Panal (9 km SSW), Canta Rana, Ceibo Chachagua (10 km SW), Las Mercedes, Punta Arena (11 km SW), La Virgen, and Filiberto Morales (15 km WSW).

Geological summary: Telica, one of Nicaragua's most active volcanoes, has erupted frequently since the beginning of the Spanish era. This volcano group consists of several interlocking cones and vents with a general NW alignment. Sixteenth-century eruptions were reported at symmetrical Santa Clara volcano at the SW end of the group. However, its eroded and breached crater has been covered by forests throughout historical time, and these eruptions may have originated from Telica, whose upper slopes in contrast are unvegetated. The steep-sided cone of Telica is truncated by a 700-m-wide double crater; the southern crater, the source of recent eruptions, is 120 m deep. El Liston, immediately E, has several nested craters. The fumaroles and boiling mudpots of Hervideros de San Jacinto, SE of Telica, form a prominent geothermal area frequented by tourists, and geothermal exploration has occurred nearby.

Ongoing activity

Aira, Kyushu (Japan)

Based on satellite and wind model data, the Darwin VAAC reported that during 4-7 December ash plumes from Dukono rose to 2.1 km (7,000 ft) a.s.l. and drifted NE, E, and SE. 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: 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.

Dukono, Halmahera (Indonesia)

Volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, observed explosions during 28-30 November and 3 December that sent ash plumes up to 4.5 km (14,800 ft) a.s.l. and drifted NE and E. Ashfall was reported in Severo-Kurilsk on 28 November. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

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.

Ibu, Halmahera (Indonesia)

KVERT reported that strong explosions at Karymsky were last observed on 8 November 2019 and a thermal anomaly was last visible in satellite images on 19 November 2019. Gas-and-steam emissions persist. Since activity had significantly decreased, the Alert Level was lowered to Yellow (the second lowest level on a four-color scale) on 3 December.

Geological summary: The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, contained several small crater lakes through much of historical time. The outer crater, 1.2 km wide, is breached on the north side, creating a steep-walled valley. A large parasitic cone is located ENE of the summit. A smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. Only a few eruptions have been recorded in historical time, the first a small explosive eruption from the summit crater in 1911. An eruption producing a lava dome that eventually covered much of the floor of the inner summit crater began in December 1998.

Karymsky, Eastern Kamchatka (Russia)

KVERT reported that strong explosions at Karymsky were last observed on 8 November 2019 and a thermal anomaly was last visible in satellite images on 19 November 2019. Gas-and-steam emissions persist. Since activity had significantly decreased, the Alert Level was lowered to Yellow (the second lowest level on a four-color scale) on 3 December.

Geological summary: Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Klyuchevskoy, Central Kamchatka (Russia)

KVERT reported that Strombolian and Vulcanian activity at Klyuchevskoy continued during 27 November-4 December and lava advanced down the Apakhonchich drainage on the SE flank. A large, bright thermal anomaly was identified daily in satellite images. During 20-21 and 23-26 November steam-and-gas plumes with some ash rose to 7 km (23,000 ft) a.s.l. and drifted 300 km NW and E. The Aviation Color Code remined at Orange (the second highest level on a four-color scale).

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

Korovin, Andreanof Islands (USA)

Seismic activity at Korovin had decreased, and satellite images showed no signs of unrest over the previous several weeks. AVO lowered the Alert Level to Green and the Aviation Color Code to Normal on 3 December.

Geological summary: Korovin, the most frequently active volcano of the large volcanic complex at the NE tip of Atka Island, contains a 1533-m-high double summit with two craters located along a NW-SE line. The NW summit has a small crater, but the 1-km-wide crater of the SE cone has an unusual, open cylindrical vent of widely variable depth that sometimes contains a crater lake or a high magma column. A fresh-looking cinder cone lies on the flank of partially dissected Konia volcano, located on the SE flank. The volcano is dominantly basaltic in composition, although some late-stage dacitic lava flows are present on both Korovin and Konia. This volcano is located within the Aleutian Islands, a UNESCO Biosphere Reserve property.

Nevado del Ruiz, Colombia

Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that during 1-8 December seismicity at Nevado del Ruiz was generally characterized by higher number of earthquakes that had larger magnitudes than the previous week. Several episodes of drumbeat signals were recorded, indicating ascent or growth of a lava dome in Arenas Crater. Gas-and-ash emissions were sometimes visible in webcam images. Two thermal anomalies were visible in satellite data. 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.

Semeru, Eastern Java (Indonesia)

PVMBG reported that the eruption at Semeru continued during 1-8 December. Rock avalanches were recorded by the seismic network almost daily and were visible most days, traveling 200-1,500 m down the Kobokan drainage. Eruptive events and rockfalls generated pyroclastic flows that traveled as far as 2.5 km down the Kobokan drainage on the SE flank during 1-3 and 5-6 December. BNPB noted that deposits from the 1 December pyroclastic flow were as thick as 15 m. According to the Darwin VAAC, ash plumes rose to altitudes of 4-6.1 km (13,000-20,000 ft) a.s.l., or 300-2,400 m above the summit, and drifted E and NE during 2 and 5-6 December. PVMBG noted that incandescent material was ejected 50-100 m above the summit during 5-8 December. The Alert Level remained at 2 (on a scale of 1-4), with a general exclusion zone of 1 km and extensions to 4 km in the SSE sector.

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. This volcano is located within the Bromo Tengger Semeru-Arjuno, a UNESCO Biosphere Reserve property.

Sheveluch, Central Kamchatka (Russia)

KVERT reported that a thermal anomaly over Sheveluch was identified in satellite images during 27 November-4 December. A gas-and-steam plume drifted 60 km NE on 30 November. The Aviation Color Code remained at Orange (the second-highest level on a four-color scale).

Geological summary: The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. 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 dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. 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.

Sinabung, Indonesia

PVMBG reported that an ash plume rose as high as 500 m above Sinabung’s summit on 2 December. Block avalanches were recorded by the seismic network almost daily, though they were not visually confirmed; however, on 6 December, they were observed traveling 300-500 m down the E and SE flanks. The Alert Level remained at 3 (on a scale of 1-4), with a general exclusion zone of 3 km that extends 5 km SE and 4 km NE.

Geological summary: Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. The youngest deposit is a SE-flank pyroclastic flow 14C dated by Hendrasto et al. (2012) at 740-880 CE. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

Suwanosejima, Ryukyu Islands (Japan)

JMA reported nighttime incandescence and intermittent eruptive activity at Suwanosejima’s Ontake Crater during 27 November-4 December. A total of 17 explosions were recorded, ejecting bombs up to 600 m away from the crater and producing gray-and-white plumes that rose 1.5 km above the crater rim. Ashfall was reported in Toshima village (4 km SSW). The Alert Level remained at 2 (on a 5-level scale).

Geological summary: The 8-km-long, spindle-shaped 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. Suwanosejima, one of Japan's most frequently active volcanoes, was in a state of intermittent strombolian activity from Otake, the NE summit crater, that began in 1949 and lasted until 1996, after which periods of inactivity lengthened. The largest historical 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 horseshoe-shaped 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, Chile

SERNAGEOMIN reported that a long-period (LP) event and associated explosion were recorded by Villarrica’s seismic network at 1844 on 5 December. An ash plume rose 160 m and drifted SSE, depositing ash onto the flanks. Incandescent material was also ejected onto the SSE flanks. The Alert Level remained at Yellow, the second lowest level on a four-color scale. ONEMI maintained an Alert Level Yellow (the middle level on a three-color scale) for the municipalities of Villarrica, Pucón (16 km N), Curarrehue, and the commune of Panguipulli, and the exclusion zone for the public of 500 m around the crater.

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.

Whakaari/White Island, North Island (New Zealand)

GeoNet reported that Whakaari/White Island observations and monitoring data indicated a gradual trend to lower activity levels during the previous two weeks. An overflight of the island on 2 December confirmed that ash emissions stopped and were not visible in satellite images during 2-7 December. Volcanic tremor levels and the number of local earthquakes decreased. Deformation data indicated subsidence around the active vents and parts of the Main Crater wall. Hot steam-and-gas emissions persisted. The Volcanic Alert Level was lowered to 1 and the Aviation Color Code was lowered to Green on 7 December.

Geological summary: The uninhabited Whakaari/White Island is the 2 x 2.4 km emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes. The SE side of the crater is open at sea level, with the recent activity centered about 1 km from the shore close to the rear crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. The formation of many new vents during the 19th and 20th centuries caused rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities. The official government name Whakaari/White Island is a combination of the full Maori name of Te Puia o Whakaari ("The Dramatic Volcano") and White Island (referencing the constant steam plume) given by Captain James Cook in 1769.

Source: GVP

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