The Weekly Volcanic Activity Report: December 1 – 7, 2021

the-weekly-volcanic-activity-report-december-1-7-2021

New activity/unrest was reported for 4 volcanoes from December 1 to 7, 2021. During the same period, ongoing activity was reported for 15 volcanoes.

New activity/unrest: Ambae, Vanuatu | Nyiragongo, DR Congo | Sangay, Ecuador | Semeru, Eastern Java (Indonesia).

Ongoing activity: Aira, Kyushu (Japan) | Etna, Sicily (Italy) | Fuego, Guatemala | Great Sitkin, Andreanof Islands (USA) | Grimsvotn, Iceland | Karymsky, Eastern Kamchatka (Russia) | Kilauea, Hawaiian Islands (USA) | La Palma, Spain | Lewotolok, Lembata Island (Indonesia) | Merapi, Central Java (Indonesia) | Pavlof, United States | Santa Maria, Guatemala | Semisopochnoi, Aleutian Islands (USA) | Sheveluch, Central Kamchatka (Russia) | Suwanosejima, Ryukyu Islands (Japan).

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

Ambae, Vanuatu

15.389°S, 167.835°E, Summit elev. 1496 m

The Vanuatu Meteorology and Geo-Hazards Department (VMGD) reported that steam emissions were visible rising an average of 250 m from Ambae’s Lake Voui during 5-7 December. A still image of video taken from an airplane showed brown water surrounding an active and growing cone that was ejecting wet tephra less than 10 m above the lake’s surface. The Alert Level remained at 1 (on a scale of 0-5) and the public was warned to stay outside of the Danger Zone defined as a 2-km radius around the 2017-2018 active vents in Lake Voui and away from drainages during heavy rains.

Geological summary: The island of Ambae, also known as Aoba, is a massive 2,500 km3 basaltic shield that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW-trending rift zone dotted with scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. That large central edifice is also called Manaro Voui or Lombenben volcano. Post-caldera explosive eruptions formed the summit craters about 360 years ago. A tuff cone was constructed within Lake Voui (or Vui) about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast.

Nyiragongo, DR Congo

1.52°S, 29.25°E, Summit elev. 3470 m

According to a news article seismic signals at Nyiragongo were dominated by long-period earthquakes during 30 November-5 December. Residents of Goma observed incandescence emanating from the crater on 4 December.

Geological summary: One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes of a stratovolcano contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

Sangay, Ecuador

2.005°S, 78.341°W, Summit elev. 5286 m

IG reported that during 1-2 December activity at Sangay was characterized by increased seismicity, explosions and ash emissions, and a new lava flow on the N flank. The SAGA seismic station, SW of the volcano, recorded a swarm of long-period events beginning at 1600 on 1 December that indicated fluid movements. The amplitude and frequency of the events intensified, and by 2356 the rate had increased from 32 to 60 events per hour. At 0403 on 2 December the SAGA station recorded a major explosion. Based on Washington VAAC advisories two eruption plumes rose 7-10 km above the summit and drifted W, and a third rose almost 1.8 km and drifted NW, though IG noted that the lack of reported ashfall in the nearest towns 25 km away indicated low ash content. Thermal satellite data showed that a new lava flow had emerged on the upper N flank by 2 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 horseshoe-shaped 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 sculpted by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of a historical eruption was in 1628. More or less 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.

Semeru, Eastern Java (Indonesia)

8.108°S, 112.922°E, Summit elev. 3657 m

PMVBG reported collapses of the lava dome in Semeru’s Jonggring Seloko Crater and SE-flank flow during 1-6 December. On 1 December material collapsed from the unstable distal end of a 1-km-long lava flow in the SE-flank Kobokan drainage, sending a pyroclastic flow 700 m down the valley. Subsequent avalanches were recorded by the seismic network that day and on 3 December were not visually confirmed, likely due to several days of rainy conditions. At 1330 on 4 December the seismic network recorded avalanche signals. A larger collapse began at 1447 was seen by an observer at the Mount Semeru Volcano Observation Post and identified in data collected by PVMBG. Avalanches of incandescent material from the summit dome and SE-flank lava flow descended 500-800 m. Pyroclastic flows were visible at 1510 descending the Kobokan drainage and a sulfur odor was noted. At 1520 a large pyroclastic flow produced a large roiling and expanding ash cloud that eventually rose to 15 km (50,000 ft) a.s.l. Reports from residents described darkness from airborne ash and rainy/foggy conditions. Pyroclastic material was deposited in two districts in the Lumajang regency, and eight districts in the neighboring Malang regency were covered with ash. Preliminary estimates suggested that deposits extended at least 16 km SE from the summit.

According to the Darwin VAAC satellite observations acquired at 1630 showed a detached ash cloud drifting SW at an altitude of 15 km (50,000 ft) a.s.l. At 1740 the ash cloud continued to drift SW and a second ash cloud was drifting W at 9.1 km (30,000 ft) a.s.l. The second ash cloud had detached by 1840. On 5 December satellite images showed the two ash clouds still drifting SW and W, and possible diffuse ash emissions rising to 4.6 km (15,000 ft) a.s.l.; ash had dissipated by 1000.

Following the 4 December pyroclastic flow Badan Penanggulangan Bencana Daerah (BPBD) issued a warning to residents to stay away from drainages due to lahar hazards and began evacuating people in high-risk areas. Ten people trapped in a building could not be reached because of scalding hot deposits but were later rescued. Almost all of the houses in the Curah Kobokan area had been destroyed, mainly by pyroclastic flows, though some residents reported roof collapses from ashfall. One area of Curah Kobokan was inundated by hot lahars that took down trees. Pyroclastic flows also destroyed the Gladak Perak bridge, 13 km SE of the summit, which linked residents of Pronojiwo and Lumajang; the national road leading to Malang was blocked by tephra and fallen trees. According to news articles and BNPB, by the next day 14 people were confirmed to have died, 57 had been injured and taken to hospitals (more than a dozen of were in critical condition due to severe burns), and at least seven residents and sand miners working along the river in Curah Kobokan were missing. About 1,300 people had relocated to evacuation centers or alternative housing.

Additional pyroclastic flows during 5-6 December descended 2-3 km SE, and incandescent avalanches descended 500 m. At 0855 on 6 December a pyroclastic flow traveled 4 km down the SE drainage, temporarily halting rescue and recovery efforts. Later that day, the head of BNPB, police officers, and others conducted a 15-minute overflight of Curah Kobokan and observed steam plumes rising from the deposits. Initial estimates were that 2,970 houses and 38 educational facilities across several sub-districts in Lumajang Regency had been destroyed or damaged by the pyroclastic flows. Authorities also traveled to the fallen bridge and other nearby locations, noting damaged vegetation, fallen trees, and volcanic deposits up to 30 cm thick along the road.

By 7 December an estimated 4,250 residents were displaced in about 20 evacuation centers; most people originating from the Lumajang Regency and fewer from the Malang and Blitar regencies. The number of fatalities reached 34, with another 22 people missing. Search efforts focused on the villages of Renteng, Sumberwuluh, and Kobokan Curah, but daily afternoon rains hampered rescue and recovery efforts.

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.

Ongoing activity

Aira, Kyushu (Japan)

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

JMA reported that incandescence from Minamidake Crater (at Aira Caldera’s Sakurajima volcano) was visible at night during 29 November-6 December. An eruptive event at 1702 on 2 December generated a plume that rose 1.3 km above the crater rim. 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.

Etna, Sicily (Italy)

37.748°N, 14.999°E, Summit elev. 3320 m

INGV reported that during 29 November-5 December eruptive activity at Etna was concentrated at the Northeast Crater (NEC) and the Southeast Crater (SEC), while only minor gas emissions rose from the Voragine and Bocca Nuova craters. Webcam images showed diffuse and discontinuous ash emissions from NEC on 1 December that quickly dissipated near the summit. On the morning of 4 December INGV staff working near the summit observed sporadic and diffuse ash emissions rising from SEC and quickly dissipating around the summit. During the afternoon and through the next day webcam images recorded Strombolian activity at SEC, in addition to the ash emissions.

Geological summary: Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical 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 horseshoe-shaped 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, Guatemala

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

INSIVUMEH reported that 3-12 explosions per hour were recorded at Fuego during 30 November-7 December, generating ash plumes as high as 1 km above the crater rim and periodic shock waves that were felt in communities around the volcano. Ash plumes drifted as far as 25 km SW and W, causing almost daily ashfall 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), and San Pedro Yepocapa (8 km NW). Block avalanches descended the Ceniza (SSW), Seca (W), Trinidad (S), Taniluyá (SW), Las Lajas (SE), and El Jute drainages, often reaching vegetated areas. Explosions ejected incandescent material up to 100-200 m above the summit during 30 November-3 December. A new lava flow emerged during the morning of 5 December and lengthened to 400 m by the next day. During 5-6 December explosions ejected incandescent material 100 m above the summit.

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 at Great Sitkin likely continued during 1-7 December. Elevated surface temperatures at the summit were periodically detected through the week. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

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.

Grimsvotn, Iceland

64.416°N, 17.316°W, Summit elev. 1719 m

The Icelandic Meteorological Office (IMO) reported that the jökulhlaup (glacial outburst flood) due to subsidence of the ice shelf in Grímsvötn’s caldera continued until 6 December. Subsidence of the ice shelf into the underlying lake had begun around 24 November in an area SE of Grímsfjall. Water from the lake drained from the E side of Skeiðarárjökull and from a channel in the middle of a trail into the Gígjukvísl River, causing rising waters first detected in that river overnight during 30 November-1 December. By 2 December the flow rate in the river was 930 meters per second, triple what was detected three days before, and 10 times the normal seasonal rate. Daily measurements showed that the flow rate continued to rise, likely peaking at 2,800 meters per second during the morning of 5 December; a second measurement later that day showed a lower discharge rate of 2,310 meters per second. The ice shelf continued to subside, though more slowly, and water turbulence in the lake had also decreased; the data indicated that the lake was mostly empty of water. A number of detected earthquakes were attributed to subsiding and breaking ice.

By 6 December the ice shelf had subsided a total of about 77 m. At 0615 an M 2.3 earthquake was immediately followed by a M 3.6 one minute later. Five more earthquakes were recorded during 1500-2130, though all were below M 1. IMO raised the Aviation Color Code to Orange (the second highest level on a four-color scale) based on the increased seismicity during the previous few days, the larger events that morning, and considerations such as short run-up times seen before previous eruptions, and those past eruptions occasionally following flood events. Seismic tremor had decreased by the next day, and no signs of eruptive activity were indicated in gas or deformation data. On 7 December the Aviation Color Code was lowered to Yellow.

Geological summary: Grímsvötn, Iceland's most frequently active volcano in historical time, lies largely beneath the vast Vatnajökull icecap. The caldera lake is covered by a 200-m-thick ice shelf, and only the southern rim of the 6 x 8 km caldera is exposed. The geothermal area in the caldera causes frequent jökulhlaups (glacier outburst floods) when melting raises the water level high enough to lift its ice dam. Long NE-SW-trending fissure systems extend from the central volcano. The most prominent of these is the noted Laki (Skaftar) fissure, which extends to the SW and produced the world's largest known historical lava flow during an eruption in 1783. The 15-cu-km basaltic Laki lavas were erupted over a 7-month period from a 27-km-long fissure system. Extensive crop damage and livestock losses caused a severe famine that resulted in the loss of one-fifth of the population of Iceland.

Karymsky, Eastern Kamchatka (Russia)

54.049°N, 159.443°E, Summit elev. 1513 m

KVERT reported that on 25 November explosions at Karymsky generated ash plumes that rose as high as 6 km (19,700 ft) a.s.l. and drifted 30 km NW. A thermal anomaly was visible in satellite images during27-29 November. Explosions on 2 December produced ash plumes that rose up to 4 km (13,100 ft) a.s.l. and drifted 100 km ENE. Dates are based on UTC times. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

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.

Kilauea, Hawaiian Islands (USA)

19.421°N, 155.287°W, Summit elev. 1222 m

HVO reported that lava effusion continued at a vent in the lower W wall of Kilauea’s Halema`uma`u Crater during 1-2 December. The rate of effusion sharply decreased, along with volcanic tremor levels, during 1600-1800 on 3 December. A small part of the vent cone collapsed at around 1700. No surface activity was observed on 5 December and most of the next day though weather conditions hindered visual confirmation; a few small hotspots around the vent were visible in thermal camera images. Lava was visible in the vent at about 1730 on 6 December and within 30 minutes was flowing into the lake. By 0300 on 7 December lava had covered the prior extent of the lava lake. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Geological summary: Kilauea, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 km2, destroying nearly 200 houses and adding new coastline to the island.

La Palma, Spain

28.57°N, 17.83°W, Summit elev. 2426 m

The eruption at La Palma continued during 1-7 December, characterized by Strombolian explosions and lava fountaining/jetting from multiple existing and new vents, advancing and sometimes branching lava flows, and almost daily ash emissions. Seismicity persisted at variable but elevated levels, with earthquake locations distributed at depths of 10-15 km and 30-40 km. Seismicity was intense at both levels during 30 November-2 December, though the intensity at deeper levels began to wane; in general, earthquake activity was low by the end of the week. Volcanic tremor levels fluctuated at medium to intense levels early in the week but by 3 December were also at low levels.

Several vents in the main cone continued to effuse lava, eject tephra, and emit ash-and-gas plumes. Lava moved W through pre-existing lava channels, lava tubes, over older flows, and over new ground, increasing the flow field that consists of overlapping flows (numbered 1-12) and two lava deltas. Persistent Strombolian activity was sometimes intense at the NE-flank vent during 1-3 December, and lava continued to feed flow 8 and the N delta. Lava fountains rose 400-500 m above the vent on 2 December. A new pyroclastic cone had formed around the vent, though it was unstable, and blocks from collapses of parts of it were transported downslope by lava flows. The northernmost flow, flow 12, traveled over new ground in the Fronton area and then rejoined flow 8 downslope. The flows reached part of the Tacande highway on 3 December. The vents in the main cone were quieter, periodically emitting ash and gasses. A N-S-oriented crack opened in an area 100 m S of the main vent, likely from subsidence, because it was not hot or emitting gas. The NE vent was quiet by 4 December.

On 3 December a new fissure opened on the SE of the main cone and produced Strombolian activity and fast-moving lava flows that traveled SW, along flow 10. The flow continued to advance W on 4 December, though at a slower rate as it moved over new ground in gaps between flows 3 and 11. Several new vents along an E-W fissure located W of Montaña del Cogote opened at noon on 4 December and produced multiple fast-moving lava flows. The flows descended SW over new ground, crossing into the municipalities of Tazacorte and Los Llanos de Aridane, destroying 60 homes. The flow joined flow 9, reached the sea cliff in the Las Hoyas area by 5 December, and descended the cliff the next day. During 6-7 December lava advanced W through multiple tubes and fed flows 1 and 2, and the S delta. The NE vent was quiet for a few days, but sporadic Strombolian activity and ash emissions had returned. Cracks and fractures in the upper part of the cone were visible. Several vents in the central and SE parts of the main cone also produced sporadic Strombolian activity and ash emissions. By 7 December lava had covered an estimated 11.82 square kilometers. The number of people that had evacuated and were staying in hotels had increased to 537.

Gas and ash emissions periodically impacted island residents. Suspended ash and high concentrations of volcanic gases triggered a few air-quality alerts mostly affecting the W part of the island; authorities warned residents in some areas to stay indoors. Residents and essential personnel were occasionally barred from entering the exclusion zones to irrigate crops and remove ash from streets and buildings. Ash-and-gas plumes visible during 1-3 and 6-7 December rose as high as 3.5 km a.s.l.; volcanic plumes drifted W, SW, and SSW all week, away from the airport. Daily measurements indicated that sulfur dioxide emissions persisted at “high” levels, indicating values of 1,000 to 29,999 tons per day.

Geological summary: The 47-km-long wedge-shaped island of La Palma, the NW-most of the Canary Islands, is composed of two large volcanic centers. The older northern one is cut by the massive steep-walled Caldera Taburiente, one of several massive collapse scarps produced by edifice failure to the SW. The younger Cumbre Vieja, the southern volcano, is one of the most active in the Canaries. The elongated volcano dates back to about 125,000 years ago and is oriented N-S. Eruptions during the past 7,000 years have formed abundant cinder cones and craters along the axis of Cumbre Vieja, producing fissure-fed lava flows that descend steeply to the sea. Eruptions recorded since the 15th century have produced mild explosive activity and lava flows that damaged populated areas. The southern tip of the island is mantled by a broad lava field emplaced during the 1677-1678 eruption. Lava flows also reached the sea in 1585, 1646, 1712, 1949, and 1971.

Lewotolok, Lembata Island (Indonesia)

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

PVMBG reported that the eruption at Lewotolok continued during 1-7 December. Daily white-and-gray ash plumes that were sometimes dense rose as high as 800 m above the summit. Incandescent material was ejected from the vent on most days, and up to 300 m during 6-7 December, accompanied by roaring and rumbling. The Alert Level remained at 3 (on a scale of 1-4) and the public was warned to stay 3 km away from the summit crater.

Geological summary: The Lewotolok (or Lewotolo) stratovolcano occupies the eastern end of an elongated peninsula extending north into the Flores Sea, connected to Lembata (formerly Lomblen) Island by a narrow isthmus. It is symmetrical when viewed from the north and east. A small cone with a 130-m-wide crater constructed at the SE side of a larger crater forms the volcano's high point. Many lava flows have reached the coastline. Eruptions recorded since 1660 have consisted of explosive activity from the summit crater.

Merapi, Central Java (Indonesia)

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

BPPTKG reported no notable morphological changes to Merapi’s summit lava dome, though the dome just below the SW rim had decreased about 2 m in height during 26 November-2 December. The estimated dome volumes were 1.61 million cubic meters for the SW dome and almost 2.95 million cubic meters for the summit dome. The intensity of the seismic signals was higher than the week before. As many as 170 lava avalanches traveled a maximum of 2 km SW. Two pyroclastic flows traveled a maximum of 3 km SW on 1 December. In a VONA (Volcano Observatory Notice for Aviation), PVMBG stated that at 2104 on 1 December an ash plume rose 1 km above the summit and drifted E. According to BPPTKG a pyroclastic flow traveled 1.8 km down the Bebeng drainage on the SW flank at 1644 on 6 December. The event lasted two minutes and 40 seconds based on seismic data. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-5 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.

Pavlof, United States

55.417°N, 161.894°W, Summit elev. 2493 m

AVO reported that the eruption at Pavlof continued during 1-7 December, focused at a vent on the upper SE flank. Seismicity remained elevated and several daily explosions were detected using infrasound data. Elevated surface temperatures were observed in satellite data during 1-2 December, though cloud cover often prevented observations. No emissions were visible in mostly cloudy satellite and webcam views during 1-3 December. Minor ash emissions were visible in webcam images on 4 December and, based on webcam images and a pilot observation, the next day a diffuse ash plume rose as high as 3 km (10,000 ft) a.s.l. and drifted tens of kilometers beyond the volcano. The Volcano Alert Level remained at Watch and the Aviation Color Code remained at Orange.

Geological summary: The most active volcano of the Aleutian arc, Pavlof is a 2519-m-high Holocene stratovolcano that was constructed along a line of vents extending NE from the Emmons Lake caldera. Pavlof and its twin volcano to the NE, 2142-m-high Pavlof Sister, form a dramatic pair of symmetrical, glacier-covered stratovolcanoes that tower above Pavlof and Volcano bays. A third cone, Little Pavlof, is a smaller volcano on the SW flank of Pavlof volcano, near the rim of Emmons Lake caldera. Unlike Pavlof Sister, Pavlof has been frequently active in historical time, typically producing Strombolian to Vulcanian explosive eruptions from the summit vents and occasional lava flows. The active vents lie near the summit on the north and east sides. The largest historical eruption took place in 1911, at the end of a 5-year-long eruptive episode, when a fissure opened on the N flank, ejecting large blocks and issuing lava flows.

Santa Maria, 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 1-7 December. Avalanches generated by both lava effusion at the WSW part of Caliente dome and collapsing material descended the flanks in multiple directions, often reaching the base of the dome. Periodically the avalanches produced curtains of ash along their paths that dissipated near the volcano. Some of the avalanches were preceded by explosions detected by the seismic network and some were audible several kilometers away. During 2-3 and 6-7 December ash plumes rose 500 m above the summit and drifted 10 km NW and W, causing ashfall in areas downwind including San Marcos Palajunoj (8 km SW) and Loma Linda (6 km WSW). During 3-4 December ash-and-steam plumes rose 900 m and drifted SW and W.

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.

Semisopochnoi, Aleutian Islands (USA)

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

AVO reported that low-level eruptive activity and elevated seismicity at Semisopochnoi's North Cerberus crater continued during 1-7 December. Several daily explosions were detected in seismic and infrasound data. Weather clouds sometimes obscured satellite and webcam views of the volcano, though on most days low-level ash-and-steam plumes rising no higher than 1.5 km (5,000 ft) a.s.l. were visible mostly in webcam images. During 3-4 December a diffuse ash plume was identified in a satellite image drifting about 100 km E. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

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 was constructed within the caldera during the Holocene. Each of the peaks contains a summit crater; lava flows on the N flank of Cerberus 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 Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone could have been recently active.

Sheveluch, Central Kamchatka (Russia)

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

KVERT reported that a thermal anomaly over Sheveluch was identified in satellite images during 26 November-3 December. 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.

Suwanosejima, Ryukyu Islands (Japan)

29.638°N, 129.714°E, Summit elev. 796 m

JMA reported that during 29 November-6 December about 47 explosions at Suwanosejima's Ontake Crater produced eruption plumes that rose as high as 1.7 km above the crater rim and ejected blocks 600-700 m away from the crater. Plumes from non-explosive events rose as high has 2.3 km. Crater incandescence was visible nightly and ashfall was reported in Toshima village (4 km SSW). The Alert Level remained at 3 and the public was warned to stay 2 km away from the crater.

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.

Reference:

Global Volcanism Program, 2021. Report on Grimsvotn (Iceland). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 1 December-7 December 2021. Smithsonian Institution and US Geological Survey.

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