The Weekly Volcanic Activity Report: October 13 - 19, 2021

The Weekly Volcanic Activity Report: October 13 - 19, 2021

New activity/unrest was reported for 6 volcanoes from October 13 to 19, 2021. During the same period, ongoing activity was reported for 18 volcanoes.

New activity/unrest: Asosan, Kyushu (Japan) | Kilauea, Hawaiian Islands (USA) | Manam, Papua New Guinea | Pagan, Mariana Islands (USA) | Rabaul, New Britain (Papua New Guinea) | Vulcano, Aeolian Islands (Italy).

Ongoing activity: Aira, Kyushu (Japan) | Bagana, Bougainville (Papua New Guinea) | Ebeko, Paramushir Island (Russia) | Erta Ale, Ethiopia | Great Sitkin, Andreanof Islands (USA) | Karymsky, Eastern Kamchatka (Russia) | Kavachi, Solomon Islands | Krysuvik-Trolladyngja, Iceland | Lewotolok, Lembata Island (Indonesia) | Merapi, Central Java (Indonesia) | Pavlof, United States | Rincon de la Vieja, Costa Rica | Semeru, Eastern Java (Indonesia) | Semisopochnoi, Aleutian Islands (USA) | Sheveluch, Central Kamchatka (Russia) | Suwanosejima, Ryukyu Islands (Japan) | Taal, Luzon (Philippines) | 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.

New activity/unrest

Asosan, Kyushu (Japan)

32.884°N, 131.104°E, Summit elev. 1592 m

According to JMA the number of volcanic tremor signals at Asosan began on 12 October. Tremor amplitude began increasing at 1530 on 13 October, prompting JMA to raise the Alert Level to 2 (on a scale of 1-5) almost two hours later. White plumes rose 1.4 km above Nakadake Crater. An eruption was detected at 0443 on 14 October; weather clouds prevented visual confirmation of an eruption plume, though ejected incandescent material was visible in thermal camera images. During a field visit to the volcano later that day, scientists confirmed ashfall in several areas, including parts of Takamori Town (Kumamoto Prefecture), Taketa City (Oita Prefecture), and Takachiho Town (Miyazaki Prefecture). Small eruptive events occurred at 1057 and 1325 on 15 October. Volcanic tremor amplitude increased at 1400 on 18 October. During an overflight scientists observed ash deposits extending SE from Nakadake Crater. Volcanic tremor amplitude continued to fluctuate at high levels on 19 October. At 1143 on 20 October a notable eruption ejected blocks 900 m S and produced an ash plume that rose 3.5 km above the crater rim and drifted E. Pyroclastic flows descended 1.3 km W. The Alert Level was raised to 3 at 1148 and warned the public to stay 2 km away from Nakadake Crater.

Geological summary: The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Kilauea, Hawaiian Islands (USA)

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

HVO reported that the summit eruption at Kilauea continued in Halema`uma`u Crater during 12-19 October. A 10-m-wide, horseshoe-shaped spatter rampart had formed around the W vent and was open to the E where lava was feeding the lake. For about 10 hours on 12 October a new vent N of the W vent produced 10-15-m-high lava fountains. Lava fountains from the W vent rose as high as 20 m and fed the lava lake which was 46 m deep by 18 October. The lava lake was not level with the deepest parts measured around the W vent; the W end was 4-5 m higher than the N and S parts of the lake and 12 m higher than the E end. Cooled and crusted parts of the lake’s surface overturned, or “foundered,” in all parts of the lake except the E part. The sulfur dioxide emission rate was high at 1,600-6,800 tonnes per day during 12-14 and 16-17 October. 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.

Manam, Papua New Guinea

4.08°S, 145.037°E, Summit elev. 1807 m

RVO reported that sporadic small ash emissions from Manam’s Southern Crater were observed starting at the end of September. Nighttime incandescence began on 8 October and incandescent material was occasionally ejected from the crater. The activity was characterized as moderately Strombolian with incandescent material rolling down SW Valley, visibly appearing as short lava flows. The Darwin VAAC noted that on 18 October an ash plume rose to 2.4 km (8,000 ft) a.s.l. and drifted NW. A thermal anomaly was visible in satellite images.

RVO stated that at around 0800 on 20 October a large explosion at Southern Crater produced ash plumes that rose at least 1 km above the summit and drifted N and NW. According to the Darwin VAAC ash plumes rose as high as 15.2 km (50,000 ft) a.s.l. between 0840-0950, expanded radially, and then drifted E. Lower-level plumes rose 4.6-5.5 km (15,000-18,000 ft) a.s.l. and drifted NW. Later that day a collapse of newly erupted material, as well deposits from the previous few weeks, produced a debris flow that originated at the head of the valley and descended the SW Valley.

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.

Pagan, Mariana Islands (USA)

18.13°N, 145.8°E, Summit elev. 570 m

The U.S. Geological Survey reported that ash and sulfur dioxide emissions from Pagan were last detected on 6 September. The Aviation Color Code and the Volcano Alert Level were both lowered to Unassigned on 24 September; Pagan is monitored with satellite imagery, distal geophysical data, and mariner reports and not ground-based instruments.

Geological summary: Pagan Island, the largest and one of the most active of the Mariana Islands volcanoes, consists of two stratovolcanoes connected by a narrow isthmus. Both North and South Pagan stratovolcanoes were constructed within calderas, 7 and 4 km in diameter, respectively. North Pagan at the NE end of the island rises above the flat floor of the northern caldera, which may have formed less than 1,000 years ago. South Pagan is a stratovolcano with an elongated summit containing four distinct craters. Almost all of the recorded eruptions, which date back to the 17th century, have originated from North Pagan. The largest eruption during historical time took place in 1981 and prompted the evacuation of the sparsely populated island.

Rabaul, New Britain (Papua New Guinea)

4.271°S, 152.203°E, Summit elev. 688 m

On 6 October RVO raised the Alert Level for Rabaul to Stage 1 (the lowest level on a four-stage scale) due to ongoing deformation and recent increases in seismicity. During the month of September, the seismic network detected a total of 22 high-frequency volcano-tectonic earthquakes, which was more than the 12 recorded in August. The earthquakes were distributed in the Beehives, Vulcan, Greet Harbour, and Namanula areas. Deformation data from a GPS station located at the S part of Matupit Island showed a continuing trend of uplift, with 39 mm/month in August and 35-39 mm/month in September. Diffuse white fumarolic plumes rose from the crater floor and inner walls.

Geological summary: The low-lying Rabaul caldera on the tip of the Gazelle Peninsula at the NE end of New Britain forms a broad sheltered harbor utilized by what was the island's largest city prior to a major eruption in 1994. The outer flanks of the 688-m-high asymmetrical pyroclastic shield volcano are formed by thick pyroclastic-flow deposits. The 8 x 14 km caldera is widely breached on the east, where its floor is flooded by Blanche Bay and was formed about 1400 years ago. An earlier caldera-forming eruption about 7100 years ago is now considered to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the northern and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and western caldera walls. Several of these, including Vulcan cone, which was formed during a large eruption in 1878, have produced major explosive activity during historical time. A powerful explosive eruption in 1994 occurred simultaneously from Vulcan and Tavurvur volcanoes and forced the temporary abandonment of Rabaul city.

Vulcano, Aeolian Islands (Italy)

38.404°N, 14.962°E, Summit elev. 500 m

INGV continued to monitor elevated activity at Vulcano during 12-19 October. Scientists collected temperature, water chemistry, and gas-emissions data from four fumarolic vents located inside La Fossa Crater near the rim and from one vent near the beach. According to news articles, elevated levels of carbon dioxide impacted nearby residents in Porto Levante causing a few families to leave their homes on 13 October. Several residents had reported inexplicable illnesses and some deaths of domestic animals the previous week. On 14 October authorities restricted public access to the crater. The Dipartimento della Protezione Civile maintained the Alert Level at Yellow (the second lowest level on a four-color scale).

Geological summary: The word volcano is derived from Vulcano stratovolcano in Italy's Aeolian Islands. Vulcano was constructed during six stages over the past 136,000 years. Two overlapping calderas, the 2.5-km-wide Caldera del Piano on the SE and the 4-km-wide Caldera della Fossa on the NW, were formed at about 100,000 and 24,000-15,000 years ago, respectively, and volcanism has migrated north over time. La Fossa cone, active throughout the Holocene and the location of most historical eruptions, occupies the 3-km-wide Caldera della Fossa at the NW end of the elongated 3 x 7 km island. The Vulcanello lava platform is a low, roughly circular peninsula on the northern tip of Vulcano that was formed as an island beginning more than 2,000 years ago and was connected to the main island in about 1550 CE. Vulcanello is capped by three pyroclastic cones and was active intermittently until the 16th century. Explosive activity took place at the Fossa cone from 1898 to 1900.

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 11-18 October. The sulfur dioxide emission rate was 800 tons per day on 11 October. A very small eruptive event was recorded on 14 October. 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.

Bagana, Bougainville (Papua New Guinea)

6.137°S, 155.196°E, Summit elev. 1855 m

The Darwin VAAC reported that on 14 October an ash plume from Bagana rose to 2.1 km (7,000 ft) a.s.l. and drifted NE based on satellite and wind model data.

Geological summary: Bagana volcano, occupying a remote portion of central Bougainville Island, is one of Melanesia's youngest and most active volcanoes. This massive symmetrical cone was largely constructed by an accumulation of viscous andesitic lava flows. The entire edifice could have been constructed in about 300 years at its present rate of lava production. Eruptive activity is frequent and characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although explosive activity occasionally producing pyroclastic flows also occurs. Lava flows form dramatic, freshly preserved tongue-shaped lobes up to 50 m thick with prominent levees that descend the flanks on all sides.

Ebeko, Paramushir Island (Russia)

50.686°N, 156.014°E, Summit elev. 1103 m

According to volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, an explosion on 10 October produced an ash plume that rose as high as 2.5 km (8,200 ft) a.s.l. and drifted NE. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

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.

Erta Ale, Ethiopia

13.6°N, 40.67°E, Summit elev. 613 m

During 15 September-15 October satellite data showed thermal anomalies of variable intensities in Erta Ale’s S pit crater and occasional thermal anomalies at the N pit. An anomaly was detected in the N, NW, and W parts of the N pit crater on 15 October.

Geological summary: The Erta Ale basaltic shield volcano is the most active in Ethiopia, with a 50-km-wide edifice that rises more than 600 m from below sea level in the barren Danakil depression. It is the namesake and most prominent feature of the Erta Ale Range. The volcano includes a 0.7 x 1.6 km elliptical summit crater hosting steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located SE of the summit and is bounded by curvilinear fault scarps on the SE side. Fresh-looking basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera usually also holds at least one long-term lava lake that has been active since at least 1967, or possibly since 1906. Recent fissure eruptions have occurred on the N flank.

Great Sitkin, Andreanof Islands (USA)

52.076°N, 176.13°W, Summit elev. 1740 m

AVO reported that lava effusion continued at Great Sitkin during 13-19 October. Seismicity remained elevated and was characterized by small earthquakes consistent with lava effusion, though an outage affected geophysical data streams during 16-18 October. Satellite images acquired on 11 October showed that lava filled more than half of the summit crater, flowing onto the S and W flanks, and had recently reached the N crater rim. Lava traveled 330 m down the S flank, 350 m down the W flank, descended small valleys, and in some areas, advanced over snow and ice. Blocks that had detached from the end of the W flow descended 450 m. 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.

Karymsky, Eastern Kamchatka (Russia)

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

A thermal anomaly over Karymsky was identified in satellite images during 8-9 October. On 19 October KVERT lowered the Aviation Color Code to Yellow (the second lowest level on a four-color scale), noting that only gas-and-steam emissions persisted after the last ash explosions were recorded on 25 September. On 20 October explosions generated ash plumes that rose as high as 4 km (13,100 ft) a.s.l. and drifted almost 90 km ENE. KVERT raised the Aviation Color Code to Orange.

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.

Kavachi, Solomon Islands

8.991°S, 157.979°E, Summit elev. -20 m

Satellite data showed discolored water around and to the SW of Kavachi on 12 October. Discolored water was not obviously visible in images from 2, 7, and 17 October.

Geological summary: Named for a sea-god of the Gatokae and Vangunu peoples, Kavachi is one of the most active submarine volcanoes in the SW Pacific, located in the Solomon Islands south of Vangunu Island. Sometimes referred to as Rejo te Kvachi ("Kavachi's Oven"), this shallow submarine basaltic-to-andesitic volcano has produced ephemeral islands up to 1 km long many times since its first recorded eruption during 1939. Residents of the nearby islands of Vanguna and Nggatokae (Gatokae) reported "fire on the water" prior to 1939, a possible reference to earlier eruptions. The roughly conical edifice rises from water depths of 1.1-1.2 km on the north and greater depths to the SE. Frequent shallow submarine and occasional subaerial eruptions produce phreatomagmatic explosions that eject steam, ash, and incandescent bombs. On a number of occasions lava flows were observed on the ephemeral islands.

Krysuvik-Trolladyngja, Iceland

63.917°N, 22.067°W, Summit elev. 360 m

Icelandic Meteorological Office (IMO) reported that during 18 September-18 October no lava effusion was detected at the Krýsuvík-Trölladyngja volcanic system. The seismic swarm that had begun on 26 September in an area SW of Keilir (about 10 km NE of the fifth vent), at the N end of the dike intrusion, had significantly decreased in mid-October. The Aviation Color Code was lowered to Yellow (the second lowest level on a four-color scale) on 18 October. IMO noted that gas emissions were ongoing, though with very low concentrations of eruptive gases. Minor thermal anomalies were detected less often; incandescence from previously emplaced lava flows was occasionally visible at night. IMO also stated that residual heat, gases, and incandescence may continue for weeks to months.

Geological summary: The Krýsuvík-Trölladyngja volcanic system is described by the Catalogue of Icelandic Volcanoes as an approximately 50-km-long composite fissure swarm trending about N38°E, including a 30-km-long swarm of fissures, with no central volcano. It is one of the volcanic systems arranged en-echelon along the Reykjanes Peninsula west of Kleifarvatn lake. The Fagradalsfjall and Krýsuvík fissure swarms are considered splits or secondary swarms of the Krýsuvík–Trölladyngja volcanic system. Small shield volcanoes have produced a large portion of the erupted volume within the system. Several eruptions have taken place since the settlement of Iceland, including the eruption of a large basaltic lava flow from the Ogmundargigar crater row around the 12th century. The latest eruption, identified through tephrochronology, took place during the 14th century.

Lewotolok, Lembata Island (Indonesia)

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

PVMBG reported that the eruption at Lewotolok continued during 13-19 October. White, gray, and black plumes generally rose as high as 1 km above the summit and drifted in multiple directions. Rumbling and banging sounds were reported almost daily. Incandescent material was ejected most days as far as 100 m from the vent and as high as 300 m above the vent. 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 minor morphological changes to Merapi’s SW lava dome, located just below the SW rim, and the dome in the summit crater during 8-14 October. The SW dome grew about 2 m taller and had an estimated volume of 1.61 million cubic meters, while the summit lava dome grew about 4 m taller had an estimated volume of 2.93 million cubic meters. As many as 41 lava avalanches traveled a maximum of 2 km SW. 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 13-19 October and was focused at a vent on the upper SE flank, near the location of the 2007 vent. Seismicity remained elevated. Two small explosions were recorded in infrasound and seismic data on both 14 and 16 October. A few explosions were recorded during 17-18 October; ash deposits on the flanks were visible in satellite images. Cloudy conditions obscured satellite and webcam images most days. The Volcano Alert Level and Aviation Color Code remained at Watch and Orange, respectively.

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.

Rincon de la Vieja, Costa Rica

10.83°N, 85.324°W, Summit elev. 1916 m

OVSICORI-UNA reported that at 0750 on 13 October an eruption at Rincón de la Vieja produced a plume that rose 500 m above the crater rim and drifted SW. Fumarolic activity inside the crater was visible during 14-15 October.

Geological summary: Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A Plinian eruption producing the 0.25 km3 Río Blanca tephra about 3,500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Semeru, Eastern Java (Indonesia)

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

PVMBG reported that gray-and-white emissions rose 200-500 m above Semeru’s summit and drifted SW, W, and N during 12-13 and 15-16 October. Weather clouds often prevented visual observations of the summit. The Alert Level remained at 2 (on a scale of 1-4), with a general exclusion zone of 1 km and extensions to 5 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.

Semisopochnoi, Aleutian Islands (USA)

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

AVO reported that eruptive activity at Semisopochnoi's North Cerberus crater continued during 13-19 October. Seismicity remained elevated and daily minor explosions were detected in infrasound data. Although weather clouds often prevented webcam and satellite views, intermittent, low-level ash emissions were visible rising to altitudes up to 3 km (10,000 ft a.s.l.) and drifting E on 13 October. Ash plumes rose as high as 1.5 km (5,000 ft) a.s.l. on 18 October. 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 8-15 October. 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 13 explosions at Suwanosejima's Ontake Crater produced eruption plumes that rose as high as 2.7 km above the crater rim during 11-18 October. Large volcanic bombs were ejected 500-700 m from the crater. 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.

Taal, Luzon (Philippines)

14.002°N, 120.993°E, Summit elev. 311 m

PHIVOLCS reported that upwelling of hot volcanic fluids in Taal’s crater lake was visible during 13-18 October, and gas-and-steam plumes rose 1.2-3 km above the lake and drifted in multiple directions. Sulfur dioxide emissions averaged 6,393-12,611 tonnes/day, though on 15 October the emissions peaked at 23,576 tonnes/day, which was the second highest ever sulfur dioxide gas flux recorded at the volcano. Dense vog spread over the Taal Caldera region was noted on 15 October. Earthquake activity resumed on 11 October after a brief lull that first began on 27 September; 145 events characterized as mostly weak low-frequency earthquakes and volcanic tremor were recorded during 11-15 October. Volcanic tremor persisted through 18 October. The Volcano Alert Level remained at a 2 (on a scale of 0-5). PHIVOLCS reminded the public that the entire Taal Volcano Island is a Permanent Danger Zone (PDZ) and that boating on Taal Lake was prohibited.

Geological summary: Taal is one of the most active volcanoes in the Philippines and has produced some of its most powerful historical eruptions. Though not topographically prominent, its prehistorical eruptions have greatly changed the landscape of SW Luzon. The 15 x 20 km Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2 surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, and several eruptive centers lie submerged beneath the lake. The 5-km-wide Volcano Island in north-central Lake Taal is the location of all historical eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones that have grown about 25% in area during historical time. Powerful pyroclastic flows and surges from historical eruptions have caused many fatalities.

Whakaari/White Island, North Island (New Zealand)

37.52°S, 177.18°E, Summit elev. 294 m

On 18 October GeoNet reported results from a recent overflight of Whakaari/White Island. Gas measurements showed that sulfur dioxide emissions had decreased from 520 tons per day recorded at the end of September to 267 tons per day. Temperatures in the main vent area were as high as 220 degrees Celsius, similar to temperatures measure two weeks prior. Minor ash deposits from intermittent ash emissions were visible in the area close to the active vents. Seismicity was characterized by low levels of volcanic tremor and occasional low-frequency volcanic earthquakes. The Volcanic Alert Level remained at 2 and the Aviation Color Code remained at Yellow.

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.

Reference:

Smithsonian / US Geological Survey Weekly Volcanic Activity Report - 13 October-19 October 2021 - Managing Editor: Sally Kuhn Sennert


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