The Weekly Volcanic Activity Report: October 26 – November 1, 2022

the weekly volcanic activity report

New activity/unrest was reported for 6 volcanoes from October 26 to November 1, 2022. During the same period, ongoing activity was reported for 16 volcanoes.

New activity/unrest: Bezymianny, Central Kamchatka (Russia) | Cotopaxi, Ecuador | Kerinci, Central Sumatra | Manam, Northeast of New Guinea | Taal, Luzon (Philippines) | Villarrica, Central Chile.

Ongoing activity: Aira, Kyushu (Japan) | Alaid, Kuril Islands (Russia) | Bagana, Bougainville (Papua New Guinea) | Ebeko, Paramushir Island (Russia) | Great Sitkin, Andreanof Islands (USA) | Kilauea, Hawaiian Islands (USA) | Krakatau, Sunda Strait | Maly Semyachik, Eastern Kamchatka (Russia) | Mauna Loa, Hawaiian Islands (USA) | Mayon, Luzon (Philippines) | Merapi, Central Java | Nevado del Ruiz, Colombia | Pavlof, Alaska Peninsula, Alaska | Sheveluch, Central Kamchatka (Russia) | Suwanosejima, Ryukyu Islands (Japan) | Yasur, Vanuatu.

New activity/unrest

Bezymianny, Central Kamchatka (Russia)

55.972°N, 160.595°E | Summit elev. 2882 m

KVERT reported that notable activity continued after the strong explosive 23-24 October phase at Bezymianny through 27 October. Intense fumarolic activity was visible, the lava dome was incandescent at night, and collapses from the dome produced avalanches of hot material. Ash plumes from the collapses were sometimes large; on 26 October an ash cloud 10×13 km in dimension drifted 70 km E on 26 October, prompting KVERT to raise the Aviation Color Code to Orange (the second highest level on a four-color scale) the next day. Dates are based on UTC times; specific events are in local time where noted.

Geological summary: The modern Bezymianny, much smaller than its massive neighbors Kamen and Kliuchevskoi on the Kamchatka Peninsula, was formed about 4,700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7,000 years ago. Three periods of intensified activity have occurred during the past 3,000 years. The latest period, which was preceded by a 1,000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large open crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Cotopaxi, Ecuador

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

IG issued a report that included data analysis and additional information about the minor eruptive activity at Cotopaxi recorded during 21-22 October. The eruption began with a high-frequency earthquake recorded at 1944 on 21 October and was followed by an episode of volcanic tremor from 1950 on 21 October to 0040 on 22 October. A diffuse gas-and-ash cloud rose 1.7-2.3 km above the summit and drifted NE. Ashfall was reported in the José Rivas Refuge for climbers on the N flank. Parque Nacional Cotopaxi closed to visitors due to the emissions. A small thermal anomaly in the summit crater was identified in satellite images on 23 October; a small anomaly had been repeatedly visible since the previous eruption during August-November 2015, though it had been absent since 12 November 2020.

On 22 October scientists measured sulfur dioxide emissions using a mobile Differential Optical Absorption Spectroscopy (DOAS) instrument in an area spanning near the W entrance to Parque Nacional Cotopaxi to areas in the park. They measured higher values, 1,580 tons per day, nearer to the volcano. Analysis of ash samples collected by IG scientists at the José Rivas Refuge revealed that about 22 percent was juvenile material, indicating a magmatic component to the eruption.

Parque Nacional Cotopaxi reopened on 26 October. Seismicity was at moderate levels that same day with the number of events per day progressively decreasing according to a news report. During an overflight of the summit crater on 27 October, scientists observed gas-and-steam emissions rising 500 m above the carter rim, obscuring views into the crater.

The amplitude of the tremor signal on 21 October was about half of that recorded during the 2015 eruption and the tremor signal only lasted about four hours whereas in 2015 some periods lasted several days. There was no notable precursory activity including anomalous seismic activity and deformation detected in satellite or GPS data. The Washington VAAC had previously reported ash emissions on 4 July 2016, 23 January 2017, 15 July 2018, and 10 January 2020, though none were associated with increased seismicity or ashfall. Climbers had previously reported ashfall on occasion, with the last report on 27 November 2021. Servicio Nacional de Gestión de Riesgos y Emergencias (SNGRE) maintained the Alert Level at Yellow (the second lowest level on a four-color scale).

Geological summary: The symmetrical, glacier-covered, Cotopaxi stratovolcano is Ecuador’s most well-known volcano and one of its most active. The steep-sided cone is capped by nested summit craters, the largest of which is about 550 x 800 m in diameter. Deep valleys scoured by lahars radiate from the summit of the andesitic volcano, and large andesitic lava flows extend to its base. The modern edifice has been constructed since a major collapse sometime prior to about 5,000 years ago. Pyroclastic flows (often confused in historical accounts with lava flows) have accompanied many explosive eruptions, and lahars have frequently devastated adjacent valleys. Strong eruptions took place in 1744, 1768, and 1877. Pyroclastic flows descended all sides of the volcano in 1877, and lahars traveled more than 100 km into the Pacific Ocean and western Amazon basin. Smaller eruptions have been frequent since that time.

Kerinci, Central Sumatra

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

PVMBG reported that on 27 October a somewhat dense, gray-and-black plume rose around 300 m above Kerinci’s summit and drifted E. The Aviation Color Code was raised to Orange (the second highest level on a four-color scale). The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to remain outside of the 3-km exclusion zone.

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

Manam, Northeast of New Guinea

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

The Darwin VAAC reported that on 29 October an ash plume from Manam rose to 1.5 km (5,000 ft) and drifted NW based on satellite images. The plume had dissipated within three hours.

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.

Taal, Luzon (Philippines)

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

PHIVOLCS reported continuing unrest at Taal during 25-31 October. Sulfur dioxide emissions averaged 544 tonnes per day on 27 October. There were 2-16 daily counts of small phreatomagmatic bursts during 25-29 October. The Tokyo VAAC noted that three ash plumes rose as high as 600 m (2,000 ft) a.s.l. and drifted NW and SW during 26-28 October based on SIGMETS (Significant Meteorological statements) issued by the Ninoy Aquino International Airport. Six volcanic earthquakes and a three-minute-long tremor signal were recorded during 25-26 October, four periods of volcanic tremor were recorded during 28-29 October, and 64 periods were recorded during 31 October-1 November. Upwelling gasses and hot fluids in the lake were visible early in the week; white steam emissions rose as high as 600 m above the lake on most of the days. The Alert Level remained at 1 (on a scale of 0-5), and PHIVOLCS reminded the public that the entire Taal Volcano Island was a Permanent Danger Zone (PDZ).

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 observed eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones. Powerful pyroclastic flows and surges have caused many fatalities.

Villarrica, Central Chile

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

POVI reported that Strombolian explosions at Villarrica intensified on 31 October and ejected material onto the upper flanks. A lava fountain rising above the crater rim was visible on 1 November. The Alert Level remained at Green, the lowest level on a four-color scale.

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.

Ongoing activity

Aira, Kyushu (Japan)

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

JMA reported ongoing eruptive activity at Minamidake Crater (at Aira Caldera’s Sakurajima volcano) and nighttime crater incandescence. Two eruptive events and one explosion were recorded during 24-28 October. Volcanic plumes rose as high as 1.2 km above the crater rim and large blocks were ejected as far as 1.3 km from the vent. Very small eruptive events were occasionally recorded during 28-31 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.

Alaid, Kuril Islands (Russia)

50.861°N, 155.565°E | Summit elev. 2285 m

KVERT reported that the eruption at Alaid was ongoing during 20-27 October. An intense daily thermal anomaly was identified in satellite images. Ash plumes drifted more than 700 m NE and SE. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Dates are based on UTC times; specific events are in local time where noted.

Geological summary: The highest and northernmost volcano of the Kuril Islands, 2285-m-high Alaid is a symmetrical stratovolcano when viewed from the north, but has a 1.5-km-wide summit crater that is breached widely to the south. Alaid is the northernmost of a chain of volcanoes constructed west of the main Kuril archipelago. Numerous pyroclastic cones dot the lower flanks of this basaltic to basaltic-andesite volcano, particularly on the NW and SE sides, including an offshore cone formed during the 1933-34 eruption. Strong explosive eruptions have occurred from the summit crater beginning in the 18th century. Reports of eruptions in 1770, 1789, 1821, 1829, 1843, 1848, and 1858 were considered incorrect by Gorshkov (1970). Explosive eruptions in 1790 and 1981 were among the largest in the Kuril Islands during historical time.

Bagana, Bougainville (Papua New Guinea)

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

The Darwin VAAC reported that during 31 October-1 November ash plumes from Bagana rose to 2.1-2.7 km (7,000-9,000 ft) a.s.l. and drifted NE, N, and WSW based on satellite data. An intense thermal anomaly was present at the summit.

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

KVERT reported that moderate activity at Ebeko was ongoing. According to volcanologists in Severo-Kurilsk (Paramushir Island, about 7 km E) explosions during 22 and 25-27 October generated ash plumes that rose to 2.5 km (8,200 ft) a.s.l. and drifted NE. A thermal anomaly was identified in satellite images on 26 October. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Dates are based on UTC times; specific events are in local time where noted.

Geological summary: The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.

Great Sitkin, Andreanof Islands (USA)

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

AVO reported that seismicity at Great Sitkin was very low during 25 October-1 November and nothing significant was seen in partly cloudy satellite or web camera views. Lava effusion likely continued. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geological summary: The Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger parasitic volcano capped by a small, 0.8 x 1.2 km ice-filled summit caldera was constructed within a large late-Pleistocene or early Holocene scarp formed by massive edifice failure that truncated an ancestral volcano and produced a submarine debris avalanche. Deposits from this and an older debris avalanche from a source to the south cover a broad area of the ocean floor north of the volcano. The summit lies along the eastern rim of the younger collapse scarp. Deposits from an earlier caldera-forming eruption of unknown age cover the flanks of the island to a depth up to 6 m. The small younger caldera was partially filled by lava domes emplaced in 1945 and 1974, and five small older flank lava domes, two of which lie on the coastline, were constructed along northwest- and NNW-trending lines. Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano. Historical eruptions have been recorded since the late-19th century.

Kilauea, Hawaiian Islands (USA)

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

HVO reported that lava continued to effuse from a vent in the lower W wall of Kilauea’s Halema`uma`u Crater during 25 October-1 November entering the lava lake and flowing onto the crater floor. The active part of the lake remained at a steady level all week. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Geological summary: Kilauea overlaps the E flank of the massive Mauna Loa shield volcano in the island of Hawaii. Eruptions are prominent in Polynesian legends; written documentation since 1820 records frequent summit and flank lava flow eruptions interspersed with periods of long-term lava lake activity at Halemaumau crater in the summit caldera until 1924. The 3 x 5 km caldera was formed in several stages about 1,500 years ago and during the 18th century; eruptions have also originated from the lengthy East and Southwest rift zones, which extend to the ocean in both directions. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1,100 years old; 70% of the surface is younger than 600 years. The long-term eruption from the East rift zone between 1983 and 2018 produced lava flows covering more than 100 km2, destroyed hundreds of houses, and added new coastline.

Krakatau, Sunda Strait

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

PVMBG reported that multiple ash plumes were visible in webcam images rising from Anak Krakatau during 26-28 October. Dense gray ash plumes rose as high as 300 m above the summit and drifted NE at 0949 on 26 October, 1205 on 27 October, and 0438 and 1502 on 28 October. Eruptive events were also recorded at 1838 on 26 October, 1955 on 27 October, and 0438 on 28 October, though were not visually confirmed. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay at least 5 km away from the crater.

Geological summary: The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of that volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption caused more than 36,000 fatalities, most as a result of tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

Maly Semyachik, Eastern Kamchatka (Russia)

54.135°N, 159.674°E | Summit elev. 1527 m

Although Maly Semyachik was not erupting, KVERT raised the Aviation Color Code to Orange (the second highest level on a four-color scale) on 28 October, noting that a plume of ash, re-suspended by strong winds, was visible in satellite images drifting 123 km SE. Within three hours the Aviation Color Code was lowered back to Green. Dates are based on UTC times; specific events are in local time where noted.

Geological summary: Maly Semyachik is a compound stratovolcano located in a 10-km-wide caldera within the 15 x 20 km mid-Pleistocene Stena-Soboliny caldera. Following construction during the late Pleistocene of the Paleo-Semiachik volcano beginning about 20,000 years before present (BP), activity migrated to the SW, forming Meso-Semiachik (about 11,000-9,000 BP) and Ceno-Semiachik (about 8,000 BP to the present). An initial stage lasting about 3,500 years was dominantly explosive, constructing the present cone. A second stage beginning about 4,400 years ago was marked by alternating constructive and destructive processes. A crater lake fills the historically active Troitsky Crater, which formed during a large explosive eruption about 400 years ago.

Mauna Loa, Hawaiian Islands (USA)

19.475°N, 155.608°W | Summit elev. 4170 m

HVO reported continuing unrest at Mauna Loa during 25 October-1 November. The seismic network detected 19-41 daily small-magnitude (below M 3) earthquakes 3-5 km beneath Mokua’weoweo caldera and 1-8 km beneath the upper NW flank of Mauna Loa. Data from Global Positioning System (GPS) instruments at the summit and flanks showed continuing inflation, though data from tiltmeters at the summit did not show significant surface deformation over the past week. The Volcano Alert Level remained at Advisory (the second lowest level on a four-level scale) and the Aviation Color Code remained at Yellow (the second lowest level on a four-color scale).

Geological summary: Massive Mauna Loa shield volcano rises almost 9 km above the sea floor to form the world’s largest active volcano. Flank eruptions are predominately from the lengthy NE and SW rift zones, and the summit is cut by the Mokuaweoweo caldera, which sits within an older and larger 6 x 8 km caldera. Two of the youngest large debris avalanches documented in Hawaii traveled nearly 100 km from Mauna Loa; the second of the Alika avalanches was emplaced about 105,000 years ago (Moore et al. 1989). Almost 90% of the surface of the basaltic shield volcano is covered by lavas less than 4000 years old (Lockwood and Lipman, 1987). During a 750-year eruptive period beginning about 1500 years ago, a series of voluminous overflows from a summit lava lake covered about one fourth of the volcano’s surface. The ensuing 750-year period, from shortly after the formation of Mokuaweoweo caldera until the present, saw an additional quarter of the volcano covered with lava flows predominately from summit and NW rift zone vents.

Mayon, Luzon (Philippines)

13.257°N, 123.685°E | Summit elev. 2462 m

On 28 October PHIVOLCS warned of potential lahars around Mayon due to intense rains from an impending tropical storm. The rains could generate lahars in several drainages, including in the Miisi, Binaan, Anoling, Quirangay, Maninila, Masarawag, Muladbucad, Nasisi, Mabinit, Matan-ag, and Basud. Communities along the middle and lower flanks and in areas downstream were vulnerable to lahars. The Alert Level remained at 2 (on a 0-5 scale) and the public was reminded to stay outside of the 6-km-radius Permanent Danger Zone.

Geological summary: Symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the most active volcano of the Philippines. The steep upper slopes are capped by a small summit crater. Recorded eruptions since 1616 CE range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often damaged populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

Merapi, Central Java

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

BPPTKG reported that the eruption at Merapi continued during 21-27 October and seismicity remained at high levels. The SW lava dome produced as many as 14 minor lava avalanches that traveled as far as 1.5 km down the Bebeng drainage on the SW flank. No significant morphological changes to the central and SW lava domes were evident in drone photographs. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-7 km away from the summit based on location.

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

Nevado del Ruiz, Colombia

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

On 1 November Servicio Geológico Colombiano’s (SGC) reported that during the previous week seismicity at Nevado del Ruiz was variable and indicated continuing growth of the lava dome in Arenas Crater. The number and size of seismic signals indicating fluid movement had decreased compared to the week before. Some of the signals were associated with gas-and-ash emissions. Although seismic signals indicating rock fracturing decreased in number, magnitudes were higher previous week. The hypocenters were located 0.2-7 km deep, mainly beneath the NE and SW parts of Arenas Crater, and beneath the E, SE, and NW flanks. The largest event was a local M 1.8 that was recorded at 0518 on 28 October at a depth of 1.8 km below the crater. Several low-to-moderate thermal anomalies in Arenas Crater were identified in satellite images and minor changes to the dome and crater floor were visible. Plumes of steam and gas (mainly sulfur dioxide) continued to be emitted, rising as high as 1.8 km above the summit on 31 October and drifting SE, ESE, and ENE. 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.

Pavlof, Alaska Peninsula, Alaska

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

AVO reported that a minor eruption at a vent on Pavlof’s upper E flank was ongoing during 26 October-1 November and nearly continuous seismic tremor was recorded. Multiple explosions, detected almost daily in seismic and infrasound data, had intensified during the previous week. No significant activity was observed in cloudy-to-partly-cloudy satellite and webcam views during most of the week; diffuse steam-and-ash plume rose less than 3 km (10,000 ft) a.s.l. during 31 October-1 November and deposited minor amounts of tephra on the E flank. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geological summary: The 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.

Sheveluch, Central Kamchatka (Russia)

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

KVERT reported that the ongoing eruption at Sheveluch during 20-27 October was generally characterized by explosions, hot avalanches, and lava-dome extrusion. A daily thermal anomaly was identified in satellite images. Collapses generated hot avalanches and ash plumes that drifted 80 km SE and NW during 24-25 October. The Aviation Color Code remained at Orange (the second highest level on a four-color scale). Dates are based on UTC times; specific events are in local time where noted.

Geological summary: The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1,300 km3 andesitic volcano is one of Kamchatka’s largest and most active volcanic structures, with at least 60 large eruptions during the Holocene. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes occur on its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large open caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Suwanosejima, Ryukyu Islands (Japan)

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

JMA reported that the eruption at Suwanosejima’s Ontake Crater continued during 24-31 October and crater incandescence was visible nightly. A total of six explosions produced eruption plumes that rose as high as 2.1 km above the crater rim and ejected blocks as far as 300 m from the vent. Occasional rumbling noises and ashfall were reported in Toshima village (3.5 km SSW). The number of volcanic earthquakes increased starting at 0600 on 31 October; a total of about 355 events, located beneath the W flank, were recorded by 1500. The Alert Level remained at 2 and the public was warned to stay 1 km away from the crater.

Geological summary: The 8-km-long island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit is truncated by a large breached crater extending to the sea on the east flank that was formed by edifice collapse. One of Japan’s most frequently active volcanoes, it was in a state of intermittent Strombolian activity from Otake, the NE summit crater, between 1949 and 1996, after which periods of inactivity lengthened. The largest recorded eruption took place in 1813-14, when thick scoria deposits blanketed residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed, forming a large debris avalanche and creating the open Sakuchi caldera, which extends to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

Yasur, Vanuatu

19.532°S, 169.447°E | Summit elev. 361 m

On 27 October Vanuatu Meteorology and Geohazards Department (VMGD) reported that activity at Yasur continued at a high level of “major unrest,” as defined by the Alert Level 2 status (the middle level on a scale of 0-4). Ash-and-gas emissions and low-to-moderate explosions continued to be recorded, with bombs falling in and around the crater. The public was reminded to not enter the restricted area within 600 m around the cone, defined by Danger Zone A on the hazard map.

Geological summary: Yasur, the best-known and most frequently visited of the Vanuatu volcanoes, has exhibited essentially continuous Strombolian and Vulcanian activity since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island, this mostly unvegetated pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide open feature associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

References:

Smithsonian / US Geological Survey Weekly Volcanic Activity Report: October 26 – November 1, 2022 -Managing Editor: Sally Kuhn Sennert

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