The Weekly Volcanic Activity Report: September 25 - October 1, 2019

New activity was reported for 3 volcanoes from September 25 – October 1, 2019. During the same period, ongoing activity was reported for 19 volcanoes.

New activity/unrest: Copahue, Central Chile-Argentina border | Poas, Costa Rica | Ulawun, New Britain (Papua New Guinea).

New activity/unrest

Copahue, Central Chile-Argentina border

37.856°S, 71.183°W, Summit elev. 2953 m

On 30 September OVDAS-SERNAGEOMIN, ONEMI, and SEGEMAR reported that three long-period (LP) earthquakes with notable magnitudes were located about 5.8 km NE of Copahue’s El Agrio Crater. In addition, abundant LP and volcano-tectonic (VT) signals with relatively lower magnitudes were also located in the same area. Some of the events were felt by residents of Caviahue (10 km E) and Copahue 7 km NE) in Argentina. SERNAGEOMIN raised the Alert Level to Orange (second highest level on a four-color scale) and ONEMI updated the Yellow Alert (the middle level on a three-color scale) for residents, noting a restriction for entering a 5-km radius from El Agrio Crater. The seismic network recorded a local M 3.1 VT earthquake at 2340 on 30 September, and a local M 3.7 VT event at 0628 on 1 October. The report also noted that 14 lower-energy events (largest was M 2.4) were recorded.

Geological summary: Volcán Copahue is an elongated composite cone constructed along the Chile-Argentina border within the 6.5 x 8.5 km wide Trapa-Trapa caldera that formed between 0.6 and 0.4 million years ago near the NW margin of the 20 x 15 km Pliocene Caviahue (Del Agrio) caldera. The eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains a briny, acidic 300-m-wide crater lake (also referred to as El Agrio or Del Agrio) and displays intense fumarolic activity. Acidic hot springs occur below the eastern outlet of the crater lake, contributing to the acidity of the Río Agrio, and another geothermal zone is located within Caviahue caldera about 7 km NE of the summit. Infrequent mild-to-moderate explosive eruptions have been recorded since the 18th century. Twentieth-century eruptions from the crater lake have ejected pyroclastic rocks and chilled liquid sulfur fragments.

Poas, Costa Rica

10.2°N, 84.233°W, Summit elev. 2708 m

OVSICORI-UNA reported that during 16-26 September sulfur dioxide emissions from Poás drifted W and NE, causing a sulfur odor in Alajuela, Heredia, San José, and Cartago. Acidic rain was recorded at the official’s house in the Poás Volcano National Park (PNVP) on 23 September and at Universidad Nacional Costa Rica (UNA) in Heredia on 26 September. At 0540 on 30 September a five-minute-long phreatic eruption ejected sediment, and produced a plume that rose 2 km above the crater rim and drifted SW. Ashfall and a sulfur odor was reported in Trojas de Sarchi and Grecia. Officials closed the PNVP because of the eruption and ongoing elevated seismicity; the park remained closed the next day.

Geological summary: The broad, well-vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Ulawun, New Britain (Papua New Guinea)

5.05°S, 151.33°E, Summit elev. 2334 m

RVO reported that small, discrete, volcano-tectonic earthquakes at Ulawun began occurring more regularly around 1000 on 30 September; by 1130 they were frequent and by 1220 they were characterized as a swarm. The magnitude of the events overall increased with time and some were felt by residents and accompanied by booming sounds. Events were less frequent and intense during 1730-1930. Sometime afterwards RSAM values erratically increased, reaching a high of 10,000 units between 0130 and 0200 on 1 October. The Alert Level was raised to Stage 2 (the second lowest level on a four-stage scale).

Periods of volcano-tectonic earthquakes slowly transformed into continuous tremor with distinct bursts of high-frequency signals marking discrete volcano-tectonic events during 0430-0500 on 1 October. During this time a new vent opened in a deep valley on the SSW flank at 700 m elevation. The eruption was described as a distinct incandescent glow formed from ejecting material rising less than 100 m above the vent. By dawn light-gray ash plumes were visible rising several hundred meters and drifting NW. Lava fountaining continued throughout the day, and gray ash plumes rose several kilometers above the vent and drifted W. RVO recommended that the Alert Level be raised to Stage 3. On 2 October lava fountains rose several hundred meters and ash-and-steam plumes rose to variable heights between 2 and 5 km, causing ashfall in Navo (W). A lava flow which emerged during the night traveled 1-2 km NW, though visibility was hindered due to weather conditions. Loud rumbling and roaring was noted. Seismicity remained high with RSAM values passing 12,000 units.

Geological summary: The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

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 occasionally visible at night during 24-30 September. Very small eruptive events were recorded. The Alert Level remained at 3 (on a 5-level scale).

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.

Asosan, Kyushu (Japan)

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

JMA reported that during 25-30 September ash plumes rose as high as 1.6 km above Asosan’s summit crater rim and drifted NE and NW, causing ashfall in areas downwind. The sulfur dioxide emission rate was 2,600 tons per day on 26 September. The Alert Level remained at 2 (on a scale of 1-5).

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.

Dukono, Halmahera (Indonesia)

1.693°N, 127.894°E, Summit elev. 1229 m

Based on satellite and wind model data, and information from PVMBG, the Darwin VAAC reported that during 25 September-1 October ash plumes from Dukono rose to an altitude of 2.1 km (7,000 ft) a.s.l. and drifted in multiple directions. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to remain outside of the 2-km exclusion zone.

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

Ebeko, Paramushir Island (Russia)

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

Volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, observed explosions during 22-23 September that sent ash plumes up to 3 km (10,000 ft) a.s.l. Ash plumes drifted E and NE, causing ashfall in Severo-Kurilsk. 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.

Etna, Sicily (Italy)

37.748°N, 14.999°E, Summit elev. 3295 m

INGV reported that intense Strombolian activity from vents at the bottom of Etna’s Voragine Crater (VOR) continued during 23-29 September. Gas emissions from Northeast Crater (NEC) were intense and continuous, and ash plumes were occasionally visible and sometimes accompanied by incandescent flashes. A large ash emission rose from the crater on 27 September and drifted S.

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.

Ibu, Halmahera (Indonesia)

1.488°N, 127.63°E, Summit elev. 1325 m

The Darwin VAAC reported that on 28 September ash plumes from Ibu rose to altitudes of 1.8-2.1 km (6,00-7,000 ft) a.s.l. and drifted WNW based on satellite images and weather models. PVMBG reported that at 1806 on 30 September an ash plume rose about 800 m above the crater rim and drifted N. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to stay at least 2 km away from the active crater, and 3.5 km away on the N side.

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

Karangetang, Siau Island (Indonesia)

2.781°N, 125.407°E, Summit elev. 1797 m

PVMBG reported that during 25 September-1 October lava continued to effuse from Karangetang’s Main Crater (S), traveling as far as 1.5 km down the Nanitu, Pangi, and Sense drainages on the SW and W flanks. Sometimes dense white plumes rose to 300 m above the summit. On 27 and 29 September the Darwin VAAC noted that ash plumes rose to 2.1-2.4 km (7,000-8,000 ft) a.s.l. (about 330-640 m above the crater rim) and drifted SW and W. The Alert Level remained at 2 (on a scale of 1-4).

Geological summary: Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi island. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia's most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented in the historical record (Catalog of Active Volcanoes of the World: Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.

Karymsky, Eastern Kamchatka (Russia)

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

KVERT reported that a thermal anomaly over Karymsky was visible in satellite images on 19 September. 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.

Krakatau, Indonesia

6.102°S, 105.423°E, Summit elev. 813 m

PVMBG reported that Anak Krakatau’s seismic network recorded 10 eruptive events during 23-29 September. A webcam at the summit recorded diffuse white plumes rising as high as 150 m from the vent at the bottom of the crater. Eruptive events recorded by the webcam at 0813 on 25 September, 0555 and 0835 on 26 September, and 1520 on 27 September generated dense gray-and-white ash plumes that rose 150-200 m from the vent and generally drifted N. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to remain outside of the 2-km-radius hazard zone 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 Krakatau edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of this ancestral 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, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating 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.

Manam, Papua New Guinea

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

The Darwin VAAC reported that on 29 September diffuse ash plumes from Manam rose to altitudes of 2.4-2.7 km (8,000-9,000 ft) a.s.l. and drifted W, based on satellite data and weather models. A sulfur dioxide signature in the plume was also detected. On 30 September RVO reported increased seismicity; the VAAC noted ongoing emissions and a persistent thermal anomaly.

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 1807-m-high basaltic-andesitic stratovolcano to its lower flanks. These "avalanche 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 historical eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent historical eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Merapi, Central Java (Indonesia)

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

PVMBG reported that the lava dome at Merapi slowly grew during 20-26 September and was an estimated 468,000 cubic meters, based on 19 September measurements based on drone photos. Extruded lava fell into the upper parts of the SE flank, generating three block-and-ash flows that traveled as far as 1.5 km down the Gendol drainage. Diffuse white plumes rose as high as 75 m above the summit. The Alert Level remained at 2 (on a scale of 1-4), and residents were warned to stay outside of the 3-km exclusion zone.

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 2000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequently growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive 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 during historical time.

Nevados de Chillan, Chile

36.868°S, 71.378°W, Summit elev. 3180 m

ONEMI and SERNAGEOMIN reported that during 24 September-1 October white-to-gray gas plumes from Nevados de Chillán’s Nicanor Crater rose as high as 1.3 km above the rim and drifted NE, E, and SE. Explosions sometimes ejected incandescent material onto the flanks. A lava flow on the NNE flank continued to advance at a low rate. Ashfall was reported 15 km WNW in Las Trancas on 24 September. The Alert Level remained at Orange, the second highest level on a four-color scale. ONEMI maintained an Alert Level Yellow (the middle level on a three-color scale) for the communities of Pinto, Coihueco, and San Fabián, and stated that the public should stay at least 3 km away from the crater on the SW flank and 5 km away on the ENE flank.

Geological summary: The compound volcano of Nevados de Chillán is one of the most active of the Central Andes. Three late-Pleistocene to Holocene stratovolcanoes were constructed along a NNW-SSE line within three nested Pleistocene calderas, which produced ignimbrite sheets extending more than 100 km into the Central Depression of Chile. The largest stratovolcano, dominantly andesitic, Cerro Blanco (Volcán Nevado), is located at the NW end of the group. Volcán Viejo (Volcán Chillán), which was the main active vent during the 17th-19th centuries, occupies the SE end. The new Volcán Nuevo lava-dome complex formed between 1906 and 1945 between the two volcanoes and grew to exceed Volcán Viejo in elevation. The Volcán Arrau dome complex was constructed SE of Volcán Nuevo between 1973 and 1986 and eventually exceeded its height.

Popocatepetl, Mexico

19.023°N, 98.622°W, Summit elev. 5393 m

CENAPRED reported that each day during 25 September-1 October there were 123-224 steam-and-gas emissions from Popocatépetl, some of which contained ash. As many as 10 explosions were recorded each day and crater incandescence was sometimes visible at night. During an overflight on 27 September observatory staff, scientists, and civil protection staff observed a lava dome, 30 m in diameter, at the bottom of the inner crater. The inner crater was 350 m in diameter and 150 m deep based on thermal images and photographs. The Alert Level remained at Yellow, Phase Two (middle level on a three-color scale).

Geological summary: Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Sabancaya, Peru

15.787°S, 71.857°W, Summit elev. 5960 m

Instituto Geofísico del Perú (IGP) reported that an average of 15 low-to-medium intensity explosions per day occurred at Sabancaya during 23-29 September. Gas-and-ash plumes rose as high as 1.7 km above the summit and drifted NW, W, and SW. There were 11 thermal anomalies identified in satellite data. The Alert Level remained at Orange (the second highest level on a four-color scale) and the public were warned to stay outside of a 12-km radius.

Geological summary: Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning "tongue of fire" in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions date back to 1750.

Sheveluch, Central Kamchatka (Russia)

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

KVERT reported that a thermal anomaly over Sheveluch’s lava dome was identified daily in satellite images during 20-27 September. Explosions recorded during 20-21, 23, and 26 September produced ash plumes that rose to 7 km (23,000 ft) a.s.l. and drifted 580 km ESE. 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.

Shishaldin, Fox Islands (USA)

54.756°N, 163.97°W, Summit elev. 2857 m

On 26 September AVO reported that seismicity at Shishaldin had decreased during the previous few weeks to levels slightly above background. Satellite images indicated decreased surface temperatures at the summit over the same period and showed collapse and slumping of the floor of the summit crater, suggesting a withdrawal of magma. Tiltmeter data suggested that the collapse may have occurred on 19 September. The Aviation Color Code was lowered to Yellow and the Volcano Alert Level was lowered to Advisory.

Geological summary: The beautifully symmetrical volcano of Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The 2857-m-high, glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steady steam plume rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is Holocene in age and largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the west and NE sides at 1500-1800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century.

Suwanosejima, Ryukyu Islands (Japan)

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

JMA reported that during 20-27 September white plumes rose 800 m above the rim of Suwanosejima’s Ontake Crater and crater incandescence was visible at night. The Alert Level remained at 2 (on a 5-level scale).

Geological summary: The 8-km-long, spindle-shaped island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit of the volcano 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.

Tangkubanparahu, Western Java (Indonesia)

6.77°S, 107.6°E, Summit elev. 2084 m

PVMBG reported that during 23-29 September diffuse white water vapor plumes rose 200 m above the vent on Tangkubanparahu's Ratu Crater floor. The seismic network recorded continuous tremor. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to stay 1.5 km away from the active crater.

Geological summary: Tangkubanparahu (also known as Tangkuban Perahu) is a broad shield-like stratovolcano overlooking Indonesia's former capital city of Bandung. The volcano was constructed within the 6 x 8 km Pleistocene Sunda caldera, which formed about 190,000 years ago. The volcano's low profile is the subject of legends referring to the mountain of the "upturned boat." The rim of Sunda caldera forms a prominent ridge on the western side; elsewhere the caldera rim is largely buried by deposits of Tangkubanparahu volcano. The dominantly small phreatic historical eruptions recorded since the 19th century have originated from several nested craters within an elliptical 1 x 1.5 km summit depression.

White Island, North Island (New Zealand)

37.52°S, 177.18°E, Summit elev. 321 m

GeoNet reported observing small-scale geyser-like explosions of mud and steam at White Island’s active vent area during the previous three weeks. The ejecta rose as high as 10 m above the active vents on the W part of the crater floor. An increase in frequency of these events was caused by crater lake water that has been rising since early August, covering the active vents. The geysering does not represent increased volcanic activity; the Volcanic Alert Level remained at 1 (the second lowest level on a 0-5 scale) and the Aviation Color Code remained at Green.

Geological summary: Uninhabited 2 x 2.4 km White Island, one of New Zealand's most active volcanoes, is the 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 summit crater appears to be breached to the SE, because the shoreline corresponds to the level of several notches in the SE crater wall. Volckner Rocks, four sea stacks that are remnants of a lava dome, lie 5 km NNE. Intermittent moderate phreatomagmatic and strombolian eruptions have occurred throughout the short historical period beginning in 1826, but its activity also forms a prominent part of Maori legends. Formation of many new vents during the 19th and 20th centuries has produced 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.

Source: GVP

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