New activity/unrest was reported for 3 volcanoes between November 28 and December 4, 2018. During the same period, ongoing activity was reported for 17 volcanoes.
New activity/unrest: Akan, Hokkaido (Japan) | Mayon, Luzon (Philippines) | Veniaminof, United States.
Ongoing activity: Aira, Kyushu (Japan) | Bagana, Bougainville (Papua New Guinea) | Chiles-Cerro Negro, Colombia-Ecuador | Copahue, Central Chile-Argentina border | Dukono, Halmahera (Indonesia) | Ebeko, Paramushir Island (Russia) | Kadovar, Papua New Guinea | Kirishimayama, Kyushu (Japan) | Krakatau, Indonesia | Kuchinoerabujima, Ryukyu Islands (Japan) | Merapi, Central Java (Indonesia) | Popocatepetl, Mexico | Rincon de la Vieja, Costa Rica | Sabancaya, Peru | Sheveluch, Central Kamchatka (Russia) | Suwanosejima, Ryukyu Islands (Japan) | Turrialba, Costa Rica.
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, notices of volcanic activity posted are preliminary and subject to change as events are studied in more detail. This is not a comprehensive list of all of Earth’s volcanoes erupting during the week. Carefully reviewed, detailed reports on various volcanoes are published monthly in the Bulletin of the Global Volcanism Network.
Akan, Hokkaido (Japan)
43.384°N, 144.013°E, Elevation 1499 m
JMA reported that the number of earthquakes with shallow hypocenters and epicenters near Ponmachineshiri Crater, a summit crater of Me-Akan (also known as Meakan-dake, which means Meakan Peak) of the Akan volcanic complex, increased at 1800 on 20 November. Another seismic increase occurred on 23 November, in number and amplitude of events, prompting JMA to raise the Alert Level to 2 (the second lowest level on a 5-level scale).
Geological background: Akan is a 13 x 24 km caldera located immediately SW of Kussharo caldera. The elongated, irregular outline of the caldera rim reflects its incremental formation during major explosive eruptions from the early to mid-Pleistocene. Growth of four post-caldera stratovolcanoes, three at the SW end of the caldera and the other at the NE side, has restricted the size of the caldera lake. Conical Oakandake was frequently active during the Holocene. The 1-km-wide Nakamachineshiri crater of Meakandake was formed during a major pumice-and-scoria eruption about 13,500 years ago. Within the Akan volcanic complex, only the Meakandake group, east of Lake Akan, has been historically active, producing mild phreatic eruptions since the beginning of the 19th century. Meakandake is composed of nine overlapping cones. The main cone of Meakandake proper has a triple crater at its summit. Historical eruptions at Meakandake have consisted of minor phreatic explosions, but four major magmatic eruptions including pyroclastic flows have occurred during the Holocene.
Mayon, Luzon (Philippines)
13.257°N, 123.685°E, Summit elev. 2462 m
PHIVOLCS reported that during 27 November-4 December white steam plumes rose from Mayon daily, and crater incandescence was visible almost nightly. At 0533 on 27 November a phreatic event generated a grayish-white ash plume that rose 300-500 m and drifted SW. A one-minute-long event that began at 0941 on 30 November produced another grayish-white ash plume. The Alert Level remained at 2 (on a 0-5 scale) and PHIVOLCS reminded residents to stay away from the 6-km-radius Permanent Danger Zone and the 7-km Extended Danger Zone on the SSW and ENE flanks.
Geological background: Beautifully symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the Philippines’ most active volcano. The structurally simple edifice has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions date back to 1616 and 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 devastated populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.
Veniaminof, United States
56.17°N, 159.38°W, Summit elev. 2507 m
AVO reported that the eruption of lava from the cone in Veniaminof’s ice-filled summit caldera continued during 27 November-3 December. Satellite and webcam data showed elevated surface temperatures. Steam and diffuse ash plumes were periodically identified in webcam and satellite images. During 27-28 November acoustic waves were recorded by regional infrasound sensors. Continuous low-amplitude tremor was recorded until the network went offline following a M 7 tectonic earthquake near Anchorage on 30 November. The Aviation Color Code remained at Orange (the second highest level on a four-color scale) and the Volcano Alert Level remained at Watch (the second highest level on a four-level scale).
Geological background: Massive Veniaminof volcano, one of the highest and largest volcanoes on the Alaska Peninsula, is truncated by a steep-walled, 8 x 11 km, glacier-filled caldera that formed around 3700 years ago. The caldera rim is up to 520 m high on the north, is deeply notched on the west by Cone Glacier, and is covered by an ice sheet on the south. Post-caldera vents are located along a NW-SE zone bisecting the caldera that extends 55 km from near the Bering Sea coast, across the caldera, and down the Pacific flank. Historical eruptions probably all originated from the westernmost and most prominent of two intra-caldera cones, which rises about 300 m above the surrounding icefield. The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.
Aira, Kyushu (Japan)
31.593°N, 130.657°E, Summit elev. 1117 m
JMA reported that nine events at Minamidake crater (at Aira Caldera’s Sakurajima volcano) were recorded during 26 November-3 December, producing ash plumes that rose as high as 1.8 km above the crater rim. Incandescence was periodically visible at night. An explosion at 0218 on 1 December generated a plume that rose 2.5 km and ejected tephra 1.1 km from the crater. The Alert Level remained at 3 (on a 5-level scale).
Geological background: 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
On 1 December the Darwin VAAC reported that ash plumes from Bagana were visible in satellite images drifting SE at an altitude of 3 km (10,000 ft) a.s.l. The report also noted the presence of a strong thermal anomaly, and that ash plumes which previously rose to 6.1 km (20,000 ft) a.s.l. had dissipated. Steam plumes drifted SE on 2 December.
Geological background: 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.
Chiles-Cerro Negro, Colombia-Ecuador
0.817°N, 77.938°W, Summit elev. 4698 m
Servicio Geológico Colombiano (SGC) reported that a seismic swarm below Cerro Negro de Mayasquer and Chiles volcanoes began at 0100 on 3 December. The events were classified as volcano-tectonic, with epicenters located up to 6 km from the summit of Chiles volcano, at depths of less than 8 km (4.7 km a.s.l.). The maximum local magnitude was 2.3. From the beginning of the swarm until the time of the report posting (1640) there were about 5,400 recorded events, making the swarm the largest since 2015. The report also noted that seismicity had gradually been increasing in recent weeks. The Alert Level remained at Yellow (level 2 of 4).
Geological background: The Chiles-Cerro Negro volcanic complex includes both the Pleistocene Chiles and the Cerro Negro de Mayasquer stratovolcanoes astride the Colombia-Ecuador border. Cerro Negro has a caldera open to the west, with andesitic and dacitic lava flows of possible Holocene age (Hall 1992, pers. comm.) and solfataras on the shore of a small crater lake. An eruption reported in 1936 may have been from Reventador (Catalog of Active Volcanoes of the World). The higher, glacier-covered summit of Chiles, about 4 km ESE of Cerro Negro, last erupted about 160,000 years ago, but it has a caldera open to the north with hot springs and an active hydrothermal system on its eastern flank.
Copahue, Central Chile-Argentina border
37.856°S, 71.183°W, Summit elev. 2953 m
The Buenos Aires VAAC reported that on 2 December a narrow ash plume from Copahue was visible in satellite images drifting ESE.
Geological background: 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 at Copahue since the 18th century. Twentieth-century eruptions from the crater lake have ejected pyroclastic rocks and chilled liquid sulfur fragments.
Dukono, Halmahera (Indonesia)
1.693°N, 127.894°E, Summit elev. 1229 m
Based on satellite data, wind model data, and notices from PVMBG, the Darwin VAAC reported that during 21-27 November ash plumes from Dukono rose to altitudes of 1.5-2.1 km (5,000-7,000 ft) a.s.l. and drifted NE, E, and SE. The Alert Level remained at 2 (on a scale of 1-4), and visitors were warned to remain outside of the 2-km exclusion zone.
Geological background: 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 23-30 November that sent ash plumes to 4 km (13,100 ft) a.s.l. Ash plumes drifted E. A weak thermal anomaly was identified in satellite data on 24 November, and ashfall was reported in Severo-Kurilsk on 27 and 29 November. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).
Geological background: 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.
Kadovar, Papua New Guinea
3.608°S, 144.588°E, Summit elev. 365 m
Based on satellite data and wind model data, the Darwin VAAC reported that during 27-28 November ash plumes from Kadovar rose to an altitude of 0.9 km (3,000 ft) a.s.l. and drifted SE and E. On 2 December ash plumes rose to 1.2 km (4,000 ft) a.s.l. and drifted WSW and W.
Geological background: The 2-km-wide island of Kadovar is the emergent summit of a Bismarck Sea stratovolcano of Holocene age. Kadovar is part of the Schouten Islands, and lies off the coast of New Guinea, about 25 km N of the mouth of the Sepik River. The village of Gewai is perched on the crater rim. A 365-m-high lava dome forming the high point of the andesitic volcano fills an arcuate landslide scarp that is open to the south, and submarine debris-avalanche deposits occur in that direction. Thick lava flows with columnar jointing forms low cliffs along the coast. The youthful island lacks fringing or offshore reefs. No certain historical eruptions are known; the latest activity was a period of heightened thermal phenomena in 1976.
Kirishimayama, Kyushu (Japan)
31.934°N, 130.862°E, Summit elev. 1700 m
JMA reported that vigorous fumarolic activity on the S side of Iwo-yama (also called Ioyama), on the NW flank of the Karakuni-dake stratovolcano in the Kirishimayama volcano group, continued during 30 November-3 December. Fumarolic plumes rose 100 m above the vent, and hot mud was ejected from the vent. A hot pool of water persisted on the S side of the area. Fumarolic plumes rose 50 m above a vent 500 m W of Iwo-yama. The Alert Level remained at 2 (the second lowest level on a scale of 1-5).
Geological background: Kirishimayama is a large group of more than 20 Quaternary volcanoes located north of Kagoshima Bay. The late-Pleistocene to Holocene dominantly andesitic group consists of stratovolcanoes, pyroclastic cones, maars, and underlying shield volcanoes located over an area of 20 x 30 km. The larger stratovolcanoes are scattered throughout the field, with the centrally located, 1700-m-high Karakunidake being the highest. Onamiike and Miike, the two largest maars, are located SW of Karakunidake and at its far eastern end, respectively. Holocene eruptions have been concentrated along an E-W line of vents from Miike to Ohachi, and at Shinmoedake to the NE. Frequent small-to-moderate explosive eruptions have been recorded since the 8th century.
6.102°S, 105.423°E, Summit elev. 813 m
PVMBG reported that events at Anak Krakatau were recorded at 1131 on 1 December, at 1408 on 2 December, and at 0816 on 3 December, each lasting between 46 and 69 seconds. Ash plumes from the events rose 500-700 m and drifted NE and N. The Alert Level remained at 2 (on a scale of 1-4); residents and visitors were warned not to approach the volcano within 2 km of the crater.
Geological background: 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 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 volcanoes, and left only a remnant of Rakata volcano. 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.
Kuchinoerabujima, Ryukyu Islands (Japan)
30.443°N, 130.217°E, Summit elev. 657 m
JMA reported that during 28 November-3 December intermittent events at Kuchinoerabujima’s Shindake Crater generated plumes that rose as high as 1.5 km above the crater rim. The Alert Level remained at 3 (on a scale of 1-5).
Geological background: A group of young stratovolcanoes forms the eastern end of the irregularly shaped island of Kuchinoerabujima in the northern Ryukyu Islands, 15 km west of Yakushima. The Furudake, Shindake, and Noikeyama cones were erupted from south to north, respectively, forming a composite cone with multiple craters. The youngest cone, centrally-located Shintake, formed after the NW side of Furutake was breached by an explosion. All historical eruptions have occurred from Shintake, although a lava flow from the S flank of Furutake that reached the coast has a very fresh morphology. Frequent explosive eruptions have taken place from Shintake since 1840; the largest of these was in December 1933. Several villages on the 4 x 12 km island are located within a few kilometers of the active crater and have suffered damage from eruptions.
Merapi, Central Java (Indonesia)
7.54°S, 110.446°E, Summit elev. 2910 m
PVMBG reported that during 23-29 November the lava dome in Merapi’s summit crater grew at a rate of 2,500 cubic meters per day. By 29 November the volume of the dome, based on photos taken from the SE, was an estimated 329,000 cubic meters. White emissions of variable density rose a maximum of 400 m above the summit. The Alert Level remained at 2 (on a scale of 1-4), and residents were warned to remain outside of the 3-km exclusion zone.
Geological background: 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.
19.023°N, 98.622°W, Summit elev. 5393 m
CENAPRED reported that each day during 28 November-3 December there were 16-79 steam-and-gas emissions from Popocatépetl. Periods of volcanic tremor were detected almost daily. Explosions at 0509 and 0922 on 2 December ejected incandescent material onto the upper flanks, and generated ash plumes that rose 2.5 km above the crater rim and drifted NE. More explosions at 1543 and 1745 produced ash plumes that rose 1.5 km and drifted NE. The Alert Level remained at Yellow, Phase Two (middle level on a three-color scale).
Geological background: 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.
Rincon de la Vieja, Costa Rica
10.83°N, 85.324°W, Summit elev. 1916 m
OVSICORI-UNA reported a one-minute-long eruption at Rincón de la Vieja began at 1054 on 3 December. Weather conditions prevented webcam views and estimates of plume heights.
Geological background: 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 that was 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 1916-m-high 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 3500 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.
15.787°S, 71.857°W, Summit elev. 5960 m
Observatorio Vulcanológico del Sur del IGP (OVS-IGP) and Observatorio Vulcanológico del INGEMMET (OVI) reported that an average of 21 explosions per day occurred at Sabancaya during 26 November-2 December. Long-period seismic events were recorded, and hybrid earthquakes were infrequent and of low magnitude. Gas-and-ash plumes rose as high as 2.5 km above the crater rim and drifted 30 km N, E, and SE. MIROVA detected eight thermal anomalies, and on 28 November the sulfur-dioxide gas flux was high at 4,600 tons per day. The report noted that the public should not approach the crater within a 12-km radius.
Geological background: 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 was identified in satellite images on 23 November; weather clouds prevented views of the volcano during 24-30 November. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).
Geological background: 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 four explosions at Suwanosejima’s Ontake Crater were recorded during 22-30 November. The highest ash plume rose 2 km, and material was ejected 300 m from the crater. Ashfall was reported in an area 4 km SSW on 23 November. Crater incandescence was visible at night. The Alert Level remained at 2 (on a 5-level scale).
Geological background: 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.
Turrialba, Costa Rica
10.025°N, 83.767°W, Summit elev. 3340 m
OVSICORI-UNA reported intermittent pulses of ash and some periods of continuous ash emissions from Turrialba during 28 November-3 December. Ash plumes rose as high as 500 m above the crater rim and drifted N, NW, and SW. Ashfall was reported in Santo Domingo (36 km WSW) on 2 December.
Geological background: Turrialba, the easternmost of Costa Rica’s Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive edifice covers an area of 500 km2. Three well-defined craters occur at the upper SW end of a broad 800 x 2200 m summit depression that is breached to the NE. Most activity originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred during the past 3500 years. A series of explosive eruptions during the 19th century were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters.