New activity/unrest was reported for 5 volcanoes between April 12 and 18, 2017. During the same period, ongoing activity was reported for 14 volcanoes.
New activity/unrest: Aira, Kyushu (Japan) | Ibu, Halmahera (Indonesia) | Kambalny, Southern Kamchatka (Russia) | Manam, Papua New Guinea | Poas, Costa Rica.
Ongoing activity: Bagana, Bougainville (Papua New Guinea) | Bezymianny, Central Kamchatka (Russia) | Bogoslof, Fox Islands (USA) | Colima, Mexico | Dukono, Halmahera (Indonesia) | Ebeko, Paramushir Island (Russia) | Etna, Sicily (Italy) | Kilauea, Hawaiian Islands (USA) | Nevado del Ruiz, Colombia | Nevados de Chillan, Chile | Sabancaya, Peru | Sheveluch, Central Kamchatka (Russia) | Sinabung, Indonesia | Turrialba, Costa Rica.
Aira, Kyushu (Japan)
31.593°N, 130.657°E, Elevation 1117 m
JMA reported that a very small eruption at Minamidake summit crater (at Aira Caldera’s Sakurajima volcano) occurred on 16 April. 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.
Ibu, Halmahera (Indonesia)
1.488°N, 127.63°E, Elevation 1325 m
Based on ground and satellite observations, PVMBG and the Darwin VAAC reported that during 12-13 and 17 April ash plumes from Ibu rose 1.5-1.8 km (4,900-5,900 ft) a.s.l. and drifted S and SW.
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.
Kambalny, Southern Kamchatka (Russia)
51.306°N, 156.875°E, Elevation 2116 m
KVERT reported that observers in the South Kamchatka Sanctuary noted an ash plume from Kambalny rising to an altitude of 7 km (23,000 ft) a.s.l. on 9 April. Ash plumes identified in satellite images drifted 50 km NE on 9 April and about 170 km SE the next day. The Aviation Color Code remained at Orange.
Geological summary: The southernmost major stratovolcano on the Kamchatka peninsula, 2116-m-high Kambalny has a summit crater that is breached to the SE. Five Holocene cinder cones on the W and SE flanks have produced fresh-looking lava flows. Beginning about 6300 radiocarbon years ago, a series of major collapses of the edifice produced at least three debris-avalanche deposits. The last major eruption took place about 600 years ago, although younger tephra layers have been found, and an eruption was reported in 1767. Active fumarolic areas are found on the flanks of the volcano, which is located south of the massive Pauzhetka volcano-tectonic depression.
Manam, Papua New Guinea
4.08°S, 145.037°E, Elevation 1807 m
RVO reported that incandescence from both Manam's Southern Crater and Main Crater fluctuated in intensity during 1-15 April, and incandescent material was occasionally ejected from the craters. RSAM values averaged around 100. On 15 April RSAM values fluctuated, with a peak of 450 at 0600 and other peaks throughout the day, though with RSAM values not as high. RVO interpreted the high RSAM values as changes in seismicity from discrete low-frequency earthquakes, to sub-continuous volcanic tremor, and then to continuous volcanic tremor.
During 0300-0800 on 16 April RSAM values were high (peaking at 400); there were no reports of associated anomalous eruptive activity, though RVO noted communication problems. Based on RSAM data, a small-to-medium eruption began between 1400 and 1600 on 16 April. Seismicity was initially erratic, and peaked at about 0030 and 0100 on 17 April. A Dugulava village resident (S side of island) briefly viewed the eruption and reported that incandescent material was ejected from the crater and fell into the N and SW valleys. Rumbling and roaring was also heard. Activity decreased around 0600 and remained low until the next day. Strong Strombolian activity at Southern Crater was observed at about 1300 on 18 April, and roaring and rumbling was heard. Dense and dark ash clouds rose a few hundred meters above the crater rim and drifted NW. Two small pyroclastic flows descended the SE and SW valleys, terminating at about 1 km a.s.l. At about 1500 Strombolian activity subsided, coinciding with a very loud explosion. Activity fluctuated though was low until 2100, and then afterwards light-gray ash plumes rose above the crater. White-to-gray ash plumes rose above Main Crater during 17-18 April, and small ejections of material occurred about every five minutes.
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.
Poas, Costa Rica
10.2°N, 84.233°W, Elevation 2708 m
OVSICORI-UNA reported that a strong 40-minute phreatic eruption from an area in between the lava dome and the hot lake at Poás was recorded on 12 April starting at 1830. An eruption column consisting of water, altered rocks, sediments, and gases was produced; the height of the column could not be determined due to poor visibility. Ash fell around the crater and to the NW in Bajos del Toro. A water-level increase of 2 m in the Desague River, with headwaters at the S part of the crater, was noted. According to news articles the National Emergency Committee (CNE) evacuated residents living near the Desague River. The Poás Volcano National Park closed the next day.
At 1546 on 13 April an eight-minute-long eruption produced a plume that rose 500 m above the crater rim. The event rendered a webcam on the N rim inoperable. Events at 0758 (strong) and 1055 on 14 April generated plumes of an unknown height. A 10-minute-long event which began at 0810 on 15 April again produced a plume of unknown height. Frequent (2-3 events per hour) small short-lived phreatic eruptions were recorded by seismographs during 15-16 April. A plume that rose 500 m followed an eruption at 0946 on 16 April. Later that day, at 1350, an event generated a plume that rose 1 km. A news article reported that boulders as large as 2 m in diameter fell in an area 30 m away from a tourist trail, breaking a water pipe. Rocks also damaged fences and concrete floors in viewing areas. Small, frequent, and short-lived phreatic eruptions continued to be recorded through 18 April. A video posted by a news outlet showed an explosion ejecting incandescent material.
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.
Bagana, Bougainville (Papua New Guinea)
6.137°S, 155.196°E, Elevation 1855 m
Based on analyses of satellite imagery and model data, the Darwin VAAC reported that during 16-17 April ash plumes from Bagana rose to altitudes of 1.8-2.1 km (6,000-7,000 ft) a.s.l. and drifted N, SE, and S.
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.
Bezymianny, Central Kamchatka (Russia)
55.972°N, 160.595°E, Elevation 2882 m
KVERT reported that during 7-14 April lava continued to advance down the NW flank of Bezymianny's lava dome. A thermal anomaly was identified in satellite images daily. The Aviation Color Code remained at Orange.
Geological summary: Prior to its noted 1955-56 eruption, Bezymianny had been considered extinct. The modern volcano, much smaller in size than its massive neighbors Kamen and Kliuchevskoi, was formed about 4700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7000 years ago. Three periods of intensified activity have occurred during the past 3000 years. The latest period, which was preceded by a 1000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large horseshoe-shaped 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.
Bogoslof, Fox Islands (USA)
53.93°N, 168.03°W, Elevation 150 m
Increased seismicity at Bogoslof was recorded by stations on nearby islands starting around 1501 on 15 April, prompting AVO to raise the Aviation Color Code to Orange and the Volcano Alert Level to Watch. The seismic activity subsided a few hours later; there was no evidence of renewed eruptive activity from infrasound, lightning, or satellite data during 15-18 April.
Geological summary: Bogoslof is the emergent summit of a submarine volcano that lies 40 km north of the main Aleutian arc. It rises 1500 m above the Bering Sea floor. Repeated construction and destruction of lava domes at different locations during historical time has greatly modified the appearance of this "Jack-in-the-Box" volcano and has introduced a confusing nomenclature applied during frequent visits of exploring expeditions. The present triangular-shaped, 0.75 x 2 km island consists of remnants of lava domes emplaced from 1796 to 1992. Castle Rock (Old Bogoslof) is a steep-sided pinnacle that is a remnant of a spine from the 1796 eruption. Fire Island (New Bogoslof), a small island located about 600 m NW of Bogoslof Island, is a remnant of a lava dome that was formed in 1883.
19.514°N, 103.62°W, Elevation 3850 m
On 14 April the Centro Universitario de Estudios e Investigaciones de Vulcanologia - Universidad de Colima reported that during the previous week seismic data revealed 48 high-frequency events, 30 long-period events, 3.3 hours of tremor, 10 landslides, and two explosions.
Geological summary: The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the 4320 m high point of the complex) on the north and the 3850-m-high historically active Volcán de Colima at the south. A group of cinder cones of late-Pleistocene age is located on the floor of the Colima graben west and east of the Colima complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, and have produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions (most recently in 1913) have destroyed the summit and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.
Dukono, Halmahera (Indonesia)
1.693°N, 127.894°E, Elevation 1229 m
Based on analyses of satellite imagery, wind model data, and notices from PVMBG, the Darwin VAAC reported that during 12-18 April ash plumes from Dukono rose to an altitude of 2.1 km (7,000 ft) a.s.l. and drifted S, SW, W, and N.
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, Elevation 1103 m
KVERT reported that during 7-14 April several explosions at Ebeko were observed by residents of Severo-Kurilsk (Paramushir Island) about 7 km E. Ash plumes rose as high as 2.6 km (8,500 ft) a.s.l. Minor amounts of ash fell in Severo-Kurilsk on 12 April. 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)
37.734°N, 15.004°E, Elevation 3330 m
INGV reported that the effusive eruption from a vent in the saddle between Etna's Southeast Crater (SEC) - New Southeast Crater (NSEC) cone complex ended during 8-9 April. During 10-11 April lava effused from a vent located at the S base of the SEC. The lava flow traveled SE and flowed several hundred meters down the W wall of the Valle del Bove. In the evening of 13 April short-lived explosive activity occurred at a vent at the S flank of the SEC cone at about 3,200 m elevation. That vent and another at 3,150 m elevation produced lava flows for a few hours. Lava also effused from the vent at the S base of SEC, 3,010 m elevation, during 13-14 April, traveling SE and down the W wall of the Valle del Bove on top of the flows from 10-11 April.
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 at Etna. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more of the three prominent summit craters, the Central Crater, NE Crater, and SE Crater (the latter formed in 1978). 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.
Kilauea, Hawaiian Islands (USA)
19.421°N, 155.287°W, Elevation 1222 m
During 12-18 April HVO reported that the lava lake continued to rise, fall, and spatter in Kilauea’s Overlook crater. Webcams recorded incandescence from long-active sources within Pu'u 'O'o Crater, from a vent high on the NE flank of the cone, and from a small lava pond in a pit on the W side of the crater. The 61G lava flow, originating from a vent on Pu'u 'O'o Crater's E flank, continued to enter the ocean at Kamokuna. A growing lava delta is building where the lava enters the water. Surface lava flows were active above the pali.
Geological summary: Kilauea volcano, which overlaps the east flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 sq km, destroying nearly 200 houses and adding new coastline to the island.
Nevado del Ruiz, Colombia
4.892°N, 75.324°W, Elevation 5279 m
Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that at 1822 on 14 April a seismic event at Nevado del Ruiz was recorded, associated with a gas-and-ash emission recorded by the webcam that rose almost 1.2 km above the crater. The Alert Level remained at III (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 >200 sq km. 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.
Nevados de Chillan, Chile
36.863°S, 71.377°W, Elevation 3212 m
The Buenos Aires VAAC reported that on 17 April a webcam recorded the ejection of incandescent material from Nevados de Chillán, and a possible ash plume that rose to 3.7 km (12,000 ft) a.s.l.
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.
15.78°S, 71.85°W, Elevation 5967 m
Observatorio Vulcanológico del Sur del IGP (OVS-IGP) and Observatorio Vulcanológico del INGEMMET (OVI) reported that during 10-16 April seismicity at Sabancaya increased compared to the previous week, with an average of 37 explosions recorded per day. Ash plumes rose as high as 3 km above the crater rim (13 April) and drifted more than 40 km NW and SE. The Buenos Aires VAAC reported that on 17 April ash plumes rose to an altitude of 7.9 km (26,000 ft) a.s.l. and drifted SE. The next day ash emissions were recorded by the webcam. The Alert Level remained at Orange (the second highest level on a four-color scale).
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, Elevation 3283 m
KVERT reported that during 7-14 April lava-dome extrusion onto Sheveluch’s N flank was accompanied by strong fumarolic activity, dome incandescence, ash explosions, and hot avalanches. Satellite images showed a daily thermal anomaly over the dome, and an ash plume that drifted 82 km SW on 10 April. 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 cu km 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.
3.17°N, 98.392°E, Elevation 2460 m
Based on PVMBG observations, satellite images, and wind data, the Darwin VAAC reported that during 12-15 and 17 April ash plumes from Sinabung rose to altitudes of 3-4.6 km (10,000-15,000 ft) a.s.l. and drifted W, SW, and E.
Geological summary: Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.
Turrialba, Costa Rica
10.025°N, 83.767°W, Elevation 3340 m
OVSICORI-UNA reported a passive ash emission from Turrialba on 16 April. An event at 0751 on 17 April generated a plume with minor ash content that rose 500 m above the crater and drifted SW. A diffuse plume consisting of gas and sometimes ash rose 1 km above the crater and drifted W on 18 April.
Geological summary: 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 3340-m-high Turrialba is exceeded in height only by Irazú, covers an area of 500 sq km, and is one of Costa Rica's most voluminous volcanoes. 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.