New activity/unrest was observed at 9 volcanoes from March 18 - 24, 2015. During the same period, ongoing activity was observed at 10 volcanoes.
New activity/unrest: Chirinkotan, Kuril Islands (Russia) | Fuego, Guatemala | Lewotobi, Flores Island (Indonesia) | Moyorodake [Medvezhia], Iturup (Etorofu) Island (Japan/Russia) | Popocatepetl, Mexico | Sinarka, Shiashkotan Island (Russia) | Tongariro, North Island (New Zealand) | Turrialba, Costa Rica | Villarrica, Chile
Ongoing activity: Aira, Kyushu (Japan) | Chirpoi, Kuril Islands (Russia) | Colima, Mexico | Karymsky, Eastern Kamchatka (Russia) | Kilauea, Hawaiian Islands (USA) | Klyuchevskoy, Central Kamchatka (Russia) | Sheveluch, Central Kamchatka (Russia) | Shishaldin, Fox Islands (USA) | Talang, Indonesia | Zhupanovsky, Eastern Kamchatka (Russia)
Chirinkotan, Kuril Islands (Russia)
48.98°N, 153.48°E, Summit elev. 724 m
SVERT reported that during 19-21 March a thermal anomaly over Chirinkotan was detected in satellite images. The Aviation Color Code was raised to Yellow on 20 March.
Geologic summary: The small, mostly unvegetated 3-km-wide island of Chirinkotan occupies the far end of an E-W-trending volcanic chain that extends nearly 50 km west of the central part of the main Kuril Islands arc. Chirinkotan is the emergent summit of a volcano that rises 3000 m from the floor of the Kuril Basin. A small 1-km-wide caldera about 300-400 m deep is open to the SE. Lava flows from a cone within the breached crater reached the north shore of the island. Historical eruptions have been recorded at Chirinkotan since the 18th century. Fresh lava flows also descended the SE flank of Chirinkotan during an eruption in the 1880s that was observed by the English fur trader Captain Snow.
14.473°N, 90.88°W, Summit elev. 3763 m
INSIVUMEH reported that during 21-23 March explosions at Fuego generated ash plumes that rose 750-950 m above the crater and drifted 10-12 km W and SW. Ash fell in nearby areas including Panimache I and II (8 km SW), Morelia (9 km SW), and Santa Sofía (12 km SW). Incandescent tephra was ejected 100 m high during 22-23 March.
Geologic summary: Volcán Fuego, one of Central America's most active volcanoes, is one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between 3763-m-high Fuego and its twin volcano to the north, Acatenango. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at Acatenango. In contrast to the mostly andesitic Acatenango, eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.
Lewotobi, Flores Island (Indonesia)
8.542°S, 122.775°E, Summit elev. 1703 m
PVMBG reported that white plumes were observed rising 15-20 m above Lewotobi during periods of clear weather from 1 February to17 March. Seismicity increased significantly on 13 March, especially volcanic earthquakes and shallow volcanic earthquakes; harmonic tremor, Tornillo events, and tectonic events were also detected. On 17 March the Alert Level was raised to 2 (on a scale of 1-4). Residents and tourists were warned not to approach the craters within a 1-km radius.
Geologic summary: The Lewotobi "husband and wife" twin volcano (also known as Lewetobi) in eastern Flores Island is composed of the Lewotobi Lakilaki and Lewotobi Perempuan stratovolcanoes. Their summits are less than 2 km apart along a NW-SE line. The conical 1584-m-high Lewotobi Lakilaki has been frequently active during the 19th and 20th centuries, while the taller and broader 1703-m-high Lewotobi Perempuan has erupted only twice in historical time. Small lava domes have grown during the 20th century in the crescentic summit craters of both volcanoes, which are open to the north. A prominent flank cone, Iliwokar, occurs on the E flank of Lewotobi Perampuan.
Moyorodake [Medvezhia], Iturup (Etorofu) Island (Japan/Russia)
45.389°N, 148.838°E, Summit elev. 1124 m
SVERT reported that satellite images showed a weak thermal anomaly over Kudryavy, a stratovolcano of the Medvezhia volcanic complex, on 18 March.
Geologic summary: The Moyorodake volcanic complex (also known as Medvezhia) occupies the NE end of Iturup (Etorofu) Island. Two overlapping calderas, 14 x 18 and 10 x 12 km in diameter, were formed during the Pleistocene. The caldera floor contains several lava domes, cinder cones and associated lava fields, and a small lake. Four small closely spaced stratovolcanoes were constructed along an E-W line on the eastern side of the complex. The easternmost and highest, Medvezhii, lies outside the western caldera, along the Pacific coast. Srednii, Tukap, and Kudriavy (Moyorodake) volcanoes lie immediately to the west. Historically active Moyorodake is younger than 2000 years; it and Tukap remain fumarolically active. The westernmost of the post-caldera cones, Menshoi Brat, is a large lava dome with flank scoria cones, one of which has produced a series of young lava flows up to 4.5 km long that reached Slavnoe Lake. Eruptions of Moyorodake have been documented since the 18th century, although lava flows from cinder cones on the flanks of Menshoi Brat were also probably erupted within the past few centuries.
19.023°N, 98.622°W, Summit elev. 5426 m
CENAPRED reported that during 18-24 March the seismic network at Popocatépetl recorded 90-222 daily emissions and 1-13 explosions. Cloud cover often prevented observations of the crater, although ash plumes and nighttime crater incandescence were noted. At 0344 on 22 March an explosion ejected incandescent tephra onto the flanks and produced an ash plume that rose 1 km above the crater rim and drifted NE. An ash plume rose 1 km and drifted SE on 23 March. An ash plume rose 1 km on 24 March. The Alert Level remained at Yellow, Phase Two.
Geologic summary: Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, towers to 5426 m 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 from Popocatépetl 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 precolumbian time.
Sinarka, Shiashkotan Island (Russia)
48.875°N, 154.175°E, Summit elev. 934 m
SVERT reported that satellite images showed steam-and-gas emissions from Sinarka on 16 March and a weak thermal anomaly on 21 March.
Geologic summary: Sinarka volcano, occupying the northern end of Shiashkotan Island in the central Kuriles, has a complex structure. A small, 2-km-wide depression open to the NW has been largely filled and overtopped by an andesitic postglacial central cone that itself contains a lava dome that forms the 934 m high point of the island. Another lava dome, Zheltokamennaya Mountain, lies 1.5 km to the SW along the buried SW rim of the caldera, and a smaller dome lies along the northern caldera rim. Historical eruptions have occurred at Sinarka during the 17th and 18th centuries. The last and largest of these, during 1872-78, was once thought to originate from Kuntomintar volcano at the southern end of the island, but is now attributed to Sinarka volcano (Gorshkov, 1970).
Tongariro, North Island (New Zealand)
39.157°S, 175.632°E, Summit elev. 1978 m
On 23 March GeoNet reported that during the previous two to three weeks an increase in the number and magnitude of earthquakes at Tongariro was detected by the seismographs around Ngauruhoe. The earthquakes were shallow, with depths less than 5 km. The report noted that although earthquakes are not unusual near Ngauruhoe, it had been some time since significant numbers or events above M 1 were recorded. The Volcanic Alert Level was raised to 1 (on a scale of 0-5).
Geologic summary: Tongariro is a large andesitic volcanic massif, located immediately NE of Ruapehu volcano, that is composed of more than a dozen composite cones constructed over a period of 275,000 years. Vents along a NE-trending zone extending from Saddle Cone (below Ruapehu volcano) to Te Mari crater (including vents at the present-day location of Ngauruhoe) were active during several hundred years around 10,000 years ago, producing the largest known eruptions at the Tongariro complex during the Holocene. North Crater stratovolcano, one of the largest features of the massif, is truncated by a broad, shallow crater filled by a solidified lava lake that is cut on the NW side by a small explosion crater. The youngest cone of the complex, Ngauruhoe, has grown to become the highest peak of the massif since its birth about 2500 years ago. The symmetrical, steep-sided Ngauruhoe, along with its neighbor Ruapehu to the south, have been New Zealand's most active volcanoes during historical time.
Turrialba, Costa Rica
10.025°N, 83.767°W, Summit elev. 3340 m
OVSICORI-UNA reported that on 18 March gas, vapor, and ash plumes rose from Turrialba's Cráter Oeste and seismicity remained high. Observers in Finca La Central (2 km SW) noted gas-and-steam emissions. On 19 March at 0806 and 1007 gas and water vapor emissions rose from the crater; the emissions at 1007 rose from Cráter Central and contained a small amount of ash. At 1400 the webcam recorded strong emissions of gas, vapor, and tephra from Cráter Oeste. A national park official heard two booming sounds at 1530. At around 1000 on 23 March a gas, vapor, and ash plume rose from Cráter Oeste, causing ashfall in areas E and SE of the crater including Cráter Central and el Mirador. In addition a dense and vigorous gas-and-vapor plume caused Parque Nacional Volcán Turrialba authorities to recommend masks for protection against gas inhalation.
Geologic 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.
39.42°S, 71.93°W, Summit elev. 2847 m
OVDAS-SERNAGEOMIN reported that at night on 17 March explosions at Villarrica ejected tephra onto the flanks and produced nighttime incandescence. Pulsating ash plumes rose 300 m and drifted E. Seismicity increased and was characterized by low-magnitude tremor. The Alert Level was raised to Orange (the second highest level on a four-color scale) and the public was warned to stay outside of a 5-km radius around the crater and away from drainages. During 19-22 March pulsating plumes recorded by the webcam had a greater concentration of ash, and rose 100-500 m and drifted NE. Moderate levels of tremor were detected. Although cloud cover often prevented observations of the crater, incandescence was occasionally seen at night. During 22-24 March continued gas-and-ash emissions rose 400-500 m and drifted SW; the plumes were less dense, shorter, and contained less ash content. Incandescent material continued to be ejected from the crater, but with less frequency, and was deposited near the crater on the NE flank.
Geologic 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 Villarrica's flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano have been 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 sq km of the volcano, and lahars have damaged towns on its flanks.
Aira, Kyushu (Japan)
31.593°N, 130.657°E, Summit elev. 1117 m
Based on JMA notices, the Tokyo VAAC reported explosions from Aira Caldera’s Sakurajima volcano during 18-25 March; plumes rose to altitudes of 1.5-3 km (5,000-10,000 ft) a.s.l. and drifted S, SE, E, and NE during 18-19 and 21-25 March. JMA reported that 19 explosions from Showa Crater ejected tephra as far as 1,300 m during 20-23 March. Incandescence from the crater was periodically visible at night, and inflation continued to be detected. The Alert Level remained at 3 (on a scale of 1-5).
Geologic 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.
Chirpoi, Kuril Islands (Russia)
46.525°N, 150.875°E, Summit elev. 742 m
SVERT reported that satellite images over Snow, a volcano of Chirpoi, showed faint stream-and-gas emissions on 16 March and a thermal anomaly during 17-20 March. Cloud cover obscured views on other days during 21-23 March. The Aviation Color Code remained at Yellow.
Geologic summary: Chirpoi, a small island lying between the larger islands of Simushir and Urup, contains a half dozen volcanic edifices constructed within an 8-9 km wide, partially submerged caldera. The southern rim of the caldera is exposed on nearby Brat Chirpoev Island. The symmetrical Cherny volcano, which forms the 691 m high point of the island, erupted twice during the 18th and 19th centuries. The youngest volcano, Snow, originated between 1770 and 1810. It is composed almost entirely of lava flows, many of which have reached the sea on the southern coast. No historical eruptions are known from 742-m-high Brat Chirpoev, but its youthful morphology suggests recent strombolian activity.
19.514°N, 103.62°W, Summit elev. 3850 m
Based on satellite images, Mexico City MWO, webcam images, and METAR notices, the Washington VAAC reported that during 18-24 March daily ash plumes from Colima rose to altitudes of 4.9-8.2 km (16,000-27,000 ft) a.s.l. and drifted 40-150 km NNE, NE, ENE, and E.
Geologic 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.
Karymsky, Eastern Kamchatka (Russia)
54.049°N, 159.443°E, Summit elev. 1513 m
KVERT reported that during 13-20 March moderate activity at Karymsky probably continued. Cloud-free satellite images showed no activity. The Aviation Color Code remained at Orange.
Geologic 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.
Kilauea, Hawaiian Islands (USA)
19.421°N, 155.287°W, Summit elev. 1222 m
During 18-24 March HVO reported that Kilauea’s 27 June NE-trending lava flow continued to be active with several small and scattered breakouts within the flow-field margins, upslope of the leading front. The three main areas of breakouts were the 21 February breakout on the flank of Pu'u 'O'o, the 9 March breakout near the forested cone of Kahauale'a (burning trees were visible), and a relatively small breakout 5 km farther NE of Pu'u 'O'o. At Pu'u 'O'o Crater, glow emanated from several outgassing openings in the crater floor. A small lava pond was visible in the central Pu'u 'O'o vent; on 23 March a tiny lava flow erupted from the vent. The circulating lava lake occasionally rose and fell in the deep pit within Halema'uma'u Crater. Gas emissions remained elevated.
Geologic 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 of Kilauea 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.
Klyuchevskoy, Central Kamchatka (Russia)
56.056°N, 160.642°E, Summit elev. 4754 m
KVERT reported that during 13-20 March the eruption at Klyuchevskoy continued but the energy of the explosions decreased significantly. Explosions generated ash plumes that rose to altitudes of 5-5.5 km (16,400-18,000 ft) a.s.l. During 16-17 March satellite images showed a weak thermal anomaly over the volcano and ash plumes that drifted 90 km E. Ash plumes were again detected in images during 22-23 March. On 25 March the Aviation Color Code was lowered to Yellow.
Geologic summary: Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.
Sheveluch, Central Kamchatka (Russia)
56.653°N, 161.36°E, Summit elev. 3283 m
KVERT reported that during 13-20 March lava-dome extrusion onto Sheveluch’s N flank was accompanied by incandescence, hot block avalanches, and fumarolic activity. Strong explosions on 16 March generated ash plumes that rose to an altitude of 9 km (29,500 ft) a.s.l. and drifted 200 km E; ashfall was reported in Ust-Kamchatsk Village, 85 km SE. A daily thermal anomaly was visible in satellite images. The Aviation Color Code remained at Orange.
Geologic 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.
Shishaldin, Fox Islands (USA)
54.756°N, 163.97°W, Summit elev. 2857 m
AVO reported that seismicity at Shishaldin continued to be elevated over background levels during 18-24 March, indicating that low-level eruptive activity confined to the summit crater likely continued. Nothing significant was observed in mostly cloudy satellite and web camera images; slight steaming at the summit was visible during 22-23 March. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.
Geologic 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.
0.978°S, 100.679°E, Summit elev. 2597 m
PVMBG reported that during 1 January-18 March diffuse white plumes rose at most 200 m above Talang’s Gabuo, Utama, Selatan, and Kapundan Panjang craters. Seismicity was low, no deformation was detected, and water temperatures had not significantly changed. On 20 March the Alert Level was lowered to 1 (on a scale of 1-4). Visitors and tourists were warned to stay away from the craters.
Geologic summary: Talang, which forms a twin volcano with the extinct Pasar Arbaa volcano, lies ESE of the major city of Padang and rises NW of Dibawah Lake. Talang has two crater lakes on its flanks; the largest of these is 1 x 2 km wide Danau Talang. Most historical eruptions have not occurred from the summit of the volcano, which lacks a crater. Historical eruptions from Gunung Talang volcano have mostly involved small-to-moderate explosive activity first documented in the 19th century that originated from a series of small craters in a valley on the upper NE flank.
Zhupanovsky, Eastern Kamchatka (Russia)
53.589°N, 159.15°E, Summit elev. 2899 m
KVERT reported that a moderate explosive eruption at Zhupanovsky continued during 13-20 March. A webcam recorded incandescence from the crater on 15 March. Satellite images detected ash plumes drifting 350 km NE and S at an altitude of 7 km (23,000 ft) a.s.l. on 12 and 15 March. A thermal anomaly was also detected during 14-17 March. The Aviation Color Code remained at Orange.
Geologic summary: The Zhupanovsky volcanic massif consists of four overlapping stratovolcanoes along a WNW-trending ridge. The elongated volcanic complex was constructed within a Pliocene-early Pleistocene caldera whose rim is exposed only on the eastern side. Three of the stratovolcanoes were built during the Pleistocene, the fourth is Holocene in age and was the source of all of Zhupanovsky's historical eruptions. An early Holocene stage of frequent moderate and weak eruptions from 7000 to 5000 years before present (BP) was succeeded by a period of infrequent larger eruptions that produced pyroclastic flows. The last major eruption took place about 800-900 years BP. Historical eruptions have consisted of relatively minor explosions from the third cone.