New activity/unrest was observed at 8 volcanoes from April 29 – May 5, 2015. During the same period, ongoing activity was observed at 15 volcanoes.
New activity/unrest: Axial Seamount, Juan de Fuca Ridge | Bulusan, Luzon (Philippines) | Calbuco, Chile | Dempo, Indonesia | Karangetang [Api Siau], Siau Island (Indonesia) | Kilauea, Hawaiian Islands (USA) | Tungurahua, Ecuador | Ubinas, Peru.
Ongoing activity: Aira, Kyushu (Japan) | Asosan, Kyushu (Japan) | Chirinkotan, Kuril Islands (Russia) | Chirpoi, Kuril Islands (Russia) | Colima, Mexico | Dukono, Halmahera (Indonesia) | Karymsky, Eastern Kamchatka (Russia) | Manam, Papua New Guinea | Popocatepetl, Mexico | Ruapehu, North Island (New Zealand) | Sheveluch, Central Kamchatka (Russia) | Shishaldin, Fox Islands (USA) | Turrialba, Costa Rica | Villarrica, Chile | Zhupanovsky, Eastern Kamchatka (Russia).
Axial Seamount, Juan de Fuca Ridge
45.95°N, 130°W, Elevation -1410 m
Geologists reported that starting at 2230 on 23 April thousands of small earthquakes were detected at the Axial Seamount, and then the seafloor dropped by 2.4 m over a three-day period. It was unclear if the earthquakes and deflation meant an eruption or a large intrusion of magma that did not reach the surface.
Geologic summary: Axial Seamount rises 700 m above the mean level of the central Juan de Fuca Ridge crest about 480 km west of Cannon Beach, Oregon to within about 1400 m of the sea surface. The volcano is the most magmatically robust and seismically active site on the Juan de Fuca Ridge between the Blanco Fracture Zone and the Cobb offset. The summit is marked by an unusual rectangular-shaped caldera (3 x 8 km) that lies between two rift zones and is estimated to have formed about 31,000 years ago. The caldera is breached to the SE and is defined on three sides by boundary faults of up to 150 m relief. Hydrothermal vents colonized with biological communities are located near the caldera fault or along the rift zones. Following the discovery of hydrothermal venting north of the caldera in 1983. Detailed mapping and sampling efforts have identified more than 50 lava flows since about 410 AD (Clague et al., 2013). Eruptions producing fissure-fed lava flows that buried previously installed seafloor instrumentation were detected seismically and geodetically in 1998 and 2011 and confirmed shortly after each eruption during submersible dives.
Bulusan, Luzon (Philippines)
12.77°N, 124.05°E, Elevation 1565 m
PHIVOLCS reported that at 0809 on 1 May a steam-and-ash explosion from Bulusan was detected for five minutes by the seismic network. Dense rain clouds at the summit prevented visual observations at the time, but during a clear period around 1030 gray-white steam plumes were observed rising 200 m above the NW vent and drifting WNW. Minor ashfall affected areas to the W and NW, including Bolos, Cogon, Gulang-Gulang, Sangkayon, Tinampo, and Umagom in Irosin, Sorsogon, and Puting Sapa in Juban, Sorsogon.
Only five volcanic earthquakes had been recorded during the past week prior to the event; after the event the network detected 62 volcanic earthquakes within an eight-hour period. Alert Level 0 and the 4-km restricted zone, the Permanent Danger Zone (PDZ), were maintained due to the possibility of sudden and hazardous steam-driven or phreatic eruptions.
Geologic summary: Luzon's southernmost volcano, Bulusan, was constructed along the rim of the 11-km-diameter dacitic-to-rhyolitic Irosin caldera, which was formed about 36,000 years ago. Bulusan lies at the SE end of the Bicol volcanic arc occupying the peninsula of the same name that forms the elongated SE tip of Luzon. A broad, flat moat is located below the topographically prominent SW rim of Irosin caldera; the NE rim is buried by the andesitic Bulusan complex. Bulusan is flanked by several other large intracaldera lava domes and cones, including the prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the NE. The summit of 1565-m-high Bulusan volcano is unvegetated and contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Many moderate explosive eruptions have been recorded at Bulusan since the mid-19th century.
41.326°S, 72.614°W, Elevation 2003 m
OVDAS-SERNAGEOMIN reported that on 29 April a weak ash plume rose as high as 1.5 km above Calbuco and seismicity remained stable. An event that began at 1308 on 30 April produced an ash plume that rose 3-5 km and drifted SE. A small lahar in the Blanco River may have been caused by a pyroclastic flow. Tremor amplitude increased and became sustained after the event. On 2 May the number of earthquakes increased. Seismicity significantly increased on 3 May, characterized by a swarm of volcano-tectonic events, and then decreased afterwards. Seismicity was low and stable on 5 May. A plume rose less than 1 km during 1-3 May; cloud cover prevented visual observations of the volcano during 4-5 May. According to ONEMI, the number of evacuees totaled 6,685 on 5 May. The Alert Level remained at Red (the highest level on a four-color scale).
Geologic summary: Along with its neighbor Osorno, Calbuco is one of the most active volcanoes of the southern Chilean Andes. The isolated late-Pleistocene to Holocene andesitic volcano rises to 2003 m south of Lake Llanquihué in the Chilean lake district. Guanahuca, Guenauca, Huanauca, and Huanaque, all listed as synonyms of Calbuco (Catalog of Active Volcanoes of the World), are actually synonyms of nearby Osorno volcano (Moreno 1985, pers. comm.). The 2003-m-high Calbuco is elongated in a SW-NE direction and is capped by a 400-500 m wide summit crater. The complex evolution of Calbuco included edifice collapse of an intermediate edifice during the late Pleistocene that produced a 3 cu km debris avalanche that reached the lake. Calbuco has erupted frequently during the Holocene, and one of the largest historical eruptions in southern Chile took place from Calbuco in 1893-1894 and concluded with lava dome emplacement. Subsequent eruptions have enlarged the lava-dome complex in the summit crater.
4.03°S, 103.13°E, Elevation 3173 m
Observers at the PVMBG Dempo observation post reported that during 0730-0900 on 27 April diffuse gray-white plumes rose 50 m above Dempo crater. Seismicity had increased during April as compared to the previous month. On 29 April the Alert Level was raised to 2 (on a scale from 1-4). Visitors and residents were advised not to go within a 1-km radius of the summit.
Geologic summary: Dempo is a prominent 3173-m-high stratovolcano that rises above the Pasumah Plain of SE Sumatra. The andesitic Dempo volcanic complex has two main peaks, Gunung Dempo and Gunung Marapi, constructed near the SE rim of a 3 x 5 km caldera breached to the north. The one called Dempo is slightly lower, with an elevation of 3049 m and lies at the SE end of the summit complex. The taller Marapi cone, with a summit elevation 3173 m, was constructed within a crater cutting the older Gunung Dempo edifice. Remnants of 7 craters are found at or near the summit of the complex, with volcanism migrating to the WNW with time. The large, 800 x 1100 m wide historically active summit crater cuts the NW side of Gunung Marapi (not to be confused with Marapi volcano 500 km to the NW in Sumatra) and contains a 400-m-wide lake located at the far NW end of the crater complex. Historical eruptions have been restricted to small-to-moderate explosive activity that produced ashfall near the volcano.
Karangetang [Api Siau], Siau Island (Indonesia)
2.78°N, 125.4°E, Elevation 1784 m
Based on observations conducted at the Karangetang Volcano Observation Post in the village of Salili, PVMBG reported that white plumes rose as high as 350 m above Karangetang's main crater and 25 m above Crater II during 22-29 April. Incandescence from the lava dome was observed at night. Lava flows began to appear on 22 April; incandescent avalanches from the fronts of 150-m-long lava flows traveled as far as 2 km towards Batuawang and Kahetang drainages (E) during 22-29 April. On 26 April pyroclastic flows traveled 2.2 km towards Kahetang drainage. On 28 April explosions produced plumes and ejected incandescent material 50 m high. The Alert Level remained at 3 (on a scale of 1-4); visitors and residents were warned not to climb Karangetang any higher than 500 a.s.l.
Geologic summary: Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, north of Sulawesi. The 1784-m-high stratovolcano contains five summit craters along a N-S line. Karangetang 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 has also produced pyroclastic flows.
Kilauea, Hawaiian Islands (USA)
19.421°N, 155.287°W, Elevation 1222 m
In a special statement on 29 April, HVO reported that beginning at 2140 the night before the lava lake in Kilauea’s Halema'uma'u Crater overflowed it's rim multiple times, sending lobate sheets of pahoehoe as far as 130 m across the crater floor. The report also noted that a few explosions in the lake triggered by falling wall rock had occurred; one at 1020 on 28 April ejected boulders of molten spatter (2 m in diameter) onto the rim of Halema'uma'u Crater, in the vicinity of the closed visitor overlook fence. Spatter also blanketed an area 100 m along the rim and 50 m back. This area had been closed to the public since 2007.
The accumulating lava had built up a rim around the lake that was a few meters above the crater floor. On 30 April the lava-lake surface was about 4 m below the new rim. During 1-2 May the lake level was near or at the rim, and overflowed onto the floor several times. During 2-3 May the lake surface was 3-5 m above the original, pre-flow crater floor. A collapse of a portion of the crater wall at 1320 on 3 May impacted the lake and triggered a small explosion, ejecting fist-sized clasts onto the crater rim. Lava overflowed the rim several times during 4-5 May.
During 29 April-5 May Kilauea’s 27 June NE-trending lava flow continued to be active with three areas of breakouts within and along the flow-field margins, within 8 km of Pu'u 'O'o. 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, and a relatively small forked breakout 5-6 km farther NE of Pu'u 'O'o. Forest burned about 8 km NE of the crater.
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.
1.467°S, 78.442°W, Elevation 5023 m
IG reported moderate activity at Tungurahua on 29 April, and low levels during 30 April-5 May. Minor steam plumes were visible most days even though inclement weather often obscured views of the crater area.
Geologic summary: Tungurahua, a steep-sided andesitic-dacitic stratovolcano that towers more than 3 km above its northern base, is one of Ecuador's most active volcanoes. Three major edifices have been sequentially constructed since the mid-Pleistocene over a basement of metamorphic rocks. Tungurahua II was built within the past 14,000 years following the collapse of the initial edifice. Tungurahua II itself collapsed about 3000 years ago and produced a large debris-avalanche deposit and a horseshoe-shaped caldera open to the west, inside which the modern glacier-capped stratovolcano (Tungurahua III) was constructed. Historical eruptions have all originated from the summit crater, accompanied by strong explosions and sometimes by pyroclastic flows and lava flows that reached populated areas at the volcano's base. Prior to a long-term eruption beginning in 1999 that caused the temporary evacuation of the city of Baños at the foot of the volcano, the last major eruption had occurred from 1916 to 1918, although minor activity continued until 1925.
16.355°S, 70.903°W, Elevation 5672 m
Instituto Geofísico del Perú (IGP) Observatorio Volcanológico del Sur (OVS) reported that during 29 April-5 May long-period and tornillo-type earthquakes continued to decrease while volcano-tectonic events increased. Hybrid events were at a low level, however, an increase in the number of events were detected on 29 April. Overall the dominant signal was spasmodic tremor associated with ash-and-steam emissions. Constant steam emissions were visually observed even though cloud cover often prevented observations. Ash emission increased on 1 May, rising as high as 800 m above the crater.
Geologic summary: A small, 1.4-km-wide caldera cuts the top of Ubinas, Peru's most active volcano, giving it a truncated appearance. It is the northernmost of three young volcanoes located along a regional structural lineament about 50 km behind the main volcanic front of Perú. The growth and destruction of Ubinas I was followed by construction of Ubinas II beginning in the mid-Pleistocene. The upper slopes of the andesitic-to-rhyolitic Ubinas II stratovolcano are composed primarily of andesitic and trachyandesitic lava flows and steepen to nearly 45 degrees. The steep-walled, 150-m-deep summit caldera contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits from the collapse of the SE flank about 3700 years ago extend 10 km from the volcano. Widespread plinian pumice-fall deposits include one of Holocene age about 1000 years ago. Holocene lava flows are visible on the flanks, but historical activity, documented since the 16th century, has consisted of intermittent minor-to-moderate explosive eruptions.
Aira, Kyushu (Japan)
31.593°N, 130.657°E, Elevation 1117 m
JMA reported that 12 explosions from Showa Crater at Aira Caldera’s Sakurajima volcano ejected tephra as far as 1,300 m during 27 April-1 May. Incandescence from the crater was visible at night. An explosion at 0720 on 27 April generated a large ash plume that rose 3.5 km above the crater. The next day an explosive eruption was detected by the seismic network for 40 minutes. A very small pyroclastic flow traveled 500 m down the SE flank of Showa Crater. The Alert Level remained at 3 (on a scale of 1-5). Based on JMA notices, the Tokyo VAAC reported that explosions during 29 April-5 May generated plumes which rose to altitudes of 1.8-3.4 km (6,000-11,000 ft) a.s.l. and drifted in multiple directions.
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.
Asosan, Kyushu (Japan)
32.884°N, 131.104°E, Elevation 1592 m
JMA reported that, based on seismic data, the eruption from Asosan’s Nakadake Crater that began on 25 November 2014 continued during 27 April-1 May. Ashfall was reported in areas to the SE and NE on 27 April. Field surveys were conducted on 27 April and 1 May; observers noted an off-white plume rising from the vent. A plume rose as high as 1.2 km above the crater rim on 29 April. The Alert Level remained at 2 (on a scale of 1-5).
Geologic 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 cu km 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 AD. 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.
Chirinkotan, Kuril Islands (Russia)
48.98°N, 153.48°E, Elevation 724 m
SVERT reported that on 30 April a thermal anomaly over Chirinkotan was detected in satellite images. Cloud cover prevented views of the volcano on the other days during 27 April-4 May. The Aviation Color Code remained at Yellow.
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.
Chirpoi, Kuril Islands (Russia)
46.525°N, 150.875°E, Elevation 742 m
SVERT reported that satellite images over Snow, a volcano of Chirpoi, showed a thermal anomaly on 28 and 30 April, and 1 May. Cloud cover obscured views on other days during 27 April-4 May. 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, Elevation 3850 m
Based on satellite images, the Washington VAAC reported that on 30 April an ash plume from Colima drifted 30 km E before dissipating. Another ash plume drifted almost 20 km E. On 2 May an ash puff rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted 150 km ENE to W. Another ash plume rose to an altitude of 6.7 km (22,000 ft) a.s.l. and drifted E. Later that day an ash plume drifted almost 85 km E before dissipating.
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.
Dukono, Halmahera (Indonesia)
1.68°N, 127.88°E, Elevation 1335 m
Based on analyses of satellite imagery and wind data, the Darwin VAAC reported that during 29 April-3 May ash plumes from Dukono rose to an altitude of 2.4-2.7 km (8,000-9,000 ft) a.s.l. and drifted 55-185 km E and SE.
Geologic 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.
Karymsky, Eastern Kamchatka (Russia)
54.049°N, 159.443°E, Elevation 1513 m
KVERT reported moderate activity at Karymsky during 17 April-1 May. Satellite images showed ash plumes drifting about 140 km NE on 27 April. 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.
Manam, Papua New Guinea
4.08°S, 145.037°E, Elevation 1807 m
Based on observations of satellite imagery and wind data analyses, the Darwin VAAC reported that on 30 April an ash plume from Manam drifted 150 km NW at an altitude of 2.4 km (8,000 ft) a.s.l.
Geologic 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.
19.023°N, 98.622°W, Elevation 5426 m
CENAPRED reported that during 8-14 April the seismic network recorded 13-77 gas and steam emissions, with another 204 emissions recorded over 1-2 May. Ash accompanied the emissions during 1-3 May. Gas-and-steam plumes were visible, although cloud cover mostly prevented observations. Nighttime crater incandescence was often noted. A series of explosions during 2218-2301 on 30 April ejected incandescent tephra 200 m onto the NE flank. Sequences of explosions were also detected during 0758-1356 on 1 May and during 0411-0935 on 2 May. Ashfall was reported in San Pedro Benito Juárez (10-12 km SE) in the municipality of Atlixco Puebla on 2 May. Explosions were also detected during 3-5 May. 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.
Ruapehu, North Island (New Zealand)
39.28°S, 175.57°E, Elevation 2797 m
GeoNet reported that water temperatures of Ruapehu's summit Crater Lake had been increasing since early December 2014, rising from 15 degrees Celsius to over 40 degrees in late January-early February. The temperatures declined to 31 degrees in mid-March, and then climbed again to 37-39 degrees. No other changes were detected at the lake. In addition, over the previous 2-3 weeks intermittent moderate-to-strong levels of volcanic tremor were detected, which had been some of the strongest recorded there over the past eight years. The report noted that historically there had not been a direct link between volcanic tremor and discrete volcanic eruptions or sequences of eruptions. The Aviation Colour Code remained at Green and the Volcanic Alert Level remained at 1 (signs of volcano unrest).
Geologic summary: Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The 110 cu km dominantly andesitic volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 cu km ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake, is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.
Sheveluch, Central Kamchatka (Russia)
56.653°N, 161.36°E, Elevation 3283 m
KVERT reported that during 24 April-1 May lava-dome extrusion onto Sheveluch’s N flank was accompanied by incandescence, hot block avalanches, and fumarolic activity. A daily thermal anomaly was also detected 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, Elevation 2857 m
AVO reported that seismicity at Shishaldin continued to be elevated over background levels 29 April-5 May indicating that low-level eruptive activity confined to the summit crater likely continued. Cloud cover frequently prevented satellite and webcam observations. Weakly elevated temperatures in the crater were detected on 4 May. 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.
Turrialba, Costa Rica
10.025°N, 83.767°W, Elevation 3340 m
OVSICORI-UNA reported that a 4-minute-long ash emission from Turrialba occurred at 0836 on 1 May. The ash plume rose about 500 m above the crater and drifted SW. Ash emissions that began at 1524 on 4 May lasted 23 minutes, and produced an ash plume that rose 2.5 km and drifted SW. The eruption ejected ballistics 1 km from the crater. Most of the ashfall occurred around the crater. Reports of minor ashfall and sulfur odors came from San José (Moravia, Coronado, Mata de Plátano, La Uruca, Guadalupe, Tibás, Calle Blancos, San Pedro Montes de Oca, Sabanilla Montes de Oca, Pavas, Zapote, Escazú, S of San José, Paso Ancho, Curridabat, Santa Ana), and a few localities in the eastern region of Heredia. On 5 May intermittent emissions of gas and ash rose 500 m; inclement weather prevented satellite observations.
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, Elevation 2847 m
OVDAS-SERNAGEOMIN reported moderate seismic activity during 29 April-5 May. Nighttime crater incandescence and a thermal anomaly detected daily in satellite images suggested an active lava lake, with mild and periodic Strombolian activity. Gas emissions were visible in the daytime. The Alert Level remained at 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.
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.
Zhupanovsky, Eastern Kamchatka (Russia)
53.589°N, 159.15°E, Elevation 2899 m
KVERT reported that moderate activity continued at Zhupanovsky during 24 April-1 May. Satellite images detected a thermal anomaly over the volcano on 25 and 28 April. 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.
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