New activity/unrest was observed at 6 volcanoes from September 30 – October 6, 2015. During the same period, ongoing activity was reported for 17 volcanoes.
New activity/unrest: Alaid, Kuril Islands (Russia) | Copahue, Central Chile-Argentina border | Grimsvotn, Iceland | Michael, South Sandwich Islands (UK) | Nevado del Ruiz, Colombia | Veniaminof, United States
Ongoing activity: Aira, Kyushu (Japan) | Cleveland, Chuginadak Island (USA) | Colima, Mexico | Cotopaxi, Ecuador | Dukono, Halmahera (Indonesia) | Fuego, Guatemala | Karymsky, Eastern Kamchatka (Russia) | Kilauea, Hawaiian Islands (USA) | Pacaya, Guatemala | Piton de la Fournaise, Reunion Island (France) | Popocatepetl, Mexico | Santa Maria, Guatemala | Semeru, Eastern Java (Indonesia) | Sheveluch, Central Kamchatka (Russia) | Shishaldin, Fox Islands (USA) | Sinabung, Indonesia | Tungurahua, Ecuador
Alaid, Kuril Islands (Russia)
50.861°N, 155.565°E, Summit elev. 2285 m
KVERT reported that an intense thermal anomaly was detected in satellite images over Alaid starting at 0305 on 2 October, possibly due to the onset of Strombolian activity. The Aviation Color Code was raised to Yellow (the second lowest level on a four-color scale).
Geologic summary: The highest and northernmost volcano of the Kuril Islands, 2285-m-high Alaid is a symmetrical stratovolcano when viewed from the north, but has a 1.5-km-wide summit crater that is breached widely to the south. Alaid is the northernmost of a chain of volcanoes constructed west of the main Kuril archipelago and rises 3000 m from the floor of the Sea of Okhotsk. Numerous pyroclastic cones dot the lower flanks of basaltic to basaltic-andesite Alaid volcano, particularly on the NW and SE sides, including an offshore cone formed during the 1933-34 eruption. Strong explosive eruptions have occurred from the summit crater beginning in the 18th century. Reports of eruptions in 1770, 1789, 1821, 1829, 1843, 1848, and 1858 were considered incorrect by Gorshkov (1970). Explosive eruptions in 1790 and 1981 were among the largest in the Kuril Islands during historical time.
Copahue, Central Chile-Argentina border
37.856°S, 71.183°W, Summit elev. 2953 m
On 6 October SERNAGEOMIN reported that beginning at 0202 observers noted sporadic crater glow at Copahue, indicative of small explosions in Agrio Crater. A grayish plume rose 200 m above the crater and drifted SE. SERNAGEOMIN lowered the Alert Level to Yellow and recommended no entry into a restricted area within 2.5 km of the crater. ONEMI maintained Level Yellow for the community of Alto Biobío (40 km W) in the Biobío region (since 3 June 2013).
Geologic summary: Volcán Copahue is an elongated composite cone constructed along the Chile-Argentina border within the 6.5 x 8.5 km wide Trapa-Trapa caldera that formed between 0.6 and 0.4 million years ago near the NW margin of the 20 x 15 km Pliocene Caviahue (Del Agrio) caldera. The eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains a briny, acidic 300-m-wide crater lake (also referred to as El Agrio or Del Agrio) and displays intense fumarolic activity. Acidic hot springs occur below the eastern outlet of the crater lake, contributing to the acidity of the Río Agrio, and another geothermal zone is located within Caviahue caldera about 7 km NE of the summit. Infrequent mild-to-moderate explosive eruptions have been recorded at Copahue since the 18th century. Twentieth-century eruptions from the crater lake have ejected pyroclastic rocks and chilled liquid sulfur fragments.
64.42°N, 17.33°W, Summit elev. 1725 m
According to the Icelandic Meteorological Office, the water level of the Skaftá river at Sveinstindur (the closest gauging station at 28 km downstream from the ice margin) and electrical conductivity both rose on 29 September, indicating the beginning of a glacial outburst flood (jökulhlaup), originating from Grímsvötn's Eastern Skaftá ice cauldron. GPS measurements indicated that the ice surface above the lake began to subside late on 27 September; the rate progressively increased reflecting increased discharge from the lake.
At 0330 on 1 October the discharge rate detected at Sveinstindur was higher than 1,300 m³/s, the highest rate recorded since the station was established in 1971. At around 1000, floodwater was also detected in Skaftárdalur at a discharge rate of ~400 m³/s and was rising quickly. GPS data from the eastern ice cauldron showed over 66 m of subsidence since 1800 on 27 September. IMO warned that hydrogen sulfide released from the floodwater as it drains is particularly potent at the river outlet from the ice margin, where concentrations may reach poisonous levels. The cauldrons drain every two years on average, producing floods of up to 1,500 cubic meters per second. During fieldwork later that day volcanologists observed where the jökulhlaup had burst through the glacier at several locations 1-2 km from the terminus. Ice fragments a few tens of centimeters in diameter were scattered near the terminus; ice blocks 3-5 m high and 10 m long were deposited close to the outflow points.
On 2 October IMO noted that the jökulhlaup was possibly the largest to have occurred from the Skaftá cauldrons. The discharge rate peaked at 0200, just short of 2,100 m³/s, however true discharge rate was thought to have been considerably greater (3,000 m³/s) since water flooded outside of the gauged area. The discharge rate peaked at 1300 at Eldvatn near Ásar at an approximate rate of 2,200 m³/s. According to a news article, the high waters in the Skaftá River damaged the bridge over Eldvatn prompting authorities to close the bridge during 4-5 October.
Geologic summary: Grímsvötn, Iceland's most frequently active volcano in historical time, lies largely beneath the vast Vatnajökull icecap. The caldera lake is covered by a 200-m-thick ice shelf, and only the southern rim of the 6 x 8 km caldera is exposed. The geothermal area in the caldera causes frequent jökulhlaups (glacier outburst floods) when melting raises the water level high enough to lift its ice dam. Long NE-SW-trending fissure systems extend from the central volcano. The most prominent of these is the noted Laki (Skaftar) fissure, which extends to the SW and produced the world's largest known historical lava flow during an eruption in 1783. The 15-cu-km basaltic Laki lavas were erupted over a 7-month period from a 27-km-long fissure system. Extensive crop damage and livestock losses caused a severe famine that resulted in the loss of one-fifth of the population of Iceland.
Michael, South Sandwich Islands (UK)
57.787°S, 26.46°W, Summit elev. 990 m
The MODVOLC thermal alert system detected thermal anomalies over Michael’s summit crater during 30 September-7 October (GMT time, local -2).
Geologic summary: The young constructional Mount Michael stratovolcano dominates glacier-covered Saunders Island. The symmetrical 990-m-high edifice has a 700-m-wide summit crater and a remnant of a somma rim to the SE. Tephra layers visible in ice cliffs surrounding the island are evidence of recent eruptions. Ash clouds were reported from the summit crater in 1819, and an effusive eruption was inferred to have occurred from a north-flank fissure around the end of the 19th century and beginning of the 20th century. A low ice-free lava platform, Blackstone Plain, is located on the north coast, surrounding a group of former sea stacks. A cluster of parasitic cones on the SE flank, the Ashen Hills, appear to have been modified since 1820 (LeMasurier and Thomson 1990). Vapor emission is frequently reported from the summit crater. Recent AVHRR and MODIS satellite imagery has revealed evidence for lava lake activity in the summit crater.
Nevado del Ruiz, Colombia
4.892°N, 75.324°W, Summit elev. 5279 m
Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that during 28 September-5 October seismicity at Nevado del Ruiz was characterized by long-period earthquakes and short-duration volcanic tremor associated with gas-and-ash emissions. Earthquakes occurred at depths between 0.6 and 7 km. The largest event was recorded at 0138 on 4 October; the event was a local M 1.4, occurring at a depth of 4 km. Minor thermal anomalies over the crater were detected in satellite images on 28 and 30 September. Significant amounts of water-vapor and gas were emitted from the crater during the week. On 29 September a gas-and-ash plume rose 2 km above the crater and drifted mainly NW. The Alert Level remained at III (Yellow; "changes in the behavior of volcanic activity").
Geologic 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.
Veniaminof, United States
56.17°N, 159.38°W, Summit elev. 2507 m
Volcanic tremor at Veniaminof increased during 30 September-1 October, prompting AVO to raise the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory. Slightly elevated levels of seismicity continued through at least 6 October.
Geologic summary: 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 reaches an elevation of 2156 m and 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 during 28 September-2 October emissions rose from both Showa Crater and Minami-Dake Crater at Aira Caldera’s Sakurajima volcano. The Alert Level remained at 3 (on a 5-level scale).
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.
Cleveland, Chuginadak Island (USA)
52.825°N, 169.944°W, Summit elev. 1730 m
AVO reported that during 30 September-6 October low-level unrest at Cleveland likely continued. Weakly elevated surface temperatures were detected in satellite images during 29-30 September. Minor steaming was recorded by the webcam on 1 October. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.
Geologic summary: Beautifully symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited, dumbbell-shaped Chuginadak Island. It lies SE across Carlisle Pass strait from Carlisle volcano and NE across Chuginadak Pass strait from Herbert volcano. Cleveland is joined to the rest of Chuginadak Island by a low isthmus. The 1730-m-high Mount Cleveland is the highest of the Islands of the Four Mountains group and is one of the most active of the Aleutian Islands. The native name for Mount Cleveland, Chuginadak, refers to the Aleut goddess of fire, who was thought to reside on the volcano. Numerous large lava flows descend the steep-sided flanks. It is possible that some 18th-to-19th century eruptions attributed to Carlisle should be ascribed to Cleveland (Miller et al., 1998). In 1944 Cleveland produced the only known fatality from an Aleutian eruption. Recent eruptions have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks.
19.514°N, 103.62°W, Summit elev. 3850 m
Based on satellite images, wind data, webcam views, and notices from the Mexico City MWO, the Washington VAAC reported that during 3-5 October ash plumes from Colima rose to altitudes of 5.5-8.2 km (18,000-27,000 ft) a.s.l. and drifted N, NNE, and NE.
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.
0.677°S, 78.436°W, Summit elev. 5911 m
During an overflight of Cotopaxi on 29 September, IG scientists observed low-energy pulsating emissions with low or no ash content that rose 1 km above the crater and drifted W. Fracturing continued on both the upper and lower parts of the glacier, at the toes. Rapid melting had occurred from the glacier on the upper E flank which resulted in material falling onto the lower part of the glacier. New thermal anomalies on the upper parts of the outer crater were identified, likely from newly deposited material. During 30 September-6 October gas-and-water vapor plumes sometimes with low ash content rose as high as 2 km and drifted in multiple directions. Ashfall was reported in Tanicuchí (25 km SW) on 1 October.
Geologic summary: Symmetrical, glacier-clad Cotopaxi stratovolcano is Ecuador's most well-known volcano and one of its most active. The steep-sided cone is capped by nested summit craters, the largest of which is about 550 x 800 m in diameter. Deep valleys scoured by lahars radiate from the summit of the andesitic volcano, and large andesitic lava flows extend as far as the base of Cotopaxi. The modern conical volcano has been constructed since a major edifice collapse sometime prior to about 5000 years ago. Pyroclastic flows (often confused in historical accounts with lava flows) have accompanied many explosive eruptions of Cotopaxi, and lahars have frequently devastated adjacent valleys. The most violent historical eruptions took place in 1744, 1768, and 1877. Pyroclastic flows descended all sides of the volcano in 1877, and lahars traveled more than 100 km into the Pacific Ocean and western Amazon basin. The last significant eruption of Cotopaxi took place in 1904.
Dukono, Halmahera (Indonesia)
1.68°N, 127.88°E, Summit elev. 1335 m
Based on analyses of satellite imagery and wind data, the Darwin VAAC reported that during 30 September-2 October and during 4-6 October ash plumes from Dukono rose to an altitude of 2.1 km (7,000 ft) a.s.l. and drifted 55-260 km NW, N, and NE.
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.
14.473°N, 90.88°W, Summit elev. 3763 m
INSIVUMEH reported that during 30 September-1 October explosions at Fuego occurred at a rate of 4-6 per hour, generating ash plumes that rose 950 m above the crater and drifted 10 km W. Some explosions produced shock waves. Ash fell in Sangre de Cristo and possibly in San Pedro Yepocapa. During 3-6 October ash plumes from explosions rose 450 m and drifted 10 km W and SW. Shock waves vibrated local structures. Incandescent material was ejected 150 m high, and avalanches descended the Trinidad (S) and Santa Teresa (W) drainages. Advancing lava flows in those same two drainages were 400-600 m long. Ashfall was reported in Panimache I and II, Santa Sofía, and Morelia. In a special report from 7 October, INSIVUMEH noted that activity at Fuego had been at a high level during recent weeks. The lava flows continued to advance; the flows were 1 km long and 700 m long in the Trinidad and Santa Teresa drainages, respectfully. Gas-and-ash plumes rose over 1 km and drifted 12 km W and SW.
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.
Karymsky, Eastern Kamchatka (Russia)
54.049°N, 159.443°E, Summit elev. 1513 m
KVERT reported that moderate explosive activity at Karymsky continued during 25 September-2 October. Cloud cover prevented satellite views. 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
HVO reported that seismicity beneath Kilauea's summit, upper East Rift Zone, and Southwest Rift Zone was at background levels during 30 September-6 October. The lava lake continued to circulate and spatter in the Overlook vent. The June 27th NE-trending lava flow continued to be active within 3-7 km NE of Pu'u 'O'o Crater. A small lava pond, not visible with the webcams, remained active in a pit on the W side of the crater floor.
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.
14.381°N, 90.601°W, Summit elev. 2552 m
INSIVUMEH reported that during 30 September-1 October and 3-6 October fumarolic plumes rose from Pacaya's Mackenney cone and drifted S. Low-frequency tremor was detected and incandescence from the crater was visible at night. Weak explosions were detected during 5-6 October.
Geologic summary: Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.
Piton de la Fournaise, Reunion Island (France)
21.244°S, 55.708°E, Summit elev. 2632 m
OVPDLF reported that seismicity at Piton de la Fournaise slowly increased during 24 September-2 October, and deformation data showed a trend of deflation since 27 September. Inclement weather inhibited gas flow measurements; the few measurements taken showed a slight increase in sulfur dioxide emissions. During fieldwork on 27 September volcanologists noted continuous lava fountains. Small lava flows were active, though the fronts of the two larger ones were not progressing.
Geologic summary: The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.
19.023°N, 98.622°W, Summit elev. 5426 m
CENAPRED reported that during 30 September-6 October the seismic network at Popocatépetl recorded 23-142 daily emissions consisting of water vapor, gas, and sometimes ash; cloud cover often prevented visual observations. Variable nighttime or morning crater incandescence was observed most days, and 1-7 daily explosions were registered. On 3 October a gas, steam, and ash plume rose 2 km and drifted NW. During a series of explosions on 6 October, material was ejected onto the N flank, not far from the crater. Gas, steam, and ash plumes drifted NE. 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.
Santa Maria, Guatemala
14.756°N, 91.552°W, Summit elev. 3772 m
INSIVUMEH reported that during 5-6 October explosions from Santa María's Santiaguito lava-dome complex generated ash plume that rose 700 m and drifted SW. Ashfall was reported in Monte Claro (S).
Geologic summary: Symmetrical, forest-covered Santa María volcano is one of the most prominent of a chain of large stratovolcanoes that rises dramatically above the Pacific coastal plain of Guatemala. The 3772-m-high stratovolcano has a sharp-topped, conical profile that is cut on the SW flank by a large, 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank and was formed during a catastrophic eruption in 1902. The renowned plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four westward-younging vents, the most recent of which is Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.
Semeru, Eastern Java (Indonesia)
8.108°S, 112.92°E, Summit elev. 3676 m
PVMBG reported that during August-29 September both white plumes and gray-to-brownish plumes from Semeru were observed rising as high as 600 m above the crater and drifting in multiple directions; inclement weather sometimes prevented observations. Rockslides from the crater traveled 500 m down the S flank in August. Seismicity was dominated by explosions and emission signals. The Alert Level remained at 2 (on a scale from 1-4); visitors and residents were warned to avoid the SE flank within 4 km of the crater.
Geologic summary: Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises abruptly to 3676 m above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano. Semeru has been in almost continuous eruption since 1967.
Sheveluch, Central Kamchatka (Russia)
56.653°N, 161.36°E, Summit elev. 3283 m
KVERT reported that during 25 September-2 October lava-dome extrusion onto Sheveluch’s N flank was accompanied by fumarolic activity, dome incandescence, and hot avalanches. Satellite images detected a daily thermal anomaly over the dome. On 26 September a 30 x 15 km ash cloud generated by an avalanche rose to an altitude of 4 km (13,000 ft) a.s.l. and drifted 130 km SE. A strong explosion at 0959 on 4 October generated an ash plume that rose to an altitude of 6.5 km (21,300 ft) a.s.l. and drifted SE. 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 30 September-4 October, indicating that low-level eruptive activity confined to the summit crater continued. Cloud cover often prevented satellite and webcam observations. 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.
3.17°N, 98.392°E, Summit elev. 2460 m
PVMBG reported that during 21-28 September foggy weather sometimes prevented visual observations of Sinabung and the growing lava dome in the summit crater. Lava flows on the flanks were incandescent as far as 3 km E to SE. As many as five pyroclastic flows per day were detected, traveling as far as 4 km ESE. Ash plumes rose as high as 4.5 km. Seismicity consisted of avalanche signals, low-frequency and hybrid events, tremor, tectonic events, and volcanic earthquakes. Seismicity fluctuated at high levels, although it had declined compared to the previous week. The Alert Level remained at 4 (on a scale of 1-4), indicating that people within 7 km of the volcano on the SSE sector, and within 6 km in the ESE sector, should evacuate.
Geologic 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, 2460-m-high andesitic-to-dacitic volcano 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.
1.467°S, 78.442°W, Summit elev. 5023 m
IG reported moderate-to-high seismic activity at Tungurahua during 30 September-6 October, characterized by long-period events, volcano-tectonic events, and signals indicating emissions. Cloud cover often prevented visual observations; steam-and-vapor plumes were observed on a few days. On 4 October ashfall was reported in Manzanó (8 km SW). The next day residents in Manzanó heard an explosion; ashfall was reported there as well as in Cahuají (8 km SW).
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.
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