Smithsonian / USGS Weekly Volcanic Activity Report 29 July-4 August 2015
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Smithsonian / USGS Weekly Volcanic Activity Report
29 July-4 August 2015
Sally Kuhn Sennert - Weekly Report Editor (kuhns@xxxxxx)
URL: http://www.volcano.si.edu/reports_weekly.cfm
New Activity/Unrest: Cleveland, Chuginadak Island (USA) | Colima, Mexico | Gamalama, Halmahera (Indonesia) | Manam, Papua New Guinea | Nevado del Ruiz, Colombia | Piton de la Fournaise, Reunion Island (France) | Raung, Eastern Java (Indonesia) | Suwanosejima, Ryukyu Islands (Japan)
Ongoing Activity: Dukono, Halmahera (Indonesia) | Karangetang, Siau Island (Indonesia) | Karymsky, Eastern Kamchatka (Russia) | Kilauea, Hawaiian Islands (USA) | Sheveluch, Central Kamchatka (Russia) | Shishaldin, Fox Islands (USA) | Sinabung, Indonesia | Tungurahua, Ecuador
The Weekly Volcanic Activity Report is a cooperative project between the Smithsonian's Global Volcanism Program and the US Geological Survey's Volcano Hazards Program. Updated by 2300 UTC every Wednesday, notices of volcanic activity posted on these pages are preliminary and subject to change as events are studied in more detail. This is not a comprehensive list of all of Earth's volcanoes erupting during the week, but rather a summary of activity at volcanoes that meet criteria discussed in detail in the "Criteria and Disclaimers" section. Carefully reviewed, detailed reports on various volcanoes are published monthly in the Bulletin of the Global Volcanism Network.
Note: Many news agencies do not archive the articles they post on the Internet, and therefore the links to some sources may not be active. To obtain information about the cited articles that are no longer available on the Internet contact the source.
New Activity/Unrest
Cleveland | Chuginadak Island (USA) | 52.825°N, 169.944°W | Summit elev. 1730 m
AVO reported that during 29 July-4 August satellite images detected strongly elevated surface temperatures at Cleveland's summit consistent with growth of a new lava dome. A field crew working in the area on 1 August reported frequent rockfalls on the volcano. A weak infrasound signal was much smaller than the explosion detected on 21 July; the signal may have been related to gas emissions, also consistent with lava-dome effusion. A very small gas plume was visible in webcam images during 2-3 August, and steam emissions were observed on 4 August. 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.
Source: US Geological Survey Alaska Volcano Observatory (AVO) http://www.avo.alaska.edu/
Colima | Mexico | 19.514°N, 103.62°W | Summit elev. 3850 m
Based on satellite images and the Mexico City MWO, the Washington VAAC reported that multiple ash plumes from Colima rose to an altitude of 5.5 km (15,000 ft) a.s.l. and drifted 110 km WSW and SW on 31 July. On 3 August a gas plume possibly containing ash drifted 30-40 km N and W. The next day an ash plume rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted over 35 km NW.
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.
Source: Washington Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/messages.html
Gamalama | Halmahera (Indonesia) | 0.8°N, 127.33°E | Summit elev. 1715 m
On 4 August, BNPB reported that Gamalama continued to erupt, although with low intensity. Tremor was continuous. The Alert Level remained at 2 (on a scale of 1-4); visitors and residents were warned not to approach the crater within a radius of 1.5 km. The total number of evacuees in shelters was 1,791. Based on local observations, a SIGMET and wind data, and satellite images, the Darwin VAAC reported that an ash plume drifted over 20 km NW on 4 August.
Geologic Summary. Gamalama (Peak of Ternate) is a near-conical stratovolcano that comprises the entire island of Ternate off the western coast of Halmahera and is one of Indonesia's most active volcanoes. The island of Ternate was a major regional center in the Portuguese and Dutch spice trade for several centuries, which contributed to the thorough documentation of Gamalama's historical activity. Three cones, progressively younger to the north, form the summit of Gamalama, which reaches 1715 m. Several maars and vents define a rift zone, parallel to the Halmahera island arc, that cuts the volcano. Eruptions, recorded frequently since the 16th century, typically originated from the summit craters, although flank eruptions have occurred in 1763, 1770, 1775, and 1962-63.
Sources: Badan Nacional Penanggulangan Bencana (BNPB) http://www.bnpb.go.id/;
Darwin Volcanic Ash Advisory Centre (VAAC) ftp://ftp.bom.gov.au/anon/gen/vaac/
Manam | Papua New Guinea | 4.08°S, 145.037°E | Summit elev. 1807 m
RVO reported that an eruption at Manam's Southern Crater began at about 1130 on 31 July with low roaring noises. Soon after, variously-sized scoria were ejected; fist-sized scoria fell in Warisi village on the E side of the island, and clasts 10-20 cm in diameter fell on the N side of the island in Baliau. Two people were knocked unconscious after being hit with scoria. According to a news article residents started evacuating around midday. Residents in Bogia (25-30 km SSW of Manam on the N coast of the mainland) reported ashfall at around 1245, and by 1300 the sky was darker. Ashfall was also reported in Potsdam (on the coast, NW of Bogia). RVO stated that at around 1330, immediately after scoria fall ceased, dark gray ash emissions rose from the crater. Based on satellite images and ground observations, the Darwin VAAC reported that the ash plume rose to an altitude of 19.8 km (65,000 ft) a.s.l., spread out in multiple directions, and then drifted 370 km SW. By 1740 RVO noted that activity had declined and emission turned to light gray, and by the next morning only dense white emission were observed.
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.
Sources: Rabaul Volcano Observatory (RVO);
Darwin Volcanic Ash Advisory Centre (VAAC) ftp://ftp.bom.gov.au/anon/gen/vaac/;
Loop http://www.looppng.com/content/hickey-says-people-moving-out
Nevado del Ruiz | Colombia | 4.892°N, 75.324°W | Summit elev. 5279 m
The Washington VAAC reported bright thermal anomalies at Nevado del Ruiz visible in satellite images on 31 July; a brief increase in seismicity was detected, and the thermal anomaly was weaker in subsequent images.
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.
Source: Washington Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/messages.html
Piton de la Fournaise | Reunion Island (France) | 21.244°S, 55.708°E | Summit elev. 2632 m
OVPDLF reported that a sharp increase in seismicity at Piton de la Fournaise, increased gas emissions, and deformation recorded on 30 July prompted an Alert Level increase and an evacuation. A fissure eruption began the next day at 0920, preceded by 90 minutes of high seismicity and 80 minutes of major deformation; it was confirmed by a hiker and then by observation of a gas plume. A 1-km-long fissure opened in the NE part of the l'Enclos Fouqué caldera and produced dozens of lava fountains. Based on satellite images and gas data the flow rate was estimated to be 28 cubic meters per second initially and then 11 cubic meters per second later that day. A gas plume rose to altitudes of 3.2-3.5 km (10,500-11,500 ft) a.s.l. By the evening there were only five fountains, and a lava flow had traveled as far E as Plaine des Osmondes (NE part of the caldera). According to a news article, lava fountains were 40 m high, forming 20-m-high cones on 31 July. At 1115 on 2 August tremor stopped, after several hours of fluctuating intensity, and lava was no longer being effused.
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.
Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF) http://www.ipgp.fr/fr;
The Island Packet http://www.islandpacket.com/2015/08/01/3861341/highly-active-volcano-erupts-on.html
Raung | Eastern Java (Indonesia) | 8.125°S, 114.042°E | Summit elev. 3332 m
On 4 August BNPB reported that during the previous three days the Strombolian eruption at Raung increased in intensity. Ash fell in Sempu, Songgon, Glenmore, Gambiran, and Banyuwangi. On 4 August dense blackish gray ash plumes rose 800 m and drifted SE. Based on satellite-image and wind data, the Darwin VAAC reported that during 29 July-4 August multiple ash plumes rose to altitudes of 4.3-4.9 km (14,000-16,000 ft) a.s.l. and drifted as far as 240 km in multiple directions. The Alert Level remained at 3 (on a scale of 1-4), and the public was reminded not to approach the crater within a 3-km radius.
Geologic Summary. Raung, one of Java's most active volcanoes, is a massive stratovolcano in easternmost Java that was constructed SW of the rim of Ijen caldera. The 3332-m-high, unvegetated summit of Gunung Raung is truncated by a dramatic steep-walled, 2-km-wide caldera that has been the site of frequent historical eruptions. A prehistoric collapse of Gunung Gadung on the W flank produced a large debris avalanche that traveled 79 km, reaching nearly to the Indian Ocean. Raung contains several centers constructed along a NE-SW line, with Gunung Suket and Gunung Gadung stratovolcanoes being located to the NE and W, respectively.
Sources: Badan Nacional Penanggulangan Bencana (BNPB) http://www.bnpb.go.id/;
Darwin Volcanic Ash Advisory Centre (VAAC) ftp://ftp.bom.gov.au/anon/gen/vaac/
Suwanosejima | Ryukyu Islands (Japan) | 29.638°N, 129.714°E | Summit elev. 796 m
Based on JMA notices, satellite-image analyses, and pilot observations, the Tokyo VAAC reported that ash plumes from Suwanosejima rose to altitudes of 2.1-3 km (7,000-10,000 ft) a.s.l. and drifted E, SW, and W during 30-31 July and 4 August. On 2 August an ash plume rose to an altitude of 4 km (13,000 ft) a.s.l.
Geologic Summary. The 8-km-long, spindle-shaped island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit of the volcano is truncated by a large breached crater extending to the sea on the east flank that was formed by edifice collapse. Suwanosejima, one of Japan's most frequently active volcanoes, was in a state of intermittent strombolian activity from Otake, the NE summit crater, that began in 1949 and lasted until 1996, after which periods of inactivity lengthened. The largest historical eruption took place in 1813-14, when thick scoria deposits blanketed residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed forming a large debris avalanche and creating the horseshoe-shaped Sakuchi caldera, which extends to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 persons live on the island.
Source: Tokyo Volcanic Ash Advisory Center (VAAC) http://ds.data.jma.go.jp/svd/vaac/data/vaac_list.html
Ongoing Activity
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 29 July-4 August ash plumes from Dukono rose to altitudes of 2.1-3 km (7,000-10,000 ft) a.s.l. and drifted 55-155 km NW, N, NE, and ENE.
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.
Source: Darwin Volcanic Ash Advisory Centre (VAAC) ftp://ftp.bom.gov.au/anon/gen/vaac/
Karangetang | Siau Island (Indonesia) | 2.78°N, 125.4°E | Summit elev. 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 250 m above the Main Crater and 25 m above Crater II during 22-29 July; foggy conditions occasionally prevented views. Incandescence from the lava dome was observed at night. Incandescent avalanches from the fronts of 150-m-long lava flows traveled as far as 2.5 km E down the Batuawang and Kahetang drainages. Seismicity was dominated by tremor and signals characteristic of avalanches, with rare volcanic earthquakes. The Alert Level remained at 3 (on a scale of 1-4); visitors and residents were warned not to approach Karangetang within a 4-km radius.
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.
Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM) http://www.vsi.esdm.go.id/
Karymsky | Eastern Kamchatka (Russia) | 54.049°N, 159.443°E | Summit elev. 1513 m
KVERT reported that moderate explosive activity at Karymsky continued during 24-31 July. Satellite images detected a daily thermal anomaly, as well as ash plumes that drifted 65 km E and NW during 25 and 27-30 July. Helicopter pilots observed explosions on 28 July; ash plumes rose to an altitude of 4 km (13,100 ft) a.s.l. and drifted N. 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.
Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php
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 29 July-4 August. The lava lake continued to circulate and spatter in the Overlook vent. Webcams recorded multiple incandescent outgassing vents within Pu'u 'O'o; for 45 minutes on 31 July a lava flow effused from a vent on the E part of the crater floor. The June 27th NE-trending lava flow continued to be active with surface flows within 4-8 km NE of Pu'u 'O'o 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.
Source: US Geological Survey Hawaiian Volcano Observatory (HVO) http://hvo.wr.usgs.gov/
Sheveluch | Central Kamchatka (Russia) | 56.653°N, 161.36°E | Summit elev. 3283 m
KVERT reported that during 24-31 July lava-dome extrusion onto Sheveluch’s N flank was accompanied by fumarolic activity, dome incandescence, and hot avalanches. Satellite images showed a daily thermal anomaly over the dome. 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.
Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php
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 28 July-4 August indicating that low-level eruptive activity confined to the summit crater continued. Cloud cover sometimes prevented satellite and webcam observations; elevated surface temperatures were sometimes detected in satellite images. Satellite images detected a 24-km-long steam plume drifting SE on 28 July and vigorous steaming and plumes drifting SW on 31 July. A steam plume was recorded by the webcam on 2 August. 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.
Source: US Geological Survey Alaska Volcano Observatory (AVO) http://www.avo.alaska.edu/
Sinabung | Indonesia | 3.17°N, 98.392°E | Summit elev. 2460 m
On 4 August BNPB reported that the eruption at Sinabung continued at a very high level. Lava was incandescent as far as 1.5 km SE and E down the flanks, and multiple avalanches were detected. Pyroclastic flows traveled at most 3 km ESE and SE, and ash plumes rose 2 km. The Alert Level remained at 4 (on a scale of 1-4), with an exclusion zone of 7 km from the volcano on the SE sector, and 6 km in the E sector. There were 3,152 families (11,114 people) displaced in 10 shelters, and an additional 2,053 families (6,179 people) in temporary shelters.
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.
Source: Badan Nacional Penanggulangan Bencana (BNPB) http://www.bnpb.go.id/
Tungurahua | Ecuador | 1.467°S, 78.442°W | Summit elev. 5023 m
IG reported moderate seismic activity at Tungurahua during 29 July-4 August, characterized by long-period events and tremor. Cloud cover often prevented visual observations. On 31 July a steam-and-ash plume drifted W, producing ashfall in Pillate (8 km W), Choglontus (13 km WSW), Bilbao (8 km W), and El Manzano (8 km SW), Mocha (25 km W), and Tisaleo (29 km NW). A steam-and-ash plume drifted W on 1 August.
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.
Source: Instituto Geofísico-Escuela Politécnica Nacional (IG) http://www.igepn.edu.ec/
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