New activity/unrest was observed at 5 volcanoes between September 7 and 13, 2016. During the same period, ongoing activity was observed at 14 volcanoes.
New activity/unrest: Klyuchevskoy, Central Kamchatka (Russia) | Mayon, Luzon (Philippines) | Piton de la Fournaise, Reunion Island (France) | Sabancaya, Peru | White Island, North Island (New Zealand).
Ongoing activity: Bagana, Bougainville (Papua New Guinea) | Colima, Mexico | Dukono, Halmahera (Indonesia) | Fuego, Guatemala | Grimsvotn, Iceland | Karymsky, Eastern Kamchatka (Russia) | Kilauea, Hawaiian Islands (USA) | Nevado del Ruiz, Colombia | Popocatepetl, Mexico | Ruapehu, North Island (New Zealand) | Santa Maria, Guatemala | Sheveluch, Central Kamchatka (Russia) | Turrialba, Costa Rica | Yasur, Vanuatu.
Klyuchevskoy, Central Kamchatka (Russia)
56.056°N, 160.642°E, Elevation 4754 m
KVERT reported that a Strombolian eruption at Klyuchevskoy continued during 2-9 September. Volcanic bombs that were ejected above the summit crater and the cinder cone landed in the Apakhonchich drainage on the E flank. A lava flow traveled down the Apakhonchich drainage and also down the SW flank. Satellite images showed a large and bright daily thermal anomaly at the volcano.
At 0943 and 1443 on 7 September explosions generated ash plumes that rose to altitudes of 6.5-7.5 km (21,300-24,600 ft) a.s.l. and drifted as far as 75 km SSW and ESE. The Aviation Color Code was raised to Red (the highest level on a four-color scale), and then lowered back to Orange within a few hours. Explosions at 1804 on 7 September produced ash plumes that rose as high as 7 km (23,000 ft) a.s.l. and drifted 45 km NE. At 0034, 0758, 1341, and 1850 on 8 September explosions generated ash plumes that rose to altitudes of 7-7.5 km (23,000-24,600 ft) a.s.l. and drifted as far as 145 km NE, NW, W, and SW. Ash plumes from explosions on 9 September did not go as high, rising to altitudes of 3-5 km (10,000-16,400 ft) a.s.l. and drifting 315-535 km SW. Minor ash deposits at Koryaksky and Avachinsky volcanoes were detected during 2100-2140; ash plumes continued to drift and dissipate over the Avachinsky bay.
Geological summary: Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.
Mayon, Luzon (Philippines)
13.257°N, 123.685°E, Elevation 2462 m
On 8 September PHIVOLCS noted that recent changes at Mayon prompted a change in the Alert level from 0 to 1 (on a 0-5 scale). Continuous gas measurements consistently showed increased sulfur dioxide emissions above the baseline level of 500 tonnes/day, sometimes as high as 1,000 tonnes/day, since July. Global Positioning System data and tilt measurements showed a consistent inflationary trend since July, and precise leveling and electronic distance surveys the last week of August also indicated edifice inflation, possibly due to magma movement at depth. An earthquake swarm (146 events) located 10 km SE during 3-6 August likely indicated rock fracturing processes but may or may not be associated with magmatic activity. Steam emissions from the crater ranged from weak to moderate. PHIVOLCS reminded residents of the 6-km-radius Permanent Danger Zone (PDZ) around the volcano.
Geological summary: Beautifully symmetrical Mayon volcano, which rises to 2462 m above the Albay Gulf, is the Philippines' most active volcano. The structurally simple volcano has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions at this basaltic-andesitic volcano date back to 1616 and range from strombolian to basaltic plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas. Mayon's most violent eruption, in 1814, killed more than 1200 people and devastated several towns.
Piton de la Fournaise, Reunion Island (France)
21.244°S, 55.708°E, Elevation 2632 m
OVPDLF reported that seismicity at Piton de la Fournaise was low in August, following an elevated number of volcano-tectonic events the second half of July. Gas emissions were low and dominated by water vapor; CO2 emissions had been elevated during 21-27 July. Inflation had stopped in early August and slight deflation was detected through 2 September.
Seismicity increased on 10 September, and elevated levels of SO2 at fumaroles were detected. A seismic crisis began at 0735 on 11 September, characterized by several earthquakes per minute. Deformation suggested magma migrating to the surface. Volcanic tremor began at 0841, synonymous with the beginning of the eruption. Several fissures opened in the N part of the l'Enclos Fouqué caldera, between Puy Mi-côte and the July 2015 eruption site, and produced a dozen 15-30-m-high lava fountains distributed over several hundred meters. Tremor levels decreased by a factor of four, and by 2100 were stable. The eruption continued on 12 September.
Geological 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.
15.78°S, 71.85°W, Elevation 5967 m
Observatorio Vulcanológico del INGEMMET (OVI) reported that during a field inspection of Sabancaya on 25 August scientists noted five new fumarolic areas; two were located in the N part of the summit area, and three were on the NE flank. The number of hybrid earthquakes increased during 25-27 August. A small explosion at 0651 on 27 August produced a dense ash plume that rose 1 km above the crater and drifted E.
Geological summary: Sabancaya, located on the saddle between 6288-m-high Ampato and 6025-m-high Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three volcanoes, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. Both Nevado Ampato and Nevado Sabancaya are only slightly affected by glacial erosion and consist of a series of lava domes aligned along a NW-SW trend. The name of 5967-m-high Sabancaya (meaning "tongue of fire" in the Quechua Indian language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions date back to 1750.
White Island, North Island (New Zealand)
37.52°S, 177.18°E, Elevation 321 m
GeoNet reported that on 6 September scientists visited White Island for routine monitoring and maintenance of the monitoring network. Observations during the visit confirmed that Crater Lake was growing though at a lower level (28.4 m below the overflow level) since the 27 April eruption removed 13-15 m of lake floor sediments. Thermal IR images of a rocky lava mound in the back of the 1978/90 Crater (in the same area a lava dome grew in 2012) revealed two areas of hot gas output; temperatures in one area had decreased since August while temperatures in the second area had remained at similar levels.
On 13 September minor and passive ash emissions rose from the vent on the 2012 lava dome. The Volcanic Alert Level was raised from 1 to 3 (Minor Volcanic Eruption) and the Aviation Colour Code was raised from Green to Orange. Based on ground observations and satellite data the ash plume drifted E. Seismic activity and gas flux remained low, and there were no measureable acoustic signals. Minor ash emissions continued the next day.
Geological summary: Uninhabited 2 x 2.4 km White Island, one of New Zealand's most active volcanoes, is the emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The 321-m-high island consists of two overlapping andesitic-to-dacitic stratovolcanoes; the summit crater appears to be breached to the SE because the shoreline corresponds to the level of several notches in the SE crater wall. Volckner Rocks, four sea stacks that are remnants of a lava dome, lie 5 km NNE of White Island. Intermittent moderate phreatomagmatic and strombolian eruptions have occurred at White Island throughout the short historical period beginning in 1826, but its activity also forms a prominent part of Maori legends. Formation of many new vents during the 19th and 20th centuries has produced rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project.
Bagana, Bougainville (Papua New Guinea)
6.137°S, 155.196°E, Elevation 1855 m
Based on analyses of satellite imagery and model data, the Darwin VAAC reported that on 7 September ash plumes from Bagana rose to an altitude of 2.1 km (7,000 ft) a.s.l. and drifted over 35 km NW and W. On 9 September an ash plume rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted 65-160 km SW.
Geological summary: Bagana volcano, occupying a remote portion of central Bougainville Island, is one of Melanesia's youngest and most active volcanoes. This massive symmetrical, roughly 1850-m-high cone was largely constructed by an accumulation of viscous andesitic lava flows. The entire edifice could have been constructed in about 300 years at its present rate of lava production. Eruptive activity is frequent and characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although explosive activity occasionally producing pyroclastic flows also occurs. Lava flows form dramatic, freshly preserved tongue-shaped lobes up to 50-m-thick with prominent levees that descend the volcano's flanks on all sides. Satellite thermal measurements indicate a continuous eruption from before February 2000 through at least late August 2014.
19.514°N, 103.62°W, Elevation 3850 m
Based on satellite and webcam images, the Washington VAAC reported that on 7 September an ash plume from Colima rose to an altitude of 4.9 km (16,000 ft) a.s.l. and drifted W.
Geological summary: The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the 4320 m high point of the complex) on the north and the 3850-m-high historically active Volcán de Colima at the south. A group of cinder cones of late-Pleistocene age is located on the floor of the Colima graben west and east of the Colima complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, and have produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions (most recently in 1913) have destroyed the summit and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.
Dukono, Halmahera (Indonesia)
1.693°N, 127.894°E, Elevation 1229 m
Based on analyses of satellite imagery and model data, the Darwin VAAC reported that during 7-13 September ash plumes from Dukono rose to an altitude of 2.4 km (8,000 ft) a.s.l. and drifted as far as 115 km NE, E, ESE, and SE.
Geological summary: Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.
14.473°N, 90.88°W, Elevation 3763 m
On 8 September INSIVUMEH reported that the 12th eruptive episode at Fuego in 2016 had ended. Weak explosions produced ash plumes that rose as high as 750 m above the crater and drifted more than 8 km W and SW. Lava fountains rose 100 m above the crater rim; the lava flow in the Las Lajas (SE) drainage was no longer advancing. During 11-13 September explosions produced ash plumes that rose 450-850 m and drifted 6-10 km NW, W, and SW. Explosions ejected incandescent material as high as 150 m above the crater rim.
Geological 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.
64.416°N, 17.316°W, Elevation 1719 m
On 8 September the Icelandic Meteorological Office (IMO) stated that the water level of the Skaftá river at Sveinstindur (the closest gauging station at 28 km downstream from the ice margin) rose significantly in the previous 24 hours, suggesting the beginning of a glacial outburst flood (jökulhlaup), originating from Grímsvötn's Western Skaftá ice cauldron. The discharge rate of Skaftá at Sveinstindur was 270 m³/s. 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.
Geological 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.
Karymsky, Eastern Kamchatka (Russia)
54.049°N, 159.443°E, Elevation 1513 m
KVERT reported that Karymsky was quiet during March-August, noting that the last moderate explosion occurred in February and the last thermal anomaly over the volcano was detected in May. On 2 September the Aviation Color Code was lowered to Green (the lowest level on a four-color scale).
Geological 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, Elevation 1222 m
During 7-13 September HVO reported that the lava lake continued to rise and fall, circulate, and spatter in Kilauea’s Overlook vent. The lake level fluctuated between 5 and 20 m below the Halema’uma’u floor, and was easily visible from the Jaggar Museum (NW rim of Kilauea Caldera). The 61G lava flow, originating from a vent on Pu'u 'O'o Crater's E flank, continued to enter the ocean at multiple areas near Kamokuna. A large section of the W part of the delta had collapsed on 5 September, causing a small explosion. Scattered breakouts were active 1.7-2 km inland from the coast.
Geological summary: Kilauea volcano, which overlaps the east flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 sq km, destroying nearly 200 houses and adding new coastline to the island.
Nevado del Ruiz, Colombia
4.892°N, 75.324°W, Elevation 5279 m
Based on satellite images, the Washington VAAC reported that ash emissions at Nevado del Ruiz began at 0615 on 13 September, producing a plume that rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted W. By 1345 the ash had dissipated.
Geological summary: Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers >200 sq km. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.
19.023°N, 98.622°W, Elevation 5426 m
During an overflight of Popocatépetl on 30 August CENAPRED scientists confirmed that explosions during 27-28 August had destroyed lava dome 69 (first identified on 1 August). The crater which had hosted the dome was 300 m in diameter and 30 m deep.
Each day during 7-13 September there were 35-133 emissions, some of which contained minor amounts of ash on 8 September. Cloud cover sometimes prevented observations, though gas-and-steam plumes were visible daily. Crater incandescence was visible at night and sometimes was more intense in conjunction with emissions. An explosion at 1450 on 8 September produced an ash plume that rose 1.5 km above the crater. On 11 September an explosion at 0925 generated a plume that rose 1 km, and an explosion at 2323 ejected incandescent material onto the flanks. The Alert Level remained at Yellow, Phase Two.
Geological 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
On 7 September GeoNet reported that the temperature of Ruapehu’s summit Crater Lake had been declining, cooling to 12 ºC on 15 August which was the lowest temperature since the 1995/1996 eruptions, but had recently started to rapidly heat. The temperature began to slowly and variably rise in late August; however, by 2 September a rising trend was apparent. On 4 September tremor levels also increased, and remained elevated. The Volcanic Alert Level remained at 1 (minor volcanic unrest) and the Aviation Colour Code remained at Green.
Geological 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.
Santa Maria, Guatemala
14.756°N, 91.552°W, Elevation 3772 m
INSIVUMEH reported that a strong explosion at 1455 on 11 September generated a dense ash plume that rose 2.5 km above Santa María's Santiaguito lava-dome complex and drifted 25 km W and SW. A moderate explosion during 11-12 September produced an ash plume that rose 900 m and drifted SW.
Geological 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.
Sheveluch, Central Kamchatka (Russia)
56.653°N, 161.36°E, Elevation 3283 m
KVERT reported that during 2-9 September lava-dome extrusion onto Sheveluch’s N flank was accompanied by strong fumarolic activity, dome incandescence,ash explosions, and hot avalanches. Satellite images showed a daily thermal anomaly over the dome. The Aviation Color Code remained at Orange.
Geological summary: The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 cu km volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.
Turrialba, Costa Rica
10.025°N, 83.767°W, Elevation 3340 m
OVSICORI-UNA reported that at 0200 on 13 September ash emissions from Turrialba rose 300 m and drifted NNW.
Geological summary: Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive 3340-m-high Turrialba is exceeded in height only by Irazú, covers an area of 500 sq km, and is one of Costa Rica's most voluminous volcanoes. Three well-defined craters occur at the upper SW end of a broad 800 x 2200 m summit depression that is breached to the NE. Most activity originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred during the past 3500 years. A series of explosive eruptions during the 19th century were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters.
19.53°S, 169.442°E, Elevation 361 m
On 9 September the Vanuatu Geohazards Observatory stated that the Alert Level for Yasur remained at 2 (on a scale of 0-4) and that explosions continued to be intense. VGO reminded residents and tourists that hazardous areas were near and around the volcanic crater, within a 600-m-radius permanent exclusion zone, and that volcanic ash and gas could reach areas impacted by trade winds.
Geological summary: Yasur, the best-known and most frequently visited of the Vanuatu volcanoes, has been in more-or-less continuous strombolian and vulcanian activity since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island, this mostly unvegetated pyroclastic cone has a nearly circular, 400-m-wide summit crater. Yasur is largely contained within the small Yenkahe caldera and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide, horseshoe-shaped caldera associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.