The Weekly Volcanic Activity Report: May 9 - 15, 2018

The Weekly Volcanic Activity Report: May 9 - 15, 2018

New activity/unrest was reported for 5 volcanoes between May 9 and 15, 2018. During the same period, ongoing activity was reported for 15 volcanoes.

New activity/unrest: Kilauea, Hawaiian Islands (USA) | Merapi, Central Java (Indonesia) | Oraefajokull, Iceland | Piton de la Fournaise, Reunion Island (France) | Sangeang Api, Indonesia.

Ongoing activity: Aira, Kyushu (Japan) | Bagana, Bougainville (Papua New Guinea) | Dukono, Halmahera (Indonesia) | Ebeko, Paramushir Island (Russia) | Fuego, Guatemala | Karymsky, Eastern Kamchatka (Russia) | Kirishimayama, Kyushu (Japan) | Langila, New Britain (Papua New Guinea) | Popocatepetl, Mexico | Reventador, Ecuador | Sabancaya, Peru | Sheveluch, Central Kamchatka (Russia) | Stromboli, Aeolian Islands (Italy) | Suwanosejima, Ryukyu Islands (Japan) | Turrialba, Costa Rica.

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 23:00 UTC every Wednesday, notices of volcanic activity posted 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. Carefully reviewed, detailed reports on various volcanoes are published monthly in the Bulletin of the Global Volcanism Network.

New activity/unrest

Kilauea, Hawaiian Islands (USA)

19.421°N, 155.287°W, Summit elev. 1222 m

On 9 May the intermittent eruption of lava in Leilani Estates in the lower East Rift Zone (ERZ) of Kilauea continued. In the northeast part of the area, fissure 15 extended across Poihiki Road, generating a pahoehoe flow about 20 m (66 ft) long. In the summit caldera, steady lowering of the Overlook Crater lava lake within Halema`uma`u crater raised the potential for steam-driven explosions if the lava column dropped to the groundwater level and allowed water into the conduit. On 10 and 11 May, little new extrusive activity was noted from the ERZ fissures, though there were continued earthquakes, ground deformation, and considerable gas discharge. Tiltmeters recorded ongoing deflation and the Overlook crater lava level continued to drop. 

Fissure 16 opened at 0645 on 12 May near the end of Hinalo Road. It produced a lava flow that traveled about 230 m before stalling around 1430. An area that had been actively steaming developed into fissure 17, reported at 1800 just east of fissure 16, and was actively spattering and degassing. At the summit, rockfalls from the steep walls into Overlook crater generated intermittent small steam-and-ash clouds throughout the day. 

Lava eruptions continued on 13 May along the lower ERZ. Aerial observations showed that a new outbreak in the early morning about 900 m NE of the end of Hinalo Street and 900 m S of Highway 132 was several hundred yards long and ejected spatter along with a slow-moving lava flow. By late in the day this activity from fissure 17 was dominated by lava fountaining, explosions that sent spatter bombs to 100 m into the air, and several advancing lava flow lobes moving generally NE; as of 1900 one lobe was 2 m thick and advancing roughly parallel to Highway 132. Steady, vigorous plumes of steam and occasionally minor amounts of ash rose from the Overlook vent and drifted downwind to the SW. Later in the day, ash clouds rose up to 650 m (2,000 ft) above the vent. Several strong earthquakes shook the Hawaiian Volcano Observatory and the surrounding area overnight. 

Activity on the morning of 14 May in the lower ERZ was dominated by lava fountaining, explosions of spatter more than 30 m (100 ft) into the air, and an advancing flow from fissure 17 at the NE end of the fissure system. As of 0630, the fissure 17 flow had traveled about 1.6 km roughly ESE parallel to the rift zone. Fissure 18 was weakly active. A 19th fissure spotted around 0800 just NE of Pohoiki Road and N of Hinalo Street produced a sluggish lava flow. Volcanic gas emissions remained elevated throughout the area downwind of the vents. Deflationary tilt at the summit continued and seismicity remained elevated. 

On the morning of 15 May activity remained concentrated at fissure 17. The lava flow had advanced about 380 m since 1430 on 14 May. At 0645 the flow was nearly 2.5 km long. However, the advance of the flow had slowed significantly since that afternoon. Also in the morning a new fissure (20) located near fissure 18 produced two small pads of lava. Ash emission from the Overlook crater increased compared to previous days. Although varying in intensity, at times the plume contained enough ash to be gray in color. Variable pulses sent the cloud to an estimated 1-1.3 km (3-4,000 ft) above the ground. The ash cloud drifted generally W and SW from the summit and ash fell in the Ka'u Desert. On 15 May the Aviation Color Code was raised from Orange to Red and the Volcano Alert Level remained at Warning.

Geological summary: Kilauea, which overlaps the E 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 km2, destroying nearly 200 houses and adding new coastline to the island.

Merapi, Central Java (Indonesia)

7.54°S, 110.446°E, Summit elev. 2910 m

PVMBG reported that an explosive eruption occurred at 0740 on 11 May. The eruption began with a small roar and vibrations that were felt at the observation post for 10 minutes. The eruption plume rose to 5.5 km (18,000 ft) above the peak. There was no seismic precursor and no seismic activity continued after the event. PVMBG did not change the alert level from Green/Normal; they interpreted the event as a minor eruption triggered by the accumulation of volcanic gases unlikely to be followed by further eruptions.

Geological summary: Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequently growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities during historical time.

Oraefajokull, Iceland

64.05°N, 16.633°W, Summit elev. 2010 m

On 4 May, the Icelandic Met Office reduced the Aviation Color Code at Öræfajökull from Yellow to Green due to signs of reduced activity. Since September 2017 there has been less earthquake activity, stable hydrological and geochemical measurements, and reduced geothermal heat output. There has been possible minor ongoing inflation, but no signs of an imminent eruption.

Geological summary: Öraefajökull, Iceland's highest peak, is a broad glacier-clad central volcano at the SE end of the Vatnajökull icecap. A 4 x 5 km subglacial caldera truncates the summit of the dominantly basaltic and rhyolitic volcano. The extensive summit icecap is drained through deep glacial valleys dissecting the SW-to-SE flanks. The largest-volume volcano in Iceland, 2119-m-high Öraefajökull was mostly constructed during Pleistocene glacial and interglacial periods. Holocene activity has been dominated by explosive summit eruptions, although flank lava effusions have also occurred. A major silicic eruption in 1362 CE was Iceland's largest historical explosive eruption. It and another eruption during 1727-28 were accompanied by major jökulhlaups (glacier outburst floods) that caused property damage and fatalities.

Piton de la Fournaise, Reunion Island (France)

21.244°S, 55.708°E, Summit elev. 2632 m

OVPF reported that the eruption at Piton de la Fournaise, which began on 27 April from fissures at Rivals Crater, continued through 15 May. Field reconnaissance on 10 May revealed that activity was focused on the main cone, with some activity from a second cone that was ejecting material 10-20 m high. Over the next two days the crater of the main cone narrowed and lava projections at both cones became rare. Lava flows during this time were often confined to tubes, with some breakouts at the change in slope below Piton de Bert, about 3 km from the active cone. Burning vegetation as a result of the breakouts was visible on and at the foot of the rampart. Based on satellite data when surface flows were visible, lava emission rates were estimated to be about 1-2 cubic meters/second. Tremor intensity fluctuated over the week, with a sharp increase during 0500 and 0900 on 15 May.

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.

Sangeang Api, Indonesia

8.2°S, 119.07°E, Summit elev. 1949 m

Based on a VONA from PVMBG, on 9 May a gas emission was observed at 1807 from Sangeang Api that rose to 4,150 m (13,000 ft) a.s.l. and drifted west. On 9 May the Aviation Color Code was changed from unassigned to Yellow.

Geological summary: Sangeang Api volcano, one of the most active in the Lesser Sunda Islands, forms a small 13-km-wide island off the NE coast of Sumbawa Island. Two large trachybasaltic-to-tranchyandesitic volcanic cones, 1949-m-high Doro Api and 1795-m-high Doro Mantoi, were constructed in the center and on the eastern rim, respectively, of an older, largely obscured caldera. Flank vents occur on the south side of Doro Mantoi and near the northern coast. Intermittent historical eruptions have been recorded since 1512, most of them during in the 20th century.

Ongoing activity

Aira, Kyushu (Japan)

31.593°N, 130.657°E, Summit elev. 1117 m

JMA reported that during 7-11 May there were 12 events, three of which were explosions, at Minamidake crater (at Aira caldera’s Sakurajima volcano). Tephra was ejected as far as 700 m from the crater, and ash plumes rose as high as 2.8 km (9,200 ft) above the crater rim. The Alert Level remained at 3 (on a 5-level scale).

Geological 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.

Bagana, Bougainville (Papua New Guinea)

6.137°S, 155.196°E, Summit elev. 1855 m

Based on analyses of satellite imagery and model data, the Darwin VAAC reported that on 11 May at 0900 an ash plume from Bagana rose to an altitude of 2.1 km (7,000 ft) a.s.l. and drifted SW. The plume dispersed within six hours.

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 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 flanks on all sides.

Dukono, Halmahera (Indonesia)

1.693°N, 127.894°E, Summit elev. 1229 m

Based on analyses of satellite imagery, wind model data, and notices from PVMBG, the Darwin VAAC reported that during 9-15 May ash plumes from Dukono rose to altitudes of 1.5-2 km (4,500-6,000 ft) a.s.l. and drifted E and S.

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.

Ebeko, Paramushir Island (Russia)

50.686°N, 156.014°E, Summit elev. 1103 m

Volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, observed explosions at Ebeko on 4 May and during 6-10 May that sent ash plumes as high as 2.4 km (7,875 ft) a.s.l. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geological summary: The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.

Fuego, Guatemala

14.473°N, 90.88°W, Summit elev. 3763 m

Small ash explosions at Fuego on 11 and 12 May rose to 5 km (15,000 ft) a.s.l., or approximately 1 km (3,280 ft) above the summit. The ash dispersed quickly to the southwest and was visible on webcams.

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.

Karymsky, Eastern Kamchatka (Russia)

54.049°N, 159.443°E, Summit elev. 1513 m

Based on satellite data, KVERT reported that during 11-14 May explosions at Karymsky generated ash plumes that rose as high as 3.5 km (11,500 ft) and drifted 145 km SW. The Aviation Color Code remained at Orange (the second highest 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.

Kirishimayama, Kyushu (Japan)

31.934°N, 130.862°E, Summit elev. 1700 m

JMA reported that at Shinmoedake (Shinmoe peak), a stratovolcano of the Kirishimayama volcano group, an eruption occurred between 1444 and 1610 on 14 May. The plume rose to 4.5 km (15,000 ft) above the crater and drifted SE. A pyroclastic flow travelled 2 km down the flank. Volcanic earthquake rates under the crater increased after the eruption. Shallow, low-frequency earthquakes and tremor were also reported. The Alert Level remained at 3 (on a scale of 1-5).

Geological summary: Kirishimayama is a large group of more than 20 Quaternary volcanoes located north of Kagoshima Bay. The late-Pleistocene to Holocene dominantly andesitic group consists of stratovolcanoes, pyroclastic cones, maars, and underlying shield volcanoes located over an area of 20 x 30 km. The larger stratovolcanoes are scattered throughout the field, with the centrally located, 1700-m-high Karakunidake being the highest. Onamiike and Miike, the two largest maars, are located SW of Karakunidake and at its far eastern end, respectively. Holocene eruptions have been concentrated along an E-W line of vents from Miike to Ohachi, and at Shinmoedake to the NE. Frequent small-to-moderate explosive eruptions have been recorded since the 8th century.

Langila, New Britain (Papua New Guinea)

5.525°S, 148.42°E, Summit elev. 1330 m

Based on analyses of satellite imagery and model data, the Darwin VAAC reported that on 13 May at 0709 an ash plume from Langila rose to an altitude of 5.5 km (17,000 ft) a.s.l. and drifted W. An image acquired around six hours later indicated that the ash from the event had dissipated.

Geological summary: Langila, one of the most active volcanoes of New Britain, consists of a group of four small overlapping composite basaltic-andesitic cones on the lower eastern flank of the extinct Talawe volcano. Talawe is the highest volcano in the Cape Gloucester area of NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE; Langila volcano was constructed NE of the breached crater of Talawe. An extensive lava field reaches the coast on the north and NE sides of Langila. Frequent mild-to-moderate explosive eruptions, sometimes accompanied by lava flows, have been recorded since the 19th century from three active craters at the summit of Langila. The youngest and smallest crater (no. 3 crater) was formed in 1960 and has a diameter of 150 m.

Popocatepetl, Mexico

19.023°N, 98.622°W, Summit elev. 5393 m

CENAPRED reported that each day during 9-15 May there were 51-137 steam and gas emissions from Popocatépetl as well as ongoing incandescence from the summit. Additionally, three explosions were recorded: at 1834 on 11 May, at 0912 on 11 May, and at 1452 on 14 May. These explosions dispersed ash to the S and SW. Volcano-tectonic earthquakes with magnitudes up to M 2.8 also occurred throughout the time period.

Geological summary: Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 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 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 Pre-Columbian time.

Reventador, Ecuador

0.077°S, 77.656°W, Summit elev. 3562 m

During 9-15 May, IG reported ongoing high levels of eruptive activity at Reventador. Steam, gas, and ash emissions continued, with plumes moving to the N and W. On 12 and 13 May, a small lava flow was observed on the E flank 700 m below the summit.

Geological summary: Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic Volcán El Reventador stratovolcano rises to 3562 m above the jungles of the western Amazon basin. A 4-km-wide caldera widely breached to the east was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1300 m above the caldera floor to a height comparable to the caldera rim. It has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. The largest historical eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

Sabancaya, Peru

15.787°S, 71.857°W, Summit elev. 5960 m

Intermittent ash and gas emissions at Sabancaya during 9-15 May were reported by the Buenos Aires VAAC, with plume altitudes reaching 7-9 km (2,300-3,000 ft) a.s.l.

Geological summary: Sabancaya, located in the saddle NE of Ampato and SE of 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, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning "tongue of fire" in the Quechua 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.

Sheveluch, Central Kamchatka (Russia)

56.653°N, 161.36°E, Summit elev. 3283 m

KVERT reported that a weak thermal anomaly over Sheveluch was identified in satellite images during 10-14 May. 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 km3 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.

Stromboli, Aeolian Islands (Italy)

38.789°N, 15.213°E, Summit elev. 924 m

INGV reported typical activity at Stromboli from 7 to 13 May, with 2-4 hourly low-intensity explosions to heights of less than 80 m (300 ft) above the crater, in the North crater area. Fine ash as well as lapilli and bombs were ejected. The South Central crater area vents produced between 5-12 hourly, low-intensity explosions, also to heights of less than 80 m above the crater. Continuous degassing was also observed from these vents. On 13 May there was an increased frequency of explosions, with 16 events/hour. No significant variations were reported in seismological, deformation, or geochemical parameters.

Geological summary: Spectacular incandescent nighttime explosions at this volcano have long attracted visitors to the "Lighthouse of the Mediterranean." Stromboli, the NE-most of the Aeolian Islands, has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period from about 13,000 to 5000 years ago was followed by formation of the modern edifice. The active summit vents are located at the head of the Sciara del Fuoco, a prominent horseshoe-shaped scarp formed about 5000 years ago as a result of the most recent of a series of slope failures that extend to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Suwanosejima, Ryukyu Islands (Japan)

29.638°N, 129.714°E, Summit elev. 796 m

The Tokyo VAAC reported that explosions occurred at Suwanosejima on 15 May, based on information from JMA.

Geological 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 people live on the island.

Turrialba, Costa Rica

10.025°N, 83.767°W, Summit elev. 3340 m

OVSICORI reported that there were strong emissions of SO2 from Turrialba, accompanied by vigorous fumarolic activity and jetting noises. An ash plume was reported on 10 May, with ashfall in La Pastora de Santa Cruz de Turrialba and Pacayas. A weak water vapor and gas plume was detected at 0920 on 13 May, rising 300-500 m (1000-1600 ft) above the summit. Seismicity was low, with low-amplitude long-period earthquakes and some low-amplitude tremor. Continuous low-amplitude tremor was report on 13 May.

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 edifice covers an area of 500 km2. 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.

Source: GVP

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