The Weekly Volcanic Activity Report: April 4 - 10, 2018

The Weekly Volcanic Activity Report: April 4 - 10, 2018

New activity/unrest was reported for 5 volcanoes between April 4 and 10, 2018. During the same period, ongoing activity was reported for 14 volcanoes.

New activity/unrest: Ambae, Vanuatu | Kirishimayama, Kyushu (Japan) | Lascar, Chile | Nevados de Chillan, Chile | Sinabung, Indonesia.

Ongoing activity: Agung, Bali (Indonesia) | Aira, Kyushu (Japan) | Bezymianny, Central Kamchatka (Russia) | Cleveland, Chuginadak Island (USA) | Copahue, Central Chile-Argentina border | Dukono, Halmahera (Indonesia) | Ebeko, Paramushir Island (Russia) | Fuego, Guatemala | Kilauea, Hawaiian Islands (USA) | Mayon, Luzon (Philippines) | Pacaya, Guatemala | Sabancaya, Peru | 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

Ambae, Vanuatu

15.4°S, 167.83°E, Summit elev. 1496 m

Vanuatu Geohazards Observatory (VGO) reported sustained ash and/or gas emissions from Ambae’s Lake Voui during March through 4 April. Satellite data showed a significant sulfur dioxide gas emission (~0.15 Tg SO2) beginning in the very early hours of 6 April, indicating that the SO2 emission was the largest since Calbuco in April 2015. No significant high-altitude ash plume accompanied the emission, though the eruption generated lightning detected by the WWLLN (World Wide Lightning Location Network). Pictures of local areas posted on social media showed the continuing and significant ashfall on the island. Within a few days, by 8 April, the sulfur dioxide plume had spread across an area from the E coast of Australia to Tahiti, a distance of about 6,000 km. The Alert Level remained at 3 (on a scale of 0-5).

Geologic summary: Ambae, also known as Aoba, is a massive 2500 km3 basaltic shield that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW-trending rift zone dotted with scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes is located at the summit within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. Post-caldera explosive eruptions formed the summit craters of Lake Voui (also spelled Vui) and Lake Manaro Ngoru about 360 years ago. A tuff cone was constructed within Lake Voui about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast.

Kirishimayama, Kyushu (Japan)

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

JMA reported that an explosive eruption at Shinmoedake (Shinmoe peak), a stratovolcano of the Kirishimayama volcano group, occurred at 0531 on 5 April and generated an ash plume that rose 8 km above the crater rim. According to news articles lightning was detected in the ash plume. JMA noted that incandescent tephra was ejected 1.1 km from the vent, and a pyroclastic flow traveled 800 m down the SE flank. Sulfur dioxide emissions increased to 1,400 tons/day, from 300 tons/day last measured on 28 March. The eruption possibly ceased at 0715. During an overflight later that day scientists confirmed a large amount of ashfall in parts of Kobayashi City and other areas of the Miyazaki Prefecture, in part of Takahara Town, and in areas of the Kumamoto prefecture. White plumes rose 200 m during 6-9 April. The Alert Level remained at 3 (on a scale of 1-5).

Geologic 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.

Lascar, Chile

23.37°S, 67.73°W, Summit elev. 5592 m

OVDAS-SERNAGEOMIN reported that, although seismicity at Láscar during March was low, characteristics of the signals were similar to patterns observed prior to previous minor phreatic explosions, particularly before events in 2013 and 2015. The Alert Level was raised to Yellow (second highest level on a four-color scale); SERNAGEOMIN recommended no entry into a restricted area within 5 km of the crater. ONEMI declared an Alert Level Yellow (the middle level on a three-color scale) for San Pedro de Atacama.

Geologic summary: Láscar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters. Prominent lava flows descend its NW flanks. An older, higher stratovolcano 5 km E, Volcán Aguas Calientes, displays a well-developed summit crater and a probable Holocene lava flow near its summit (de Silva and Francis, 1991). Láscar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires.

Nevados de Chillan, Chile

36.868°S, 71.378°W, Summit elev. 3180 m

Servicio Nacional de Geología and Minería (SERNAGEOMIN) Observatorio Volcanológico de Los Andes del Sur (OVDAS) reported continuing activity through 5 April associated with growth of the Gil-Cruz lava dome in Nevados de Chillán’s Nicanor Crater. During 16-31 March the seismic network recorded 44 volcano-tectonic events with maximum local magnitude (ML) of 2.6. In addition, there were 3,874 earthquakes associated with fluid movement; of those 2,645 earthquakes were long-period events. A total of 1,229 tremor events were also detected. Explosive events totaled 765, mainly accompanying magmatic gas emissions and/or acoustic signals recorded by microphones on the flanks. Acoustic pressure from explosions increased on 24 March, and culminated with two major explosions on 30 and 31 March exceeding pressures much higher than previously recorded since the emergence of the dome. Webcam images showed mainly gas emission from explosions, rising no higher than 2 km above the crater rim. Incandescence associated with some explosions was sporadically visible at night.

During an overflight on 3 April scientists observed intermittent whitish-to-grayish emissions rising from the SE-NW-trending fissure on the lava dome’s surface. They also noted lapilli deposits as far as 1 km. Even though subsidence in the central part of the dome was visible, the dome had grown compared to the last observation on 11 March. The dome had extended E to the edge of Nicanor Crater and rose higher than the crater rim, although was mostly circular. The maximum temperature of the dome surface was 670 degrees Celsius. The report noted that a decrease in daily seismic events (suggesting pressurization), two significant explosions, and the dome growing higher than the crater rim prompted OVDAS- SERNAGEOMIN to raise the Alert Level to Orange, the second highest level on a four-color scale. ONEMI maintained an Alert Level Yellow (the middle level on a three-color scale) for the communities of Pinto, Coihueco, and San Fabián.

Geologic summary: The compound volcano of Nevados de Chillán is one of the most active of the Central Andes. Three late-Pleistocene to Holocene stratovolcanoes were constructed along a NNW-SSE line within three nested Pleistocene calderas, which produced ignimbrite sheets extending more than 100 km into the Central Depression of Chile. The largest stratovolcano, dominantly andesitic, Cerro Blanco (Volcán Nevado), is located at the NW end of the group. Volcán Viejo (Volcán Chillán), which was the main active vent during the 17th-19th centuries, occupies the SE end. The new Volcán Nuevo lava-dome complex formed between 1906 and 1945 between the two volcanoes and grew to exceed Volcán Viejo in elevation. The Volcán Arrau dome complex was constructed SE of Volcán Nuevo between 1973 and 1986 and eventually exceeded its height.

Sinabung, Indonesia

3.17°N, 98.392°E, Summit elev. 2460 m

PVMBG and BNPB reported that an eruption at Sinabung at 1607 on 6 April generated a dark gray ash plume that rose 5 km above the crater, and a pyroclastic flow that descended the SE and SW flanks 3.5 km. The Alert Level remained at 4 (on a scale of 1-4), with a general exclusion zone of 3 km and extensions of 7 km on the SSE sector, 6 km in the ESE sector, and 4 km in the NNE sector. According to news articles, ashfall affected hundreds of hectares of agricultural land in the district of Karo, North Sumatra, and the Alas Leuser airport was closed on 7 April due to ash. The Alert Level remained at 4 (on a scale of 1-4), with a general exclusion zone of 3 km and extensions of 7 km on the SSE sector, 6 km in the ESE sector, and 4 km in the NNE sector.

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 andesitic-to-dacitic edifice 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.

Ongoing activity

Agung, Bali (Indonesia)

8.343°S, 115.508°E, Summit elev. 2997 m

PVMBG reported that an event at Agung at 1737 on 5 April generated an ash plume that rose 500 m above the crater rim and drifted W. Seismicity was dominated by high- and low-frequency earthquakes. The Alert Level remained at 3 (on a scale of 1-4) and the exclusion zone continued at a 4-km radius.

Geologic summary: Symmetrical Agung stratovolcano, Bali's highest and most sacred mountain, towers over the eastern end of the island. The volcano, whose name means "Paramount," rises above the SE caldera rim of neighboring Batur volcano, and the northern and southern flanks extend to the coast. The summit area extends 1.5 km E-W, with the high point on the W and a steep-walled 800-m-wide crater on the E. The Pawon cone is located low on the SE flank. Only a few eruptions dating back to the early 19th century have been recorded in historical time. The 1963-64 eruption, one of the largest in the 20th century, produced voluminous ashfall along with devastating pyroclastic flows and lahars that caused extensive damage and many fatalities.

Aira, Kyushu (Japan)

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

JMA reported that there were two events and 10 explosions at Minamidake crater (at Aira Caldera’s Sakurajima volcano) during 2-9 April. Tephra was ejected as far as 1.1 km from the crater, and plumes rose as high as 3.4 km above the crater rim. An event at Showa Crater generated a plume that rose 1.3 km. An explosion at 0909 on 9 April at Minamidake crater ejected large boulders 1.3 km, and produced a plume that rose 1 km. 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.

Bezymianny, Central Kamchatka (Russia)

55.972°N, 160.595°E, Summit elev. 2882 m

KVERT reported that a thermal anomaly over Bezymianny was identified in satellite images during 29-30 March and 2-3 April. The Aviation Color Code remained at Yellow.

Geologic summary: Prior to its noted 1955-56 eruption, Bezymianny had been considered extinct. The modern volcano, much smaller in size than its massive neighbors Kamen and Kliuchevskoi, was formed about 4700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7000 years ago. Three periods of intensified activity have occurred during the past 3000 years. The latest period, which was preceded by a 1000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large horseshoe-shaped crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Cleveland, Chuginadak Island (USA)

52.825°N, 169.944°W, Summit elev. 1730 m

AVO reported that seismic and infrasound sensors recorded a small explosion at Cleveland at 0355 on 4 April. A subsequent satellite image indicated that hot material ejected from the event was deposited on the W flank, possibly reaching the coastline. A small ash cloud drifted SW at or below 4.6 km (15,000 ft) a.s.l. The Aviation Color Code was raised to Orange and the Volcano Alert Level was raised to Watch. Hours later, a small, short-duration seismic event coupled with satellite data suggested a small ash emission. The Alert level was lowered back to Yellow/Advisory on 6 April due to no further signs of activity.

Geologic summary: The 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. Joined to the rest of Chuginadak Island by a low isthmus, 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, 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.

Copahue, Central Chile-Argentina border

37.856°S, 71.183°W, Summit elev. 2953 m

According to ONEMI, OVDAS-SERNAGEOMIN reported that during 1-31 March there were 83 volcano-tectonic events recorded at Copahue, and 204 earthquakes indicting fluid movement. Tremor levels increased on 24 March, the same day as the phreatic explosion, though by the next day decreased to baseline levels. Webcams recorded gas plumes rising from El Agrio crater as high as 1 km. During an overflight on 3 April scientists observed the crater lake, and continuous white gas plumes rising almost 400 m. The Alert Level remained at Yellow (second highest level on a four-color scale); SERNAGEOMIN recommended no entry into a restricted area within 1 km of the crater. ONEMI maintained an Alert Level Yellow (the middle level on a three-color scale) for the municipality of Alto Biobío.

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.

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 4-10 April ash plumes from Dukono rose to altitudes of 1.5-2.1 km (5,000-7,000 ft) a.s.l. and drifted in multiple directions.

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.

Ebeko, Paramushir Island (Russia)

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

Based on observations by volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, explosions during 31 March-6 April generated ash plumes that rose as high as 2.7 km (8,900 ft) a.s.l. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geologic 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

INSIVUMEH reported that during 7-10 April explosions at Fuego generated ash plumes that rose as high as 1.1 km and drifted 10-15 km SW and S. Sometimes the explosions were accompanied by weak shock waves. Incandescent material was ejected as high as 200 m above the crater rim, and generated avalanches of material in the Seca (Santa Teresa, W), Cenizas (SSW), Las Lajas (SE), and Trinidad (S) ravines. During 9-10 April ash fell in areas downwind including in Santa Sofía (12 km SW), Morelia (9 km SW), Panimaché (8 km SW), Sangre de Cristo (8 km WSW), and San Pedro Yepocapa (8 km NW).

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.

Kilauea, Hawaiian Islands (USA)

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

During 4-10 April HVO reported that the lava lake continued to rise, fall, and spatter in Kilauea’s Overlook crater. Surface lava flows were active above Pulama pali. Webcams recorded spattering from a small lava pond in a pit on the W side of Pu'u 'O'o Crater. The lava flow from a vent on the SE part of the crater floor continued to expand through 6 April. A rockfall at 1028 on 6 April triggered an explosion in the lava lake, damaging the webcam power system on the crater rim.

Geologic 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.

Mayon, Luzon (Philippines)

13.257°N, 123.685°E, Summit elev. 2462 m

PHIVOLCS reported that during 4-10 April white steam plumes from Mayon drifted WNW, WSW, and SW. Crater incandescence was visible at night. The sulfur dioxide flux was 899 tonnes/day on 5 April. Tiltmeter data recorded deflation since 20 February despite short-term episodes of inflation at the lower and middle flanks. Precise leveling data showed deflation during 22-29 March relative to surveys conducted during 10-19 March. Overall ground deformation data suggested inflation compared to baseline levels. The Alert Level remained at 2 (on a 0-5 scale) and PHIVOLCS reminded residents to stay away from the 6-km-radius Permanent Danger Zone and the 7-km Extended Danger Zone on the SSW and ENE flanks.

Geologic summary: Beautifully symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the Philippines' most active volcano. The structurally simple edifice has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions 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. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

Pacaya, Guatemala

14.382°N, 90.601°W, Summit elev. 2569 m

INSIVUMEH reported that during 7-10 April Strombolian explosions at Pacaya’s Mackenney Crater ejected material as high as 40 m above the crater rim. Lava flows had traveled 250 m down the NW flank, 200 m down the W flank, and 150 m down the SW flank.

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.

Sabancaya, Peru

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

Observatorio Vulcanológico del Sur del IGP (OVS-IGP) and Observatorio Vulcanológico del INGEMMET (OVI) reported that explosive activity at Sabancaya was similar compared to the previous week; explosions averaged 15 per day during 2-8 April. Seismicity was dominated by long-period events, with signals indicating emissions. Gas-and-ash plumes rose as high as 3.2 km above the crater rim and drifted 30 km NE, SE, and S. Ashfall was reported in Achoma (25 km NE), Chivay (36 km NE), and Huanca. The MIROVA system detected three thermal anomalies. The report noted that the public should not to approach the crater within a 12-km radius.

Geologic 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.

Suwanosejima, Ryukyu Islands (Japan)

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

Based on JMA notices and satellite data, the Tokyo VAAC reported that during 4-6 and 9 April explosions at Suwanosejima produced plumes that rose 1.2-2.4 km (4,000-8,000 ft) a.s.l. and drifted N, NE, and E.

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 people live on the island.

Turrialba, Costa Rica

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

OVSICORI-UNA reported that events at Turrialba at 1230 on 5 April and 0609 on 9 April generated plumes that rose 500 and 300 m above the crater rim, and drifted S and W, respectively.

Geologic summary: Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive 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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