The Weekly Volcanic Activity Report: April 25 - May 1, 2018

The Weekly Volcanic Activity Report: April 25 - May 1, 2018

New activity/unrest was reported for 9 volcanoes between April 18 and 24, 2018. During the same period, ongoing activity was reported for 14 volcanoes.

New activity/unrest: Ibu, Halmahera (Indonesia) | Karymsky, Eastern Kamchatka (Russia) | Kilauea, Hawaiian Islands (USA) | Kirishimayama, Kyushu (Japan) | Kusatsu-Shiranesan, Honshu (Japan) | Marapi, Indonesia | Piton de la Fournaise, Reunion Island (France) | San Cristobal, Nicaragua | Semeru, Eastern Java (Indonesia).

Ongoing activity: Agung, Bali (Indonesia) | Aira, Kyushu (Japan) | Dukono, Halmahera (Indonesia) | Ebeko, Paramushir Island (Russia) | Kikai, Japan | Pacaya, Guatemala | Popocatepetl, Mexico | Reventador, Ecuador | Sabancaya, Peru | Sheveluch, Central Kamchatka (Russia) | Stromboli, Aeolian Islands (Italy) | Suwanosejima, Ryukyu Islands (Japan) | Turrialba, Costa Rica | Yasur, Vanuatu.

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

Ibu, Halmahera (Indonesia)

1.488°N, 127.63°E, Summit elev. 1325 m

PVMBG reported that at 1822 on 30 April an eruption at Ibu generated a dark gray ash plume that rose at least 500 m above the crater rim and drifted E. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to stay at least 2 km away from the active crater, and 3.5 km away on the N side.

Geologic summary: The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, contained several small crater lakes through much of historical time. The outer crater, 1.2 km wide, is breached on the north side, creating a steep-walled valley. A large parasitic cone is located ENE of the summit. A smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. Only a few eruptions have been recorded in historical time, the first a small explosive eruption from the summit crater in 1911. An eruption producing a lava dome that eventually covered much of the floor of the inner summit crater began in December 1998.

Karymsky, Eastern Kamchatka (Russia)

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

On 26 April KVERT reported that the last explosive event at Karymsky occurred on 27 January, and the last thermal anomaly was detected on 26 March; activity remained at a low level. The Aviation Color Code was lowered to Green (the lowest level on a four-color scale). Explosive activity was identified in satellite images beginning at 1825 on 28 April, prompting KVERT to raise the Alert Level to Orange. Ash plumes rose as high as 5.5 km (18,000 ft) a.s.l. and drifted 150 km NE.

Geologic summary: Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Kilauea, Hawaiian Islands (USA)

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

During 25 April-1 May HVO reported that the lava lake continued to rise, fall, and spatter in Kilauea’s Overlook crater. The lake level was high enough to produce lava flows onto the Halema'uma'u crater floor through 27 April, but afterwards fell to about 15-16 m below the new elevated rim. The lake level rose again, to just below the rim of the Overlook crater vent. Since 21 April about 2/3 of the crater floor had been covered by new lava flows.

Episode 61g lava flows were active above Pulama pali, within 2 km of the active vent. A marked increase in seismicity and ground deformation at Pu'u 'O'o Crater was detected just after 1400 on 30 April, following weeks of uplift and increasing lava levels within the cone. Within a few minutes a webcam on the crater rim recorded the first of two crater floor collapses; the second collapse began at 1520 and lasted about an hour. Thought poor weather conditions inhibited views at times, a webcam recorded what were likely small explosions from the W side of the crater as the floor collapsed. At 1800 seismicity remained elevated, though ground deformation had significantly slowed. A large amount of red ash was produced from the collapses, and deposited around the crater as well as in areas up-rift as far as Mauna Ulu.

Following the collapses of Pu'u 'O'o’s crater floor, seismicity and deformation increased along a large section of the East Rift Zone, in an area 9-16 km down-rift (with seismicity occurring as far E as highway 130), indicating an intrusion of magma. By 0830 on 1 May activity had significantly decreased. During an overflight that day a new, nearly continuous, 1-km-long crack was found on the W (up-rift) side of Pu'u 'O'o. The crack was steaming, and aligned in a segment with small pads of newly-erupted lava and spatter. Thermal images of Pu'u 'O'o Crater suggested that smaller drops of the crater floor likely continued on 1 May.

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.

Kirishimayama, Kyushu (Japan)

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

JMA reported that a very small explosion at Iwo-yama (also called Ioyama, NW flank of Karakuni-dake), a stratovolcano of the Kirishimayama volcano group, occurred at 1815 on 26 April and produced a milky white plume that rose over 200 m. The event continued until around 1826. The event occurred from a fumarole in the vicinity of the highway, on the W side of Iwo-yama, first observed on 20 April. During a field survey on 30 April observers noted muddy water flowing as far as 500 m W. 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.

Kusatsu-Shiranesan, Honshu (Japan)

36.618°N, 138.528°E, Summit elev. 2165 m

JMA reported that on 21 April the number of volcanic earthquakes at Yugama crater (Kusatsu-Shiranesan complex) increased and deformation was also recorded. The Alert Level for the crater area was raised to 2 (on a 5-level scale) the next day. Deformation slowed on 23 April. Seismicity decreased on 23 April though continued to be somewhat elevated, and low-frequency events were recorded on 24 April. No surficial changes were noted during an overflight on 26 April.

Geologic summary: The Kusatsu-Shiranesan complex, located immediately north of Asama volcano, consists of a series of overlapping pyroclastic cones and three crater lakes. The andesitic-to-dacitic volcano was formed in three eruptive stages beginning in the early to mid-Pleistocene. The Pleistocene Oshi pyroclastic flow produced extensive welded tuffs and non-welded pumice that covers much of the E, S, and SW flanks. The latest eruptive stage began about 14,000 years ago. Historical eruptions have consisted of phreatic explosions from the acidic crater lakes or their margins. Fumaroles and hot springs that dot the flanks have strongly acidified many rivers draining from the volcano. The crater was the site of active sulfur mining for many years during the 19th and 20th centuries.

Marapi, Indonesia

0.38°S, 100.474°E, Summit elev. 2885 m

On 27 April a phreatic eruption at Marapi produced an ash plumes that rose 300 m above the crater rim. The Alert Level remained at 2 (on a scale of 1-4). Residents and visitors were advised not to enter an area within 3 km of the summit.

Geologic summary: Gunung Marapi, not to be confused with the better-known Merapi volcano on Java, is Sumatra's most active volcano. This massive complex stratovolcano rises 2000 m above the Bukittinggi plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide Bancah caldera. The summit craters are located along an ENE-WSW line, with volcanism migrating to the west. More than 50 eruptions, typically consisting of small-to-moderate explosive activity, have been recorded since the end of the 18th century; no lava flows outside the summit craters have been reported in historical time.

Piton de la Fournaise, Reunion Island (France)

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

OVPF reported that seismicity at Piton de la Fournaise increased on 21 April, and then significantly on 23 April. A seismic crisis which began at 2015 on 27 April was accompanied by rapid deformation, indicating magma migrating towards the surface. The onset of tremor at 2350 heralded the beginning of the eruption, though the first visual confirmation of the eruption was recorded by the webcams at 0015 on 28 April.

The eruption took place from fissures at Rivals Crater, and the SW flank of Dolomieu crater. During an overflight around 0830, scientists noted that four fissures had opened, one of which intersected the crater. Lava fountains less than 30 m high rose from the entire length of the fourth fissure, which was 300 m long and at a lower elevation that Rival Crater. Several small lava flows formed a larger flow which traveled 200-300 m S towards the Enclos Fouqué. Tremor steadily decreased throughout the day, and by the end of the day the lava flow had slowed in an area around 300 m away from the rampart. During 29-30 April tremor levels were relatively stable, with a few fluctuations related to morphological changes at the eruptive site such as cone building. During an overflight around 1020 on 30 April scientists observed three active vents (S of Rival Crater). The third vent, in a 5-m-high cone, was mostly closed over, though it continued to produced lava flows. The middle and most active cone was about 30-40 m long and 10-15 m high, and had a vent with a lava lake. Large bubbles of lava rose from the lake and exploded into lava fountains. Lava fountains from the northernmost vent rose no more than 15 m high. Lava flows had traveled 150 m and 1.2 km; the longer lava flow had reached the S rampart and traveled an additional 400 m E along it.

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.

San Cristobal, Nicaragua

12.702°N, 87.004°W, Summit elev. 1745 m

INETER reported that at 1320 on 22 April a small explosion at San Cristóbal generated a gas-and-ash plume that rose 800 m and drifted SW, causing ashfall in the La Bolsa region and Hacienda Las Rojas.

Geologic summary: The San Cristóbal volcanic complex, consisting of five principal volcanic edifices, forms the NW end of the Marrabios Range. The symmetrical 1745-m-high youngest cone, named San Cristóbal (also known as El Viejo), is Nicaragua's highest volcano and is capped by a 500 x 600 m wide crater. El Chonco, with several flank lava domes, is located 4 km W of San Cristóbal; it and the eroded Moyotepe volcano, 4 km NE of San Cristóbal, are of Pleistocene age. Volcán Casita, containing an elongated summit crater, lies immediately east of San Cristóbal and was the site of a catastrophic landslide and lahar in 1998. The Plio-Pleistocene La Pelona caldera is located at the eastern end of the complex. Historical eruptions from San Cristóbal, consisting of small-to-moderate explosive activity, have been reported since the 16th century. Some other 16th-century eruptions attributed to Casita volcano are uncertain and may pertain to other Marrabios Range volcanoes.

Semeru, Eastern Java (Indonesia)

8.108°S, 112.922°E, Summit elev. 3657 m

Based on analysis of satellite images, the Darwin VAAC reported that on April a short-lived, discreet eruption at Semeru generated an ash plume that rose to an altitude of 3.4 km (11,000 ft) a.s.l. and drifted NW.

Geologic summary: Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.

Ongoing activity

Agung, Bali (Indonesia)

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

PVMBG reported that at 2245 on 30 April an event at Agung generated an ash plume that rose 1.5 km above the crater rim and drifted SW. Seismicity was dominated by low-frequency earthquakes related to gas-and-steam emissions. 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 nine events and 30 explosions at Minamidake crater (at Aira Caldera’s Sakurajima volcano) during 20 April-1 May. Tephra was ejected as far as 1.3 km from the crater, and ash plumes rose as high as 3.3 km above the crater rim. Crater incandescence was visible at night on 20, 23, 26, and 30 April. 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.

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 25 April-1 May ash plumes from Dukono rose to altitudes of 1.5-2.1 km (5,000-7,000 ft) a.s.l. and drifted NE, E, and SE.

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

Volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, observed explosions during 21 and 25 April that sent ash plumes as high as 2.5 km (8,200 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.

Kikai, Japan

30.793°N, 130.305°E, Summit elev. 704 m

JMA reported that the number of volcanic earthquakes at Satsuma Iwo-jima, a subaerial part of Kikai’s NW caldera rim, was low during 20-26 April. White plumes rose as high as 700 m above the Iwo-dake lava dome; incandescence from the crater had not been visible since 12 April. During field surveys on 25 and 26 April observers noted a slight expansion of a thermally anomalous area compared to 24-25 March observations, and a decrease in sulfur dioxide flux from 600 tons/day on 24 March to 300 tons/day. The Alert Level was reduced to 1 (on a 5-level scale) on 27 April.

Geologic summary: Kikai is a mostly submerged, 19-km-wide caldera near the northern end of the Ryukyu Islands south of Kyushu. Kikai was the source of one of the world's largest Holocene eruptions about 6300 years ago. Rhyolitic pyroclastic flows traveled across the sea for a total distance of 100 km to southern Kyushu, and ashfall reached the northern Japanese island of Hokkaido. The eruption devastated southern and central Kyushu, which remained uninhabited for several centuries. Post-caldera eruptions formed Iodake lava dome and Inamuradake scoria cone, as well as submarine lava domes. Historical eruptions have occurred in the 20th century at or near Satsuma-Iojima (also known as Tokara-Iojima), a small 3 x 6 km island forming part of the NW caldera rim. Showa-Iojima lava dome (also known as Iojima-Shinto), a small island 2 km east of Tokara-Iojima, was formed during submarine eruptions in 1934 and 1935. Mild-to-moderate explosive eruptions have occurred during the past few decades from Iodake, a rhyolitic lava dome at the eastern end of Tokara-Iojima.

Pacaya, Guatemala

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

INSIVUMEH and CONRED reported that during 27-28 April seismicity at Pacaya had increased, and moderate-to-strong explosions ejected material as high as 150 m above the crater rim. Lava originating from the 2010 fissure traveled about 500 m NW, towards Cerro Chino. The report noted that ejected material has filled the crater.

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.

Popocatepetl, Mexico

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

CENAPRED reported that each day during 25 April-1 May there were 63-114 steam and gas emissions from Popocatépetl, often containing ash. Incandescence from the crater was visible at night. As many as five explosions per day were recorded during 25-29 April, with resulting eruption plumes rising around 1 km above the crater rim. The Alert Level remained at Yellow, Phase Two.

Geologic 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 24 April-1 May IG reported a high level of seismic activity including explosions, long-period earthquakes, harmonic tremor, and signals indicating emissions at Reventador. Steam, gas, and ash plumes sometimes rose higher than 1 km above the crater rim and drifted NE, NW, and W. On 27 April incandescent blocks rolled as far as 800 m down the flanks, and a small pyroclastic flow traveled down the E flank.

Geologic 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

Observatorio Vulcanológico del Sur del IGP (OVS-IGP) and Observatorio Vulcanológico del INGEMMET (OVI) reported that explosive activity at Sabancaya was similar to the previous week; explosions averaged 22 per day during 23-29 April. Seismicity was dominated by long-period events and signals indicating emissions. Gas-and-ash plumes rose as high as 2 km above the crater rim and drifted 30 km NE and SE. 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.

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 21 and 23-25 April. 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 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 that on 24 April an intense explosive sequence occurred at vents on Stromboli’s south-central crater terrace area. The first explosion, recorded at 1105, ejected an abundant amount of ash, incandescent material, and large blocks to a height of 250 m that fell onto the summit area and along the Sciara del Fuoco. An explosive event at 1106 was characterized by modest lava fountaining. The last event, recorded at 1110, ejected pyroclastic material, though it was less intense than the first. An ash plume from the sequence quickly dispersed SE.

Geologic 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

Based on JMA notices and satellite data, the Tokyo VAAC reported an explosion at Suwanosejima on 24 April, and that events during 27-29 April produced plumes that rose 1.2-2.1 km (4,000-7,000 ft) a.s.l. and drifted in multiple directions.

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 an event at Turrialba at 0700 on 26 April generated a small ash plume that rose 300 m above the crater rim and drifted W.

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.

Yasur, Vanuatu

19.532°S, 169.447°E, Summit elev. 361 m

On 25 April the Vanuatu Meteorology and Geo-hazards Department (VMGD) reported that ongoing explosive activity at Yasur was confined to the crater. The Alert Level remained at 2 (on a scale of 0-4). VGO reminded residents and tourists that hazardous areas were near and around the volcanic crater, within a 395-m-radius permanent exclusion zone, and that volcanic ash and gas could reach areas impacted by trade winds.

Geologic 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. The active cone 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.

Source: GVP

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