Active volcanoes in the world: April 24 – April 30, 2013
This week, two volcanoes had new activity, whereas ongoing activity was reported for 19 volcanoes. This report covers active volcanoes in the world recorded from April 24 – April 30, 2013 based on Smithsonian/USGS criteria.
New activity/unrest: | Antuco, Central Chile | Tungurahua, Ecuador
Ongoing activity: | Batu Tara, Komba Island (Indonesia) | Chirpoi, Kuril Islands (Russia) | Etna, Sicily (Italy) | Fuego, Guatemala | Gaua, Banks Islands (SW Pacific) | Kilauea, Hawaii (USA) | Kizimen, Eastern Kamchatka (Russia) | Manam, Northeast of New Guinea (SW Pacific) | Pacaya, Guatemala | Paluweh, Lesser Sunda Islands (Indonesia) | Popocatépetl, México | Rabaul, New Britain | Sakura-jima, Kyushu | Sangay, Ecuador | Santa María, Guatemala | Shiveluch, Central Kamchatka (Russia) | Soufrière Hills, Montserrat | Tolbachik, Central Kamchatka (Russia) | White Island, New Zealand
The Weekly Volcanic Activity Report is a cooperative project between the Smithsonian’s Global Volcanism Program and the US Geological Survey’s Volcano Hazards Program. Updated by 2300 UTC every Wednesday, notices of volcanic activity posted on these pages are preliminary and subject to change as events are studied in more detail. This is not a comprehensive list of all of Earth’s volcanoes erupting during the week, but rather a summary of activity at volcanoes that meet criteria discussed in detail in the “Criteria and Disclaimers” section. Carefully reviewed, detailed reports on various volcanoes are published monthly in the Bulletin of the Global Volcanism Network.
ANTUCO, Central Chile
37.406°S, 71.349°W; summit elev. 2979 m
The Buenos Aires VAAC reported that only gas and steam rose from Antuco on 20 April; although a pilot reported ash emissions, ash was not identified in satellite imagery or by web camera during clear skies.
Geologic summary: Antuco volcano, constructed to the NE of the Pleistocene Sierra Velluda stratovolcano, rises dramatically above the SW shore of Laguna de la Laja. Antuco has a complicated history beginning with construction of the basaltic-to-andesitic Sierra Veluda and Cerro Condor stratovolcanoes of Pliocene-Pleistocene age. Construction of the Antuco I volcano was followed by edifice failure at the beginning of the Holocene that produced a large debris avalanche which traveled down the Río Laja to the west and left a large 5-km-wide horseshoe-shaped caldera breached to the west. The steep-sided modern basaltic-to-andesitic cone of has grown 1000 m since then; flank fissures and cones have also been active. Moderate explosive eruptions were recorded in the 18th and 19th centuries from both summit and flank vents, and historical lava flows have traveled into the Río Laja drainage.
1.467°S, 78.442°W; summit elev. 5023 m
IG reported that during 24-26 April activity at Tungurahua was low. On 27 April seismic activity increased; an ash plume rose 2 km above the crater and drifted NW, causing ashfall in Juive (7 km NNW). During the morning on 28 April steam-and-ash plumes rose 1-4 km and drifted at least 100 km SW and W. Later that day several explosions produced ash plumes that rose as high as 3.5 km and drifted W. Ashfall was reported in Baños (8 km N), Chacauco (NW), Bilbao (8 km W), Cusúa (8 km NW), Juive, Pondoa (8 km N), and Pillate (8 km W). At 1830 a steam-and-ash plume rose 5 km, and drifted SW and then W. Another explosion ejected incandescent blocks that fell on the flanks 400 m below the crater. During breaks in cloud cover on 29 April dark gray emissions were observed drifting ESE. Ashfall was reported in El Manzano (8 km SW), Cahuají (8 km SW), Puela (8 km SW), Penipe (15 km SW), and Riobamba (30 km S). An explosion caused structures to vibrate. On 30 April explosions produced ash plumes that rose 1.5-2 km and drifted WSW.
Geologic summary: The steep-sided Tungurahua stratovolcano towers more than 3 km above its northern base. It sits ~140 km S of Quito, Ecuador’s capital city, and is one of Ecuador’s most active volcanoes. Historical eruptions have all originated from the summit crater. They have been accompanied by strong explosions and sometimes by pyroclastic flows and lava flows that reached populated areas at the volcano’s base. The last major eruption took place from 1916 to 1918, although minor activity continued until 1925. The latest eruption began in October 1999 and prompted temporary evacuation of the town of Baños on the N side of the volcano.
BATU TARA, Komba Island (Indonesia)
7.792°S, 123.579°E; summit elev. 748 m
Based on analyses of satellite imagery and wind data, the Darwin Volcanic Ash Advisory Centre (VAAC) reported that during 24-30 April ash plumes from Batu Tara rose to altitudes of 1.5-2.1 km (5,000-7,000 ft) a.s.l. and drifted 35-110 km W, WNW, and NW.
Geologic summary: The small isolated island of Batu Tara in the Flores Sea about 50 km north of Lembata (formerly Lomblen) Island contains a scarp on the eastern side similar to the Sciara del Fuoco of Italy’s Stromboli volcano. Vegetation covers the flanks of Batu Tara to within 50 m of the 748-m-high summit. Batu Tara lies north of the main volcanic arc and is noted for its potassic leucite-bearing basanitic and tephritic rocks. The first historical eruption from Batu Tara, during 1847-52, produced explosions and a lava flow.
CHIRPOI, Kuril Islands (Russia)
46.525°N, 150.875°E; summit elev. 742 m
SVERT reported that a weak thermal anomaly over Snow, a volcano of Chirpoi, was detected in satellite images on 24 and 26 April.
Geologic summary: Chirpoi, a small island lying between the larger islands of Simushir and Urup, contains a half dozen volcanic edifices constructed within an 8-9 km wide, partially submerged caldera. The southern rim of the caldera is exposed on nearby Brat Chirpoev Island. Two volcanoes on Chirpoi Island have been historically active. The symmetrical Cherny volcano, which forms the 691 m high point of the island, erupted twice during the 18th and 19th centuries. The youngest volcano, Snow, originated between 1770 and 1810. It is composed almost entirely of lava flows, many of which have reached the sea on the southern coast. No historical eruptions are known from 742-m-high Brat Chirpoev, but its youthful morphology suggests recent strombolian activity.
ETNA, Sicily (Italy)
37.734°N, 15.004°E; summit elev. 3330 m
Sezione di Catania – Osservatorio Etneo reported that the thirteenth lava-fountaining episode of 2013 began at Etna’s New Southeast Crater (NSEC) on 27 April. Activity increased on 21 April and was characterized by Strombolian explosions and frequent ash emissions. Eruptive activity and the volcanic tremor amplitude gradually increased in the evening of 26 April. Just after sunset on 27 April lava fountains rose 300-500 m, and lava flows from the SE and NE flanks of the NSEC cone and from the saddle between the two Southeast Crater (SEC) cones traveled S and N.
Geologic summary: Mount Etna, towering above Catania, Sicily’s second largest city, has one of the world’s longest documented records of historical volcanism, dating back to 1500 BC. Historical lava flows cover much of the surface of this massive basaltic stratovolcano, the highest and most voluminous in Italy. Two styles of eruptive activity typically occur at Etna. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more of the three prominent summit craters, the Central Crater, NE Crater, and SE Crater. Flank eruptions, typically with higher effusion rates, occur less frequently and originate from fissures that open progressively downward from near the summit. A period of more intense intermittent explosive eruptions from Etna’s summit craters began in 1995. The active volcano is monitored by the Instituto Nazionale di Geofisica e Volcanologia (INGV) in Catania.
14.473°N, 90.880°W; summit elev. 3763 m
INSIVUMEH reported that during 23-26 April explosions from Fuego generated ash plumes that rose 250-600 m above the crater and drifted at most 10 km W, SW, S, and SE. Incandescent material was ejected 100-200 m above the crater. In a special bulletin on 25 April INSIVUMEH noted that the energy of the explosions had increased, producing rumblings and shock waves that vibrated structures in Panimaché, Morelia, and Sangre de Cristo, as far as 10 km S and SW. A 300-m-long lava flow was active on the S flank in the Trinidad drainage. On 26 April a lava flow in the Taniluya drainage (SW) traveled as far as 400 m. On 28 April activity again increased and 700-m-long lava flows were active in the Taniluya and Ceniza drainages. Incandescent block avalanches reached vegetated areas. Cloud cover prevented observations of the crater. On 29 April explosions generated ash plumes that rose 550 m above the crater and drifted 10 km SSW. Lava flows remained active.
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 3,763-m-high Fuego and its twin volcano to the N, Acatenango. Construction of Meseta volcano continued until the late Pleistocene or early Holocene, after which growth of the modern Fuego volcano continued the southward migration of volcanism that began at Acatenango. Frequent vigorous historical eruptions have been recorded at Fuego since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows. The last major explosive eruption from Fuego took place in 1974, producing spectacular pyroclastic flows visible from Antigua.
GAUA, Banks Islands (SW Pacific)
14.27°S, 167.50°E; summit elev. 797 m
The Wellington VAAC reported that on 29 April a plume from Gaua was observed from an aircraft. Satellite imagery did not indicate ash.
Geologic summary: The roughly 20-km-diameter Gaua Island, also known as Santa Maria, consists of a basaltic-to-andesitic stratovolcano with an 6 x 9 km wide summit caldera. Small parasitic vents near the caldera rim fed Pleistocene lava flows that reached the coast on several sides of the island; several littoral cones were formed where these lava flows reached the sea. Quiet collapse that formed the roughly 700-m-deep caldera was followed by extensive ash eruptions. Construction of the historically active cone of Mount Garat (Gharat) and other small cinder cones in the SW part of the caldera has left a crescent-shaped caldera lake. The symmetrical, flat-topped Mount Garat cone is topped by three pit craters. The onset of eruptive activity from a vent high on the SE flank of Mount Garat in 1962 ended a long period of dormancy.
KILAUEA, Hawaii (USA)
19.421°N, 155.287°W; summit elev. 1222 m
During 24-30 April HVO reported that the circulating lava lake periodically rose and fell in the deep pit within Kilauea’s Halema’uma’u Crater. The plume from the vent continued to deposit variable amounts of ash, spatter, and Pele’s hair onto nearby areas.
At Pu’u ‘O’o Crater, glow emanated from three spatter cones, a small lava pond on the crater floor, and cracks in a recently emplaced lava flow on the crater floor. Small lava flows issued from the SW spatter cone on 24 April. On 28 April lava gushed from the N spatter cone for more than 2.5 hours, covering the N portion of the crater floor. A second flow was observed on 29 April. Peace Day activity, fed by lava tubes extending from Pu’u ‘O’o, consisted of lava flows active above the pali SE of Pu’u ‘O’o, on the pali, and on the coastal plain. Lava also entered the ocean at two or three locations spanning the National Park boundary.
Geologic summary: Kilauea, one of five coalescing volcanoes that comprise the island of Hawaii, is one of the world’s most active volcanoes. Eruptions at Kilauea originate primarily from the summit caldera or along one of the lengthy E and SW rift zones that extend from the caldera to the sea. About 90% of the surface of Kilauea is formed of lava flows less than about 1,100 years old; 70% of the volcano’s surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 sq km, destroying nearly 200 houses and adding new coastline to the island.
KIZIMEN, Eastern Kamchatka (Russia)
55.130°N, 160.32°E; summit elev. 2376 m
KVERT reported that during 19-26 April moderate seismic activity continued at Kizimen. Video and satellite data showed that lava continued to extrude from the summit, producing incandescence, strong gas-and-steam activity, and hot avalanches on the W and E flanks. Cloud-free satellite images detected a thermal anomaly over the volcano. The Aviation Color Code remained at Orange.
Geologic summary: Kizimen is an isolated, conical stratovolcano that is morphologically similar to Mount St. Helens prior to its 1980 eruption. The summit of Kizimen consists of overlapping lava domes, and blocky lava flows descend the flanks of the volcano, which is the westernmost of a volcanic chain north of Kronotsky volcano. The 2,376-m-high Kizimen was formed during four eruptive cycles beginning about 12,000 years ago and lasting 2,000-3,500 years. The largest eruptions took place about 10,000 and 8300-8400 years ago, and three periods of longterm lava-dome growth have occurred. The latest eruptive cycle began about 3,000 years ago with a large explosion and was followed by lava-dome growth lasting intermittently about 1,000 years. An explosive eruption about 1,100 years ago produced a lateral blast and created a 1.0 x 0.7 km wide crater breached to the NE, inside which a small lava dome (the fourth at Kizimen) has grown. A single explosive eruption, during 1927-28, has been recorded in historical time.
MANAM, Northeast of New Guinea (SW Pacific)
4.080°S, 145.037°E; summit elev. 1807 m
RVO reported that on 23 April dense white vapor plumes occasionally rose from Manam’s Southern Crater. During 25-28 April ash clouds rose from the new sub-terminal vent E of Southern Crater inside southeast valley. The ash clouds rose 600 m and drifted NW. Loud booming noises were heard each day; however, between 0700 and 1900 on 27 April the noises became frequent, louder, and explosive in nature, and were heard at Bogia, 25-30 km SSW of Manam on the N coast of the mainland. Strong explosions vibrated structures on the island.
Geologic summary: The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country’s most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical 1807-m-high basaltic-andesitic stratovolcano to its lower flanks. These “avalanche valleys,” regularly spaced 90 degrees apart, channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Two summit craters are present; both are active, although most historical eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE avalanche valley. Frequent historical eruptions, typically of mild-to-moderate scale, have been recorded at Manam since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.
14.381°N, 90.601°W; summit elev. 2552 m
INSIVUMEH reported that on 23 April fumarolic plumes from Pacaya’s MacKenney cone rose 100 m and drifted N. On 24 April tephra was ejected 25 m high by weak explosions. Incandescence from the crater was observed through the night, and explosions were detected the next day. Incandescence and explosions were again detected on 29 April.
Geologic summary: Eruptions from Pacaya, one of Guatemala’s most active volcanoes, are frequently visible from Guatemala City, the nation’s capital. Pacaya is a complex volcano constructed on the southern rim of the 14 x 16 Pleistocene Amatitlan caldera. A cluster of dacitic lava domes occupies the caldera floor. The Pacaya massif includes the Cerro Grande lava dome and a younger volcano to the SW. Collapse of Pacaya volcano about 1,100 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. During the past several decades, activity at Pacaya has consisted of frequent Strombolian eruptions with intermittent lava flow extrusion on the flanks of MacKenney cone, punctuated by occasional larger explosive eruptions.
PALUWEH, Lesser Sunda Islands (Indonesia)
8.32°S, 121.708°E; summit elev. 875 m
Based on analyses of satellite imagery and wind data, the Darwin VAAC reported that during 29-30 April ashplumes from Paluweh rose to altitudes of 2.1-3 km (7,000-10,000 ft) a.s.l. and drifted 35-110 km NW and W.
Geologic summary: Paluweh volcano, also known as Rokatenda, forms the 8-km-wide island of Paluweh N of the volcanic arc that cuts across Flores Island. Although the volcano rises about 3,000 m above the sea floor, its summit reaches only 875 m above sea level. The broad irregular summit region contains overlapping craters up to 900 m wide and several lava domes. Several flank vents occur along a NW-trending fissure. The largest historical eruption of Paluweh occurred in 1928, when a strong explosive eruption was accompanied by landslide-induced tsunamis and lava-dome emplacement.
19.023°N, 98.622°W; summit elev. 5426 m
CENAPRED reported that during 24-27 April seismicity at Popocatépetl indicated continuing gas-and-steam emissions that sometimes contained ash. Incandescence from the crater was often observed at night. Gas-and-steam plumes rose 1 km and drifted NE and ESE. On 24 April an explosion generated a steam-and-ash plume that rose 1.2 km above the crater and drifted W; incandescent tephra ejected from the crater landed 500 m away on the N flank. On 25 April a dense steam-and-gas plume rose 1.5 km and drifted W. The next day an explosion generated a gas-and-ash plume that rose 2 km. Atmospheric clouds made observations difficult. On 28 April gas-and-ash plumes rose 1.2 km and drifted NE, and on 29 April gas-and-ash plumes rose 1 km; cloud cover continued to impede observations. On 30 April an explosion generated an ash plume that rose 300 m and drifted E. Ejected incandescent tephra landed 800 m away on the NE flank. Gas-and-vapor plumes rose 500 m. The Alert Level remained at Yellow, Phase Two.
Geologic summary: Popocatépetl, whose name is the Aztec word for smoking mountain, towers to 5,426 m 70 km SE of Mexico City and is North America’s second-highest volcano. Frequent historical eruptions have been recorded since the beginning of the Spanish colonial era. A small eruption on 21 December 1994 ended five decades of quiescence. Since 1996 small lava domes have incrementally been constructed within the summit crater and destroyed by explosive eruptions. Intermittent small-to-moderate gas-and-ash eruptions have continued, occasionally producing ashfall in neighboring towns and villages.
RABAUL, New Britain
4.271°S, 152.203°E; summit elev. 688 m
RVO reported that during 24-28 April white vapor plumes sometimes containing ash rose at most 200 m from Rabaul caldera’s Tavurvur cone and drifted SE. Roaring and rumbling noises also continued but the intensity was low.
Geologic summary: The low-lying Rabaul caldera on the tip of the Gazelle Peninsula at the NE end of New Britain forms a broad sheltered harbor. The outer flanks of the 688-m-high asymmetrical pyroclastic shield volcano are formed by thick pyroclastic-flow deposits. The 8 x 14 km caldera is widely breached on the E, where its floor is flooded by Blanche Bay. Two major Holocene caldera-forming eruptions at Rabaul took place as recently as 3,500 and 1,400 years ago. Three small stratovolcanoes lie outside the northern and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and western caldera walls. Several of these, including Vulcan cone, which was formed during a large eruption in 1878, have produced major explosive activity during historical time. A powerful explosive eruption in 1994 occurred simultaneously from Vulcan and Tavurvur volcanoes and forced the temporary abandonment of Rabaul city.
31.585°N, 130.657°E; summit elev. 1117 m
JMA reported that during 22-25 April four explosions from Sakura-jima’s Showa Crater ejected tephra at most 1.3 km from the crater. Crater incandescence was occasionally detected at night. Based on a pilot report, the TokyoVAAC reported that ash plumes drifted NE and SE at altitudes of 2.7-3 km (9,000-10,000 ft) a.s.l. during 24-25 April. Explosions on 26 and during 28-29 April produced plumes that rose to altitudes of 1.8-2.1 km (6,000-7,000 ft) a.s.l. and drifted SE and NE.
Geologic summary: Sakura-jima, one of Japan’s most active volcanoes, is a post-caldera cone of the Aira calderaat the northern half of Kagoshima Bay. Eruption of the voluminous Ito pyroclastic flow was associated with the formation of the 17 x 23-km-wide Aira caldera about 22,000 years ago. The construction of Sakura-jima began about 13,000 years ago and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kita-dake summit cone ended about 4,850 years ago, after which eruptions took place at Minami-dake. Frequent historical eruptions, recorded since the 8th century, have depositedash 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.
2.002°S, 78.341°W; summit elev. 5230 m
Based on analyses of satellite imagery and a SIGMET aviation notice, the Washington VAAC reported that on 26 April two brief ash emissions from Sangay drifted SW and dissipated within 20 km. A thermal anomaly was visible in infrared satellite images.
Geologic summary: The isolated Sangay volcano, located E of the Andean crest, is the southernmost of Ecuador’s volcanoes, and its most active. It has been in frequent eruption for the past several centuries. The steep-sided, 5,230-m-high glacier-covered volcano grew within horseshoe-shaped calderas of two previous edifices, which were destroyed by collapse to the E, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. Sangay towers above the tropical jungle on the E side; on the other sides flat plains of ash from the volcano have been sculpted by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of an historical eruption was in 1628. More or less continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The more or less constant eruptive activity has caused frequent changes to the morphology of the summit crater complex.
SANTA MARIA, Guatemala
14.756°N, 91.552°W; summit elev. 3772 m
INSIVUMEH reported that on 23 April two explosions were accompanied by white plumes that rose 800 m above Santa María’s Santiaguito lava-dome complex and drifted SW. The next day explosions produced ash plumes that rose 600 m and drifted SSW. Avalanches were generated by active lava flows on the SW flank. Explosions were heard on 25 April but cloud cover prevented visual confirmation. On 28 April a small explosion generated a white plume that rose 500 m and drifted NE. Explosions on 29 April produced ash plumes that rose 800 m and drifted SE, causing ashfall in San Jose, La Quina, and areas near Calahuache.
Geologic summary: Symmetrical, forest-covered Santa María volcano is one of a chain of large stratovolcanoesthat rises dramatically above the Pacific coastal plain of Guatemala. The stratovolcano has a sharp-topped, conical profile that is cut on the SW flank by a large, 1-km-wide crater, which formed during a catastrophic eruption in 1902 and extends from just below the summit to the lower flank. The renowned Plinian eruption of 1902 followed a long repose period and devastated much of SW Guatemala. The large dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four westward-younging vents, accompanied by almost continuous minor explosions and periodiclava extrusion, larger explosions, pyroclastic flows, and lahars.
SHIVELUCH, Central Kamchatka (Russia)
56.653°N, 161.360°E; summit elev. 3283 m
Based on visual observations and analyses of satellite data, KVERT reported that during 19-26 April a viscous lavaflow effused on the NW flank of Shiveluch’s lava dome, accompanied by hot avalanches, incandescence, andfumarolic activity. Satellite imagery showed a daily thermal anomaly on the lava dome. The Aviation Color Coderemained at Orange.
Geologic summary: The high, isolated massif of Shiveluch volcano (also spelled Sheveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group and forms one of Kamchatka’s largest and most active volcanoes. The currently active Molodoy Shiveluch lava-dome complex was constructed during the Holocene within a large breached caldera formed by collapse of the massive late-Pleistocene Strary Shiveluch volcano. At least 60 large eruptions of Shiveluch have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Frequent collapses of lava-dome complexes, most recently in 1964, have produced large debris avalanches whose deposits cover much of the floor of the breached caldera. Intermittent explosive eruptions began in the 1990s from a new lava dome that began growing in 1980. The largest historical eruptions from Shiveluch occurred in 1854 and 1964.
SOUFRIERE HILLS, Montserrat
16.72°N, 62.18°W; summit elev. 915 m
MVO reported that during 19-26 April activity at the Soufrière Hills lava dome was at a low level. There had been no good views of the lava dome for over a month, but reports from helicopter pilots suggested that the most of the large slab that was on the E side of the lava dome was gone, likely removed during the pyroclastic flow on 28 March. The Hazard Level remained at 2 (on a scale of 1-5).
Geologic summary: The complex dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. English’s Crater, a 1-km-wide crater breached widely to the E, was formed during an eruption about 4,000 years ago in which the summit collapsed, producing a large submarine debris avalanche. Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits at Soufrière Hills. Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but with the exception of a 17th-century eruption that produced the Castle Peak lava dome, no historical eruptions were recorded on Montserrat until 1995. Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth andpyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption.
TOLBACHIK, Central Kamchatka (Russia)
55.830°N, 160.330°E; summit elev. 3682 m
KVERT reported that the S fissure along the W side of Tolbachinsky Dol, a lava plateau on the SW side of Tolbachik, continued to produce very fluid lava flows during 19-26 April that traveled to the W, S, and E sides of the plateau. Cinder cones continued to grow along the S fissure. Gas-and-ash plumes rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted in multiple directions. A large thermal anomaly on the N part of Tolbachinsky Dol was visible daily in satellite imagery. The Aviation Color Code remained at Orange.
Geologic summary: The massive Tolbachik basaltic volcano is located at the southern end of the dominantlyandesitic Kliuchevskaya volcano group. The Tolbachik massif is composed of two overlapping, but morphologically dissimilar volcanoes. The flat-topped Plosky Tolbachik shield volcano with its nested Holocene Hawaiian-typecalderas up to 3 km in diameter is located east of the older and higher sharp-topped Ostry Tolbachik stratovolcano. The summit caldera at Plosky Tolbachik was formed in association with major lava effusion about 6500 years ago and simultaneously with a major southward-directed sector collapse of Ostry Tolbachik volcano. Lengthy rift zones extending NE and SSW of the volcano have erupted voluminous basaltic lava flows during the Holocene, with activity during the past two thousand years being confined to the narrow axial zone of the rifts. The 1975-76 eruption originating from the SSW-flank fissure system and the summit was the largest historical basaltic eruption in Kamchatka.
WHITE ISLAND, New Zealand
37.52°S, 177.18°E; summit elev. 321 m
On 29 April GeoNet Data Centre reported that activity at White Island remained at a persistently low level, characterized by tremor and degassing. No mud or ash eruptions had been observed since early April. A volcanologist visited the island the previous week and observed that increased rainfall had caused the two lakes to merge together into one larger lake. The temperature of the lake was 62 degrees Celsius and the lava-dometemperature was 200 degrees. The lower level of activity prompted GeoNet to reduce the Aviation Colour Code to Green (indicating no active eruption). The Volcano Alert Level remained at 1 (on a scale of 0-5).
Geologic summary: The uninhabited 2 x 2.4 km White Island, one of New Zealand’s most active volcanoes, is the emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The 321-m-high island consists of two overlapping stratovolcanoes; the summit crater appears to be breached to the SE because the shoreline corresponds to the level of several notches in the SE crater wall. Throughout the shorthistorical period beginning in 1826 the volcano has had long periods of continuous hydrothermal activity and steam release, punctuated by small-to-medium eruptions. Its activity also forms a prominent part of Maori legends. The most recent eruptive episode, which began on 7 March 2000, included the largest eruption at White Island in the past 20 years on 27 July.