New activity/unrest was reported for 6 volcanoes between April 5 and 11, 2017. During the same period, ongoing activity was reported for 18 volcanoes.
New activity/unrest: Aira, Kyushu (Japan) | Banda Api, Indonesia | Cerro Azul, Isla Isabela (Ecuador) | Dempo, Indonesia | Ibu, Halmahera (Indonesia) | Kambalny, Southern Kamchatka (Russia).
Ongoing activity: Bagana, Bougainville (Papua New Guinea) | Bezymianny, Central Kamchatka (Russia) | Bogoslof, Fox Islands (USA) | Chirinkotan, Kuril Islands (Russia) | Cleveland, Chuginadak Island (USA) | Colima, Mexico | Dukono, Halmahera (Indonesia) | Ebeko, Paramushir Island (Russia) | Etna, Sicily (Italy) | Fuego, Guatemala | Kilauea, Hawaiian Islands (USA) | Klyuchevskoy, Central Kamchatka (Russia) | Nevado del Ruiz, Colombia | Nevados de Chillan, Chile | Pacaya, Guatemala | Sabancaya, Peru | Sheveluch, Central Kamchatka (Russia) | Sinabung, Indonesia.
Aira, Kyushu (Japan)
31.593°N, 130.657°E, Elevation 1117 m
JMA reported that an explosion from the Minamidake summit crater (at Aira Caldera’s Sakurajima volcano) at 1004 on 4 April generated an ash plume that rose 1.2 km above the crater rim. During field work later that day, scientists observed ashfall in Sakurajima Koike-cho in Kagoshima (3 km NW). The Alert Level remained at 3 (on a 5-level scale).
Geological summary: The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan's most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the Aira caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim of Aira caldera and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4850 years ago, after which eruptions took place at Minamidake. Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu's largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.
Banda Api, Indonesia
4.523°S, 129.881°E, Elevation 596 m
PVMBG reported that seismicity at Banda Api had been increasing since the beginning of March, though during 1-4 April seismic patterns were similar to those recorded before an eruption in 1988. The Alert Level was raised to 2 (on a scale of 1-4); visitors and residents were warned not to approach Banda Api within a 1-km radius of the summit area.
Geological summary: The small island volcano of Banda Api is the NE-most volcano in the Sunda-Banda arc and has a long period of historical observation because of its key location in the Portuguese and Dutch spice trade. The basaltic-to-rhyodacitic volcano is located in the SW corner of a 7-km-wide mostly submerged caldera that comprises the northernmost of a chain of volcanic islands in the Banda Sea. At least two episodes of caldera formation are thought to have occurred, with the arcuate islands of Lonthor and Neira considered to be remnants of the pre-caldera volcanoes. A conical peak rises to about 600 m at the center of the 3-km-wide Banda Api island. Historical eruptions have been recorded since 1586, mostly consisting of Strombolian eruptions from the summit crater, but larger explosive eruptions have occurred and occasional lava flows have reached the coast.
Cerro Azul, Isla Isabela (Ecuador)
0.92°S, 91.408°W, Elevation 1640 m
IG reported that deformation data showed continued inflation after 20 March, indicating that the volume of the magma intrusion below Cerro Azul's SSE flank had increased. Seismicity decreased after 25 March possibly signifying a halt in the intrusion.
Geological summary: Located at the SW tip of the J-shaped Isabela Island, Cerro Azul contains a steep-walled 4 x 5 km nested summit caldera complex that is one of the smallest diameter, but at 650 m one of the deepest in the Galápagos Islands. The 1640-m-high shield volcano is the second highest of the archipelago. A conspicuous bench occupies the SW and west sides of the caldera, which formed during several episodes of collapse. Youthful lava flows cover much of the caldera floor, which has also contained ephemeral lakes. A prominent tuff cone located at the ENE side of the caldera is evidence of episodic hydrovolcanism. Numerous spatter cones dot the western flanks. Fresh-looking lava flows, many erupted from circumferential fissures, descend the NE and NW flanks. Historical eruptions date back only to 1932, but Cerro Azul has been one of the most active Galápagos volcanoes since that time. Solfataric activity continues within the caldera.
4.03°S, 103.13°E, Elevation 3173 m
Observers at the PVMBG Dempo observation post reported that during January and February no plumes rose from Dempo's crater, and during 1 March-4 April diffuse white plumes rose no higher than 50 m above the crater. Seismicity increased from 21 March to 4 April. The Alert Level was raised to 2 (on a scale from 1-4) on 5 April. Visitors and residents were advised not to approach the craters within 3 km.
Geological summary: Dempo is a prominent 3173-m-high stratovolcano that rises above the Pasumah Plain of SE Sumatra. The andesitic Dempo volcanic complex has two main peaks, Gunung Dempo and Gunung Marapi, constructed near the SE rim of a 3 x 5 km caldera breached to the north. The one called Dempo is slightly lower, with an elevation of 3049 m and lies at the SE end of the summit complex. The taller Marapi cone, with a summit elevation 3173 m, was constructed within a crater cutting the older Gunung Dempo edifice. Remnants of 7 craters are found at or near the summit of the complex, with volcanism migrating to the WNW with time. The large, 800 x 1100 m wide historically active summit crater cuts the NW side of Gunung Marapi (not to be confused with Marapi volcano 500 km to the NW in Sumatra) and contains a 400-m-wide lake located at the far NW end of the crater complex. Historical eruptions have been restricted to small-to-moderate explosive activity that produced ashfall near the volcano.
Ibu, Halmahera (Indonesia)
1.488°N, 127.63°E, Elevation 1325 m
Based on ground observations, PVMBG reported that during 7-8 April ash plumes from Ibu rose to an altitude of 1.7 km (5,500 ft) a.s.l. and drifted N. During 10-11 April ash plumes rose to altitudes of 1.5-1.6 km (4,900-5,200 ft) a.s.l. and drifted S.
Geological 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.
Kambalny, Southern Kamchatka (Russia)
51.306°N, 156.875°E, Elevation 2116 m
Based on satellite data, KVERT reported that Kambalny was quiet on 1 April. Explosions on 2 April generated ash plumes that rose to an altitude of 7 km (23,000 ft) a.s.l., and then minor ash emissions occurred at least through 6 April. Ash plumes drifted 200 km E and SE during 2-4 April, and a thermal anomaly was identified in satellite images during 3-4 April. The Aviation Color Code remained at Orange.
Geological summary: The southernmost major stratovolcano on the Kamchatka peninsula, 2116-m-high Kambalny has a summit crater that is breached to the SE. Five Holocene cinder cones on the W and SE flanks have produced fresh-looking lava flows. Beginning about 6300 radiocarbon years ago, a series of major collapses of the edifice produced at least three debris-avalanche deposits. The last major eruption took place about 600 years ago, although younger tephra layers have been found, and an eruption was reported in 1767. Active fumarolic areas are found on the flanks of the volcano, which is located south of the massive Pauzhetka volcano-tectonic depression.
Bagana, Bougainville (Papua New Guinea)
6.137°S, 155.196°E, Elevation 1855 m
Based on analyses of satellite imagery and wind model data, the Darwin VAAC reported that during 6-9 April ash plumes from Bagana rose to an altitude of 2.1 km (7,000 ft) a.s.l. and drifted NE, E, S, and W.
Geological summary: Bagana volcano, occupying a remote portion of central Bougainville Island, is one of Melanesia's youngest and most active volcanoes. This massive symmetrical cone was largely constructed by an accumulation of viscous andesitic lava flows. The entire edifice could have been constructed in about 300 years at its present rate of lava production. Eruptive activity is frequent and characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although explosive activity occasionally producing pyroclastic flows also occurs. Lava flows form dramatic, freshly preserved tongue-shaped lobes up to 50 m thick with prominent levees that descend the flanks on all sides.
Bezymianny, Central Kamchatka (Russia)
55.972°N, 160.595°E, Elevation 2882 m
KVERT reported that during 1-6 April lava continued to advance down the NW flank of Bezymianny's lava dome. A thermal anomaly was identified in satellite images daily. The Aviation Color Code remained at Orange.
Geological 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.
Bogoslof, Fox Islands (USA)
53.93°N, 168.03°W, Elevation 150 m
On 5 April AVO reported that the Aviation Color Code for Bogoslof was lowered to Yellow and the Volcano Alert Level was lowered to Advisory based on the absence of detected activity at the volcano for the past three weeks; the last large explosion occurred on 8 March. No significant volcanic activity was detected in seismic, infrasound, or satellite data during 6-11 April.
Geological summary: Bogoslof is the emergent summit of a submarine volcano that lies 40 km north of the main Aleutian arc. It rises 1500 m above the Bering Sea floor. Repeated construction and destruction of lava domes at different locations during historical time has greatly modified the appearance of this "Jack-in-the-Box" volcano and has introduced a confusing nomenclature applied during frequent visits of exploring expeditions. The present triangular-shaped, 0.75 x 2 km island consists of remnants of lava domes emplaced from 1796 to 1992. Castle Rock (Old Bogoslof) is a steep-sided pinnacle that is a remnant of a spine from the 1796 eruption. Fire Island (New Bogoslof), a small island located about 600 m NW of Bogoslof Island, is a remnant of a lava dome that was formed in 1883.
Chirinkotan, Kuril Islands (Russia)
48.98°N, 153.48°E, Elevation 724 m
Based on Tokyo VAAC data, SVERT reported that on 7 April an ash plume from Chirinkotan rose to an altitude of 5 km (16,400 ft) a.s.l. and drifted NE. The Aviation Color Code remained at Yellow (on a four-color scale).
Geological summary: The small, mostly unvegetated 3-km-wide island of Chirinkotan occupies the far end of an E-W-trending volcanic chain that extends nearly 50 km west of the central part of the main Kuril Islands arc. Chirinkotan is the emergent summit of a volcano that rises 3000 m from the floor of the Kuril Basin. A small 1-km-wide caldera about 300-400 m deep is open to the SE. Lava flows from a cone within the breached crater reached the north shore of the island. Historical eruptions have been recorded at Chirinkotan since the 18th century. Fresh lava flows also descended the SE flank of Chirinkotan during an eruption in the 1880s that was observed by the English fur trader Captain Snow.
Cleveland, Chuginadak Island (USA)
52.825°N, 169.944°W, Elevation 1730 m
AVO reported that no significant volcanic activity at Cleveland was detected in seismic, infrasound, or satellite data since an explosion occurred on 24 March. The Aviation Color Code was lowered to Yellow and the Volcano Alert Level was lowered to Advisory on 5 April.
Geological summary: 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. Cleveland is joined to the rest of Chuginadak Island by a low isthmus. The 1730-m-high Mount 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 for Mount Cleveland, 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.
19.514°N, 103.62°W, Elevation 3850 m
On 7 April the Centro Universitario de Estudios e Investigaciones de Vulcanologia - Universidad de Colima reported that during the previous week the seismic data revealed 38 high-frequency events, 23 long-period events, 2.4 hours of tremor, 18 landslides, and two low-intensity explosions. The sulfur dioxide flux was as high as 640 tons/day.
Geological summary: The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the 4320 m high point of the complex) on the north and the 3850-m-high historically active Volcán de Colima at the south. A group of cinder cones of late-Pleistocene age is located on the floor of the Colima graben west and east of the Colima complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, and have produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions (most recently in 1913) have destroyed the summit and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.
Dukono, Halmahera (Indonesia)
1.693°N, 127.894°E, Elevation 1229 m
Based on analyses of satellite imagery, wind model data, and notices from PVMBG, the Darwin VAAC reported that during 5-11 April ash plumes from Dukono rose to altitudes of 1.8-2.1 km (6,000-7,000 ft) a.s.l. and drifted NE, SE, and S.
Geological summary: Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.
Ebeko, Paramushir Island (Russia)
50.686°N, 156.014°E, Elevation 1103 m
KVERT reported that during 4-6 April several explosions at Ebeko were observed by residents of Severo-Kurilsk (Paramushir Island) about 7 km E. Ash plumes rose as high as 4 km (13,100 ft) a.s.l. Minor amounts of ash fell in Severo-Kurilsk on 6 April. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).
Geological summary: The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.
Etna, Sicily (Italy)
37.734°N, 15.004°E, Elevation 3330 m
INGV reported that the eruptive episode that began on 15 March from a vent in the saddle between Etna's Southeast Crater (SEC) - New Southeast Crater (NSEC) cone complex was characterized by Strombolian activity and ash emissions. Lava had traveled down into the Valle del Bove from the W rim; by the afternoon of 18 March almost continuous collapses of parts of the lava flow produced several avalanches of incandescent material which reached the base of the wall. Explosive activity had greatly declined earlier that morning. The collapsing stopped by early the next evening, 19 March, and the lava reached the base of the valley. That lava flow stopped advancing on 20 March though a few lava flows closer to the vent remained active the next few days.
On 21 March a new lava flow expanded SSW, but then stopped in the last days of March at an elevation of 2,300 m. A few more lava flows had followed a similar path in early April and then also stopped at the same elevation. Around 28 March a new pit crater had formed on the S part of the pyroclastic cone which had formed around the SEC-NSEC saddle vent. Strong glow form the pit crater was observed at night.
Geological 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 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east. 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 (the latter formed in 1978). Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.
14.473°N, 90.88°W, Elevation 3763 m
INSIVUMEH reported that during 6-11 April explosions at Fuego generated ash plumes that rose as high as 850 m above the crater rim and drifted as far as11 km W, SW, and S. Ashfall was reported in areas downwind including Panimaché I and II (8 km SW), Morelia (9 km SW), and Santa Sofía (12 km SW). Rumbling from the explosions was sometimes heard. During 10-11 April incandescent material was ejected 100-150 m above the crater, generating minor avalanches in the area of the cone.
Geological summary: Volcán Fuego, one of Central America's most active volcanoes, is one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between 3763-m-high Fuego and its twin volcano to the north, Acatenango. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at Acatenango. In contrast to the mostly andesitic Acatenango, eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.
Kilauea, Hawaiian Islands (USA)
19.421°N, 155.287°W, Elevation 1222 m
During 5-11 April HVO reported that the lava lake continued to rise, fall, and spatter in Kilauea’s Overlook crater. Webcams recorded incandescence from long-active sources within Pu'u 'O'o Crater, from a vent high on the NE flank of the cone, and from a small lava pond in a pit on the W side of the crater. The 61G lava flow, originating from a vent on Pu'u 'O'o Crater's E flank, continued to enter the ocean at Kamokuna from the end of the lava tube, about 20 m above the water. A growing lava delta was an estimated 25 m out from the base of the sea cliff by 10 April. Surface lava flows were active above the pali and on the coastal plain.
Geological summary: Kilauea volcano, which overlaps the east flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 sq km, destroying nearly 200 houses and adding new coastline to the island.
Klyuchevskoy, Central Kamchatka (Russia)
56.056°N, 160.642°E, Elevation 4754 m
KVERT reported that during 1-4 April explosions at Klyuchevskoy generated ash plumes that rose to altitudes of 5-6 km (16,400-19,700 ft) a.s.l. Satellite images showed a thermal anomaly over the volcano during 1-2 and 4 April, and ash plumes that drifted 400 km in multiple directions. No explosions were recorded after 4 April; the Aviation Color Code was lowered to Yellow on 10 April.
Geological summary: Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.
Nevado del Ruiz, Colombia
4.892°N, 75.324°W, Elevation 5279 m
Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that during 4-11 April seismicity at Nevado del Ruiz continued to indicate unrest. Signals indicating fracturing rock slightly increased in both size and number as compared to the previous week. During 10-11 April a period of short-duration and very low energy drumbeat signals were recorded, indicating rising magma. Water vapor and gas continued to be emitted. Gas, steam, and ash plumes rose 1.5 km above the crater rim on 10 April and drifted NW. Thermal anomalies were identified on 4, 6, and 7 April. The Alert Level remained at III (Yellow; the second lowest level on a four-color scale).
Geological summary: Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers >200 sq km. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.
Nevados de Chillan, Chile
36.863°S, 71.377°W, Elevation 3212 m
The Buenos Aires VAAC reported that on 6 and 8 April a webcam recorded ash emissions rising from Nevados de Chillán and dissipating quickly. On 6 April the emissions rose as high as 4 km (13,000 ft) a.s.l. Minor ash emissions were observed on 10 April.
Geological 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.
14.381°N, 90.601°W, Elevation 2552 m
INSIVUMEH reported that incandescence from Pacaya’s Mackenney cone was visible at night and at dawn during 6-11 April. Weak explosions accompanied by rumbling was sometimes noted.
Geological 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.
15.78°S, 71.85°W, Elevation 5967 m
Observatorio Vulcanológico del Sur del IGP (OVS-IGP) and Observatorio Vulcanológico del INGEMMET (OVI) reported that during 3-9 April seismicity at Sabancaya declined compared to the previous week, with an average of 27 explosions recorded per day. Ash plumes rose as high as 3.2 km above the crater rim (on 8 April) and drifted more than 40 km NW and NE. Ashfall was reported in Pinchollo (20 km N), Maca, and Chivay. The Buenos Aires VAAC reported that diffuse ash plumes drifted 100 km E on 9 April. Intermittent ash emissions during 10-11 April rose as high as 7 km (23,000 ft) a.s.l. and drifted SE. The Alert Level remained at Orange (the second highest level on a four-color scale).
Geological summary: Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning "tongue of fire" in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions date back to 1750.
Sheveluch, Central Kamchatka (Russia)
56.653°N, 161.36°E, Elevation 3283 m
KVERT reported that during 1-6 April lava-dome extrusion onto Sheveluch’s N flank was accompanied by strong fumarolic activity, dome incandescence, ash explosions, and hot avalanches. Satellite images showed a daily thermal anomaly over the dome, and ash plumes that drifted 20 km SE on 3 April. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).
Geological summary: The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 cu km volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.
3.17°N, 98.392°E, Elevation 2460 m
Based on PVMBG observations and wind data, the Darwin VAAC reported that during 7 and 9-11 April ash plumes from Sinabung rose to altitudes of 3.4-8.2 km (11,000-27,000 ft) a.s.l. and drifted E, SE, and WNW.
Geological 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.