New activity/unrest was observed at 4 volcanoes from July 22 - 28, 2015. During the same period, ongoing activity was observed at 17 volcanoes.
New activity/unrest: Chirinkotan, Kuril Islands (Russia) | Cleveland, Chuginadak Island (USA) | Kick 'em Jenny, North of Grenada | Nevado del Ruiz, Colombia | Raung, Eastern Java (Indonesia).
Ongoing activity: Aira, Kyushu (Japan) | Ambrym, Vanuatu | Dukono, Halmahera (Indonesia) | Karangetang, Siau Island (Indonesia) | Karymsky, Eastern Kamchatka (Russia) | Kerinci, Indonesia | Kilauea, Hawaiian Islands (USA) | Krakatau, Indonesia | Lokon-Empung, Sulawesi (Indonesia) | Papandayan, Western Java (Indonesia) | Popocatepetl, Mexico | Semeru, Eastern Java (Indonesia) | Sheveluch, Central Kamchatka (Russia) | Shishaldin, Fox Islands (USA) | Sinabung, Indonesia | Tengger Caldera, Eastern Java (Indonesia) | Ubinas, Peru.
Chirinkotan, Kuril Islands (Russia)
48.98°N, 153.48°E, Summit elev. 724 m
Based on satellite image observations, the Tokyo VAAC reported that a possible eruption at Chirinkotan on 26 July may have produced an ash plume that rose to an altitude of 4.6 km (15,000 ft) a.s.l. and drifted NW. A subsequent notice the next day stated that ash was observed in images and then dissipated.
Geologic 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, Summit elev. 1730 m
AVO reported that during an overflight of Cleveland on 24 July a local field crew observed a thin layer of ash on the upper flanks (confirming a small explosion the week before) and vigorous steaming from the summit area. A small steam plume was recorded by the webcam on 27 July. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.
Geologic 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.
Kick 'em Jenny, North of Grenada
2.3°N, 61.64°W, Summit elev. -185 m
The University of the West Indies (UWI) Seismic Research Centre (SRC) reported that seismic activity at Kick 'em Jenny had increased on 11 July. Another increase occurred on 23 July from 0125 to 0300, characterized by a "strong continuous signal." More than 400 micro and small earthquakes had been recorded since 11 July; the largest event was M 3.3. The Alert Level was raised to Orange (the second highest level on a 5-color scale) on 23 July.
At about 0200 on 24 July an hour-long explosion signal was recorded. Afterward, and through the next day, seismicity declined. The report encouraged mariners to observe an exclusion zone with a 5-km radius of the crater. Scientists observed nothing out of the ordinary at the surface above the volcano during an overflight on 25 July, and by 1800 no activity was recorded. On 26 July the Alert Level was lowered to Yellow.
Geologic summary: Kick 'em Jenny, a historically active submarine volcano 8 km off the north shore of Grenada, rises 1300 m from the sea floor. Recent bathymetric surveys have shown evidence for a major arcuate collapse structure that was the source of a submarine debris avalanche that traveled more than 15 km to the west. Bathymetry also revealed another submarine cone to the SE, Kick 'em Jack, and submarine lava domes to its south. These and subaerial tuff rings and lava flows at Ile de Caille and other nearby islands may represent a single large volcanic complex. Numerous historical eruptions, mostly documented by acoustic signals, have occurred at Kick 'em Jenny since 1939, when an eruption cloud rose 275 m above the sea surface. Prior to the 1939 eruption, which was witnessed by a large number of people in northern Grenada, there had been no written mention of Kick 'em Jenny. Eruptions have involved both explosive activity and the quiet extrusion of lava flows and lava domes in the summit crater; deep rumbling noises have sometimes been heard onshore. Historical eruptions have modified the morphology of the summit crater.
Nevado del Ruiz, Colombia
4.892°N, 75.324°W, Summit elev. 5279 m
Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico and Sismológico de Manizales reported increased tremor at Nevado del Ruiz during the morning of 26 July. The webcam recorded an ash plume at 0830 that rose 3 km and drifted NW to SW; ashfall was reported in areas downwind including the municipalities of Chinchiná, Palestina, Santa Rosa de Cabal, Dosquebradas, and Pereira. Later than day seismicity decreased and the webcam showed gas-and-steam emissions that rose 300 m.
Geologic 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.
Raung, Eastern Java (Indonesia)
8.125°S, 114.042°E, Summit elev. 3332 m
PVMBG reported that the eruption at Raung was ongoing during 16-23 July. Ash plumes rose 2 km and incandescence at the crater was visible. Seismicity fluctuated but remained elevated. The Alert Level remained at 3 (on a scale of 1-4), and the public was reminded not to approach the crater within a 3-km radius. Based on PVMBG information, and satellite-image and pilot observations, the Darwin VAAC reported that during 22-28 July ash multiple ash plumes from Raung rose to varying altitudes of 4.3-5.2 km (14,000-17,000 ft) a.s.l. and drifted as far as 400 km NW, W, SSW, S, and SSE. A news article from 29 July noted that 18 flights at most had been canceled during the previous few days due to the ash plumes, and that the Notohadinegoro Airport (2,100 km SW) had been temporarily closed.
Geologic summary: Raung, one of Java's most active volcanoes, is a massive stratovolcano in easternmost Java that was constructed SW of the rim of Ijen caldera. The 3332-m-high, unvegetated summit of Gunung Raung is truncated by a dramatic steep-walled, 2-km-wide caldera that has been the site of frequent historical eruptions. A prehistoric collapse of Gunung Gadung on the W flank produced a large debris avalanche that traveled 79 km, reaching nearly to the Indian Ocean. Raung contains several centers constructed along a NE-SW line, with Gunung Suket and Gunung Gadung stratovolcanoes being located to the NE and W, respectively.
Aira, Kyushu (Japan)
31.593°N, 130.657°E, Summit elev. 1117 m
JMA reported that during 21-24 July a small-scale, non-explosive event at Showa Crater (Aira Caldera’s Sakurajima volcano) was recorded, and incandescence from the crater was visible on 23 July. An explosion on 25 July ejected tephra as far as 800 m away. 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.
16.25°S, 168.12°E, Summit elev. 1334 m
On 22 July the Vanuatu Geohazards Observatory issued a statement reminding residents and visitors that Ambrym remained active; the Alert Level remained at 2 (on a scale of 0-5). Areas deemed hazardous were near and around the active vents (Benbow, Maben-Mbwelesu, Niri-Mbwelesu, and Mbwelesu), and in downwind areas prone to ashfall.
Geologic summary: Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides arc. A thick, almost exclusively pyroclastic sequence, initially dacitic, then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major plinian eruption with dacitic pyroclastic flows about 1900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the caldera floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.
Dukono, Halmahera (Indonesia)
1.68°N, 127.88°E, Summit elev. 1335 m
Based on analyses of satellite imagery and wind data, the Darwin VAAC reported that during 26-27 July ash plumes from Dukono rose to an altitude of 2.1 km (7,000 ft) a.s.l. and drifted 25-55 km NW, N, and NE.
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.
Karangetang, Siau Island (Indonesia)
2.78°N, 125.4°E, Summit elev. 1784 m
Based on observations conducted at the Karangetang Volcano Observation Post in the village of Salili, PVMBG reported that white plumes rose as high as 200 m above the Main Crater and 25 m above Crater II during 15 and 19-22 July; foggy conditions prevented views during 13-14 and 16-18 July. Incandescence from the lava dome was observed at night. Incandescent avalanches from the fronts of 75-m-long lava flows traveled as far as 2.3 km E down the Batuawang and Kahetang drainages. Seismicity was dominated by signals characteristic of avalanches, with rare volcanic earthquakes. The Alert Level remained at 3 (on a scale of 1-4); visitors and residents were warned not to approach Karangetang within a 4-km radius.
Geologic summary: Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, north of Sulawesi. The 1784-m-high stratovolcano contains five summit craters along a N-S line. Karangetang is one of Indonesia's most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented in the historical record (Catalog of Active Volcanoes of the World: Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts has also produced pyroclastic flows.
Karymsky, Eastern Kamchatka (Russia)
54.049°N, 159.443°E, Summit elev. 1513 m
KVERT reported that moderate activity at Karymsky likely continued during 17-24 July. Satellite images detected a thermal anomaly on 17 July as well as an ash cloud (8 km long and 5 km wide) that drifted 113 km E. Volcanologists observed multiple explosions during 21-22 July; ash plumes that rose as high as 2 km a.s.l. and drifted SE. The Aviation Color Code remained at Orange.
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.
1.697°S, 101.264°E, Summit elev. 3800 m
PVMBG reported that during 1 April-12 July white plumes from Kerinci rose 50-300 m and drifted E and W. Seismicity was dominated by signals indicating emissions (270 events per day on average) as well as shallow volcanic earthquakes (4 per day on average). 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: The 3800-m-high Gunung Kerinci in central Sumatra forms Indonesia's highest volcano and is one of the most active in Sumatra. Kerinci is capped by an unvegetated young summit cone that was constructed NE of an older crater remnant. The volcano contains a deep 600-m-wide summit crater often partially filled by a small crater lake that lies on the NE crater floor, opposite the SW-rim summit of Kerinci. The massive 13 x 25 km wide volcano towers 2400-3300 m above surrounding plains and is elongated in a N-S direction. The frequently active Gunung Kerinci has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838.
Kilauea, Hawaiian Islands (USA)
19.421°N, 155.287°W, Summit elev. 1222 m
HVO reported that seismicity beneath Kilauea's summit, upper East Rift Zone, and Southwest Rift Zone was at background levels during 15-22 July. The lava lake continued to circulate and spatter in the Overlook vent; occasional collapses of material briefly agitated the lake surface. Webcams recorded multiple incandescent outgassing vents within Pu'u 'O'o. The June 27th NE-trending lava flow continued to be active within 4-8 km NE of Pu'u 'O'o Crater.
Geologic 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 of Kilauea 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.
6.102°S, 105.423°E, Summit elev. 813 m
PVMBG reported that during 1 June-12 July diffuse white plumes were observed rising 25 m above Anak Krakatau, although foggy weather often prevented observations. Seismicity fluctuated at a high level, and continued to be dominated by shallow and deep volcanic earthquakes. Signals indicating emissions were also recorded. The Alert Level remained at 2 (on a scale of 1-4). Residents and visitors were warned not to approach the volcano within 1 km of the crater.
Geologic summary: The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan volcanoes, and left only a remnant of Rakata volcano. This eruption, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.
Lokon-Empung, Sulawesi (Indonesia)
1.358°N, 124.792°E, Summit elev. 1580 m
PVMBG reported that during 15-22 July observers at the Lokon Observation Post in Kakaskasen Tomohon, North Sulawesi (4 km from the crater) reported that, although inclement weather sometimes obscured views of Lokon-Empung's Tompaluan Crater, white plumes were observed rising as high as 75 m above the crater. The number of volcanic earthquakes declined but still remained higher than levels recorded during 25 May-10 July. Signals indicating emissions were occasionally detected. The Alert Level remained at 3 (on a scale of 1-4). Residents and tourists were reminded not to approach Tompaluan Crater within a radius of 2.5 km.
Geologic summary: The twin volcanoes Lokon and Empung, rising about 800 m above the plain of Tondano, are among the most active volcanoes of Sulawesi. Lokon, the higher of the two peaks (whose summits are only 2.2 km apart), has a flat, craterless top. The morphologically younger Empung volcano has a 400-m-wide, 150-m-deep crater that erupted last in the 18th century, but all subsequent eruptions have originated from Tompaluan, a 150 x 250 m wide double crater situated in the saddle between the two peaks. Historical eruptions have primarily produced small-to-moderate ash plumes that have occasionally damaged croplands and houses, but lava-dome growth and pyroclastic flows have also occurred.
Papandayan, Western Java (Indonesia)
7.32°S, 107.73°E, Summit elev. 2665 m
PVMBG reported that during 1 June-13 July seismicity at Papandayan was dominated by shallow volcanic earthquakes but also consisted of deep volcanic earthquakes, low-frequency earthquakes, harmonic tremor, and hybrid events. Visual monitoring occurred from the Pakuwon Village post; where observers noted white plumes rising at most 30 m above the crater. The Alert Level remained at 2 (on a scale of 1-4); residents and tourists were reminded not to approach the craters within a 1-km radius.
Geologic summary: Papandayan is a complex stratovolcano with four large summit craters, the youngest of which was breached to the NE by collapse during a brief eruption in 1772 and contains active fumarole fields. The broad 1.1-km-wide, flat-floored Alun-Alun crater truncates the summit of Papandayan, and Gunung Puntang to the north gives the volcano a twin-peaked appearance. Several episodes of collapse have given the volcano an irregular profile and produced debris avalanches that have impacted lowland areas beyond the volcano. A sulfur-encrusted fumarole field occupies historically active Kawah Mas ("Golden Crater"). After its first historical eruption in 1772, in which collapse of the NE flank produced a catastrophic debris avalanche that destroyed 40 villages and killed nearly 3000 persons, only small phreatic eruptions had occurred prior to an explosive eruption that began in November 2002.
19.023°N, 98.622°W, Summit elev. 5426 m
CENAPRED reported that during 22-28 July the seismic network at Popocatépetl recorded 34-102 daily emissions consisting of water vapor, gas, and sometimes ash; cloud cover often prevented visual observations. Variable nighttime crater incandescence was observed, and explosions were detected almost daily. Gas-and-ash plumes rose 1.5 km on 26 July, and two explosions on 27 July produced ash plumes that rose less than 1 km. The Alert Level remained at Yellow, Phase Two.
Geologic summary: Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, towers to 5426 m 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 from Popocatépetl 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 precolumbian time.
Semeru, Eastern Java (Indonesia)
8.108°S, 112.92°E, Summit elev. 3676 m
PVMBG reported that both white plumes and gray to brownish-gray plumes from Semeru were observed rising as high as 600 m above the crater and drifting N, NW, W, and SW during 1 April-13 July; inclement weather sometimes prevented observations. Ashfall was reported in Sawur and surrounding areas in April, and incandescent avalanches that traveled as far as 1 km were observed in May. Seismicity was dominated by explosions and emission signals. The Alert Level remained at 2 (on a scale from 1-4); visitors and residents were warned to avoid the SE flank within 4 km of the crater.
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 abruptly to 3676 m 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. Semeru has been in almost continuous eruption since 1967.
Sheveluch, Central Kamchatka (Russia)
56.653°N, 161.36°E, Summit elev. 3283 m
KVERT reported that during 17-24 July lava-dome extrusion onto Sheveluch’s N flank was accompanied by fumarolic activity, dome incandescence, and hot avalanches. Satellite images showed a daily thermal anomaly over the dome. 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 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.
Shishaldin, Fox Islands (USA)
54.756°N, 163.97°W, Summit elev. 2857 m
AVO reported that seismicity at Shishaldin continued to be elevated over background levels 22-28 July, indicating that low-level eruptive activity confined to the summit crater likely continued. Cloud cover prevented satellite and webcam observations. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.
Geologic summary: The beautifully symmetrical volcano of Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The 2857-m-high, glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steady steam plume rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is Holocene in age and largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the west and NE sides at 1500-1800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century.
3.17°N, 98.392°E, Summit elev. 2460 m
Based on satellite images, webcam views, weather models, and information from PVMBG, the Darwin VAAC reported that on 23 July an explosion at Sinabung generated an ash plume that rose to an altitude of 7 km (23,000 ft) a.s.l. and drifted 25-55 km W. An explosion on 26 July generated an ash plume that rose to an altitude of 3.7 km (12,000 ft) a.s.l. and drifted E.
Geologic summary: Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical, 2460-m-high andesitic-to-dacitic volcano 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.
Tengger Caldera, Eastern Java (Indonesia)
7.942°S, 112.95°E, Summit elev. 2329 m
PVMBG reported that during 1 March-13 July white plumes from Tengger Caldera's Bromo cone rose as high as 100 m above the crater, and a sulfur dioxide odor was periodically noted at the Bromo observation post. Seismicity was dominated by tremor, but also included volcanic earthquakes. The Alert Level remained at 2 (on a scale of 1-4). Residents and visitors were warned not to approach the crater within a radius of 1 km.
Geologic summary: The 16-km-wide Tengger caldera is located at the northern end of a volcanic massif extending from Semeru volcano. The massive volcanic complex dates back to about 820,000 years ago and consists of five overlapping stratovolcanoes, each truncated by a caldera. Lava domes, pyroclastic cones, and a maar occupy the flanks of the massif. The Ngadisari caldera at the NE end of the complex formed about 150,000 years ago and is now drained through the Sapikerep valley. The most recent of the calderas is the 9 x 10 km wide Sandsea caldera at the SW end of the complex, which formed incrementally during the late Pleistocene and early Holocene. An overlapping cluster of post-caldera cones was constructed on the floor of the Sandsea caldera within the past several thousand years. The youngest of these is Bromo, one of Java's most active and most frequently visited volcanoes.
16.355°S, 70.903°W, Summit elev. 5672 m
Instituto Geofísico del Perú (IGP) Observatorio Volcanológico del Sur (OVS) reported that during 21-26 July seismic activity at Ubinas increased, particularly during 25-26 July. Constant gas, steam, and ash emissions were observed during 21-24 July. On 25 July bluish gas emissions were observed most of the day until a strong explosion (the strongest so far in 2015) at 1903 ejected ash, lapilli, and ballistics. Lapilli and some 1-2-cm-long fragments fell in the towns of Ubinas (6.5 km SSE) and Escacha. Another explosion was registered at 2003.
Geologic summary: A small, 1.4-km-wide caldera cuts the top of Ubinas, Peru's most active volcano, giving it a truncated appearance. It is the northernmost of three young volcanoes located along a regional structural lineament about 50 km behind the main volcanic front of Perú. The growth and destruction of Ubinas I was followed by construction of Ubinas II beginning in the mid-Pleistocene. The upper slopes of the andesitic-to-rhyolitic Ubinas II stratovolcano are composed primarily of andesitic and trachyandesitic lava flows and steepen to nearly 45 degrees. The steep-walled, 150-m-deep summit caldera contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits from the collapse of the SE flank about 3700 years ago extend 10 km from the volcano. Widespread plinian pumice-fall deposits include one of Holocene age about 1000 years ago. Holocene lava flows are visible on the flanks, but historical activity, documented since the 16th century, has consisted of intermittent minor-to-moderate explosive eruptions.