The Weekly Volcanic Activity Report: September 11 – 17, 2019

New activity/unrest was reported for 4 volcanoes from September 11 to 17, 2019. During the same period, ongoing activity was reported for 15 volcanoes.

New activity/unrest: Alaid, Kuril Islands (Russia) | Copahue, Central Chile-Argentina border | Nevados de Chillan, Chile | Villarrica, Chile

Ongoing activity: Aira, Kyushu (Japan) | Asosan, Kyushu (Japan) | Dukono, Halmahera (Indonesia) | Ebeko, Paramushir Island (Russia) | Etna, Sicily (Italy) | Karangetang, Siau Island (Indonesia) | Karymsky, Eastern Kamchatka (Russia) | Krakatau, Indonesia | Merapi, Central Java (Indonesia) | Pacaya, Guatemala | Sangeang Api, Indonesia | Sheveluch, Central Kamchatka (Russia) | Shishaldin, Fox Islands (USA) | Tangkubanparahu, Western Java (Indonesia) | Ubinas, Peru

New activity/unrest

Alaid, Kuril Islands (Russia)

50.861°N, 155.565°E, Summit elev. 2285 m

The Tokyo VAAC reported that on 11 September an ash plume from Alaid identified in satellite images rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted SE.

Geological summary: The highest and northernmost volcano of the Kuril Islands, 2285-m-high Alaid is a symmetrical stratovolcano when viewed from the north, but has a 1.5-km-wide summit crater that is breached widely to the south. Alaid is the northernmost of a chain of volcanoes constructed west of the main Kuril archipelago. Numerous pyroclastic cones dot the lower flanks of this basaltic to basaltic-andesite volcano, particularly on the NW and SE sides, including an offshore cone formed during the 1933-34 eruption. Strong explosive eruptions have occurred from the summit crater beginning in the 18th century. Reports of eruptions in 1770, 1789, 1821, 1829, 1843, 1848, and 1858 were considered incorrect by Gorshkov (1970). Explosive eruptions in 1790 and 1981 were among the largest in the Kuril Islands during historical time.

Copahue, Central Chile-Argentina border

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

OVDAS-SERNAGEOMIN reported that a long-period (LP) earthquake at Copahue recorded at 1657 on 11 September correlated with an infrasound signal from an explosion; a gas-and-ash emission rose to low heights. A larger explosion, recorded at 2245 along with an LP earthquake, produced a plume that rose 250 m above the crater rim. Incandescent deposits around the vent were visible at night, and a 3-km-long ash deposit, covering an area of 3.4 square kilometers, was visible on the ESE flank. The Alert Level remained at Yellow (second lowest level on a four-color scale); SERNAGEOMIN recommended no entry into a restricted area within 500 m of the crater. ONEMI maintained the Alert Level at Yellow (the middle level on a three-color scale) for the municipality of Alto Biobío.

Geological summary: Volcán Copahue is an elongated composite cone constructed along the Chile-Argentina border within the 6.5 x 8.5 km wide Trapa-Trapa caldera that formed between 0.6 and 0.4 million years ago near the NW margin of the 20 x 15 km Pliocene Caviahue (Del Agrio) caldera. The eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains a briny, acidic 300-m-wide crater lake (also referred to as El Agrio or Del Agrio) and displays intense fumarolic activity. Acidic hot springs occur below the eastern outlet of the crater lake, contributing to the acidity of the Río Agrio, and another geothermal zone is located within Caviahue caldera about 7 km NE of the summit. Infrequent mild-to-moderate explosive eruptions have been recorded since the 18th century. Twentieth-century eruptions from the crater lake have ejected pyroclastic rocks and chilled liquid sulfur fragments.

Nevados de Chillan, Chile

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

ONEMI and SERNAGEOMIN reported that during 10-17 September white-to-gray gas plumes from Nevados de Chillán’s Nicanor Crater rose 400-800 m above the rim and drifted NE, E, and SE. Explosions sometimes ejected incandescent material onto the E and SE flanks. A lava flow on the NNE flank was 100 m wide, 5 m thick, and had advanced 600 m by 14 September. The Alert Level remained at Orange, the second highest level on a four-color scale. ONEMI maintained an Alert Level Yellow (the middle level on a three-color scale) for the communities of Pinto, Coihueco, and San Fabián, and stated that the public should stay at least 3 km away from the crater on the SW flank and 5 km away on the ENE flank.

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.

Villarrica, Chile

39.42°S, 71.93°W, Summit elev. 2847 m

Video from an 11 September overflight of Villarrica, conducted by the Carabineros Región de La Araucanía, showed an active cone on the crater floor. ONEMI and SERNAGEOMIN noted that the activity was consistent with the elevated seismicity detected by the seismic network during the previous few days. Seismicity and explosive activity in the crater both began decreasing on 12 September and continued a downward trend at least through 16 September. Discrete tremor signals disappeared during 15-16 September, with moderate levels of continuous tremor dominating the signal. No explosions were detected. SERNAGEOMIN lowered the Alert Level to Yellow, the second lowest level on a four-color scale. ONEMI maintained an Alert Level Yellow (the middle level on a three-color scale) for the municipalities of Villarrica, Pucón (16 km N), Curarrehue, and the commune of Panguipulli, and changed the exclusion zone for the public to a radius of 1 km around the crater.

Geological summary: Glacier-clad Villarrica, one of Chile's most active volcanoes, rises above the lake and town of the same name. It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. A 6-km-wide caldera formed during the late Pleistocene. A 2-km-wide caldera that formed about 3500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesitic cone at the NW margin of the Pleistocene caldera. More than 30 scoria cones and fissure vents dot the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Historical eruptions, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

Ongoing activity

Aira, Kyushu (Japan)

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

JMA reported that inflation at Minamidake crater (at Aira Caldera’s Sakurajima volcano) began to be detected on 9 September and was similar to the deformation recorded just before a notable eruption on 16 June 2018. An eruption recorded at 0746 on 16 September produced an ash plume that rose 2.8 km above the crater rim and drifted SW. A series of eruptive events were recorded during 0830-1110. Deformation ceased after the events. An explosion at 0927 on 17 September generated an ash plume that rose 1 km and ejected blocks as far as 1.1 km. Two eruptive events later than day produced ash plumes that rose 1.6 km. 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.

Asosan, Kyushu (Japan)

32.884°N, 131.104°E, Summit elev. 1592 m

JMA reported that during 10-13 September ash plumes rose 1.6 km above Asosan’s summit crater rim. The sulfur dioxide emission rate was 1,600 tons per day on 11 September. The Alert Level remained at 2 (on a scale of 1-5).

Geological summary: The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Dukono, Halmahera (Indonesia)

1.693°N, 127.894°E, Summit elev. 1229 m

Based on satellite and wind model data, and information from PVMBG, the Darwin VAAC reported that during 11-17 September ash plumes from Dukono rose to altitudes of 1.8-2.1 km (6,000-7,000 ft) a.s.l. and drifted N, NNE, and NE. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to remain outside of the 2-km exclusion zone.

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, Summit elev. 1103 m

Volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, observed explosions during 7-13 September that sent ash plumes up to 3 km (10,000 ft) a.s.l. and drifted S, SE, and N. Ash fell in Severo-Kurilsk on 6 September. A thermal anomaly was identified in satellite images on 8 September. 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)

37.748°N, 14.999°E, Summit elev. 3295 m

INGV reported that Strombolian activity at Etna’s Northeast Crater (NEC) likely began on 8 September. Continuous Strombolian activity recorded between 2000 on 9 September and 0700 on 10 September produced diffuse ash emissions which quickly dissipated. The most intense part of the eruptive period occurred during 2000-2200. Minor ashfall was reported in Piedimonte Etneo, Giarre-Riposto, and Rifugio Citelli. Incandescence from the activity had significantly subsided by 0300 on 10 September, coincident with the ejection of lava fragments outside of the crater. Dilute ash puffs were continuously observed at dawn the next day. Strombolian activity ceased around 0540 and then resumed around 0800. Weather conditions hindered observations at times on 11 September but clear observations after 2000 allowed for the confirmation of continuing explosive activity at varying intensity at NEC.

Ash emission from Voragine Crater began during the morning of 12 September and gradually increased in frequency. Activity further intensified at 1200 as Strombolian activity commenced and tephra ejected out of the crater was deposited at the base of Bocca Nuova Crater. Strong Strombolian explosions were felt in Zafferana Etnea, Aci S. Antonio, Pedara, and neighboring areas.

Webcam and field observations on 13 September confirmed continuing activity at NEC and Voragine craters. Diffuse ash plumes rose from NEC and dispersed near the summit area. Strombolian activity at Voragine Crater ejected coarse tephra as high as 20 m above the crater rim and produced diffuse ash emissions. Impact craters from the ejected tephra were distributed mostly in the W part of the area between Bocca Nuova and Voragine craters down to 3,000 m elevation. Activity continued on 14 September. During an overflight on 15 September observers noted that a scoria cone had formed in Voragine Crater, and diffuse ash emissions continued to rise from NEC.

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, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. 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.

Karangetang, Siau Island (Indonesia)

2.781°N, 125.407°E, Summit elev. 1797 m

PVMBG reported that during 9-15 September lava continued to effuse from Karangetang’s Main Crater (S) and Dua Crater (N), traveling as far as 1.5 km down the Nanitu, Pangi, and Sense drainages on the SW flank. Sometimes dense white plumes rose to 100 m above the summit. According to the Darwin VAAC an ash plume rose almost 650 m above the summit and drifted E on 11 September. The Alert Level remained at 2 (on a scale of 1-4).

Geological summary: Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi island. The stratovolcano contains five summit craters along a N-S line. It 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 have produced pyroclastic flows.

Karymsky, Eastern Kamchatka (Russia)

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

KVERT reported that a thermal anomaly over Karymsky was visible in satellite images on 10 September. The Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Geological 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.

Krakatau, Indonesia

6.102°S, 105.423°E, Summit elev. 813 m

PVMBG reported that Anak Krakatau’s seismic network recorded five eruptive events during 9-15 September. A webcam at the summit recorded diffuse white plumes rising 150 m from the bottom of the crater, and dense gray-and-white ash plumes rising 300 m. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to remain outside of the 2-km-radius hazard zone from the crater.

Geological 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 or 535 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, and left only a remnant of Rakata. 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.

Merapi, Central Java (Indonesia)

7.54°S, 110.446°E, Summit elev. 2910 m

PVMBG reported that during 9-15 September the lava-dome volume at Merapi did not change and was an estimated 461,000 cubic meters, based on analyses of drone images on 8 August. Extruded lava fell into the upper parts of the SE flank, generating block-and-ash flows that traveled as far as 1.1 km down the Gendol drainage. Diffuse white plumes rose as high as 100 m above the summit. The Alert Level remained at 2 (on a scale of 1-4), and residents were warned to stay outside of the 3-km exclusion zone.

Geological summary: Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequently growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities during historical time.

Pacaya, Guatemala

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

A special report from INSIVUMEH noted that seismic activity at Pacaya had increased on 8 September, with RSAM values reaching 7,000 units by 13 September, coincident with increased explosive activity at Mackenney Crater. Explosions from a growing cone in the crater ejected material as high as 75 m above the cone. Lava effusion increased; lava flows advancing on the N and NW flank towards Cerro Chino were about 500 m long. Avalanches of blocks up to 1 m in diameter were produced by the flow front. Similar activity was observed during 15-16 September.

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.

Sangeang Api, Indonesia

8.2°S, 119.07°E, Summit elev. 1912 m

The Darwin VAAC reported that on 11 September a diffuse ash plume from Sangeang Api was identified in satellite images rising to 3 km (10,000 ft) a.s.l. and drifting N. The Alert Level remained at 2 (on a scale of 1-4).

Geological summary: Sangeang Api volcano, one of the most active in the Lesser Sunda Islands, forms a small 13-km-wide island off the NE coast of Sumbawa Island. Two large trachybasaltic-to-tranchyandesitic volcanic cones, Doro Api and Doro Mantoi, were constructed in the center and on the eastern rim, respectively, of an older, largely obscured caldera. Flank vents occur on the south side of Doro Mantoi and near the northern coast. Intermittent historical eruptions have been recorded since 1512, most of them during in the 20th century.

Sheveluch, Central Kamchatka (Russia)

56.653°N, 161.36°E, Summit elev. 3283 m

KVERT reported that a thermal anomaly over Sheveluch’s lava dome was identified daily in satellite images during 6-9 and 12 September. Resuspended ash formed plumes that drifted 250 km ESE during 11-12 September. Satellite and webcam data recorded ash emissions and a gas-and-steam plume with some ash drifting 50 km ESE on 12 September. 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 km3 volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Shishaldin, Fox Islands (USA)

54.756°N, 163.97°W, Summit elev. 2857 m

Low-level lava fountaining and minor explosive activity within Shishaldin’s summit crater was last observed on 17 August and likely continued during 11-17 September; continuous tremor was recorded by the seismic network and elevated surface temperatures were visible in satellite images. The webcam possibly recorded a steam emission on 16 September. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

Geological 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.

Tangkubanparahu, Western Java (Indonesia)

6.77°S, 107.6°E, Summit elev. 2084 m

PVMBG reported that phreatic events, accompanied by roaring, continued at Tangkubanparahu's Ratu Crater during 9-15 September, though no larger eruptions were recorded. Ash-and-steam emissions rose as high as 20 m above the vent and steam plumes rose as high as 200 m. The seismic network recorded continuous tremor. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to stay 1.5 km away from the active crater.

Geological summary: Tangkubanparahu (also known as Tangkuban Perahu) is a broad shield-like stratovolcano overlooking Indonesia's former capital city of Bandung. The volcano was constructed within the 6 x 8 km Pleistocene Sunda caldera, which formed about 190,000 years ago. The volcano's low profile is the subject of legends referring to the mountain of the "upturned boat." The rim of Sunda caldera forms a prominent ridge on the western side; elsewhere the caldera rim is largely buried by deposits of Tangkubanparahu volcano. The dominantly small phreatic historical eruptions recorded since the 19th century have originated from several nested craters within an elliptical 1 x 1.5 km summit depression.

Ubinas, Peru

16.355°S, 70.903°W, Summit elev. 5672 m

During 10-15 September the number of seismic events at Ubinas totaled 4,093, with volcano-tectonic (VT) signals being the most numerous, averaging 572 events per day, and all having magnitudes under M 2.5. Hybrid events averaged 299 events per day. Continuous emissions of blueish gas and water vapor were recorded by the webcam rising to heights less than 1.5 km above the summit. Two thermal anomalies were recorded by the MIROVA system. An explosion at 0725 on 12 September produced a gas-and-ash plume that rose 1.5 km and affected several districts S and SE in the Moquegua region. The Alert Level remained at Orange (the second highest level on a four-color scale) and the public were warned to stay outside of a 10-km radius.

Geological 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.

Source: GVP