The Weekly Volcanic Activity Report: July 28 - August 3, 2021

The Weekly Volcanic Activity Report: July 28 - August 3, 2021

New activity/unrest was reported for 7 volcanoes from July 28 to August 3, 2021. During the same period, ongoing activity was reported for 16 volcanoes.

New activity/unrest: Dieng Volcanic Complex, Central Java (Indonesia) | Great Sitkin, Andreanof Islands (USA) | Nyiragongo, DR Congo | Pagan, Mariana Islands (USA) | Savo, Solomon Islands | Semisopochnoi, Aleutian Islands (USA) | Ulawun, New Britain (Papua New Guinea).

Ongoing activity: Aira, Kyushu (Japan) | Aniakchak, United States | Bagana, Bougainville (Papua New Guinea) | Dukono, Halmahera (Indonesia) | Ebeko, Paramushir Island (Russia) | Gareloi, United States | Kadovar, Papua New Guinea | Karymsky, Eastern Kamchatka (Russia) | Krysuvik-Trolladyngja, Iceland | Lewotolok, Lembata Island (Indonesia) | Mayon, Luzon (Philippines) | Merapi, Central Java (Indonesia) | Rincon de la Vieja, Costa Rica | Sheveluch, Central Kamchatka (Russia) | Sinabung, Indonesia | Suwanosejima, Ryukyu Islands (Japan).

The Weekly Volcanic Activity Report is a cooperative project between the Smithsonian's Global Volcanism Program and the US Geological Survey's Volcano Hazards Program. Updated by 23:00 UTC every Wednesday, these reports are preliminary and subject to change as events are studied in more detail. This is not a comprehensive list of all of Earth's volcanoes erupting during the week, but rather a summary of activity at volcanoes that meet criteria discussed in detail in the "Criteria and Disclaimers" section. Carefully reviewed, detailed reports about recent activity are published in issues of the Bulletin of the Global Volcanism Network.

New activity/unrest

Dieng Volcanic Complex, Central Java (Indonesia)

7.2°S, 109.879°E, Summit elev. 2565 m

PVMBG reported that on 30 July a burst of mud originated from the Siglagah thermal feature (Dieng Volcanic Complex), located on a steep hill, about 1 km NE of the center of Pagerkandang cone. The event caused an audible banging noise and sent a mudflow, 1-3 m thick, 10 m N. Observers that had visited the site in July saw gas emissions rising 10-30 m high and occasionally heard “bursting” noises up to 100 m away. The event was not accompanied by an increase in seismicity; the Alert Level remained at 1 (on a scale of 1-4), and the public was warned to stay away from the thermal area.

Geological summary: The Dieng plateau in the highlands of central Java is renowned both for the variety of its volcanic scenery and as a sacred area housing Java's oldest Hindu temples, dating back to the 9th century CE. The Dieng volcanic complex consists of two or more stratovolcanoes and more than 20 small craters and cones of Pleistocene-to-Holocene age over a 6 x 14 km area. Prahu stratovolcano was truncated by a large Pleistocene caldera, which was subsequently filled by a series of dissected to youthful cones, lava domes, and craters, many containing lakes. Lava flows cover much of the plateau, but have not occurred in historical time, when activity has been restricted to minor phreatic eruptions. Toxic gas emissions are a hazard at several craters and have caused fatalities. The abundant thermal features and high heat flow make Dieng a major geothermal prospect.

Great Sitkin, Andreanof Islands (USA)

52.076°N, 176.13°W, Summit elev. 1740 m

AVO reported that unrest continued at Great Sitkin during 28 July-3 August. Seismicity remained elevated and a small swarm was recorded during 1-2 August. Elevated surface temperatures and a north-drifting steam plume were identified in satellite images during 27-28 July. Minor steam emissions were visible during 31 July-3 August. The circular lava dome in the crater had grown to 180 m in diameter based on measurements taken using a 3 August satellite image. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Geological summary: The Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger parasitic volcano capped by a small, 0.8 x 1.2 km ice-filled summit caldera was constructed within a large late-Pleistocene or early Holocene scarp formed by massive edifice failure that truncated an ancestral volcano and produced a submarine debris avalanche. Deposits from this and an older debris avalanche from a source to the south cover a broad area of the ocean floor north of the volcano. The summit lies along the eastern rim of the younger collapse scarp. Deposits from an earlier caldera-forming eruption of unknown age cover the flanks of the island to a depth up to 6 m. The small younger caldera was partially filled by lava domes emplaced in 1945 and 1974, and five small older flank lava domes, two of which lie on the coastline, were constructed along northwest- and NNW-trending lines. Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano. Historical eruptions have been recorded since the late-19th century.

Nyiragongo, DR Congo

1.52°S, 29.25°E, Summit elev. 3470 m

Goma Volcano Observatory (GVO) reported that a small area of incandescence from the floor of Nyiragongo’s collapsed crater was visible in a 26 July satellite image.

Geological summary: One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes of a stratovolcano contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

Pagan, Mariana Islands (USA)

18.13°N, 145.8°E, Summit elev. 570 m

Residents reported felt earthquakes and observed minor emissions at Pagan at around 1430 on 29 July. The Aviation Color Code and the Volcano Alert Level were raised to Yellow/Advisory, respectively.

Geological summary: Pagan Island, the largest and one of the most active of the Mariana Islands volcanoes, consists of two stratovolcanoes connected by a narrow isthmus. Both North and South Pagan stratovolcanoes were constructed within calderas, 7 and 4 km in diameter, respectively. North Pagan at the NE end of the island rises above the flat floor of the northern caldera, which may have formed less than 1,000 years ago. South Pagan is a stratovolcano with an elongated summit containing four distinct craters. Almost all of the recorded eruptions, which date back to the 17th century, have originated from North Pagan. The largest eruption during historical time took place in 1981 and prompted the evacuation of the sparsely populated island.

Savo, Solomon Islands

9.13°S, 159.82°E, Summit elev. 485 m

According to a news source, residents on Savo in the Solomon Islands reported increased seismicity to authorities on 28 July. Two days later a team from the Geological Survey Division (GSD) and the National Disaster Management Office (NDMO) investigated the volcano. They saw steam-and-gas emissions rising from an area in the crater, possibly indicating an active fissure, and interviewed residents. The GSD briefed the National Disaster Operations Committee and other authorities on 31 July, confirming the increased seismicity, and prompting a preparedness response. Response actions included continuing to monitor the island, deploying technical teams, and issuing Volcano Safety Messages to inform residents of the island as well as in surrounding areas.

Geological summary: The 6 x 7 km island of Savo consists of a forested andesitic-to-dacitic stratovolcano with a shallow, elliptical 1 x 1.5 km wide summit crater. Lava domes of historical age are located on the crater floor and its NE rim, and older domes occur on the flanks of the volcano. Pyroclastic flows and mudflows traveled down valleys from the summit crater to form debris fans along the coast. Thermal areas located in the summit crater, the south to SE flanks, and offshore include areas of steaming ground, fumaroles, small geysers, and hot springs. Spanish explorers arrived in 1568 during the first historical eruption of Savo. Pyroclastic flows during the climactic phase killed almost all inhabitants of the island, and oral traditions also note the expansion of the island on the northern side. Other eruptive episodes occurred during the mid-17th century and during the 1830s to 1840s.

Semisopochnoi, Aleutian Islands (USA)

51.93°N, 179.58°E, Summit elev. 1221 m

AVO reported that seismicity at Semisopochnoi had increased in recent days. A notable increase at 0200 on 31 July prompted AVO to raise the Aviation Color Code to Orange and the Volcano Alert Level to Watch a few hours later. Additionally, increased infrasound recorded by local stations suggested low-level emissions. Weather clouds obscured satellite views, though a possible sulfur dioxide plume was detected. Steaming was visible in webcam images. Increased seismicity and elevated activity in infrasound data were recorded during 31 July-1 August, and multiple, discrete, energetic explosions were detected during 1-3 August. Weather clouds again obscured satellite views; steaming was visible in webcam views. Beginning at 1015 on 2 August the local networks recorded an explosion and an intense burst of seismic and acoustic tremor that lasted for about 15 minutes. A small ash cloud was visible in satellite images drifting 60 km N at altitudes of 1.5-3 km (5,000-10,000 ft) a.s.l. Ash emissions from the active vent in North Crater were visible in webcam views on the morning of 3 August.

Geological summary: Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island's northern part. The three-peaked Mount Cerberus was constructed within the caldera during the Holocene. Each of the peaks contains a summit crater; lava flows on the N flank of Cerberus appear younger than those on the south side. Other post-caldera volcanoes include the symmetrical Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented eruptions have originated from Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone could have been recently active.

Ulawun, New Britain (Papua New Guinea)

5.05°S, 151.33°E, Summit elev. 2334 m

According to the Darwin VAAC, pilots observed ash plumes from Ulawun on 29 July and 3 August rising 3-3.4 km (10,000-11,000 ft) a.s.l. and drifting E and SSE, respectively. Weather clouds prevented satellite confirmation of the emissions.

Geological summary: The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Ongoing activity

Aira, Kyushu (Japan)

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

JMA reported that incandescence from Minamidake Crater (at Aira Caldera’s Sakurajima volcano) was visible at night during 26 July-2 August. An eruptive event at 2009 on 28 July produced a plume that rose 1.3 km above the crater rim. A very small eruptive event was recorded on 2 August. The Alert Level remained at 3 (on a 5-level scale), and residents were warned to stay 2 km away from the crater.

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.

Aniakchak, United States

56.88°N, 158.17°W, Summit elev. 1341 m

AVO reported that strong winds in a region N of Aniakchak and E of Port Heiden resuspended ash and blew it N on 2 August. A dense cloud of possible resuspended ash near ground levels was identified in Port Heiden webcam views. The cloud was also visible in satellite data drifting about 200 km N. The report noted that resuspended ash clouds typically do not rise above 5 km (16,400 ft) a.s.l. The cloud was not a result of volcanic activity; the Aviation Color Code and the Volcano Alert Level remained at Green and Normal, respectively.

Geological summary: One of the most dramatic calderas of the Aleutian arc, the 10-km-wide Aniakchak caldera formed around 3,400 years ago during a voluminous eruption in which pyroclastic flows traveled more than 50 km N to the Bering Sea and also reached the Pacific Ocean to the south. At least 40 explosive eruptions have been documented during the past 10,000 years, making it the most active volcano of the eastern Aleutian arc. A dominantly andesitic pre-caldera volcano was constructed above basement Mesozoic and Tertiary sedimentary rocks that are exposed in the caldera walls to elevations of about 610 m. The ice-free caldera floor contains many pyroclastic cones, tuff cones, maars, and lava domes. Surprise Lake on the NE side drains through The Gates, a steep-walled breach on the east side of the 1-km-high caldera rim that was the site of catastrophic draining of a once larger lake about 1850 years BP. Vent Mountain and Half Cone are two long-lived vents on the south-central and NW caldera floor, respectively. The first and only confirmed historical eruption took place in 1931 from vents on the west and SW caldera floor.

Bagana, Bougainville (Papua New Guinea)

6.137°S, 155.196°E, Summit elev. 1855 m

The Darwin VAAC reported that on 31 July an ash plume from Bagana rose to 4.6 km (15,000 ft) a.s.l. based on a pilot observation. A few hours later steam emissions were identified in satellite images.

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.

Dukono, Halmahera (Indonesia)

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

Based on satellite and wind model data, the Darwin VAAC reported that during 27-30 July and 1-3 August ash plumes from Dukono rose to 1.8-2.1 km (6,000-7,000 ft) a.s.l. and drifted NE, E, and SE. 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

A thermal anomaly over Ebeko was identified in satellite images on 25 July. According to volcanologists in Severo-Kurilsk (Paramushir Island), about 7 km E of Ebeko, explosions during 26-28 July produced ash plumes that rose as high as 2 km (6,600 ft) a.s.l. and drifted E. 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.

Gareloi, United States

51.79°N, 178.794°W, Summit elev. 1573 m

AVO reported that the elevated seismicity first detected at Gareloi in May had continued through June and then declined to background levels. On 28 July the Aviation Color Code was lowered to Green and the Volcano Alert Level was lowered to Normal.

Geological summary: The 8 x 10 km Gareloi Island, the northernmost volcano of the Delarof Group at the western end of the Andreanof Islands, consists of a stratovolcano with two summits and a prominent SE-trending fissure. The fissure was formed during an eruption in 1929 and extends from the southern summit to the sea. Steep sea cliffs that are cut into rocks of an older, eroded center are found on the SW coast, and submarine deposits of three debris avalanches produced by edifice collapse are found offshore. Young lava flows cover the older volcano from the summit to the coast along three broad axes trending NW, ENE, and S. The 1929 eruption originated from 13 craters along a 4-km-long fissure. Phreatic explosions were followed by the ejection of glassy pumice, lapilli, scoria, and older blocks, as well as by the emission of four short, steep lava flows, one of which reached the SE coast.

Kadovar, Papua New Guinea

3.608°S, 144.588°E, Summit elev. 365 m

Based on satellite and wind model data, the Darwin VAAC reported that on 1 August an ash plume from Kadovar rose to an altitude of 1.5 km (5,000 ft) a.s.l. and drifted W.

Geological summary: The 2-km-wide island of Kadovar is the emergent summit of a Bismarck Sea stratovolcano of Holocene age. It is part of the Schouten Islands, and lies off the coast of New Guinea, about 25 km N of the mouth of the Sepik River. Prior to an eruption that began in 2018, a lava dome formed the high point of the andesitic volcano, filling an arcuate landslide scarp open to the south; submarine debris-avalanche deposits occur in that direction. Thick lava flows with columnar jointing forms low cliffs along the coast. The youthful island lacks fringing or offshore reefs. A period of heightened thermal phenomena took place in 1976. An eruption began in January 2018 that included lava effusion from vents at the summit and at the E coast.

Karymsky, Eastern Kamchatka (Russia)

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

KVERT reported that a thermal anomaly over Karymsky was identified in satellite images during 23-30 July. Multiple explosions during the week produced ash plumes that rose to 2 km (6,600 ft) a.s.l. and drifted about 350 km E. 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.

Krysuvik-Trolladyngja, Iceland

63.917°N, 22.067°W, Summit elev. 360 m

The fissure eruption in the W part of the Krýsuvík-Trölladyngja volcanic system, close to Fagradalsfjall on the Reykjanes Peninsula, continued during 28 July-3 August. Lava fountaining and overflows from the fifth vent occurred at intervals of 10-15 hours, with similarly long periods of no activity in between; this pattern emerged around 17 July. According to the Institute of Earth Sciences an overflight was conducted on 27 July; based on new measurements, the lava effusion rate averaged 11 cubic meters per second during 2-27 July, though the average since 17 July was likely lower. The area of the flow field had grown to 4.3 square kilometers, and the total volume erupted was 109 million cubic meters. Lava flowed into the Meradalir Valley and areas to the W and did not advance in the Geldingadalur, Nátthaga, and Sydri Meradalir (SE of the fifth vent) valleys. The flows in Meradalir thickened about 1 m per day. The Aviation Color Code remained at Orange due to the lack of ash and tephra emissions, though IMO warned of the potential for lapilli and scoria fallout within a 650 m radius of the active vent. Authorities also warned of gas emissions hazards.

Geological summary: The Krýsuvík-Trölladyngja volcanic system is described by the Catalogue of Icelandic Volcanoes as an approximately 50-km-long composite fissure swarm trending about N38°E, including a 30-km-long swarm of fissures, with no central volcano. It is one of the volcanic systems arranged en-echelon along the Reykjanes Peninsula west of Kleifarvatn lake. The Fagradalsfjall and Krýsuvík fissure swarms are considered splits or secondary swarms of the Krýsuvík–Trölladyngja volcanic system. Small shield volcanoes have produced a large portion of the erupted volume within the system. Several eruptions have taken place since the settlement of Iceland, including the eruption of a large basaltic lava flow from the Ogmundargigar crater row around the 12th century. The latest eruption, identified through tephrochronology, took place during the 14th century.

Lewotolok, Lembata Island (Indonesia)

8.274°S, 123.508°E, Summit elev. 1431 m

PVMBG reported that the Strombolian eruption at Lewotolok continued during 27 July-2 August. Daily white, gray, and black plumes rose as high as 1 km above the summit and drifted in multiple directions. At 0023 on 28 July an eruptive event accompanied by a loud bang ejected incandescent lava 700-800 m from the crater. At 0722 another event ejected incandescent lava 1 km SE. Vegetated areas on the S and SW flanks caught fire, which quickly spread to the SE and W flanks due to dry conditions, burning forest as far as 2 km from the crater. At 0840 on 30 July lava was again ejected 1 km SE and loud rumbling was reported. By the morning of 30 July, the fire on the flanks was less intense and declining, but remained active at least through 1 August. Banging noises were reported on 31 July and 2 August. The Alert Level remained at 3 (on a scale of 1-4) and the public was warned to stay 3 km away from the summit crater.

Geological summary: The Lewotolok (or Lewotolo) stratovolcano occupies the eastern end of an elongated peninsula extending north into the Flores Sea, connected to Lembata (formerly Lomblen) Island by a narrow isthmus. It is symmetrical when viewed from the north and east. A small cone with a 130-m-wide crater constructed at the SE side of a larger crater forms the volcano's high point. Many lava flows have reached the coastline. Eruptions recorded since 1660 have consisted of explosive activity from the summit crater.

Mayon, Luzon (Philippines)

13.257°N, 123.685°E, Summit elev. 2462 m

On 30 July PHIVOLCS lowered the Alert Level for Mayon to 0 (on a 0-5 scale) noting that activity had declined to baseline levels over the previous several months. Ground deformation data indicated tectonic origins rather than magmatic or hydrothermal causes. The frequency of volcanic earthquakes had declined to baseline levels (0-5 events/day) during the previous six months and sulfur dioxide flux had dropped to 156 tonnes/day on 14 July, below the baseline of 500 tonnes/day. Dim crater incandescence from hot gas emissions at the summit continued to be visible in camera images; the last time it was visually observed was in May 2021. PHIVOLCS reminded residents to stay away from the 6-km-radius Permanent Danger Zone.

Geological summary: Beautifully symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the Philippines' most active volcano. The structurally simple edifice has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions date back to 1616 and range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

Merapi, Central Java (Indonesia)

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

BPPTKG reported that the lava dome just below Merapi’s SW rim and the lava dome in the summit crater both remained active during 23-29 July. The SW rim lava-dome volume was an estimated 1.878 million cubic meters and material continued to collapse down the flank. The volume of the summit lava dome was 2.817 million cubic meters. A total of four pyroclastic flows descended the SW flank as far as 2.5 km. Lava avalanches traveled a maximum of 1.2 km SE (29 times), 2 km SW (145 times), 800 m W (four times), and 500 m NW (one time). Avalanches of material that descended the W flank originated from lava emplaced in 1992 and 1998, and material that descended the NW flank is from 1948 lava. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 5 km away from the summit.

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 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent 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.

Rincon de la Vieja, Costa Rica

10.83°N, 85.324°W, Summit elev. 1916 m

OVSICORI-UNA reported that an eruptive event at Rincón de la Vieja was recorded at 1133 on 1 August, though weather conditions prevented visual confirmation of emissions.

Geological summary: Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A Plinian eruption producing the 0.25 km3 Río Blanca tephra about 3,500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Sheveluch, Central Kamchatka (Russia)

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

KVERT reported that a thermal anomaly over Sheveluch was identified in satellite images during 23-30 July. Activity was notable on 26 July with collapses of lava-dome blocks and small explosions. A gas-and-steam plume with some ash was visible in satellite data drifting 45 km E that same day. 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.

Sinabung, Indonesia

3.17°N, 98.392°E, Summit elev. 2460 m

PVMBG reported that at 1320 on 28 July an eruption at Sinabung produced dense ash plumes that rose as high as 4.5 km above the summit that drifted E and S; pyroclastic flows traveled as far as 1 km down the E and SE flanks. The event lasted over 12 minutes, and caused ashfall in areas to the E including the subdistricts of Namanteran, Merdeka, Berastagi, and Simpang Empat. White plumes rose up to 500 m above the summit during 29 July-2 August; weather conditions sometimes prevented visual observations. 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: 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. The youngest deposit is a SE-flank pyroclastic flow 14C dated by Hendrasto et al. (2012) at 740-880 CE. 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.

Suwanosejima, Ryukyu Islands (Japan)

29.638°N, 129.714°E, Summit elev. 796 m

JMA reported that during 26-30 July bombs ejected from Suwanosejima's Ontake Crater landed as far as 500 m away from the crater and plumes rose as high as 3.3 km above the rim. Explosive activity had been elevated during June and most of July, with ejected bombs landing as far as 1 km from the crater. Activity peaked on 22 July but then declined afterwards. The Alert Level was lowered to 2 (on a 5-level scale) at 1100 on 29 July and JMA warned the public to stay 1 km away from the crater.

Geological summary: The 8-km-long, spindle-shaped island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit is truncated by a large breached crater extending to the sea on the east flank that was formed by edifice collapse. Suwanosejima, one of Japan's most frequently active volcanoes, was in a state of intermittent strombolian activity from Otake, the NE summit crater, that began in 1949 and lasted until 1996, after which periods of inactivity lengthened. The largest historical eruption took place in 1813-14, when thick scoria deposits blanketed residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed forming a large debris avalanche and creating the horseshoe-shaped Sakuchi caldera, which extends to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

Source: GVP


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