The Weekly Volcanic Activity Report: December 11 - 17, 2019

The Weekly Volcanic Activity Report: December 11 - 17, 2019

New activity/unrest was reported for 4 volcanoes from December 11 - 17, 2019. During the same period, ongoing activity was reported for 10 volcanoes.

New activity/unrest: Bezymianny, Central Kamchatka (Russia) | Nishinoshima, Japan | Semisopochnoi, United States | White Island, North Island (New Zealand).

Ongoing activity: Aira, Kyushu (Japan) | Asosan, Kyushu (Japan) | Dukono, Halmahera (Indonesia) | Ebeko, Paramushir Island (Russia) | Karangetang, Siau Island (Indonesia) | Klyuchevskoy, Central Kamchatka (Russia) | Sangay, Ecuador | Sangeang Api, Indonesia | Sheveluch, Central Kamchatka (Russia) | Shishaldin, Fox Islands (USA).

New activity/unrest

Bezymianny, Central Kamchatka (Russia)

55.972°N, 160.595°E, Summit elev. 2882 m

Activity at Bezymianny began to increase at the beginning of December, characterized by nighttime crater incandescence, strong fumarolic emissions, a lava flow, and gradually increasing temperatures of a satellite-detected thermal anomaly. KVERT increased the Aviation Color Code to Orange (the second highest level on a four-color scale) on 13 December.

Geological summary: Prior to its noted 1955-56 eruption, Bezymianny had been considered extinct. The modern volcano, much smaller in size than its massive neighbors Kamen and Kliuchevskoi, was formed about 4700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7000 years ago. Three periods of intensified activity have occurred during the past 3000 years. The latest period, which was preceded by a 1000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large horseshoe-shaped crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Nishinoshima, Japan

27.247°N, 140.874°E, Summit elev. 25 m

The Japan Coast Guard (JCG) reported that during an overflight of Nishinoshima on 15 December surveyors observed that explosions were occurring from the main crater of the pyroclastic cone every second to several seconds. Blocks were ejected as high as 300 m above the crater rim; red hot blocks were scattered at the base of the cone. Gray plumes rose from the crater, and lava continued flowing E into the sea. A new crater had opened on the N flank of the cone and effused lava that flowed NW down to the sea. JMA expanded the marine exclusion zone around the island to 2.5 km the next day.

Geological summary: The small island of Nishinoshima was enlarged when several new islands coalesced during an eruption in 1973-74. Another eruption that began offshore in 2013 completely covered the previous exposed surface and enlarged the island again. Water discoloration has been observed on several occasions since. The island is the summit of a massive submarine volcano that has prominent satellitic peaks to the S, W, and NE. The summit of the southern cone rises to within 214 m of the sea surface 9 km SSE.

Semisopochnoi, United States

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

AVO reported that during 10-17 December activity at Semisopochnoi remained elevated, with bursts of tremor and small explosions detected in both seismic and infrasound data. An 80-km-long gas-and-steam plume possibly containing ash was visible in satellite images during 11-12 December. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.

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 1221-m-high Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island's northern part. The three-peaked 774-m-high Mount Cerberus volcano was constructed during the Holocene within the caldera. Each of the peaks contains a summit crater; lava flows on the northern flank of Cerberus appear younger than those on the southern side. Other post-caldera volcanoes include the symmetrical 855-m-high 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 historical eruptions have originated from Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone within the caldera could have been active during historical time.

White Island, North Island (New Zealand)

37.52°S, 177.18°E, Summit elev. 294 m

GeoNet reported that the deadly 9 December eruption at White island modified the active crater area. The basin previously containing a hot acidic lake was mostly filled by debris with numerous, isolated ponds after the event. During overflights observers identified three main vents within a 100-square-meter area. Volcanic tremor significantly increased at around 0400 on 11 December and was accompanied by vigorous steaming and localized mud jetting from the active vent area. By the early evening tremor was at the highest level recorded since the 2016 eruption. On 12 December the Volcanic Alert Level was lowered to 2 (since no more eruptions had occurred since 9 December), though the Aviation Color Code remained at Orange. Later that day tremor levels decreased but remained very high compared to normal levels. Energetic steam-and-mud bursts continued from the active vent area. Gas emissions had increased compared to 10 December measurements. Tremor levels continued to decline during 12-13 December and then significantly dropped later on 13 December. During an overflight on 13 December observers noted small-scale gas jetting and steam bursts from the active vents. High heat flow was confirmed by a glow emanating from the vent area in overnight webcam images during 12-15 December; high-temperature (more than 200 degrees Celsius) volcanic gas was being emitted at a high rate when observed during an overflight on 15 December. GeoNet noted that data from various measurements suggested a magma source not far below the surface, possibly as shallow as tens of meters deep. According to the New Zealand Police the death toll from the 9 December eruption was 15, with two people still missing.

Geological summary: The uninhabited White Island, also know as Whakaari in the Maori language, is the 2 x 2.4 km emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes. The summit crater appears to be breached to the SE, because the shoreline corresponds to the level of several notches in the SE crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of eruptions since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. Formation of many new vents during the 19th and 20th centuries has produced rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities.

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 9-16 December. There were 15 explosions and 10 non-explosive eruptive events detected by the seismic network. Ash plumes rose 2.4 km above the crater rim, although explosions at 0115 and 2109 on 10 December generated ash plumes that rose 3 km above the crater rim. Blocks were ejected as far as 1.3 km away from the crater. 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 the eruption at Asosan that began on 7 October continued through 16 December. Ash plumes rose as high as 1 km and caused ashfall in areas downwind. The sulfur dioxide emission rate was 3,000-3,300 tons per day on 11 and 16 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 December ash plumes from Dukono rose to altitudes of 1.8-2.1 km (6,000-7,000 ft) a.s.l. and drifted in multiple directions. 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 6-13 December that sent ash plumes up to 4 km (13,100 ft) a.s.l. Ash plumes drifted E, causing ashfall in Severo-Kurilsk during 10-12 December. 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.

Karangetang, Siau Island (Indonesia)

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

PVMBG reported that during 9-15 December lava continued to effuse from Karangetang’s Main Crater (S), traveling as far as 1.8 km down the Nanitu, Pangi, and Sense drainages on the SW and W flanks. Sometimes dense white plumes rose to 500 m above the summit. Incandescence from both summit craters was visible at night. 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.

Klyuchevskoy, Central Kamchatka (Russia)

56.056°N, 160.642°E, Summit elev. 4754 m

KVERT reported that a weak thermal anomaly over Klyuchevskoy was identified in satellite images during 5, 7, and 11-12 December, and Strombolian activity was visible during 11-12 December. An ash plume rose to 4.5 km (14,800 ft) a.s.l. and drifted 30 km SE. The Aviation Color Code remained at Orange.

Geological summary: Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Sangay, Ecuador

2.005°S, 78.341°W, Summit elev. 5286 m

Based on information from the Guayaquil MWO, satellite images, and wind model data, the Washington VAAC reported that during 10-17 December ash plumes from Sangay rose to 5.8-7.3 km (19,000-24,000 ft) a.s.l. and drifted in multiple directions. A thermal anomaly was visible on 17 December.

Geological summary: The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador's volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within horseshoe-shaped calderas of two previous edifices, which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been sculpted by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of a historical eruption was in 1628. More or less continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

Sangeang Api, Indonesia

8.2°S, 119.07°E, Summit elev. 1912 m

The Darwin VAAC reported that during 11-13 and 17 December discrete ash emissions from Sangeang Api rose to an altitude of 2.4 km (8,000 ft) a.s.l. and drifted NW and W. A thermal anomaly was visible on 27 November. 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 was identified in satellite images during 6-13 December. 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

AVO reported that seismicity at Shishaldin remained elevated during 10-11 December; low-level tremor was detected along with three small explosions. Elevated surface temperatures were identified in satellite images and a steam plume drifting from the summit was visible in webcam images. A short-lived explosion began at 0710 on 12 December and lasted about three minutes, coincident with a three-minute long period of elevated tremor. The event generated an ash plume that rose to altitudes of 6.1-7.6 km (20,000-25,000 ft) a.s.l., drifted almost 85 km/hour WNW, and then dissipated a few hours later. Three lightning strokes were detected between 0715 and 0717. The explosion may have collapsed the summit spatter cone. Highly elevated surface temperatures were visible in satellite images during 12-13 December, and the webcam showed nighttime incandescence and a robust steam plume emanating from the summit. Seismicity remained elevated through 16 December and elevated surface temperatures continued to be detected. A plume appearing to contain ash drifted from the summit on 14 December. A lava flow was reported by a pilot on 16 December; the next day satellite images showed a 2-km-long flow on the NW flank. 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.

Source: GVP

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