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Report on Suwanosejima (Japan) — 29 July-4 August 2020

Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 29 July-4 August 2020
Managing Editor: Sally Kuhn Sennert

Please cite this report as:

Global Volcanism Program, 2020. Report on Suwanosejima (Japan). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 29 July-4 August 2020. Smithsonian Institution and US Geological Survey.

Volcano Profile |  Weekly Report (29 July-4 August 2020)


Suwanosejima

Japan

29.638°N, 129.714°E; summit elev. 796 m

All times are local (unless otherwise noted)


JMA reported that nighttime incandescence at Suwanosejima’s Ontake Crater was occasionally visible during 24-31 July. Occasional eruptive events were recorded. An explosion at 1200 on 27 July generated a gray plume that rose as high as 2 km above the crater rim. The Tokyo VAAC reported that during 1-3 August ash plumes rose to 1.8-2.4 km (6,000-8,000 ft) a.s.l. and drifted NW and W. The Alert Level remained at 2 (on a 5-level scale).

Geologic Background. 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.

Sources: Japan Meteorological Agency (JMA), Tokyo Volcanic Ash Advisory Center (VAAC)