Report on Suwanosejima (Japan) — 14 August-20 August 2002

Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 14 August-20 August 2002
Managing Editor: Gari Mayberry

Please cite this report as:

Global Volcanism Program, 2002. Report on Suwanosejima (Japan). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 14 August-20 August 2002. Smithsonian Institution and US Geological Survey.

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Suwanosejima

Japan

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

All times are local (unless otherwise noted)


Small explosive eruptions occurred at Suwanose-jima on 19 August. JMA reported that on the 19th two periods of continuous acoustic signals were recorded for 20-30 minutes each beginning around 0000 and 0630. The signals were the largest recorded thus far this year. Explosions and rumbling were heard from Toshima village, and an ash plume drifted to the SW. Volcanic tremor with continuous large acoustic signals was also recorded later in the day during 0940-0950 and 1410-1500. Small tremor events also occurred, and ash rose above the summit to an unknown height and drifted SE.

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 of the volcano 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) via the Volcano Research Center, Kyodo News, Associated Press