Report on Suwanosejima (Japan) — November 1981
Scientific Event Alert Network Bulletin, vol. 6, no. 11 (November 1981)
Managing Editor: Lindsay McClelland.
Suwanosejima (Japan) Three days of explosions
Please cite this report as:
Global Volcanism Program, 1981. Report on Suwanosejima (Japan). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 6:11. Smithsonian Institution.
29.638°N, 129.714°E; summit elev. 796 m
All times are local (unless otherwise noted)
After two months of quiesence, Crater B was active 25-28 November. Ash was ejected on 25 November. Explosive sounds were recorded from about 0200 on the 26th. Activity intensified to register 5-6 explosions/minute from 1230 to 1700 that day, then declined to about 10/hour. From 1700 on the 27th to 0200 on the 28th about four explosions/hour were recorded. On 28 November activity was limited to continuous emission of white vapor. The ash and blocks ejected during the activity caused no damage.
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.
Information Contacts: JMA, Tokyo.