Report on Suwanosejima (Japan) — September 1979
Scientific Event Alert Network Bulletin, vol. 4, no. 9 (September 1979)
Managing Editor: David Squires.
Suwanosejima (Japan) Six hours of explosions; air shocks rattle doors and windows 90 km away
Please cite this report as:
Global Volcanism Program, 1979. Report on Suwanosejima (Japan). In: Squires, D (ed.), Scientific Event Alert Network Bulletin, 4:9. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.SEAN197909-282030.
29.638°N, 129.714°E; summit elev. 796 m
All times are local (unless otherwise noted)
"On-take vent exploded on 5 September, after a few small explosions on 20 July (table 1). Explosive activity continued from about 2000 on 5 September to 0100 on 6 September. Incandescent columns rose 500 m above the crater and explosions occurred every 10 seconds during the most active stage on the 5th. Explosive sounds (rumblings) were heard at Yaku-shima Island, 90 km NE of Suwanose-jima, and windows and doors on Yaku-shima were rattled by air vibrations. Ash fell in the sea E of Suwanose-jima.
"A village of 65 people lies on Suwanose-jima Island. People there said that the activity on 5 September was one of the strongest of the many explosive periods since 1956. No damage was caused by the explosions. Explosions at the volcano had become less frequent this year than before."
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.