Report on Aira (Japan) — January 1985
Scientific Event Alert Network Bulletin, vol. 10, no. 1 (January 1985)
Managing Editor: Lindsay McClelland.
Aira (Japan) Explosions with strong air shocks; 1984 activity summary
Please cite this report as:
Global Volcanism Program, 1985. Report on Aira (Japan) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 10:1. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198501-282080.
31.593°N, 130.657°E; summit elev. 1117 m
All times are local (unless otherwise noted)
Explosive activity at the summit crater of Minami-dake declined August-November, then increased in December when 59 explosions were recorded. An explosion at 1820 on 20 December was accompanied by an air shock powerful enough to have been recorded at Uwajima (260 km NE); ash and lapilli up to 2 cm in diameter fell on the road at the S foot and broke a car windshield. An explosion at 2132 on the 31st was accompanied by another strong air shock that broke 11 windowpanes in three of the hotels at the S foot. The rate of explosions decreased in January, when 20 were recorded. A strong air shock recorded at Uwajima, Nobeoka (140 km NE), Kumamoto (135 km N, and other places broke a windowpane in a S-foot hotel on 23 January.
Geologic Background. 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.
Information Contacts: JMA, Tokyo.