Report on Aira (Japan) — February 1985
Scientific Event Alert Network Bulletin, vol. 10, no. 2 (February 1985)
Managing Editor: Lindsay McClelland.
Aira (Japan) Explosion lofts lapilli that break 43 windshields
Please cite this report as:
Global Volcanism Program, 1985. Report on Aira (Japan). In: McClelland, L (ed.), Scientific Event Alert Network Bulletin, 10:2. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198502-282080.
31.593°N, 130.657°E; summit elev. 1117 m
All times are local (unless otherwise noted)
An explosion at the summit crater of Minami-dake on 24 February at about 1030 ejected a plume to 4 km height. Lapilli 4-5 cm in diameter fell as far as 5 km SE of the crater, damaging 43 cars at the S foot and in Tarumizu City (5 km SE). Brush fires started by hot tephra quickly died. An air shock was recorded in Miyazaki, about 75 km to the NE. In the 4 hours after 1200, 140 swarm earthquakes were recorded.
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: T. Tiba, National Science Museum, Tokyo; Kyodo News Service, Tokyo.