Report on Aira (Japan) — July 1986
Scientific Event Alert Network Bulletin, vol. 11, no. 7 (July 1986)
Managing Editor: Lindsay McClelland.
Aira (Japan) Explosions; heavy ashfall
Please cite this report as:
Global Volcanism Program, 1986. Report on Aira (Japan). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 11:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198607-282080.
31.593°N, 130.657°E; summit elev. 1117 m
All times are local (unless otherwise noted)
There were four recorded explosions . . . in July, on the 1st, 6th, 19th and 20th. Ashfall was heavy during the last part of the month, especially on the 28th and 30th. Some facilities of the National Railroad malfunctioned due to ashfall, causing delays in train operation on the 29th. Monthly ashfall accumulation was 1,533 g/m2, sixth highest since 1969 (when observation of ash accumulation started at KLMO). The maximum plume height over the crater was 3,000 m on 28 July.
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.