Report on Aira (Japan) — November 1986
Scientific Event Alert Network Bulletin, vol. 11, no. 11 (November 1986)
Managing Editor: Lindsay McClelland.
Aira (Japan) Ash and block eruptions; 2.5 m block injures six people
Please cite this report as:
Global Volcanism Program, 1986. Report on Aira (Japan) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 11:11. Smithsonian Institution.
31.593°N, 130.657°E; summit elev. 1117 m
All times are local (unless otherwise noted)
At 1602 on 23 November, the 206th explosion recorded this year ejected a 2.5-m-diameter block onto a one-story concrete building at the foot of the volcano, 3 km S of the crater. Six people in the building were injured as the block, estimated to weigh 5 metric tons, broke through the roof and ground floor of the hotel and landed in the basement. Two other large blocks (1-1.5 m diameter) that landed near the hotel created a depression and started a grass fire. On 27 November, at 0532, 300-m eruption columns were emitted. Observers heard a loud explosion and saw blocks being ejected. Twelve explosions were recorded in November, and total ash accumulation was 52 g/m2, at [KLMO].
During October, 21 explosions were recorded and earthquake swarms occured on 9 days. The ash cloud reached its maximun height of 2,000 m above the crater on 11, 12, and 30 October. At 1150 on 30 October a large amount of lapilli was ejected, damaging three car windshields. A total of 25 g/m2 of ash accumulated at [KLMO].
Geological Summary. 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; NHK Television Network, Tokyo; The Daily Yomiuri newspaper, Tokyo; Kyodo News Agency, Tokyo; UPI.