Report on Aira (Japan) — September 1981
Scientific Event Alert Network Bulletin, vol. 6, no. 9 (September 1981)
Managing Editor: Lindsay McClelland.
Aira (Japan) Frequent explosions, mud-like ejection
Please cite this report as:
Global Volcanism Program, 1981. Report on Aira (Japan) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 6:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198109-282080
31.593°N, 130.657°E; summit elev. 1117 m
All times are local (unless otherwise noted)
Frequent explosions from the summit crater of Minami-dake continued through September, after increasing from one in July to 34 in August. None of the 38 recorded in September caused any damage. Ash clouds higher than 2 km above the summit were observed on 13, 14, 18, 20, and 23 September. On the 13th an ash cloud that rose to 2.6 km was ejected simultaneously with [dense powder] that covered a 100 x 100 m area on the W slope of the active crater. The highest cloud rose to 2.7 km, also on the 13th.
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, Tokyo.