Report on Aira (Japan) — August 1978
Scientific Event Alert Network Bulletin, vol. 3, no. 8 (August 1978)
Managing Editor: David Squires.
Aira (Japan) Continuing earthquake swarms and explosions
Please cite this report as:
Global Volcanism Program, 1978. Report on Aira (Japan). In: Squires, D (ed.), Scientific Event Alert Network Bulletin, 3:8. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN197808-282080.
31.593°N, 130.657°E; summit elev. 1117 m
All times are local (unless otherwise noted)
During July, 25 explosions from the summit crater of Minami-dake were recorded. Large quantities of tephra (blocks, lapilli, and ash) were ejected by three explosions on 30-31 July. Strong [SE] winds from a typhoon carried the ejecta to [an inhabited area] 10 km [NW of] the crater. Three persons were slightly injured, and [windowpanes] were broken in 62 houses and 45 cars. More than 50 earthquake swarms, each lasting several hours, occurred during 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, Tokyo.