Report on Aira (Japan) — September 1976
Natural Science Event Bulletin, vol. 1, no. 12 (September 1976)
Managing Editor: David Squires.
Aira (Japan) Daily explosions during June-September; frequent ashfall
Please cite this report as:
Global Volcanism Program, 1976. Report on Aira (Japan). In: Squires, D. (ed.), Natural Science Event Bulletin, 1:12. Smithsonian Institution. https://doi.org/10.5479/si.GVP.NSEB197609-282080.
31.593°N, 130.657°E; summit elev. 1117 m
All times are local (unless otherwise noted)
An explosion at 0727 on 5 June deposited a small amount of lapilli (to 1 cm in diameter) at Kurokami, 5 km E of the crater. Maximum June ash cloud height exceeded 3000 m. Ashfalls were frequent during late June at Kagoshima City, 10 km W of the crater. Volcanic earthquakes occurred frequently. July explosions were small, but ash emission was heavy. The maximum height of ash clouds was 3000 m. Kagoshima City continued to experience frequent ash falls. The July 26th explosion occurred at 0357, producing a felt air shock. Vibrations continued to be felt after the explosion at Higashi-Sakura-jima, 3 km SSW of the crater.
Detonations, air shocks, cinder falls, [an incandescent column], and frequent ashfalls were noted during August. The maximum eruption cloud height 1-10 September was 2000 m.
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.