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Report on Aira (Japan) — December 1976


Natural Science Event Bulletin, vol. 1, no. 15 (December 1976)
Managing Editor: David Squires.

Aira (Japan) Continued frequent small explosions and ashfall

Please cite this report as:

Global Volcanism Program, 1976. Report on Aira (Japan) (Squires, D., ed.). Natural Science Event Bulletin, 1:15. Smithsonian Institution. https://doi.org/10.5479/si.GVP.NSEB197612-282080



31.5772°N, 130.6589°E; summit elev. 1117 m

All times are local (unless otherwise noted)

Almost all 1 November-20 December explosions were small. Strong detonations, air shocks and [incandescent columns] were sometimes observed at the Kagoshima meteorological observatory. Emission of [ash] clouds, some of which rose 3000 m above the crater, was almost continuous, and ashfalls around the crater were frequent. At the time of one of these (21 October at 1228), a large quantity of ash moved down the W slope, but it was not possible to confirm it as a nuée ardente. On 4 November at 1700, an overflight revealed a red-hot lava mass [or mound] (40 m across) at the bottom of the summit crater. A weak [reflection of] glow, probably caused by the lava, was sometimes seen during October.

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 caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim and built an island that was joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4,850 years ago, after which eruptions took place at Minamidake. Frequent eruptions since the 8th century have deposited ash on the city of Kagoshima, located across Kagoshima Bay only 8 km from the summit. The largest recorded eruption took place during 1471-76.

Information Contacts: JMA, Tokyo.