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Report on Aira (Japan) — September 1979


Scientific Event Alert Network Bulletin, vol. 4, no. 9 (September 1979)
Managing Editor: David Squires.

Aira (Japan) Explosions resume after 110-day hiatus

Please cite this report as:

Global Volcanism Program, 1979. Report on Aira (Japan) (Squires, D., ed.). Scientific Event Alert Network Bulletin, 4:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN197909-282080



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

All times are local (unless otherwise noted)

The following is a report from Manabu Komiya. "Sakura-jima exploded on 19 August after 110 days of quiescence, producing an ash cloud 1 km high. It was the 46th explosion of this year. Five more explosions occurred in early September, but none caused any damage. The fact that no explosion had occurred in 110 days does not immediately suggest decreasing volcanism, because intermittent ash emission without explosive shocks had occurred through the explosion-free period, as frequently as before. Daily ash emission often caused ashfalls at cities and towns near the volcano. Volcanic gas that flowed down the flanks damaged vegetation, adding to the damage caused by falling ash. Reflected glow above the crater was often observed at night during July and early August. Swarms of B-type earthquakes . . . (one burst consisted of hundreds of earthquakes) were recorded a few times per month in June and August. These facts indicate that the lava mound on the crater floor persisted or grew during this period. An aerial inspection on 30 July revealed a large mound that had reached a volume of 7 x 103 m, twice that of May."

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.