Report on Aira (Japan) — July 1978
Scientific Event Alert Network Bulletin, vol. 3, no. 7 (July 1978)
Managing Editor: David Squires.
Aira (Japan) Frequent explosions continue
Please cite this report as:
Global Volcanism Program, 1978. Report on Aira (Japan). In: Squires, D. (ed.), Scientific Event Alert Network Bulletin, 3:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN197807-282080.
31.593°N, 130.657°E; summit elev. 1117 m
All times are local (unless otherwise noted)
About 20 earthquakes . . . were recorded in June. . . . Consequently, JMA scientists believe that a large volume of magma remained on or just under the crater bottom in early June. Reuters reported a loud explosion on 21 July, producing a 1600-m eruption column, and two explosions on 23 July, throwing incandescent ejecta 2,500 m above the vent. UPI reported that strong winds from a typhoon spread about 2.5 cm of ash within 5 km of the summit after an explosion on 31 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; Reuters; UPI; D. Shackelford, CA.