Report on Aira (Japan) — April 1998
Bulletin of the Global Volcanism Network, vol. 23, no. 4 (April 1998)
Managing Editor: Richard Wunderman.
Aira (Japan) Amid ongoing explosions, a 19 May seismic swarm yields 220 earthquakes in 4 hours
Please cite this report as:
Global Volcanism Program, 1998. Report on Aira (Japan). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 23:4. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199804-282080.
31.593°N, 130.657°E; summit elev. 1117 m
All times are local (unless otherwise noted)
In accord with ongoing eruptions, careful monitoring, and close communication with aviators, frequent notices of activity at Sakura-jima were released during March-May. According to various advisories, an eruption at 0130 on 2 March sent ash to ~1.8 km where it drifted 20 km S; an eruption at 0816 on 24 March sent ash to ~1.8 km where it drifted SE; and an eruption at 0505 on 5 April sent ash to ~2.0 km where it drifted N. An advisory noted an eruption at 0253 on 13 April but no ash cloud information was reported.
A Japan Meteorological Agency (JMA) volcanic advisory on 19 May stated that a swarm of volcanic earthquakes started at about 1700; in the following 4 hours, approximately 220 earthquakes were recorded. Daily earthquake counts were 334 on 19 May and 41 on 20 May. During 20-21 May, the volcano produced ten eruptions, nine of which were explosive. JMA scientists warned that the volcano's activity might increase following the swarm. As of 21 May, 49 explosions had occurred at Sakura-jima in 1998.
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: Volcano Research Center, Earthquake Research Institute (ERI), University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan; Volcanological Division, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan.