Report on Aira (Japan) — January 1981
Scientific Event Alert Network Bulletin, vol. 6, no. 1 (January 1981)
Managing Editor: Lindsay McClelland.
Aira (Japan) Earthquake swarm followed by glow and explosions
Please cite this report as:
Global Volcanism Program, 1981. Report on Aira (Japan). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 6:1. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198101-282080.
31.593°N, 130.657°E; summit elev. 1117 m
All times are local (unless otherwise noted)
A burst of B-type earthquakes that began at 0200 on 18 January prompted the JMA observatory at Sakura-jima to issue an explosion warning at 0930. Reflected glow was seen over the summit that night. Four strong explosions occurred during the next two days (figure 6). Each of the first three produced a 200-m-high incandescent column. The fourth, strongest explosion at 1632 on 20 January ejected an incandescent block that formed a 1.3-m-diameter crater when it fell near an inhabited area. Similar occurrences of B-type earthquake bursts, reflected glow of the lava mound in the crater, and explosions were observed in July and August 1979. None of the January explosions caused any damage.
|Figure 6. Summary table of explosions from Minami-dake crater at Sakura-jima, 1981. Data courtesy of JMA.|
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.