Report on Aira (Japan) — December 1983
Scientific Event Alert Network Bulletin, vol. 8, no. 12 (December 1983)
Managing Editor: Lindsay McClelland.
Aira (Japan) Tephra from strong explosions damage cars and buildings
Please cite this report as:
Global Volcanism Program, 1983. Report on Aira (Japan) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 8:12. Smithsonian Institution.
31.593°N, 130.657°E; summit elev. 1117 m
All times are local (unless otherwise noted)
Recorded explosive eruptions from the summit crater of Minami-dake were frequent in August  and September (36), fewer in October (21) and November (16). In mid-August strong wind carried a large amount of ejecta to the inhabited area around the volcano, damaging cars and houses. On 14 August lapilli as large as 6-7 cm in diameter fell on Nojiri, at the foot of Sakura-jima 4 km SW of Minami-dake, breaking or cracking windshields on 16 cars, a house windowpane, and the roof of a hut. Radio news from Kagoshima reported that windshields on three cars were cracked by lapilli as large as 1-3 cm in diameter at Tarumizu Wharf, on the S side of the city. An explosion at 0153 on 16 August scattered lapilli up to 2.5 cm in diameter between Mochiki and Yumoto (3.5 km SSW of Minami-dake), where windshields on 26 cars ware cracked.
Explosive activity remained at a high level in September. Incandescent blocks from an explosion at 1148 on 12 September started a flank [brush] fire. A heavy ashfall on 17-18 September deposited 270 g/m2 of ash at JMA's Kagoshima Observatory (table 5); a Kagoshima streetcar derailed on 19 September due to ash on the tracks. A large air shock from an explosion at 1518 on 20 September broke windows in Kagoshima, and another explosion at 1638 sent lapilli as large as 1 cm in diameter toward the N. Five debris flows moved down S flank valleys on 1, 10, 20, and 21 September. Bursts of discrete seismic events were frequent in September. Bursts on 19 and 28 September lasted for about 10 hours and included large events.
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 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.