Report on Aira (Japan) — November 1982
Scientific Event Alert Network Bulletin, vol. 7, no. 11 (November 1982)
Managing Editor: Lindsay McClelland.
Aira (Japan) Explosions decline, but plane encounters plume
Please cite this report as:
Global Volcanism Program, 1982. Report on Aira (Japan) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 7:11. Smithsonian Institution.
31.593°N, 130.657°E; summit elev. 1117 m
All times are local (unless otherwise noted)
Explosive activity at the summit crater of Minami-dake and local seismicity have declined since September. Two explosions were recorded in September, 6 in October, and 4 in November. An explosion at 1130 on 17 September was followed by continuous ash ejection, without explosion [shocks], lasting for 98 minutes and resulting in heavy ashfall on the S half of the city of Kagoshima, about 15 km NW. In October, ash ejection occurred every day, although few explosions were recorded. The frequent ash ejection was accompanied by an increase in the number of recorded tremor events, which totaled 334 hours in October.
Each of the November explosions produced lapilli ejection, air shocks, and sounds. At 1523 on 23 November, the largest explosion of the 3-month period sent an eruption cloud to 3 km. The cloud was observed from the JMA's Miyakonojo Weather Station, 45 km ENE. An Air Nauru jet carrying 39 passengers and flying at about 3 km altitude entered the cloud 23 km ESE of Sakura-jima at 1545, 6 minutes after leaving Kagoshima Airport. The impact of the lapilli produced hairline cracks in three cockpit windows, prompting the pilot to return to Kagoshima, where he landed safely. At the SE foot of the volcano, a car windshield was destroyed.
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; UPI.