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Report on Aira (Japan) — April 1980


Scientific Event Alert Network Bulletin, vol. 5, no. 4 (April 1980)
Managing Editor: David Squires.

Aira (Japan) Explosions and incandescent tephra

Please cite this report as:

Global Volcanism Program, 1980. Report on Aira (Japan) (Squires, D., ed.). Scientific Event Alert Network Bulletin, 5:4. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198004-282080



31.5772°N, 130.6589°E; summit elev. 1117 m

All times are local (unless otherwise noted)

Twenty explosions from Sakura-jima were recorded in February and 10 in March (figure 5), none of which caused any damage. Ash emission without explosions occurred less frequently in February and March than has been usual over the past 5 years.

Figure (see Caption) Figure 5. Summary table of explosions from Minami-dake crater at Sakura-jima, 1980. Data courtesy of JMA.

Two bursts of B-type earthquakes were recorded in the 2-month period. About 1,000 events occurred in 11 hours on 13 February and about 500 in 5 hours on 15 March. Both of these bursts, thought by JMA geologists to be caused by magma rising in the vent, were followed by increased explosion activity. In addition, columns of incandescent tephra were ejected after the February earthquakes. On 14 February, two columns rose 200 m at 0438 and a 400-m column was ejected at 2137.

Activity beginning late 15 February was typical of the more prolonged eruptive periods that have characterized Sakura-jima since explosions resumed in August 1979. Soon after a loud explosion at 2241, two columns of incandescent tephra rose 200 m above the summit. Ejection of incandescent blocks was almost continuous until about midnight, then occurred every few minutes until 0110 on the 16th. Lapilli up to 3 cm in diameter fell on inhabited areas, but caused no damage. Much lightning was seen in the eruption clouds. Strong, continuous air vibrations rattled windows in towns at the base of the volcano. A seismograph recorded strong tremor until about 0100 on 16 February. By about 0300, eruptive activity had declined, and vapor emission or weak ash ejection continued until the 9 March explosion.

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 caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim and built an island that was joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4,850 years ago, after which eruptions took place at Minamidake. Frequent eruptions since the 8th century have deposited ash on the city of Kagoshima, located across Kagoshima Bay only 8 km from the summit. The largest recorded eruption took place during 1471-76.

Information Contacts: JMA, Tokyo.