No explosions were recorded in August, the first explosion-free month since September 1990. However, ash eruptions without explosion shocks were seen nine times in August. Ash plumes rose 3.5 km . . . on 15 August and 3.2 km on 21 August. The KLMO . . . counts explosions detected by seismometer, microbarometer, felt air-shocks, and sounds. Quiet ash eruptions are detected visually. No swarms of volcanic earthquakes were reported during August.

Similar activity continued through 15 September, with three recorded explosions and seven quiet eruptions. On 7 September at 0552, the first explosion since 29 July ejected a 3-km ash plume with electrical discharges. Ash rose 3.5 km in a quiet eruption on 4 September.

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.