In September, three explosions . . . were recorded. Two of the September explosions were followed by air shocks. Ash emission without explosion sounds occurred throughout the month. On 9 September at 0713, an explosion preceded emission of the month's highest plume (2,800 m). At the observatory, 523 g/m² of ash accumulated during 13 days of ashfall in September. A total of 1,833 volcanic earthquakes were detected at the B station and earthquake swarms were recorded on five days (2, 3, 8, 9, and 29 September).

Activity was low during the first half of October but increased later in the month. Eight explosions were recorded, bringing the year's total to 150. Ashfall at [KLMO] dropped to 393 g/m² in October. On 23 October, an ash plume reached 2,000 m altitude.

Satellite data showed a plume on 30 August that reached an estimated altitude of 3,600 m and extended ~110 km SE. On 27 September at 2329, a plume extended 40-50 km SE of the volcano, and on 13 October at 2137, a 3,000-m plume extended ~40 km ENE.

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; W. Gould, NOAA.