JMA reported ongoing eruptive activity at Minamidake Crater (Aira Caldera’s Sakurajima volcano) characterized as explosions and eruptive events during 5-12 August. Nighttime crater incandescence was visible in webcam images. An explosion at 0037 on 6 August produced an ash plume that rose 3 km above the crater rim and drifted SW and ejected large blocks 1.3-1.7 km from the crater rim. A large amount of ash fell in Kagoshima City (about 10 km W) within an hour after the explosion. An explosion at 2137 generated an ash plume that rose 800 m above the crater rim before merging into weather clouds and ejected large blocks 800-1,100 m from the crater rim. An ash plume from an explosion at 1444 on 7 August rose 2.3 km above the crater rim and drifted S. Eruptive events at 0329 on 6 August, 1207 on 7 August, 2308 on 8 August, 1913 and 2239 on 9 August, and 0541 on 12 August produced ash plumes that rose 1.1-1.7 km above the crater rim and rose above the crater or drifted S and SE. The Alert Level remained at 3 (on a 5-level scale), and the public was warned to stay 1 km away from both craters.

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.

Source: Japan Meteorological Agency (JMA)