During 11-15 August JMA reported 14 explosions from Showa Crater at Aira Caldera’s Sakurajima volcano that ejected ballistics 800-1300 m away. During 15-18 August were four more explosions with similar ballistic ejections. The explosions were accompanied by volcanic earthquakes and volcanic tremor. On most days faint to clear incandescence was visible using a high-sensitivity camera at night. On 13-17 August the Tokyo VAAC reported explosions with plumes that rose to an altitude of 1.5-3 km (5,000-10,000 ft) a.s.l. and drifted NE and N, though volcanic ash could not be identified in satellite data. The Alert Level remained at 3 (on a scale of 1-5).

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.

Sources: Japan Meteorological Agency (JMA), Tokyo Volcanic Ash Advisory Center (VAAC)