JMA reported ongoing activity at both Minamidake Crater and Showa Crater (Aira Caldera’s Sakurajima volcano) during 28 August-4 September. Incandescence at Minamidake was observed nightly. An explosion at 0640 on 31 August from the same crater ejected large blocks 400 m away and likely produced a plume that was obscured by weather clouds. Very small eruptive events continued to be detected during the rest of the week. A very small eruption at Showa Crater was also recorded on 4 September. The Alert Level remained at 3 (on a 5-level scale), and the public was warned to stay 2 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)