JMA reported ongoing activity at both Minamidake Crater and Showa Crater (Aira Caldera’s Sakurajima volcano) during 4-11 September. Incandescence at Minamidake was observed nightly. Very small eruptive events occurred at both craters on 4 September. Sulfur dioxide emissions were slightly high at 1,600 tons per day on that same day. An explosion on 1512 on 9 September produced an ash plume that rose 800 m above the crater rim and ejected large blocks 500-700 m from the crater. Another explosion at 0018 on 11 September generated an ash plume that rose 1.1 km and ejected large blocks 300-500 m; an ash plume rose 1.3 km from an explosion at 1642 on that same day. 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)