JMA reported that during 30 March-6 April incandescence from Minamidake Crater (at Aira Caldera’s Sakurajima volcano) was visible nightly. The seismic network recorded 22 eruptive events and one explosion (at 1558 on 4 April). The highest plume during the period rose to 3.8 km above the crater rim, visible at 1621 on 4 April. Material was ejected 500-900 m away from the crater. The Alert Level remained at 3 (on a 5-level scale).

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)