JMA reported that on 1 April an explosion at Aira Caldera’s Sakurajima volcano generated an ash plume that rose 2 km above Showa's crater rim. An explosion at Minamidake summit crater also produced an ash plume which rose 800 m above its crater rim. Three of five explosions detected at Showa during 1-4 April generated ash plumes that rose as high as 3.5 km, and ejected tephra as far as 1,300 m. Reports of falling tephra, 2 cm in diameter, came from a town 3 km away. At 0608 on 3 April an ash plume from an explosion rose 700 m above Minamidake. 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)