Based on information from JMA, the Tokyo VAAC reported that during 16-20 and 22 May explosions from Sakura-jima produced plumes that rose to altitudes of 1.8-3.7 km (6,000-12,000 ft) a.s.l. and drifted multiple directions. Pilots observed ash plumes during 16-17 May that rose to altitudes of 2.7-4 km (9,000-13,000 ft) a.s.l. and drifted E and SE. Explosions were detected during 21-22 May.

JMA reported that during 18-21 May explosive eruptions from Showa Crater occurred multiple times and ejected tephra as far as 1.8 km from the crater. Incandescence from the crater was observed at night. Very small eruptions from Minami-dake Crater occurred on 18 and 19 May, and a small pyroclastic flow traveled 300 m down the Showa crater flanks on 21 May.

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)