JMA reported 31 explosions during 11-18 May from Showa Crater at Aira Caldera’s Sakurajima volcano, some that ejected tephra as far as 1,800 m. Incandescence from the crater was visible at night on 11 May. The next day a very small explosion at Minami-Dake Crater generated a 200-m-high plume. Three larger explosions from Showa Crater, at 2104 and 2200 on 13 May, and 0416 on 14 May, generated ash plumes that rose as high as 3.5 km. Tephra, about 2 cm in diameter, and ashfall reported in Kagoshima Kurokami was attributed to the explosion at 2104 on 13 May. During 15-18 May ash plumes rose as high as 3 km twice, except from an explosion at 1732 on 17 May, an event that produced a 3.8-km-high ash plume. 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)