JMA reported that during 10-14 March two explosions from Showa Crater at Aira Caldera’s Sakurajima volcano ejected tephra as far as 1,300 m. Incandescence from the crater was detected at night. Volcanologists conducting a field survey on 10 March noted that sulfur dioxide emissions were 190 tons per day, lower than the 1,900 tons per day they measured on 4 March. The Alert Level remained at 3 (on a scale of 1-5).

The Tokyo VAAC reported explosions during 12 and 15-17 March. On 12 March pilots observed ash plumes that rose to altitudes of 1.2-1.8 km (4,000-6,000 ft) a.s.l. and drifted N. During 15-18 March plumes rose to altitudes of 1.8-2.7 km (6,000-9,000 ft) a.s.l. and drifted E, SE, and S. Pilots observed ash plumes drifting SE at an altitude of 3.4 km (11,000 ft) a.s.l. on 16 March, and drifting SE at an altitude of 3 km (10,000 ft) a.s.l. on 18 March.

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)