During 8-16 September JMA maintained Alert Level 3 for Aira Caldera’s Sakurajima volcano. Volcanic earthquakes and tremor were detected during this time period. There were 12 explosions that ejected tephra up to 1,300 m above Showa crater. Sustained eruptions from the crater were recorded on 10 and 11 September and nighttime incandescence was detected during 11-16 September.

During 10-16 September JMA reported ash eruptions, causing the Tokyo VAAC to issue regular advisories; however, ash was not visible in satellite images.

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)