The Japan Meteorological Agency (JMA) reported ongoing eruptive activity at Minamidake Crater (Aira Caldera’s Sakurajima volcano) during 16-30 December; activity intensified on 23 December and remained elevated. Nightly crater incandescence was visible in webcam images. Occasional small eruptive events were recorded during 16-19 December. On 17 December sulfur dioxide emissions were averaging 3,400 tons per day. Eruptive events at 1340, 1847, 1939, and 2112 on 20 December produced ash plumes that rose 1-1.3 km above the crater rim and drifted N and NE. Explosions at 0059 on 21 December and 0029 on 22 December produced ash plumes that rose 700-900 m above the crater rim and drifted N and SE. The explosions ejected large blocks 300-500 m from the crater rim. An explosion at 0710 on 23 December generated an ash plume that rose 1.6 km above the crater rim and drifted SE and ejected large blocks 300-500 m from the crater rim. An explosion almost 20 minutes later, at 0729, produced an ash plume that rose 3.4 km above the crater rim and drifted SE. Large blocks were ejected 600-1,000 m from the crater. Plumes had not risen more than 3 km since an explosion produced a 4-km-high plume on 18 October. On 24 December sulfur dioxide emissions were averaging 2,000 tons per day. Another ash plume from an eruptive event at 1641 on 27 December rose 2.2 km above the crater rim and drifted SE. At 1719 an explosion generated an ash plume that rose 900 m and drifted SE, and ejected large blocks 500-800 m from the crater rim. An explosion at 0812 on 29 December generated an ash plume that rose 500 m and drifted SE, and ejected blocks 500-700 m from the rim. A few hours later an ash plume from an explosion at 1128 rose 1.5 km above the crater rim and drifted SE, followed by an eruptive event at 1506 that sent an ash plume to 1.2 km above the crater rim and drifted SE. The Alert Level remained at 3 (on a 5-level scale), and the public was warned to stay 1 km away from both craters.

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)