JMA reported ongoing eruptive activity at Minamidake Crater (Aira Caldera’s Sakurajima volcano) during 11-18 March with nighttime crater incandescence. Sulfur dioxide emissions were extremely high, averaging 3,100 tons per day on 12 March. During an overflight on 13 March emissions obscured views of Minamidake Crater, though observers noted no changes at the either the Showa Crater geothermal area or around the flanks of both craters. An explosion at 0536 on 13 March produced an ash plume that rose 1 km above the crater rim and drifted S and ejected large blocks 300-500 m from the vent. Eruptive events at 1345 on 13 March and at 0450 and 0538 on 15 March generated ash plumes that rose 1-2.9 km above the crater rim and drifted SE. An ash plume from an explosion at 2158 on 16 March rose 600 m above the crater rim and drifted NE; large blocks were ejected 600-900 m from the vent. The Alert Level remained at 3 (on a 5-level scale), and the public was warned to stay 2 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)