Report on Aira (Japan) — 1 March-7 March 2023
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
1 March-7 March 2023
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2023. Report on Aira (Japan). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 1 March-7 March 2023. Smithsonian Institution and US Geological Survey.
31.593°N, 130.657°E; summit elev. 1117 m
All times are local (unless otherwise noted)
JMA reported ongoing eruptive activity at Minamidake Crater and Showa Crater (at Aira Caldera’s Sakurajima volcano) during 27 February-6 March. Incandescence was visible nightly at Minamidake and during 3-6 March at Showa. Explosions at Minamidake were recorded on 28 February and 1, 3, and 4 March, and non-explosive eruptive events were occasionally recorded. Eruption plumes rose as high as 2.8 km above the Minamidake Crater rim and large blocks were ejected as far as 1.3 km from the vent. Non-explosive eruptive events were occasionally recorded at Showa during 27 February-2 March and four explosions occurred during 3-6 March. Eruption plumes rose as high as 2.7 km above the Showa rim and large blocks were ejected 500-800 m from the vent. Sulfur dioxide emissions were extremely high at 3,500 tons per day on 2 March. The Alert Level remained at 3 (on a 5-level scale), and residents were 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 Aira caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim of Aira caldera and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4850 years ago, after which eruptions took place at Minamidake. Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu's largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.