Report on Aira (Japan) — 7 June-13 June 2023
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 7 June-13 June 2023
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2023. Report on Aira (Japan) (Sennert, S, ed.). Weekly Volcanic Activity Report, 7 June-13 June 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 activity at both Minamidake Crater and Showa Crater (Aira Caldera’s Sakurajima volcano) during 5-12 June. Eruptive events at Showa were recorded at 0211, 0352, 0440, and 1436 on 5 June and generated ash plumes that rose as high as 1.5 km above the crater rim and sometimes drifted E and SE. Explosions at Minamidake produced ash plumes that rose 1.5 and 2.5 km above the crater rim at 0012 on 5 June and 1401 on 7 June, respectively, and ejected blocks 500-700 m from the vent. Ash-and-gas emissions were continuous with plumes rising as high as 1.5 km and then declining to 800 m during 1401-1505 on 7 June, and drifting SE. Since the volcano is so active, JMA noted that only emissions above a certain threshold of density and height get reported; at 1505 the emission characteristics declined to below that threshold. 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 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.