Report on Aira (Japan) — 8 February-14 February 2023
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
8 February-14 February 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, 8 February-14 February 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 Aira Caldera’s Sakurajima volcano during 6-12 February and nightly crater incandescence. Three eruptive events and two explosions were recorded at Minamidake Crater. The first explosion, at 1815 on 9 November, generated an ash plume that rose 2 km above the crater rim and drifted N and ejected large blocks 600-900 m from the crater rim. The second explosion, at 1007 on 11 February, produced an ash plume that rose 1.7 km and ejected large blocks 600-900 m from the crater rim. An ash plume from an eruptive event at 1323 on 12 February rose 1.7 km and drifted E.
A very small eruption at Showa Crater at 1052 on 8 February produced an ash plume that rose 800 m above the crater rim. This was the first eruption at Showa Crater since 3 April 2018. Ash plumes from events recorded at 1110 and 1425 rose as high as 1 km and drifted SE and SW, respectively, and blocks were ejected 200-300 m from the crater. Ashfall was reported in an area from Arimura-cho (4.5 km SE) to Furusato-cho (3 km S). The Alert Level remained at 3 (on a 5-level scale), and residents were warned to stay 2 km away from the crater.
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.