Report on Aira (Japan) — 27 July-2 August 2022
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
27 July-2 August 2022
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2022. Report on Aira (Japan). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 27 July-2 August 2022. Smithsonian Institution and US Geological Survey.
31.593°N, 130.657°E; summit elev. 1117 m
All times are local (unless otherwise noted)
JMA lowered the Alert Level for Aira Caldera’s Sakurajima volcano to 3 (on a 5-level scale) on 27 July, noting that after the larger eruption on 24 July material had not been ejected more than 2 km from the crater; residents were warned to stay 2 km away from the crater. During 25 July-1 August the seismic network recorded about 11 explosions and 19 eruptive events, producing plumes that rose as high as 2.2 km above the summit and ejected material far as 1.1 km. Crater incandescence was visible nightly. No deformation was detected.
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.