Report on Aira (Japan) — 15 February-21 February 2023
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 15 February-21 February 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, 15 February-21 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 Minamidake Crater (at Aira Caldera’s Sakurajima volcano) during 13-20 February and crater incandescence was visible nightly. Five explosions and five eruptive events were recorded during the week. One of the explosions, at 1448 on 14 February, produced an ash plume that rose 2.4 km above the crater rim and ejected large blocks 1.1 km from the vent. Blocks 3 cm in diameter fell near the Arimura Lava Observatory in Arimura-cho, Kagoshima City, about 3 km SE. An explosion on 19 February produced an eruption plume that rose 1.2 km and ejected blocks that fell 1.1 km away. A very small eruptive event occurred at Showa Crater on 20 February. 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.