Report on Aira (Japan) — 19 July-25 July 2023
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 19 July-25 July 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, 19 July-25 July 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 16-24 July. Very small eruptive events occasionally occurred at Minamidake and incandescence was observed at night. An eruptive event at Showa on 16 July produced an ash plume that rose 1.2 km above the crater rim and drifted N. An explosion at the same crater at 2314 produced an ash plume that rose 1.8 km above the crater rim and drifted N, and also ejected blocks 300-500 m from the vent. Explosions at 1224 and 1232 on 17 July generated ash plumes that rose 2-2.5 km and drifted N, with blocks ejected 500-800 m from the vent. At 2044 on 17 July an ash plume from an explosion rose 1.2 km and drifted N. Sulfur dioxide emissions were very high, averaging 3,200 tons per day on 20 July. 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.