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Report on Aira (Japan) — 25 October-31 October 2023


Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 25 October-31 October 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, 25 October-31 October 2023. Smithsonian Institution and US Geological Survey.

Weekly Report (25 October-31 October 2023)



31.5772°N, 130.6589°E; summit elev. 1117 m

All times are local (unless otherwise noted)

JMA reported ongoing activity at Minamidake Crater (Aira Caldera’s Sakurajima volcano) during 23-30 October, with incandescence at the crater observed nightly. An eruptive period was recorded during 0346-0430 on 24 October; at 0346 a notable ash plume rose as high as 3.4 km above the crater rim and drifted E and ejected large blocks 1-1.3 km from the crater rim. At 0416 an ash plume rose 2.1 km above the crater rim and drifted E. A large amount of ashfall, likely from those events, was observed in Kurokami Town during a field survey later that day. Sulfur dioxide emissions were high on 25 October, averaging 2,200 tons per day. During an aerial observation on 25 October scientists noted that the N side of Showa Crater had slightly enlarged compared to the previous observations on 8 March. A high-temperature geothermal area on the Minamidake Crater floor was also visible. Periods of inflation were recorded in deformation data during 0000-1400 on 26 October and 0100-1600 on 28 October. An eruptive event at 0116 on 30 October produced an ash plume that rose 1 km above the crater rim and drifted N. 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 caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim and built an island that was joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4,850 years ago, after which eruptions took place at Minamidake. Frequent eruptions since the 8th century have deposited ash on the city of Kagoshima, located across Kagoshima Bay only 8 km from the summit. The largest recorded eruption took place during 1471-76.

Source: Japan Meteorological Agency (JMA)