Report on Aira (Japan) — 7 April-13 April 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
7 April-13 April 2021
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2021. Report on Aira (Japan). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 7 April-13 April 2021. 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 that at 0641 on 5 April and explosion at Minamidake Crater (at Aira Caldera’s Sakurajima volcano) produced an ash plume that rose as high as 3 km above the crater rim and ejected material 800-1,000 m away from the crater. Five explosions were recorded during 9-12 April. The highest ash plume rose 2.1 km and bombs were ejected as far as 900 m from the crater. Crater incandescence was visible nightly. The Alert Level remained at 3 (on a 5-level scale).
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.