Report on Aira (Japan) — 18 September-24 September 2019
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 18 September-24 September 2019
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2019. Report on Aira (Japan). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 18 September-24 September 2019. 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 incandescence from Minamidake crater (at Aira Caldera’s Sakurajima volcano) was occasionally visible at night during 17-24 September. There were 30 eruptive events, 11 of which were explosive. Plumes rose as high as 2.6 km above the crater rim, and material was ejected as far as 1.7 km from the crater. On 20 September one of the explosions produced an ash plume that rose 3.4 km above the crater rim before merging into weather clouds. Large blocks were ejected 500-700 m. The Alert Level remained at 3 (on a 5-level scale).
Geologic Background. 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.