Report on Aira (Japan) — 2 October-8 October 2019
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 2 October-8 October 2019
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2019. Report on Aira (Japan) (Sennert, S, ed.). Weekly Volcanic Activity Report, 2 October-8 October 2019. Smithsonian Institution and US Geological Survey.
31.5772°N, 130.6589°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 30 September-7 October. The sulfur dioxide emission rate was high, at 2,000 tons/day, measured during fieldwork on 1 October. An explosion was recorded at 0055 on 4 October but weather clouds prevented visual confirmation. Two explosions during 6-7 October generated ash plumes that rose as high as 2.4 km above the crater rim and ejected large blocks 1.1 km away. 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 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.