Report on Aira (Japan) — 12 August-18 August 2015
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 12 August-18 August 2015
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2015. Report on Aira (Japan) (Sennert, S, ed.). Weekly Volcanic Activity Report, 12 August-18 August 2015. Smithsonian Institution and US Geological Survey.
31.593°N, 130.657°E; summit elev. 1117 m
All times are local (unless otherwise noted)
On 15 August JMA reported an increase in the frequency of volcanic earthquakes detected under Minami-Dake Crater (Aira Caldera’s Sakurajima volcano) and that inflation became more rapid. This activity suggested an increase in the possibility of larger-scale explosions, prompting JMA to raise the Alert Level to 4 (on a 5-level scale). Elevated activity continued to be detected through 18 August.
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.