Report on Aira (Japan) — 13 May-19 May 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 13 May-19 May 2015
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2015. Report on Aira (Japan). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 13 May-19 May 2015. 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 31 explosions during 11-18 May from Showa Crater at Aira Caldera’s Sakurajima volcano, some that ejected tephra as far as 1,800 m. Incandescence from the crater was visible at night on 11 May. The next day a very small explosion at Minami-Dake Crater generated a 200-m-high plume. Three larger explosions from Showa Crater, at 2104 and 2200 on 13 May, and 0416 on 14 May, generated ash plumes that rose as high as 3.5 km. Tephra, about 2 cm in diameter, and ashfall reported in Kagoshima Kurokami was attributed to the explosion at 2104 on 13 May. During 15-18 May ash plumes rose as high as 3 km twice, except from an explosion at 1732 on 17 May, an event that produced a 3.8-km-high ash plume. 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.