Report on Aira (Japan) — 4 March-10 March 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 4 March-10 March 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, 4 March-10 March 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 that seven explosions from Showa Crater at Aira Caldera’s Sakurajima volcano ejected tephra as far as 1,300 m during 2-6 March. Incandescence from the crater was periodically visible at night, and inflation continued to be detected. During a field survey conducted on 4 March scientists observed deposits of tephra, up to 2 cm in diameter, in an area 3 km S of Showa Crater. The Alert Level remained at 3 (on a scale of 1-5). The Tokyo VAAC reported that during 4-5 and 7-8 March plumes rose to altitudes of 1.5-3.7 km (5,000-12,000 ft) a.s.l. and drifted in multiple directions.
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.