Report on Aira (Japan) — 1 April-7 April 2015
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 1 April-7 April 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, 1 April-7 April 2015. 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 20 explosions from Showa Crater at Aira Caldera’s Sakurajima volcano ejected tephra as far as 1,300 m during 30 March-3 April. Incandescence from the crater was periodically visible at night, and inflation continued to be detected. The Alert Level remained at 3 (on a scale of 1-5). Based on JMA notices, the Tokyo VAAC reported that explosions during 1-2, 5, and 7 April generated plumes which rose to altitudes of 1.5-3.4 km (5,000-11,000 ft) a.s.l. and drifted E and NE. Pilots observed ash plumes that rose to an altitude of 3 km (10,000 ft) on 1 April and 1.5 km (5,000 ft) a.s.l. on 7 April.
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.