Report on Aira (Japan) — 15 April-21 April 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
15 April-21 April 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, 15 April-21 April 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 23 explosions from Showa Crater at Aira Caldera’s Sakurajima volcano during 13-17 April. Incandescence from the crater was visible at night on 14 April. An explosion at 1355 on 17 April generated a large ash plume that rose 3 km above the crater, and a second explosion ejected tephra as far as 1,800 m. 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 15-18 and 20-21 April generated plumes which rose to altitudes of 1.2-4.6 km (4,000-15,000 ft) a.s.l. and drifted E and SE.
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.