Report on Aira (Japan) — 4 February-10 February 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
4 February-10 February 2009
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2009. Report on Aira (Japan). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 4 February-10 February 2009. 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 Sakura-jima erupted explosively eight times during 1-2 February; bombs were deposited as far away as 800 m from the Showa crater (on the E slope of Minami-dake, or "south mountain," at an elevation of about 800 m). JMA raised the Alert Level from 2 to 3 on 2 February. Based on information from JMA, the Tokyo VAAC reported that during 4-5 February explosions and eruptions produced plumes that rose to altitudes of 2.1-2.4 km (7,000-8,000 ft) a.s.l. and drifted SE. On 9 February a pilot reported that an ash plume rose to an altitude of 2.4 km (8,000 ft) a.s.l. and drifted 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.