Report on Aira (Japan) — 3 February-9 February 2016
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 3 February-9 February 2016
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2016. Report on Aira (Japan). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 3 February-9 February 2016. 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 an explosive eruption at Showa Crater (at Aira Caldera’s Sakurajima volcano) began at 1856 on 5 February and generated an ash plume that rose 1.3-1.8 km above the crater rim. Lightning was observed in the ash cloud, and incandescent tephra was ejected as far as 1.8 km onto the flanks. The Alert Level was raised to 3 (on a 5-level scale); it had previously been lowered to 2 on 25 November 2015. During an overflight the next day scientists did not see any significant changes to the crater; a plume obscured views of Minamidake summit crater. Sulfur dioxide emissions were 100 tons/day, which was the same level measured on 3 February.
Explosions were detected on 8 February. Based on JMA reports and satellite data, the Tokyo VAAC reported that during 8-9 February ash plumes rose to altitudes of 1.5-3.3 km (5,000-11,000 ft) a.s.l. and drifted E and SE.
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.