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Report on Aira (Japan) — 19 August-25 August 2015


Aira

Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 19 August-25 August 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, 19 August-25 August 2015. Smithsonian Institution and US Geological Survey.

Weekly Report (19 August-25 August 2015)

Aira

Japan

31.5772°N, 130.6589°E; summit elev. 1117 m

All times are local (unless otherwise noted)


JMA reported that a small-scale explosion from Showa Crater (Aira Caldera’s Sakurajima volcano) occurred on 19 August. In a report from 21 August JMA noted that the possibility of larger-scale eruption had decreased since 15 August. Deformation data during 15-16 August suggested a dike intrusion beneath Minamidake Crater, centered 1-3 km below sea level, with an estimated volume of 2 million cubic meters. Small-scale explosions at Showa Crater occurred on 21 and 23 August. The Alert Level remained at 4 (on a 5-level scale).

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.

Source: Japan Meteorological Agency (JMA)