Report on Aira (Japan) — March 1995
Bulletin of the Global Volcanism Network, vol. 20, no. 3 (March 1995)
Managing Editor: Richard Wunderman.
Aira (Japan) Explosive eruptions send plumes 3-4 km above the summit
Please cite this report as:
Global Volcanism Program, 1995. Report on Aira (Japan) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 20:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199503-282080
Aira
Japan
31.5772°N, 130.6589°E; summit elev. 1117 m
All times are local (unless otherwise noted)
Explosive volcanism continued in February and March from Minami-dake crater but caused no damage. There were a total of 22 eruptions in February, including 12 explosive ones. Activity increased somewhat in March with 36 eruptions, 24 of which were explosive. The highest monthly ash plumes occurred on 11 February (3 km) and on 8 March (4 km). Ashfall measured 10 km W at the Kagoshima Meteorological Observatory (KMO) was 30 g/m2 in February. Although there were more eruptions, only 9 g/m2 of ash fell at KMO during March.
An earthquake swarm that started at 1600 on 23 February lasted 9 hours and consisted of 99 events registered at Station B, 2.3 km NE of Minami-dake crater. This episode caused the KMO to issue a Volcanic Advisory noting the restlessness of the volcano. Station B also registered 208.8 hours of volcanic tremor and a total of 424 volcanic earthquakes during February. Another earthquake swarm between 0000 on 26 March and 0300 on 28 March produced 2,041 earthquakes and 828 tremors, causing another two Volcanic Advisories. However, total amount of tremor in March (164.3 hours) was less than in February.
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.
Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.
