Sixteen explosions occurred from the summit crater of Minami-dake during February. Ash emission between explosions remained infrequent, as it has since December. Yosihiro Sawada reports that high-amplitude volcanic tremor ended in November 1978, and shallow B-type earthquakes began to be recorded. An earthquake swarm in mid-December preceded the emplacement of a new incandescent lava [mound] on the [crater] floor of Minami-dake, after which explosions became more frequent.

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: JMA, Tokyo; Y. Sawada, MRI, Tokyo; D. Shackelford, CA.