Powerful explosions from the summit crater of Minami-dake have become more frequent since summer 1977 (figures 2 and 3). Beginning in August, explosions have been preceded by earthquake swarms lasting several days. . . . This pattern has often occurred 4-5 times/month and has enabled scientists at the JMA's Sakura-jima Observatory to [forecast] the explosions. The frequent property damage that has occurred near the volcano since last summer continued in March and April. Many windowpanes and a car windshield were broken by airshocks and tephra during March. Incandescence was also observed during March and April.

Figure 3. Summary table of explosions from Minami-dake crater at Sakura-jima, 1978. Data courtesy of JMA.

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.