Explosive activity at the summit crater of Minami-dake intensified in February, when 35 explosions were recorded (figure 11). The largest, at 1030 on the 24th, ejected a plume to an altitude of more than 4 km and was accompanied by a strong air shock that saturated the microbarograph at the Kagoshima Observatory. A strong NW wind carried a large amount of lapilli toward the SE foot. Between Arimura (3 km SSE) and Ushinefumoto (6 km ESE, in the middle of the city of Tarumizu), 28 car windshields were broken. Tile or slate roofs on 53 houses were slightly damaged at Ushinefumoto, and a windowpane was broken at Arimura. The number of recorded explosions increased to 54 in March, although the number expelling a large amount of ejecta decreased. Swarms of volcanic earthquakes were observed on 4, 17, and 19 February and 2, 8-9, and 24 March. On 31 March, an explosion sent lapilli 4-5 cm in diameter toward the SE foot, where 4 car windshields were cracked.

Figure 11. Summary table of explosions from Minami-dake crater at Sakura-jima, 1985. 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.