An explosive eruption from Naka-dake crater began at 1510 on 13 June. Activity lasted more than 1 hour, producing a 1,500-2,000-m-high steam and ash column, and thundering sounds. [Blocks] larger than a man's head were thrown 400 m above the crater rim. Kyodo radio reported that the eruption reintensified during the night of 15-16 June. Hot tephra was ejected to 200 m above the crater rim, accompanied by a roaring noise. Doors and windows rattled in nearby houses and some residents fled the area, according to police reports. . . .

Geological Summary. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Information Contacts: T. Tiba, National Science Museum; Kyodo Radio.