The explosion of Naka-dake, Volcano Aso on the 6th of September, 1979

Abstract

On the 6th of September, 1979, the explosive eruption happened at the 1st crater of Naka-dake, the only active crater of Volcano Aso. The eruptive energy amounts to 5x10¹⁸ erg. The distribution of ejecta was particularly shaped, that is, in a butterfly pattern. Moreover, the ground motions at several observing points arranged near the crater were predominant in horizontal and transversal component. These observed results suggest us that two openings were formed at the crater bottom and generated a force of single couple type.