6. Rauch-ring and the Explosion Mechanism at Akita-Komaga-take(V. Features of the Activity of the 1970-71 Eruption of Akita-Komagatake)

Abstract

Rauch-ring was observed, probably for the first time in Japan, during the 1970 eruption of Mt. Komagatake in Akita Prefecture. The explosion accompanied by the ring was registered by an 8mm movie and a tape recorder installed around the crater. The explosion column was white and rose vertically up to some fifty meters from the crater rim. At this height the ring was released from the column, and was about seven meters in diameter with the average ascending velocity of about six meters per second. In order to investigate the mechanism of this extremely rare phenomenon of “Rauch-ring” and the explosion itself, analyses of the distribution of the explosion energy and others, are made on the explosion sound recorded on the tape, and the seismogram observed simultaneously by chance. In addition, an explanation is given concerning the mechanism of the whole volcanic activity of Akita-Komagatake by analyzing the seismological observation.