火山の爆発過程における噴煙および火山ガスの放出について

Abstract

TV camera was installed at Sakurajima Volcanological Observatory to study the mecha-nism of volcanic explosion. At first, the sequence of phenomina occurred in a volcanicexplosion was examined, analyzing the observed pictures. The occurrence of an explosion-quake below the crater preceded tbe emsision of volcanic gases and ejecta from the ventby a few seconds. Visible shock wave passing through the atmosphere above the craterwas also recorded as the moving pictures. The velocity of shock wave is estimated to beMach 1. 3-1. 5.Furthermore, the growth of eruption column in the initial stage of explosion was examined.Expansion of volcanic cloud was predominant for 3-10 seconds. Emission rate of volcanic gaseswas estimated to be 10 2-10 3 tons/sec assuming that the volume of volcanic gases is nearlyequal to that of volcanic cloud in the initial stage of explosion. It is inferred that theoccurrence of the atmospheric shock wave results from the high emission rate of volcanicgases.