Abstract
Volcano Aso which had been almost dormant since April, 1952, suddenly became active at the end of April, 1953., Repeated explosions occurred in Nakadake crater, the first of which occurred at 11h31m, April 27, the second at 02h16m, April 28, the third at 22h56m, April 29, and the fourth at 10h35m hours, May 4., Two or three additional explosions occurred in June, July and September., Each explosion occurred with sone forerunning slight earthquakes, after a repose period (3-17 hours) of the seismometer., The pre-eruption repose period was especially marked for the first, second, and third eruptions., The new ejecta are dark, somewhat glassy, pyroxene-andesites, the origin of which may be accessory or essential., The largest one is about five tons in weight., The blocks of tuff constructing the wall of the crater were also ejected., Some of them contain strongly deliquescent material, the chemical composition of which is shown in Table 1., Ash was thrown up in the air and scattered mostly northward, sometimes falling on and around the villages of Miyaji and Bochu in the northern part of the so-called "Aso Caldera".,
