ERUPTED MATERIAL AND SEQUENCE OF EVENTS DURING THE BEZYMYANNYI ERUPTION OF MARCH 30, 1956. DIRECTED BLAST DEPOSITS

Abstract

This paper presents the results of a detailed study of pyroclastic deposits produced on Bezymyannyi Volcano on March 30, 1956: composition, stratigraphy, grain size, mechanical and thermal effects. It is shown that the directed blast was caused by the explosion of a magma body that had been intruded in the edifice during the pre-climacteric phase of the eruption. The material thrown out by the explosion propagated along the eastern foot of the volcano as a pyroclastic surge (a turbulent flow of a hot gas and pyroclastics mixture). The speed of the surge was higher than 60 m/s (at a distance of 10 km from the cone), its effective temperature was ca. 300°C. The resulting deposits are classified as a directed-blast pyroclastic surge.