History of Akagi Volcano

Abstract

Mt. Akagi is a Quaternary volcano situated in the northwestern margin of the Kanto Plain, Gunma Prefecture. This is a conical volcano with a small caldera (2-4 km across) at the summit. The history of this volcano is divided into three stages as follows : (1) the older stratovolcano (2) the younger stratovolcano (3) the central cone. In the first stage a great deal of andesite lavas effused, accompanied with considerable volumes of scoria falls and flows, as the result a cone about 2500m high above sea level and about 60 cubic kilometers in volume was formed. Through the second stage paroxysmal activities were dominant erupting pyroclastic falls and flows about 40 cubic kilometers in volume. Just before the third stage the small caldera was formed in the summit of the younger stratovolcano composed of loose pyroclastic materials. In the caldera two dacite dome lavas extruded. The domes are underlain by the Kanuma pumice fall deposit which is correlated with the upper Musashino loam (several ten thousand years B.P.) and overlain by the Itahana pumice fall deposit (10000-20000 years B.P.). So it is presumed that the activity of Akagi Volcano was finished by 20000-30000 years B.P.