1. Geology of Akita-Komagatake Volcano(II. The Make-up of Akita-Komagatake)

Abstract

Akita-Komagatake is a dissected strato-volcano, resting on the Tertiary basement. It has well-developed southeast and northwest slopes and a horseshoe-shaped caldera of Hawaiian type, 3×1.5km across, in which lie the central cones of Medake, Kodake and Otsuboike. Of these Medake is the largest and the recent activity occurred near its summit. The summa connecting Odake, Byobudake, Mitsuneyama and Yokodake, consists of lavas and pyroclastics, traversed by many dykes. To the north Katakurayama forms a parastic cone, which has a large explosion crater. Onamedake, the highest peak of Komagatake, lies within this explosion crater where lacustrine sediments are found associated with sulfur deposits. The volcano was built by alternation of lavas and pyroclastic materials of olivine pyroxene basalts and pyroxene andesites, with or without olivine phenocrysts. They belong to the tholeiitic series of types IVc, and Vc, and rarely IIc, representing a fine example of tholeiitic series among the volcanoes of Northeast Japan.