Volcanic activity of the initial-early stage in the Asama-Eboshi volcanoes

Abstract

Asama-Eboshi volcanoes including an active volcano (Asama volcano) is located in East Japan. We determined the K-Ar ages of 8 volcanic rock samples of the initial-early stage with aim of elucidating temporal and spatial changes in this volcanoes. The initial-early stage of Asama-Eboshi volcanoes formed a stratovolcano which has fixed eruption area and some volcanic bodies like monogenic volcanoes which have widespread eruption area. Volcanic activity of the latter is limited to short term ca. 0.8 Ma and ca. 0.3 Ma. Volcanic field until ca. 0.3 Ma is also around Eboshidake area, after that volcanic field is widespread from Sampogamine to Asama area. Thus, it is believe that activity field expanded toward east after 0.3 Ma rapidly.