Abstract
We revised the volcanic history of the Yatsugatake area, located in the eastern area of Nagano Prefecture, central Japan, by means of volcanostratigraphy, K-Ar age determination and magnetostratigraphy. As a result, it was clarified that the volcanic activities occurred at around 1.2-0.8 Ma and 0.5-0 Ma in the Northern Yatsugatake area, and at around 0.5-0.1 Ma in the Southern Yatsugatake area. As the volcanic activities older than 0.8 Ma are restricted only in the northern area, the volcanoes in this area are newly defined as “Yabashira Volcanoes”. We also redefined “Yatsugatake Volcanoes” as those which were formed in both northern and southern areas after 0.5 Ma. The Yabashira Volcanoes have more than four eruptive centers, which are lined up in the NW-SE direction. The arrangement of these volcanic centers is different from the N-S arrangement of the volcanic centers of the Yatsugatake Volcanoes. To the west of the Yabashira Volcanoes, the volcanic ejecta of the same age including those in Yashigamine, Kirigamine and Wadatoge areas are distributed, forming a volcanic field spreading in the E-W direction within the area of Yatsugatake-Chushin Highland area.
