Geology and Volcanic History of Hachimandake Volcanic Group, the East of Hakkoda Caldera, Northeast Japan

Abstract

 The stratigraphy and spatio-temporal distribution of the Early Pleistocene volcanic rocks in the east of Hakkoda Caldera, Northeast Japan were revealed. The Hachimandake Volcanic Group (HVG) was newly distinguished in this area. Volcanic activity of the HVG occurred during 2.5-1.4 Ma. Basaltic andesite magma erupted from several eruptive centers and formed several small volcanic bodies in the east of the present Hakkoda Caldera. Volcanic activity of the HVG is characterized by repeated outflows of basaltic andesite lava flows, each several meters thick. Volcanic activity of the HVG was notably smaller than that of Minami- and Kita-Hakkoda Volcanic Groups from 1.1 Ma to the present. Dacite to rhyolite pyroclastic flows were found to have occurred simultaneously during HVG activity. Those source vents are unknown.