Abstract
The early volcanic eruptive products, five tephra layers, of Hokkaido-Komagatake volcano located in southwest Hokkaido were found beneath Ko-h(17 ka). All tephras are predominantly abundant in plagioclase and spongy glass, and contain orthopyroxene and clinopyroxene. The refractive index of orthopyroxene (γ) ranges from 1.706 to 1.713. These mineral characteristics indicate that the tephras were supplied from Hokkaido-Komagatake volcano. The age of the earliest volcanic activity of E-x, situated beneath Toya ash, was estimated to be a middle stage of OIS5d, according to a pollen analysis of the peat layer intercalated beneath the E-x. An interval of the early stage volcanic activities from E-x to Ko-h was assessed between 12 ka and 32 ka judging from tephra ages and the thickness of loess deposits interbedded between tephra layers.
