Abstract
Mt. Sanbe, located in the the middle of the Shimane Prefecture, southwest Japan, erupted in the late Quaternary. Researchers remain divided on the stratigraphy and the classification of the stages of activity. We have re-examined the stratigraphy and activity of deposits younger than the AT tephra. Petrography of the volcanic products and bulk rock chemistry were also examined using XRF and INAA. Based on these data, new stratigraphic units are distinguished which we have redefine as the Hikageyama Lava, Hatasedani Pyroclastic Flow Deposit, Oda Surge Deposit, Oda Pyroclastic Flow Deposit, Ukinuno Pumice Fall Deposit, Midorigaoka Pyroclastic Flow Deposit, Ukinuno Ash Fall Deposit, Kiriwari Ash Fall Deposit, Shigaku Ash Fall Deposit, Shigaku Pyroclastic Flow Deposit, Tsunoi Ash Fall Deposit, Shitsumi Ash Fall Deposit, Tateishi Debris Avalanche Deposit, Sanbe Dome Lava, Taiheizan Pyroclastic Deposit, Ibidani Debris Avalanche Deposit and Summit Ash Deposit. Six soil deposits identified between the tephras. These are the Ikeda Paleosol, Fourth Black Soil, Third Black Soil, Second Black Soil, First Black Soil and the Summit Black Soil. Glass shards from the widespread AT and K-Ah tephras were found in the Ikeda Paleosol and the Third Black Soil, respectively. These soils represent hiatuses in volcanic activity. The active stages of Sanbe Volcano are also redefined from Stages IV to VIII based on the soil deposits.
