Age of the Sukawa Volcanic Debris Avalanche Deposit at the Western Foot of the Zao Volcanoes

Radiocarbon dating and pollen analysis have been done on two peat beds lying above and below the Sukawa volcanic debris avalanche deposit. A nearly 100m thick avalanche of the Sukawa volcanic debris which occured on the south side of Mt. Ryu-zan representing the western section of the Zao volcanoes spread over an area of about 1 to 7km wide and 12km long. Our study indicates that the Sukawa avalanche deposit gives an age not much older than 40, 000 years B. P. and is assignable to a horizon between the subinterglacial to subglacial stages on the basis of palynological evidence. These data enable a tentative correlation of the avalanche episode with the early-glacial to plani-glacial substage in the Würm Ice Age.