三瓶火山の山頂火山灰について

Sanbe volcano，located in Shimane Prefecture，Southwest Japan，erupted in the late Quatemary．The last emption was between 3500-3700 y.B.P.．
On the summit of Mt．Sanbe，the Taiheizan Pyroclastic Deposit and the 1 st Soil Deposit are unconfomably overlain by the Summit Ash Deposit，which in turn is unconfimably overlain by the Summit Soil Deposit．
Conventional radio carbon ages of the 1st Soil Deposit and the Summit Soil Deposit are 1390±60 and 500±60 y.B.P. respectively．Biotite grain ratios of pyroclastic deposits from the summit of Mt．Sanbe have been determined and the ancient documents about the Sanbe area have been consulted．
If the Summit Ash Deposit was derived from the emption of Sanbe Volcano，Mt．Sanbe can be regarded as an active volcano，as defined by the Japan Meteorological Agency，in having erupted during the last 2000 years．