2019 Volume 58 Issue 2 Pages 149-162
Colluvium deposits distributed at the foot of the caldera wall of the Aso volcano are estimated to be piled-up materials derived from steep slopes. They are composed of poorly sorted gravel beds including andesite, welded tuff, and tephra blocks, and form sharp alluvial cones. Therefore, numerous shallow landslides caused by heavy rainfall and/or large earthquake vibrations may have brought about these deposits after the completion of the caldera wall.
In order to determine the ages of depositional events of such materials, we carried out the dating of three charred materials and four paleosols collected from the colluvium deposits. Calendar-calibrated AMS 14C dating indicates that more than 15 depositional events occurred during the past 26,000 years at five investigation points. Based on this relation, the recurrence interval of such events is estimated to be on the order of 103 years in this area.
