Remains of the Iwasa checkpoint on the Noneyama-kaido as an ancient road located in ridge-top area formed by gravitational deformation, the Muroto Peninsula, Japan

The Noneyama-kaido is an ancient road traversed from the east coast to the west coast of Muroto Peninsula, eastern Kochi Prefecture, Japan. The Tosa-han（Tosa domain）set the Iwasa checkpoint along with the road in the early Edo period. The remains of the Iwasa checkpoint are located on the ridge-top area ; however, the archaeological investigation has not been conducted until now. From the viewpoint of geomorphology and geology, there are many landscapes formed by gravitational slope deformation such as up-hill and down-hill facing scarps on ridges in and around the study area. In this study, we discussed the relationship between the location of the ruin and geomorphological process based on geomorphological interpretation of advanced topographic maps created from the data of the airborne laser survey system of the study area. The results show that the remains of the Iwasa checkpoint are located at flat surface with reasonable size on the ridge top shaped by toppling-type rock creep. In addition, the geological structure formed by rock creep zone made a reservoir of groundwater which was used as a resource of daily life water for local residents of the Iwasa checkpoint.