Abstract
Coral cays are low-lying island which is formed by the gravel on the coral reef, in this position slightly higher than a field. In past research, there are reported that have been formed by loss and its terrain changes in short-term of high waves. But many parts of the mechanism are unknown, because it is difficult to obtain observation data. In this study, we investigated the mechanism for changing the terrain by hydraulic model tests and field surveys on Barasu island where is near north Iriomote Island.
As a result, the following conclusions were obtained. (1) Although geographical feature change of deposition, erosion, and movement is repeated by the strong external force by the short time of a typhoon, the moving direction of an island is agreement with the excellence direction of the external force which made the flow the subject. (2) At the coral gravels which is mainly by branch coral, we confirmed that 0.7 m/s is to be critical flow velocities for movement near bottom in general.
