THE TOPOGRAPHIC CHANGE MECHANISM OF CORAL CAYS

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 were reported that formed and disappeared by short-term of high waves. But many parts of the mechanism are unknown because of difficulty of observation data acquisition. In this study, we investigated the mechanism for topographic change by laboratory model experiment and field surveys on Barasu Island near the north side of Iriomote Island. In order to understand the topography change mechanism of coral reef cays, the field survey of Barasu Island and model experiment were conducted. Topographic change of deposition, erosion, and movement was repeated by the strong external force at the time of a typhoon, And, it turned out that the move direction of Barasu Island is qualitatively in agreement with the excellence direction of the external force. Moreover, although it was erosive in the external force of one direction, when the external force of two directions was received, it checked that Barasu Island was expanded.