Roles of Typhoons and Beach Rocks in the Formation and the Deformation of Sand Cays

The morphology of sand cays developed in Miyako Island and Kumejima Island, Okinawa Prefecture, Japan, was investigated. The variation of submerged sand area, potential zone for sand cay formation, was found to be well correlated with a typhoon index, proposed to quantify the influence of typhoon on sand cay morphology. The analysis of sediments sampled around sand cays indicated the importance of the presence of beach rocks in the formation of the sand cay.