Coastal dunes are U-shaped and found only in humid coastal areas and never in arid regions. They are made when the stabilizing plant cover of a linear dune is destroyed exposing the sand to the wind. The size and morphology of coastal dunes are dependent on the complex interaction between controlling winds, sediment supply and the geomorphology of the nearshore and beach environment. At the most basic level, dunes can be divided into those that form the direct supply sediment from the beach face and those that form the subsequent modification of primary dunes.