Over millenniums, streams and rivers moved the weathered remains of these rocks down to the sea. There are several theories as to how the islands were formed from this sand. All theories involve wave and wind action and fluctuating sea levels shaping the barrier islands that lie parallel to the gulf coast. These islands are ever-changing, moving constantly to the west. Littoral currents wear away the eastern ends and build up the western ends.
Violent storms cause overwash that rearranges large amounts of sand.
Constant winds, on a smaller scale, shift and build dunes. Change by the winds is slowed only by the protective covering of grasses and other vegetation growing on the dune line nearest the gulf. The elaborate stem and root system of the sea oat, in particular, is vital to the protection and stabilization of barrier islands. So important in fact, that the picking or disturbing of sea oats and other vegetation is strictly prohibited. They effectively reduce the destructive force of violent storms before reaching the mainland.