Barrier islands, among the most transient landforms on the planet, are common along the Atlantic and Gulf Coasts of North America, from Cape Cod southward. Formed by the action of waves and currents, these narrow islands are essentially offshore dunes, stabilized by a variety of grasses, shrubs and trees; this natural vegetation, tolerant of the salty and sandy conditions, is derived from seeds that blow out from the mainland (man has since added his own assortment of ornamental species).
Initially inhabited only by sea birds, marine mollusks and temporary visitors (such as sea turtles), most of the islands now harbor beach resorts, perched precariously on these shifting mounds of sand. While modern structures are anchored into the deep bedrock, all development on the offshore islands is prone to damage or destruction from the tropical storms and hurricanes that sweep across the region. In addition, island wildlife is threatened by mainland species (such as raccoons) that now reach these sandy refuges via man-made bridges.
Barrier islands form along coasts were the Continental Shelf is broad and shallow, making them especially susceptible to storm surge and wave erosion. Islands not destroyed or cut apart by storms will eventually merge with the mainland as the intervening bay is filled in by river sediment and by sand pushed through the inlets. Of course, humans keep their boat channels open by dredging, but, in time, nature will have her way!
