Barrier Island

A barrier island is a long, narrow depositional landform of sand running parallel to the mainland coast and separated from it by a lagoon, bay, or tidal marsh. It builds from longshore sediment transport and shoreface deposition and migrates landward over time through overwash and tidal-inlet processes as sea level rises. Barrier islands front many low-lying coasts and absorb storm-surge and wave energy before it reaches the mainland, so they are first-line natural defenses. Under sea-level rise and reduced sediment supply they narrow and roll over, which is why barrier-island response is central to coastal-hazard and shoreline-management planning.