Coastal Plain

A coastal plain is a low-relief lowland bordering a coast, formed by emergence of the former sea floor or by sediment progradation across a shallow margin. It typically slopes gently seaward and continues offshore as the continental shelf, the two being one structural surface split by present sea level. Classic examples are the US Atlantic and Gulf coastal plains, underlain by seaward-thickening wedges of marine and deltaic strata. Low gradient makes coastal plains prone to wide tidal flats, barrier islands, estuaries, and rapid shoreline shift with small sea-level change. They host major ports and are exposed to surge and inundation.