coast, land bordering an ocean or other large body of water. The line of contact between the land and water surfaces is called the shoreline. It fluctuates with the waves and tides. Sometimes the terms coast and shore are used synonymously, but often shore is interpreted to mean only the zone between the shorelines at high tide and low tide, and coast indicates a strip of land of indefinite width landward of the shore. Classically, coasts have been designated as submergent if they resulted from a rise in the relative sea level and emergent if they resulted from a decline. Young submergent coasts usually are irregular and have deep water offshore and many good harbors, either bays or estuaries. Much of the coast of New England and most of the Atlantic coast of Europe are young submergent coasts according to this classification scheme. Gradually the submergent coast, subjected to erosive attacks of the ocean and other agents, becomes mature. Headlands are worn back to form cliffs, at the base of which deposits of eroded material accumulate as fringing beaches; spits and bars also grow up from material that is carried by currents and deposited in deeper water. The shoreline is called mature when it is smooth, the headlands having been cut away and the bays either filled up or closed off by spits. Emergent shorelines usually have shallow water for some distance offshore. Such shorelines are found along the Atlantic coast of the SE United States and along part of the coast of Argentina, near the Río de la Plata. This classification system does not adequately describe many coasts, partly because many of them exhibit features of both submergence and emergence. Because of these and other problems a classification system that is based on the most recent and predominant geologic agent forming the coast has become popular. Under this scheme, there are essentially two major types of coasts. Primary coasts are youthful coasts formed where the sea rests against a land mass whose topography was formed by terrestrial agents. These coasts include land erosion coasts (Maine), volcanic coasts (Hawaii), deposition coasts (Nile Delta coast), and fault coasts (Red Sea). Secondary coasts are formed chiefly and most recently by marine agents, and may even be primary coasts that have been severely modified by wave action. These coasts include wave erosion coasts, marine deposition coasts, and coasts built by organisms (reefs and mangrove coasts). The nature of the coastline of a country or a state is an important factor in its economic development because it relates to defense, fishing, recreation, and overseas commerce.
See C. A. M. King, Beaches and Coasts (2d ed. 1972).