Beach

A beach is the part of a shoreline consisting of natural materials spread across the boundary between land and water — such as sand, gravel (small rocks), or shells — found along oceans, seas, large lakes, and some rivers. Currents and water movement continuously shift these materials, so beach shape constantly changes.

A beach is not considered settled land. It is a dynamic system in which currents, incoming and outgoing waves (tides), wind, and sand all interact. When incoming sand exceeds outgoing sand, the beach widens; when it is less, the beach narrows.

Formation

Sources of beach material include rivers carrying sediment from land into the sea, the breaking down of rocks along the shore by currents, and biological material from the ocean such as shells and coral fragments. When currents strike the shore at an angle, they create a longshore current that moves sand along the beach.

Beach zones

A beach typically has three zones: the lower zone, which is always underwater; the middle zone, where waves rise as they approach and fall as they recede; and the upper zone, which is dry and reached only by large storms. Beyond this, there may be sand dunes shaped by wind, sometimes stabilized by vegetation.

Color and sand type

Beach color is determined by what it is composed of. Sand rich in quartz is white or pale; sand from volcanic rock is dark or black; areas with much coral have notably white sand. Some beaches consist of gravel and rounded rocks, which indicate strong currents.

Uses and threats

Beaches serve recreation, fishing, and tourism, and are also habitats for seabirds and sea turtles (turtles) that nest in the sand. Coastal development, sand extraction, and rising sea levels reduce beach width. Many countries attempt to replenish eroded beaches by adding sand, but this method is temporary and costly.