A beach is a coastal landform, a wide strip of sand or gravel, often bordering a rocky coastline, where wave action deposits sediment. Beaches are often popular places for recreation, such as swimming and sunbathing. They are also a natural habitat for many ocean creatures, including sea birds and turtles. Beach vegetation includes grasses and shrubs, and in some cases, palm or mangrove trees.
The shape of a beach is shaped by wave action and the characteristics of the sediment it contains. The portion of the beach that is above water at high tide is called the berm, and may contain vegetation. The part of the beach below the tidal zone, which is submerged at low tide, is known as the foreshore or low-tide terrace. Beaches that are exposed at both low and high tide, with a series of ridges or troughs that run parallel to the shoreline, are known as a bar-trough system.
Some beaches are heavily polluted, with debris washing ashore from urban areas, or with waste, such as sewage and chemicals, from drain pipes. The beach can be a source of bacteria and viruses, which can make people sick.
Beach erosion is a constant process, but the rate of change depends on the nature of the sand and the size and strength of waves. The shape of a beach can change from hour to hour, or even from season to season, as wave action destroys and then builds the beach.
Sandbars, which are long ridges of sand that extend offshore from the beach, are built by waves breaking on them. The swirling turbulence of these waves excavates a trough in the beach and, as the water rises back over the bar, some of this sand is carried forward on the crest of the wave. In addition, sand deposited in the trough by rip currents and by waves that break on the offshore side of the bar add to the accumulation.
A beach is also formed by sand moving from other parts of the coast, such as lagoons and estuaries, and by sediment deposited from the air by winds. Sediment from rivers and streams is also sometimes found on beaches.
The surface of a beach is generally flat, with a gradual slope toward the water, but it can have slight undulations, such as oscillation ripples and swash or rill furrows, or large crescent elements (concave seaward) known as beach cusps. These features are usually present on sand beaches. On rocky beaches, they are more difficult to observe because the bare rock is often visible on the surface of the water. On a sandy beach, these features are easily recognizable in the form of swash line and lower beach margin. Beaches can also be rocky, as on the coast of Texas, or they can have significant sand bars and dunes that reach well into deep water. Beaches can be tropical or icy cold. Beaches are found around the world, from the warm and sunny shores of Florida to the frozen coast of Antarctica.