A beach is a landform alongside a water body that consists of loose particles — such as sand, gravel, pebbles, cobbles, or shells — that either accrete (accumulate) on the shore during periods of accretion or are washed away during periods of erosion. The term is often used to distinguish a sandy beach from a rocky or cliffy coast.
Beaches are continually changing, and the nature of their composition depends on local wave and wind conditions. Sand is the most common beach material, but it may also consist of any other granular matter that moving water can carry and deposit, including rock debris from offshore rocks or cliffs, sediments from headland erosion or slumping (such as scree), and even organic waste such as decomposed seaweed or the remains of mollusc shells.
The most familiar type of beach is a free beach, which extends to the water’s edge and is not enclosed by structures such as groynes or piers. Free beaches typically feature a gently sloping ridge of sand that is separated from the open sea by a shallow lagoon, with a beach bar at low tide and an offshore ocean bank at high tide.
Seaside towns and resorts are built around many beaches, and they may host a wide range of recreational activities. Beaches may also be home to a wide variety of marine life, from fish and other aquatic creatures to whales and seals.
Most beaches have a limited area of open water at low tide, and this is the most common location for swimming. However, many beaches have restricted access because of the presence of hazards such as rip currents and shallow reefs. Some beaches are public property, while others are privately owned or operated.
Beaches are sometimes contaminated with human waste from urban areas and agricultural runoff from adjacent land. These pollutants wash down the coast and into the ocean, where they can affect the health of beachgoers. The bacteria in raw sewage and the chemicals from fertilizers and pesticides can kill fish, birds, and other sea life, as well as humans who swim or bathe in contaminated waters.
The sand on most beaches is composed of quartz and some data sgp feldspars, but the sand on tropical and coralline beaches contains calcium carbonate from the skeletons of marine organisms and mollusc shells. In some places, sands composed of calcareous minerals form a barrier bar. A bar is a submerged ridge of sand that separates a beach from the open water and is maintained below the level of still-water waves by the turbulence of breaking waves. In some cases, bars are eroded by offshore currents and may disappear altogether. In other situations, they are buried by sand washed in from the adjacent beach.