A beach is the land along the edge of a body of water and is made up of loose particles like sand, cobbles and shells. It may be found at the ocean but it can also form along rivers, lakes and some large ponds.
Beaches are constantly changing on timescales from a few weeks to several years, with some even undergoing sudden changes in profile and composition over the course of hours during severe storms. Beaches are a buffer that protect nearshore land from erosion by dissipating the energy of waves that would otherwise impact coastal terrains.
Most beaches in the world are characterized by terrigenous or siliceous sand, but there are exceptions. In the tropics, for example, many beaches consist of biogenic sand primarily made up of the skeletal fragments of marine organisms. These beach sands are lighter in color than terrigenous sands, and they usually have a more finely grained texture.
Beach sands typically have a higher crystalline content than upland sands and may contain heavier minerals such as micas, feldspars and quartz. The sands at tropical beaches are also rich in calcium carbonate, which is deposited from evaporating seawater on bits of marine organisms and other materials.
The size and shape of a beach are determined largely by the amount of sediment that is available to the waves, wind and currents. The availability of sand is influenced by the distance to the source, the speed and turbidity of the flowing fluid and the degree of compaction of the sand. In addition, vegetation on a beach can help to reduce erosion by slowing the movement of water and wind over the surface.
A beach can be divided into four zones: the swash zone, beach face, wrack line and berm. The zone closest to the water is called the swash zone, with the sandy material being finer than that farther inland. Wave action breaks down and carries the finer beach sands into deeper waters. The larger, more rounded particles remain at the water’s edge.
Beaches need a constant supply of material from the uplands to grow, and this is often limited by human activities such as urban development, dams and rerouting rivers. The loss of erodible land by these activities and by natural processes can reduce the availability of beach-building materials, leading to beach recession.