A beach is a landform that is exposed at low tide and consists of sediments deposited by waves and winds on the shoreline. Although beaches are often associated with oceans, they can also be found by lakes and alongside rivers. Beaches are made mainly of sand, but they can be composed of any granular material that wave action can wear down into smaller particles (such as silt, gravel, cobble, and shingle). Beaches can be either geologically formed (from the weathering of rocks) or biologically formed (from the breakdown of coral skeletons, shells, and the remains of marine plants and animals).
The most distinctive features of beaches are their crests (tops) and faces (slopes leading down to water). These features are the result of the dynamic interactions between waves and sediments. In general, a beach develops when strong wave action deposits sand and a lack of currents prevents the sand from being carried away. Waves can be constructive or destructive; the latter are high energy waves that produce a backwash of water that washes up on the foreshore, removing beach material, and then carries it out to sea. Constructive waves are lower energy waves with weaker backwashes and stronger swashes, which deposit sand and maintain beaches.
In addition to the processes that shape and form beaches, they are also significantly influenced by human forces. These influences include building activities on the beach, and indirect effects such as coastal erosion from sea level rise and climate change. Beaches are also subject to sudden changes in sea and land levels, which can substantially alter their shape, location, and composition in a short time.
As well as sand and gravel, many beaches contain other materials, such as rock debris, driftwood, seaweed, and marine organisms. Much of this material is buried beneath the sand in the intertidal zone, which can be exposed at low tide. These areas are important habitats for a variety of marine species.
Beaches are constantly changing, with new materials deposited daily by tides and waves, and old materials carried ashore and reshaped by wind and waves. Beaches are popular for recreational purposes, and many have facilities such as lifeguard posts, showers, changing rooms, shacks, bars, and restaurants.
Beach flora, especially those with network root systems such as creepers, sand palms, and sea grasses, help stabilize beach berms and prevent inland movement of dunes. They also trap sand particles and rainwater, enriching the surface layer of the dune, and provide a food source for a wide range of marine and terrestrial organisms.