A beach is a landform along the edge of a body of water, usually the ocean. It is made of loose particles such as sand, pebbles, shells and rocks that are deposited by waves and currents. Beaches are found around the world and are popular places for recreational activities such as swimming, walking, sunbathing, playing beach games and picnicking. Beaches are a dynamic landscape that is constantly changing, and the characteristics of each beach depend on the processes that shape it.
The process of beach formation starts with weathering, where rocks are broken down into smaller pieces by the action of wind and water. The fragments are then carried by streams and rivers to the coast where they are deposited. The sediments that form beaches can also come from biological or chemical sources. Shells and corals left behind by dying or dead organisms are a common source of beach material. Some beaches are entirely composed of this kind of material, while others are rich in gravel and sand that has been washed from the land.
Beach profiles can vary considerably, but there are several conspicuous elements in most. Nearly always there is a ridged area above the waterline, known as the beach berm, which was formed by the wave-swept front of a previous storm. Below the ridges, there is often a low-tide terrace that may be covered with seaweed and other plants that cannot be moved by waves or other forces.
Closer to the water, there are usually a series of eroding sand ridges called dune crests that slope downward and away from the beach. This is followed by a lower beach terrace, and further down the coast, there can be troughs and submerged sandbars.
Sandbars are ephemeral features that appear and disappear depending on the conditions of the sea. They are created by sand transport and are typically composed of sand, but can be any granular material that the waves can move (such as silt, gravel, cobble or shingle). In general, a sandbar is more stable than a beach because the larger grains of sand can sink more easily and are less prone to erosion by the waves.
Beaches also have a wide variety of surface textures and compositions, which are influenced by the nature and quantity of the sediment, how much water or wind moves it, and whether or not there is any vegetation present. Fine sediment tends to compact and settle in still water, whereas coarser material will remain suspended in turbulent waters. A beach will be more resistant to erosion if it is covered by established vegetation, because the roots of this vegetation act as a barrier against fluid flow.
Beaches are a fascinating place to observe natural geological and biological processes in action. They are one of the primary places where land-dwelling humans can experience the wonders of the ocean, and each tidal cycle brings new surprises as the interactions between the beach and the sea change the appearance and structure of the beach.