A beach is a depositional landform formed from sand, gravel, and crushed seashells that have been carried by waves to a coastline. There are three different types of beaches: the first, a narrow strip of sediment bordering a rocky or cliffy coast; the second, a broad, flat marine or fluvial accumulation of sand (free beaches); and the third, a very long, narrow coastal barrier of sediments that may stretch for dozens or hundreds of miles, often dissected by tidal inlets and lagoons.
Beaches are the primary places that land-dwelling humans can experience and enjoy the ocean. They are important environmental, economic and cultural resources. Many have been developed for recreational use, including swimming and sunbathing, and some support tourist industries. In addition, they are a source of minerals and fossils, and they provide habitats for a variety of organisms.
The composition of a beach is determined by the type of rocks and sediments that lie near the shore, as well as how those rocks and sediments erode. There are several different types of erosion, but the most common occurs when waves strike the beach, a process called attrition. When sand strikes other objects it can also be eroded, through abrasion and hydraulic action. There are some other processes that can cause sand to disappear from the beach, such as chemical weathering and corrosion.
Because beaches are so close to the water, they can change very quickly. Even on a regular visit, one might notice that the width of a beach or its slope changes, as well as the presence or absence of shells or other debris. This is because of the forces of nature, but also because of human contributions, such as trash.
As powerful swells and waves sweep up the coastline, they carry a great deal of sediment offshore to the sandbanks that are sometimes found at the edge of a beach. This sand moves back on beaches during less-powerful swells and waves, but it can also drift far offshore in areas known as submarine canyons. Beaches may also have layers of mud, which is made up of fine-grained mineral sediments, such as silt and clay, that are not easily moved by waves.
A sandbar is a small bar of sand or other granular material toto sgp that forms at a point on the coastline. Sandbars may be made of any material that moving water can work with, such as soil, silt, sand, gravel, cobble, shingle or boulders. Some sandbars form at trough bars, where breaking waves set up a shoreward current with a compensating counter-current along the bottom, and others are located further offshore, representing the breakpoint of even larger waves. There are also bay head and barrier bars, which are found in shallow waters, estuaries, tidal inlets and lagoons. Barrier bars are more likely to be found in open seas, but they can also occur along tidal inlets and lagoons. A bay head or barrier bar is the most common form of sandbar in a bay, estuary or tidal inlet.