A beach is a strip of land along the edge of a body of water. It is usually composed of sand, although it could be any kind of granular matter that the water has access to and can shift around (such as silt, gravel, cobble, shingle or boulders). Beach material accumulates during periods of accretion, and moves away during periods of erosion.
Beaches are formed through a complex series of natural processes that take place over long periods of time. They begin with weathering, the process of rock-mass erosion that slowly wears rocks down to the point where they can be moved by flowing water and deposited on the shore. Sand is then added to the mix, which may consist of sand from nearby beaches or sand that has been relocated from other areas. As more sand is deposited, the shape of the beach changes. The beach’s slope may steepen or flatten, the width and depth of the shoreline change, and the composition of the sand can vary from coarse to fine, or from a high shell content to no shells at all.
Water that flows over the beach during incoming waves is known as swash, and it contains sand grains that are suspended in water. Some of this swash percolates into the sand, forming new deposits of sand; the rest is washed back out to sea during receding waves, a process called backwash. As a result, beaches are constantly changing – in fact, they can change significantly within a few hours during high-energy wave events.
Sediment can also be transported from one beach to another over long distances. As a river encounters a delta, for instance, its sediment load is deposited and creates a fan-shaped pattern of sediment that spreads out into channels. This type of deposit is also common in lakes and other bodies of stagnant water.
Mud that forms on beaches is typically the result of the deposition of fine-grained, clay-like materials from coastal marshes or the leachate (residue) of beach nourishment projects that use too much sand with a very fine grain size. Such mud typically has plant fragments embedded in it and may also contain bits of shell.
Commercial sea bathing became popular in the 19th century, and by the late 1800s resorts that featured beaches were becoming widespread in the United States and other parts of the world. Beaches were promoted as a place for health, fun and frivolity; they were considered to be a “good cure” for many kinds of ailments. They also became an important source of income for local communities, and they continue to be a very popular destination for recreational activities.