A beach is an area of land where the sea meets the shore. Most beaches consist of sand, although some are composed of rock, shells, or other materials. Beaches are usually flat with a gentle slope toward the water, but they can also be steep or even hilly. Beaches change shape and composition constantly, depending on the forces that act upon them.
Waves and currents are the main forces that create, alter, and destroy beaches. These processes cause erosion of rocks offshore, and sediment is then carried up the beach by waves or longshore currents. The type of sand at a beach depends on the grain size and the way the material is deposited. Beaches with fine sand tend to be flatter with gentler slopes, while those with coarse sand are generally steeper. The type of sand at tidal pools is also determined by the grain size and the ability of the sand to absorb backwash.
Beaches are also subject to the forces of weathering and erosion, which wear away at their surface and erode sediment from their depths. Over time, erosion can turn large boulders into sand grains. Beaches are often used by people for recreational activities, such as swimming, sunbathing, surfing, and windsurfing. People have been using beaches for thousands of years. Commercial sea bathing developed in the United States and other parts of the world during the 19th century.
Beach debris includes garbage, cans, plastic bags, and other waste. It may also include marine organisms, such as crabs and sea anemones. In addition, some beaches are polluted by sewage, which washes out to sea during strong storms.
The nature of a beach depends on the energy of waves and wind. A beach that faces highly energetic wave and wind systems will have coarse, well-compacted sand, while those that face moderate to low energies will have fine, loosely compacted sand.
Sediment that is deposited by waves or currents on the beach may be transported from a distance of a few meters to hundreds of kilometers. Tides and ocean currents deposit new sediment on the beach every day. This changes the composition of a beach and sometimes forms new habitats for plant and animal species.
The part of a beach that is most active during a tidal cycle is called the beach berm. The berm has a crest and a face, with the crest being the top of the beach and the face being the slope towards the water. Beach berms have many different forms, including oscillation ripples and swash or rill furrows at the base of the beach. The swash and rill furrows are created by wave agitation, and their height depends on the velocity of the wave that created them. Some of the swash and rill furrows move sand up the beach, while others move it down to the sea.