A beach is a strip of land that slopes downward to water along a coast (either ocean, lagoon, bay, estuary, or lake). It may be made of any material that will wash down and accumulate on the shoreline: rock fragments such as pebbles or cobbles; sand; or mud. Beaches are continuously changing, either accumulating during periods of accretion or eroding during periods of retreat. They are usually rocky or sandy in texture and often have vegetation such as sea grasses and other beach plants.
A wide variety of wildlife live on beaches, including crabs, insects, birds, and sea turtles that lay their eggs there. In some cases, beach plants and animals have even been adapted to living in salty seawater. Beaches are populated by people as well, and they may have amenities such as boardwalks and lifeguard towers.
The formation of a beach begins with wave action. The constant wearing down of bigger pieces of rock and other material by waves causes them to gradually lose their size until they turn into fine grains of sand. This process is known as sedimentation. The size of these grains depends on the energy of the waves and other factors. Beaches dominated by higher energy waves tend to have larger grains than those exposed to lower energy waves.
Beaches can be located in bodies of fresh water, such as lakes or rivers, but they are most familiar to people living near seas and oceans. They can also be found in lagoons, such as the coral reefs that parallel many of the coasts of Texas and Florida in the United States. Beaches also form on barrier reefs that separate lagoons from the open sea and can stretch for dozens or even hundreds of miles.
The zone of the beach that is covered or uncovered by the swash of waves is known as the berm or swash zone. The area of the beach above the swash zone is called the beach face and may have sand dunes or other types of sedimentary forelands. The beach may have horns or embayments that are losing sand and beach cusps that are gaining sand.
Beaches can be contaminated by sewage and other waste washed up on them by storms or river run-off. They can also be impacted by changes in sea and land levels, which can affect the position of a shoreline or change the amount of sediment that is deposited. Despite their problems, beaches remain an important resource for humans and other organisms, and they continue to provide much-needed recreation and aesthetic beauty.