A beach is a landform along the edge of a body of water, usually the ocean. It comprises loose materials, including sand, pebbles and shells. Beaches are popular places for recreational activities such as swimming, sunbathing, surfing and playing beach sports. They also serve a vital ecological function in dissipating wave energy and preventing coastal erosion.
Many beaches have dunes, a form of barrier that separates the beach from the sea. These often have shrubs, trees and grasses growing on them. Animals such as crabs, insects and birds use these plants for food and shelter. Sea turtles lay their eggs on ocean beaches. Beach plants include sand-dune grasses, sea oats and dune flowers. Beaches can also be inhabited by humans. In addition to people who visit the beach for recreation, beaches may have human-built structures such as lifeguard posts, changing rooms, showers and shacks. Beaches can also have hospitality venues (such as resorts, hotels and restaurants) and housing, both for permanent and seasonal residents.
Most beaches are composed of sand, which is created when rock and other sediment are worn down by repeated pounding by waves and the ebb and flow of tides. The pounding of waves and the motions of the ocean currents wear down rocks and pebbles, making them smaller and rounder. This action creates sand, which is typically made of the minerals quartz and feldspar. Quartz tinted with iron oxide appears light brown and feldspar is tan, giving beaches their characteristic sandy color.
Beaches are constantly changing in size and shape, sometimes on a scale of weeks or days during major storms. They are the result of a complex interplay between multiple processes that act at different rates in different locations.
The most important process that forms beaches is the interaction between waves and the sediment they carry ashore. The movement of waves is a constant process that involves the swash, which occurs when a breaking wave moves up the foreshore, and the backwash, which occurs when a retreating wave leaves behind it a deposit of sediment. Destructive waves have stronger swashes and more backwashes than constructive waves. These waves tend to remove material from the beach, whereas low energy constructive waves promote accumulation.
Other important processes that affect beach formation include weathering and erosion of rocky coastlines, the formation of sand bars and the interaction between beaches and tidal channels. Beaches may be nourished, or built up, with additional sediments from the seabed to replace eroded material.
Depending on local conditions, beaches can be categorized as sandy or rocky. A rocky beach is typically composed of a high proportion of large rocks, while a sandy beach has more fine-grained sediments. Some beaches are also characterized by a high concentration of fossils, which can provide clues about the past environment of the area. Beach nourishment must be carefully planned so that new sediments have time to compact and stabilize before aggressive wave or wind action erodes them.