A beach is a landform on the seashore that is composed of loose sediments, typically sand but sometimes gravel, cobble, or shingle. Most beaches are created by wave action and currents, but they may also be formed by erosion of rocks offshore or by a collapsed headland, slumping of cliffs, or by marine biological activity such as coral reef growth. A beach may be affected by a variety of environmental factors, including runoff from nearby land, public safety hazards like rip currents and debris, the presence of vegetation, water temperature and quality, marine life, and human-related activities such as fishing, boating, piers and amusement parks.
Most beaches are constantly changing, with waves bringing in new materials and carrying away others, and with winds and tides altering their shape. Beaches are primarily the result of erosion processes but they can be influenced by human actions such as dumping construction debris or marine pollution. The process by which a beach is changed depends on the nature and quantity of the materials that form it, the size of particles in the material, how compacted the sediments are, and the presence of established vegetation.
Sand is the primary material of most beaches, but it may also contain other materials such as seaweed or fragments of other marine organisms. Many beaches are characterized by high concentrations of salt in the sand, which is caused by ocean currents and waves stirring up the sand and dissolving some of it. Other beach characteristics may include a high percentage of fine particles (silt, clay, and organic material), a wide range of particle sizes, and the presence of flora and fauna.
Beaches are a major source of water recreation and are important economic contributors in some areas. Beaches are often visited for recreational purposes, such as swimming, sunbathing, walking, jogging, playing volleyball, and surfing. Beaches are also important habitats for marine species, and some are used for commercial shellfish harvesting.
Some beaches are privately owned, but in most places the general public has a right to access publicly-owned beachfront land. The exact boundaries of such rights vary by jurisdiction; in the United States, for example, public beaches are bounded by the mean high tide line and the mean low tide line.
A sandbar is an offshore ridge of sand or coarse sediment that forms when the swirling turbulence of waves breaking off a beach excavates a trough in the sandy bottom. Some of the sand is carried forward onto the beach, but some of it is trapped in the trough and becomes part of the bar. Other sand is added to the bar by waves and sand suspended in backwash and rip currents, and some of it is deposited from deeper waters. Bars can vary in size from a few meters long to marine depositions that extend for hundreds of kilometers along a coast, which are often called barrier islands. Beach nourishment is the act of introducing material to a beach in order to enhance its recreational or ecological functions.