A beach is a landform along a sea or lake shore that consists of sediments, such as sand. It is usually located adjacent to a rocky coastline or the outer edge of a sand bar, a narrow trough along a sandy coast formed where waves first break. A beach is also a general term used to refer to any sand or other material that accumulates on a shoreline and slopes down toward the water.
The size and shape of a beach varies widely, depending on the type and amount of sediment available to be eroded by waves and currents and the rate at which that sediment is delivered by longshore and tidal currents. Beaches are typically dominated by fine to medium-grained, rounded, and compacted sand particles. However, they may contain gravel, cobbles, silt, mud, and other granular materials.
Many beaches are characterized by a dune system consisting of sand dunes that are separated by areas of vegetated wrack lines and tidal pools. Dune systems are built by the action of wind, waves, and tides, forming and shifting sand inland, sometimes as far as a few hundred meters, creating an extensive barrier that separates lagoons from the open sea and often protects low-lying coastal land and vegetation from wave and wind erosion.
Sands on beaches are typically composed of quartz, with a small percentage of feldspar and a few other heavier minerals. In the tropics, beaches are often covered with a more coarse sand made of coral skeletons and other sources of calcium carbonate—the same compound that gives calcite its characteristic white color and is found in most shells and the skeletal remains of marine organisms.
In addition to sand and other material that are eroded from the shoreline, beaches also contain debris washed ashore, such as wood and rock fragments, pieces of concrete, and household or commercial waste. Beaches are also home to flora and fauna that have adapted to life in the coastal environment.
Beaches can be classified into four distinct zones based on the size of the particles they contain: the swash zone, beach face, wrack line, and berm. Particles tend to be finer closer to the water, where they are constantly broken down by moving wave and currents.
Beaches are a dynamic, continuously changing landscape. They are the site of constant erosion and depositation, with major changes in shape, length, and depth occurring over periods of years or even decades. Frequent or severe wave events such as tsunami and tidal surges can substantially alter the location, appearance, and characteristics of a beach within hours.