A beach is a narrow, gently sloping strip of land that extends along the shoreline of an ocean, sea, lake, or river. It is a depositional landform, meaning that it forms when sediment is carried by waves and deposited on the coast. The sediment that covers beaches may consist of sand, gravel, crushed shells, or other material. Many animals and plants live on and around beaches. People use beaches for recreation and to relax.
Beaches are constantly changing, with some parts gaining materials and others losing them. Beach erosion and transportation is primarily driven by wave and current activity, but also by the geology of the surrounding area. Waves beat against the coastline, eroding and wearing away rocks until they become sand or finer sediment. Sand, mud, and other materials are then carried by currents and waves to other locations, sometimes far from the original source of the sediment.
The composition of a particular beach varies, depending on its location and the size, shape, and density of its sand grains. Beach sand usually contains silt, clay, and a variety of rock fragments. It can also contain marine organisms such as crabs and sea anemones. Beach sand can range in color from white to black, and it may contain tan, yellow, or red sand resulting from the type of rock that is present in the region.
Beach erosion and transportation is caused by wave action and water currents, but can also be influenced by factors such as wind direction and rainfall. A beach is usually divided into multiple zones, including the backshore (a zone that is submerged during high tide), the foreshore (the area between the high and low tide lines), and the nearshore (a zone that is sheltered from strong wave action).
Sand is sorted as it moves along the beach by its size, with smaller, lighter materials being transported farther than larger, heavier particles. In some places, a long, thin bar of sand can form offshore. This bar, known as a trough or sandbar, is formed when waves break near the shore and create a shoreward-moving bottom current that is balanced by a counter-current from the sea floor. Other bars are located further offshore and may be composed of sand, gravel, cobble, or even boulders.
Beaches are found along the edges of oceans, seas, lakes, and rivers, but they are not a natural feature of any body of water. Instead, they are the mostly dry interface between land and water. Although water is not a natural substance to have a beach, lakes and rivers can certainly have ‘beaches’; these are more properly called sandbars or river banks.