A beach is a strip of land that lies next to a stretch of water (ocean, lake, river, gulf, lagoon, bay, estuary, or lake). It may be covered with rocks, pebbles, sand, mud, or other sediment. The sand and other materials are usually the product of weathering and erosion.
The beach profile varies greatly depending on wave parameters, tide height, and sediment composition and distribution. It is typically characterized by several parts, including an upper terrace, a foredune, and submerged sandbars or troughs running parallel to the shoreline.
In the temperate regions of the world, most beaches are covered with sands composed mainly of quartz. Some sands are made of feldspar, and a few have heavier minerals, such as calcium carbonate, oolites, or shell fragments.
On the tropical coasts of the world, however, a majority of beaches are covered with sands that consist primarily of calcium carbonate. These sands are formed when cold oceanic waters flow onto warm shallow banks. The calcium carbonate is precipitated on bits of shell, quartz grains, or other surfaces.
Erosion occurs when wind and waves sweep sand up and then wash it back down, creating different positions along the beach. It is a process that can occur on many different types of beaches, but it is most common on barrier-island beaches, which are sand islands detached from the mainland by a lagoon or bay.
When waves break over a beach, it moves sand upward and then down, and then moves it in a pattern along the beach that is zigzag-like. The sand moves in this direction because the incoming waves and winds hit the beach at an angle. This motion is known as swash.
Continual swash over time also moves the sediment that is part of the beach in a direction that is parallel to the beach. This process is called longshore drift, and it is important for the survival of the beach.
This longshore drift moves the sand from points where it is first placed on the beach to points farther down the beach, where the sand is deposited. Anything that disrupts this movement can destroy the beach.
Some sand is carried offshore by the waves into deeper water or into sound and marshes behind barrier islands. Some sand is washed into the sea by storms, while some sand is swept up from ocean depths into the waves.
On most beaches, the sand is deposited in a way that allows it to move in a direction that is parallel to the direction of waves. This is called swash, and it is controlled by the tide.
During summer, sand bars appear close to the shore. In winter, they appear farther out. This is because the waves are able to reach these sand bars easier during warm months than they can during cold ones.
The beach can also be a place where animals and plants live. Various creatures rely on the sand for food and shelter. For example, sea turtles lay their eggs on beaches. Other animals, such as sand lizards and frogs, use the sand to hide from predators. These sand-dwelling animals can also be the source of sediment that is carried out of the beach into the ocean.