Beaches are broad areas of sand and other sediment, often sheltered by reefs or other features. They can range from sandy coastlines in temperate regions to cliffy stretches of sand and pebbles in the tropics. Beaches are constantly changing as waves and tides deposit and remove materials. In some places, beaches are enriched with natural materials such as corals, shells, seaweed and marine organisms. In other places, beaches contain manmade materials such as discarded glass, plastics and metals.
Beach formation is a complex and long process. It begins with weathering, the breaking down of rocks by wind and water. Over time, rocks are broken down into smaller and smaller pieces until they reach the coast and become sand. Beaches may also be formed by the deposition of volcanic lava.
Most beaches are made of fine to medium sand, but they can also be formed from coarser-grained material such as boulders (64-256 mm in diameter) or cobbles (larger rock fragments). The grains of sand on a beach often show examples of particle imbrication, where flatter grains lean against each other with the lower edge of one partially resting on the upper surface of another.
Along with sand, most beaches are covered by other natural and manmade materials. Corals and other marine organisms are common on many tropical beaches. In temperate areas, beaches often are covered in driftwood and logs, castaways from the logging industry. In some places, such as the Skeleton Coast on the northern coast of Namibia, beaches are augmented by bones of whales and seals from shipwrecks. Throughout the world, a variety of other natural and manmade materials can be found on beaches–from shells to sewage and garbage.
Beach profile is the way in which a beach varies in shape and size when viewed from above. The upper part of a beach is a foredune or series of sand ridges, called berms, that are acted on by wave action. The foredune usually rises above the high-tide line, with the upper surface of the berms inclining seaward and the lower surfaces rising to or above the waterline. Below the berms is a low-tide terrace that is sometimes referred to as a foreshore or low-tide beach. Crumbling sand cliffs may develop beneath the foreshore and form a submarine beach.