Beaches
A beach is a landform along the water's edge, usually made of loose particles like sand or pebbles and cobbles. A beach's size, shape, composition and location depend on how it changes with the tides, the wind and waves. The most famous beaches are those along the world's ocean coastline, but beaches can also be found in lakes and rivers, even some large ponds. The main thing that distinguishes a beach from other coastal features is its sandy quality, but many beaches contain all six grain sizes as defined by the Udden-Wentworth scale (see picture).
Unlike most rock formations, which can be classified only by geologists, most beaches can be described in general terms by the average sand grains per square inch they have. This is what gives the beaches their distinctive appearance and texture, which are often described as smooth and silky to the touch. The size of a beach's sand grains, and how they are arranged, determines a beach's accretion rate, its slope and its position along the coast.
Most beaches are not stable, moving either inland or seaward over long periods of time, or both. Freak wave events may substantially change the size, shape and location of a beach within hours. Well-stabilized foreshore areas tend to accrete, while unstabilized ones are likely to erode.
The sand of a particular beach is a very special mixture that reveals the unique history of its surroundings. In the temperate parts of the world, most beach sand is composed of quartz with a little bit of feldspar and other minerals. But in the tropics, the mix is much different. Beach sand in these regions contains mostly the skeletal remains of marine organisms, with a few bits of calcium carbonate and other heavy minerals.
A sandbar is a submerged or partly exposed ridge of sand or coarse sediment that extends offshore from a beach. The swirling turbulence of breaking waves excavates a trough in the sand bottom and deposits sand on the offshore flank of the trough. Sand suspended in backwash and rip currents adds to the bar, which is normally kept below still-water (half-wave height) level by the plunge of the breaking waves.
Beaches are an important natural resource, providing habitat for wildlife and a popular place for recreational activities in shallow water. They are also an economic and cultural asset, attracting visitors to resorts, hotels and restaurants in their immediate area. However, a beach's beauty and ecology are threatened by the effects of human activity. The removal of vegetation from the foreshore, burning and clearing of sand dunes, and the pollution of marine waters from land use all affect the characteristics of a beach. A beach can be preserved by restoring its natural vegetation cover. This is an important goal for the preservation of the planet's ocean beaches.