Beaches

Beaches are shores built of unconsolidated sediment, most commonly sand. But you can also find beaches composed of cobbles and boulders and clay and silt. Located between land and sea, from low water to highest elevations subjected to waves, they are among the most dynamic of environments. Waves and currents constantly move beach material, and wind also plays an important role, blowing finer material away from the beach, where

Muir Beach, California (Courtesy of Scott Horst)

it accumulates as sand dunes. Over time, beaches change their width and thickness as sources of sediment, the rise and fall of sea level, and uplift and subsidence affect the area. Typically, beach sediments come from the land through stream transport or erosion of adjacent cliffs.

Along the southern part of coastal United States, where the coastal area is low and sandy, long, straight beaches are typical. Along shorelines adjacent to mountainous regions, or where bedrock is adjacent to the sea (as along the coast of southern Maine), curved beaches are more common.

Barrier beaches are long strips of sand that are separated from the mainland by a body of water. Spits are beaches that extend from the land and terminate in open water. Tombolos are beaches that connect an island to the mainland or another island.

Because the beach environment is so dynamic, large plants are absent, and the animals are typically burrowers. They have mechanisms for utilizing the minute particles of food that are entrapped in the spaces between the sand grains.

As the beach slopes upward, away from the sea, it is subject to less wave action—creating a rough parallelism on the types of animals found. Beaches usually contain a small variety of species, but they tend to abundant.

—Sidney Horenstein

See also: Atolls; Barrier Islands; Coastal Wetlands; Coral Reefs; Estuaries; Lagoons; Oceans; Tides

Bibliography

Bascom, Willard. 1980. Waves and Beaches. Garden City, NY: Doubleday; Hamblin, W. Kenneth, and Eric H. Christiansen. 2000. The Earth's Dynamic Systems. Upper Saddle River, NJ: Prentice Hall; Laing, David. 1991. The Earth System. Dubuque, IA: Wm. C. Brown; Plummer, Charles C., David McGeary, and Diane Carlson. 2002. Physical Geology, 9th ed. New York: McGraw-Hill.

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