A beach is a strip of sandy or other loose sediment that borders a sea, lake, ocean, or other large body of water. It is a depositional landform, which means that over time it builds up sediment. This buildup occurs primarily through wave action. Beaches are dynamic, changing constantly from hour to hour and season to season.
Beach sediments include sand, gravel, crushed seashells, and organic material like plant debris, as well as marine organisms such as crabs and sea anemones. They can also include abrasive materials, such as tiny particles of rock. Beach materials can come from a wide area, but they are often sourced locally by erosion or deposition. For example, black basalt rock from Hawaii contributes to the dark color of some beaches; coral reefs offshore provide a significant source of white sand for other beaches. Beaches are not only a source of sand, but also offer protection from erosion and storm surges by acting as a natural barrier against the sea.
The nature of beach sediments depends on their particle size and state of compaction, as well as the speed and turbidity of wind and water. For example, fine-grained sediments, which make up the bulk of most beaches, tend to move quickly when disturbed by waves or wind. Such sediments may be suspended in the water or blown by waves into deeper waters or into the marshes and mudflats behind barrier islands. Beaches with coarser-grained sediments, including silt and clay, generally are stable because the larger grains resist movement in the water.
Many beach types are created by erosion and sediment drift, which form bars of sand on either side of the surf zone. These bars can be long and wide or narrow and short. Beaches can also have an irregular or regular shape, or they can be completely flat and backed by dunes.
Beaches are the habitat of many species, from seaweed and marine organisms to birds and fish. They are also important recreation areas. People enjoy swimming, fishing, sunbathing, and walking along beaches. They can also be a valuable resource for recreational activities such as surfing and windsurfing.
Many beaches have been polluted by waste from human activity. Waves and currents carry pollutants to beaches from rivers, streams, and drainage systems in the surrounding land. They can contain bacteria, raw sewage, and toxic chemicals. Many beaches are closed after severe storms due to the amount of contamination washed ashore. These pollutants can cause illness and even death to humans, marine animals, and plants. They can also damage the natural habitat of the beach. Beaches can be restored through beach nourishment, where sand and other materials are pumped onto the shore to support the health of the beach. These projects are not always successful and they are controversial. Some people oppose beach nourishment because they believe that beaches should be left in their natural condition. Others feel that the benefits of beach nourishment justify the use of public funds.