A beach is a geographical formation of loose sediments, usually sand, gravel or pebbles, located along a body of water (including lakes, seas and oceans). Beaches are important habitats for marine organisms and are central to the economy, culture and tourism in many coastal areas. They are subject to natural processes of erosion and sedimentation, but they also may be manipulated by human actions such as beach nourishment.
The material that makes up a beach changes from hour to hour and season to season. Sands vary in composition and include the whole range of sediment sizes from clay to boulders, as classified by a geological classification system known as the Udden-Wentworth scale. Beaches may contain fragments of a variety of materials such as shells, calcite, coral and algae. The sand of some beaches contains a substance called ooids, light-colored ovals of calcium carbonate that resemble mint candies and which form by precipitation from supersaturated seawater.
Many beaches are formed when sand and other materials carried by the surf wash up against a cliff or other type of barrier. When the waves retreat, they leave behind a beach with an upper terrace called a dunes or foredune, an intermediate terrace sometimes with a series of ridges called berms and, below that, a lower terrace often covered by seaweed, marine plants and tidal pools.
Some beaches are formed by erosion of the underlying materials such as gravel and rocks or even bedrock. This can happen in places where the sea is especially powerful, or when weather conditions are right, such as after a hurricane.
Depending on the composition of the beach, wave action can create sandbars offshore from a beach and even create the ocean banks or “backshore” of coastal plains and soundside marshes. Sandbars can shift suddenly, creating dangerous conditions for swimmers and boaters, so visitors should always swim in designated areas, obey rip current warnings, and follow other safety guidelines.
Beaches can be polluted by the discharge of raw sewage, chemical and oil spills, as well as garbage. They can also be affected by contamination from a wide range of chemicals, such as pesticides and fertilizers, that are washed from inland farmlands and cities into coastal waters or by runoff from urban stormwater drainage pipes.
Because beaches are constantly changing, people have data sgp developed a number of ways to support their health and maintain their appearance, including beach nourishment. Beach nourishment involves pumping sand onto beaches to help them retain their shape and to fill in areas where erosion is occurring. The sand can come from nearby beaches, from the continental shelf or from other sources. Beach nourishment has been used in many beach cities around the world and, because it is done under careful control, many of these nourished beaches appear quite natural and are not immediately recognized by tourists as artificial. In the case of Waikiki Beach in Honolulu, for example, sand was shipped from Manhattan Beach, California throughout most of the 20th century to help preserve its famous white sands.