A beach is a narrow strip of land along the edge of an ocean, lake or river. It is formed of materials such as sand, rocks and seashells that have been eroded and washed down by waves and currents. In addition, beaches are often home to a variety of plant and animal species that live in the coastal environment. Beaches vary in appearance and size, depending on factors such as the size of waves and sediment availability.
The composition of a beach changes hour by hour and season by season, as wind and water move sand and other materials from one place to another. The composition of a beach depends on the nature and quantity of upstream sediments, the speed and turbidity of water flow and wind, the particle size of the materials and their state of compaction. Particles that are dense and compacted resist erosion better than loose or finer particles. Established beach flora (such as grasses and palms with complex network root systems) help stabilize dunes by trapping sand particles and slowing the fluid flow at the surface layer.
Waves act as the primary agent in changing a beach’s shape, by eroding some areas and depositing sediment in others. They also alter beach features, such as the height of the crest or tideline and the width of the beach. Beaches can also be altered by human forces, including bad construction practices that degrade the dunes and coastline, beach nourishment to build up a depleted beach, and changes in storm patterns or ocean currents that affect the amount of material moving on or off a beach.
A typical beach has several distinct segments when viewed in profile from the air. At the top is an area of bare sand that may be bounded by beach ridges, or berms, created from the sediments deposited by the waves of a previous storm. Behind these are a series of terraces, the lower ones being submerged at low tide. The beach slopes gradually toward the waterline, with the foredune being the steepest portion of the beach.
In the center of a beach is an area of shallow water that is often covered with marine debris and has a high proportion of underwater sand, known as the submarine beach. Beaches can be found at the edges of lakes, rivers and even ponds. Beaches at lakes and rivers tend to be calmer than those at the ocean and may have a different ecosystem that includes a different type of marine life.