Located along the shore of a waterbody, a beach is a narrow, gently sloping strip of land. It may be made of sand or rock fragments, and may contain manmade structures such as lifeguard posts or changing rooms. Many beaches are also used for recreational purposes. Sea turtles lay their eggs on ocean beaches. Some beaches are actively restored through practices such as beach nourishment.
In the tropics, beaches are composed of skeletal remnants of marine organisms such as coral reefs. In temperate latitudes, sands are composed of feldspars and quartz. The minerals are hard, but they are less dense than rocks, so they are softer and easier to move by waves and currents. The sand grains are usually light brown or snow white in color. The minerals are often tinted with iron oxide. The sand is often a light color because it has been worn away by wind and weathering. Some beaches are covered with a layer of gravel or other manmade material.
The size and shape of a beach depends on the movement of waves and currents. A typical beach consists of a berm or face, a shallow offshore bar, and a beach zone. The face is the area where sand is deposited in a wave-shaped pattern. The crest of the berm or face may have a trough or a series of long shore bars. The beach zone is the zone of sand accumulation above the water line. The dimensions of the beach zone depend on the tide height and sediment distribution. Some of the beaches in the tropics are sand-colored, while others are pink or black. Other beaches are green or a shade of red.
A beach can be made of sand, mud, or rock. It can also be formed of materials such as shells and seaweed. These materials can be carried by waves or wind, and may be derived from local sediment. In some areas, beach material can travel hundreds of kilometers. This process is called longshore drift.
The waves and ocean currents move sand, rocks, and other debris around the coastline. During the summer, the waves build up the beach. However, the waves also wear down the sand and rocks. In winter, the storm winds toss the sand into the air. The waves may wash the sand and leave it in distinctive fine layers in the beach sediment. These are sometimes called swash or backwash.
The sand on a beach is sorted by size. The larger grains are classified as mud or boulders, while the smaller grains are classified as silt. These types of sand are lighter in color and are less dense. The sand on a beach can be derived from ocean sediment, or may be organically derived from biologic components in the nearby ocean. Occasionally, the sand is derived from volcanic rock. Some sands are composed of calcium carbonate, which is the same stuff found in the skeletons of corals.
The active beach profile is the result of a complex interaction of sand transport and wind. It varies greatly depending on a number of factors. For example, the size and composition of the sand may determine the shape of the beach berm or beach terrace. It is common for the beach to have a series of beach ridges. Other minor relief forms can occur, such as swash or rill furrows, oscillation ripples, or beach cusps.