A beach is a landform along the coastline of an ocean, sea or lake that typically consists of loose particles such as sand, gravel, shingle or pebbles. The particles can be from rock or from biological sources such as mollusc shells or coralline algae.
Beaches vary in size, shape, composition and texture depending on prevailing weather and wave action. They may be wide and gentle or steep and rough, and may have a high or low shell content.
The materials that form a beach typically include rocks (such as quartz, feldspar, and limestone), biological material, such as sand-colored mollusc shells, or coralline algae. The beaches of most temperate regions are composed mainly of quartz, but in the tropics, calcareous beaches are common.
Some beaches are very fine and clear, while others are coarse and cloudy or have a brownish coloration that is often caused by oxidized sand grains from broken down shells. In Hawaii, beaches are usually gray or tan in color, though some may be black due to the presence of black basalt rock.
Many beaches also contain sand dunes, which are natural reshaping processes of beach surfaces as they are affected by changing water levels and sediment supply. These sand dunes are typically shaped by tides, but they can also be reshaped by large cyclonic storms or tidal currents.
During storms, the relative water-land level and sediment supply change, resulting in redistribution of beach sediments in a short period of time. This can reconfigure beaches, sometimes within hours of the storm’s arrival.
When a beach becomes progressively more developed, the surface can form parabolic dunes with their summits coastward. This process can occur as the beach erodes and retreats or as sand is delivered to an area of developed dunes. Eventually the sand dunes are broken through by waves, and the cemented strata behind them become exposed as beach rocks.
Sand dunes can be reshaped by human activity such as beach nourishment projects that use materials with too much mud in them. Coastal development and the dumping of waste into the sea cause a number of issues at the beach including erosion, pollution and deterioration.
A sandbar is an offshore bar that forms off the beach where a current pushing toward the shore meets a current pushing away from the shore. This creates a narrow water column called a trough, which is flanked by sand and other sediments. This type of bar is common at the head of bays, where water pushes out to sea as it enters the bay. It can also be a feature of underwater tidal deltas, which are fan-shaped deposits of sand and other sediments that occur in enclosed bodies of water where ocean waters flow into them.
Normally, sand depositions are confined to the front of the bar. However, because of the rip currents that travel through the bar and the backwash of the water in the water body that it is located in, more sand depositions occur off-shore, especially in deeper water. This complete process results in a beautiful and scenic landmark that is known as a sandbar.