A beach is a landform alongside a body of water that consists of loose materials including sand, shells, seaweed, and marine organisms. Its shape is constantly changing, as waves and wind carry sediment from one place to another. Beaches also vary in their composition, with some being predominantly sand and others having significant amounts of shells.
Many people visit beaches to swim, walk, surf, play volleyball, or sunbathe. Beaches are also vital to the health of coastal ecosystems, providing habitat for birds, fish, crabs, and other animals. However, if beaches are not well maintained, they can become polluted and degraded. Beaches can be protected by reducing beachgoer pollution, including removing trash from the shoreline and refraining from taking shells or other marine organisms.
Beaches can be found all over the world, in oceans and lakes, as well as on rivers and streams. They range in size from a few meters to hundreds of kilometers. The characteristics of a beach are determined by the nature of the wave energy in the area, the type of sediment (sand or shingle), and the way it is affected by tides and longshore currents.
Most beach material is sand, but it can also be clay or gravel. Some beaches are white or tan, while others are black, grey, or red. The color of the beach material depends on its source, such as eroded bits of coral reef near the shore, volcanic ash that was blown into the sea from a nearby lava flow, or weathered quartz from a distant mountain range.
In addition to sand, beach material may include silt or clay particles that are too large to be seen by the naked eye. Such fine grains of sediment can be washed away by waves or move slowly to deeper waters, or they may be deposited in the sounds and marshes behind barrier islands. In some cases these particles form layers of mud on beaches.
The main feature of a beach is its berm, which is the part that is above water during some parts of the tide cycle. A beach berm has a crest and a face, the latter being the slope that leads down to the water from the crest. If a beach is dominated by sand, its face is usually flat or gently sloping.
If a beach is predominantly shells, its face tends to be steeper. A beach’s crest and face can be separated by a gap known as a trough or rip current channel. Beaches with a high proportion of sand are usually straight, with the exception of sandbars.
A beach’s sandbars form through sand transport, which occurs when waves cause the beach berm to slope more gradually at one end than at the other. This causes waves to slow more at the shallower end and, in effect, refract, or change direction like light passing through a prism.