A beach is a narrow strip of land along the edge of an ocean or another large body of water. Most beaches are covered in sand, pebbles, and rock fragments. These materials are the result of weathering and erosion, which occur when waves break against rocky cliffs or coral reefs. Erosion also wears away at the beach itself over time, reducing its width. Beaches often experience gradual growth in size as the erosion process wears away sand and other sediment, which is then carried downstream by the current. Beaches can also grow in size due to river deltas, which carry eroded sediment toward the ocean.
The shape and composition of a beach depend on its geological history and the environment surrounding it. For example, sand beaches are typically found on coasts exposed to strong winds and waves. The sand in these beaches is usually coarse and is composed of sand particles that are larger than 1 mm, such as gravel or cobbles. These particles are washed from inland by rivers, blown by wind, or deposited by waves.
Erosion can have positive effects on a beach, including creating a more gentle slope. However, it can also cause a beach to shrink in length. In addition, erosion can make an area too shallow for safe swimming. This is why many beaches are protected by seawalls, which are made of stone or other materials, and built to prevent sand from washing away.
Beaches also form sandbars, which are areas of sand that appear near the shore during low tide. They can be surrounded by water or be connected to the beach by a lagoon. Beachgoers often use sandbars as places to sit, swim, and play. The formation of sandbars is dependent on the water’s movement, including the speed of waves and currents. When there are stronger currents and faster moving waves, sandbars may be formed further out from the beach.
The quality of a beach is also influenced by its human residents. For instance, some people choose to live close to a beach, which can cause it to become more popular with tourists. This can cause the beach to be overrun with garbage and other debris. In order to protect their homes, people sometimes build seawalls made of sand or concrete.
The type of wave that reaches the beach also affects its formation and future erosion. Constructive waves, which allow the sand to settle and compact between waves, lead to a firm beach surface that resists future erosion. Destructive waves, on the other hand, allow sand to remain suspended in the water, which can weaken the beach’s surface and encourage future erosion. The amount of beach material that is moved by a particular wave depends on its height, wavelength, and energy. This information is used to predict how much sediment a beach will lose in a given period of time. For example, a wave that moves sand at a rate of 2 cm/h will move about 5 m of sediment in a year.