A beach is a narrow strip of land where sand gathers along the shore of a body of water. It is a natural habitat that supports many plants and animals, and offers recreational opportunities for people such as swimming, sunbathing and building sandcastles. Beaches can be at oceans, lakes or rivers. They can vary in size, shape and sand color. The sand that makes up beaches is made from small grains of rock, including eroded rocks from far away and nearby locations.
Waves and currents continuously transport sand and other sediments along the coastline, adding it to beaches. This process is called deposition. The size of a beach depends on the energy of the waves and the amount of sediment available. Waves that are strong and close to the shore deposit a lot of sand and sediment. Waves that are weak and farther out from the shore deposits less. A beach also depends on the speed at which the water moves. Faster moving water creates a more turbulent environment that results in more erosion, while slower moving water creates a more gentle environment with less erosion and no current.
Beaches have different colors and characteristics because of the materials that make up their sand. For example, coral beaches, which are common on warm tropical islands, have white sand that is powdery because it is made from the skeletons of corals. Beaches at lakes or rivers have mud-colored sand, while volcanic beaches often have black sand that was formed from molten lava.
The size and shape of a beach depend on how the waves move, what is beneath the sand, and how far inland the shoreline extends. Beach slopes are usually gradual, but they can be steeper in places where waves break over submarine ridges or submerged bars. Beaches may also have a reef or man-made structure that protects them from erosion.
A sandbar is an offshore ridge or hill of sand that is typically above the water’s surface at low tide. It is built by swirling turbulence from breaking waves that excavates a trough into the sandy bottom and carries sand forward over the bar. Some sand suspended in the backwash and in rip currents adds to the bar, as well.
Beach erosion is a constant process that can be both beneficial and harmful, depending on where the sand ends up. Erosion can sculpt beaches and create beautiful scenery, but it can also cause problems such as erosion of buildings and loss of lifeguard towers.
Beaches that are close to the mouth of a river or stream tend to be muddy or soft, and they can have unique ecosystems with marine life. They are subject to flooding during rainstorms, and their erosion rate is faster than beaches farther inland because of the higher water levels. Some beaches are protected by reefs, while others are lined with seawalls to prevent erosion. A beach may also be a location where people swim, fish and surf.