A beach is a landform along the edge of a body of water. It usually consists of sand, pebbles, and sometimes shells. It is often a popular destination for swimming, sunbathing, and playing beach games. Beaches are constantly changing, as the weather and tidal action bring new materials in and take away others.
The term beach also describes the area that is dry at low tide and submerged at high tide, as well as the tidal flats and (parts of) salt marshes that lie between the ocean and the shore. A beach is a natural environment, and the material that makes up a beach comes from erosion over many years. Waves and wind wear down the rocky cliffs of a coastline, turning huge boulders into tiny particles of sand. These particles are swept by waves into the sea and carried by the current.
Sand, along with rock and other sediment, is the most common beach material. However, some beaches are made of gravel instead of sand. Gravel beaches are found in areas where the sea has eroded a softer rock, such as limestone or coral. Other beaches are formed of silt, mud, and other fine particles that have been deposited by rivers. Rivers that carry large amounts of sediment may deposit a delta, which spreads out across the ocean floor.
Erosion is generally thought to decrease the size of beaches, but this is not always the case. In fact, some beaches actually grow in size. This occurs when waves erode the underwater debris that collects on the bottom of the ocean, including seaweed, shells, and marine animals. The eroded material is washed up onto the beach and eventually deposits as sediment.
Other kinds of beach erosion occur as a result of human activities. Dams, urban development, and rerouting rivers reduce the amount of erodible material available near bodies of water. Without this erodible material, the waves have less to carry and they may recede from the coast, causing beaches to shrink.
People combat beach erosion by building seawalls, structures made of concrete or other material that are built to prevent sand and other beach materials from drifting away. Another solution is beach nourishment, which involves pumping sand back onto the beach to replace lost material. Beach nourishment is a controversial practice, since it can be difficult to predict the amount of sand needed to replenish the beach and protect the environment.