A beach is a narrow, gently sloping strip of land along the edge of a body of water – such as an ocean, lake or river. It is covered by a mix of materials including sand, pebbles, rocks and seashell fragments. Beaches are constantly changing, a process called erosion and deposition.
The composition of a beach depends on the nature and quantity of sediments upstream of it, the speed of flow and the turbidity of the water and wind. Sediments are eroded more easily in fast-flowing waters than in still ones, and are deposited on a beach according to their particle size, state of compaction and the force that moves them. Plants that grow on a beach act as a natural barrier to erosion, slowing the fluid flow and reducing its erosive power. The presence of vegetation also helps to stabilise a beach by holding sand together, especially when it is wet.
Waves are the main force that shapes beaches. When a wave breaks near the shore, it deposits sediments (including sand, rock and shells) on the beach. These sediments may have been displaced by previous waves or carried from far away by currents.
When waves hit a beach, they may be broken into a series of rolling waves known as a swell. The swell then breaks into smaller waves called surf. The surf zone is the most dynamic part of a beach because it is where most of the waves break. The surf zone can be a shallow lagoon, or it may be an area of deep and powerful waves that are sometimes difficult to wade through.
Beaches are often formed where waves have a lot of energy but the coastline is fairly soft, allowing them to deposit sediment without being swept away by strong currents. A sheltered environment is also needed for beaches to form, such as a bay or cove.
Different beaches have a range of colours, influenced by the material from which they are made. Some are dark, like black or grey sands, while others are white. Many beaches have a mix of sand from geological sources such as eroded bits of a nearby rocky reef and biologically derived sand from the breakdown of coral skeletons or the shells of marine plants and animals.
Many people love to visit beaches, and they play important economic and social roles in some communities. Some beaches have facilities for recreation and tourism, such as lifeguard posts, changing rooms, showers and shacks. Other beaches are undeveloped and pristine, and provide an ideal habitat for wildlife such as seabirds and seals. A beach can also be a great place to explore the underwater world, with its colourful array of seaweed and tiny hermit crabs. There are even a few beaches where you can see the glow of bioluminescent algae, such as those found on the Sargasso Sea. A beach can also have a wide variety of human activities, from walking and surfing to fishing and boating.