A beach is a landform along a body of water that may be salt or freshwater. A beach is usually characterized by a sandy or pebbly surface, often backed by sand dunes, and often inhabited by a variety of plants, animals, and birds. Beaches are shaped by the constant movement of waves, currents, and winds. The movement of these forces erodes the rocks and sediments located near a coastline, depositing them farther inland. During the process of erosion, a beach forms by attrition (rocks hitting together), abrasion (rocks rubbing against each other), hydraulic action (water driven into cracks), and corrosion (chemical breakdown of large, medium, and small rocks or sediments).
The size and shape of a beach depends on the characteristics of the surrounding landforms. Beaches that have a sandy surface tend to slope at a slower rate than rocky beaches. This difference in slope is caused by the size of the particles that make up a beach. Rocks and coral reefs offshore can be significant sources of sand particles. Other sources include fish that nibble on algae attached to rocks and coral outcrops, digesting the organic material and discarding the particles.
In addition, the beach morphology is affected by whether the surrounding landscape is rocky, vegetated, or covered in vegetation. Vegetated beaches have a tendency to resist erosion because flora with extensive network root systems, such as creepers and grasses, stabilize the foredunes. In contrast, bare ground and exposed sand are susceptible to erosion because they lack the structure of a flora-dominated dune system.
A beach is also a place of natural wonders, with many different types of creatures living in and around it. Crabs, insects, and birds all feed on the sand, and sea turtles lay their eggs on ocean beaches. The sand itself has a number of properties that are important to beach users, including its softness and consistency. The sand on some beaches has been colored by minerals, with black sand found in Hawaii because of the olivine mineral in the basalt that formed it.
Natural coastal erosion is a constant process, and a beach that experiences consistent deterioration over a long period of time is said to be in retreat. Beach erosion can be accelerated by a number of factors, including human activity. Urban development, dams, and the rerouting of rivers reduce the amount of erodible land located near bodies of water, and this decreases the supply of particles that can be deposited along coastlines.
A beach can be restored through a process called beach nourishment, in which new sand is added to the area directly above where waves break. It is important to add sand in this way so that it can compact and settle before aggressive wave or wind action erodes it. It is also important to add sand that contains foreign material not normally found in that area, in order to introduce flora and fauna to the beach. Beach nourishment activities must be carried out carefully to prevent degradation of the berm and dunes, especially when herbicides are used or pedestrian traffic is allowed on the dune system.