A beach is a narrow strip of land that stretches along the edge of a body of water. It’s covered with materials like sand, pebbles, and rocks and may include fragments of seaweed, marine organisms, or even fossils. Beaches are constantly changing, with tides and wind bringing new materials to the area and taking away others. These materials come from many places, including eroded bits of rock from nearby cliffs and coral reefs, and sand blown in by winds from rivers or ocean currents.
Most beaches are composed of sand, which is made up of very small pieces of mineral or rock material. Beach sand is usually finer than sediments found in rivers and streams, and it may contain heavy minerals like magnetite, pyrite, galena, or garnets. These are heavier than other particles, so they tend to remain in beach sand. Beaches are also characterized by their shape and structure, which are the result of erosion processes that take place at or near the shoreline.
Waves erode beaches by attrition, abrasion, and hydraulic action. Attrition is when rocks rub together, abrasion is when they’re hit by waves or other moving objects, and hydraulic action is a process where water flows through cracks in rock. The type of erosion that takes place at a particular beach depends on the characteristics of the underlying rock and the environment. Rocks with a more crystalline structure, for example, erode more slowly than sedimentary rocks because they are more resistant to mechanical force.
The size of particles in the beach sand is an important factor in how steep its slope is. Beaches with very fine particles have flatter beaches, while those with coarser material have more steep slopes. The size of the particles is determined by what’s happening upstream: rivers and other bodies of water carry coarser-grained sand downstream, while winds blow finer sand upward.
A beach’s slope is also determined by the amount of backwash, or the return flow of sand and other material that has been carried by waves into deeper waters. If there’s a lot of backwash, the beach becomes wider, and if there’s little or none, the beach recedes. Beach recession can also be caused by human activities, such as building construction or rerouting rivers, which reduce the availability of erodible material near bodies of water.
Sand and other materials found in beaches are a rich source of nutrients for plants and animals. Many birds, insects, and other creatures gather food from beach sand, while crabs dig through it to find other edible items. Beaches are also home to a variety of marine animals, including fish and sea turtles.