A beach is a landform along the shore of a sea or ocean. It is made up of a wide range of materials – sand, gravel, cobbles, rock, and even shells. Beach material accumulates on the beach during periods of accretion and is washed away by waves during periods of erosion. Unlike the coast, which refers to a general zone of land and water, beaches are specific deposits of particular materials.
The size of a beach’s sediment is related to its wave energy, which influences the type and intensity of wave activity. Beaches composed of coarse sand are typically dominated by the mechanical actions of wave swash. These forces cause the sand to rub against itself and to become smaller, smoother, and finer, or denser. Sand with a high silica content (silica is a mineral) tends to be very white, while beaches of lower silica content appear darker.
Sand grain size also affects a beach’s slope. Beaches with fine sand have flatter slopes between the high and low tide lines because they absorb less of the water that washes up from the ocean. Coarse sand, on the other hand, is more resistant to water absorption, so more of the wave swash moves back down toward the sea than up toward the beach.
In addition to sand grains, the composition of a beach is affected by its local geology and by human activities. Beaches that are fed by offshore sand bars usually have higher energy and steeper slopes. This is because the wave action that creates these bars also generates the incident waves that erode the beach.
Beach nourishment is an important part of a beach’s maintenance. Care is taken to deposit new sand so that it compacts before the aggressive wave and wind action that erodes the established sand can erode it.
During this process, the new sand is usually placed between the existing sand and the surf line. Ideally, the placement is such that the new sand is equidistant from the beach crest and is separated by a groyne or embayment that encourages scouring behind it and reduces the rate of erosion on the adjacent beach.
The rocks, pebbles, and sand that make up a beach are a mixture of different minerals. The color of a beach is determined by the types and amounts of these minerals. For example, coral or black basalt provide the material for the dark sand of some beaches. Quartz and feldspar, on the other hand, provide the tan or light brown sand of most beaches. These colors are the result of weathering processes. Over time, these mineral particles wear down and erode, leaving behind the finer and lighter sand that gives beaches their characteristic color. These sands then get washed and re-deposited by the pounding of waves and the ebb and flow of tides. This continuous cycle ensures that a beach is always changing. Beaches that are not regularly maintained will lose their shape and structure.