Beaches are narrow stretches of land deposited on the edge of an ocean, lake or river. The material they are made from varies widely, but usually includes sand, pebbles and small rocks, as well as fragments of seashells. The beach can be very wide, extending for many kilometers, or it can be narrow, with only a few hundred yards of coastline.
The material that makes up the beach is created by a variety of processes including erosion, saltation and sediment delivery. Sand is the most common material, though it may also include pebbles, shingle and other coarser materials. The type of sand used depends on the local weathering conditions and can vary from place to place. Generally, the sand is light colored and translucent. It is primarily quartz and feldspar. Some beaches have a light brown coloration, which is often caused by iron-stained shells that break down and become mixed with the quartz sand grains.
Continual swash and backwash over time moves the sand in a flow direction parallel to the shore. This is called longshore drift. It is a natural process that occurs without the aid of human intervention.
Most sand beaches have some degree of relief, such as oscillation ripples, swash or rill furrows and beach cusps (concave seaward). In areas where the seawater is shallow and the waves are strong, the surface contours of sand beaches are higher during the storm season (winter in temperate regions) than in the rest of the year. This is due to the increase in wave energy and the shorter periods between breaking wave crests.
Beach erosion is a complex process that involves a number of interacting factors such as tides, waves, tidal currents, wind, storms, and groundwater movement. Freak waves such as tsunami and tidal waves can significantly alter the shape, profile and location of a beach in a matter of hours.
Sea level changes have been associated with beach erosion in recent times, and these changes are likely to continue into the future. Similarly, weather systems such as the El Nino-Southern Oscillation (ENSO) can affect coastal erosion by causing extreme weather events.
There are three major types of beaches: free beaches, barrier beaches and reef beaches. All these have different characteristics and are characterized by their coastal configuration, the nature of the sediment delivered and the rate at which it is moved by the ocean or lake.
Barrier beaches consist of a strip of sand bounded on all sides by a rocky headland or cliff. They are formed by the eroding action of a single rock or by the repeated erosion and slumping of adjacent rocks. The sand and other sediments accumulated along the headland create the barrier, and the eroded and slumped rocks form the reef.
Reef beaches are the result of the eroding action of a coral reef offshore. They are often narrow and sandy or sand-covered, with a thicker layer of sand on the inner edge. These beaches are mainly found in the Pacific region.