A beach is a landform that results from the accumulation of sediment. Typically, this is made up of sand or gravel but can also include crushed seashells and other organic material. It forms along the coast of an ocean, sea or lake. Beaches are very dynamic, and their shape, width and slope change with every tidal cycle.
A number of processes contribute to the formation of beaches. These include weathering, the breaking down of rocks into smaller pieces; erosion, which is the wearing away of rock by flowing water; and deposition, when waves carry materials like sand and shells from deeper water onto the shore. These processes can occur over a very long period of time and result in beaches that are wider or narrower, more gentle or steep, have more or less shell content, or even contain no shells at all.
Many people associate beaches with the sea, but a beach can also be found along the shores of lakes, rivers and some large ponds. Beaches are very dynamic, and the type of beach you see today is very different from the one you saw last week.
Sand beaches are characterized by the fact that they are made up of fine-grained particles (quartz, silt and clay) that are suspended in water rather than in solid rock. They may have a high or low sand content, and the particles can be smooth, round or coarse. Beaches are dominated by wave action, and the motion of the waves causes a variety of features on the surface, including oscillation ripples, swash or rill furrows, and the well-known beach cusps, which are concave seaward.
Another feature of beaches is sandbars, which are areas of sand that extend out into the water from the beach. These form when waves erode parts of the coastline over an extended period of time. Sandbars can be exposed during the summer, but are buried at other times. They can be quite large and may extend for a considerable distance from the beach.
In addition, a beach can have rocky sections that are separated from the rest of the shore by sand bars and channels between them. This is called a barrier beach.
The overall pattern of a beach is determined by the balance between erosion and deposition, with erosion prevailing most of the time. This is because waves break more often in sheltered areas than they do in open water, and this process wears away the softer rock along the shoreline.
The net movement of sand along the beach is called longshore drift, and it normally moves from north to south on both coasts of the United States. This is because swells come from the North Pacific or the North Atlantic, and the motion of waves in these bodies of water pushes the sand along the beach. This movement is more pronounced in the surf zone than in the rest of the beach area. However, in some places the movement of sand is counteracted by offshore currents that pull it back into deeper waters.