A beach is the zone of sand, rock or gravel deposited by the tide or waves. It is also a popular recreational area for swimming and sunbathing.
A beach can be many kilometers long or very short. It is usually made of different materials – sand, gravel, pebbles, cobbles or shells. It is constantly changing as weather, tides and ocean currents shift it around.
Some of the most interesting and recognizable relief forms on beaches are oscillation ripples, swash or rill furrows and the well-known beach cusps (concave seaward) at the beach margin. These are caused by strong waves with a strong backwash which, as they recede, carry sand back to the beach.
The type of wave that reaches the coastline also affects beach formation. Constructive waves, which allow the water to recede and the beach particles to stop moving between waves, result in compacted sediment which prevents future erosion. Destructive waves, which do not allow the water to recede, are more likely to create sand bars or other types of beaches that can be easily eroded by the next wave.
Beaches are a very complex and dynamic landform that can be hundreds of meters or thousands of kilometers long. The most dramatic changes occur during storm surges, tidal waves or tsunamis. These events can rapidly change the shape, profile and location of a beach within hours or days.
These changes often entail the reworking of a beach’s underlying bedrock. This can lead to the development of pockets, or lobes, where bedrock is exposed between rocky coastal outcrops. This can be seen along the eastern United States and Canadian coasts.
This reworking of the underlying bedrock, which is called accretion, can take many years to complete. However, some beaches are so unstable that they erode in as little as several days.
Another major factor in the reworking of a beach is human activity. Urban development, dam projects and rerouting of rivers may reduce the amount of erodible land that is available for waves to deposit sediment on.
The resulting reduction in sand is known as beach recession. This recession can be triggered by human activities such as beach nourishment or by the natural processes that cause beaches to reorganize themselves.
In some areas, the sand on a beach is primarily quartz or feldspar, while in others it is mainly calcium carbonate. Some of these sands are iron-stained, leaving a light brown color. These colors are attributed to the presence of shells that have broken down in the surf zone and mixed with the quartz sand grains.
A beach is an important habitat for birds and other marine mammals. It is a place where they can find food and shelter, as well as nutrients that they need to thrive. This is why it’s so important to protect beaches from pollution. Trash and debris left on beaches can be toxic for wildlife, especially marine mammals. In addition, it can disrupt the nutrient supply of tide pools and prevent algae or sea plants from growing.