Most people are familiar with the concept of a beach, the fascinating and beautiful intersection of very different terrestrial and marine environments. But beaches are much more than just places for humans to play, as they are lively ecosystems that guard coastlines from erosion and floods while providing habitat for an amazing diversity of marine organisms.
A beach is a strip of sediment bordering a sea or lake shore that is acted upon by waves and currents. The characteristics of beaches vary greatly from place to place. They are characterized by the kinds of materials they contain and the way in which those materials are delivered to the coast.
The sediments that make up beaches can be made of a variety of materials, including sand, gravel, rock fragments and shells. They can also be a combination of these materials. Some beaches are mostly made of rocks and pebbles that have been worn smooth over time by the pounding action of waves. Other beaches are almost entirely sand, with the color varying from white to black or gray depending on the minerals in the sand.
These characteristics of a beach are controlled by both the size and frequency of wave activity, as well as the composition and slope of the sediments. A beach that has a very steep slope will be made up of coarser sediments, such as silt or mud. Beaches that have a more gentle slope are often covered with finer sediments, such as clay and sand.
In addition to the physical characteristics of a beach, its surface can be covered with a variety of ripples and other relief features. Ripples typically have long, curvy crests and are formed by wave action. They are a common feature of sandy beaches.
Other relief forms found on a beach include oscillation ripples and swash ripples, which are smaller and more regular than the crests of wave ripples. Beaches may also have a pattern of gully and trough lines or beach cusps, which are crescent-shaped areas that are concave seaward.
The shape of a beach changes rapidly from hour to hour and season to season. Wave action can destroy a beach and then build it anew within the course of a day. Beaches can also be permanently altered by human activities.
Beaches are also dynamic ecosystems, and many of the organisms that live there are buried in the sand and only exposed at low tide. They depend on the availability of food sources in the intertidal zone and on the water temperature to survive.
Because of their dynamic nature, beaches are important ecosystems for the preservation of biodiversity. In fact, they provide a habitat for many species that are endangered or threatened. In addition, they protect the coastline from flooding and erosion, and they are also a source of food for fish, birds and other wildlife. They also serve as buffers against the intrusion of pollutants from inland sources. This is because pollutants such as raw sewage, toxic chemicals and petroleum waste may be carried by rivers or storm drainage to beaches.