A beach is a place to soak up the sun, relax to the rhythm of surf and tune out for a while. But if you take the time to pay attention, there is much more going on at a beach than meets the eye: Piping plovers moving in and out with the waves, crabs scurrying around, sea turtle paths tracking to and from the ocean. And then there is the sand itself, which tells its own unique story of how a beach has been formed and has evolved over the years.
Beaches come in a variety of shapes and sizes and have a range of characteristics that are often very different from one another. Beach widths can change from wide to narrow, slopes can steepen or flatten, and the amount of shell content can vary widely. Beach composition can be affected by many factors including wave size, the speed of sediment movement and geology of the region.
Generally, a beach is made up of sand with some smaller particles such as gravel, cobbles, rocks and shells mixed in. These particles may have been pulverized from larger objects by the action of waves and wind over thousands or even hundreds of thousands of years. The sand itself may be composed of quartz, feldspars and other minerals or it might be cemented together by calcium carbonate precipitated from the water.
In some cases, a beach may have no bars in the nearshore zone and therefore the tendency is for sediment to move seaward into deeper water or landward into marshes and sounds behind barrier islands. In other instances a beach will have several bars. The most frequent type of bar is a longshore bar, where the sand is swept in from one side to the other by prevailing waves. Bars can also form where reentrant channels (such as bays, rias and inlets) meet the main beach. When a bar forms across the front of such an reentrant, the resulting feature is called a tombolo.
If a beach has several bars, it is said to have a multi-bar system. In this case the sand moves in and out of the sea at various rates, which allows for the formation of a broad beach with a gentle slope. If there is no multi-bar system, the beach is usually a narrow, exposed area that is only accessible at low tide.
Beaches are constantly changing from hour to hour and season to season. Wave action can destroy a beach and then build it back up all within the same day, depending on swell size, current speed and wind conditions. The color of a beach is also dependent on the local geology and can be black, white, tan or any shade in between. Beaches that are dominated by volcanic rock can have black or tan sand while beaches with coral or white sand tend to be white.