Beaches are areas of loose sediment (sand, gravel, cobbles) controlled by ocean processes. Waves and currents move the accumulated sediment constantly creating, eroding and changing the coastlines.

Kitty Hawk, North Carolina

Most beaches have several characteristic features. First are offshore bars, which help protect beaches from erosion. Next is the foreshore, which rises from the water toward the crest of the next feature: a berm. On low-lying shores, dunes form behind beaches. Dunes look like rolling hills of sand and are blown into place by the wind. New, smaller dunes are often changing shape as the wind continues to affect them. More established (older) dunes hold sand in place with vegetation, such as sea oats.

When people picture beaches, they often think of the ones near where they grew up. Most of the shores along the US's East Coast and Florida's Gulf Coast are white. The white sand comes from granite, which has been broken down, or weathered, into quartz and feldspar.

But did you know some beaches have black sand? Some islands in the Pacific Ocean do. This comes from the weathering of volcanic rock.

Dunes at Jockey's Ridge State Park in Kill Devil Hills, North Carolina

Other beaches are made of cobbles, or small stones. Waves and currents cause these stones to churn and pound over each other. Little life can exist in such a severe environment.

A primary influence on the formation and evolution of a beach is something called a longshore current. This current flows parallel to the beach, causing waves to strike the beach at an angle. The longshore current can carry large amounts of sand along the coast and can form spits (narrow peninsulas of sand), barrier islands and tombolos (narrow sand deposits connecting a near-shore island with the beach).