Primary and Secondary Coasts

Primary and Secondary Coasts

Surfers, swimmers and sunbathers use beaches for recreation. People fish off beaches for food. Since many people take their vacations at the beach, lots of beaches in tropical locations are important to their country’s economy. Entire cities, regions and countries depend on the money tourists spend while visiting the beach. Beaches are naturally very dynamic places, but people try to control them and build permanent structures, such as houses, restaurants, shops and hotels, on or near the shore. The natural erosion and deposition of beaches becomes a problem. Beaches con disappear over time, or even over night during severe storms. Beaches are areas of loose sediment (sand, gravel, cobbles) controlled by ocean processes. 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. Waves and currents move the accumulated sediment constantly creating, eroding and changing the coastlines.

There are many different types of coasts; beaches are just one type. Coasts are divided into two categories: primary coasts, which were created by non-marine processes, and secondary coasts, which were formed by marine action. Primary coasts happen because of changes in the land, such as river deltas or lava flows. Primary coasts are created by erosion, deposition, or tectonic activity. Many of these coastlines were formed as the sea level rose during the last 18,000 years, submerging river and glacial valleys to form bays and fjords. River deltas are an example of a primary coast. They form where a river deposits soil and other material as it enters the sea.

Primary coasts are divided into two categories: submergent and emergent coasts. Submergent coastlines result from a general sea-level rise and crustal subsidence. Most of the eastern United States has submergent coastlines. One example is the Chesapeake Bay. Emergent coastlines result from the land being lifted, either by tectonic activity or rebound from the weight of heavy glaciers, which exposes the former sea bottom bit by bit forming continuously new shoreline.