User:Donald Albury/Coastal barriers

Coastal barriers are landforms along coasts consisting of unconsolidated sediments, primarily sand and gravel. They are generally separated from the mainland by open water, tidal creeks, or marshes. They often shield the mainland coast from the full brunt of storms.

Needed for formation:
 * Supply of sediment
 * Low slope
 * Moderate wave energy
 * Low to moderate tide range

Types of coastal barriers:
 * Barrier islands
 * Barrier spits or peninsulas
 * Bay barriers

Barriers are land forms consisting of unconsolidated sediments (sand or gravel) abutting or just off-shore of land masses. Coastal barriers are shaped by waves, wind, tide and currents,

Structure
Coastal barriers are usually linear and parallel to the main shoreline, in most cases forming chains. They are shaped by waves, wind, tides, and longshore drift. Barriers typically consist of the following elements:
 * Facing the open-water is the beach, the area that is regularly covered and uncovered by waves and tides. Normal wave action usually adds sediment to the beach, while storms often move sediment off of the beach into deeper water, or across the barrier to beyond the landward edge of the barrier.
 * On barriers composed primarily of sand, a frontal dune ridge runs most of the length of the barrier just behind the beach. The dune ridge often protects the area behind the barrier from high water levels and waves during storms, but severe storm surges may overwash the dune ridge, carrying sand to behind the barrier.
 * There may be one or more secondary dune ridges behind the frontal dune ridge. Swales lie between such dune ridges, often holding fresh or brackish marshes and ponds.
 * The backside or landward margin of a barrier may border on a body of water, such as a lagoon, bay, tidal creek, or lake. In other cases the backside borders a tidal mudflat or tidal marsh.

Distribution
Coastal barriers are found on the coasts of every continent, except Antarctica, and on some larger islands. They are also found on inland seas and large lakes. The largest system of coastal barriers is on the Atlantic coast of North America, stretching 3,100 km from Labrador to southern Florida.