The Formation of Sandy Beaches and Dunes
Beaches
- Types of Beaches
- Reflective Beach
- Low wave energy
- Large sediment size
- Low tidal range
- Steep slope
- Dissipative beach
- High wave energy
- Small sediment size
- High tidal range
- Lower slope
- 3 Essential Prerequisites:
- Abundant supply of loose sand where there is lack of vegetation
- Wind energy source that is capable of moving sand grains
- A topography where the sand particles lose their momentum and eventually settle out
· Shrubs, rocks, or fence posts
- The structure and composition of sand grains however, depends on the geology of the mountains, which have been eroded away by wind and water.
· Fine Muds (<.05 millimeters in diameter)
· Coarse Sands (.5 to 1.0 millimeters in diameter)
- The wind, therefore, moves individual grains of sand along an inclined surface, until they reach the new territory and pile up on the base.
- Over the years, if the wind direction is uniform, the dunes will gradually shift.
- Eventually, vegetation will stabilize a dune/beach, and will prevent the movement of the grain.
- Sand grains seldom travel more than a few feet from above the ground.
- Beaches are the result of wave action by which waves or currents move sand or other loose sediments. Beach materials come from erosion of rocks offshore.
- The shape of a beach depends on whether or not the waves are constructive or destructive, and whether the material is sand or shingle. Constructive waves move material up the beach while destructive waves move the material down the beach. On sandy beaches, the backwash of the waves removes material forming a gently sloping beach.
Dunes
Coastal Dunes
gravity
· Creates a relatively steep slope, generally with a maximum of about 30 degrees, wihch is called angle of repose
- Are an important part of many coastal areas, and are large piles of sand that have accumulated by processes
- Vegetation is one of the best and most widespread facilitators of dune development, and any type of plant can serve as the focus for anchoring wind-driven sediment
- A dune ride- a linear arrangement of dunes, one dune wide - is the typical configuration of dunes just landward of the beach
- Although dunes are beyond the regular influence of waves, they are vulnerable to even the most modest storm surges
- Rising sea level exposes dunes to further erosion
- The winds that form the dune also can mote it - sometimes great distances
gravity
· Creates a relatively steep slope, generally with a maximum of about 30 degrees, wihch is called angle of repose