|MadSci Network: Earth Sciences|
David, it turns out that there are indeed many barrier islands (and also spits, which are essentially the same thing) on all three coasts (East, West, Gulf), but that the conditions for barrier island formation are just better on the East coast in general. Although no one knows exactly why some places form barrier islands and some don't, several key requirements are: -Low gradient (gentle slope)off of the shelf off shore -Abundant sediment supply (large drainage areas with abundant rain) -Low to moderate tidal range (to reduce the erosion of the barrier islands) -Wide shelf off shore to provide ample sediment and a long distance to deep water -Wide, low-relief coastal plain -Absence of submarine canyons (which would drain sediments to deep water) -Lack of seismic activity that can destroy islands -Long wavelength swells that approach the beach at an angle so sediment can get moved along the coast to replenish the islands -Coastal drowning(caused by rising ocean or sinking coast) that introduces more sediment below the water line Where these conditions exist, barrier islands are more likely to form - but even then, there is no gaurantee. It turns out that these conditions are far more common on the East and Gulf coasts than the West coast so barrier islands tend to be more common in the East and the Gulf. references: http://www.csc.noaa.gov/beachnourishment/html/geo/barrier.htm http://madmonster.williams.edu/GEOS.104/L.24.coast.types.html http://people.uncw.edu/hosier/BIE/bieclschd/present/distrib.htm
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