Sand's incredible journey.

Sand's incredible journey

As beaches along the East Coast erode, one might wonder if natural processes will replenish the disappearing sand. The answer, according to a Virginia geologist, is no--at least not until the next ice age lowers sea levels.

Dennis A. Darby of Old Dominion University in Norfolk, Va., bases his conclusion on a study of the origins of East Coast sand. By tracing certain iron-titanium sand grains, he found that most sand along the coast and continental shelf as far south as Hatteras, N.C., comes from the north--either from the drainage of the Hudson River or from glacial deposits along Long Island and southern New England. Previous studies had tracked northern sand only as far south as the Delaware coast.

For sand from the Hudson to reach the Carolina coast, it had to move in steps, possibly taking millions of years, says Darby. The reason is that as sand moves along a coast, water currents push it into large bays or estuaries such as the Chesapeake. An embayment will continue to fill with sand until sea levels drop and the accumulated grit is flushed down onto the continental shelf, says Darby. For this reason, sand can travel only as far as the next bay in a single glacial cycle. Darby concludes that most beaches will not receive a major restocking of sand until the next ice age.