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How? On the West Coast, houses perched atop cliffs create new runoff patterns for rainfall and irrigation; combined with seepage from septic systems, the drainage weakens the land itself. On the East and Gulf coasts, the major problem is destruction of beaches and sand dunes that normally check the ocean's force. Of particular concern are the 295 barrier islands -- strips of sand dune, marsh and sometimes forest -- that protect most of the U.S. coast from Maine to Texas. Not surprisingly, they are considered prime development spots: Atlantic City, N.J., Virginia Beach, Va., and Hilton Head, S.C., among others, were all built on barrier islands.
It is mainly the dunes, explains the National Park Service's Soller, that keep coastal areas, including barrier islands, intact. "The natural process is for dunes to roll over on themselves," he says. When the ocean breaks through, "what was once the secondary dune becomes the primary dune. The beach retreats as the ocean level rises. When you have houses on the beach, there's no place for the dunes to move."
In Ocean City, Md., developers hoping to reinvent Miami Beach, where a single mile of oceanfront is now worth an estimated $500 million, began building high-rises on the dune line in the 1970s. So that people on the lower floors could have an unimpeded view of the ocean, the dunes were simply bulldozed away. Since then, the ocean has come to see the tourists: beneath many buildings, pilings are exposed to the waves. At Garden City, S.C., just south of Myrtle Beach, where big condos dot the waterfront, crumbled seawalls and wrecked swimming pools testify to the power of storms unchecked by protective dunes.
Sand dunes can also be destroyed in subtler ways. For a dune to form in the first place, sand must somehow be trapped, much as a snow fence traps drifting snow. That something is dune grass. After the dunes form, the roots anchor the sand in place. "Dune grass is pretty hardy stuff," explains Stephen Leatherman, a University of Maryland coastal-erosion expert. "It can take salt spray and high winds. But it just never evolved to take heavy pedestrian traffic or dune buggies." Since the plants depend on chlorophyll in their green leafy parts to convert sunlight into food, he says, and since there is only so much food reserve in the roots, "a couple of weekends with a few hundred people walking back and forth to the beach, or a single pass from an off-road vehicle, kills off the dune grass."
On the Gulf Coast, the erosion of dry land is only part of the problem. Vast areas of wetlands normally protected by barrier islands off Louisiana are disappearing as well. In both Louisiana and Texas, where channels deep enough for barges have been cut through marshes, the dredging and waves caused by ship and boat traffic have accelerated the normal process of shoreline loss. What is more, salt water from the Gulf of Mexico has flowed into the marshes, endangering local fisheries.