The two main types of barrier islands form either on river deltas, such as those on the Mississippi Delta, or on coastal plains, such as the North Carolina Outer Banks. The most common type are coastal plain barrier islands and to form they require a combination of rising sea level, high wave energy, and sand that can be pushed into piles by storms, according to Pilkey.
"The sea level is rising now, which provides a crooked shoreline," he said. "Nature abhors a crooked shoreline, so nature is trying to straighten the shoreline out."
In places with plenty of wave energy and sand to move about, this process of straightening out involves eroding the bits of land that stick out from the mainland and forming straight-edged barrier islands. The islands, separated from the mainland by an estuary, absorb the brunt of coastal storms.
Coastal scientists say storms are essential, inevitable events that pile sand on the islands, open inlets, close inlets, and help the islands migrate inland or seaward, depending on whether sea level is rising or falling.
"I guess it is fair to say that barrier islands are the most dynamic, large-scale features on the surface of the Earth," said Pilkey.
In this era of rising sea level, barrier islands such as the Outer Banks are trying to migrate inland. Storms such as Hurricane Isabel are essential to this process, said Riggs. They wash tons of sand across the island from sea to sound. Vegetation colonizes and stabilizes the newly deposited sand, providing a base for the island to shift onto.
The problem, say coastal geologists, is that humans and their desire for permanent settlements are not in harmony with the ever-evolving barrier-island ecosystem.
"We think we can put roads out there like we normally build roads in upland regions, and the minute we put something out there we want to protect it. All of a sudden we are at war with the ocean," said Riggs.
Tracy Rice, a former coastal scientist with the U.S. Fish and Wildlife Service in North Carolina who left the service in July to work for a private consulting firm in Reinholds, Pennsylvania, said the lesson of Hurricane Isabel is that the ocean will win the war.
"The formation of Isabel Inlet was a purely natural process, and it occurred regardless of the presence of a human-maintained dune ridge and highway," said Rice.
Humans made their first significant mark on the Outer Banks in the 1930s when the Works Progress Administration and the Civilian Conservation Corps built a dune ridge along the Outer Banks to help stabilize the islands.
Since then, the dune has been continuously maintained. Whenever storms push the dune sand over the island, trying to keep the Outer Banks above the rising sea level and making what coastal scientists call a platform for the islands to migrate onto, crews are dispatched to push the sand back and rebuild the dune.
The dune was first rebuilt after every storm by the National Park Service until the 1970s. When the park service called it quits, the North Carolina Department of Transportation moved in to protect U.S. Highway 12, which was constructed after World War II, according to Rice.
Varnedoe of the transportation department recognizes the vulnerability of the road to damage from storms, but says he has a job to do. "Our mission is to try to maintain the highway access that has been established there and keep the road open. When we have storms we get it opened up and get the sand off the road."
The latest chapter in the ongoing war is the filling in of Isabel Inlet and rebuilding the highway there.
According to Riggs, because the estuarine side of the islands has been deprived of over-washed sand for years as crews work furiously to maintain the road and dune, the islands are severely weakened, making them prone to form more inlets as the inevitable storms hit.
"One has to ask 'what is the function of a barrier island?' Is it a transportation corridor for the DOT and economic development of this dynamic, changing system, or does it have another function in the short-term health and maintenance of the barrier island system?" said Riggs.
According to Pilkey, U.S. Highway 12 has been allowed to all but stop nature's course in the Outer Banks so that thousands of people can access their million-dollar homes inside the Cape Hatteras National Seashore. This is a clear sign, he said, "that we have lost sight of the forest for the trees."
Varnedoe said the Department of Transportation knows it can't ultimately beat nature. So while filling Isabel Inlet seemed like a necessary, immediate fix, a task force regularly meets to discuss what will be best over the long term. One possibility is the construction of a causeway on the estuary side of the islands. "I think that has huge promise," said Pilkey.
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