Leslye Davis/The New York Times
Many of the sand dunes that are critical in protecting Fire Island, a barrier island off the coast of Long Island, were destroyed or shifted by Hurricane Sandy.
FIRE ISLAND, N.Y. — Starting at the water's edge, B. J. Reynolds had rolled his surveying pole about 200 feet inland across the beach, the GPS receiver on top producing continuous elevation data that was recorded in a computer in his backpack.
Now Mr. Reynolds, a technician with the United States Geological Survey, had reached the line of dunes that runs the length of the 31-mile barrier island. To complete the elevation profile of this slice of the beach-dune system, he needed to run the equipment to the top.
"When we came out here before the storm, we could walk right up the dune," Mr. Reynolds said. But that storm — Hurricane Sandy — had obliterated much of the dune, leaving a steep scarp face about 12 feet high. So a colleague from the National Park Service, Jordan Raphael, scrambled to the top, threw down a rope and hauled the pole and backpack up, taking the final measurements.
The work — in all, Mr. Reynolds and Mr. Raphael took about 10 profiles at intervals along the island on two brisk and sparkling days last week — is part of an effort by scientists to take advantage of a storm like no other in recent memory to learn more about how Fire Island, and all barrier islands, respond to and recover from major natural events.
"We have the experiment of a lifetime sitting in our laps," said Cheryl J. Hapke, a geological survey scientist who has studied Fire Island since 2006.
Already, Dr. Hapke and others have learned a lot about how the narrow island behaved during the storm — pretty much as expected, they say. And in the seven weeks since the storm they are already seeing signs of natural recovery, as waves remold the beaches and windblown sand builds up at the foot of the dune scarps.
What the scientists learn will help government agencies, including the Army Corps of Engineers, in their lengthy effort to determine how best to maintain parts of Fire Island, to protect the private vacation communities on its western half, which were hit hard by Hurricane Sandy, and to ensure that the island continues to do what it did during the storm — safeguard the Long Island mainland a few miles north across the Great South Bay.
"Barrier islands are supposed to take the brunt of storms," said Chris Soller, superintendent of the Fire Island National Seashore. "And Fire Island did that."
Dr. Hapke, a geologist, will be analyzing the latest elevation profiles, comparing them with ones taken on Oct. 28, just before the storm hit, and at various times since, and other data, including aerial surveys of the island made using laser range-finding equipment called lidar. (The geological survey is currently analyzing lidar data for New Jersey and other affected coastal areas as well.)
For Dr. Hapke, the data, and her trained eyes, already are telling her that the storm wrought major changes.
"Sandy completely flattened this beach," she said, looking around as the survey team took a break at this pristine spot in the national seashore east of Davis Park, one of the worst hit communities. The beach is now about eight feet lower, an elevation loss that is typical.
The scarped dunes extend as far as the eye can see up and down the island. In many places 50 feet or more of dune are gone, exposing heavier and redder garnet sand that separated into layers over time since being deposited as glacial ice retreated thousands of years ago.
At many low spots along the dunes, the surge from the storm completely overtopped them. In three locations on the eastern half, the surging waters carved new channels, breaches that allow water to flow between the ocean and bay. At other locations the island remained intact but the waters pushed enormous amounts of sand inland, raising elevations on the bay side.
Overall, Mr. Soller said, the storm shifted so much sand inland that Fire Island probably migrated north, toward the mainland, by about 65 to 85 feet.
"This was an amazingly powerful storm that reshaped the island dramatically and moved it," he said.
But such migration was not unexpected. "Storms are the driver" that shape and move barrier islands, Dr. Hapke said.
This article has been revised to reflect the following correction:
Correction: December 20, 2012
An article on Tuesday about the effect of Hurricane Sandy on Fire Island misstated the name of one of the private communities on the island. It is Davis Park, not Davis Beach.
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