The Changing Shape of the Cape & Islands: The Atlantic Shoreline
“Eleven thousand years ago Georges Bank was above water,” says Greg Berman, coastal processes specialist for the Woods Hole Oceanographic Institute. “Back then it would have been possible to walk from the Cape to Georges Bank. With much more land visible, the Outer Cape was not getting hit with the large storms of today which come across the Atlantic, so erosion was much less.”
According to Berman, it was 6,000 years ago when the coastal erosion of Cape Cod began accelerating. The bluffs, which are retreating to this day, once extended as much as four miles farther east than they currently stand. Interestingly, although much of the eastern-facing coastline is retreating, there is an area which is actually growing. Due to wave conditions and sediment migration, much of what was lost from the eroding bluffs traveled north to create Provincetown and south to create Monomoy Island.
Dan Zoto, an archaeologist at the Cape Cod Museum of Natural History, says that it was about 3,000 years ago when the sea level stabilized. He explains the importance of the stabilization: “Sea level stabilization allowed for the initial formation of barrier beaches,” he says, “and not long after came the beginnings of salt marshes in the estuaries and along tidal rivers. It is at this time, approximately 3,000 years ago, that we see intense use of these estuarine environments by Native peoples.” In other words, sea level stabilization allowed for the year-round habitation of Cape Cod.
Mark Adams, coastal geologist, geographer and cartographer at the Cape Cod National Seashore since 1991, expands on Greg Berman’s points. “Geologists have put together a picture of change going back to the glaciers about 22,000 years ago,” Adams says. “The erosion and accretion we see today has been going on for about 6,000 years, but the conditions began to change marginally in the industrial period over the last two centuries. We see the cliffs of the Outer Cape retreating at a rate of about 3 to 5 feet per year, so in my 20-year tenure that would be up to 100 feet of retreat.”
Today the east coast of Cape Cod is in a state of constant flux. In the town of Chatham it begins with the area once known as North Beach. Before 1987 there was a long barrier beach stretching down from Nauset Beach toward Monomoy Island. The rates of erosion along this barrier beach ranged from as high as 19 feet per year to 3 feet per year between 1938 and 1974. In January 1987 a powerful nor’easter caused the ocean to finally break through the barrier. The ocean poured through the hole into the Chatham shore and Pleasant Bay. This break created the popular Lighthouse Beach, located across the street from Chatham Lighthouse.
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