Changes in the Cape Cod Coastline

Beaches are dynamic, living landscape features. Coast barrier beaches, which are long and narrow, and run parallel to shore, are a good example. These undergo constant change, as they are raised up, shifted, and torn through. Inlets open, then close. As sand erodes in one place, it is redeposited in another.


Before the last Ice Age ended 10,000 years ago, Stellwagen Bank, 19 miles northeast of Provincetown, and Georges Bank, 62 miles east of Cape Cod, were both above water—it was in fact possible to walk from Cape Cod to Georges Bank.


As the Ice Age ended, melting glaciers led to sea level rise. With Georges Bank and Stellwagen Bank submerged, there was nothing to protect Cape Cod’s coastline from large Atlantic waves.


Six thousand years ago, bluffs facing the Atlantic extended as much as four miles east of our current coastline. However, as those areas eroded, sand was redeposited both to the north, at Provincetown’s “fist,” and to the south at Chatham’s Monomoy Island, the Cape’s “elbow.”


Today, geologists believe that barrier beaches go through a cycle of 150 years, during which time one long, continuous beach forms, then is broken open, then gradually fills back in. Chatham’s barrier beach is in the midst of once such cycle.


Before 1987, North Beach extended as one long spit, from Nauset Beach in the north, to as far as North Monomoy Island in the south. In 1987, a nor’easter broke through the barrier beach. Today, the original beach is divided into North Beach, North Beach Island, and South Beach. North and South Monomoy Islands are now joined together by the redeposition of sand eroded from the barrier beach.


Truro’s Ballston Beach is another example of this cycle. During a blizzard in February of 2013, the storm surge broke through the dune barrier, pushing seawater 900 feet inland. The town’s Department of Public Works trucking in 4,000 cubic yards of sand to fill the breach, only to have it torn open again in January of 2015.


The eroding sand travels north to Provincetown, where Race Point Beach sees an accretion of roughly seven feet per year. In contrast, the protected beaches facing Cape Cod Bay or Nantucket Sound are eroding about one foot per year, and the hard-hit, Atlantic-facing coast is eroding at a rate of three to five feet per year.


All this means is that in the end, Mother Nature will do as she pleases.Beaches are dynamic, living landscape features. Coast barrier beaches, which are long and narrow, and run parallel to shore, are a good example. These undergo constant change, as they are raised up, shifted, and torn through. Inlets open, then close. As sand erodes in one place, it is redeposited in another.


Before the last Ice Age ended 10,000 years ago, Stellwagen Bank, 19 miles northeast of Provincetown, and Georges Bank, 62 miles east of Cape Cod, were both above water—it was in fact possible to walk from Cape Cod to Georges Bank.


As the Ice Age ended, melting glaciers led to sea level rise. With Georges Bank and Stellwagen Bank submerged, there was nothing to protect Cape Cod’s coastline from large Atlantic waves.


Six thousand years ago, bluffs facing the Atlantic extended as much as four miles east of our current coastline. However, as those areas eroded, sand was redeposited both to the north, at Provincetown’s “fist,” and to the south at Chatham’s Monomoy Island, the Cape’s “elbow.”


Today, geologists believe that barrier beaches go through a cycle of 150 years, during which time one long, continuous beach forms, then is broken open, then gradually fills back in. Chatham’s barrier beach is in the midst of once such cycle.


Before 1987, North Beach extended as one long spit, from Nauset Beach in the north, to as far as North Monomoy Island in the south. In 1987, a nor’easter broke through the barrier beach. Today, the original beach is divided into North Beach, North Beach Island, and South Beach. North and South Monomoy Islands are now joined together by the redeposition of sand eroded from the barrier beach.


Truro’s Ballston Beach is another example of this cycle. During a blizzard in February of 2013, the storm surge broke through the dune barrier, pushing seawater 900 feet inland. The town’s Department of Public Works trucking in 4,000 cubic yards of sand to fill the breach, only to have it torn open again in January of 2015.


The eroding sand travels north to Provincetown, where Race Point Beach sees an accretion of roughly seven feet per year. In contrast, the protected beaches facing Cape Cod Bay or Nantucket Sound are eroding about one foot per year, and the hard-hit, Atlantic-facing coast is eroding at a rate of three to five feet per year.


All this means is that in the end, Mother Nature will do as she pleases.


 
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