Sankaty Head Geology

Sankaty Head Geology. . , If you were on this spot 23,000 years ago you'd be facing a sloping wall of ice--a massive glacier was 1000 miles away in Northern Canada. Two lobes of that Laurentide Ice Sheet, the Cape Cod Boy Lobe to the west and the South Channel Lobe to the east, came together here., By about 21,000 years ago, the ice stopped its southward push and over time deposited its mountainous payload of rock, sand, silt and clay. After centuries of erosion, all that is left is this fragile bluff., During glaciation so much water was locked up in the ice that sea level was about 400 feet lower than it is today. As the ice melted sea level began to rise. About 6,000 years ago, the ocean began flooding the coastal plain and eroding these glacial leftovers, the backbones of Nantucket, Martha's Vineyard and Cape Cod., Rising sea level and the erosion of these glacial headlands left behind the treacherous shoals that have played a part in at least 750 documented shipwrecks and untold loss of life. Sankaty Head, another glacial remnant, became an ideal place for a lighthouse., When Sankaty Light first shone its beacon over those shoals in 1850, it was about 280 feet from the edge of the bluff. When it was moved in October of 2007, it was 68 feet away. As sea level continues to rise and the erosion that comes with it persists, the distant future of Nantucket remains uncertain., Lower right caption: , Aerial view of Sankaty Head taken in April of 2007 showing the extent of the continuing erosion , Photo: Rob Benchley