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Why Rockport (and the rest of Cape Ann) is so Rocky
If you ever visit Rockport, not the tourist part, but put on your sturdiest hiking boots and really walk the coastline of Rockport, you'll find it mezmerizing with its enormous granite boulders that do not contour to the foot but most be danced over, headlands with striations carved in the stone, fossels set deeply underfoot, and the areas that are sandblasted flat cut with chiseled stairsteps. Numerous quarries dot the inner landscape in areas like Halibut Point State Park with its vistas that look out over thousands of miles of ocean or, if you're a people person, up towards the distant beaches of new Hampshire. The mysterious and vast Dogtown that is shared between Rockport and Gloucester has incredible geologic formations that the last ice age left and wind and time continue to subtly change so that even a yearly visit brings about a different photograph.
The town of Rockport and it's rocky coastline that is visited today was shaped by the last ice age, the Laurentide Glaciation, that occurred 21,000 years ago. The ice had what is called a lobate form, meaning three lobes covered Massachusetts down to Cape Cod close to the islands of Martha's Vineyard and Nantucket. As the earth warmed up again 3,000 years later, these lobes retreated at different rates. It left the Massachusetts coastline with a low topographical relief with very few areas reaching above 60 meters (196 feet) above sea level.
Much of the coastline from the Boston area up through New Hampshire and far up into Maine have marine deposits. With careful observation, evidence of fossils that were once set into, or still deeply set into the rock can be seen though closer to the tides it has, of course, had a chance to be less clearly defined.
The bedrock is faulted intrusive rock from the Paleozoic. Intrusive rock is formed by the crystallization of magma. The magma was from deep in the earth cooling slowly so that the crystals grew slowly thereby growing larger. The enormous intrusive granite is exposed at the surface with thin glacial deposits covering the bedrock. The granite of the Cape Ann peninsula is extremely dense and perfect for quarrying, the evidence of which is a large part of the areas history. The unique density of the granite is because of the pressure from sedimentary rock that once covered the bedrock. As the ice sheet eroded the sedimentary rock 15,000 years ago, it brought the granite close to the surface.
The Cape Ann peninsula is designated as a terminal moraine. Terminal moraines, or end moraines, are ridges of debris deposited at the end of the glacier. Glaciers churn the debris they carry from top to bottom where they deposit it in terminal moraines. The longer the end of the glacier stays in one spot the more deposits will be left behind.
The melting ice sheet left behind extensive vast areas of rocky debris including huge boulders that were carved into awe-inspiring shapes. As the glacier retreated, large areas of debris were deposited all over the area. Dogtown is famously covered with these rocks and boulders, the most famous of which is the called the Whale Jaw, an enormous eruption of granite that split in two pieces and looks decidedly like a whale breaching the surface. Dogtown is an almost 4000 acre area set aside by Gloucester and Rockport as a municipal watershed. Bike paths in the area range from easy to expert. It has incredibly unusual geological formations and remnants of the terminal moraine for the amatuer geologist to be thrilled by and photographers to compose breathtaking still lifes in their viewfinders.
Rockport, indeed all of Cape Ann, is a wonderous geological adventure. It would be a worth the time and money to plan a trip.
- Dogtown, Gloucester, Massachusetts | Btrails by Bikemag
Dogtown bike trail description.
Massachusetts State geological information with links to geothermal and seismological information.