|An artist's rendition of a glacial lake.|
When the Laurentide Ice Sheet retreated about 18,000 years ago, features called glacial lakes were formed. They were fed a constant supply of meltwater by the nearby glacier and these streams deposited sand and gravel into the lakes. In this region, two particularly prominent lakes were Lake Sudbury and Lake Concord.
Lake Sudbury formed first, and it was located just south of present day Massachusetts Rt. 2. It was about 4 miles wide and 20 miles long. It was around 90 feet deep. Later, as the glacier retreated more, Lake Concord was created north of Rt. 2. On its northern side it was contained by ice and on the south and west it was contained by higher ground.
|A map showing the general coastlines of Lake Sudbury and Concord.|
It is thought that there were also many chunks of ice in these lakes that had yet to melt, making it likely that instead of being one huge expanse of water, they were actually made of many smaller lakes. This possibility also makes it unlikely that there were many waves on the lakes and therefore less erosion would have occurred. Scientists have searched for evidence of erosion from waves, but they have been unsuccessful, which adds proof to the idea that these lakes were choked with pieces of the glacier.
Eventually, since these lakes are no longer present, all the water drained away through the various streams and rivers that formed during this time. This left behind a lake basin filled with clay and silt. In fact, colonial settlers in Massachusetts used this clay to make bricks to build their houses with. They also left behind features such as kame deltas, which you can learn about here.
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"Map of Concord, Mass." Map. Geological Survey Professional Paper. Vol. 475. Washington: United States Government Printing Office, 1963. 143. Google EBook. Google. Web. 28 May 2013. <http://books.google.com/books?
Pickering, Byron. Glacial Lake Missoula. Digital image. ENB 105. N.p., n.d. Web. 28 May 2013. <http://1.bp.blogspot.com/-