Glacial Plucking

Oswegatchcie Hills, Niantic, CT

Walking along the yellow trail I came across this glacier boulder.  I think this is an example of a process known as glacial plucking.  During the last glacier period here, about 24,000 years ago, the glaciers that covered Connecticut were constantly flowing to the south.  As temperatures warmed, water would flow into crevices within the rocks where it would freeze during the night and expand, thus causing the rock to split.  The constant movement of the glacier would "pluck" the split rock and move it a short distance from the the original outcrop. This process went on for about 5,000 years.  In this case it looks like a couple of rocks were plucked from the main outcrop, and fortunately formed a natural marker for the trail.  The rock itself is pretty typical of this area, a granite gneiss which I think is known as Potter Hill Granite Gneiss, which dates back to the Proterozoic.