21,000 years ago Connecticut and Long Island Sound were completely covered with a layer of ice at least a mile thick. These materials were left behind as the glacier melted, creating Hammonasset Beach State Park. Winds and waves have continued to sculpt the area since that time. The Wisconsinan glacier first advanced into Connecticut from the north about 26,000 years ago. The ice front reached as far south as the southern edge of Long Island in this area, before its advance stopped. Then as the summer melt exceeded the winter snowfall, the glacial front gradually receded to the north, even as the ice continued to move south. The melting ice left behind large piles of rock debris, silt- to boulder-sized, carried by the ice.
Sometimes the ice front was stationary for a longer period, causing larger deposits of glacial material to build up. These long, linear piles of unsorted clay- to boulder-sized materials are called moraines. A little less than 17,500 years ago the ice front paused on a line from Hammonasset through Ledyard to Queens River, RI, depositing the Hammonasset-Ledyard-Queens River Moraine, a double moraine. To see the moraine, travel to Meigs Point beach. The southern moraine starts just east of the groin and continues northeast along the shore as a string of uneven, low rises, with various breaks, until disappearing into the entrance to Clinton Harbor. A trail follows the ridge top of the moraine. Along the water's edge all that remains of the moraine are huge boulders where wave action has removed all but the largest rocks, the ultimate coarse-grained beach!
As you follow the trail, look at the various sized materials in the ridge, ranging in size from microscopic clay particles to huge boulders -- typical moraine materials. From below the ridge top, down among the boulders, you can look back at the ridge in some places and see the exposed interior of the moraine. Here there are smaller rocks as well as gravel, sand and silt-sized particles. This is how the materials were originally dropped by the melting ice, all in a mixed jumble.
The southern moraine is especially well exposed because the waves keep eroding the Sound side, allowing the internal structure of the moraine to be exposed. Where waves have removed the smaller materials, boulder lag beaches remain, areas of boulders scattered along the water's edge. The longshore currents have probably carried the finer materials to the east to form the beach out to Cedar Island.
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