The southern margin of Fresh Pond is a 2,000 to 3,000-foot- wide moraine that the Laurentide ice sheet pushed into a curved mound around 21,000 years ago (Skehan 173). Around 15,000 years ago, the glacier retreated. Harvard University Smithsonian Astronomical Observatory sits on the crest of the Moraine (Illinois). Thrust faults in overridden sand and gravel indicate that the glacier was moving from northwest to southeast (Chute).
One side of the moraine is very steep (the northwest side) . The moraine is poorly sorted, with pebbles and sand of different sizes.
One side of the moraine is very steep (the northwest side) . The moraine is poorly sorted, with pebbles and sand of different sizes.
Formation of End Moraine
1. Melting at a glacier margin causes the ice to thin
2. Ground-up rock debris carried in the base of the ice or dragged along beneath the glacier is deposited.
3. When the maximum extent of the glacier remains in the same place for a relatively long time, debris flows to the glacier's leading edge and piles up to form a large end moraine.
2. Ground-up rock debris carried in the base of the ice or dragged along beneath the glacier is deposited.
3. When the maximum extent of the glacier remains in the same place for a relatively long time, debris flows to the glacier's leading edge and piles up to form a large end moraine.
4. The glacier then starts to retreat leaving an unsorted pile of rock behind
Here is a brief video about moraines: