How did glaciers have an impact on Pennsylvania’s topography?
The Survey’s Educational Series booklet 6, “Pennsylvania and the Ice Age” * escribes the effects of continental glaciers on Pennsylvania’s landscape. Glaciers came into both northeastern and northwestern Pennsylvania, most recently during the “Wisconsinan” glaciation about 15,000 to 20,000 years ago. Glaciers had a profound impact on both corners of the state and on the state’s rivers. The glaciers that reached northwestern Pennsylvania advanced through the Erie basin from Canada, picking up a variety of rock types on the way. As the glacier stalled, the load of sediment and rocks was deposited beneath and along the margin of the glacier. Glaciers advanced into northwestern Pennsylvania as many as 7 times during the last 2 million years. The appearance of the landscape was changed considerably by the glaciers. Valleys were partially or completely filled in and hilltops were eroded, resulting in an area of much lower relief than in the adjacent area outside the glaciated area. The lands
