About 50% of the state’s land area is covered by forests and the only lowlands (Atlantic Coastal Plains) are situated in the extreme southeastern corner of the state. The Appalachian Mountains slice through the center of Pennsylvania. The Allegheny and Pocono Mountains form the state’s most significant subranges.

About 30 percent of Pennsylvania was covered by glaciers during the Ice Age. These glaciers helped to sculpt the hills and valleys of Pennsylvania and deposited materials such as boulders, sediment, and other debris, including pieces of Canada now found in Pennsylvania. …

Pennsylvania’s glacial lakes are all “kettle” lakes. They were formed in the late Pleistocene period when gigantic blocks of ice broke free from a retreating continental ice sheet, in this case the Wisconsin Glacier, and were left behind in the rock debris and gravel moraine.

U-shaped valleys, hanging valleys, cirques, horns, and aretes are features sculpted by ice. The eroded material is later deposited as large glacial erratics, in moraines, stratified drift, outwash plains, and drumlins. Varves are a very useful yearly deposit that forms in glacial lakes.

A drumlin is another example of a deposit left behind by a glacier. It’s described as an elongated hill composed of glacial till. Unlike moraines, which form in rows of sediment, drumlins look like the backs of whales as they breach the surface of the ocean, and where there is one drumlin, you will likely find others.

The Pinedale (central Rocky Mountains) or Fraser (Cordilleran ice sheet) glaciation was the last of the major glaciations to appear in the Rocky Mountains in the United States. The Pinedale lasted from around 30,000 to 10,000 years ago, and was at its greatest extent between 23,500 and 21,000 years ago.

Landforms

• Central Lowlands.
• Appalachian Plateaus.
• Ridge and Valley.
• New England.
• Piedmont.
• Atlantic Coastal Plain.

The pebbles and boulders may be faceted and striated from grinding while lodged in the glacier. Some till deposits show limited organization of the fragments: large numbers of stones may lie with their long axes parallel to the flow direction of the glacier.

Glacial deposits are of two distinct types:

• Glacial till: material directly deposited from glacial ice. Till includes a mixture of undifferentiated material ranging from clay size to boulders, the usual composition of a moraine.
• Fluvial and outwash sediments: sediments deposited by water.

Today, glacial deposits formed during the Permo-Carboniferous glaciation (about 300 million years ago) are found in Antarctica, Africa, South America, India and Australia.

From studying glacial deposits, they know that the northwestern and northeastern corners of Pennsylvania were affected by several glacial advances — the most recent being approximately 22,000 years ago. The style of glaciation was quite different in the two corners of Pennsylvania, as are the associated glacial deposits.

In the northeastern corner, most likely due to a more rugged land surface, erosional processes dominated. Deposits from older glaciers were eroded away by overriding younger glaciers.

Glacial sediments in this area contain very little in the way of far-traveled clasts; rather, the pieces of rock within the sediments are from local sandstones, siltstones, and shales. Here are some of the important impacts of glaciers in Pennsylvania:

The deposits included lots of carbonate minerals from the limestone and dolostone bedrock of the Erie basin, and they included far-traveled clasts of igneous and metamorphic rocks that were plucked from the Canadian Shield. In the northeastern corner, most likely due to a more rugged land surface, erosional processes dominated.