The forensics of past glaciers:
- Are there huge boulders that couldn’t be moved by the wind or rivers?
- Are there little hills and ridges made of rocks, dirt, sediment?
- Can you see polished bedrock with scratches on it all going in the same direction?
These are just some clues that glacier detectives look for to tell where glaciers were in the past. Mountaineers noticed boulders, scratches on the bedrock, and other deposits near the edge of the glacier in the European Alps. When they saw similar features way down valley, they made the assumption that these deposits were also deposited by glaciers when the glaciers were larger. People who lived in the European Alps could imagine the glaciers in those mountain growing and shrinking over time.
One European traveled to Maine in the 1800s to explore the landscape for evidence of past glaciers. He found scratches! He found boulders! He found rocky deposits! He declared that glaciers must have covered Maine at some time in the past. But where is the nearest glacier to Maine today? The Greenland Ice Sheet is closer to Maine than the Barnes Ice Cap on Baffin Island, but the Barnes Ice Cap could be thought of the last remaining piece of the Laurentide Ice Sheet (the massive ice sheet that covered northern North America during the last ice age).