How do mountain glaciers carve U-shaped valleys?
Quick Answer
Glaciers erode both the floor and walls of a valley as they flow downhill. Over time, a narrow V-shaped river valley becomes a broad U-shaped glacial valley.
The Full Story
Mountain glaciers are powerful moving masses of ice that can grind, pluck, and scrape bedrock as they advance. They widen valleys by eroding the sides as well as deepening the floor, unlike rivers, which mainly cut downward. This produces a characteristic U-shaped cross section with steep walls and a flat or rounded bottom. Classic examples include Yosemite Valley and the glacial valleys of the Alps and New Zealand. The shape is one of the clearest signs that ice, not a river, did the carving.
Key Facts
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Suggested video title for this topic:
"Why do some valleys look like giant scoops instead of river cuts?"
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