Why do some mountain valleys have U-shapes instead of V-shapes?
Quick Answer
U-shaped valleys are carved by moving glaciers, which widen and deepen the valley floor and walls. Rivers usually cut narrower V-shaped valleys instead.
The Full Story
A river erodes mostly downward, creating a narrow V-shaped cross-section. A glacier, by contrast, is a thick moving mass of ice that scrapes not only the bottom but also the sides of a valley. Over time, this erosive power broadens the valley into a U-shape with steep walls and a flatter floor. Many alpine landscapes in places like Switzerland, Norway, and New Zealand show this signature clearly. The shape is a clue that ice, not just water, once dominated the landscape.
Key Facts
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"Why do glaciers carve valleys into giant U-shapes?"
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