Why are some valleys V-shaped while others are U-shaped?

Answer: Rivers cut downward into narrow V-shaped valleys, while glaciers scrape out broad U-shaped valleys.

Rivers cut downward into narrow V-shaped valleys, while glaciers scrape out broad U-shaped valleys. ✓ — Correct! Rivers erode downward, carving narrow V-shaped valleys with steep sides. Glaciers erode both downward and sideways, scouring broad U-shaped valleys with flat floors and steep walls. Yosemite Valley is a classic glacial U.

Heavy rainfall deepens valleys into V-shapes, while light rainfall leaves them U-shaped. — Wrong. Rainfall affects erosion speed, but not the shape. The shape comes from the erosion mechanism—rivers create V-shapes, glaciers create U-shapes—not from how much rain falls.

Older valleys become V-shaped over time, while younger valleys remain U-shaped. — Wrong. Age can make a valley deeper, but it does not determine the shape. The shape is set by the erosion type—water creates V, ice creates U—not by how long the valley has existed.