A U-shaped valley is the shape left after a valley has been overdeepened by a glacier. The original V-shaped valley, which would have been made by a river, is widened and deepened after the ice has eroded the sides and bottom of the valley. V-shaped valleys have a wide flat floor, which may contain ribbon lakes (long and narrow) and mis-fit streams (so called because they are too small to have made the valley).

The sides of U-shaped valleys may have hanging valleys, which are side valleys that are left high on the side of a main valley that has been deepened by glaciation. Streams flowing in a hanging valley may form a waterfall as it flows down the steepened sides. The valley sides may also have truncated spurs which are the ends of sloping ridges cut off (or truncated) by the valley glacier which tends to flow straighter than a river.

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The map above shows a simplified version of what a U-shaped valley and hanging valley would look like on a OS map.