There are various forms of valley associated with glaciation that may be referred to as glacial valleys.
A valley carved by glaciers is normally U-shaped. The valley becomes visible upon the recession of the glacier that forms it. When the ice recedes or thaws, the valley remains, often littered with small boulders that were transported within the ice. Floor gradient does not affect the valley’s shape, it is the glacier’s size that does. Continuously flowing glaciers – especially in the ice age – and large-sized glaciers carve wide, deep incised valleys.
Examples of U-shaped valleys are found in every mountainous region that has experienced glaciation, usually during the Pleistocene ice ages. Most present U-shaped valleys started as V-shaped before glaciation. The glaciers carved it out wider and deeper, simultaneously changing the shape. This proceeds through the glacial erosion processes of glaciation and abrasion, which results in large rocky material (glacial till) being carried in the glacier. A material called boulder clay is deposited on the floor of the valley. As the ice melts and retreats, the valley is left with very steep sides and a wide, flat floor. A river or stream may remain in the valley. This replaces the original stream or river and is known as a misfit stream because it is smaller than one would expect given the size of its valley.
Other interesting glacially carved valleys include:
- Yosemite Valley (USA)
- Side valleys of the Austrian river Salzach for their parallel directions and hanging mouths.
- Some Scottish glens full with bushes and flowers.
- That of the St. Mary River in Glacier National Park in Montana, USA
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