Valley
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- This article is about the physical-geographic term. For places named "Valley" see Valley (disambiguation).
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A valley is a landform, which can range from a few square miles (square kilometers) to hundreds or even thousands of square miles (square kilometers) in area. It is typically a low-lying area of land, surrounded by higher areas such as mountains or hills.
Valleys are formed by numerous geographical processes. Glacial valleys, which are usually U- rather than V-shaped, were formed tens of thousands of years ago (most likely during the last Ice Age) by the massive erosive power of glaciers. Several glacial valleys can be found in the English Lake District and many can be found in Alpine countries. Rift valleys, such as the Great Rift Valley, are formed by the expansion of the Earth's crust due to tectonic activity beneath the Earth's surface. Valleys are, however, most commonly formed by fluvial activity (the action of running water, such as rivers), which erodes the landscape.
Famous valleys
- Copper Canyon
- Death Valley
- Grand Canyon
- Great Rift Valley
- Loire Valley
- Napa Valley
- Rhone Valley
- Shenandoah Valley
- Valley of the Kings
- San Fernando Valley
Extraterrestrial valleys
Planets and moons other than the Earth can also have valley-like features. Lunar valleys can be formed due to a linked chain of impact craters. Smaller valleys, known as rilles, can be formed due lava flows or because of contractions in cooling lava sheets.
The Valles Marineris formation on Mars is a valley nearly 4000 km in length. It was originally formed by tectonic forces, but has been expanded by erosion.
See also
es:Valle he:גיא nl:Vallei ja:谷 no:Dal pl:Dolina pt:Vale (geografia) ru:Долина