Valley
From Freepedia
- This article is about the physical-geographic term. For places named "Valley" see Valley (disambiguation).
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.
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Hollows
A hollow is loose name for a valley in the earth. It is commonly used in New England to describe such geographic features. Hollows may be formed by river valleys such as Mansfield Hollow or they may be relatively dry clefts with a notch like characteristic in that they have a height of land and consequent water divide in their bases. A hollow such as this is Boston Hollow.
Famous valleys
- California Central Valley
- Copper Canyon
- Death Valley
- Grand Canyon
- Great Rift Valley
- Loire Valley
- Napa Valley
- Rhone Valley
- Shenandoah Valley
- Valley of the Kings
- San Fernando Valley
- Santa Clara Valley (Silicon 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.
