Valley
At lower latitudes and altitudes, these glacially formed valleys may have been created or enlarged during ice ages but now are ice-free and occupied by streams or rivers.
In areas of limestone bedrock, dry valleys may also result from drainage now taking place underground rather than at the surface.
Many different types of valleys are described by geographers, using terms that may be global in use or else applied only locally.
Most commonly, they arise from erosion over long periods by moving water and are known as river valleys.
The presence of more resistant rock bands, of geological faults, fractures, and folds may determine the course of the stream and result in a twisting course with interlocking spurs.
More lateral erosion takes place in the middle section of a river's course, as strong currents on the outside of its curve erode the bank.
Conversely, deposition may take place on the inside of curves where the current is much slacker, the process leading to the river assuming a meandering character.
They typically have a U-shaped cross-section and are characteristic landforms of mountain areas where glaciation has occurred or continues to take place.
[4] The uppermost part of a glacial valley frequently consists of one or more 'armchair-shaped' hollows, or 'cirques', excavated by the rotational movement downslope of a cirque glacier.
Abrasion by rock material embedded within the moving glacial ice causes the widening and deepening of the valley to produce the characteristic U or trough shape with relatively steep, even vertical sides and a relatively flat bottom.
In places, a rock basin may be excavated which may later be filled with water to form a ribbon lake or else by sediments.
Their cross-sections exhibit steep-sided flanks similar to fjord walls, and their flat bottoms are typical of subglacial glacial erosion.
As a result, its meltwaters flowed parallel to the ice margin to reach the North Sea basin, forming huge, flat valleys known as Urstromtäler.
on the sunny side) because the climate is very mild: even in winter when the valley's floor is filled with fog, these villages are in sunshine.
In some stress-tectonic regions of the Rocky Mountains or the Alps (e.g. Salzburg), the side valleys are parallel to each other, and are hanging.
Corrie is used more widely by geographers as a synonym for (glacial) cirque, as is the word cwm borrowed from Welsh.
[16] The word dale occurs widely in place names in the north of England and, to a lesser extent, in southern Scotland.
[19] The term combe (also encountered as coombe) is widespread in southern England and describes a short valley set into a hillside.
In prehistory, the rivers were used as a source of fresh water and food (fish and game), as well as a place to wash and a sewer.
The proximity of water moderated temperature extremes and provided a source for irrigation, stimulating the development of agriculture.
Siting of settlements within valleys is influenced by many factors, including the need to avoid flooding and the location of river crossing points.
Numerous elongate depressions have been identified on the surface of Mars, Venus, the Moon, and other planets and their satellites and are known as valles (singular: 'vallis').
