Glacial valleys U-shaped valley on the Afon Fathew near Dolgoch, Wales A glaciated valley in the Mount Hood Wilderness showing a characteristic U-shape, the bottom's rocky 'rubble' accretion and the broad shoulders įor various lists of river valleys, see Category:River valleys. Such rejuvenation may also result in the production of river terraces. lowered global sea level during an ice age. Rapid down-cutting may result from localized uplift of the land surface or rejuvenation of the watercourse as a result for example of a reduction in the base level to which the river is eroded, e.g. Some sections of a stream or river valleys may have vertically incised their course to such an extent that the valley they occupy is best described as a gorge, ravine, or canyon. A typical river basin or drainage basin will incorporate each of these different types of valleys.

In the lower valley, gradients are lowest, meanders may be much broader and a broader floodplain may result. 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. 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. In the middle valley, as numerous streams have coalesced, the valley is typically wider, the flow slower and both erosion and deposition may take place. 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. In the upper valley, the stream will most effectively erode its bed through corrasion to produce a steep-sided V-shaped valley. Typically the flow will increase downstream and the gradient will decrease. The development of a river valley is affected by the character of the bedrock over which the river or stream flows, the elevational difference between its top and bottom, and indeed the climate. River valleys The valley of Halikko River in Halikko, Finland Valley of Palakaria river springing from Vitosha Mountain, seen in the background, in Bulgaria The valley floor is typically formed by river sediments and may have fluvial terraces. The flat (or relatively flat) portion of a valley between its sides is referred to as the valley floor. All three processes can contribute to the development of a valley over geological time. Other valleys may arise principally through tectonic processes such as rifting. In polar areas and at high altitudes, valleys may be eroded by glaciers these typically have a U-shaped profile in cross-section, in contrast to river valleys, which tend to have a V-shaped profile. Typically small valleys containing streams feed into larger valleys which in turn feed into larger valleys again, eventually reaching the ocean or perhaps an internal drainage basin. Most commonly, they arise from erosion over long periods by moving water and are known as river valleys. Valleys may arise through several different processes. Many different types of valleys are described by geographers, using terms that may be global in use or else applied only locally. Rift valleys arise principally from earth movements, rather than erosion. In areas of limestone bedrock, dry valleys may also result from drainage now taking place underground rather than at the surface. In desert areas, valleys may be entirely dry or carry a watercourse only rarely. These glaciers may remain present in valleys in high mountains or polar areas.Īt 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. Some valleys are formed through erosion by glacial ice. Most valleys are formed by erosion of the land surface by rivers or streams over a very long period. Fljótsdalur in East Iceland, a rather flat valley The Frades Valley in the mountainous region of Rio de Janeiro state, Brazil Baemsagol valley of Jirisan, KoreaĪ valley is an elongated low area often running between hills or mountains, which will typically contain a river or stream running from one end to the other. JSTOR ( May 2013) ( Learn how and when to remove this template message)Ĭalchaquí Valley in Argentina U-shaped valley in Glacier National Park, Montana, United States Romsdalen in Western Norway has almost vertical walls.Unsourced material may be challenged and removed.

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V shaped contour line definition