The valley ( river ) is a negative, linearly elongated shape of the relief with a uniform fall. It is usually formed as a result of the erosive activity of flowing water. River water, washing away the banks and the bottom  , forms a river valley.
Small forms of river valleys are scours , beams , ravines , created by non-permanent (periodic) watercourses.
Valleys usually form entire systems; one valley opens into another, and that, in turn, into the third, and so on, until their confluent waterways flow into one body of water in one common channel .
The following main elements of the valley        are distinguished by hydrologists, geologists and geomorphologists:
- slopes - areas of the earth's surface that limit the valley from the sides
- bottom or bed - the lowest and relatively flat part of the valley, enclosed between the soles of the slopes.
- the bottom of the slopes - the line of pairing the slopes with the bottom of the valley
- curb - the place of junction of the slopes of the valley with the surface of the adjacent terrain
- the terraces are relatively horizontal platforms located at different heights above the modern valley floor.
In young valleys, the bottom is undeveloped, and the slopes approach the river itself, being at the same time the banks of the river flowing in it.
The slopes of the valley can be high or low , steep or gentle . The slope of both slopes of the valley are the same or different ( asymmetric ). The asymmetry of the valleys is caused by the Baer law : in the Northern Hemisphere , the right is more steep, and in the Southern Hemisphere the left is more abrupt.
In its upper reaches, the valley most often begins with a catchment basin or an ice circus . Less common valleys with open upper reaches. The estuarine (lower) part of the valley is often accompanied by a delta or a cone , or it represents the gulf of a reservoir, into which the river flows, in the form of a lip or estuary .
The river valleys are a very complex, branched and at the same time connected with each other a single system of landscapes . They are clearly separated geographically and in sharp contrast in their morphology with the surrounding continental landscapes. Constantly changing direction, wandering river flow leads to a large variability of the valley landscape, to its continuous and deep restructuring. River valleys are constantly rejuvenated, they can always be observed as the most initial stages of relief formation and the development of biogeocenoses , and later. Specific for river valleys and have no analogues among the zonal types of landscapes hydrological features: spring-summer floods , rain and wind floods . The unity of the river valleys is manifested in a large synchronism of spills on the entire longitudinal profile of the valley. Floodplains of the lowland rivers serve as good grasslands; in places safe from erosion, they are plowed open, terraces are also used for planting all sorts of crops, often serving as locations for settlements (especially in mountainous countries); the slopes of the valleys are often covered with forest.
There are mountain and flat valleys. The former are characterized by significant depth with a relatively small width and an uneven fall in the longitudinal profile. The latter, as a rule, are wide, have insignificant depth and steepness of the slopes, small slopes, etc.
The valley, except for fluvial, that is, formed by the action of flowing water, can also be tectonic if its appearance is associated with the geological structure of the relief. These include the Alai Valley in Central Asia and the California Valley in North America .
- Yandex.Kartinki . yandex.ru. The date of circulation is July 17, 2017.
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