Valley
A valley is a caused by the interplay of erosion and denudation, elongated ordinarily open to the at least one side of the hollow form in the landscape. The line-like erosion takes place by a river, the areal denudation by gravitational mass movements. The lowest line is called depending on the shape depth line, bottom or valley floor. This has a monotone ( same direction ) gradient. For a different form or other development processes (eg glacial erosion ), one speaks not of a valley but by Talung or talähnlichen shapes (eg, glacial trough ).
- 4.1 narrow valley
- 4.2 gorge
- 4.3 Canyon
- 4.4 Breakthrough valleys
- 4.5 wadis and arroyos
- 5.1 U-shaped valleys and fjords
- 5.2 Urstromtäler
- 5.3 Glacial troughs and fjords
- 5.4 Ria
Etymology
The word goes back to the Indo-European root Dhel " bend cavity bulge " and is related to the word dent.
Talentstehung
Line adhesive flowing waters (rivers ), can erode the material ( erosion), lead to the lowering of the river bed. It is immaterial whether the depth or lateral erosion predominates. With the lowering of the riverbed attacks the valley slopes ( or walls ) to the denudation. This means that the Talbegrenzungen be removed and lowered, but never deeper than the river. Rivers play in Talentstehung extent a supporting role, as they provide for their catchment area, the lowest line up to which the entire ablation can work. They therefore constitute a regional erosion base, thus they are the regulator of land forming. Due to the different erosion and Denudationstypen and the different removal rates gives rise to various valley forms.
May not be called valleys open hollow forms that are not caused by fluvial erosion. This mainly grabens, whose sole Namely, a river flow, whose slopes but not emerged by erosion. Also elongated hollow forms between dune ridges (eg Draa dunes), beach ridges, moraines, etc. are not referred to as valleys, but as Talungen, Talzüge, valley furrows, ridges, valleys or troughs described. Also forms that arise from temporary erosion processes with rapid change (such as occur for instance in badlands, gullies or ravines the case), not called valleys.
The valley formation is modified by the geological storage conditions of the rocks and any existing tectonic processes (eg mountain building ). The climatic conditions that affect the runoff and weathering intensity significantly, have a significant impact on the valley formation.
Basic valley forms
Gorge, ravine
A canyon or gorge is formed at a very powerful deep erosion of a river. Lateral erosion and denudation play no or only a minor role. Therefore gorge valleys have walls as Talbegrenzung, the river fills the bottom of the valley completely.
V-shaped valley
A V-shaped valley formed at an approximate balance between vertical erosion and slope denudation. In cross-section Kerbtälter are V-shaped. The valley is filled out completely or almost completely by the fact flowing river.
Sohlental, Kastental
If a full flow of both depth and lateral erosion, creates a distinctly developed and bottom. The river thus fills the valley no longer completely. Depending on the presence or absence of denudation distinction is sole valleys with slopes as limiting or box valleys bounded by walls.
There are transitional types, which are called Kerbsohlental or Sohlenkerbtal Between Deep, V-shaped valley and the Sohlen-/Kastentälern.
Mulde
Trough valleys are located in areas with strong denudation. Both the depth and the lateral erosion kick back against it. The strong slope denudation leads to shallow valley slopes. The transition to the actual valley floor is blurry. Trough valleys are preferentially formed in the periglacial and in the humid tropics. In both climate regions have strong denudation.
Special valley forms
The valley forms listed here are produced under certain storage conditions of the rocks in tectonic activity or under particular climatic conditions.
Narrow valley
A narrow valley or a gorge is the umbrella term for a Talungsabschnitt with a very narrow valley floor. The cross section is V-shaped or U-shaped ball. The lake has a natural virtually no freedom of movement in the valley. In traffic engineering term is also Talpass, is found in place names, the expression Klause.
Canyon
A canyon is a narrow, steep valley cut, usually in a mountain range. The Talbegrenzung consists of walls or steep slopes. Gullies by cutting even smaller watercourses in was solid, bulky rock. Preferably, it is formed in plutonic rocks like granite. The deep erosion outweighs the denudation strong.
Canyon
A canyon is formed by cutting a deep river in a plateau with superimposed horizontal layers of rock. The rocks have a different resistiveness opposite the ablation. The slopes of a canyon are therefore stepped stair-like and alternately steep and much flatter. It affects both vertical erosion and denudation.
Breakthrough valleys
Breakthrough valleys cut through a mountain range. Antecedent breakthrough valleys caused by cutting of a river in the resulting by tectonic uplift of a mountain level. Here, a river he had acquired in the lowlands meander deep into the mountains resulting cut ( Zwangsmäander ). Epigenetic breakthrough valleys emerge without tectonics, when a river at the erosion in the depth encounters a Härtling and then attacks him erosive.
Wadis and arroyos
A wadi is a dry valley in desert areas, which will temporarily cause only after heavy rains water. There are also in humid climates today arroyos, if the conditions that led to the emergence of the valley, no longer exist. An example of this are the numerous dry valleys in Northern Germany or the dry valleys in karst areas such as the Swabian and Franconian Alb. This arose when during the ice age, water from precipitation due to the then existing permafrost could not seep and was forced to surface runoff.
Talähnliche forms
As talähnliche forms hollow forms are referred to, which have more or less very similar to valleys, but have different formation conditions.
U-shaped valleys and fjords
U-shaped valleys are overprinted by glacial valleys and therefore no valleys in the sense of the above definition. They can be called " river bed " of a glacier called. Fjords are drowned U-shaped valleys.
Urstromtäler
Glacial valleys (actually wide sole valleys ), which deliver the meltwater of glacial Inlandeisvorstöße parallel to the ice edge have the result of subsequent overprinting now only restrict the characteristics of a valley. Especially the same direction gradient is now mostly gone.
Glacial troughs and fjords
Glacial troughs created under the glacier by meltwater erosion. Its present form relies heavily on the shape of the Toteisblöcke that once filled the gutter. They have therefore in most cases not the same intimate gradient. Fjords are drowned glacial troughs.
Ria
A Ria is a deep penetrating into the mainland bay, which is caused by flooding of a former river valley.
General talent development
Especially in the upper reaches of the rivers is flowing water cuts the due to the large gap quickly erosive strong in the rock and leads to the formation of a ravine or gorge. Depending on the nature of the rock follows it downstream a V-shaped valley or gorge. These are mainly found in the high mountains. The depth of erosion is so strong that the weathering of slopes and their removal can not follow. The rock walls of the gorges are thus nearly perpendicular and only as wide as its riverbed. The maximum depth of a gorge is determined by the critical height of the cliffs. If this is exceeded, due to the instability rockfalls and landslides. The slopes are shifted back and flatten the vertical valley sides. This has an intense lateral erosion of slopes result.
Did the valley is predominantly a V-shape, it is called a V-shaped valley. The shift back is characterized by a strong material removal on the slopes, which can withstand the deep erosion of the river. The flatter, the valley slopes, the discontinuous itself represents the denudation If there is initially in a deep gorge still regularly rockfalls, lateral erosion occurs later only with appropriate meteorological events. This Denudationen shall then be monitored by slip or glide as well as in the form of debris flows and other Fließungen.
Notched sole valleys are characterized by a smaller depth of erosion and a small but real side erosion. The transition from the V-shaped valley to Sohlental is fluid. Erosion on the slopes, the water is forced to move the removed material. Is the slope of the valley low, the water begins to meander. At the undercut slope it is true then often on the side of the valley and picks up this intensely. Deposits of material occur simultaneously in the slip, which widens the sole of the valley.
The notched mountains is completely eroded with time and leveled it; the difference in elevation between valley floor and mountain peaks decreases again. In the always flatter terrain the Kerbsohlental becomes a broader Sohlental. The reason for the reduction of the level difference between the valley floor and mountains must not be due to erosion. It can also be caused by tectonics.