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Station 9: Talformen und ihre Wirkung

General Information

Valleys such as the Leinbachtal where you find yourself right now, develop over a great many years, through the flow of streaming waters that carve away at the land and carry along materials. Even the tiny Leinbach that flows right in front of you was capable of forming this large valley! Here you can learn all about how valleys develop and the various forms that they can take on!

Functionality of the Station

The chart shows two predominant valley forms of the Leinbachtas. By scanning the QR code attached, detailed information regarding these and other valley forms can be downloaded.

 

More Informations:

Valley Types and their Development

A valley can be defined as an elongated hollow form of varying dimensions with a characteristic cross-section that has developed based on the geomorphological and geoecological conditions at the time of its formation, and that displays the influence of tectonic, eustatic and epigenetic forces along its longitudinal profile. Put in layman’s terms, a valley is a long hollow form along the earth’s surface, open at one side, and formed by weathering processes and the erosive influence of streaming waters or glaciers. Generally speaking, a valley is narrower when the deep erosion is stronger and the rock is harder.

The following are the various types of ideal basic forms:

          Ravine

          Gorge

          Canyon

          V-shaped valley

          U-shaped valley

          Box-valley

          Tough-valley

 

Ravine

[Lenz 1993: 188ff.]A ravine is a deeply cut mountain valley, which due to a combination of intensive deep erosion, and either minor or absent erosion of the slopes, creates an erosion-profile with almost vertical rock walls. The longitudinal profile is normally steep and irregular. The ravine is equally wide as the riverbed. Ravines only develop in resistant and stable rock formations. The possible depth of a ravine is limited by the critical height of its rock walls; were this to be exceeded then slides and rock falls would ensue. Examples of a ravine are the Breitachklamm and Partnachklamm in the Allgäu [Leser 2009: 244ff.].

 

Gorge

[Lenz 1993: 188ff.]A gorge develops when a ravine undergoes rock slides and rock falls. The slopes are somewhat beveled, and the form of the gorge is marked by deep erosion with minor but increasing erosion of the slopes. Examples of gorges include the Upper and Lower Rhine gorges (Graubünden/Switzerland), and  the Wutach, Murg and Wehra gorges (Southern Black Forest) [Leser 2009: 244ff.].

 

Canyon

A special form of the V-shaped valley is the canyon. This type of valley results from prevailing deep erosion. Because of the flat layering of the rock strata which have differing levels of resistance, the canyon develops its characteristic step-like cross-section, a feature that differentiates it from a V-shaped valley. The deep erosion and the process of slope erosion which it effects, create either flat or steep slope sections, based on the different levels of resistance of different types of rock. Examples include the Colorado Canyon (Arizona/USA) as well as the Fish River Canyon (Namibia) [Leser 2009: 244ff.].

 

V-shaped Valley

Naturally, this type of valley’s name refers to its identifiable V-shaped cross-section. Above all, this type of valley reflects the force of both strong deep erosion and slope erosion. Through horizontal erosion, the debris of slope erosion that fall to the foot of the slope are taken into the streaming water, and carried away. Thus the side slopes directly border the riverbed, and the flow direction, valley direction, the length of the valley as well as the length of the river correspond largely with one another. If the deep erosion were to cease, the V-shaped valley would transform into a U-shaped valley. Examples of V-shaped valleys include the great many narrow valleys in the Central Upland Range (Bodetal/Harz), the Schwarztal (Thuringian Forest), Queichtal (Palatinate Forest), and the Weisetal (Black Forest) [Ahnert 2003: 221] [Leser 2009: 244ff.].

 

U-shaped Valley

The U-shaped valley is also named due to the shape of its characteristic cross-section. The development of such a valley occurs over many stages. Firstly it develops in much the same way as a V-shaped valley, with steep and elongated slopes meeting the river directly. This is reflective of both the strong deep erosion and slope erosion that is present. Enhanced horizontal erosion compounded with still-prevailing deep erosion drives the further development of the valley into a U-shaped type, with the valley floor widening. As a result of river accumulation, the floor of the valley can develop into a gravel bed. Examples include, amongst others, the Rhine Valley and the Moselle Valley [Leser 2009:244ff.].

 

Box Valley

The box valley is a special exception between the U-shaped valley and a gorge that arises due to the quality of the rock. It results from simultaneously strong deep and horizontal erosion combined with an excess amount of transportable materials. Steep, almost vertical walls, and a flat valley floor are the main features of a box valley. The valley floor is usually comprised of bedrock. Examples include the Upper Danube Valley (Schwäbische Alb), the Upper Neckar Valley (Gäuland), and various wadis on the edge of the Sahara (e.g. Wadi Draa).[Leser 2009: 244ff.].

 

Trough-valley

The name of this valley type refers again to the shape of the valley cross-section; in this case it resembles a trough. The main features of this type are the soft contours marking the transition from the surrounding slopes to the deepest part of the valley; this form develops because of slope erosion by means of material delivery. The dominant influence on the development of this type of valley is the flushing of the area with water. Deep erosion is in this case mostly absent. Examples include the many little valleys on plateaus in the Central Upland range and in rolling hill landscapes with easily erodible sedimentary rock and loose sediments, and with or without loess covering (Selz and Wiesbach/Rhenish-Hessian Hills) [Leser 2009: 244ff.].

All figures: [Lenz 1993, 188 pp.]

 

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