Dry valley

Dry valleys are created by the erosion of water valleys, which only temporarily or not at all have running water.

Main reasons:

  • Changes in climate, especially increasing dryness ( aridity ).
  • In humid regions water is discharged underground. Two processes lead to the formation of these valleys: the Karst and the formation of periglacial valleys.

Dry valleys in arid and semi -arid areas

In the semi-arid low rainfall areas, rivers are often only in the rainy season or during heavy rain events active ( intermittent waters). Typical forms are the wadis in Eurasia. In Europe, common in the Mediterranean, are the Arroyos ( Spanish), or the torrents (Italian: torrents and their gravel beds) and Wied's in Malta.

In arid regions, which have previously received precipitation from existing dry valleys. In the episodic occurring rainfall, most of which are very violent, they are reactivated briefly again. In North Africa and the Middle East wadis transport the rainwater partly over very long distances, so that repeatedly drown desert Visitors who are not aware of the danger, in wadis.

Karstic dry valleys

The underground drainage is a characteristic of the Karst, so dry valleys belong to the geomorphology of the karst. By (usually large-scale ) tectonic movements a water-soluble rocks (eg, limestone, gypsum, salt) is raised and reaches the area of the ground water or directly to the surface. Drainage takes place first above ground. Due to the solubility of the rock and water penetration to existing fractures or cart it comes underground to the solution and thus to the formation of caves. Is a deepened the receiving water, the water table is also placed deeper. In this area, it is then amplified to the formation of caves and increasing relocation of drainage into the ground.

Initially taking the amount of water in the rivers from (examples of rivers with infiltration routes: Donauversickerung, Loneversickerung, Haut Doubs / Loue source Jura ). The seepage areas or cracks in the limestone are larger and take the forms of Ponoren to. If this makes the Karst System ( underground water holes or cave systems ) large enough to completely contain the most of the year the river is only with high amount of water about by floods following heavy rain or snow melt, the water bed reactivated ( turloughs in the Burren or " Hungerbrunnen " on the Alb ). Finally, the river shifted completely into the ground, the former valley is dry all year round. A special feature are valleys that remain dry, because a river with great relief energy broke through in a different direction and created a new Abflusstal and thus dry out the old bed allowed (see Flussanzapfung ).

In Germany there are dry valleys, for example, in the Swabian Alb, Franconian Alb, the south-eastern Black Forest, in the Paffrather Kalkmulde or shell limestone plateaus in the northwest and southeast of Thuringia:

Completely dry:

  • Wental ( Albuch, Alb )
  • Hasental, a glacial valley of the Miocene, above the Filsursprungs (Mean Swabian Alb)
  • Aitrach (lower part of Ur - Wutach / " Feldberg Danube" in the Black Forest )
  • Schlade ( Bergisch Gladbach)

Intermittent:

  • Lonetal and Hungerbrunnental on the Ostalb
  • Helbetal and Schaftal in the northwest of Thuringia.

Periglacial dry valleys

The formation of the Central Europe very widespread periglacial dry valleys took place with permafrost under glacial climatic conditions.

The by temporary thawing of near-surface layers ( "active layer", see Kryoturbation ) resulting melting and precipitation water was forced through the sealing effect of the frozen subsoil to the surface run-off. Pronounced Gelifluktion ( " floor tiles " ) on the waterlogged land surface and the Sedimentverfrachtung by melt water runoff in the landscape formed from depressions and valleys.

In subsequent interglacials started by resolution of the permafrost re- infiltration of river water into the permeable or fractured ground so that periglacial valleys could dry out. One example is the Rummeln in flaming.

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