A water gap is a geographical term for a valley, the river passing through the mountain range its current run (apparently) breaks through, often it is perpendicular to the strike of the rocks.
- 2.1 Danube
- 2.2 Other rivers
Causes the formation of rift valleys
Usually the mountains is oblique or transverse to the general direction of flow, and the water erodes it over the course of millions of years along tectonic weakness or fault lines. The geologist has a gap through its large surface exposed outcrops interesting views of the rocks and the bending of its layers since the orogeny. Since lift mountain region have until today to 1-3 mm per year, some rivers deep one in the same measure. Cobbles and gravels deposited during floods in the basin of the upper course or below the breakthroughs while fine gravel and sand get a majority in the main river. Due to the material removal, the river cuts further resistant towards its source down into the underground one. This process is known as headward erosion.
Breakthrough valleys are identified by their genesis divided into:
- Antecedent breakthrough valleys
- Epigenetic breakdown valleys
- Overflow breakthrough valleys.
Antezedentes transverse valley
Antecedent breakthrough valleys are valleys of rivers whose direction it was clear even before the onset of mountain uplift. With the tectonic uplift accompanied the river cut into the rising mountains, a place to relocate its river bed. The Middle Rhine Valley between Bingen and Koblenz ( Rhine Gorge ) is a antezedentes transverse valley.
Epigenetic transverse valley
Epigenetic breakthrough valleys are valleys that were originally based on unconsolidated sediments that covered a buried mountain or Härtlingsrücken. By lowering the surface by fluvial erosion and denudation these back are exposed and thus exempted from the less resistive sedimentary cover. By deep erosion that characterizes the deepening of the river bed, the river was able to cut into the Härtlingsrücken and thus to form the valley.
Overflow breakthrough valleys caused by the fact that behind a naturally deposited mass of debris (eg landslide ) water accumulates and eventually overflows at the lowest point. Due to the high slope of this overflow is deepened by headward erosion, whereby the resulting reservoir is drained. Lake sediments ( lacustrine sediments ) above such breakthrough witness to this mode of origin of rift valleys.
Major breakthrough valleys in the catchment area of the Danube are:
- The Danube Gorge at Beuron in the Upper Danube Nature Park, where the fledgling River has a deep bed dug through the Jura Mountains of the Swabian Alb
- The Danube Gorge at World Castle, a 180 m deep valley with steep rock walls
- Neuburger forest with the lion wall
- The Sauwald between Passau and Upper Austria ( Neuburg continuation of the forest on the east side of the Inn )
- The Wachau in Lower Austria ( from Melk to Krems)
- The Vienna Gate in Klosterneuburg
- The Danube Bend below Esztergom (north of Budapest) and
- Iron Gate by the Southern Carpathians between Serbia and Romania.
- Middle Rhine, the Rhine gorge cut through the Rhenish Slate Mountains between Bingen and Rüdesheim on the Rhine in the south and Bonn-Bad Godesberg and Bonn upper Kassel in the north - Bingerloch
- Porta Westfalica, breakthrough of the Weser by the Wiehen / Wesergebirge
- Porta Hassiaca, breakthrough of Eder in the Waberner level
- Schwalm gate, break the Schwalm from the Löwensteiner reason in the Schwalmaue
- The Thuringian Gate
- The Gesäuse in the middle reaches of the river Enns
- The Three Gorges of the Yangtze River ( Qutang Gorge, Wu Gorge, Xiling Gorge ), China
- The Považie at Strečno ( Small Fatra, Slovakia)
- The Red Tower pass in the middle reaches of the Olt, Romania
- The Delaware Water Gap ( Delaware breakthrough ) of the Delaware River in the Appalachian Mountains between the U.S. states of New Jersey and Pennsylvania
- The Manawatu Gorge on the North Island of New Zealand
- The Iskar Gorge in Bulgaria