Natural arch

Rock gates, also known as sheet rock or surf gates, bridges are broken or window-like rock formations caused by erosion. Depending on the size, shape, origin and environment are other names to bear, about rock bridge, stone or rock arch, natural bridge or Brandungstor. The opening is completely surrounded by rock, and the thickness of the perforated rock formation is of about the same order of magnitude as the width and height. This erosion forms are available in very different sizes, from the little thumb- thick hole measured up to more than a hundred meters openings surmounted by rocks.

Demarcation

The erosion forms mentioned can occur in all rock types. They are short-lived in directly erodible rocks or in environments with high erosion energy, such as the surf zone of cliffs. Durable large forms most frequently form in sandstone and limestone, as these resistive rocks are susceptible to solution by water and weathering.

The designation of such natural openings depends on its size, shape, origin and environment. Rock or Naturtor and rocks windows are of different sizes, a rock or natural bridge was formed by water that often passed through it in the form of a stream or river. Rock, natural stone arches and are characterized by their shape, and often not primarily caused by water. Surf gates caused by the effect of the ocean surf to cliffs.

In the following, all these forms are summarized under the term " rock gate ".

In English such erosion forms or Natural Arch Natural Bridge are called. After the division of the Natural Arch and Bridge Society, a Natural Arch formed without the participation of running water. Such forms are in the western U.S. and frequently arise there mainly in sandstone. The Natural Bridge is being built, however, by the action of flowing water and is permanently or temporarily traversed in many cases by a stream or river. A further subdivision of these main groups is possible, among other things, the form or the emergence.

Formation

The emergence of stone arches and rock bridges is achieved by removing parts of natural rock formations, usually by erosion. In the microscopic level, this is about the dissolution of cement, in the formation of macroscopic fracturing through various processes, such as pressure relief or tectonic processes such as uplift or strain, and widening through erosion or falling of material. Both types of development can run separately or in combination.

Rock gates are formed only under special conditions. The decisive factors are the type of rock or participate rocks that form the rock formation and the combination of erosion processes that act on them. The reason for the education are the effects of water, temperature changes, gravity or tectonic forces. Wind usually plays no direct role in the formation, but it can be an important factor in the further development, for example by the abrasive action of entrained sand grains ( corrasion in combination with processes of deflation).

Favor or cause, among other things below with different operations, a formation of rock gates in detail:

• Tectonic uplift can lead to the formation of clefts and crevices as well as for cutting of rivers into the ground

• Glacier activity can be steep and vertical rock walls and strong rugged terrain occur, the melting of glaciers favors erosion by large amounts of water

• The incision of river meanders into the ground may progress to the approximation of flux loops, so that only a relatively thin rock wall connects the future Umlaufberg with the valley walls and a rock fall can form a stone arch

• In advance of a Flussanzapfung forms in some cases also a relatively thin wall of rock, in which the formation of a Felsentors is favored

• The emergence of subterranean streams by karstification and the collapse of parts of the caves thus formed or their coalescence

• The formation of lava tubes and the collapse of parts of the tube

• The formation of clefts and crevices and their widening by erosion processes, as well as the removal of less resistive layers in a horizontal or inclined layer packet

• The activity of the surf, which leads to a strong erosion in the surf area by the carrying of sand and stones, while higher areas are only slightly affected. Moreover, it leads to a very different ablation different hard rock games

• Rock reinforcement by pressure stiffening. Directed pressure leads to a reinforcement of a rock, for example, by recrystallization of the rock constituents. The lateral deviation of the direction of stress in a rock formation through a column or a hole leads to a reinforcement of the side areas and thus there to a greater resistance to erosion

• Secretion by depressurization, as occurs for example in the exposure of previously located below the surface rocks, favored the formation of clefts and crevices, often parallel to the surface of a rock wall ( desquamation )

• Chemical weathering, temperature, weathering and the occurrence of freeze-thaw cycles lead to the widening of fissures and crevices or loss of rock strength

• Different erosion of adjacent, different resistant rocks.

Occurrence

In Central Europe, rock gates find for example in the Elbe Sandstone Mountains, on the shores of Helgoland, the Dahn Rockland, in the Luxembourg Switzerland, in the Swabian and Franconian Alb, or in the Karawanken at the Uschowa.

Three unusually large rocks goals in the region Wulong, China represent the largest concentration of corresponding formations in Asia dar.

Surf gates are formed on all suitable coasts, in Europe about to Helgoland and in the chalk cliffs on both sides of the Channel coast, or in Brittany ( Pointe de Dinan, Pointe du Van ). The largest natural sandstone rock bridge in Europe is located in the Bohemian Switzerland Prebischtor. Among many other rock gates of the Elbe sandstone rock arch and this is caused by Sandsteinverkarstung.

A known concentration of over 2000 stone arches found in Arches National Park in the U.S. state of Utah. There, a heterogeneous sandstone layer was broken by local swellings of a salt dome in parallel ribs. Under the conditions of a desert to more than 1500 meters above sea level with harsh climate, the erosion is most pronounced there, which has led to the emergence of many and very different stone arches.