Egergraben

The Egergraben ( Ohře trench, Oherský příkop ) is a geographical and regional geological unit area in the northwest of the Czech Republic or in Northern Bohemia. He is a northeast-southwest oriented, running south parallel to the Erzgebirge ( Ore Hory ) and with respect to its origin associated with this.

Geography

The morphologically designed as part of the lowland Egergrabens is located entirely in the Czech Republic, roughly between the towns of Cheb ( Eger) in the southwest and Ústí nad Labem ( Usti nad Labem ) in the northeast. Its south-western portion is drained by the eponymous river Eger ( Ohře ) and separates the Ore from the Imperial Forest ( Slavkov ) and Doupov Mountains ( Doupovské hory). In the northeast, the valley continues as North Bohemian Basin in the Valley of Biela and there separated from the Ore Mountains Bohemian Highlands ( České Středohoří ), while the Eger, the Czech Central Mountains and flows south flows around Leitmeritz ( Litoměřice ) into the Elbe.

Geology

The Egergraben in the geological sense includes, depending on the definition, an in some cases much larger area than the river valleys of Eger and Biela. In any case, Doupov Mountains and Central Mountains with added.

The Egergraben can be used as paleo- rift, that is, be regarded as a grave breach now largely inactive. It belongs to the so-called European Cenozoic rift system and formed by the long-range effect of the formation of the Alps during the Tertiary. The northern drift of the African continental plate elicited increased stresses in the earth's crust in Central Europe. These tensions were reduced by tectonic movements took place again at dislocations in leveled and to a large extent by powerful layers of sediment covered Variscan basement. Along such, northeast - southwest ( Erzgebirge ) trending fracture zones and accordingly Northwest Southeast ( hercynian ) oriented cross faults dropped from the Eocene or early Oligocene to late Miocene, some 40 or 35 and 9 million years ago, the Egergraben in the northwestern part of the Bohemian mass, and separated by the Erzgebirgsscholle from the rest of the Bohemian crowd. Subsequently, the Erzgebirge was also lifted. Since the uplift mainly at the fracture zone between the Erzgebirge and Egergraben ( Erzgebirgsabbruch ) took place, the Ore Mountains in Saxony lying increases its northwestern flank only very gradually, but falls to the southeast, at the Egergraben flank facing steeply. We speak because this geometry by a panel Scholl Mountains. The most important southern boundary fault of Egergrabens is the central mountain demolition (named after the Bohemian Central Mountains), also referred to as Litoměřice disorder. In particular, during the main phase of tectonic movements increased where cross erzgebirgische and Hercynian major faults, large amounts of basaltic magma on what led to the surface of Egergrabens to extensive volcanism. Since the resulting volcanic rocks are relatively resistant to erosion, they now form the mountains of Doupov Mountains and the Bohemian Central Mountains.

The volcanic complex structure the Egergraben along with some hercynian oriented major faults in several sub-basins: the in its present form geologically relatively young Cheb Basin ( Cheb Basin ) in the southwest, the North Bohemian Basin (Most Basin) in the northeast and the relatively narrow Sokolov Basin ( Sokolov basin) in between. Principle, one can as southwestern and northeastern foothills count for Egergraben system to also Mitterteich Basin in northeastern Bavaria and the Zittau and the Berzdorf - Radmeritzer pool in the border triangle Germany - Czech Republic - Poland.

As reduction areas were the Egergraben or its sub-basins in the Tertiary significant deposition areas. There were extensive river, lake and marsh landscapes in which the present-day North Bohemian lignite deposits formed, which are degraded in Chomutov in the must - basin or in Bogatynia in the Zittau Basin, for example. The sediments also contain a diverse flora and fauna. The fossil site Dolnice in the Cheb Basin is famous for its rich deposits of snakes, lizards and amphibians of the early Miocene, as these groups of vertebrates are much less frequent in most fossil sites same geological age. Another significant frühmiozäne vertebrate archaeological site is "Merkur - North " in the open pit Nastup - Tusimice near Chomutov in the North Bohemian Basin.

In some areas of high geothermal gradient Egergrabens have been observed from 5.5 ° C/100m, which shows that the volcanic activity in the area has not been fully extinguished. The spätvulkanischen appearances include mofettes the moor Soos and the numerous thermal springs, which are among the hottest in Europe, how the Karlovy Vary thermal spring ( Thermal Spring ) with 72 ° C outlet temperature. The occurrence of weak but significant earthquakes in the southwestern portion of the Egergrabens, particularly in the area of ​​Marianske Lazne fault on the eastern edge of the Cheb Basin, also shows that the tectonic movements have not yet been completely stopped.