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A graben is a section of crust that has lowered relative to the blocks on either side, which is a result of its bounding faults dipping towards each other. [2] The plural of graben can be either graben or grabens. Graben form low-lying features such as basins and rift valleys. [1] [2] They can be very long relative to their width.
In physical geography and geology, a horst is a raised fault block bounded by normal faults. [1] Horsts are typically found together with grabens . While a horst is lifted or remains stationary, the grabens on either side subside . [ 2 ]
Graben often occur side by side with horsts. Horst and graben structures indicate tensional forces and crustal stretching. Graben are produced from parallel normal faults, where the displacement of the hanging wall is downward, while that of the footwall is upward. The faults typically dip toward the center of the graben from both sides.
Lifted type block mountains have two steep sides exposing both sides scarps, leading to the horst and graben terrain seen in various parts of Europe including the Upper Rhine valley, a graben between two horsts – the Vosges mountains (in France) and the Black Forest (in Germany), and also the Rila – Rhodope Massif in Bulgaria, Southeast ...
With crustal extension, a series of normal faults which occur in groups, form in close proximity and dipping in opposite directions. [4] As the crust extends it fractures in series of fault planes, some blocks sink down due to gravity, creating long linear valleys or basins also known as grabens, while the blocks remaining up or uplifted produce mountains or ranges, also known as horsts.
This uplift caused massive crustal extension leading to horst and graben structures associated with normal, extensional, faults. The uplift ended in collapse around 25 Mya into the Afar depression covering more than 200,000 km 2 (77,000 sq mi) and spreading at a rate of 6 to 17 millimetres per year (0.24 to 0.67 in/year). [1]
For example, the islands of Elba is an exhumed granitic batolith over thinned continental crust, while Stromboli is a stratovolcano originated atop newly formed oceanic crust. The most recent volcanic island is Ferdinandea near Sicily, once emerged with the 1891 offshore eruption but quickly eroded below the water, remaining as the Graham Bank .
The plains are interspersed by the horst and graben structures, believed to break the Pannonian Sea surface as islands. The greatest concentration of ground at relatively high elevations is found in Lika and Gorski Kotar areas in the Dinaric Alps, but such areas are found in all regions of Croatia to some extent.