ATTERNS AND PROCESSES IN THE PHYSICAL ENVIRONMENT 4.4 Landscapes associated with faults Fault scarp Rift valley
Normal faults Sinking
Stretching of crust Stretching of crust Fig. 13 Exam Diagram: Rift valleys
Rift valleys (graben) A rift valley, or graben, is formed when a block of land slips down between sets of parallel normal faults. This is due to stretching of the crust. Lough Neagh and the lower Bann valley occupy such a rift valley. Larger rift valleys occur in Germany, such as the Rhine
Rift Valley between the Vosges and Black Forest Mountains. The Midland Valley of Scotland is another example.
Block mountain
Fault scarp
Block mountains (horsts) Uplift Reverse fault Compression of crust Compression of crust Fig. 14 Exam Diagram: Block mountains Doming
Oldest formation exposed on the surface
Youngest formation
Dome mountains are the result of a great amount of melted rock pushing its way up under the earth. The crust is heaved upward, without folding or faulting, into a rounded dome. Weathering and erosion attack the upland formed by the dome, often exposing the igneous rock at the heart of the dome mountains. Dome mountains are common in North America, e.g. the Black Mountains of South Dakota.
A block mountain (horst) is a block of land left standing between two reverse faults e.g. Vosges and Black Forest mountains. The Ox Mountains of Sligo were formed in this way. Here a block of gneiss was pushed up between reverse faults in limestone and conglomerate rocks.