Fault Block Mountains

Pressure and tension caused by plate movement, in the Earth’s crust, sometimes produce fracture or crack in rocks and then form huge faults.

Tugging movements make some blocks of land slip down along faults. Other blocks are raised up along the faults, producing steep slopes called fault scarps. Such uplifted blocks of land are called Fault-block Mountains or block mountains.

Such movements occurred in eastern Africa. Huge blocks of land sank down between long faults to form the East African rift valley, the world’s largest rift valley. Uplifting raised up the Ruwenzori range, a block mountain bordering the rift valley.

The Sierra Nevadas, in the western United States are a mountain range, which, was created when a block of land was pushed upwards along a fault. This produced a slope or fault scarp. This rises steeply above the land on the other side of the fault. From the west the Sierra Nevada Mountains ascend rather gently, but from the East, the huge broken plates shoot up rather rapidly from the Earth.

When blocks of land are pushed upwards, the rocks are displaced, such that the rock strata on one side of the fault do not match with the rock strata on the other side.