Landforms produced when the crust fractures along a fault and blocks of rock move up or down relative to one another, raising horsts (block mountains) and dropping grabens (rift valleys).
- A fault is a fracture along which displacement occurs; tensional (pulling apart) and compressional (pushing together) forces both produce faults.
- An uplifted block between two faults is a horst, giving a block mountain; a down-dropped block is a graben, giving a rift valley.
- Indian examples of block mountains include the Vindhya and Satpura ranges; the Narmada and Tapi rivers flow through rift valleys between them.
- The East African Rift Valley (running through Kenya, Ethiopia, and others) is the classic large rift; the Rhine rift valley in Europe is another.
- The Sahyadri (Western Ghats) is essentially the faulted edge of the Deccan plateau rather than a fold mountain.
The horst versus graben pair, the Narmada and Tapi as rift-valley rivers, and the Vindhya and Satpura as block mountains are frequently tested static facts.
Horst (uplifted block, block mountain) versus graben (down-dropped block, rift valley); block mountains (faulting) versus fold mountains (compression); the Narmada and Tapi flow westward through rift valleys.
Faulting raises horsts (block mountains like the Vindhyas) and drops grabens (rift valleys like the Narmada trough).