Rift valley

A long, narrow depression formed as Earth’s crust stretches and blocks of crust drop along faults. Rift valleys can develop on continents or along mid-ocean ridges.

Normal fault: A fault in which the block above the fault plane moves downward relative to the block below it. Stretching commonly drops crustal blocks along normal faults, creating the valley’s steep sides.
East African Rift: A system of active continental rifts extending through eastern Africa. Its valleys and escarpments are prominent examples of continental rifting.
Plate tectonics: The theory that Earth’s outer shell is divided into moving plates whose interactions shape the planet’s surface. Divergent plate motion supplies the regional forces that open many rift valleys.
Rift lake: A lake occupying a basin formed by crustal extension and fault-related subsidence. Subsided rift basins can collect water and form long, deep lakes.
Graben: An elongated block of crust that has subsided between two roughly parallel faults. A graben is the structural block that forms many rift-valley floors.
Baikal Rift Zone: An active continental rift system in Siberia that contains Lake Baikal. It shows how rifting can create a deep lake basin within a continent.
Divergent boundary: A boundary where two tectonic plates move away from one another. Rift valleys commonly develop above divergent boundaries or incipient ones.
Rift volcanism: Volcanic activity associated with crustal extension, thinning, and magma ascent in a rift zone. Faulting and thinning can provide pathways for magma to reach the surface.
Horst: An uplifted block of crust bounded by faults, often standing between subsided blocks. Horsts can form the raised shoulders beside a rift valley.
Rio Grande Rift: A continental rift extending from Colorado through New Mexico into northern Mexico. Its broad basins and fault-block ranges expose the structure of an inland rift.

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