A rift valley is a linear-shaped lowland between several highlands or mountain ranges created by the action of a geologic rift or fault. A rift valley is formed on a divergent plate boundary, a crustal extension, a spreading apart of the surface, which is subsequently further deepened by the forces of erosion. When the tensional forces were strong enough to cause the plate to split apart, a center block dropped down between the two blocks at its flanks, forming a graben. This drop of the center creates the nearly parallel steeply dipping walls of a rift valley when it is new. This feature is the beginning of the rift valley, but as the process continues, the valley widens, until it becomes a large basin, that fills with sediment from the rift walls and the surrounding area. One of the most well known examples of this process is the East African Rift. Rifts can occur at all elevations, from the sea floor to plateaus and mountain ranges. They can occur in continental crust or in oceanic crust. Rift valleys are often associated with a number of adjoining subsidiary or co-extensive valleys, which are typically considered part of the principal rift valley geologically. The most extensive rift valley is located along the crest of the mid-ocean ridge system and is the result of sea floor spreading. Examples of this type of rift include the Mid-Atlantic Ridge and the East Pacific Rise. This video is targeted to blind users. Attribution: Article text available under CC-BY-SA Creative Commons image source in video

• published: 06 Nov 2014
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