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rift valley

rift valley
An elongated valley formed by the depression of a block of a planet's crust between two faults or groups of approximately parallel faults (see also graben). As the faults move apart, the central area between them slips down. The friction produced by this slippage can cause earthquakes and also melt rock which is then released on the surface from volcanoes. Large and well-known rift valleys include the Great Rift Valley in East Africa, the Rheingraben, and Valles Marineris on Mars.

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