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Why can ramp valleys look similar to rift valleys?
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tectonic basins and rift valleys
Escarpments of the Great Rift Valley rising above the plain north of Samburu Game Preserve, central Kenya. Beisa oryxes graze in the foreground.
Ramp valleys and rift valleys can appear similar to a casual observer because both landforms are characterized by relatively steep, mountainous sides and flat floors. Because of these shared visual traits, early geological theories incorrectly attributed the origin of rift valleys to the processes that form ramp valleys.12
Despite their similar appearance, these valleys are produced by fundamentally different tectonic processes:
- Rift Valleys: These are formed by crustal extension, where the Earth’s crust fractures and a block of crust drops down into the space created by diverging lithospheric plates. This type of depression is known as a graben.1
- Ramp Valleys: These are formed by horizontal compression, or crustal shortening. They develop when crustal blocks are thrust toward one another and up onto an intervening block, forcing that block downward.12
While both feature steep escarpments, the edges of ramp valleys are generally less sharply defined than those of rift valleys, though the mountains surrounding ramp valleys can be significantly higher.2