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How does a ramp valley form?

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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.

A ramp valley is a type of tectonic depression formed through horizontal crustal compression, or crustal shortening, rather than the crustal extension that creates rift valleys.12

The formation process occurs when blocks of the Earth's crust are thrust toward one another and pushed up onto an intervening crustal block. This intervening block is then forced downward by the weight of the encroaching material, creating a valley. Because the surrounding margins are pushed over the valley floor, this process also results in the formation of high mountains adjacent to the depression.21

While ramp valleys and rift valleys may appear similar to a casual observer—both featuring steep sides and flat floors—they are distinct in their origin. Ramp valleys are characterized by escarpments that are generally less sharply defined than those of rift valleys, though the mountains surrounding a ramp valley can be higher. A notable example of a ramp valley is the Turfan Depression in western China.2