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How do normal faults create the steep sides of 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.

Rift valleys are formed by the extension of the Earth's crust, which causes the brittle rock to fracture and create normal faults. These faults are characterized by a steep dip angle, typically between 45° and 90°.1

The steep sides of a rift valley are created through the vertical displacement along these faults. As lithospheric plates or crustal blocks diverge, the hanging wall—the block of rock positioned above the fault—slides downward relative to the footwall. This downward movement of the hanging wall creates a depression known as a graben, while the adjacent, relatively stationary or rising blocks form the steep, mountainous margins of the valley.123

In many cases, these faults act as the primary boundaries of the valley, with the valley floor dropping thousands of meters below the surrounding plateaus. While some rift valleys are symmetrical with steep walls on both sides, others are asymmetrical, featuring one major steep fault-bounded wall and a gentler side formed by the tilting or flexing of the lithosphere.31