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Why do rift valleys often have flat floors?
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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 characterized by their relatively flat floors, a feature primarily attributed to the accumulation of materials over time. Specifically, these floors are leveled by volcanic deposition and the accumulation of marine or lacustrine sedimentation.1
While the steep, mountainous sides of these valleys are formed by the downward displacement of a crustal block between faults—a structure known as a graben—the resulting depression does not remain purely a product of tectonic movement. Instead, the initial trough created by the extension of the Earth’s crust is subsequently filled and smoothed by the deposition of sediments and volcanic materials, which creates the characteristic flat floor observed in many rift systems.21