Why are many lakes in the East African Rift System long and deep?

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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.

Many lakes in the East African Rift System are long and deep because they occupy basins formed by grabens—large, downdropped blocks of the Earth's crust created by tectonic activity.1

These rift valleys form at divergence zones where lithospheric plates are pulling apart. As the crust stretches and thins, segments of the surface subside between normal faults, creating elongated, steep-walled troughs. Because these depressions are created by the downward movement of crustal blocks rather than by erosion, they are naturally deep and often fjordlike, with some lake floors extending well below sea level.234