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

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Map of East Africa showing political boundaries, major cities, and capitals, overlaid with shaded elevation zones. Higher elevations are concentrated in Ethiopia, Kenya, and Tanzania, while lower elevations follow the coastal regions along the Indian Ocean and extend into Somalia and Mozambique. Major lakes such as Victoria, Tanganyika, and Rudolf are also marked.
Eastern Africa

Many lakes in the East African Rift Valley are long and deep because they occupy rift valleys, which are elongated troughs formed by the subsidence of the Earth's crust between faults.12

This geological process occurs as lithospheric plates diverge, causing blocks of the crust to drop down. The resulting landscape features steep, fjordlike walls and deep basins that can extend well below sea level. For example, Lake Tanganyika reaches depths of over 4,700 feet, making it one of the deepest lakes in the world.3214

While many of these lakes are characterized by their depth, some are relatively shallow due to the accumulation of thick layers of sediment on the valley floors. Additionally, the specific depth and shape of these lakes are influenced by the tectonic history of the region, including the formation of volcanoes that can block drainage and shape shorelines.5