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Why does most of the western branch of the East African Rift System have few volcanoes?

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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.

The western branch of the East African Rift System lacks extensive volcanism primarily because it is not associated with the large-scale crustal doming and asthenospheric upwelling that characterize the eastern branch.1

In the eastern branch, the formation of the rift is linked to the upwelling of hot material from the asthenosphere, which pushes up and heats the overlying lithosphere, causing it to expand and stretch. This process facilitates the rise of magma to the surface, resulting in significant volcanic activity.1

Conversely, rift valleys that lack these large domes—often created by distant tectonic forces rather than localized mantle upwelling—typically exhibit little to no volcanism. While the eastern rift in Ethiopia and Kenya and a small section of the western rift in Congo (Kinshasa) feature volcanic activity, the majority of the western rift, extending from Uganda through Lake Tanganyika and Lake Nyasa, does not.1