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How did the East African Rift System form highlands and volcanic mountains?

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A car drives along the Trans-Canada Highway with Mount Sir Donald's sharp, snow-capped peak rising above forested slopes in the Selkirk Mountains, British Columbia. — mountain Mount Sir Donald in the Selkirk Mountains, British Columbia, looms above a segment of the Trans-Canada Highway.

The East African Rift System creates highlands and volcanic mountains through the complex interaction of tectonic divergence and mantle activity.

Formation of Highlands

The high plateaus adjacent to the rift are largely the result of large-scale crustal doming. As hot material from the asthenosphere upwells, it pushes the overlying lithosphere upward and heats it, causing the crust to expand and bulge. This process elevates the surrounding landscape, creating the high plateaus that border the rift valley. Additionally, some mountainous relief is formed by horsts—blocks of crust bounded by faults that remain at high elevations as adjacent valley floors drop.1

Formation of Volcanic Mountains

Volcanic activity in the region is driven by the thinning of the lithosphere as tectonic plates separate. This thinning allows hot material from the mantle to rise to shallow depths, where it can erupt at the surface. These rift volcanoes are often more complex than those at mid-ocean ridges because the rising magma assimilates continental crust, leading to a wider variety of rock types and more explosive eruptions. This extensive volcanism has produced significant massifs, including Kilimanjaro and Mount Kenya.123