Eastern Rift Valley

The Gregory Rift is the eastern branch of the East African Rift fracture system. The rift is being caused by the separation of the Somali plate from the Nubian plate, driven by a thermal plume. Although the term is sometimes used in the narrow sense of the Kenyan Rift, the larger definition of the Gregory Rift is the set of faults and grabens extending southward from the Gulf of Aden through Ethiopia and Kenya into Northern Tanzania, passing over the local uplifts of the Ethiopian and Kenyan domes. Ancient fossils of early hominins, the ancestors of humans, have been found in the southern part of the Gregory Rift.

The Gregory Rift is named in honour of the British geologist John Walter Gregory who explored the geology of the rift in 1892-93 and 1919.

The Gregory Rift lies within the Mozambique belt, often considered to be the remains of an orogenic system similar to the Himalayas. This belt runs from Ethiopia through Kenya, Tanzania and Mozambique. The rift is widest at the northern end in the Afar region, narrowing to a few kilometers in northern Tanzania, then splaying out in the North Tanzania Divergence. The Gregory Rift has shoulders rising over 3,000 metres (9,800 ft) above sea level, 1,000 metres (3,300 ft) above the inner part of the graben. The Tanzanian portion includes Mount Kilimanjaro, the highest mountain in Africa, and the huge caldera of Ngorongoro. This portion also contains Ol Doinyo Lengai, the world's only active carbonatite volcano.

...
Wikipedia