OLDING AND FAULTING IN THE EARTH ?S CRUST The African Rift Valley – A landscape formed by faulting
The African Rift Valley is a landform made by faulting. This huge rift valley is visible from space as it is the world's largest surface fracture.
In the African Rift Valley, a newly-forming constructive plate boundary above a hotspot is in the process of splitting the African plate into two new separate plates. Geologists generally refer to these plates-to-be as the ‘Nubian plate’ (the current African plate) and the Somali plate.
The African Rift Valley formed during the last 20 million years due to the presence of a hotspot beneath the crust. The hotspot is causing the African continent to bulge and stretch and split. As the crust is pulled apart, huge parallel cracks called normal faults are formed. In the zone these faults extend over 6,000 km from the Red Sea in the north to Mozambique in the south.
As the crust in the rift valley is stretched, huge blocks of crust sink between the normal faults forming a large flat-floored rift valley or graben.
The land has subsided so much in places that it lies more than 153 m below sea level. The fault lines are marked by high fault scarps or escarpments rising steeply several thousand metres from the valley floor.
At the same time magma is forced up to the surface in places and erupts, forming volcanoes, e.g. Mount Kilimanjaro and Mount Kenya.
The African Rift Valley varies in width from 40 to 100 km and is widening at a rate of up to 4 mm per year.
Many lakes have also formed in the floor of the rift valley. The deepest is Lake Tanganyika which is nearly 1,420 m deep.
Persian Gulf
River Nile
ARABIAN PLATE
AFRICAN PLATE
Equator Kilimanjaro
Lake Victoria
Lake Tanganyika
Plate boundaries East African Rift Zone
Active volcano MOZAMBIQUE Fig. 16 Map of East Africa 61