Rift valley is a linear depression or trough created by the sinking of the intermediate crustal rocks between two or more parallel strike-dip faults. The structure is graben and the accompanying morphological feature is a rift valley.
There are many examples of a rift valley such as Mid-Atlantic Ridges, and the Red Sea Graben, East African Rift Valley and the Rhine Graben.
However, their mode of formation is rather controversial. But it is the most popular belief that the tensional forces are the main cause for the formation of a rift valley.
The rift valley is formed when two large blocks of the earth’s crust move apart. An alternate theory is that of the compressional rift bounded by reverse faults in which the central block is pushed down by the over-thrust marginal masses.
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The East African Rift Valley is the most important one. It extends from the Red Sea and continues for a distance of 300 km toward the south. This rift valley system comprises various graben-like troughs.
There are, of course, separate rift valleys ranging in width from 30 to 60 km. Some of the valley floors are occupied by rivers and lakes. Lake Nyasa, Lake Rudolf and some other lakes are located on the floors of this long rift valley.
In East Africa there are a number of parallel belts of rift valleys extending from north to south which accommodate the great lakes of the region.