Normal faults develop in areas where the land is
becoming thinner and stretching as forces within the Earth pulls the land
apart. Tension in the crust increases until the rocks break. One block of land
slips downward in relation to the other block of land. A fault plane separates
the fault blocks.
Normal fault with the fault blocks on the right dropping downward Myrna Martin
A normal fault will have a hanging wall and a footwall. The term footwall is derived from miners finding mineral deposits where inactive faults have been "filled in" with mineral deposits at their feet.
The hanging wall is the side of the fault above the fault plane where the ore deposit is located. When the ore erodes off the hanging wall it falls down onto the ground of the footwall where the miners were standing.
East Africa Rift System
The East Africa Rift System is a zone of active volcanoes and faults. The faults have created a series of rift valleys in Eastern Africa. The faulting extends more than 3000 km (1865 miles) from Ethiopia in the north to Zambezi in the south. The African Plate is in the process of splitting apart in this area forming many grabens.
Parallel faults can develop when land is pulling apart. The block of land in between the two parallel faults drops down creating a valley. Grabens are valleys that develop between these parallel faults. The name graben is a German word for grave.
Land dropping down in this rift area
The area where the grabens are located contain many lakes with lake bottoms below sea level. Lake Tanganyika is located in the area and is the second largest freshwater lake on Earth. It is possible the area may someday become an ocean if the African Plate continues to split apart.
Basin and Range areas in Africa, Mexico and the United States are examples of places where the continental crust is thinning. The land is pulling apart in some areas and other areas it is shortening. The result is a series of mountain ranges separated by rift valleys.
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