Great Escarpment, Southern Africa

The Great Escarpment is a major geological formation in Africa that consists of steep slopes from the high central Southern African plateau downward in the direction of the oceans that surround Southern Africa on three sides. While it lies predominantly within the borders of South Africa, in the east it extends northwards to form the border between Mozambique and Zimbabwe, continuing on beyond the Zambezi River valley to form the Muchinga Escarpment in eastern Zambia. and in the west it continues northwards into Namibia and Angola.

Different names are applied to different stretches of the Great Escarpment, the most well-known section being the Drakensberg (diagram on the right). The Schwarzrand and edge of the Khomas Highland in Namibia, as well as the Serra da Chela in Angola, are also well-known names.

About 180 million years ago, a mantle plume under southern Gondwana caused bulging of the continental crust in the area that would later become southern Africa. Within 10 – 20 million years rift valleys formed on either side of the central bulge, which became flooded to become the proto-Atlantic and proto-Indian Oceans. The stepped steep walls of these rift valleys formed escarpments that surrounded the newly formed Southern African subcontinent.

With the widening of the Atlantic, Indian and Southern Oceans, Southern Africa became tectonically quiescent. Earthquakes rarely occur, and there has been no volcanic or orogenic activity for about 50 million years. This resulted in an almost uninterrupted period of erosion, continuing to the present, which shaved off a layer, many kilometers thick, from the surface of the plateau. A thick layer of marine sediment was consequently deposited onto the continental shelf (the lower steps of the original rift valley walls) which surrounds the subcontinent.

During the past 20 million years, Southern Africa has experienced further massive uplifting, especially in the east, with the result that most of the plateau, despite the extensive erosion, lies above 1,000 metres (0.62 mi), tilted so that it is at its highest in the east, sloping gently downwards towards the west and south. Thus the altitude of the edge of the eastern escarpments is typically in excess of 2,000 metres (1.2 mi). It reaches its highest point (over 3,000 metres (1.9 mi)) where the escarpment forms the Lesotho – KwaZulu-Natal international border.

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Wikipedia