Great Escarpment, Southern Africa

[2] 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 lies above 1,000 m (3,300 ft) despite extensive erosion.

It reaches its highest point of over 3,000 m (9,800 ft) where the escarpment forms part of the international border between Lesotho and the South African province of KwaZulu-Natal.

[2][8] Consequently, a thick layer of marine sediment was deposited onto the continental shelf (the lower steps of the original rift valley walls) that surrounds the subcontinent, creating the present-day coastal plain.

[12] Being composed of erosion-resistant quartzitic sandstone, they remained as the less resistant overlying sediments were removed, ultimately to form the parallel formations that protrude from the coastal plain of the south and southwest Cape.

[1][13] The absence of the Great Escarpment for approximately 450 km (280 mi) to the north of Tzaneen (to reappear on the border between Zimbabwe and Mozambique in the Chimanimani Mountains) is due to a failed westerly branch of the main rift that caused Antarctica to start drifting away from southern Africa during the breakup of Gondwana about 150 million years ago.

[9] The eastern portion of the Great Escarpment within the borders of South Africa (see the accompanying map, above) is referred to as the Drakensberg (meaning "Dragon Mountains").

[1][14] The Limpopo, Mpumalanga and Lesotho Drakensberg have hard erosion-resistant upper surfaces and therefore have a very high and rugged appearance, combining steep-sided blocks and pinnacles.

The "Lesotho Mountains" are formed away from the Drakensberg escarpment by erosion gulleys that turn into deep valleys that contain the tributaries that flow into the Orange River.

The Cape Fold Mountains have been re-exposed by erosion of the coastal plain below the Great Escarpment (see "Geological origin", above), after having been covered by sediments originating from an even higher and more extensive range of mountains, comparable to the Himalayas, that developed during the assembly of Gondwana to the south of the present African continent, on the portion of Gondwana called the "Falkland Plateau", the remnants of which are at present located far to the southwest of southern Africa close to southern tip of South America.

An approximate SW-NE cross section through South Africa with the Cape Peninsula (with Table Mountain ) on the far left, and northeastern KwaZulu-Natal on the right is diagrammatic, and only roughly to scale. It shows the major geological structures (coloured layers) that dominate the southern and eastern parts of the country, as well as the relationship between the Central Plateau, the Cape Fold mountains , and the Drakensberg escarpment. The southwestern escarpment (the Roggeberg escarpment) is clearly visible on the left, but is not labelled. The significance and origin of the geological layers can be found under the headings " Karoo Supergroup " and " Cape Supergroup "
This is a stylized illustration of the Southern African Great Escarpment, based particularly on its appearance in the Great Karoo , where thick erosion resistant dolerite sills (represented by the thick black lines in the diagram) generally form the upper, sharp edge of the escarpment; in other parts of the escarpment hard erosion-resistant geological layers similarly form the upper, abrupt edge (see text); note the island remnants of the earlier extent of the plateau on the plain below the escarpment, left behind as the escarpment has gradually eroded farther inland [ 9 ]
A view of the Mpumalanga Drakensberg portion of the Great Escarpment, from God's Window , near Graskop looking south, shows the hard erosion-resistant layer that forms the upper edge of the escarpment that consists of flat-lying quartzite belonging to the Black Reef Formation, which also forms the Magaliesberg mountains near Pretoria. [ 2 ] [ 8 ]