Mountain Ranges, Deserts and Landforms of South Africa

Geography

Drainage of the desert is by dry black valleys, seasonally inundated pans, and the large salt pans of the Makgadikgadi Pan in Botswana and Etosha Pan in Namibia. The only permanent river, the Okavango, flows into a delta in the northwest, forming marshes that are rich in wildlife. Ancient dry riverbeds—called Ouramba—traverse the central northern reaches of the Kalahari and provide standing pools of water during the rainy season.

A semi-desert, with huge tracts of excellent grazing after good rains, the Kalahari supports more animals and plants than a true desert, such as the Namib Desert to the west. There is little rainfall, and the summer temperature is very high.

Climate

The climate is sub-humid rather than semi-arid in the north and east, where the dry forests, savannahs, and salt lakes prevail. South and west, where the vegetation is predominantly xeric savanna or even a semi-desert, the climate is "Kalaharian" semi-arid. The Kalaharian climate is subtropical: average annual temperature greater than or equal to 18 °C (64 °F), at peaks reaching 40 °C (104 °F) and above, with mean monthly temperature of the coldest month strictly below 18 °C (64 °F), and is semi-arid with the dry season from April to September, the coldest six months of the year. It is the southern tropical equivalent of the Sahelian climate with the wet season during summer.

History

The Kalahari Desert was not always an arid environment. Geological and paleoclimatic evidence suggests that during parts of the late Pleistocene, the region experienced significantly wetter and cooler conditions. Fossil flora and fauna from Gcwihaba Cave in northwestern Botswana indicate that the area supported more abundant vegetation and permanent water sources between roughly 30,000 and 11,000 Before Present (BP), with the most humid period occurring after 17,500 BP. Sediment cores, pollen records, and fossilized animal remains from other parts of the Kalahari, including the Makgadikgadi Pans and Okavango Basin, corroborate these findings, showing evidence of large paleolakes and river systems that once covered much of what is now desert.

Geography

The highest peak is Thabana Ntlenyana, at 3,482 m (11,424 ft). Other notable peaks include Mafadi at 3,450 metres (11,320 ft), Makoaneng at 3,416 metres (11,207 ft), Njesuthi at 3,408 metres (11,181 ft), Champagne Castle at 3,377 metres (11,079 ft), Giant's Castle at 3,315 metres (10,876 ft), Ben Macdhui at 3,001 metres (9,846 ft), and Popple Peak at 3,331 metres (10,928 ft), all of these are in the area bordering on Lesotho, which contains an area popular for hikers, Cathedral Peak. North of Lesotho the range becomes lower and less rugged until entering Mpumalanga where the quartzite mountains of the Transvaal Drakensberg are loftier and more broken and they form the eastern rim of the Transvaal Basin, the Blyde River Canyon lying within this stretch.

Geology

The Great Escarpment is composed of steep rift valley walls formed around a bulging of continental crust during the breakup of southern Gondwana that have since eroded inland from their original positions near the southern African coast, and its entire eastern portion (see the accompanying map) constitutes the Drakensberg. The Drakensberg terminate in the north near Tzaneen at about the 22° S parallel. 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.

Ecology

The high treeless peaks of the Drakensberg (from 2,500 m (8,200 ft) upward) have been described by the World Wide Fund for Nature as the Drakensberg alti-montane grasslands and woodlands ecoregion. These steep slopes are the most southerly high mountains in Africa, and being farther from the equator provide cooler habitats at lower elevations than most mountain ranges on the continent. High rainfall generates many mountain streams and rivers, including the sources of the Orange River, southern Africa's longest, and the Tugela River.

These mountains also have the world's highest waterfall, the Tugela Falls (Thukela Falls), which has a total drop of 947 m (3,107 ft) (Venezuela's Angel Falls is also a candidate for highest waterfall).

Geology

The Witwatersrand plateau consists of a 5000-to-7000-metre-thick (3.1–4.3 mi) layer of mainly sedimentary rocks laid down over a period of about 260 million years, starting approximately 2.97 billion years ago. The entire series of rocks, known as the "Witwatersrand Supergroup", consists of very hard erosion resistant quartzites, banded ironstones and some marine lava deposits, interspersed with softer, more easily eroded tillites, mudstones and conglomerates. The oldest rocks (laid down 2.97 billion years ago) form the northern scarp of the Witwatersrand plateau; the youngest (laid down 2.71 billion years ago) are those that form the southern edge of the plateau.

Gold is found in the conglomerate strata of the younger members of the Supergroup, locally referred to as banket.

History

Although gold had been discovered in various locations in South Africa, such as Barberton and Pilgrim's Rest, as well as at several sites near the Witwatersrand, these were alluvial concentrates in contemporary rivers, or in quartz veins, in the form that gold had always been found elsewhere on earth. When George Harrison, probably accompanied by George Walker, found gold on the farm Langlaagte, 5 km (3 mi) west of what would become the city of Johannesburg, in an outcrop of conglomerate rocks, in February 1886, they assumed that this was alluvial gold in an old riverbed, that had been tilted as a result of earth movements.

Description

Geologically, the range is considered a monocline; part of a rifted volcanic margin. The Lebombo monocline was aligned with the Explora Escarpment off-shore Dronning Maud Land, Antarctica, before the break-up of Gondwana. The Lebombo monocline strikes N-S and dips to the east. It is composed of a sequence of Jurassic age volcanic rock, both basaltic lavas and rhyolitic flows and tuffs. The sequence rests on essentially horizontal Karoo Supergroup sedimentary rocks of the Kalahari Craton to the west and is overlain by Cretaceous to recent sediments to the east. The alternating resistant rhyolite and easily eroded basalts produce a series of parallel sharp cuesta ridges separated by savanna plains.