The Karoo ( ; likely from Khoikhoi (also known as Khoekhoegowab/Namagowab or Hottentot language) word ) is a semidesert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its extent is also not precisely defined. The Karoo is partly defined by its topography, geology and climate, and above all, its low rainfall, arid air, cloudless skies, and extremes of heat and cold. The Karoo is also known for the exposure of fossiliferous rocks of the Karoo Supergroup, which record in detail ecological changes in the region when it formed part of southern Pangaea from the Middle Permian to the Early Jurassic, around 270 to 200 million years ago.
The Karoo formed an almost impenetrable barrier to the interior from Cape Town, and early adventurers, explorers, hunters, and travelers on the way to the Highveld unanimously denounced it as a frightening place of great heat, great frosts, great floods, and great droughts. Today, it is still a place of great heat and frosts, with an annual rainfall of between . On some of the surrounding mountains it can be higher than on the plains. However, underground water is found throughout the Karoo, which is tapped by boreholes, making permanent settlements and sheep farming possible.
The xerophytic vegetation consists of aloes, mesembryanthemums, crassulas, euphorbias, stapelias, and desert ephemerals, spaced or more apart, becoming very sparse going northwards into Bushmanland and, from there, into the Kalahari Desert. The driest region of the Karoo, however, is its southwestern corner, between the Great Escarpment and the Cederberg-Skurweberg mountain ranges, called the Tankwa Karoo, which receives only of rain annually. The eastern and north-eastern Karoo are often covered by large patches of grassland. The typical Karoo vegetation previously supported large game, sometimes in vast herds.Conolly, D. (1992). Conolly's Guide to Southern Africa. (5th Ed.) pp. 106–117. Conolly Publishers, Scottburgh.
Today, sheep thrive on the xerophytes, though each sheep requires about of grazing to sustain itself.
Divisions The Karoo is divided into the Great Karoo and the Klein Karoo. The Klein Karoo is delimited in the south by the Outeniqua–Langeberg Mountains that run east–west parallel to the coast, and in the north by the Swartberg Mountain Range that also runs east–west. The Great Karoo lies to the north of the Swartberg.
Great Karoo
The only sharp and definite boundary of the Great Karoo is formed by the most inland ranges of Cape Fold Mountains to the south and south-west. The extent of the Karoo to the north is vague, fading gradually and almost imperceptibly into the increasingly arid Bushmanland towards the north-west. To the north and north-east, it fades into the savannah and grasslands of Griqualand West and the Highveld.Norman, N., Whitfield, G. (2006) Geological Journeys. p. 206-223, 243–247, 252–273, 300–311. Struik Publishers, Cape Town. The boundary to the east grades into the grasslands of the Eastern Midlands. The Great Karoo is itself divided by the Great Escarpment into the Upper Karoo (generally above ) and the Lower Karoo on the plains below at . A great many local names, each denoting different subregions of the Great Karoo, exist, some more widely, or more generally, known than others. In the Lower Karoo, going from west to east, they are the Tankwa Karoo, the Moordenaarskaroo, the Koup, the Vlakte, and the Camdeboo Plains. The Hantam, Kareeberge, Roggeveld, and Uweveld are the better known subregions of the Upper Karoo, though most of it is simply known as the Upper Karoo, especially in the north.
Klein Karoo The Klein Karoo's boundaries are sharply defined by mountain ranges to the west, north, and south. The road between Uniondale and Willowmore is considered, by convention, to form the approximate arbitrary eastern extremity of the Klein Karoo. Its extent is much smaller than that of the Great Karoo. It is called the Klein Karoo, Afrikaans for Little Karoo.
Geography Great Karoo The Great Karoo straddles the 30° S parallel on the west of the continent, in a similar position to other semidesert areas on earth, north and south of the equator. It is in the rainfall shadow of the Cape Fold Mountains along the western coastline. The western "Lower Karoo" (the Tankwa Karoo and Moordenaarskaroo) contain remnants of the Cape Fold MountainsGeological Map of South Africa, Lesotho and Swaziland. (1970). Council for Geoscience, Geological Survey of South Africa. (e.g. the Witteberg and Anysberg Mountains) which give it a moderate hilly appearance, but further east, the Lower Karoo becomes a monotonously flat plain. The "Upper Karoo" has been intruded by dolerite sills (see below), creating multiple flat-topped hills, or Karoo Koppies, which are iconic of the Great Karoo.
The vegetation of the Upper is similar to the Lower Karoo, so few people make a distinction between the two.
The main highway (the N1) and railway line from Cape Town to the north enter the Lower Karoo from the Hex River Valley just before Touws River and follow a course about south of the Great Escarpment up to Beaufort West. Thereafter, they gradually ascend the Great Escarpment along a broad valley to Three Sisters on the Central Plateau and the Upper Karoo.
Turning north from the N1 between Touws River and Beaufort West, at Matjiesfontein, the road ascends the Great Escarpment through the Verlatenkloof Pass to reach Sutherland, at above sea level, which is reputedly the coldest town in South Africa with average minimum temperatures of during winter.Bulpin, T.V. (1992). Discovering Southern Africa. pp. 271–274, 301–314. Discovering Southern Africa Productions, Muizenberg. Parts of the eastern Mpumalangan Highveld do at times experience lower temperatures than Sutherland, but not as consistently as Sutherland does. Snowfall is not infrequent during the southern winter months. The South African Astronomical Observatory has an emplacement of telescopes about east of the town, on a small plateau above sea level, and is home to the Southern African Large Telescope, the largest optical telescope in the Southern Hemisphere. To the north, still on the Plateau, and north-west of Carnarvon, seven radio dishes form part of the Square Kilometer Array which will, 2500 in total, be scattered in other parts of South Africa and Australia, to survey the southern skies at radio frequencies. Our galaxy, the Milky Way, one of the main targets of this enterprise, is best viewed from the Southern Hemisphere.The Great Karoo . Accessed 2014-04-24. The Upper Karoo is indeed an ideal site for an astronomical observatory. This is not only because of the clear skies, absence of artificial lights, and high altitude, but also because it is tectonically completely inactive (meaning that there are no fault lines or volcanoes nearby, and no earth tremors or earthquakes occur, even at great distances).
Klein Karoo
The Klein Karoo is separated from the Great Karoo by the Swartberg Mountain range. Geographically, it is a long valley, only wide, formed by two parallel Cape Fold Mountain ranges, the Swartberg to the north, and the continuous Langeberg-Outeniqua range to the south. The northern strip of the valley, within from the foot of the Swartberg mountains is least karoo-like, in that it is a well-watered area both from the rain and the many streams that cascade down the mountain, or through narrow defiles in the Swartberg from the Great Karoo. The main towns of the region are situated along this northern strip of the Klein Karoo: Montagu, Barrydale, Ladismith, Calitzdorp, Oudtshoorn, and De Rust, as well as such well-known mission stations such as Zoar, Amalienstein, and Dysselsdorp.
The southern wide strip, north of the Langeberg range, is as arid as the western Lower Karoo, except in the east, where the Langeberg range (arbitrarily) starts to be called the Outeniqua Mountains.
The Klein Karoo can only be accessed by road through the narrow defiles cut through the surrounding Cape Fold Mountains by ancient, but still flowing, rivers. A few roads traverse the mountains over passes, the most famous and impressive of which is the Swartberg Pass between Oudtshoorn in the Klein Karoo and Prince Albert on the other side of the Swartberg mountains in the Great Karoo. Also, the main road between Oudtshoorn and George, on the coastal plain, crosses the mountains to the south via the Outeniqua Pass. The only exit from the Klein Karoo that does not involve crossing a mountain range is through the long, narrow Langkloof valley between Uniondale and Humansdorp, near Plettenberg Bay.
Geology of the Karoo The Great Karoo
In geological terms, the Karoo Supergroup refers to an extensive and geologically recent (180–310 million years old) sequence of sedimentary and igneous rocks, which is flanked to the south by the Cape Fold Mountains, and to the north by the more ancient Ventersdorp Lavas, the Transvaal Supergroup and Waterberg Supergroup. It covers two-thirds of South Africa and extends in places to below the land surface, constituting an immense volume of rocks which was formed, geologically speaking, in a short period of time. Although almost the whole of the Great Karoo is situated on Karoo Supergroup rocks, the geological Karoo rocks extend over a very much larger area, both within South Africa and Lesotho, but also beyond its borders and onto other continents that formed part of Gondwana.
Geological history of the Karoo Supergroup
The Karoo Supergroup was formed in a vast inland basin starting 320 million years ago, at a time when that part of Gondwana which would eventually become Africa, lay over the South Pole.Jackson, A.A., Stone, P. (2008). Bedrock Geology UK South. p. 6-7. Keyworth, Nottingham: British Geological Survey. Icebergs that had calved from the glaciers and ice sheets to the north deposited a thick layer of mud containing dropstones of varying origins and sizes into this basin. This became the Dwyka Group consisting primarily of tillite, the lowermost layer of the Karoo Supergroup. As Gondwana drifted northwards, the basin turned into an inland sea with extensive swampy deltas along its northern shores. The peat in these swamps eventually turned into large deposits of coal which are mined in KwaZulu-Natal and on the Highveld. This thick layer is known as the Ecca Group, which is overlain by the thick Beaufort Group, laid down on a vast plain with Mississippi-like rivers depositing mud from an immense range of mountains to the south. Ancient reptiles and amphibians prospered in the wet forests, and their remains have made the Karoo famous amongst palaeontologists. The first of these Karoo fossils was discovered in 1838 by Scotish born Andrew Geddes Bain at a road cutting near Fort Beaufort. He sent his specimens to the British Museum, where fellow Scotsman Robert Broom recognised the Karoo fossils' mammal-like characteristics in 1897.
After the Beaufort period, Southern Africa (still part of Gondwana) became an arid sand desert with only ephemeral rivers and pans. These sands consolidated to form the Stormberg Group, the remnants of which are found only in the immediate vicinity of Lesotho. Several dinosaur nests, containing eggs, some with dinosaur fetal skeletons in them, have been found in these rocks, near what had once been a swampy pan. in
Finally, about 180 million years ago, volcanic activity took place on a titanic scale. This brought an end to a flourishing reptile evolution. Some of the, mainly pre-dinosaur, reptile genera of the Karoo which became extinct are shown in the list below.