An Introduction to Botswana
Geology and Geography
The country is located in the Southern African region and the northern two thirds lie within the tropics. The Tropic of Capricorn is situated between Gaberone and Francistown. Botswana is roughly the size of France – 581,730km2. The extreme distance from north to south is about 1 100 km and from east to west just under 1 000km. The population is about 1.4 million, one of the lowest densities in Africa, with eighty percent of the people residing in the eastern third of the country. The distribution of people is due to the Kalahari to the west, an inhospitable area with limited surface water and secondly, the historical political organisation of the Tswana was such that central villages were surrounded by satellite villages, not too far from the central community. The main geographical features of Botswana is the Kalahari, covering about senventy to eighty percent of the country, The Okavango Delta, covering about 15 000km2, the Makgadikgadi Pans, covering about 12 000km2, the Chobe River and Linyanti Swamp, which form the northern boundary. The Hardveld in the east, where the landscape is decorated with sandstone,
granite and dolerite outcrops is bordered by the Sashe and Limpopo rivers. The Tsodillo Hills and the Drotsky’s Caverns in the north- west is located in the north of the country. All these areas are fully or partially incorporated into National Parks, Game Reserves or National Monuments.
About eighty percent of Botswana consist of Kalahari sands. Millions of years ago, the super continent – Gondwanaland – started breaking up, leaving Africa as a lone standing continent. Soon after this isolation, Africa was uplifted and three major basins was formed – the Chad basin in the north, the Congo basin in central Africa, and The Kalahari basin in the south. The Kalahari is the largest continouos stretch of sand in the world, covering some 2 500km2 from the orange river in the South, to the tropical forests in Zaire. The continent moved southwards causing the climate to become dry. A further violent activity took place, resulting in the formation of the Great Rift of Africa, which stretches from The Red Sea for some 5 000 km south along the east of the continent, ending in the Okavango Delta in Botswana. This raised the continent further, restricting moist air,
resulting in even drier conditions. Then, a few millions years later, the glaciation of Antartica caused further drought, by sucking up the moist air in the southern hemisphere and turning it into ice. Before the breakup of Gondwanaland, immense amounts of basaltic lavas were poured into the earth’s surface, causing Gondwanaland to be covered in vast areas of molten rock - these lavas can be as deep as 9km in places, such as in Kwa Zulu Natal in South Africa. Karoo lavas underlie most of the Kalahari sands and about half of Botswana. The rocks protrude in places and are evident along the eastern border of the country, especially in the Tuli area. There are also isolated outcrops in the west. After the break up of the super continent, geological activity quietened down and during this time an activity of great economical value, in today’s terms , took place – Diamond bearing Kimberlite pipes forced their way through the parent rock, as were discovered at Jwaneng, Orapa and Letlhakane.
After the glaciation of Antartica, a wetter period followed, and rivers started flowing, guided by the orientation of the sand dunes causing water to flow into one direction –
into Lake Makgadikgadi. Relics of these rivers are the huge fossil beds such as Okwa Valley in the Central Kalahari. This wet era also caused the great rivers of the Middle Kalahari to flow again, namely the Okavango, the Chobe and the Zambezi. Initially they flowed eastwards, but an upwarping of the earth’s crust caused the formation of a fault, interrupting the flow – resulting in the gradual filling up of the immense basin – one of the largest lakes in Africa- The Makgadikgadi. At it’s maximum is was estimated at 60 000 – 80 000 km2 – with the Okavango Depression on the one side. The drying up of the lake was well advanced about 10 000 years ago, and gradually became filled with sand. The Gumare fault, directly in line with the Selinda spillway and Linyanti swamp was then formed, constituting the southernmost point of the Great Rift of Africa. This caused a reduction in the slope of the land, a spreading of the water, and the formation of the fan shaped Okavango Delta. Today, the only river feeding the Delta is the Okavango River. The only remains of the ancient Lake, apart from the Okavango Delta, are the Nxai Pans, Lake Ngami, Lake Xau, the Mababe depression
and the two main pans of Makgadikgadi, Sowa and Ntwetwe Pans.