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Botswana - Geography

Botswana is a land of stunning beauty. The stunning beauty of the Okavango Delta, the unimaginable vastness of the Central Kalahari Game Reserve, the isolation and other-worldliness of the Makgadikgadi, the astoundingly prolific wildlife of the Chobe National Park make Botswana a very unique destination. Much of the country is part of the Kalahari Semi-Desert. Also, there is a large area called the Okavango Swamps in the northwest portion of the country.

Botswana is centrally located in the heart of Southern Africa. It shares borders with Zambia in the north, Namibia in the north and north- west, Zimbabwe in the north-east and South Africa in the south and south-east. Its central location in the Southern Africa region makes Botswana the perfect gateway for reaching the whole of the Southern African Development Community (SADC).

Rainfall varies from 650mm per year in the north-east to less than 250 mm in the south-west. Drought is a recurring problem although in early 2000 record rainfall brought serious flooding. Botswana experiences extremes of climate with winter temperatures below freezing being common in the Kalahari.

Botswana lies on the Southern African Plateau, with an average elevation of 1,000 meters (3,300 feet) above sea level. There are three ecological zones: the Central to Southwest belt (dominated by the Kalahari Desert), the Okavango Delta, and the eastern portion of the country.

More than 70 percent of the country is covered by the Kalahari Desert (Kgalagadi in Setswana), which is generally flat and sandy. Inselburgs (outcroppings of resistant rock) and koppies (weathered rocks, now blocks) dot the desert. In the north lies the Okavango Delta. The Makgadigadi salt pan is to the west; its 7,000 square kilometers lies between the Okavango Delta and the border with Zimbabwe. The eastern portion of the country is hilly and covered with vegetation. There is a variety of soil types in Botswana.

The Kalahari dominates the country with dry sand, but areas to the east have varying geography and soil types. The Limpopo River area is dominated by either dry red loam or chalklike sand. Soil fertility varies based on the amount of rainfall received. Vegetation. With more than 70 percent of Botswana covered by the Kalahari Desert, vegetation is sparse.

Botswana’s boundaries are primarily along several rivers. Bodies of water are rare throughout the interior of the country; the rivers along the perimeter provide the country with water. The Chobe River flows along Botswana’s northern border, the Nossob and Molopo Rivers along the southwest and southern boundaries respectively. The Marico, Limpopo, and Shashe Rivers flow along the eastern border.

The Okavango River in the Northwest corner, flowing from Angola, creates the world’s largest inland river delta. The delta is 15,000 square kilometers (5,800 square miles) of wetlands, including water channels, swamps, and lagoons. The Okavango Delt it attracts all sort of wild animals as it provides both water and food. In return, it provides for a large share of Botswana’s tourism income. The waters extend the delta’s usual area from 5,000 square kilometers (2,000 thousand square miles) to anywhere from 6,000 to 12,000 square kilometers (2,300 to 4,600 square miles) during rainy seasons.

Botswana is relatively flat with occasional rocky outcrops. The thick sand covering much of the country hides the underlying geology, although the east of the country is relatively well- mapped geologically. The Makgadikgadi pans represent the inland drainage basins into which several rivers such as Mosetse, Nata and Boteti flow during the wet season. Large areas of the country are designated as national parks and game reserves.

Wildlife migration routes are mostly between the inner (wet) and outer (dry) areas of the Okavango Delta. In wet seasons when there is water in all the parts of the Okavango, wild animals migrate to the outer parts of the wetland. In dry seasons when water becomes scarce, wild animals migrate to the permanent water source areas in the inner parts of the wetland.

Botswana is rich in mineral deposits. Diamonds, coal, copper and nickel are mined in large quantities. Other minerals found in the country are Gold, soda ash and salt. The country has an arid landscape. Approximately 5% of the land area is cultivated. Cattle ranching is the most significant agricultural enterprise. Farming is mainly at subsistence level and relies primarily on cattle, sheep, goats, maize, sorghum, beans, peanuts, cottonseed and other dry land crops.

Rocks of the Karoo Supergroup (259 to ~ 100 Ma) unconformably overlie approximately 70% of Botswana’s Archaean and Proterozoic rocks. In the Kokong area, the Karoo rocks are in turn overlain by an average 70 m of semi-consolidated Kalahari sediments, the age of which ranges from Upper Cretaceous to Quaternary (70 Ma to present). The Kalahari Group consists of approximately 20 meters of loose, unconsolidated aeolian sand beneath which is a more indurated sand with calcareous or siliceous cement. There is frequently a calcrete – silcrete duricrust horizon at the base of the aeolian sand. The sandstone becomes redder downwards with increasing clay content. The base of the unit is often defined by the presence of a red marl or clayey sandstone, but infrequent basal gravels do exist.

Diamonds originate some 200 miles below the Earth’s surface in the “mantle” layer. At that depth, enormous pressure is exerted on the carbon molecules, forging them into diamonds, and creating one of the strongest molecular bonds known to chemistry.

Diamonds are moved from deep in the earth to the surface in volcanic eruptions. They typically come to the surface in thin magma streams known as ‘Kimberlite pipes’. Kimberlite and olivine lamproite are the only known types of intrusive rock (primary source rocks) that may carry diamonds from the depths of the earth to the surface and may form primary diamond deposits. The principal distinction between kimberlite and olivine lamproite is based on geochemical grounds.

Botswana is host to over 240 kimberlites, most of which occur in clusters. The majority of clusters occur within the Archaean-age Kaapvaal-Zimbabwe craton. A number of kimberlites contain diamond, but only three are currently being mined. A fourth mine ran for four years on a trial-mining basis but closed in 2001. Evidence from known kimberlites world-wide suggests that only kimberlites in a cratonic setting can host economic quantities of diamond; that the older the craton, the better and that craton margins tend to be unfavorable sites for diamond-bearing bodies.

Recent studies of the Kaapvaal Craton indicate that kimberlites < 90 Ma in age may have a significantly poorer potential of entraining diamonds during eruption because of changes in the lithosphere post 90 Ma. The ages of the kimberlites which have been or are mines in Botswana range from 1.3 Ga at the Martin’s Drift western cluster to 240 Ma at Jwaneng to ~95 Ma at Orapa-Letlhakane. This kimberlite has not, despite intermittent work over a period of thirty years, been proved to be an economic proposition. Equally, older bodies such as the 500 Ma kimberlites at Martin’s Drift are not diamondbearing. Only careful studies of indicator mineral chemistry followed by bulk sampling can reveal the true macrodiamond potential of a kimberlite.