From fire and ice to diamond engagements and monumental breakups, the creation of Botswana’s landscape has been hundreds of millions of years in the making. By Mike Main
 When part of Gondwanaland, Africa and its modern continental neighbours were held in the grip of an immense ice field more than 250 million years ago. The fantastic weight of the shifting glaciers worked to scour the super-continent’s surface before conditions gradually changed, resulting in the eventual melting of the ice sheets and the formation of swamps and wetlands. Sediments of mud, clay and shale accumulated in these basins until they subsequently dried over millions of years. Ever drier times followed until much of Gondwanaland lay beneath an all-embracing desert.
Around 167 million years ago, during the mid-Jurassic Period, things really started to unravel. Lava spewed to the surface, covering vast tracts of land, as the forces behind plate tectonics started to rip the super-continent apart. The regional magnitude of these volcanic deposits and their remnants today confirm how Africa, Arabia, South America, India, Australia, New Zealand and Antarctica were all once joined together in a single landmass.
The final separation of Africa from South America eventually led to upheaval of Africa’s continental margins, creating an immense basin within its interior. For subsequent millennia, this sediment sink was slowly filled with the products of erosion, carried both by wind and water. Excessively dry conditions then took hold of the centre of southern Africa, forming the Kalahari Desert. It has persisted, in one form or another, ever since, reflecting the ever-changing conditions of climate over the last 60 million years: sometimes as a true desert, occasionally as an area of forest, or as today, a semi-arid region completely covered by vegetation.
The boundaries of Kalahari sand in the 21st century show just how extensive that original desert was. Defined by the area of wind-blown – or Aeolian – sand, it stretches from the Orange River in South Africa, north through the heartland of the continent, to a point in the Congo beyond the equator, covering an estimated 2 million square kilometres, the greatest continuous stretch of sand in the world.
There are many places in Botswana currently where the form of the old seif dunes is plainly visible beneath the vegetation. Long lines of parallel sand ridges can still be seen, in the west particularly, barely concealed beneath the trees.
Major features of the Kalahari, found mostly in the south and west, are the extraordinary pans. Oval, opalescent, smooth as billiard tables, these hard clay surfaces are the end-point of local drainage systems. On those rare occasions when there is enough rain for water to flow, it is held, sometimes for as much as four or five months, in shallow ephemeral lakes.
Considering that their fringes host the greatest diversity of plant species in the Kalahari and that their clay deposits contain concentrations of the soluble salts carried by rainwater, pans are incredibly important. These two aforementioned factors account for the almost continuous presence of wildlife grazing in their vicinity. Animals also scrape small hollows, usually in the very centre of a pan, from which they eat the clay, ingesting vital trace elements missing from their usual diet.
Surprisingly, the water in the pan – for as long as it remains – is not of great interest to man or animals. Firstly, it’s usually too salty. Secondly, most of the Kalahari’s wildlife has already adapted to finding other sources of nourishment in the arid conditions, so that they are not dependent on these ephemeral lakes.
Man, on the other hand, does rely heavily on them. Not on the surface water, rather on what lies beneath. They discovered that wells dug around the perimeter of pans often led to perched aquifers of fresh water. These are usually at accessible depths, seldom more than five to seven metres below the surface. As the pans were settled and wells established, they became like giant stepping-stones, providing a path through the thirstland where water could almost always be found. The trick, of course was to find the way from one pan to another.
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Formed, for the most part, by the action of wind, Kalahari pans almost always have dunes piled high on the downwind side. These sand structures have played a vital role in the occupation of the desert, for it is from their summits that the horizon can be scanned and a course set for the next high sand dune, which is usually plainly visible on the horizon. Once located, the next pan could be explored for water. If a well was established, another stepping stone would be added to the ever-extending chain that, in time, spanned the whole of the Kalahari.
Like knots in a hairnet, the pans of the Kalahari have provided centres of refuge and markers along the routes across the wastelands. In Botswana today, all major Kalahari villages stand beside one of these features where, long ago, the first explorers found a precious source of water.
Often mistaken for pans and, indeed, wrongly called so, are the great Makgadikgadi Pans of northern Botswana. Far from being formed by the wind, these twin giant features are actually part of an ancient sea that once covered as much as 120,000 square kilometres and linked, in a vast waterway, the modern Okavango, Chobe and Zambezi rivers. In ancient times, these rivers all flowed to the Limpopo River in the east and down it to the Indian Ocean. However, gentle rifting blocked their path and the great lake formed. Over time, the Chobe and Zambezi changed direction and the lake level gradually fell. Next it was the Okavango River that stopped feeding the natural reservoir – it had become trapped in a vast rift valley that filled with sand and absorbed all the water the river could provide. Now the Makgadikgadi, formed of grasslands and enormous areas of bare clay, lies beneath a baking sun, without the waves and wetlands it once supported. Rather than migrating streams, there are only whirling columns of dust and occasional, terrifying windstorms meandering across its breadth.
The dates of this former great lake are uncertain, but it probably formed within the last two million years. Even today, the shallow basins that remain within it periodically collect floodwater from passing storms. Within the confines of the old basin are found some of Botswana’s greatest attractions: Makgadikgadi grasslands, where wildebeest and zebra graze in huge herds; Nxai Pan National Park; the great flamingo breeding grounds of Sowa Pan; and some of the core areas of Chobe National Park, the Mababe Depression and Savute Marsh.
In a country where evaporation exceeds rainfall in every month, and where there is no standing open water, the presence of the Chobe, Zambezi, Limpopo and the Okavango rivers is vital to sustain its wildlife during the six months or so when no rain falls. Of these, the most important is the Okavango. It is a great African river, born in the highlands of Angola, which pours itself out onto Kalahari sands in a spreading alluvial fan that can cover 15,000 square kilometres. This swirl of green provides a livelihood for many and is the heart of the country’s tourist industry. It is a wonderland of lake, lagoon, island and river, and a dramatically beautiful refuge for countless animals as they seek its food resources in the dry season.
Economically, Botswana also has much for which to thank its past. Trapped beneath 250 million years of geological change still lie the remains of the old swamps formed when the great ice sheets melted. Into those swamps fell the vegetation of that time, and the resulting compression from the great weight of all that followed, led to the formation of massive coal seams – the nation now appears to hold the continent’s second-largest coal reserves. Given the insatiable demand of China and India, among others, for this product, Botswana is well placed to exploit these extraordinary reserves.
Around 100 million years ago, when the great outpouring of lava had run its course and Africa stood alone, surrounded by new oceans, there occurred another set of important geological events that have led to Botswana’s modern wealth. Diamonds, which are formed under conditions of immense pressure and temperature deep beneath the earth’s crust, were deposited into the country’s surface strata. These deposits occur when the molten matrix in which the diamonds form is subjected to such great pressure that it escapes violently upward, by literally punching its way through solid rock to reach lower pressure areas near the surface. The expanding cone of diamond-rich rock is referred to as a kimberlite pipe. Many of these structures occur in the Kalahari and help make Botswana the biggest producer of diamonds (including gem-quality stones) in the world.
It is this wealth that is building a genuine, democratic nation, one that tries to educate and nurture the health of its citizens, and one that can rightly boast of its reputation as a stable, well-developed middle-income member of the world’s community of nations.
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