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Largest
stretch of sand on earth
The Kalahari extends from south-eastern Angola across
eastern Namibia and western Botswana right down to northern
South Africa. Covering a total area of about 1.6 Mio
km², the Kalahari is considered to be the largest
continuous stretch of sand on earth. |
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The quantities
of sand are beyond imagination. They are the weathered
debris of far-away mountains, removed by rivers and
deposited in the Kalahari Basin in the course of millions
of years. When the ancient southern continent of Gondwana
disintegrated 130 million years ago, the southern rims
of the African fragment rose and a huge bowl was formed
- which still exists today: it is the Great Escarpment
in the west and the Drakensberg Mountains in the south
embracing the Kalahari Basin in the subcontinent's interior. |
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The dunes of
the Kalahari are about 15 to 30 metres high. They were
formed roughly 20,000 years ago when the northern hemisphere
experienced an ice age. Temperatures world-wide were
on average five degrees lower than they are now. The
ice cover in the north and lower temperatures everywhere
resulted in less evaporation and less humidity so that
deserts started to spread. The Kalahari dunes are arranged
in long lines which extend over hundreds of kilometres
and run parallel to one another, almost as if drawn
with a ruler, from north-west to south-east –
this is clearly visible on the satellite picture. The
valleys, by the way, are called streets. The longitudinal
alignment of the dunes is due to the prevalent direction
of the wind. About 5,000 years ago the climate became
more humid and allowed for a plant-cover which prevented
the dunes from shifting. The sand is reddish because
the grains are coated by iron oxide (rust). |
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Many
speak of the Kalahari as 'just' a semi-desert,
because average annual precipitation is more than
100 mm; in the southern parts it is even between
150 and 300 mm. However, due to temperatures reaching
highs of up to 45 degrees during the summer months
of November to February, and the permeable sandy
soil, there is very little surface water. After
good rains small lakes form in the numerous shallow
pans in the dune streets, but they dry up just
as rapidly, too. Since the potential evaporation
per year is twelve times higher than precipitation,
experts agree that the Kalahari is in fact a desert.
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This, by the
way, was realised by the inhabitants of the Kalahari
centuries ahead of the scientists: the original name
Kgalagadi means 'always dry' in the Tswana language.
Apart from the Tswana people, the southern areas of
the Kalahari are also the home of the San (Bushmen)
peoples and the Nama. |
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Different landscapes,
soils and rainfalls are the reason for subdividing the
Kalahari into eight vegetation types. The south comprises
four zones characterised by acacias, dwarf shrubs and
above all grasses. Succulents, however, are quite rare.
In order to reduce the loss of water caused by evaporation,
many plants shed their leaves at the start of the hot
summer period (from September). |
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