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Formation Of The Zambezi River

FORMATION OF THE ZAMBEZI RIVER

The understanding of geographical processes and reading from landscapes of the evidence of past geographical formations and events gives an insight into the history of the Zambezi River and its evolution.

The early Zambezi River existed as two separate river catchments. The Upper Zambezi represented by an already ancient river basin, much as it is today, draining south, and the Middle and Lower Zambezi sections of a much younger river flowing east. The Upper Zambezi, Kafue, Kavango and other rivers drained towards the present day Botswana, where a huge inland lake is evidenced from fossil beach-lines, known as palaeo-lake Makgadikgadi, and believed at its maximum to have covered an area of about 60,000 square kilometres. Water overflowing from the lake is thought to have fed into what are now the Shashe and Limpopo river drainage systems, meeting to the sea north of present-day Maputo.

Eventually the Middle and Lower Zambezi sections, by process of headward erosion down into its river bed and upstream into its basin, captured the flow of the Upper Zambezi, removing its waters from the Makgadikgadi lake and connecting the river as we know it today. Palaeo-geologists estimate this to have occurred some 125-150,000 years ago. It is also believed that this process was either triggered by, or caused, the overflowing of the vast inland lake, with significant volumes of water draining east via the Middle and Lower Zambezi and eroding deep into its bedrock. Perhaps all these events were the result of tectonic shifts in the earth’s crust, as the region is traversed with ancient fault lines.

The point where the lake overflowed and eroded into its former margins is seen at Katombora, linking the Upper and Middle Zambezi river courses that we know today.

With the reduced volume of water entering the great ancient lake its levels receded, lost to evaporation, with the empty expanse of the Makgadikgadi pans remaining today as a tiny residue of this once vast lake. However the Kavango River still remains trapped, forming the inland wildlife havens of the Okavango Delta.

The increased flow caused by the capture of the Upper Zambezi and overflowing of the great lake is thought to have given the middle sections of the river the power and force to have eroded its steadily deepening passage through the Batoka Gorge and creating the processes which have resulted in the zig-zagging retreat of the Victoria Falls themselves.

This process of erosion is still ongoing, although the flow and force of the mighty river is now much reduced. The Victoria Falls that we see today represent the latest in a series of retrogressional waterfalls, the zigzags of the gorge immediately below the Falls representing old waterfall faces. The river is predicted to continue this erosive process, eroding back from the present falls and creating new fall-lines, whilst leaving the current falls dry. These geological processes happen gradually over thousands of years, the rock worn and eroded by the tiny particles of sand carried by the river in flood, that change appears inconsequential to the human eye. In the hundred years since the first photographs and scientific measurements of the Victoria Falls were taken, there have been no perceivable changes recorded.

Read about the Zambezi Region on the following pages:

The Zambezi Basin

The Zambezi River

Exploration of the Zambezi