Most rivers run into other rivers, into lakes, or eventually, into the sea. To have a fairly large river run inland and to pour itself into the sand, is therefore an anomaly. Why is this the case?
I don’t really want to give a geology lesson, but here’s a short one anyway: It may be interesting for you to know that shortly after the break-up of Gondwanaland, the separation of Africa from South America, India, Madagascar, Australia, etc., between 140 and 90 million years ago, the Cubango, Quito, Kwando, Upper Zambezi and Kafue Rivers were all draining from the North into the Limpopo River, flowing eastwards across the continent, into the Indian Ocean.
Around 60 million years ago, however, a bulge started to develop diagonally across Africa. Since water cannot flow uphill, this cut off the route to the Limpopo, so that all these rivers were draining into an inland depression called the Kalahari Basin, thereby forming the huge inland Lake Makgadikgadi.
About 14 million years ago, dry conditions set in due to upwelling of cold water in the widening Atlantic Ocean, and the lakes in the Kalahari Basin started to dry up, also due to the fact that the Upper Zambezi River was captured by the Lower Zambezi, flowing eastwards and no longer into the Kalahari Basin. The various pans seen and visited during our trip, as well as the extensive Makgadikgadi Pan, are the remnants of this huge inland lake.
As the rift system in East Africa developed, faults started to extend into southern Africa, one of which is the Thamalakane Fault where the river with the same name (and our campsite) is now located. It marks the southeastern limit of the Delta, and the location of Maun. The delta tends to flood on an annual basis, bringing water from faraway Angola. This usually happend between February and May. Last year was a particularly dry year, however.
If you’re interested to know more, get hold of the book pictured here. It’s very very readable, written for non-geologists, very well-illustrated. An excellent way to understand the landscapes all around us, and of the development of life on this changing canvas,
We spent the day in Maun generally resting in the campsite, reading in the shade, etc. And of course, buying supplies and getting prepared for the coming days. Managed to buy some really good boerewors, very decent wine, beer, etc. You know, the essentials.
Our adventures during the coming days, in upcoming posts, will show the Okavango Delta from two very different, very exciting viewpoints…. No geology lectures there, only Adventure with a capital A, and lots of pictures. Watch this space!