The creation and underlying geology of Victoria Falls is a marvel in its own right. This World Heritage Site especially when seen at the time the Zambezi River is in full flood is a truly spectacular sight. To understand how this beautiful waterfall was created, we will study the underlying geographical processes that took place and explore how the spectacular Batoka Gorge was formed.
The bedrock in the Victoria Falls area is Basalt, a dark volcanic rock formed around 180 million years ago. The layer of Basalt was laid down over a period of one million years. This as a result of gentle volcanic eruptions. Each successive eruption of lava settling over the previous layer. This layer of Basalt is up to 300 meters (900 feet) deep in the Victoria Falls area. It creates a geological “island” in the middle of the surrounding sand. The Basalt layer is shown in GREEN on the map below. The Basalt stretches 200 km along the Zambezi River course from near Kazungula to the Matetsi River confluence with the Zambezi in the Batoka Gorge.
As the lava cooled deep cracks formed in the rock known as “joints” that generally run in an east-west trajectory. The break-up of Gondwanaland around 110 million years ago created tectonic movements. This resulted in a dramatic uplift of the central part of the continent that is Southern Africa today. The giant cracks in the Basalt layer opened further with the break-up of Gondwanaland. They gradually filled with soft sediment.
Desert conditions prevailed across the region around Victoria Falls. Around 150 million years ago tropical forests established themselves here. The Dinosaurs roamed freely around this area. At this time the waterfall we know as Victoria Falls was not in existence.
Geological changes of Victoria Falls
Around 15 million years ago there was another massive uplift of the area that is currently Zimbabwe. This caused the formation of a giant lake across the region that is now the Makgadigadi Pans in Botswana. As a result, the existing river systems were altered and new river systems were formed. All because of this uplift. The Zambezi River at this time was still flowing south from the location of the town of Katima Mulilo and into the Limpopo River on the border of South Africa.
Another 10 million years later, there was another dramatic uplift in this region. This results in a massive spill from the gigantic lake located across the Makgadigadi area. It is a flood of epic proportions that flows in an easterly direction across the Basalt rock of Victoria Falls. The floodwaters then eroded the soft sediments out of the cracks in the Basalt rock. The first waterfall was created as the water cascaded down into this crack.
As a result of this dramatic uplift, a massive spill and the drainage of the enormous lake took place. The lake was thought to have been larger than Lake Victoria that is 60,000 Sq Km. The Zambezi River then created a new course to the north of this area of up-lift. It flows across the Basalt layer and now connects with the Lower Zambezi towards the east. The lower Zambezi River system was fed by the Kafue River up untill that time.
The first waterfall
The shift in the watercourse had now created the spectacular waterfall that became the Victoria Falls sequence. The creation and geology of Victoria Falls continue to evolve in geological time. The image below illustrates the different locations of the waterfall to the current location. Victoria Falls is now in its EIGHTH position. Victoria Falls is approximately 100,000 years old.
As the geological clock continues to tick, the gradual erosion of a new joint has become evident. This is known as the Devils Cataract. It is located on the western edge (Zimbabwe side) of Victoria Falls. The joint or crack numbers 9 and 10 will come into play over the next few centuries creating a new location for the spectacular Victoria Falls.
CREDITS: Siyabona Africa, Les Burger & Brett Hilton-Barber and Lee R. Berger