Victoria Falls: Mosi-oa-Tunya – The Smoke That Thunders

Abstract

Victoria Falls are located on the Zambezi, southern Africa’s largest river. In full flood with a maximum vertical drop of 108 m, and length of 1,700 m, they form the world’s largest sheet of falling water. The Falls demarcate two sections of the Zambezi of contrasting geomorphology: the low gradient, broad channel of the Upper Zambezi and the steep gradient, narrowly incised downstream Batoka gorges, ∼100 km in length. The Victoria Falls represent the modern position of a west-migrating knickpoint that incised the lower gorges into Jurassic (Karoo-age) basalts that form the bedrock. Evolution of the Falls and lower Gorges was accompanied by deposition of Late Cenozoic sediments of the Victoria Falls Formation (VFF), which preserve a remarkable assemblage of hominin artefacts. This archaeological record provides a unique context to decipher how the Batoka gorges evolved through the Pleistocene; two contrasting estimates, obtained from these hominin artefacts, constrain estimates of headward erosion rates, westward, to between 0.042–0.052 m/year and 0.067–0.080 m/year. This faster rate means that headward erosion has incised 20 km of gorges below the Falls in 300–250 ka. The present position of the Victoria Falls reflects the culmination of evolutionary events initiated by diversion of drainage off the Kalahari plateau into the mid-Zambezi river that occupies a deep graben.