I have tried in this blog to explain the very technical processes that happened during the formation of the islands in the Okavango Delta (processes that continue every day) in a way that we all can understand. This is not to be viewed as a scientific analysis, but rather as a layman’s attempt to help us to understand how the magnificent phenomenon that is the Delta came to be what it is.
How Termite Mounds shaped the Delta:
The slow flowing flood waters of Okavango River come across a termite mound. The water flow then splits around the termite mound. When water flows around something, the water closest to the object slows down and the water furthest away speeds up. The sand and debris carried by the slower water would sink and be deposited on/next to the termite mound while the sand in the faster water would be carried further along. Slowly, over time, the termite mound would have more and more sand deposited around it. It would get larger and larger and the water flowing around it would be slowed more and more resulting in more and more sand being deposited and the termite mound growing larger and larger.
The river also carried grass and reed seeds which would be deposited on this sand bank, and they in turn would start growing. These grasses and reeds would stabilise the sand deposits and hold them together which resulted in even more sand being deposited.
Eventually the termite mount would become a small island. Tree seeds would now start growing together with the grasses, reeds and other plants. The process would continue until the typical islands that the Okavango Delta is famous for, would be formed.
As the island was growing bigger, the water was forced to flow further and further around the original termite mound. This water would start flowing faster and faster as it navigated this obstacle and would eventually cut a deeper channel around the ever expanding small island. The yearly flooding and drying of the Delta was forever changing the flow of water and the size of the islands. The winds blowing over the Kalahari would also deposit more and more sand on these islands (same process as the water deposited by the river) and they would grow bigger and bigger. One study suggests that continued island growth is also related to the deposition of aerosols and the accumulation of dust preferentially on islands and possibly to ongoing termite activity. Tall trees that characterise the island edges, trap dust carried from the floodplains, resulting particularly in the lateral growth of islands. Islands in the Okavango are considered to be the product of long-term aggradation processes.
Along with the above process another process is happening within the islands. Transpiration by vegetation is shown to result in substantial increases in groundwater salinity beneath the islands, contributing to their growth through chemical precipitation. Chemical analyses revealed that the precipitation of magnesium calcite and silica within the island soils contributes 30–40% of the total island volume.
The Okavango offers an oasis of habitat for prolific plant and animal life in a personified state of “balance in nature.” The waters of the Okavango are inhabited by an estimated 35 million fish of almost 80 species. The most abundant, three species of bream, are preserved from excessive predation by tiger fish by crocodiles who feed on the tiger fish.
Hippos flatten paths through the papyrus on their nocturnal forays to graze, allowing easier access for the sitatunga and antelope to traverse across the swamps during their daytime migrations. Belts of forest fringe the swamps with tall trees giving shade to large herds of larger game. Beyond the forest fringe the landscape forms an open savanna park land, and in these drier areas the greatest concentrations of game are accompanied by the predator families: lion, leopard, cheetah, hyena, and wild dog. It is in these forest fringes and savanna grasslands that elephants and giraffes can be found browsing with antelope of almost every kind, from buffalo, wildebeest, and kudu, to sable, roan and impala. Okavango is a delicate and unique example of dynamic equilibrium at work in nature. A place worthy of being called a “one of the greatest places on earth.”