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.

Termite mounds with start of vegetation growing on them

Termite mounds with start of vegetation growing on them

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.

Okavango Island formation

How the islands grow

 

 

 

 

 

 

 

 

 

 

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.

Aerial view of islands, termite mounds and waterways, Okavango delta, Botswana

Aerial view of islands, termite mounds and waterways, Okavango delta, Botswana

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.

Hippo paths in the swamp

You can clearly see the Hippo paths

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.”


A violent volcanic eruption that blows the top of Mount Ngorongoro, one of the highest freestanding mountains in Africa. Is that dramatic enough?

Hippo pool at Ngorongoro Crater, Tanzania

 

A violent volcanic eruption that blows the top of Mount Ngorongoro, one of the highest freestanding mountains in Africa. Is that dramatic enough?

How the Ngorongoro Area was formed:

The boring technical stuff first:
The Ngorongoro Crater finds itself on the coming together of two continental plates along what is called the Great Rift Valley. This fault in the earth extends from the Dead Sea in Israel to Botswana & Zambia where it ends some 6400 kms later. It is the volcanic action of this fault that caused Mt Ngorongoro to erupt and spew lava onto the Serengeti Plains. The Ngorongoro Crater is thought to have formed about 2.5 million years ago from a large active volcano whose cone collapsed inward after a major eruption, leaving the present vast, unbroken caldera (6th largest in the world) as its chief remnant.

These plains are mostly in the Ngorongoro Crater Conservation area

Treeless Serengeti Plains

Why are the Serengeti Plains treeless?

Once the lava had cooled back into rock, the whole of the Serengeti Plains became a huge slab of rock. Over eons, volcanic ash, dust and sand settled over this rock, grass and small bushes started growing. To the soil covering this rock is about 15cm deep. Trees cannot grow as they are unable to penetrate the rock. This is why the Serengeti Plains are almost treeless.

Crucial to our understanding of this area is that the Serengeti Plains are now mostly part of the Ngorongoro Conservation Area and NOT in the Serengeti National Park. How did this happen?

Ngorongoro Conservation Area (NCA) – the experiment:

The Serengeti National Park was declared in 1951 by the British and by 1959, the experiment that is The Ngorongoro Conservation Area (NCA) was started. It was an attempt to conserve and promote the life and interests of the Maasai who are inhabitants of the area. This is a pioneer experiment which attempted to reconcile the interests of wildlife,

Maasai pastoralists and conservation in a natural traditional setting. Land within the area is multi-use, providing protection status for wildlife while also permitting human habitation. Its uniqueness lays in the fact that the NCA is where man, livestock and wild animals live in peace: For the most part they have succeeded!

Maasai cattle can sometimes be seen grazing alongside zebras on Ngorongoro’s grassland. Most of the famous Serengeti Plains now fall in the NCA.

Bucket list, for sure.

How deep and how wide. See for yourself.

 

 

 

 

 

 

 

 

 

 

How big is the Ngorongoro Crater?

The Crater itself is one of the seven natural wonders of Africa. It is 16 to19 kms in diameter, with walls are up to 600m high. In this extinct volcano is the densest known population of lions, numbering 62. Higher up, in the rainforests of the crater rim, are leopards, about 30 large elephants, mountain reedbuck and more than 4,000 buffalos, spotted hyenas, jackals, rare wild dogs, cheetahs, and other cat species. All this in an area less than 260 square kms! Beat that!

One of the funniest and most poignant sights I had while visiting the crater was a pick-up truck (bakkie) that carried about 6 guys in orange overalls, bouncing along the crater floor. The purpose of this you may well ask? They are part of a team that permanently follows the Black Rhinos and is responsible for their protection, 24/7.

The crater is home to a small forest, The Lerai Forest, a shallow soda lake called Lake Magadi (home to huge flocks of flamingos, both greater and lesser), the Gorigor Swamp and the Ngoitokitok Springs where pods of hippo are to be found. It was quite dry when I was there and the hippos were so tightly packed in the little remaining deep water they looked like a very bumpy raft. (For this reason, I am in favour of calling a “collection” of hippos a raft)

A little shade cubs?

 

 

 

 

 

 

 

 

 

 

Shade anyone?

The north of the Crater is, on the whole, much drier and consists of the open grasslands which characterises the Crater floor; this is where the majority of the resident game resides. On a single game drive, I managed to see three prides of lions (jealousy is not a pretty thing). How many areas this size in Africa can boast the same? The Crater’s lion population, on the whole, show a complete disregard of vehicles; they will hunt within yards of a vehicle, and when exhausted even seek shade beside them.

Sode Lakes are the ideal feeding ground for flamingos

Flamingos and more in the Ngorongoro Crater

Wilderness or Zoo?

Safaris in the crater are rewarding in that the abundance and variety of wildlife seen in such a small space is unparalleled. You however have to contend with “Bakkies” with orange overalls flying past, fellow gawkers in many other safaris vehicles making it feel like Grand Central Zoo rather than a true wilderness experience (please see one of my future blogs on Wilderness Camping in the Serengeti for a more relaxed safari).

Migration in the Ngorongoro

Wildebeest herds spread over the Serengeti Plains in the Ngorongoro Crater Conservation area

The Ngorongoro Migration

While the Ngorongoro Crater is the centre piece of the NCA, the plains below are the dessert. The legendary annual wildebeest and zebra migration also passes through Ngorongoro, when over 2 million ungulates (big word I know) move south into the area in December then move out heading north in June. The ungulates (just boasting that I know a big word) 1.7 million wildebeest, 260,000 zebra, and 470,000 gazelles.

Herds of Wildebeest in January

Lake Ndutu

Not all is about the ungulates. The Lake Ndutu area to the west has significant cheetah and lion populations. Over 500 species of bird have been recorded within the NCA.

Empakai Crater, part of the Ngorongoro Conservation area

Besides Ngorongoro, there are two other craters in the area: the Olmoti and Empakai Craters. These two are located in remote and pristine places, where you can enjoy tranquil walks, cultural experiences and game viewing, against a backdrop of spectacular vistas. Among NCA’s many other treasures, a most intriguing one is the Olduvai Gorge, towards the border with Serengeti.

This where they dug up Lucy.

 

 

 

 

 

 

 

 

 

Lucy, Homo-habilis

The Olduvai Gorge archaeological site, widely regarded as the cradle of mankind and the most important prehistoric site in the world. It is at Olduvai where remains of Zinjanthropus, the world’s first humans, were discovered by Dr Louis and Mary Leakey over 50 years ago. The earliest known specimens of the human genus, Homo-habilis, as well as early hominids such as Paranthropus boisei have also been found there.

Fun Facts:

60% of all tourists to Tanzania visit the Ngorongoro area
No impala or giraffe in the crater.

Fun in the sun - Makgadikgadi style

Fun in the sun – Makgadikgadi style

5 Million Years ago:

About 5 million years ago, the Antarctic polar ice caps started to form. This resulted in Southern Africa becoming increasingly dry until about 3 million years ago an extended dry period started. During this dry period strong easterly winds blew across the middle Kalahari and formed elongated dunes the ran from east to west.

As Southern Africa became wetter, the water of the rivers of the area were channelled by these dunes and they flowed into Lake Makgadikgadi. It was also during this period that the Okavango and Zambezi rivers started to flow.

1 Million Years ago:

About 1 million years ago, the earth crust under Southern Africa experienced an upheaval which changed the course of these rivers. This fault, known as the Kalahari-Zimbabwe axis caused the rivers to flow into a large basin called Lake Makgadikgadi, which soon filled up. Lake Makgadikgadi became one of Africa’s largest lakes. This damming resulted in the formation of a series of swamps.

Flamingos in the Makgadikgadi during the wet season

Flamingos in the Makgadikgadi during the wet season

 

 

 

 

 

 

 

 

 

 

The formation of yet another fault, the Gumare fault, caused a reduction in the elevation of the land, caused the water of the Okavango River to spread out over a much larger area of land. As the Okavango River left the Angolan highlands and entered the arid flatness of the Kalahari, it slowed and dropped a million tons of sand and debris, channels became blocked and the water sought other courses, continuing to deposit its sediments wherever it travelled creating the characteristic fan shape of the Delta. Eventually the lake was filled to capacity and the water had to find a way to the ocean.

Therefore, about 20 000 years ago the waters of this great lake were forced northwards and then eastwards. This caused the middle and lower Zambezi to connect, which resulted in the formation of Victoria Falls. With the water now able to flow out of the lake, a partial draining of the lake occurred. A drier climatic period followed which caused an increase in evaporation and a decrease in the river flow.

Jack's Camp in the Makgadikgadi - clearly see where the water dried up

Jack’s Camp in the Makgadikgadi – clearly see where the water dried up

By about 10 000 years ago the drying of the Makgadikgadi Lake was in an advanced stage. Windblown sand, as well as the Okavango River depositing increasing amounts of sediment and debris in the lake, were gradually filling the lake.

Two parallel faults direct the way the Okavango enters the Kalahari Basin in an area called the Panhandle it then fans out into several channels. Some of these channels permanently have water, namely the Boro, the Thaoge and Ngugha channels. Deep water occurs in only these few channels, while vast areas of reed beds are covered by only a few inches of water.

Fault Lines Okavango

Technical map showing fault lines

The Okavango River channels are blocked by two southern faults, the Kunyere and the Thalamakane. More than 95% of the Okavango’s water evaporates before it reaches the Thamalakane fault/river. The Thalamakane Fault acts as a 150-mile-long natural dam: Here the channels abruptly change direction and join to form one river, the Boteti, which flows eastwards through a break in the fault towards the Makgadikgadi Pan. A small channel, the Nghabe River, continues southwest toward Lake Ngami, serving as both inlet and outlet depending on the strength and direction of the annual floods.

 

The Okavango is unique in that it forms a freshwater Delta, simply because it has several outlets. Even though their outflow comprises only three percent of the Okavango’s inflow, this is enough to carry away most of the salts and keep the Delta’s waters fresh. In fact there are 2 groups of outlets: west to Lake Ngami, and south and east to the Makgadikgadi Pan via the Boteti River.

Today the only remains of the Ancient Lake Makgadikgadi (apart from the Okavango Delta) are Nxai Pan, Lake Ngami, Lake Xau, the Mababe Depression, and the two main pans of Makgadikgadi (Sua and Ntwetwe Pans).

Selinda Spilway

Map showing the Selinda Spilway

The present Okavango is still connected to the Chobe-Zambezi River system via the Selinda Spillway.