The Rift Valley or also Great Rift Valley (the valley of the great flaw) is a vast geographical and geological element that extends in a north-south direction for about 6400 km, from the north of Syria (south-west Asia) to the center of Mozambique (eastern Africa). There are lots of variances in the valley’s width ranging from 30 to 100 km and in depth from a few hundred to several thousand meters.
It was created by the separation of the African and Arab tectonic plates, which began 35 million years ago (from the end of the secondary to the end of the tertiary), and the separation of East Africa from the rest of Africa, a process that began by 15 million of years.
The name of the valley was given by the explorer John Walter Gregory.
The rate of expansion of the rift valley is not uniform in the various points of its length but varies from area to area; on average, the expansion of the oceanic ridges is 2 cm per year but, as we said, it can vary from about 1 cm to about 15 cm per year and is not constant in the various geological times.
How is A Rift Valley Formed
The African Rift probably started around 40 million years ago as a simple hotspot in the Afar region. This hotspot, which coincides with an area of active volcanoes, would have peeked out from under the Africa plate and forced the plate to form a dome that cracked in three directions, forming a “Y”.
The result of this swelling and cracking can still be seen today when looking at a map. Two of the branches formed the Red Sea Rift and the Gulf of Aden Rift, separating the Arabian Plate from the African Plate.
Although these two rifts are part of the Great African Rift system, and they probably have the same point of origin, they have their own identity and should not be confused with the East African Rift. The presence of the hot spot allowed the heat of the mantle to warm the continental plate which was distended and thinned.
This thinning gives rise to a subsidence of the crust in a form of ” horst and heaven.” Once the crust has collapsed, the heat allows the two pieces on either side to pull away from each other.
After some time, the subsidence is pronounced enough to allow the rift zone to be invaded by the ocean. Subsequently, when the stretching and subsidence of the crust reaches its limit, the magma will be able to surface between the two pieces of plate and the oceanic crust will be produced (as along the Mid-Atlantic Ridge).
However, the African Rift does not form a straight line. It is separated in two in its southern part and the center (the eastern part, the East African Rift, is the best known and is presented as the western border of what will be the Somali plate).
Several lakes occupy the valley of the western branch of the Great African Rift (Lake Tanganyika, Lake Albert, and Lake Edward) while Lake Victoria is located between the two branches of the rift.
The formation of a rift does not go without the presence of volcanoes. Recently, the Nabro volcano (Eritrea), in the Afar triangle, erupted for the first time since the Holocene (10,000 years).
Kilimanjaro (Tanzania) is a mountain made up of three volcanoes, two of which are considered extinct, while the third could erupt at any time. Its last eruption dates back almost 360,000 years, but some fumaroles on the sides of the mountain remind us of its volcanic character.
The Ol Doinyo Lengai (Tanzania) is the only volcano in the world to have lava of carbonatites (a compound of carbon). In the western branch of the African rift, Congo’s Nyamuragira volcano made headlines on November 6, 2011, with its biggest eruption in 100 years.
East Side Story
The Great Rift Valley has long been considered by the scientific community to be the cradle of the human lineage, as many pre-human hominin fossils have been unearthed there. The discovery of Toumaï in Chad in 2001, however, challenged this schema.
One theory regarding the appearance of the human lineage placed the formation of the Great African Rift at the forefront.
Known as the East Side Story, it was proposed by A. Portland, then popularized by Yves Coppens in 1982.
The formation of the fault would have eventually led to a major climatic and environmental differentiation between the region located to the west, humid and wooded, and the region located to the east, much drier and occupied by the savannah. From a common stock, two lineages would have diverged, leading to the arboreal chimpanzees in the west, and to the first Hominina in the east, then to the Australopithecines, a group that probably originated the genus Homo.
The selection of bipedalism would be an adaptation to the savannah.
This initially attractive model was called into question by the finding that Australopithecines still largely arboreal locomotion, and by the discoveries in Chad of Australopithecus bahrelghazali (in 1995) and Sahelanthropus tchadensis (in 2001), 2,500 km to the west of the rift, by missions led by Michel Brunet.
The emergence of the Hominina sub-tribe appears today to paleoanthropologists as a much more complex process than the theory developed in the early 1980s by Yves Coppens.
Fossil finds in South Africa, East Africa along the Great East African Rift, and Chad, are partly explained by geological and taphonomic bias.
In many parts of Africa, the current forest cover which gives acidic soils, low sedimentation, decay, and other components have prevented fossilization, conservancy, or discovery. But many regions of Africa have likely been populated by hominins from the Pliocene.
East African Rift Valley Facts
There are landscapes before which there is only room for surrender. Lacking limits, they make us forget our own. Since they only convey freedom, they captivate us. By staging paradise, they hint that the nostalgia for Eden could make sense.
The Great Rift Valley, in Africa, awakens those sensations. The painting is immense, but nature has managed to put a frame on it. Men can look at it but hardly change it. Let’s take a look at some facts about the East African Rifts.
1. Missed Nomadism
In the majestic settings of the Rift, the lesson is obvious: when the human being was a nomad and tiptoed through the landscape, it would be said that the Earth was doing better. Before the splendid plains, full of life and mystery, the sedentary yearns for the infinity that humanity renounced.
Animals roam free, unconfined by man, in a space that has not been tamed by agriculture or houses with foundations. It would be necessary to go back millennia in Europe to experience something similar. In North America, a few centuries. But in Africa, precisely where we place the cradle of humanity, this phenomenon continues to occur.
2. An Infinite Home
The look is not enough in the Rift. You have to enjoy each sunset and each sunrise as the miracle they are, soak up the sky and the horizon, scrutinize the earth where surprises await.
Nature thus recovers the spiritual power that it possesses in the stories. It is the place where things happen and, above all, the home of the animals, which have a prominent role in almost all the stories.
3. A Geological Spectacle
Rift landscapes remain on the retina even if a camera does not have enough megapixels to cover them. Standing on a 600-meter high ledge, a green or yellow plain unfolds below us depending on the season. It would seem that nothing can interrupt it.
However, 50 km further on, in the bluish mist, a parallel vertical cornice emerges, sister to ours. The ends of that corridor are not guessed.
It is such a regular landscape that it could seem artificial.
But its greatness dispels doubts. The technology does not allow to open channels of such width and length. In that dilated space, nothing provokes a sensation of tension.
Human beings have not plowed the land or painstakingly reshaped its face. The slender volcanoes that have emerged linked to the crack seem to have been there forever, like navels of the Earth, born by spontaneous germination rather than forged by fire.
A necklace of large lakes occupy beds created by collapses that sank the land, but they only inspire placidity.
4. The Perfect Boiler
The same happens with the Ngorongoro massif and the crater of the same name, in Tanzania. This perfect caldera, 20 km in diameter, the largest on the planet –as large as the island of El Hierro–, was formed about two million years ago when a volcano the size of Kilimanjaro collapsed when the magmatic chamber at its base emptied.
We do not know if our ancestors witnessed this cataclysm, or if their adventures in neighboring lands, for example in the famous Olduvai Gorge, began later.
The safaris inside the immense circular enclosure of the Ngorongoro allow contemplating today the most desired animals of Africa in a minimum space.
And some luxury hotel located on the edge of the caldera allows rates above such incomparable views.
5. A Living Crack
The Great Rift Valley is a living rift that widens every year. A fissure that stretches to one-eighth the circumference of the Earth and, with some branches, runs between Mozambique and Lebanon.
In it, lavas recently gestated in the bowels of the planet emerge, cauterizing and then revitalizing some of the oldest soils in the world.
It is said, and it seems true, that the great Rift fault will end up splitting a fragment of the African continent.
If the crack continues to expand, the sea will invade it and form a huge island with the eastern part of Ethiopia, all of Somalia, and half of Kenya and Tanzania. As was the case with Madagascar. Or with what is now India, which, after separating from southern Africa, undertook a long drift north until it embedded itself in Asia and formed the Himalayas as a result of that encounter –the Seychelles islands are fragments broken off from the Indian subcontinent on that journey.
Or as we see in the Red Sea, a wedge between Africa and the Arabian Peninsula that is also part of the Great Rift Valley, in this case, submerged under the waters of the Indian Ocean.
6. Gregory’s Find
Geology requires a lot of imagination and Africa more than feeds it. In 1893 geologist John Walter Gregory, exploring Lakes Naivasha and Baringo, came across the impressive escarpment.
After collecting and analyzing the rocks, he understood that this valley was not like the others. That is to say, it had not been formed by the emptying, grain by grain and stone by stone, of the materials that filled that space, but by a massive collapse of the ground while the neighboring land maintained its level.
More or less as if a bridge collapsed because it could not withstand the tension produced by the gradual separation of its banks. There were other such valleys on Earth, but none could match it in size.
Hence the name Great Rift Valley (“pit”), with which Gregory baptized the place.
7. And Also Volcanoes
It was still too early to know that the earth’s crust is fragmented into plates, that these move away or come closer separating or uniting continents -and causing sinking like the Rift-, or that volcanic eruptions usually take place taking advantage of the weakness of the crust in those seams. But Gregory had found a point of the skein.
The volcanoes are precisely the other great element that makes up the landscape of the Rift. Those lava totem poles rising into the sky do more than just erupt: they bring rain, rejuvenate the land, fertilize the soil… The Ol Doinyo Lengai, the “Mountain of the Gods”, the sacred volcano of the Maasai, is today the only one active in Tanzania.
Its lava, rich in sodium and potassium carbonates and very poor in silica, unlike that of the rest of the world’s volcanoes, flows with the fluidity of water and at unusually low temperatures.
East African Rift Boundary Type
East African Rift system is a tectonic plate boundary that includes several smaller arms or plates
East African Rift Is An Example of what?
The East African Rift Valley is a classical example of a disparate boundary in a continental crust area.
Without mincing words, it’s one of the earthly wonders of the world, that shows it as a place where the earth’s tectonic forces try to create new plates by shedding the old ones away.
Why the Great Rift Valley is Important
The Rift Valley, since its discovery, has been a rich source of fossils to enable scientists to make seep examinations about human evolution, especially in the Piedmont area.
The rapidly disintegrating highlands have filled the valley with residues and made it a favorable environment for the conservation of created remains.
Rift Valley Examples
Some notable examples of rift valleys include the East African Rift Valley, Mid-Atlantic Ridge, the East Pacific Rift Valley, and the Rio Grande Rift Valley.
Author
Abbey Johnson has a Masters degree as an engineer and has over 3 years of teaching and research experience. He is happiest when on a bike and is also interested in electric energy and computer Science.