Geologi

AFRICA's GREAT RIFT VALLEY

Around 25 million years ago an un predictable geological event started which radically changed the local rules of biological evolution on this part of the African continent. Between Ethiopia and Mozambique, a distance of 5 500 km, tectonic operation gave rise to the earth's largest visible rift valley (there are larger beneath the oceans).
Also this rift creation took place according to the characteristic Y-formation. Red Sea and Aden Gulf represents Y's upper part, according to the geologists the 'real' rift arms. The southbound and "false" arm cuts through Ethiopia to the border with Kenya and Lake Turkana where it splits into two branches encircling Lake Victoria. These two arms are united again in southern Tanzania, just north of Lake Malawi, thereafter passing through Mozambique to continue along the Indian Ocean bottom.


           Från Nigel Pavitt: Africa´s Great Rift Valley

The consequences of this process were monumental. A continuous belt of rainforest from the Indian Ocean in the east to the Atlantic in the west were drilled in the north-south direction by a broad and deep crack. Mountain ranges and volcanoes shot up the kilometers high when the unimaginable geological forces over millions of years shaped a completely different landscape over an area large as Europes.
Volcanoes Kilimanjaro, Meru, Ngorongoro, Empakaai, Olmoti and many others were built of lava and then coughed up enough additioinal lava to build Serengeti savannas. Even today Ol Doinyo Lengai contributes regularly with airborne lava pond in the Serengeti. The picture is from 2008.


www.volcanodiscovery.com

With its top five kilometers above the surroundings, Mount Kilimanjaro was built out of lava. Ngorongoro Crater is a collapsed volcano that once rose higher than Kilimanjaro. On its bottom and slopes the 250 km2 and 600 meters deep crater today harbors the earth's highest concentration of wild mammals.

New landscape arose. Nigel Pavitt, a retired officer, manager and photographer, writes in his superb coffee table book Africa's Great Rift Valley:

"Without lava there would be not Ethiopian Plateau or Central Kenya Highlands. Without composite volcanic cones made largely of lava, there would be no Mounts Kilimanjaro or Kenya, the two highest mountains in Africa. Without faulting, there would be no Rwenzori Mountains, the fabled Mountains of the Moon. [ ...] By chance, these changes to landfrom, climate, and vegetation combined to stimulate human evolution."

 

With ocean winds, lava ash was carried  westwards. When the volcanic activity gradually petered out, rain and wind caused a hard surface of oxidized lava tiles on the savannahs. These turned out to be impervious to tree roots over large areas. Organic materials transported by winds gave instead grass species an opportunity. East African savannas had been created, one of the world's largest concentrations of biomass. Along with other new habitats as soda lakes and semi-deserts, evolution received free rein to fill all these new niches with species. Elephants, antelopes, lions, cheetahs, giraffes, gorillas, chimpanzees, to name but a few. Never before on earth beheld. One of them stood up on two legs, more on that under Evolution.

 

TECTONICS

Tectonic operation, i.e. the continental plates moving over the earth, was launched as an idea in 1910 by American geologist F. B. Taylor. He based his findings on the observation that today's continents without much imagination can be joined together into a single land mass. A look at the world map confirms that the pieces fit rude well together.

The German scientist Alfred Wegener developed the theory in the 1940s by claiming that a super continent once emerged and then split up, due to Earth's rotation. Today, we are pretty sure that 200 million years ago existed a super continent, today named Pangaea. Its northern part is called Laurasia, the southern part Gondwana.

Africa today constituted Gondwana's central part. 200 million years ago the continental plate broke up. South America drifted to the northwest, Australia, India, and later Madagascar to the northeast. India collided with Asia's southern section, which was compressed and as a result the Himalaya mountain range was formed (and still continues to grow in height).

South America's split from Gondwana (or Africa today) was done by a classic rift formation. A rift is a valley, on land or sea bed, formed when tectonic plates split apart. It is characterized by a Y-shaped crack. In this case, the upper left portion of the Y is today's Middle Atlantic (between West Africa and Brazil), the right upper part of the Y cuts into West Africa and forms the Congo Basin, but is otherwise not visible because it cuts to the northeast beneath the earth's surface. Lower part of the Y consists of the South Atlantic.

These facts show how tectonic activity is in operation continuesly and, not the least, what fantastic consequences it entails.