East African Trench
The East African Rift ( Engl. East African Rift System (EARS)) is part of the Great African grave breach ( Great Rift Valley ). The latter stretches around 6000 km from Syria in the north over the Jordan Valley and the Red Sea to the Gulf of Aden . The East African Rift Valley begins here in the highlands of Ethiopia , a continental rift valley whose geological activity gave rise to the highest mountains and deepest lakes in Africa . It runs through the whole of East Africa to Mozambique in two large branches .
Emergence
This deep fault in the earth's crust was probably formed 20 million years ago as a result of massive volcanic eruptions . The base of this crack, which is up to about 300 km wide, is up to 1000 m below the upper edge of the rift, but the crack continues several kilometers deep into the lithosphere . Volcanoes formed on both sides of the rift; in the eastern branch, these are the Kilimanjaro massif and the Mount Kenya massif , which was formed during renewed tectonic and volcanic activities that began 3.5 million years ago and lasted about 2 million years. At the bottom of the trench, hydrothermal springs and igneous rocks are evidence of seismic activity. In the western branch of the rift valley runs a chain of lakes that includes some of the largest and deepest lakes on earth .
course
The East African Rift Valley begins in the Afar Triangle in Ethiopia, where three divergent tectonic plates are drifting apart: the Arabian plate and the Nubian and Somali part (Somali plate ) of the African plate . One speaks of a triple point . This is where the Red Sea, which separates the African from the Arabian Plate, the mid-ocean ridge of the Indian Ocean and the East African Rift meet. Below this weak zone of the lithosphere there is a mantle diapir which , as a hot spot, contributes to the expansion of the earth's crust at this point.
The "Abyssinian Rift" divides the highlands of Ethiopia , which connects to the south of the Afar triangle.
The East African Rift then continues in an eastern and a western rift valley, the two branches enclose the Tanzania craton on which Lake Victoria lies.
Eastern trench
The chain of lakes of the eastern rift valley, beginning with Lake Turkana , has no outflows into the sea. These lakes are shallower than the lakes in the west, but have a high mineral content due to volcanic and hydrothermal activities, which is increased by evaporation. Lake Magada is a soda lake with a very high sodium carbonate content, other lakes such as Lake Bogoria are also very alkaline . In contrast, the Baringo and Naivasha Lakes are freshwater lakes.
The volcanoes of the Mount Kenya massif , the Kilimanjaro massif , the Karisimbi , the Mount Meru and the Mount Elgon as well as the crater highlands in Tanzania were formed along this rift system . The Ol Doinyo Lengai volcano is still active and is the only active natrocarbonatite volcano in the world.
Western trench
Along the western rift valley ( Albert Graben ), a chain of lakes extends with Lake Albert in the north over Lake Kivu to Lake Tanganyika (1470 m deep), bounded by some of the highest mountains in Africa, the Virunga volcanoes with the Nyiragongo (3462 m), the Mitumba Mountains as the headwaters of the Congo and Zambezi and the Ruwenzori Mountains (up to 5109 m high).
In the south it continues over Lake Malawi to Mozambique to the mouth of the Zambezi .
future
The future development of the trench is controversial among researchers. One possibility would be for the Rift Valley to continue developing. In the next ten million years, the ocean could penetrate the rift system and new ocean floor would form along the rift. Eastern Africa would form its own land mass , drifting further from the rest of the continent . The upper course of the Nile would change its river bed and possibly lose some of its sources or flow into the newly emerging arm of the Indian Ocean . The other option is for the rift valley to come to a complete rest, so that the ditch would become an aulacogen .
Paleoanthropological finds
The Rift Valley is a region where numerous paleoanthropological discoveries have been made, especially the Olduvai Gorge . The rapid erosion of the highlands filled the valley with sediments , which provided good conservation conditions for fossils from various genera of the hominini . Renewed soil loss after rainfall today exposes these fossils, so that, for example, the teams of Louis Leakey and later Richard Leakey and Meave Leakey were able to make many discoveries in this region.
Another well-known hominid site is the Middle Awash region in the so-called Afar triangle . " Lucy ", the best-known surviving skeleton of an Australopithecus afarensis , and the fossil " Ardi " of an Ardipithecus ramidus recovered between 1994 and 1997 come from this area .
More recent are the excavations of the hominid corridor project , led by Timothy Bromage and Friedemann Schrenk in Malawi .
Effects on the weather
Today it is assumed by research as likely that the rapid uplift of mountains lying in north-south direction played a major role in the development of the upright gait of human ancestors. Due to the high mountains, clouds could no longer reach East Africa unhindered, which led to the fact that the originally existing tropical rainforest gave way to an increasingly dry savannah landscape due to a lack of replenishment of moisture , at the edges of which the first representatives of the upright, immediate ancestors of man (early Hominini ) developed.
literature
- Daniel Goliasch: A continent is falling apart - The African rift system. In: Nadja Podbregar; Dieter Lohmann: In focus: geological knowledge. How does our planet work? Springer Verlag, Berlin, Heidelberg, 2013, e- ISBN 978-3-642-34791-7 , pp. 79-89.
Web links
Individual evidence
- ↑ Ocean open. How Africa is tearing apart. On: focus.de on May 7, 2009, accessed on May 5, 2019.
- ↑ a b Primeval times: East African Trench. On: planet-wissen.de , accessed on May 5, 2019.
- ↑ The elemental force of water. The East African Trench (Part 2) . Accessed May 5, 2019.
- ^ East African Trench: The Riftlink Project. On: .planet-wissen.de , accessed on May 5, 2019.
- ↑ The upright walk. On: praehistorische-archaeologie.de , accessed on May 5, 2019.
- ↑ Africa - cradle of humanity. On: planet-wissen.de , accessed on May 5, 2019.