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http://geosciencemammino.wordpress.com/ The Great Rift Valley In this region the rift valley extends in a roughly north-south direction from the Afar depression, where the rift valley joins the oceanic domains of the Red Sea and Gulf of Aden, to the Zambezi river in Mozambique. The rift valleys are enormous fractures affecting the continental plates that widen progressively with time: they represent the first stages in the complex process of extension and rupture of continents and anticipate the development of new oceanic basins between them. The process is related to the divergent movements of lithospheric plates above the underlying asthenosphere in slow convective motion. The rift valley represents the primary and most superficial response to this divergence and to the consequent application of tensional forces to the plates, which is manifested through the development of normal faults. These represent fractures with vertical displacement of the Earth's surface that accommodate the separation of portions of the crust and determine the collapse of the block in between. Major normal fault systems thus give rise to the downthrowing of the valley floor with respect to the surrounding plateaus and form the huge tectonic escarpments bordering the rift valley. These tectonic movements give rise to a diffuse seismicity and volcanism, phenomena that are typically associated with the African rift valleys. 1 – Great Rift Valley 2 – Red Sea 3 – Atlantic Ocean NOTE Divergent boundary (or divergent margin) two plates are moving in opposite directions as in a mid-ocean ridge. Transform boundary (or transform margin) two plates are sliding past each other as in the San Andreas fault of California. Convergent boundaries (or convergent margin) two plates collide to form mountains or a subduction zone. The Great African Rift Valley is the south branch of the Afar Triangle. This is therefore an example of continental rifting. The width of the rift varies between 30-100kms and the depth also varies from a few hundred to a few thousand metres. The rift is 35million years old and is still growing meaning that East Africa, including the horn of Africa (Ethiopia, Somalia and Eritrea) will break away and form its own continent (the rift being filled by the sea). LANDFORMS Many parts of the rift are already filled by lakes: some freshwater and some salinized. Lake Tanganyika is the 2nd deepest lake in the world. Secondary landforms created as a result of the rift include Mt Kenya 5,200m extinct and Mt Kilimanjaro 5,900m dormant, the two tallest mountains (composite volcanoes) in Africa. Erta Ale is also a volcano in the Rift Valley but instead is a shield volcano that continuously erupts in the Afar depression. HUMAN USES/BENEFITS •Tourist attraction i.e. beautiful scenery (lakes, mountains) •Lakes in the rift valley provide fish. •Lakes in the rift valley provide water for domestic and industrial use and irrigation for agriculture. •Lakes are used for navigation. •There is forestry on the slopes, so source of timber. •Gentle slopes are used for arable farming and settlement. •Wildlife conservation. •Salt-water lakes are used for mining. •Production of geothermal electricity from underground.