East African Rift Valley is one of the most extensive rifts on the Earth's surface; the valley is about 6,400 kilometers long, averages 48 to 64 kilometers wide and has a depth from a few hundred to several thousand meters. The huge, brittle tectonic plates that make up Earth's crust normally move only a few centimeters per year, not fast enough to be noticeable in a human lifetime. However, in the East African Rift Valley, this tectonic motion is happening with remarkable speed. The East African Rift valley is an example of an active divergent rift, one of the few areas on Earth where a continent is being actively separated (rifted) by the ongoing forces of plate tectonics.
East Africa Rift System (EARS)
The East African rift system is widely recognized as the classical example of a continental rift system, which is part of the Afro Arabian rift system that extends from the Red Sea to Mozambique in the south. The rift is assumed to mark the incipient plate boundary between the Somali and Nubian micro-plates and linked to the Afar- Red Sea- Gulf of Aden rift systems (Figure 1). As the rift extends from the Ethiopian segment southwards it splits at about 5°N into the Eastern and Western branches. The two branches of the rift skirts around the Tanzania craton and formed within the Late Proterozoic belts adjacent to the margins of the craton. However, the Eastern Branch that comprises the Afar, Ethiopian, Turkana and Kenya rifts is older and relatively more volcanically active than the western branch that comprises Albert, Kivu, Tanganyika, Rukwa and Malawi rifts. The SW branch comprises
FIGURE 1: Structural map showing the East
African Rift System
(Modified from Atekwana et al., 2004)
The rift valleys are a system of normal faults bordering a 40-60 km wide trough, funneling out toward north in the Afar region. The Kenya Rift diverges into splays towards north (Turkana) and south Tanzania (Figure 2 and 3) (Baker et al). Domal uplift and extension causes the brittle crust to fracture into a series of normal faults giving the classic horst and graben structure of rift valleys. They are generally interpreted to be listric. Listric faults may be open in their upper part, and the gap is then filled with sedimentary breccias. Geologists today still debate why and how rifting comes about, but East Africa displays this process extremely clearly. Subterranean forces broke the earth's crust apart and large chunks of the crust sunk between parallel fault lines and forced up molten rock in volcanic eruptions. Many boiling hot springs along the rift prove that volcanic activity is extremely high along the rift system. The geothermal areas of the East-African Rift System are not all of the same type. Even though related to the rift the geological settings are different. Some are volcanic, others are not. Parts of the rift zones are highly volcanic but large segments of them are sediment or lake filled grabens. Page 1 of 5
FIGURE 2: Fault pattern in northern Kenya
(From: Baker, et al., 1972)
FIGURE 3: Fault pattern in southern Kenya and northern Tanzania (From: Baker, et al., 1972)
The East African Rift is one of the most important zones of the world where the heat energy of the interior of the earth escapes to the surface in the form of volcanic eruptions, earthquakes and the upward transport of heat by hot springs and natural vapor emanations (fumaroles).
In Ethiopia Exploration work peaked during the early to mid-1980’s when exploration drilling was carried out at the Aluto-Langano geothermal field (Lakes District). Eight deep exploratory wells were drilled to a maximum depth of about 2,500 m, and four were found to be productive with a maximum geothermal reservoir temperature of about 350ºC. During the early 1990’s exploration drilling was also carried out at Tendaho (Northern Afar). Three deep (2,100 m) and three shallow wells (500 m) confirmed the existence of a high...
References: 11- WENDY MILLER-EAST AFRICAN RIFT VALLEY PROJECT-GEOLOGY 306-WINTER, 2009
12- China Daily 08/03/2005 page2
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