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Great Rift Valley

2007 Schools Wikipedia Selection. Related subjects: North American Geography

   Northern section of the Great Rift Valley. The Sinai Peninsula is in
   center and the Dead Sea and Jordan River valley above
   Enlarge
   Northern section of the Great Rift Valley. The Sinai Peninsula is in
   centre and the Dead Sea and Jordan River valley above

   The Great Rift Valley is a vast geographical and geological feature
   that runs north to south for some 5,000 km, from northern Syria in
   Southwest Asia to central Mozambique in East Africa. The valley varies
   in width from thirty to one hundred kilometers, and in depth from a few
   hundred to several thousand meters. It was named by the explorer John
   Walter Gregory.

Geography

   The northernmost part of the Rift forms the Beqaa Valley in Lebanon
   separating the Lebanon Mountains and Anti-Lebanon Mountains. To the
   south in Israel, it is known as the Hula Valley separating between the
   Galilee mountains and the Golan Heights. Further south, the valley
   becomes the Jordan River, which flows southward through from Lake Hula
   into Lake Tiberias in Israel and then continues South through the
   Jordan Valley into the Dead Sea on the Israeli-Jordanian Border. From
   the Dead Sea southwards, the Rift is occupied by the Wadi Arabah and
   then the Gulf of Aqaba and the Red Sea.
   The Jordan Rift Valley from space
   Enlarge
   The Jordan Rift Valley from space

   The southern end of the Red Sea marks a fork in the rift. The Afar
   Triangle or Danakil Depression of Eritrea is the probable location of a
   triple junction which is possibly underlain by a mantle plume. The Gulf
   of Aden is an eastward continuation of the rift - before the rift
   opened, the Arabian Peninsula was attached to the Horn of Africa - and
   from this point the rift continues as part of the Mid-oceanic ridge of
   the Indian Ocean. In a southwest direction the fault continues as the
   Great Rift Valley, which split the older Ethiopian highlands into two
   halves.

   In eastern Africa the valley divides into two, the Eastern Rift and the
   Western Rift.

   The Western Rift, also called the Albertine Rift, is edged by some of
   the highest mountains in Africa, including the Virunga Mountains,
   Mitumba Mountains, and Ruwenzori Range, and contains the Rift Valley
   lakes, which include some of the deepest lakes in the world (up to
   1,470 meters deep at Lake Tanganyika). Lake Victoria, the second
   largest area freshwater lake in the world, is considered part of the
   Rift Valley system although it actually lies between the two branches.
   The other Great Lakes are also formed by the rift.

   In Kenya the valley is deepest to the north of Nairobi. As the lakes in
   the Eastern Rift have no outlet to the sea, these lakes tend to be
   shallow and have a high mineral content as the evaporation of water
   leaves the salts behind. For example, Lake Magadi is almost solid soda
   ( sodium carbonate), and Lake Elmenteita, Lake Baringo, Lake Bogoria,
   and Lake Nakuru are all strongly alkaline, while Lake Naivasha needs to
   be supplied by freshwater springs to support its biological variety.
   Map of East Africa showing some of the historically active volcanoes
   (red triangles) and the Afar Triangle (shaded, center) — a triple
   junction where three plates are pulling away from one another: the
   Arabian Plate, and the two parts of the African Plate (the Nubian and
   the Somalian) splitting along the East African Rift Zone (USGS).
   Enlarge
   Map of East Africa showing some of the historically active volcanoes
   (red triangles) and the Afar Triangle (shaded, centre) — a triple
   junction where three plates are pulling away from one another: the
   Arabian Plate, and the two parts of the African Plate (the Nubian and
   the Somalian) splitting along the East African Rift Zone (USGS).

Geothermal activity

   The formation of the Rift Valley continues, probably driven by mantle
   plumes and ultimately a result of the African superswell. The
   associated geothermal activity and spreading at the rift has caused the
   lithosphere to thin from a typical 100 km thickness for continents to a
   mere 20 km. Though it is common for one arm of a triple junction to
   fail, if spreading continues the lithosphere may rupture several
   million years hence, splitting eastern Africa off to form a new
   landmass. In short, this will lead to the formation of a new mid-ocean
   ridge.

   The volcanic activity at this site and unusual concentration of
   hotspots has produced the volcanic mountains Mount Kilimanjaro, Mount
   Kenya, Mount Karisimbi, Mount Nyiragongo, Mount Meru and Mount Elgon as
   well as the Crater Highlands in Tanzania. The Ol Doinyo Lengai volcano
   remains active, and is currently the only natrocarbonatite volcano in
   the world.

Discoveries in human evolution

   The Rift Valley has been a rich source of fossils that allow study of
   human evolution, especially in an area known as Piedmont. Because the
   rapidly eroding highlands have filled the valley with sediments, a
   favourable environment for the preservation of remains has been
   created. The bones of several hominid ancestors of modern humans have
   been found there, including those of " Lucy", a nearly complete
   australopithecine skeleton, which was discovered by anthropologist
   Donald Johanson. Richard and Mary Leakey have also done significant
   work in this region.

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