Great Rift Valley

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Map of the Great Rift Valley MapGreatRiftValley.png
Map of the Great Rift Valley

The Great Rift Valley is a series of contiguous geographic trenches, approximately 7,000 kilometres (4,300 mi) in total length, that runs from the Beqaa Valley in Lebanon which is in Asia to Mozambique in Southeast Africa. [1] While the name continues in some usages, it is rarely used in geology as it is considered an imprecise merging of separate though related rift and fault systems.

Contents

Today, the term is most often used to refer to the valley of the East African Rift, the divergent plate boundary which extends from the Afar Triple Junction southward across eastern Africa, and is in the process of splitting the African Plate into two new separate plates. Geologists generally refer to these incipient plates as the Nubian Plate and the Somali Plate.

Theoretical extent

Diagram of a rift valley's future evolution into a sea Ocean-birth.svg
Diagram of a rift valley's future evolution into a sea
Satellite image of a graben in the Afar Depression Graben Afar ASTER 20020327.jpg
Satellite image of a graben in the Afar Depression

Today these rifts and faults are seen as distinct, although connected, but originally, the Great Rift Valley was thought to be a single feature that extended from Lebanon in the north to Mozambique in the south, where it constitutes one of two distinct physiographic provinces of the East African mountains. It included what today is called the Lebanese section of the Dead Sea Transform, the Jordan Rift Valley, Red Sea Rift and the East African Rift. [2] These rifts and faults were formed 35 million years ago.

Asia

The northeast corner of Jacob's Ford in Israel visualizes the drift of the Arabian Plate against the Nubian Plate NEcornerChastellet2009.JPG
The northeast corner of Jacob's Ford in Israel visualizes the drift of the Arabian Plate against the Nubian Plate

The northernmost parts of the Rift corresponds to the central section of what is called today the Dead Sea Transform (DST) or Rift. This midsection of the DST forms the Beqaa Valley in Lebanon, separating the Lebanon from the Anti-Lebanon Mountains. Further south it is known as the Hula Valley separating the Galilee mountains and the Golan Heights. [3]

The Jordan River begins here and flows southward through Lake Hula into the Sea of Galilee in Israel. The Rift then continues south through the Jordan Rift Valley into the Dead Sea on the Israeli-Jordanian border. From the Dead Sea southwards, the Rift is occupied by the Wadi Arabah, then the Gulf of Aqaba, and then the Red Sea. [3]

Off the southern tip of Sinai in the Red Sea, the Dead Sea Transform meets the Red Sea Rift which runs the length of the Red Sea. The Red Sea Rift comes ashore to meet the East African Rift and the Aden Ridge in the Afar Depression of East Africa. The junction of these three rifts is called the Afar Triple Junction. [3]

Africa

East African Rift Valley Great Rift Valley.png
East African Rift Valley
East Africa with active volcanoes (red triangles) and the Afar Triangle (shaded, center)--a triple junction where three plates are pulling away from one another. EAfrica.png
East Africa with active volcanoes (red triangles) and the Afar Triangle (shaded, center)—a triple junction where three plates are pulling away from one another.

The East African Rift follows the Red Sea to the end before turning inland into the Ethiopian highlands, dividing the country into two large and adjacent but separate mountainous regions. In Kenya, Uganda and the fringes of South Sudan, the Great Rift runs along two separate branches that are joined to each other only at their southern end, in Southern Tanzania along its border with Zambia. The two branches are called the Western Rift Valley and the Eastern Rift Valley.

The Western Rift, also called the Albertine Rift, is bordered by some of the highest mountains in Africa, including the Virunga Mountains, Mitumba Mountains, and Ruwenzori Range. It contains the Rift Valley lakes, which include some of the deepest lakes in the world (up to 1,470 metres (4,820 ft) deep at Lake Tanganyika).

Much of this area lies within the boundaries of national parks such as Virunga National Park in the Democratic Republic of Congo, Rwenzori National Park and Queen Elizabeth National Park in Uganda, and Volcanoes National Park in Rwanda. Lake Victoria is considered to be part of the rift valley system although it actually lies between the two branches. All of the African Great Lakes were formed as the result of the rift, and most lie in territories within 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 and tend to be shallow, they have a high mineral content as the evaporation of water leaves the salts behind. For example, Lake Magadi has high concentrations of soda (sodium carbonate) and Lake Elmenteita, Lake Bogoria, and Lake Nakuru are all strongly alkaline, while the freshwater springs supplying Lake Naivasha are essential to support its current biological variety.

The southern section of the Rift Valley includes Lake Malawi, the third-deepest freshwater body in the world, reaching 706 metres (2,316 ft) in depth and separating the Nyassa plateau of Northern Mozambique from Malawi; it ends in the Zambezi valley.

See also

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Rift valley Linear lowland created by a tectonic rift or fault

A rift valley is a linear shaped lowland between several highlands or mountain ranges created by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics. The linear depression may subsequently be further deepened by the forces of erosion. More generally the valley is likely to be filled with sedimentary deposits derived from the rift flanks and the surrounding areas. In many cases rift lakes are formed. One of the best known examples of this process is the East African Rift. On Earth, rifts can occur at all elevations, from the sea floor to plateaus and mountain ranges in continental crust or in oceanic crust. They are often associated with a number of adjoining subsidiary or co-extensive valleys, which are typically considered part of the principal rift valley geologically.

African Great Lakes Series of lakes in the Rift Valley

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The Arabian Plate is a minor tectonic plate in the northern and eastern hemispheres.

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The Jordan Rift Valley, also Jordan Valley, also called the Syro-African Depression, is an elongated depression located in modern-day Israel, Jordan, and Palestine. This geographic region includes the entire length of the Jordan River – from its sources, through the Hula Valley, the Korazim block, the Sea of Galilee, the (Lower) Jordan Valley, all the way to the Dead Sea, the lowest land elevation on Earth – and then continues through the Arabah depression, the Gulf of Aqaba whose shorelines it incorporates, until finally reaching the Red Sea proper at the Straits of Tiran.

East African Rift Active continental rift zone in East Africa

The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. In the past it was considered to be part of a larger Great Rift Valley that extended north to Asia Minor.

Afar Triangle Geological depression caused by the Afar Triple Junction

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References

  1. Merriam-Webster, Inc 편집부 (1997). MERRIAM WEBSTER'S GEOGRAPHICAL DICTIONARY 3/E(H). Merriam-Webster. p. 444. ISBN   978-0-87779-546-9.
  2. Philip Briggs; Brian Blatt (15 July 2009). Ethiopia: the Bradt travel guide. Bradt Travel Guides. p. 450. ISBN   978-1-84162-284-2.
  3. 1 2 3 G. Yirgu; C. J. (Cindy J.) Ebinger; P. K. H. Maguire (2006). The Afar Volcanic Province Within the East African Rift System: Special Publication No 259. Geological Society. pp. 306–307. ISBN   978-1-86239-196-3.

Further reading