Northern section of the Great Rift Valley. The [[Sinai Peninsula is in center 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 30-100 km and in depth from a few hundred to several thousand metres. It has been created through the rifting and separation of the
African and
Arabian tectonic plates that began around 35 million years ago in the north, and by the ongoing separation of East Africa from the rest of Africa along the East African Rift, which began about 15 million years ago. It was named by the explorer John Walter Gregory.
The northernmost part of the Rift forms the valley of the
Jordan River, which flows southward through the
Hula Lake and the
Sea of Galilee in
Israel to the
Dead Sea. From the Dead Sea southwards, the Rift is occupied by the Wadi
Arabah and then the
Gulf of Aqaba and the
Red Sea.
The southern end of the Red Sea marks a fork in the rift. 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 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.
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. Within a few million years, the lithosphere may rupture and eastern Africa will split off to form a new landmass. If spreading continues, 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.
The Rift Valley has been a rich source of
anthropological discovery, especially in
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 Maeve Leakey have also done significant work in this region.
External links
Category:Faults
de:Rift Valley
he:השבר הסורי אפריקני
nl:Grote Slenkvallei
ja:グレート・リフト・バレー
pl:Wielkie Rowy Afrykańskie
pt:Vale do Rift
fi:Itä-Afrikan hautavajoama
sv:Östafrikanska riftsystemet
zh:東非大裂谷