When Did the Rift Valleys Form?
The great rift valleys of the earth took shape during the pleistocene age, about two million years ago. They were caused mainly by volcanic eruptions powerful enough to split a mountain range, thus creating a rift between the two sides of the volcano. Rift valleys are to be found in all parts of the world where volcanic action has been common.
The most impressive example is the Great Rift Valley which extends from northern Jordan in south-west Asia to Mozambique in south eastern Africa. Many big lakes are situated within the valley’s boundaries. Extremely steep edges are characteristic of these valleys. In Africa their edges rise to heights of 10,000 feet on either side.
The Great Rift Valley also known as the East African Rift Valley is a geological work of wonder. It was first named the Great Rift Valley by John Walter Gregory a British explorer that named it in the late 1800s. This massive trench is around 3,700 miles and is located at a tectonic plate boundary that is splitting apart.
The two plates started to separate about 35 million years ago and the Rift started to form. The East African Rift Valley covers an impressive amount of land and runs from Jordan Rift Valley to Mozambique in Africa.
The most extensive rift valley is located along the crest of the mid-ocean ridge system and is the result of sea floor spreading. Examples of this type of rift include the Mid-Atlantic Ridge and the East Pacific Rise.
Many existing continental rift valleys are the result of a failed arm (aulacogen) of a triple junction, although there are two, the East African Rift and the Baikal Rift Zone, which are currently active, as well as a third which may be, the West Antarctic Rift. In these instances, not only the crust, also the entire tectonic plates, are in the process of breaking apart to create new plates. If they continue, continental rifts will eventually become oceanic rifts.
Other rift valleys are the result of bends or discontinuities in horizontally-moving (strike-slip) faults. When these bends or discontinuities are in the same direction as the relative motions along the fault, extension occurs. For example, for a right lateral-moving fault, a bend to the right will result in stretching and consequent subsidence in the area of the irregularity.
In the view of many geologists today, the Dead Sea lies in a rift which results from a leftward discontinuity in the left lateral-moving Dead Sea Transform fault. Where a fault breaks into two strands, or two faults run close to each other, crustal extension may also occur between them, as a result of differences in their motions. Both types of fault-caused extension commonly occur on a small scale, producing such features as sag ponds or landslides.