Everything about Rift Valley totally explained
A
rift valley is a linear-shaped lowland between highlands or mountain ranges created by the action of a geologic
rift or
fault. This action is manifest as crustal extension, a spreading apart of the surface which is subsequently further deepened by the forces of erosion. Rifts can occur at all elevations, from the seafloor to plateaus and mountain ranges. They can occur in
continental crust or in
oceanic crust. Rift valleys are often associated with a number of adjoining subsidiary or co-extensive valleys which are typically considered geologically part of the principal rift valley.
The most extensive rift valley is located along the crest of the
mid-ocean ridge system and is the result of
seafloor 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, but also 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 discontinuitues 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.
The largest freshwater lakes in the world are all located in rift valleys.
Lake Baikal in
Siberia, a
World Heritage Site,, lies in an active rift valley. Baikal is both the deepest lake in the world and, with 20% of all of the liquid freshwater on earth, has the greatest volume.
Lake Tanganyika, second by both measures, is in the
Albertine Rift, the westernmost arm of the active
Great Rift Valley of
East Africa and
Southwest Asia.
Lake Superior in
North America, the largest
freshwater lake by area, lies in the ancient and dormant
Midcontinent Rift. The largest subglacial lake,
Lake Vostok, may also lie in an ancient rift valley.
Lake Nipissing and
Lake Timiskaming in
Ontario and
Quebec,
Canada lie inside a rift valley called the
Ottawa-Bonnechere Graben.
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