Rift valley

Rift Valley

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Rift valley

A rift valley is a linear-shaped lowland between highlands or mountain ranges created by the action of a geologic rift

Rift

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Rift valley

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A rift valley is a linear-shaped lowland between highlands or mountain ranges created by the action of a geologic rift

Rift

In geology, a rift is a place where the Earth's Crust and lithosphere are being pulled apart and is an example of extensional tectonics.Typical rift features are a central linear downdropped geologic fault segment, called a graben, with parallel normal faulting and rift-flank uplifts on either side forming a rift valley, where the rift r...
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. When the tensional forces are strong enough to cause the plate to split apart it will do so such that a center block will drop down relative to its flanking blocks. This creates the nearly parallel steeply dipping walls. This feature is the beginning of the rift valley. As this process continues the valley gets wider and wider until it becomes a large basin that fills with sediment from the rift walls and the surrounding area. One of the better long term examples of this process is the Basin and Range province in Nevada and Utah. Rifts can occur at all elevations, from the sea floor to plateaus and mountain ranges. They can occur in continental crust

Continental crust

The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as Continental shelf....
or in oceanic crust

Oceanic crust

Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or Sima ....
. 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

Mid-ocean ridge

A mid-ocean ridge or mid-oceanic ridge is an underwater mountain range, typically having a valley known as a rift running along its spine, formed by plate tectonics....
system and is the result of sea floor spreading. Examples of this type of rift include the Mid-Atlantic Ridge

Mid-Atlantic Ridge

The Mid-Atlantic Ridge is a mid-ocean ridge, a divergent tectonics plate boundary located along the floor of the Atlantic Ocean, and the longest mountain range in the world....
and the East Pacific Rise

East Pacific Rise

The East Pacific Rise is a mid-oceanic ridge, a divergent tectonic plate boundary located along the floor of the Pacific Ocean. It separates the Pacific Plate to the west from the North American Plate, the Rivera Plate, the Cocos Plate, the Nazca Plate, and the Antarctic Plate....
.

Many existing continental rift valleys are the result of a failed arm (aulacogen

Aulacogen

In geology, an aulacogen is a failed arm of a triple junction of a plate tectonics rift system. A triple junction beneath a continental plate initiates a three way breakup of the continental plate....
) of a triple junction

Triple junction

A triple junction is the point where the boundaries of three tectonic plates meet. At the triple junction a boundary will be one of 3 types - a Mid-ocean ridge, oceanic trench or transform fault and triple junctions can be described according to the types of plate margin that meet at them....
, although there are two, the East African Rift

East African Rift

The East African Rift is part of the larger Great Rift Valley. It is a continental rift zone that appears to be a developing Divergent boundary....
and the Baikal Rift Zone

Baikal Rift Zone

The Baikal Rift Zone is a divergent plate boundary centered beneath Lake Baikal in southeastern Russia. To its west is the Eurasian Plate and to its east is the Amur Plate which is moving away from the rift toward Japan at about 4 mm per year....
, which are currently active, as well as a third which may be, the West Antarctic Rift

West Antarctic Rift

The West Antarctic Rift is a major, active rift lying between East Antarctica and West Antarctica. It encompasses the Ross Sea, the area under the Ross Ice Shelf and a part of West Antarctica....
. In these instances, not only the crust, but also entire tectonic plate

Tectonic Plate

#REDIRECT Plate tectonics...
s 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

Dead Sea

For the Brian Keene book of the same name, see Dead Sea The Dead Sea is a salt lake between Israel and the West Bank to the west, and Jordan to the east....
lies in a rift which results from a leftward discontinuity in the left lateral-moving Dead Sea Transform

Dead Sea Transform

The Dead Sea Transform fault system, also sometimes referred to as the Dead Sea Rift, is a geologic fault which extends through the Jordan River Valley in the Middle East....
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 pond

Sag pond

A sag pond is a body of water, which forms as water collects in the lowest parts of the depression that forms between two strands of an active geologic fault....
s or landslide

Landslide

File:Guatemala landslide.jpgA landslide is a List of geological phenomena which includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments....
s.

The largest freshwater lakes in the world are all located in rift valleys. Lake Baikal

Lake Baikal

Lake Baikal is in southern Siberia in Russia, located between Irkutsk Oblast to the northwest and the Buryatia to the southeast, near the city of Irkutsk....
in Siberia

Siberia

Siberia , is the name given to the vast region constituting almost all of North Asia and for the most part currently serving as the massive central and eastern portion of the Russian Federation, having served in the same capacity previously for the Soviet Union from its beginning, and the Russian Empire beginning in the 16th century....
, a World Heritage Site

World Heritage Site

A UNESCO World Heritage Site is a site that is on the list maintained by the international World Heritage Programme administered by the UNESCO World Heritage Committee, composed of 21 Sovereign state which are elected by their General Assembly for a four-year term....
,, 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

Lake Tanganyika

Lake Tanganyika is a large lake in central Africa . It is estimated to be the List of lakes by volume in the world by volume, and the List of lakes by depth, after Lake Baikal in Siberia....
, second by both measures, is in the Albertine Rift, the westernmost arm of the active Great Rift Valley

Great Rift Valley

The Great Rift Valley is a name given in the late 19th century by British explorer John Walter Gregory to the continuous geographic trough, approximately in length, that runs from northern Syria in Southwest Asia to central Mozambique in East Africa....
of East Africa

East Africa

East Africa or Eastern Africa is the easterly region of the African continent, variably defined by geography or geopolitics. In the UN subregion, 19 territories constitute Eastern Africa:...
and Southwest Asia

Southwest Asia

Southwest Asia or Southwestern Asia is the southwestern subregion of Asia. The term West Asia is sometimes used in the United Nations subregion geoscheme and in writings about the archeology and the late prehistory of the region....
. Lake Superior

Lake Superior

Lake Superior is the largest of the five Great Lakes of North America. It is bounded to the north by Ontario, Canada and Minnesota, United States, and to the south by the U.S....
in North America

North America

North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and almost totally in the western hemisphere....
, the largest freshwater

Freshwater

Freshwater is a word that refers to bodies of water such as ponds, lakes, rivers and streams containing low concentrations of dissolved salts and other total dissolved solids....
lake

Lake

A lake is a terrain feature , a body of liquid on the surface of a world that is localized to the bottom of basin and moves slowly if it moves at all....
by area, lies in the ancient and dormant Midcontinent Rift. The largest subglacial lake, Lake Vostok

Lake Vostok

Lake Vostok is the largest of more than 140 subglacial lakes found under the surface of Antarctica. It is located beneath Russia's Vostok, Antarctica, 4,000 meters under the surface of the central Antarctic ice sheet....
, may also lie in an ancient rift valley. Lake Nipissing

Lake Nipissing

Lake Nipissing is a lake in the Canadian province of Ontario. It has a surface area of , a mean elevation of above sea level, and is located between the Ottawa River and Georgian Bay....
and Lake Timiskaming

Lake Timiskaming

Lake Timiskaming is a large freshwater lake on the Provinces and territories of Canada border between Ontario and Quebec, Canada. The lake, which forms part of the Ottawa River, is in length and covers an area of almost ....
in Ontario

Ontario

Ontario is a Provinces and territories of Canada located in the Central Canada part of Canada, the largest by population and second largest, after Quebec, in total area....
and Quebec

Quebec

Quebec , in French language, Qu?bec , is a Provinces and territories of Canada in the Central Canada and Eastern Canada regions of Canada....
, Canada

Canada

Canada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean....
lie inside a rift valley called the Ottawa-Bonnechere Graben

Ottawa-Bonnechere Graben

The Ottawa-Bonnechere Graben with its branch the Timiskaming Graben, is an ancient rift valley in the Canadian Shield of Northeastern Ontario and Quebec, Canada....
.

Rift valley

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