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Rift valley

earth science Maturity 11-13 Next article →

A rift valley is a long, low area of land. It sits between higher lands or mountain ranges. These valleys are created by a geologic rift. This happens because of extensional tectonics. This term describes the pulling apart of the lithosphere. The lithosphere is the outer layer of the Earth. As the ground stretches, the land sinks down. This creates a linear depression.

Browncanyonquilotoa
Browncanyonquilotoa

Over time, forces of erosion can make these valleys even deeper. The valleys often fill with sedimentary deposits. These deposits come from the rift flanks and surrounding areas.

The process of forming a rift can happen in many ways. One method involves the breaking apart of entire tectonic plates. When this happens, the crust pulls away from itself. If this process continues, a continental rift can eventually become an oceanic rift. Another way rifts form is through faults. A fault is a crack in the Earth's crust. Some rifts happen because of bends in strike-slip faults. These are faults where rocks move horizontally past each other. If a bend occurs in the direction of the motion, extension happens. This stretching causes subsidence, which is the sinking of the ground.

Geologists categorize rifts into several different types. The most extensive rifts are found on the sea floor. These occur along the crest of the mid-ocean ridge system. This is caused by a process called sea floor spreading. Examples include the Mid-Atlantic Ridge and the East Pacific Rise. Other rifts are continental in nature. Some are the result of a failed arm of a triple junction. These failed arms are called aulacogens. On a smaller scale, faults can create minor features. These include things like landslides or small sag ponds.

Several continental rift valleys are currently active on Earth. The East African Rift is one of the most famous examples. The Rio Grande rift is another active system. The Baikal Rift Zone is a third active continental rift. Scientists also believe the West Antarctic Rift System may be active. These active rifts show how the Earth's surface is still changing. They provide a way to study how plates move and break. These systems can eventually change the map of our entire planet.

Rift valleys are often home to some of the largest lakes on Earth. Lake Baikal in Siberia is a famous example. It is a World Heritage Site located in an active rift valley. Baikal is the deepest lake in the world. It also holds the greatest volume of liquid freshwater on Earth. It contains 20% of all the liquid freshwater on our planet.

NASA - Visible Earth, Lakes of the African Rift Valley
NASA - Visible Earth, Lakes of the African Rift Valley

Lake Tanganyika is the second largest by both depth and volume. It sits in the Albertine Rift in East Africa.

Thingvallavatn Lake
Thingvallavatn Lake

Other significant lakes are also tied to rift systems. Lake Superior in North America is the largest freshwater lake by area. It lies within the ancient and dormant Midcontinent Rift. In Canada, the Ottawa-Bonnechere Graben contains Lake Nipissing and Lake Timiskaming. Some scientists believe the subglacial Lake Vostok may also lie in an ancient rift valley. These lakes show how much water can collect in these low areas. They demonstrate the long-lasting impact of geologic rifts on the landscape.

Rift valleys are not unique to Earth. We can find them on other planets and moons in our solar system. Mars has a massive rift system called Valles Marineris. This system is 4,000 km long. On Venus, the Devana Chasma is also 4,000 km long. Some natural satellites also show these features. The moon Tethys has the Ithaca Chasma, which is 2,000 km long. Charon has the Nostromo Chasma in the Pluto system.

Ottawabonnecheregrabenmap
Ottawabonnecheregrabenmap

Studying these rifts helps us understand the geology of the entire solar system.

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File:NASA - Visible Earth, Lakes of the African Rift Valley.jpg
NASA - Visible Earth, Lakes of the...
File:Browncanyonquilotoa.jpg
Browncanyonquilotoa.jpg
File:Ottawabonnecheregrabenmap.png
Ottawabonnecheregrabenmap.png
File:Thingvallavatn Lake.jpg
Thingvallavatn Lake.jpg
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