Canyon

Grand Canyon, Arizona.

Noravank Monastery complex and canyon in Armenia.

A canyon or gorge is a deep valley between cliffs, often carved from the landscape by a river. A famous example is the Grand Canyon in Arizona. In the southwestern United States, canyons are important archeologically because of the many cliff-dwellings built there, largely by the earlier inhabitants, the ancient Pueblo Peoples.

A submarine canyon is a steep-sided valley on the sea floor of the continental slope. Many submarine canyons are found as extensions to large rivers, but many others have no such association. Canyons cutting the continental slopes have been found at depths greater than two kilometers below sea level. They are formed by powerful turbidity currents, volcanic and earthquake activity. Many submarine canyons continue as submarine channels across continental rise areas and may extend for hundreds of kilometers.

Terminology

The word canyon derives from the Spanish word (cañón). The word canyon is generally used in the United States, while the word gorge is more common in Europe and Oceania, though it is also used in some parts of the United States and Canada. The word defile is occasionally used in England, to signify a narrow gorge.

Formation of canyons on land

Most canyons were formed by a process of long-time erosion from a plateau level. The cliffs are formed because harder rock strata that are resistant to erosion and weathering remain exposed on the valley walls. Canyons are much more common in arid areas than in wetter areas because weathering has a lesser effect in arid zones. Canyon walls are often formed of resistant sandstones or granite.

Sometimes large rivers run through canyons as the result of gradual geologic uplift. These are called entrenched rivers, because they are unable to easily alter their course. The Colorado River and the Snake River in the northwestern United States are two examples of tectonic uplift.

Canyons often form in areas of limestone rock. Limestone is to a certain extent soluble, so cave systems form in the rock. When these collapse a canyon is left, for example in the Mendip Hills in Somerset and Yorkshire Dales in Yorkshire, England.

Formation of submarine canyons

Submarine canyons are more common on steep slopes than on gentle slopes. They show erosion through all substrates, from unlithified sediment to crystalline rock. Various mechanisms have been proposed for the formation of these canyons, and they were subject to active debate, especially during the 1940s and 1950s.

An early theory was that they were carved during glacial times, when the sea level was about 200 meters below what it is today, and rivers flowed to the edge of the continental shelf. Indeed, many (but not all) canyons are found offshore from major rivers. Yet this mechanism cannot explain erosion reaching water depths as great as 3,000 meters, where canyons have been mapped. It has been well established (by many lines of evidence) that sea levels did not fall to those depths.

It is now understood that several mechanisms have contributed to submarine canyon formation and development, even within the same canyon. The major mechanism of canyon erosion is now thought to be turbidity currents and underwater landslides. Turbidity currents are dense, sediment-laden currents that flow downslope when an unstable mass of sediment that has been rapidly deposited on the upper slope fails, perhaps triggered by earthquakes. There is a spectrum of turbidity- or density-current types ranging from "muddy water" to massive mudflow, and evidence for both these end members can be found in deposits associated with the deeper parts of submarine canyons and channels.

Mass wasting, slumping, and submarine landslides are forms of slope failures (the effect of gravity on a hillslope) observed in submarine canyons. Mass wasting is the term used for the slower and smaller action of material moving downhill; and would commonly include the effects of bioerosion: the burrowing, ingestion, and defecation of sediment by living organisms. Slumping generally refers to rotational movement of masses on a hillside. Landslides, or slides, generally consist of the detachment and displacement of sediment masses. All are observed and are contributory processes.

Largest canyons on land

The Grand Canyon in Arizona, United States, and the Copper Canyon in Chihuahua, Mexico are two of the largest canyons in the world. Yet, the definition of "largest canyon" is rather imprecise, because a canyon system can be "large" in terms of its depth, length, or total area of the system. The definition of "deepest canyon" is similarly imprecise, especially if one includes mountain canyons as well as canyons that cut through relatively flat plateaus (which have a somewhat well-defined rim elevation). The inaccessibility of the major canyons in the Himalaya mountain range is one reason why they are usually not regarded as candidates for the biggest canyon.

The Yarlung Tsangpo Canyon, along the Yarlung Tsangpo River in Tibet, is regarded by some as the deepest canyon in the world, and it is even slightly longer than Grand Canyon. Hence it is regarded by many as the world's largest canyon, followed by the Kali Gandaki Gorge in Nepal, Polung Tsangpo Canyon in Tibet, Cotahuasi Canyon (3,535 m deep and the deepest in the Americas), and the Tekezé gorge (2000m+ deep and deepest in Africa).

Slot canyons are very narrow canyons, often with smooth walls.

Other well-known canyons

• Avon Gorge in Bristol, England
• Blyde River Canyon in Mpumalanga, South Africa
• Black Canyon of the Gunnison, Colorado, USA
• Canyon Fortaleza in Cambará do Sul, Brazil
• Canhão da Nazaré, Portugal
• Canyon Guartelá in Tibagi, Brazil
• Cañon del Sumidero in Chiapas, Mexico
• Cataract Gorge in Launceston, Australia
• Cheddar Gorge in Somerset, England
• Colca Canyon along the Colca River in Arequipa, Peru one of the deepest canyons in the world with 3269 meters.
• Columbia River Gorge in the Pacific Northwest of America.
• Cotahuasi Canyon along the Cotahuasi River in Arequipa, Peru, the deepest canyon in the world with 3535 meters.
• Fish River Canyon in Namibia
• Glen Nevis in Lochaber, Scotland
• Grand Canyon of Pennsylvania located in the Tioga State Forest in Pennsylvania, USA
• Grand Canyon of the Yellowstone located within Yellowstone National Park in Wyoming, USA
• Grand Canyon du Verdon in Provence, France
• Gorges d'Ardèche, in France
• Gorges du Tarn in France
• Hells Canyon in Idaho and Oregon, USA
• Ironbridge Gorge in Shropshire, England
• Itaimbezinho in Cambará do Sul, Brazil
• Kloof Gorge in Kloof, South Africa
• Komati Gorge, South Africa
• Lanner Gorge, South Africa
• Malacara in Praia Grande, Brazil
• Palo Duro Canyon in Texas, USA
• Pankisi Gorge in Georgia (country)
• Red River Gorge in Kentucky, USA
• Royal Gorge in Colorado, USA
• Samaria Gorge in Crete, Greece
• Tara River Canyon in Montenegro
• Taroko Gorge in Taiwan
• Three Gorges in China
• Kings Canyon in California, USA
• Vikos Gorge in Greece

Some lesser-known canyon systems are:

• Black Dragon Canyon in Utah, USA
• Swaan River makes many gorges in Pothohar plateau Pakistan.
• Gorges in the sandstone rock of the Blue Mountains west of Sydney in New South Wales, Australia.

Examples of submarine canyons

• Congo canyon, the largest river canyon, extending from the Congo river, is 800 km (500 miles) long, and 1,200m (4000 ft) deep.
• Amazon canyon, extending from the Amazon river
• Hudson canyon[1], extending from the Hudson river
• Ganges canyon, extending from the Ganges river
• Indus canyon, extending from the Indus river
• Monterey Canyon, off the coast of central California
• La Jolla and Scripps canyon, off the coast of La Jolla, southern California
• Whittard Canyon, Atlantic Ocean off southwest Ireland
• Bering Canyon, in the Bering sea
• Zhemchug Canyon the largest submarine canyon in the world, also in the Bering sea.

Canyons on other planetary bodies

• Valles Marineris on Mars is the largest known canyon in the solar system
• Ithaca Chasma on Saturn's moon Tethys

See also

• Geomorphology
• Geology
• Earth science

References

ISBN links support NWE through referral fees

• Abbott, Lon, and Terri Cook. 2004. Hiking the Grand Canyon's Geology. Seattle, WA: Mountaineers Books. ISBN 0898868955.

• Beus, Stanley S., and Michael Morales. 2003. Grand Canyon Geology. 2nd ed. New York: Oxford University Press. ISBN 0195122992.

• Erickson, Jon. 2001. Rock Formations and Unusual Geologic Structures. Exploring the Earth's Surface. New York: Facts on File. ISBN 0816043280.

• Plummer, Charles C., David McGeary, and Diane H. Carlson. 2005. Physical Geology. Boston: McGraw-Hill. ISBN 007252815X.

• Whitney, Stephen. 1996. A Field Guide to the Grand Canyon. Seattle, WA: Mountaineers. ISBN 0898864895.

External links

All links retrieved September 29, 2007.

• Grand Canyons of Earth. canyonsworldwide.com.
• Friends of the Ravines
• Etymology of "canyon"
• Pictures of a smaller Gorge in Jeffersonville, VT
• Cotahuasi Canyon
• Modern deep-water canyons

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