Acanyon (fromSpanish:cañón; archaicBritish English spelling:cañon),[1]gorge orchasm, is a deep cleft betweenescarpments orcliffs resulting fromweathering and theerosive activity of a river overgeologic time scales.[2] Rivers have a natural tendency to cut through underlying surfaces, eventually wearing away rock layers assediments are removed downstream. Ariver bed will gradually reach a baseline elevation, which is the same elevation as the body of water into which the river drains. The processes of weathering and erosion will form canyons when the river'sheadwaters andestuary are at significantly different elevations,[3] particularly through regions where softer rock layers are intermingled with harder layers more resistant to weathering.
A canyon may also refer to a rift between two mountain peaks, such as those in ranges including theRocky Mountains, theAlps, theHimalayas or theAndes. Usually, a river or stream carves out such splits between mountains. Examples of mountain-type canyons areProvo Canyon in Utah orYosemite Valley in California'sSierra Nevada. Canyons within mountains, or gorges that have an opening on only one side, are called box canyons.Slot canyons are very narrow canyons that often have smooth walls.
The wordcanyon is Spanish in origin (cañón,[4]pronounced[kaˈɲon]), with the same meaning. The word canyon is generally used inNorth America, while the wordsgorge andravine (French in origin) are used inEurope andOceania, thoughgorge andravine are also used in some parts of North America. In the United States, place names generally usecanyon in the southwest (due to their proximity toSpanish-speaking Mexico) andgorge in the northeast (which is closer toFrench Canada), with the rest of the country graduating between these two according to geography. In Canada, agorge is usually narrow while aravine is more open and often wooded. The military-derived worddefile is occasionally used in the United Kingdom. In South Africa,kloof (inKrantzkloof Nature Reserve) is used along withcanyon (as inBlyde River Canyon) andgorge (inOribi Gorge).[5]
Most canyons were formed by a process of long-timeerosion from aplateau or table-land level. Thecliffs form because harderrock strata that areresistant to erosion and weathering remain exposed on the valley walls.
Canyons are much more common in arid areas than in wet areas because physical weathering has a more localized effect in arid zones. The wind and water from the river combine to erode and cut away less resistant materials such asshales. The freezing and expansion of water also serves to help form canyons. Water seeps into cracks between the rocks and freezes, pushing the rocks apart and eventually causing large chunks to break off the canyon walls, in a process known as frost wedging.[6] Canyon walls are often formed of resistantsandstones orgranite.
Sometimes large rivers run through canyons as the result of gradual geological uplift. These are calledentrenched rivers, because they are unable to easily alter their course. In the United States, theColorado River in theSouthwest and theSnake River in theNorthwest are two examples oftectonic uplift.
Canyons often form in areas oflimestone rock. As limestone is soluble to a certain extent,cave systems form in the rock. When a cave system collapses, a canyon is left, as in theMendip Hills inSomerset andYorkshire Dales inYorkshire, England.
Abox canyon is a small canyon that is generally shorter and narrower than a river canyon, with steep walls on three sides, allowing access and egress only through the mouth of the canyon. Box canyons were frequently used in thewestern United States as convenient corrals, with their entrances fenced.[7]
The definition of "largest canyon" is imprecise, because a canyon can be large by its depth, its length, or the total area of the canyon system. Also, the inaccessibility of the major canyons in theHimalaya contributes to their not being regarded as candidates for the biggest canyon. The definition of "deepest canyon" is similarly imprecise, especially if one includes mountain canyons, as well as canyons cut through relatively flatplateaus (which have a somewhat well-defined rim elevation).
TheYarlung Tsangpo Grand Canyon (or Tsangpo Canyon), along theYarlung Tsangpo River inTibet, China, is regarded by some as the deepest canyon on Earth at 5,500 metres (18,000 ft). It is slightly longer thanGrand Canyon in the United States.[8] Others consider theKali Gandaki Gorge in midwest Nepal to be the deepest canyon, with a 6,400-metre (21,000 ft) difference between the level of the river and the peaks surrounding it.[citation needed]
Vying for the deepest canyon in the Americas is theCotahuasi Canyon andColca Canyon, in southern Peru. Both have been measured at over 3,500 metres (11,500 ft) deep.
Grand Canyon of northernArizona in the United States, with an average depth of 1,600 metres (5,200 ft) and a volume of 4.17 trillion cubic metres (147 trillion cubic feet),[9] is one of the world's largest canyons. It was among the 28 finalists of theNew 7 Wonders of Nature worldwide poll. (Some referred to it as one of theseven natural wonders of the world.)[10]
In August 2013, the discovery ofGreenland'sGrand Canyon was reported, based on the analysis of data fromOperation IceBridge. It is located under an ice sheet. At 750 kilometres (470 mi) long, it is believed to be the longest canyon in the world.[12]
Despite not being quite as deep or long as Grand Canyon, theCapertee Valley in Australia is actually 1 km wider than Grand Canyon, making it the widest canyon in the world.[13][14]
Panoramic view of theCapertee Valley in Australia, the widest largest canyon in the world
Some canyons have notable cultural significance. Evidence ofarchaic humans has been discovered in Africa'sOlduvai Gorge. In the southwestern United States, canyons are importantarcheologically because of the manycliff-dwellings built in such areas, largely by theancient Pueblo people who were their first inhabitants.
^Cohen, Callan; Spottiswoode, Claire & Rossouw, Jonathan (2006).Southern African Birdfinder. Penguin Random House South Africa. p. 210.ISBN978-1-86872-725-4.
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