A canyon (from
Spanish: cañón; archaic
British English spelling: cañon),[1]gorge or chasm, is a deep cleft between
escarpments or
cliffs resulting from
weathering and the
erosive activity of a river over
geologic time scales.[2] Rivers have a natural tendency to cut through underlying surfaces, eventually wearing away rock layers as
sediments are removed downstream. A
river 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's
headwaters and
estuary 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 the
Rocky Mountains, the
Alps, the
Himalayas or the
Andes. Usually, a river or stream carves out such splits between mountains. Examples of mountain-type canyons are
Provo Canyon in Utah or
Yosemite Valley in California's
Sierra 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 word canyon is Spanish in origin (cañón,[4]pronounced[kaˈɲon]), with the same meaning. The word canyon is generally used in
North America, while the words gorge and ravine (French in origin) are used in
Europe and
Oceania, though gorge and ravine are also used in some parts of North America. In the
United States, place names generally use canyon in the southwest (due to their proximity to
Spanish-speaking Mexico) and gorge in the northeast (which is closer to
French Canada), with the rest of the country graduating between these two according to geography. In
Canada, a gorge is usually narrow while a ravine is more open and often wooded. The military-derived word defile is occasionally used in the
United Kingdom.
Formation
Most canyons were formed by a process of long-time
erosion from a
plateau or table-land level. The
cliffs form 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 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 as
shales. 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.[5] Canyon walls are often formed of resistant
sandstones or
granite.
Sometimes large rivers run through canyons as the result of gradual geological uplift. These are called
entrenched rivers, because they are unable to easily alter their course. In the United States, the
Colorado River in the
Southwest and the
Snake River in the
Northwest are two examples of
tectonic uplift.
Canyons often form in areas of
limestone 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 the
Mendip Hills in
Somerset and
Yorkshire Dales in
Yorkshire, England.
A box 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 the
western United States as convenient corrals, with their entrances fenced.[6]
Largest
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 the
Himalaya 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 flat
plateaus (which have a somewhat well-defined rim elevation).
The
Yarlung Tsangpo Grand Canyon (or Tsangpo Canyon), along the
Yarlung Tsangpo River in
Tibet, is regarded by some as the deepest canyon in the world at 5,500 metres (18,000 ft). It is slightly longer than the
Grand Canyon in the United States.[7] Others consider the
Kali 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.
Vying for the deepest canyon in the Americas is the
Cotahuasi Canyon and
Colca Canyon, in southern Peru. Both have been measured at over 3,500 metres (11,500 ft) deep.
The
Grand Canyon of northern
Arizona 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),[8] is one of the world's largest canyons. It was among the 28 finalists of the
New 7 Wonders of Nature worldwide poll. (Some referred to it as one of the
seven natural wonders of the world.)[9]
In August 2013, the discovery of
Greenland's
Grand Canyon was reported, based on the analysis of data from
Operation 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.[11]
Despite not being quite as deep or long as the Grand Canyon, the
Capertee Valley in Australia is actually 1 km wider than the Grand Canyon, making it the widest canyon in the world.[12][13]
Panoramic view of the
Capertee Valley in Australia, the widest largest canyon in the world
Cultural significance
Some canyons have notable cultural significance. Evidence of
archaic humans has been discovered in Africa's
Olduvai Gorge. In the southwestern United States, canyons are important
archeologically because of the many
cliff-dwellings built in such areas, largely by the
ancient Pueblo people who were their first inhabitants.
Antecedent drainage stream – stream maintaining its original course and pattern despite the changes in underlying rock topPages displaying wikidata descriptions as a fallback
Canyoning – Traveling in canyons using a variety of techniques
Draw (terrain) – Terrain feature formed by two parallel ridges or spurs with low ground in betweenPages displaying short descriptions of redirect targets
^Cohen, Callan; Spottiswoode, Claire & Rossouw, Jonathan (2006). Southern African Birdfinder. Penguin Random House South Africa. p. 210.
ISBN978-1-86872-725-4.