Category:Canyon

A canyon (occasionally spelled cañon) or gorge is a deep ravine between pairs of escarpments or cliffs and is most often carved from the landscape by the erosive activity of a river over geologic timescales. Rivers have a natural tendency to cut through underlying surfaces so will eventually wear away rock layers to lessen their own pitch slowing their waters; given enough time, their bottoms will gradually reach a baseline elevation—which is the same elevation as the body of water it will eventually drain into. This action, when the river source and mouth are at much different base elevations will form a canyon,[1] particularly through regions where softer rock layers are intermingled with harder layers more resistant to weathering.

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. Canyon walls are often formed of resistant sandstones or granite. Submarine canyons form underwater, generally at the mouths of rivers.

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. Canyons often form in areas of limestone rock. As Limestone is soluble to a certain extent, cave systems form in the rock. Usually a river or stream and erosion carve out such splits between mountains. Canyons within mountains or gorges that only have an opening on one side are called box canyons. Slot canyons are very narrow canyons, often with smooth walls.