A water gap is a gap that flowing water has carved through a

mountain range A mountain range or hill range is a series of mountains or hills arranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have ari ...

mountain ridge A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a continuous elevated crest for an extended distance. The sides of the ridge slope away from the narrow top on either side. The line ...

and that still carries water today. Such gaps that no longer carry water currents are called wind gaps. Water gaps and wind gaps often offer a practical route for

road A road is a linear way for the conveyance of traffic that mostly has an improved surface for use by vehicles (motorized and non-motorized) and pedestrians. Unlike streets, the main function of roads is transportation. There are many types o ...

and

rail transport Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a prep ...

to cross the mountain barrier.

Geology

A water gap is usually an indication of a

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of ...

that is older than the current topography. The likely occurrence is that a river established its course when the landform was at a low elevation, or by a rift in a portion of the crust of the earth having a very low stream gradient and a thick layer of unconsolidated

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...

. In a hypothetical example, a river would have established its channel without regard for the deeper layers of rock. A later period of

uplift Uplift may refer to: Science * Geologic uplift, a geological process ** Tectonic uplift, a geological process * Stellar uplift, the theoretical prospect of moving a stellar mass * Uplift mountains * Llano Uplift * Nemaha Uplift Business * Upli ...

would cause increased

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is d ...

along the riverbed, exposing the underlying rock layers. As the uplift continued, the river, being large enough, would continue to erode the rising land, cutting through ridges as they formed. Water gaps are common in the Ridge-and-Valley Appalachians of eastern

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

. Alternatively, a water gap may be formed through headward erosion of two streams on opposite sides of a ridge, ultimately resulting in the

capture Capture may refer to: *Asteroid capture, a phenomenon in which an asteroid enters a stable orbit around another body *Capture, a software for lighting design, documentation and visualisation *"Capture" a song by Simon Townshend *Capture (band), an ...

of one stream by the other.

Notable examples

Chicago Portage The Chicago Portage was an ancient portage that connected the Great Lakes waterway system with the Mississippi River system. Connecting these two great water trails meant comparatively easy access from the mouth of the St Lawrence River on the Atl ...

Illinois Illinois ( ) is a state in the Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolitan areas include, Peoria and Rock ...

Saddle Point In mathematics, a saddle point or minimax point is a point on the surface of the graph of a function where the slopes (derivatives) in orthogonal directions are all zero (a critical point), but which is not a local extremum of the functi ...

runs through the city itself. *

Columbia River Gorge The Columbia River Gorge is a canyon of the Columbia River in the Pacific Northwest of the United States. Up to deep, the canyon stretches for over as the river winds westward through the Cascade Range, forming the boundary between the st ...

, Oregon and Washington, and

Wallula Gap Wallula Gap () is a large water gap of the Columbia River in the northwest United States in southeast Washington. It cuts through the Horse Heaven Hills basalt anticlines in the Columbia River Basin, just south of the confluence of the Wa ...

, Washington, United States * Cumberland Narrows, Maryland, United States * Delaware Water Gap, New Jersey and Pennsylvania, United States * Heavitree Gap, Alice Springs, Australia *

Iron Gates The Iron Gates ( ro, Porțile de Fier; sr, / or / ; Hungarian: ''Vaskapu-szoros'') is a gorge on the river Danube. It forms part of the boundary between Serbia (to the south) and Romania (north). In the broad sense it encompasses a ...

on the Danube River, forming the border between Serbia and Romania * Kali Gandaki Gorge - cuts through the world's tallest mountain range, the

Himalayas The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 10 ...

in Nepal * Manawatu Gorge, New Zealand * Middle Rhine in Germany * Pongo de Mainique, Peru - on the

Urubamba River The Urubamba River or Vilcamayo River (possibly from Quechua ''Willkamayu'', for "sacred river") is a river in Peru. Upstream it is called Vilcanota River (possibly from Aymara ''Willkanuta'', for "house of the sun"). Within the La Convención ...

* Pongo de Manseriche, Peru - on the Marañón River * Potomac Water Gap, United States * Weltenburg Narrows on the

Danube River The Danube ( ; ) is a river that was once a long-standing frontier of the Roman Empire and today connects 10 European countries, running through their territories or being a border. Originating in Germany, the Danube flows southeast for , pa ...

in Bavaria

Geology

Notable examples

See also