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 arise ...

or mountain ridge and that still carries water today. Such gaps that no longer carry water currents are called

wind gap A wind gap (or air gap) is a gap through which a waterway once flowed that is now dry as a result of stream capture. A water gap is a similar feature, but one in which a waterway still flows. Water gaps and wind gaps often provide routes which ...

s. 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 of ...

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 p ...

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 wate ...

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 Stream gradient (or stream slope) is the grade (slope), grade (or slope) of a stream measured by the ratio of drop in elevation per unit horizontal distance, usually expressed as metre, meters per kilometre, kilometer or Foot (length), feet per mile ...

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 an ...

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

rock Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wales ...

. 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 * Uplif ...

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 dis ...

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 The Ridge-and-Valley Appalachians, also called the Ridge and Valley Province or the Valley and Ridge Appalachians, are a physiographic province of the larger Appalachian division and are also a belt within the Appalachian Mountains extending ...

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 the Car ...

. Alternatively, a water gap may be formed through

headward erosion Headward erosion is erosion at the origin of a stream channel, which causes the origin to move back away from the direction of the stream flow, lengthening the stream channel.Essentials of Geology, 3rd Ed, Stephen Marshak It can also refer to ...

of two streams on opposite sides of a ridge, ultimately resulting in the capture 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 At ...

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

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 function ...

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 Wall ...

, Washington, United States *

Cumberland Narrows The Cumberland Narrows (or simply The Narrows) is a water gap in western Maryland in the United States, just west of Cumberland. Wills Creek cuts through the central ridge of the Wills Mountain Anticline at a low elevation here between Wills Mo ...

, Maryland, United States *

Delaware Water Gap Delaware Water Gap is a water gap on the border of the U.S. states of New Jersey and Pennsylvania where the Delaware River cuts through a large ridge of the Appalachian Mountains. The gap makes up the southern portion of the Delaware Water Gap ...

, New Jersey and Pennsylvania, United States *

Heavitree Gap The Heavitree Gap, or ''Ntaripe'' in the Arrernte language, is a water gap in the Northern Territory of Australia in the MacDonnell Ranges. It is the southern entrance to the city of Alice Springs and in addition to the Todd River it carries the ...

, Alice Springs, Australia * Iron Gates on the Danube River, forming the border between Serbia and Romania *

Kali Gandaki Gorge The Kali Gandaki Gorge or Andha Galchi is the Canyon, gorge of the Kali Gandaki (or Gandaki River) in the Himalayas in Nepal. By some sources, it may be one of the deepest gorges in the world. The upper part of the gorge is also called Thak Khol ...

- 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 100 ...

in Nepal * Manawatu Gorge, New Zealand *

Middle Rhine Between Bingen and Bonn, Germany, the river Rhine flows as the Middle Rhine (german: Mittelrhein) through the Rhine Gorge, a formation created by erosion, which happened at about the same rate as an uplift in the region, leaving the river a ...

in Germany *

Pongo de Mainique The Pongo de Mainique ('gate' in Quechua) is a ''water gap'' (canyon) of the Urubamba River in Peru. Inside the water gap, the river is constricted to a width of . The Pongo de Mainique is long. The elevation of the river is approximately . T ...

, 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 The Pongo de Manseriche is a gorge in northwest Peru. The Marañón River runs through this gorge (and water gap) before it reaches the Amazon Basin. The Pongo ('gate' in Quechua) de Manseriche is 3 miles (4.8 km) long, located at 4° 27� ...

, Peru - on the

Marañón River , name_etymology = , image = Maranon.jpg , image_size = 270 , image_caption = Valley of the Marañón between Chachapoyas ( Leimebamba) and Celendín , map = Maranonrivermap.png , map_size ...

Potomac Water Gap The Potomac Water Gap is a double water gap in the Blue Ridge Mountains, located at the intersection of the states of Virginia, West Virginia and Maryland, near Harpers Ferry. At , it is the lowest crossing of the Blue Ridge Mountains. Geography ...

, United States *

Weltenburg Narrows The Danube Gorge near Weltenburg (german: Donaudurchbruch bei Weltenburg) is a narrow section of the Danube Valley in the Lower Bavarian county of Landkreis Kelheim, Kelheim, which has been recognised as a nature reserve and geotope. This section ...

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