Water gap

For other uses, seeWater gap (disambiguation).

Awater gapis agapthat flowing water has carved through amountain rangeormountain ridgeand that still carries water today.Such gaps that no longer carry water currents are calledwind gaps.Water gaps and wind gaps often offer a practical route forroadandrail transportto cross the mountain barrier.

TheColumbia Rivercut theWallula Gap,seen from Main Street inWallula, Washington

Geology

View of water gaps cut by theRaystown Branchof theJuniata RiverthroughEvitts MountainandTussey Mountain,facing west from the summit ofKinton Knob,Wills Mountain,inBedford County,Pennsylvania,with the town ofBedfordin the foreground

A water gap is usually an indication of ariverthat 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 lowstream gradientand a thick layer of unconsolidatedsediment.

In a hypothetical example, a river would have established its channel without regard for the deeper layers ofrock.A later period ofupliftwould cause increasederosionalong 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 theRidge-and-Valley Appalachiansof easternNorth America.

Alternatively, a water gap may be formed throughheadward erosionof two streams on opposite sides of a ridge, ultimately resulting in thecaptureof one stream by the other.

Notable examples

Two water gaps opened by the same river in centralPennsylvania,foreground and background, separated by settlements in flat lands

• Chicago Portage,Illinois-Saddle Pointruns through the city itself.
• Columbia River Gorge,Oregon and Washington, andWallula Gap,Washington, United States
• Cumberland Narrows,Maryland, United States
• Delaware Water Gap,New Jersey and Pennsylvania, United States
• Heavitree Gap,Alice Springs, Australia
• Iron Gateson the Danube River, forming the border between Serbia and Romania
• Kali Gandaki Gorge- cuts through the world's tallest mountain range, theHimalayasin Nepal
• Manawatū Gorge,New Zealand
• Middle Rhinein Germany
• Pongo de Mainique,Peru - on theUrubamba River
• Pongo de Manseriche,Peru - on theMarañón River
• Potomac Water Gap,United States
• Weltenburg Narrowson theDanube Riverin Bavaria
• Wawa Gorge,Rodriguez,Rizal,Philippines

See also

• Antecedent drainage stream
• Defile (geography)
• Narrows
• Peneplain