Water gap
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A water gap is an opening or notch which flowing water has carved through a mountain range. Water gaps often offer a practical route for road and rail transport to cross mountain ridges.
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[edit] Geology
A water gap is usually an indication of a river that is older than the current topography. The river likely established its course when the landform was at a low elevation, with a very low stream gradient and a thick layer of unconsolidated sediment. The river therefore established its channel without regard for the deeper layers of rock. A later period of uplift caused increased erosion along the riverbed, exposing the underlying rock layers. As the uplift continued, the river, being large enough, continued 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.
Alternatively, a water gap can be formed through headward erosion of two streams on opposite sides of a ridge, ultimately resulting in the capture of one stream by the other.
[edit] Notable examples
- Delaware Water Gap, Pennsylvania and New Jersey, United States
- Manawatu Gorge, New Zealand
- Potomac Water Gap, United States
- Heavitree Gap, Alice Springs, Australia
- Numerous water gaps cutting through the North Downs and South Downs escarpments in southern England, including those of the Mole (at Dorking) and the Great Stour (from Ashford to Sandwich via Canterbury).
