Dry valley

For other uses, seeDry valley (disambiguation).

A dry valley near Rackham Hill,South Downs,England

Adry valleymay develop on many kinds ofpermeable rock,such aslimestone,chalk,sand stoneand sandy terrains that do not regularly sustain surface water flow. Such valleys do not hold surface water because it sinks into the permeablebedrock.

There are many examples of chalk dry valleys along theNorthandSouth DownsinSouthern England.Notably the National Trust-ownedDevil's DykenearBrightoncovers some 200 acres (0.81 km²) of downland scarp, and includes the deepest dry valley in the world – created when melting water eroded the chalk downland to the permafrost layer after the lastice age.The three-quarter mile long curved dry valley is around 700 feet (210 m) in height and attracts tourists with its views of Sussex, Hampshire and Kent.

Other examples include theAlkham ValleynearDover,and the Hartley Bottom and Fawkham valleys nearDartfordin north Kent.

There are many examples of limestone dry valleys in thePeak Districtand theYorkshire Wolds.A notable example is the valley of theRiver Manifoldwhich is dry, except in spate, fromWettonsouth for several miles.

Many hypotheses have been advanced to explain dry valley development.Some may have developed during periods of higherwater table,others inperiglacialconditions during which normally permeable bedrock would have been made impervious bypermafrost,thus allowing flowing water to erode it.

See also

• McMurdo Dry Valleys

External links

Media related toDry valleysat Wikimedia Commons