A dry valley may develop on many kinds of permeable rock, such as

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

chalk Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Ch ...

, sand stone and sandy terrains that do not regularly sustain surface water flow. Such valleys do not hold surface water because it sinks into the permeable bedrock. There are many examples of chalk dry valleys along the

North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating Direction (geometry), direction or geography. Etymology T ...

and

South Downs The South Downs are a range of chalk hills in the south-eastern coastal counties of England that extends for about across the south-eastern coastal counties of England from the Itchen valley of Hampshire in the west to Beachy Head, in the ...

Southern England Southern England, also known as the South of England or the South, is a sub-national part of England. Officially, it is made up of the southern, south-western and part of the eastern parts of England, consisting of the statistical regions of ...

. Notably the National Trust-owned Devil's Dyke near

Brighton Brighton ( ) is a seaside resort in the city status in the United Kingdom, city of Brighton and Hove, East Sussex, England, south of London. Archaeological evidence of settlement in the area dates back to the Bronze Age Britain, Bronze Age, R ...

covers some 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 last

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...

. The three-quarter mile long curved dry valley is around in height and attracts tourists with its views of Sussex, Hampshire and Kent. Other examples include the Alkham Valley near

Dover Dover ( ) is a town and major ferry port in Kent, southeast England. It faces France across the Strait of Dover, the narrowest part of the English Channel at from Cap Gris Nez in France. It lies southeast of Canterbury and east of Maidstone. ...

, and the Hartley Bottom and Fawkham valleys near

Dartford Dartford is the principal town in the Borough of Dartford, Kent, England. It is located south-east of Central London and is situated adjacent to the London Borough of Bexley to its west. To its north, across the Thames Estuary, is Thurrock in ...

in north Kent. There are many examples of limestone dry valleys in the

Peak District The Peak District is an Highland, upland area in central-northern England, at the southern end of the Pennines. Mostly in Derbyshire, it extends into Cheshire, Greater Manchester, Staffordshire, West Yorkshire and South Yorkshire. It is subdivi ...

and the Yorkshire Wolds. A notable example is the valley of the River Manifold which is dry, except in spate, from Wetton south for several miles. Many hypotheses have been advanced to explain dry valley development. Some may have developed during periods of higher

water table The water table is the upper surface of the phreatic zone or zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with groundwater, which may be fresh, saline, or brackish, depending on the loc ...

, others in periglacial conditions during which normally permeable bedrock would have been made impervious by

permafrost Permafrost () is soil or underwater sediment which continuously remains below for two years or more; the oldest permafrost has been continuously frozen for around 700,000 years. Whilst the shallowest permafrost has a vertical extent of below ...

, thus allowing flowing water to erode it.

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Valleys {{topography-stub

See also

References

External links