Dry valley

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A dry valley is a valley found in either Karst (limestone) or chalk terrain that no longer has a surface flow of water. There are many examples of the latter along the North and South Downs in southern England. Notably the National Trust-owned Devils Dyke near Brighton covers some 200 acres 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.

The three-quarter mile long curved dry valley is around 700 feet in height and affords splendid views into Sussex, Hampshire and Kent.

Such distinctive topography proved attractive to tourists, and in August 1887 a single track railway line opened up from nearby Brighton to transport sightseers to the foot of the hill.

During its heyday, Devil's Dyke was a huge hit with Edwardians, with 30,000 people visiting on Whit Monday in 1893.

In addition to the Steep Grade Railway, other attractions included two bandstands, an observatory, a camera obscura, fairground rides and, later, a switchback railway and an aerial cableway railway across the valley.

Other examples include the Alkham Valley near Dover, and the Hartley Bottom and Fawkham valleys near Dartford in north Kent.details

There are two theories as to how they were made, the first that the water table was once much higher, while the other is that during the ice age the area had tundra like conditions. The normally permeable chalk would have been made impervious by permafrost, thus allowing rivers to flow.

During the ice age the water was not able to flow through the limestone because it was frozen. But when the ice melted, the water on the surface of the land carved wide valleys. Today these valleys don't have any rivers because it sinks through into the limestone and flows underground in caverns. Hence why they are called 'Dry Valleys'

There are many examples in the Peak District. A notable example is the valley of the River Manifold which is dry, except in spate, from Wetton south for several miles.

[edit] See also

McMurdo Dry Valleys