Devil's Dyke, Sussex

Devil's Dyke is a 100m deep V-shaped valley on the South Downs Way in southern England, near Brighton and Hove. Devil's Dyke was a major local tourist attraction in the late 19th and early 20th centuries.Geological historyThe Dyke is formed in rocks of the Chalk Group which originated as marine sediments during the Cretaceous period.It is a misconception common amongst local residents of Brighton that the valley was formed by some kind of glacial action, the myth of a 'glacier' being a misunderstanding of accounts such as this one from the Encyclopaedia of Brighton by Timothy Carder (1990):"In reality the 300-foot-deep valley was carved by tremendous amounts of water running off the Downs during the last Ice Age when large amounts of snow thawed and the frozen chalk prevented any further absorption; erosion was aided by the freeze-thaw cycle and the valley was deepened by the 'sludging' of the saturated chalk.".The Devil's Dyke V-shaped dry valley is the result of solifluction and river erosion. More than fourteen thousand years ago, the area experienced an intensely cold climate (but not glacial conditions). Snowfields capped the South Downs. Permafrost conditions meant that the chalk was permanently frozen. In summer, the snowfields melted and saturated the top layer of soil, because the water could not permeate the frozen chalk underneath. Waterlogged material situated above the permafrost slid down the gradient, removing material by friction, exposing deeper layers of frozen chalk. When the Ice Age ended, the snowfields covering the South Downs melted, and rivers formed across Sussex. The Devil's Dyke valley was completed by one such river.