Case study: chalk in the South Downs

The South Downs is an AONB (area of outstanding natural beauty).


The Seven Sisters in East Sussex
The Seven Sisters in East Sussex
  • Chalk is a sedimentary rock made of calcium carbonate.
  • It is porous and allows water to penetrate into the rock. For this reason, surface streams (winterbournes) are only visible when the rock is saturated.
  • Dry valleys are a common feature. These were eroded by fast-flowing surface streams towards the end of the last Ice Age.
  • Where the chalk (permeable) meets an impermeable rock (frequently clay) springs form and can be seen when rivers begin to flow at the surface.
  • Chalk is eroded by solution.
  • Soils are thin which means vegetation is mainly grasses.
  • Chalk forms gentle hills inland (eg the South Downs in southern England) and steep cliffs at the coast (eg the Seven Sisters in Sussex).
  • Chalk escarpments have a gentle slope (or dip) on one side and a steeper slope (or scarp) on the other.
  • Chalk beds are good natural aquifers (underground areas that allow storage of water due to the porous nature of the rock).

Human activity

  • Pastoral farming - Mainly sheep, racehorses and some cows are farmed. Soils are too thin to allow much arable farming.
  • Settlements - Where chalk meets clay, spring-line settlements (where a ridge of permeable rock lies over impermeable rock and a line of springs form along the boundary between the two) can be seen, eg Fulking in West Sussex. Due to the good access to London, the South Downs are popular as a location for commuters and retired people.
  • Racehorse training - Stud farms and stables are common at Epsom in Surrey.
  • Quarrying - Chalk with flints is a strong building material used in cement manufacture.