Chalk and Clay Landscapes

Chalk and Clay Landscapes

1. Characteristics of chalk and clay

   • CHALK: Physically tough, Permeable, Heavily jointed, Porous, Pure form of limestone, Vulnerable to chemical weathering
   • CLAY: Weak and impermeable, Little resistance to erosion

2. Escarpments and Vales

   • Chalk and clay are formed millions of years ago in alternate layers
     • These layers are tilted at a diagonal angle to the surface as a result of tectonic activity. They are no longer horizontal
       • In the UK and Eastern Europe, these rocks were tilted by the collision of the African and Eurasian plates
         • The layers of rock all start at a similar height above sea level and erosion affects both
           • Chalk is affected by carbonation and freeze thaw action
             • Clay is affected by a wide range of weathering types
               • Overall, the chalk is more resistant to weathering and erosion than the clay
                 • Chalk weathers more slowly than clay and overtime ends up lying above the clay
                   • The higher chalk is termed an escarpment or cuesta and the lower lying clay is a vale
                     • There are two parts to the chalk escarpment. There is a steeper scarp slope that cuts across the diagonal organisation of the rock layers. There is also a gentler di p slope that goes parallel with it

3. Dry Valley

   • At the end of the ice age the limestone ground was frozen and so it was impermeable. But glaciers and ice melted and there was a lot of water and this stayed on the surface as it was still frozen (permafrost). As it did, it carved out a V-shaped valley. As the climate warmed, the limestone thawed and therefore became permeable. As a result, the river disappeared underground leaving the valley that had been carved out but without the stream

4. Spring Lines

   • Springs form at the bottom of the escarpment, where the chalk meets the clay. This is why many settlements can be found along spring lines in chalk and clay areas