Describe the characteristics of chalk and the land forms typical of chalk areas

Chalk is a type of limestone that does not develop karst scenery. However calcium carbonate levels in chalk streams have been examined demonstrating that carbonation occurs at a faster rate than in some other limestones, due to this the rock structure is not strong enough to support the formation of underground tunnels and caves. This is the reason why distinctive rolling hills and vales are common in chalk scenery areas. Chalk scenery is also closely associated with the development of escarpments or cuestas which have steep scarp slopes and gentle dip slopes. However these features are more a product of erosion than of weathering.

As with all limestone scenery, there is little surface drainage on chalk. Dry valleys are common features, and the size of these suggests different climatic conditions in earlier times. There are several theories which have been put forward explain their formation:

• Higher sea levels at the end of the last Ice Age resulted in the higher water-table levels and surface streams. Later, as sea level fell, the water-table also dropped, causing the valleys to become dry.
• The freezing of water in rock pores during glacial periods caused the chalk to become impermeable and allowed surface drainage to develop. Later, as temperatures rose and ice melted, the chalk once again became permeable causing the surface streams to disappear, leaving dry valleys behind.
• The streams and their valleys developed on an overlying layer of impermeable rock. This layer was removed by a combination of weathering and erosion, resulting in the valleys being gradually superimposed on the underlying permeable chalk.
• Surface drainage developed during periods of significantly higher rainfall than at present. When the rainfall decreased the water-table dropped, leaving behind dry valleys.