Chalk is a relatively soft rock that may be eroded or weathered in a number of different ways. It is porous, able to absorb up to 20% of its dry weight in water, and therefore highly susceptible to weathering by freeze-thaw action, which may occur over repeated annual or diurnal cycles. This frost weathering produces a mix of rubble and viscous mud, which may be washed downhill, further eroding the landscape (a process known as solifluction). At the west side of Box Hill, the hydraulic action of the River Mole has cut a cliff known as The Whites and the river bed contains coarse chalk rubble (clast), which has fallen from the steep slopes above. Since the chalk contains a very high percentage of calcium carbonate, it can be dissolved by ground water and solubilisation of the rock at the base of the hill may have produced the slabwise slumping or subsidence visible at the top of the Burford Spur. Finally, rainwater, which is mildly acidic, will dissolve and react with the chalk.