2.2 - Types of Weathering - Physical
Physical weathering is the weakening and subsequent disintegration of rock by physical forces. These physical forces include temperature fluctuation, abrasion, frost action (freezing and thawing), and salt crystal growth.
Temperature fluctuation can cause expansion or contraction of rock. When the temperature of rock increases, the rock expands. When the temperature of rock decreases, the rock contracts. This process of expansion and contraction is a physical stress and can crack or break rock. Abrasion of rock is caused by the friction of water, wind, or ice upon the rock. The continuous exposure to these elements slowly breaks down the exposed surface of the rock.
Figure 4. Frost action progressively disintegrates a rock. Image courtesy of UNL, 2005
Frost action is the repeated cycle of ice formation and ice melt in the pore spaces and fractures of rocks causing disintegration of the rock. When water in rock pores freezes, its volume increases by about 10%. This can create a significant amount of pressure on rocks. The magnitude and extent of frost action is dependent on the frequency, duration and intensity of the freezing and thawing cycles. Salt crystal growth can cause the break-up of rock materials. Crystal growth often occurs when groundwater moves into empty pores or spaces of rock by capillary action. As the water evaporates, salt crystals grow and accumulate, putting pressure on the rock and causing it to break apart. Salt crystallization is common in drier climates.