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Root Wedging
Root wedging occurs when plant roots weave their way through crevices in rocks, called joints. As the roots grow, they press against the rock and put stress on the joints they are growing in. Over time, this stress breaks the rock apart. This process can affect homeowners who have large trees growing too close to their homes. In these cases, the roots of those trees have the potential to weather the concrete foundation of a home over time, causing structural damage.
Thermal Expansion
Thermal expansion is another form of physical weathering. This occurs at different rates for different minerals, depending on how they react to heat. Common among all minerals, however, is the fact that they expand when heated and contract when cooled. The best example of this occurrence is with minerals in the desert, which can experience extreme heat during the day and extreme cold at night. This process weakens rocks and breaks them apart.
Frost Wedging
Frost wedging is a similar process to root wedging. The cause here, though, is water and ice. In colder climates, water can get into crevices in rocks of various sizes. When water happens to be trapped in these crevices, it will freeze when the weather becomes cold, such as at night in winter. When water freezes it also expands. As it does so, it places pressure on the sides of the crevice it's in. This pressure breaks up the rock over time.
Exfoliation
Over time, rock breaks off in sheets parallel to the earth's surface. As it does this it also expands because it becomes free of pressure placed on it by surrounding rocks, especially those at lower levels, where pressure increases. When the rock expands, it presses against the rock around it, causing stress that breaks apart more rock. Over time, this process shapes large pieces of rocks, like large boulders, by breaking, or peeling, off sheets of rock one after another.