physical weathering

Form of weathering responsible for the mechanical breakdown of rocks but involving no chemical change.

Forces acting on rock exposed on the Earth's surface open up any weak points in the rock and cause pieces to be broken off. Piles of jagged rock fragments called scree are formed. Processes involved include freeze-thaw (the alternate freezing and melting of ice in rock cracks or pores) and exfoliation (the alternate expansion and contraction of rocks in response to extreme changes in temperature). Physical weathering is also brought about by the growth of plants. A seed falling into a crack in a rock may germinate and the growing plant forces the crack to widen. Similarly, a tree root may grow down into a crack and split the rock. Physical weathering is one of the processes involved in the rock cycle, the formation, change, and re-formation of the Earth's outer layers.