Which method of mechanical weathering is caused by the expansion and contraction of rocks due to temperature changes?

• A. Salt wedging
• B. Frost wedging
• C. Exfoliation
• D. Biological activity

Answer: (C)

The method of mechanical weathering caused by the expansion and contraction of rocks due to temperature changes is known as exfoliation. This process occurs when rocks, particularly those that are exposed to significant temperature fluctuations, expand when heated and contract when cooled. Over time, these repeated cycles of expansion and contraction can cause the outer layers of rock to peel or flake away, similar to how the skin of an onion is removed in layers. This results in the breakdown of larger rock formations into smaller pieces without any change in their mineral composition, which is a hallmark of mechanical weathering.

In contrast, salt wedging involves the crystallization of salt in rock crevices, which can create pressure and lead to cracking. Frost wedging occurs when water enters cracks in the rocks, freezes, and expands, causing fractures to widen. Biological activity includes the physical breaking down of rocks through the activities of living organisms, such as plant roots growing into cracks. While all these processes contribute to weathering, exfoliation specifically addresses the impact of thermal expansion and contraction.