Physical (or mechanical) weathering refers to the process by which intact rock is broken down into smaller pieces or clasts without changing its chemical composition. This process creates debris or detritus, which can vary in size. Here are two phenomena that contribute to physical weathering:
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Freeze-Thaw Cycle: This phenomenon occurs when water seeps into cracks and fractures in rocks. When the temperature drops, the water freezes and expands (approximately by 9%), exerting pressure on the rock walls. When temperatures rise, the ice melts, causing the pressure to release. Over repeated freeze-thaw cycles, this expansion and contraction can lead to significant cracking and fragmentation of the rock, ultimately breaking it apart.
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Thermal Expansion and Contraction: Rocks can also undergo weathering due to temperature fluctuations. During the day, rocks may heat up and expand, while at night, cooler temperatures cause them to contract. This constant cycle of expansion and contraction can create stress within the rocks, leading to the development of cracks and fractures. Over time, these cracks can deepen and result in the physical breaking of rock into smaller pieces.
Both of these processes emphasize the mechanical nature of physical weathering, as they involve the physical breakdown of rock without altering its mineral composition.