Which factor is NOT a physical weathering process?

The correct answer is based on the distinction between physical and chemical weathering processes. Physical weathering involves the breakdown of rocks and minerals through mechanical means, without changing their chemical composition.

Freeze-thaw cycles exemplify physical weathering; as water seeps into cracks in rocks, it freezes and expands, exerting pressure that gradually breaks the rock apart. Similarly, plant root growth can physically wedge apart rocks as roots expand and grow into existing fissures, contributing to the disintegration of the rock structure.

Water erosion, while it may involve transport and movement of materials, also involves physical processes where the mechanical action of running water can erode and shape the landscape without altering the chemical makeup of the rocks being eroded.

On the other hand, chemical decomposition involves processes that change the chemical structure of rocks, such as oxidation or hydrolysis, which alter the minerals themselves. This is crucial in differentiating it from physical weathering—thus, it correctly identifies the factor that is not a physical weathering process.