Physical weathering occurs when physical processes affect the rock, such as changes in temperature or when the rock is exposed to the effects of wind, rain and waves. Water can get into cracks in a rock and, if it freezes, the ice will expand and push the cracks apart. Unsustainable agricultural practices, the industrialization of agriculture, and deforestation have all sped up the rate of erosion. Weathering breaks down and loosens the surface minerals of rock so they can be transported away by agents of erosion such as water, wind and ice.