Abrasion

• Abrasion -- a major cause of physical weathering of rocks -- is the process of rocks grinding against each other, such as when moved by wind or water. As these pieces of rock move along the ground, they grind against other rocks and cause them to break. If abrasion takes place over a long time, it changes the shape of rock formations.
  
  

Frost Wedging

• "Frost wedging" refers to the process of water sipping through cracks in rocks and then freezing. When the water freezes, it expands, causing the cracks in the rocks to expand until a layer of solid rock eventually separates into several parts. When this happens over a long time, the rock formation changes in shape.
  
  

Exfoliation

• Exfoliation -- the separation of the layers of rock that form the earth's crust -- occurs when the earth's rock crust expands because of reduced pressure at the earth's surface. The layers of rock separate along joints in the crust and turn into dome-shaped rock forms. Exfoliation causes the layers to separate by a distance of several inches to several feet.
  
  

Expansion and Contraction

• Different types of rocks and minerals expand when the temperature increases, and contract when the temperature drops, albeit at different rates. Some parts of a layer of rock may expand or contract faster than others, which causes cracking.
  
  

Pressure Release

• Most rocks formed deep below the earth's surface at high temperatures and under high pressure. Conditions such as erosion cause these rocks to rise to the surface, with its lower temperature and pressure. This unloading of pressure causes the rocks to fracture, leading to gradual physical weathering over time.