== Weathering ==
=== Physical weathering ===
Also known as freeze-thaw or frost action by some textbooks, this process is where water enters a rock cavity and freezes. As it freezes, it expands, forcing the crack wider. The ice thaws, leaving a larger gap than previously. More water enters and freezes, forcing the gap yet wider. Over time, the process continues until the rock is pried away. This is common in highland areas where the temperature is above freezing in daytime, but below freezing during the night.
=== Chemical Weathering or Carbonation ===
As rain falls, it absorbs a small amount of carbon dioxide (CO2) and forms weak carbonic acid. When it reaches the ground and soaks into the soil, it absorbs yet more CO2 from decomposing plants. This strong acid easily dissolves any rock which contains more than around 50% calcium carbonate (such as limestone or chalk), leaving very little behind. The chemical reaction involved is as follows:CaCO3(s) + H2CO3(aq) → Ca(HCO3)2(aq)Calcium carbonate + Carbonic acid → Calcium hydrogen carbonate
=== Biological Weathering ===
This is the action of animals and plants on the land. Plant roots grow between rocks and, as they grow, they slowly prise them apart. Rabbits and other burrowing animals can also be responsible for this rock break-up.