As you may already knows, rocks are very hard but a very small amount of water can break the rock apart. When water finds it way into a crack in the rock and freezes overnight, it causes the rock to expand. The next day when the rock is exposed to the sun, the water defrosts and soon at night when the temperature decreases, the water begins to freeze again. This cycle eventually repeats and overtime the repeated freeze-thaw action causes the rock to break apart. Freeze-thaw weathering occurs mostly in mountainous areas.
(Picture to the left) From the picture you can see that the rock has a deep crack in the middle. This shows that freeze-thaw weathering has occurred.