Freeze Thaw action is an example of mechanical weathering. It is also called Frost Shattering and occurs when rock disintegrates (breaks up) because of continual freezing of water and thawing of ice in upland areas. Upland areas tend to receive more rain than lowland areas. Some of this water gathers in the joints (cracks) in rocks (Diagram 1). During winter, or whenever the temperature falls below freezing point, this water freezes. When water freezes it expands by about 11%. The expansion of the ice places pressure on the joints in the rock. As a result the joints widen slightly (Diagram 2). When the water thaws, it will lie deeper in the joints. The next time the water freezes the joints will widen even more. Eventually the rock will break and collapse into smaller pieces of rock called scree.
Scree can be found on the sides of many mountains. The Great Sugarloaf in Co. Wicklow is a good example of where scree can be found.