• Mechanical weathering is the physical breaking down of rocks into smaller pieces.
  • The most common type mechanical weathering is free-thaw action.

Freeze-thaw Action

  1. Water gathers in the cracks in rocks during the day.
  2. At night, if the temperatures drop below 0 degrees Celsius, the water freezes to become ice. This puts pressure on the rock as the ice expands by up to 10%. The next day the water thaws and melts again.
  3. Repeated freezing and thawing results in the rock becoming weak and breaking into smaller pieces. These pieces then roll down the slope and gather, where they are known as scree.