freeze-thaw action

The water in materials such as poorly drained or porous masonry (or in any other such material) may alternately freeze and thaw in winter. The water expands as it freezes, tending to break up the material. Alternate freezing and thawing can also initiate potholes in a bitmac surface, frost heave, solifluxion and soil erosion.

This definition is abridged from A – Z of tree terms: A companion to British arboriculture.
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