How does freeze-thaw action create patterned ground?

Patterned ground is created through intense, repetitive freeze-thaw cycles within the active layer of soil, particularly in regions with fine-grained sediments and moisture. This process shapes the landscape through two primary mechanisms:123

• Sorting and Heaving: Constant changes in water volume during freezing and thawing stir granular sediments and move coarser particles toward the surface. Subsequent frost heaving further organizes these rocks and stones by size, forming distinct patterns such as stone rings or, when these rings coalesce, polygonal stone nets. On slopes, these features may be distorted into stone stripes by gravity.13
• Contraction Cracking: In extremely cold winters, the soil contracts, creating vertical or subvertical polygonal cracks. During the spring thaw, water enters these cracks and freezes, causing the ice to expand. This cycle repeats annually, creating large ice wedges that deform and compress the surrounding soil, resulting in patterned ground.3

While permafrost is not strictly required for these features, it often acts as an impermeable base that retains the soil moisture necessary for these frost-driven processes to occur.1