How do ice wedges form in cracks in permafrost?

Ice wedges form through a process described by the thermal contraction theory. During extremely cold winters, the frozen ground undergoes contraction, creating vertical polygonal cracks that are typically a few centimeters wide and several meters deep.12

In early spring, meltwater from snow flows into these tension cracks and freezes, creating a vertical vein of ice. When the permafrost warms and expands during the following summer, the surrounding sediment is compressed and upturned by plastic deformation.12

This cycle repeats over many years:
* Renewed Tension: During subsequent winters, the existing ice-filled crack acts as a zone of weakness, causing it to reopen due to thermal contraction.1
* Ice Accumulation: Each spring, new meltwater enters the crack and freezes, adding an increment of ice.31

Over time, this repetitive process produces a large, vertical, wedge-shaped mass of ice. These wedges often form a honeycomb network of polygonal ground on the surface, which is a widespread geomorphic feature in permafrost regions.124