How do ice wedges form in permafrost?

Ice wedges in permafrost form through a process explained by the thermal contraction theory.1

During cold winters, the frozen ground undergoes thermal contraction, creating vertical cracks that are typically a few centimeters wide and several meters deep. In early spring, meltwater from snow flows into these tension cracks and freezes, forming a vertical vein of ice that penetrates the permafrost.1

As the ground warms and expands during the summer, horizontal compression causes the surrounding frozen sediment to upturn through plastic deformation. In subsequent winters, the existing ice-filled crack acts as a zone of weakness, allowing the thermal tension to reopen it. Each spring, additional meltwater enters and freezes, incrementally increasing the size of the ice mass. Over many years, this repetitive cycle produces a large, vertical, wedge-shaped body of ice. These wedges often form interconnected polygonal networks that delineate cells of frozen ground.123