Ice wedge

[1] Over the next few months, the snow melts and the remaining water fills the cracks and the permafrost below the surface freezes it.

Once the summer months arrive, the permafrost expands; horizontal compression produces upturning of the frozen sediment by plastic deformation.

The mean annual air temperature thought needed to form ice wedges is −6° to −8 °C or colder.

These are called ice wedge casts and can be used to estimate the climate of hundreds of thousands of years ago.

These types of ice wedges grow considerably wider over their lifetime, but rarely any deeper or taller.

This means that epigenetic ice wedges can grow to at most 3–5 meters in width, but stay roughly the same depth/height as when they had formed.

[4] This allows syngenetic ice wedges to grow very deep, as the surface around them rises with the accumulation of alluvium (in floodplains), peat (in tundra), and gelifluction deposits (at the bottom of a slope), among other materials.

[4] Syngenetic ice wedges may only form if the thermal contraction and subsequent ice-veinlet growth can keep pace with the addition of new material.

[4] Anti-syngenetic ice wedges therefore only grow downwards, penetrating deeper into the soil only as the upper layers are removed by mass wasting and erosion.

Ice wedges in Sprengisandur , Iceland
Lakes in the Mackenzie delta. In the foreground, a drained lake shows large, low-centered ice-wedge polygons
Peninsula at the coast of the Arctic Ocean in the Mackenzie Delta area showing well developed ice-wedge polygons. A Caribou herd is grazing on it.
A melting pingo with surrounding ice wedge polygons near Tuktoyaktuk , Canada
Ice wedge exposed by erosion along the Beaufort Sea coast, Canada. The wedge formed by thermal contraction of the ground which opened a crack in winter. The crack filled with meltwater in the spring which then froze in the permafrost, causing the thin vertical lines of ice and sediment that form the wedge itself.