Ice wedge

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An ice wedge, another process associated with periglacial environments, is a narrow mass of ice that can be 3 or 4 meters wide at ground surface and extend up to 10 meters downwards. During winter the ground gets very cold. The water in the ground freezes and expands. Then, as the temperature falls further, (below –17°C), the soil and frozen ice acts as a solid and contracts as it gets colder, forming cracks. The cracks form in the shape of large polygons, sometimes as large as a swimming pool. They are similar to mud cracks in a drying puddle. These cracks are often several metres deep through existing permafrost layers. In the spring when the snow melts the melt-water flows into these cracks, re-freezing almost immediately until it gets near the surface. This warps the permafrost around it and can form reticular ice in the surrounding saturated soil. As the water freezes it expands and exerts pressure on the cracks, forcing them to widen. The following year the ground cracks again along the same weak points and again in spring the water flows in and refreezes, expanding the wedges even further. This process continues for many years. During summer periods sediment can fill the cracks left by the ice wedges. These are called pseudomorphs and can contain important hints of the past, such as animal remains.