What causes the formation of patterned ground in periglacial areas?

Patterned ground in periglacial areas is caused by the freeze-thaw cycle of the ground and the movement of soil and rocks.

In periglacial areas, the ground is subjected to extreme cold temperatures, causing it to freeze and thaw repeatedly. This freeze-thaw cycle is a key factor in the formation of patterned ground. When the ground freezes, it expands, and when it thaws, it contracts. This constant expansion and contraction can cause the ground to crack and shift, leading to the formation of patterns.

The type of soil and rocks in the area also play a significant role in the formation of patterned ground. In areas with a lot of fine-grained soil, the freeze-thaw cycle can cause the soil to move upwards, creating a pattern known as 'frost heave'. In areas with larger rocks, the freeze-thaw cycle can cause the rocks to move downwards, creating a pattern known as 'frost sorting'.

The movement of soil and rocks is not random, but rather follows certain patterns. For example, in frost heave, the fine-grained soil tends to move towards the surface in a circular or polygonal pattern. In frost sorting, the larger rocks tend to move towards the edges of the pattern, creating a sort of 'stone ring'.

The patterns can also be influenced by the slope of the ground. On flat ground, the patterns tend to be more circular or polygonal, while on sloping ground, the patterns tend to be more linear or striped.

In addition to the freeze-thaw cycle and the movement of soil and rocks, other factors such as wind, water, and vegetation can also influence the formation of patterned ground. For example, wind can blow fine-grained soil into certain patterns, water can erode the ground into certain patterns, and vegetation can stabilise certain patterns.

Overall, the formation of patterned ground in periglacial areas is a complex process that involves a combination of physical and chemical processes, as well as the interaction of various environmental factors.