Dominated by contrast between freezing in long winter, and thawing in short summer.
Freezing of water in active layer causes upward expansion of ground, called frost heave.
Human actions can affect the permafrost: removal of vegetation or soil exposes permafrost, creating an impassable landscape of mounds and small ponds known as thermokarst.
The ground below the active layer is rendered impermeable, so underground circulation of water is halted. Soil becomes waterlogged and swamps and thaw lakes are abundant.
Formation of ground ice is characteristic. Sometimes frozen ground contains relatively little moisture, giving rise to dry permafrost.
Ground ice occurs on a series of scales. At the smaller end, small ice needles known as pipkraker develop just beneath the soil surface, caused by water freezing in capillaries.
Ice wedges occur when the ground contracts as a result of severe cold (below -20 degrees C)
This cracking of the ground is called thermal contraction cracking.
Along the edges of the permafrost zone, palsas form. These are mounds up to 6m high (smaller ones are called thufurs), and are formed by heaving of the ground surface
Thawing of ice in the ground usually created depressions. On a large scale, particularly in Siberia, these are known as alases.
Over a period of time there is a vertical sorting of material within the ground: large particles are raised to the surface by frost heave, and fines are washed down by meltwater. Coarse fragments accumulate in areas called felsenmeer. These may then be sorted, by a number of processes including solifluction into stone polygons. As the slope angle increases, these change to stone garlands, and eventually to stone stripes.
The landforms cover the ground in parts of Alaska and Spitsbergen. The circles are due to cycles of freezing and thawing, according to Mark Kessler of UNIVERSITY OF CALIFORNIA, Santa Cruz. The cover shows raised rings of stones surrounding circular fine grained domains. The circle in the foreground of the picture is around 2m in diameter. Various processes had been proposed before (I was under the impression that the ones in the textbooks were the actual ones...) Kessler proposes a mechanism for "sorted patterned ground". He used computer models to show that there were 2 processes involved: lateral sorting and squeezing of stone domains, all within the parameters of different slopes.
Driving force is the process of FROST HEAVE: the expansion of fine-grained soils during freezing (when the sediments are wet..)
If a random layer of stones is left on the surface, frost heave makes the surface uneven. They have taken many years to form.
Aeolian processes remove the fine particles to areas where there is vegetation which traps the fine sediment. Removal of material by the wind is called deflation, and is helped by the lack of vegetation and the large amount of fine sediment available e.g from dry stream beds. Removal of fine material leaves large areas of coarser fragments called lag gravels, which have often been exploited. Loess, the material produced is a relict feature.
There are also processes related to running water. Periglacial streams will only flow for a short period during the year, and they often appear overloaded with sediment and take on a braided form. Braiding is characteristic of rivers in the Arctic, and they have been shown to transport as much as 90% of their total load as bedload. Often lateral erosion is the only type, and this is often thermal erosion: streams flowing round a meander remove slope debris and expose the permafrost which then melts to leave an overhanging stream bank: a thermo-erosional niche.
Vertical erosion occurs during time of snowmelt: up to 75% of total runoff can be produced in just a few days during this nival flood.
This flow is thought to have carved valleys in areas where presently there is no surface drainage: e.g the dry valleys in the chalk areas of S. England, for example at Brook in E.Kent.