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Periglacial Processes

Periglacial was originally used to describe places near to or on the fringe of ice sheets or glaciers.

Now it is defined more widely, usually referring to areas:

With permafrost;

With some seasonal temperature variation where the mean temperatures for at least some period in the summer rise above 0C;

Where freeze-thaw cycles dominate the landform creating processes;

Which have a distinctive ecosystem adapted to the periglacial environment.

Such areas as these now make up approximately 25% of the worlds total land area!

 

Key terms

Permafrost - Permanently frozen ground where soil temperatures have remained below 0 C for at least 2 years

Continuous Permafrost - Summers so cold that there is only a very superficial surface melting of the ground. It has been estimated to reach up to a depth of 1500 metres. Mean annual air temperatures of below -5 C all year, and as low as -50 C.

Discontinuous Permafrost - Found is slightly warmer areas so there are islands of permanently frozen ground separated by small pockets of unfrozen less cold areas. Slightly warmer zones due to proximity of surface water (rivers, lakes, and the sea). Mean annual temps of between -1 C and -5 C

Sporadic Permafrost - Found when mean annual temperature is just below 0C and the summer temperatures reach several degrees above but isolated pockets of permanently frozen ground remain below the surface.

Active Layer - summer temperatures sufficient to melt the surface layer of permafrost. This layer can be very mobile. It varies in thickness depending on latitude and vegetation cover.

Talik   - Any unfrozen material within the permafrost zone.

Generally, as you progress from the poles Southwards (in the northern hemisphere) or Northwards (in the Southern Hemisphere) the permafrost will change from continuous to discontinuous to sporadic to none.  The depth of permafrost will shrink and the depth of the active layer will increase.  This is of course influence by local variations such as mountain ranges, lakes and ocean currents.

A transect through periglacial areas

Processes;

Nivation - The effects of snow on a landscape. These include abrasion and freeze-thaw. Furthermore, melted snow triggers mass movements such as solifluction and slope wash. These processes may produce the shallow pits known as nivation hollows. In time, these hollows may trap more snow and may deepen further with more nivation so that cirques or thermocirques are formed.

 

Frost heave, The upward dislocation of soil and rocks by the freezing and expansion of soil water. Frost push occurs when cold penetrates into the ground. Large stones become chilled more rapidly than the soil. Water below such stones freezes and expands, pushing up the stones. Frost pull can alter the orientation of a large stone causing it to stand upright. This occurs when ice creeps downwards from the surface. The growth of ice crystals on the upper part and the drying of the soil around the lower part cause the stone to be pulled into a more vertical inclination.

Solifluction - This is the mass movement of soil and regolith affected by alternate freezing and thawing. It is characteristic of saturated soils in high latitudes, both within and beyond the permafrost zone.

Hydraulic pressure the movement of water through a rock profile due to pressure

Hydrostatic pressure growth of an ice lens due to the attraction of water molecules

  Think about it   
  1. 1) In a Word document locate Resolute, Yellowknife and Calgary on the map and transect above

  2. 2) Draw 3 climate graphs using the data found at this link

  3. 3) Add the graphs to the transect and map on a Word document, then comment upon your results.