periglacial areas

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Periglacial environments

This refers to the glaciated and non glaciated areas with a wide range of different latitudes which may or may not contain glaciers. These areas have intense frosts during Winter and on any snow free ground in Summer. Daily temps are below zero degrees for at least 3/4 of the year and below -10degrees for the remaining months. They have low precipitation and temps fluctuate through frequent cycles of freezing and thawing to cause ice within cracks to melt. These climate conditions give rise to a variety of processes inclduing periglacial processes which combine to produce distincitve landscapes containing some landforms that are unique to periglacial areas. 

Permafrost 

Refers to rock and soil that remain frozen because temperatures do not exceed zero degrees in the summer months for at least 2 consective years. 

Continuous permafrost- forms in the coldest areas of the world, it can extend downwards for hundreds of metres

Discontinous permafrost- more fragmented and thinner than continous permafrost

Sporadic permafrost- occurs at the margins of periglacial environments and is usually fragmented and only a few metres thick, often occuring on shady hillsides or beneath peat

Active layer

In summer, the energy balance is positive which causes ovelying snow and ice to melt away to produce a seasonally unfrozen zone above the permafrost called the active layer. 

Factors influencing the distribution and character of the permafrost

Climate, as temperature and the amount of moisture available determines the presence or absence, depth and the extent of the permafrost

On a local scale,

-proximity to water bodies is important, as lakes are relatively warm they will remain unfrozen throughout the year and have a deep active layer

-slope angle and orientation influence the amount of solar radiation and therefore melting, freeze thaw weathering and wind 

-character of the ground surface (different rock and soil types) can determine the degree and depth of permafrost 

-vegetation cover can insulate the ground from temperature extremes

-snow cover can slow the freezing process in Winter and delay the thaw and development of the active layer in spring

Ground ice formation and associated features

Frost heaving -the contraction and cracking of rapdily freezing soils, resulting in ice crystals and ice lenses as the ground above is domed upwards and stones get pushed to the surface. which results in the formation of ice wedges aswell as creating patterned ground

Frost shattering- the expansion of water by 9%, which causes block fields and screes

The migration of subsurface water to the 'freezing front' by suction, which causes

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