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Formation of Permafrost
· About 20% of Earth's surface is covered by
permafrost. Permafrost occurs at high latitudes,
or at very high altitudes, anywhere the mean
annual soil temperature is below freezing. About
half of Canada and Russia, much of northern
China, most of Greenland and Alaska, and
probably all of Antarctica are underlain by
permafrost. Areas underlain by permafrost are
classified as belonging to either the continuous
zone or the discontinuous zone. Permafrost
occurs everywhere within the continuous zone,
except under large bodies of water, and underlies
the discontinuous zone in irregular zones of
varying size. The surface layer of soil in a
permafrost zone may thaw during the warmer
months, and the upper layer of the frozen zone is
known as the permafrost table. Walking on
permafrost is extremely difficult, because the
surface is spongy, irregular, and often wet. Water
logging of the surface layer also causes slopes in
permafrost areas to be unstable and prone to
failure.…read more

Slide 2

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Collective name of different processes that occur under a snow patch, believed
to be responsible for the development of the hollows in which snow collects. It
is also thought to play a role in the early formation of corries.
The processes involved include freeze­thaw (weathering by the alternate
freezing and melting of ice) by which fallen snow gets converted into a mass of
ice and the mass movement (the downhill movement of substances under
gravity), and erosion by melt water.
Over some time, this leads to the
formation of nivation hollows which,
when enlarged, can be the beginnings
of a corrie (cirque).…read more

Slide 3

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Frost heave
Frost heaving (or a frost heave) results from ice forming beneath the surface of soil
during freezing conditions in the atmosphere. On freezing, fine grained soils expand
unevenly upwards to form small domes. As stones cool down faster than the
surrounding soil, small amounts of moisture in the soil beneath the stones freeze and
turn to ice.
By repeatedly freezing and thawing over time, these ice crystals and lenses heave
stones upwards in the soil profile.
The material is sorted and the larger stones move downwards due to their weight. On
the gentler slopes stone polygons
are created but where the ground
is steeper the stones are dragged
downhill into more regular known
as stone stripes…read more

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The effect of the summer thaw on the active layer is to release a great deal of meltwater. As
this water is unable to percolate downwards (due to the frozen ground) it saturates the soil,
reducing the internal friction between particles, thus making it highly mobile. The lack of
substantial vegetation to fix to the saturated soil means the soil begins to flow even on
slopes of only a few degrees. This process is known as solifluction.
A number of features of the local
environment contribute to active
Zillertal Alps
·frequent freeze-thaw cycles,
·saturated soils and regolith, after snow
melt and heavy rainfall,
·frost-susceptible materials, with significant
contents of silt and clay, at least at depth,
·extensive regolith across a range of slope
Regolith is a layer of loose, heterogeneous
material (elements that are not of the same
kind or nature) covering solid rock.…read more

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Solifluction Lobes
The deposits that solifluction leaves behind are rounded, tongue-like features
often forming terraces along the sides of the valley. These are stepped landforms
that may be formed beneath vegetation, pushed forward and rolled under.
Where vegetation is sparse, the stones heaved to the surface are pushed to the
front of the advancing lobe and they form a small stone bank at the front of the
lobe. These lobes are seen on many hillsides and when the frozen ground thaws
from the surface downwards each summer, meltwater can't percolate into the
permafrost so it instead, saturates the thawed surface soil and overlying
vegetative mat.
They are formed when waterlogged soil slips
down a slope due to gravity on areas of a slope
showing variations in gradient. It commonly
has a steep front and a relatively smooth upper
Solifluction lobes are visible on the tundra slope
below the snowfield.
Pinnell Mountain, Alaska
Alaska, North America…read more

Slide 6

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Open-system Pingos
· A pingo is a mound of earth-covered ice found in
the Arctic and subarctic.
· Where permafrost is discontinuous or thin,
freezing water in the upper layer of the soil leads
to expansion of ice within the soil.
· Overlying sediment on the ground is then
heaved upwards, forming a dome-shaped
feature called a pingo (less than 50m in height).
· Open-system pingos or East Greenland type
pingos are found mainly in sandier soils.…read more

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