Ice heave, frost push and other periglacial processes explained as well as the action of freeze thaw and the features it presents

1. Periglacial Processes and their
landscapes and Landforms
Lower Sixth

2. What we’ll learn today
1. There are 4 basic processes that help cause the
landscapes we see
2. There are various types of landforms and features we
need to know
3. That mass movement, snow, wind and meltwater have a
key role in the formation of landscapes
4. That many of these can be seen within the UK as Relict
features

3. Distinctive Landscapes
• These areas develop distinctive Geomorphology because of
FOUR basic processes
1. Water expands by 9% upon freezing which can cause Frost
shattering creating scree and block fields
2. The contraction and cracking of rapidly freezing soils in which
ice wedges form as well as frost heaving which creates
patterned ground
3. Migration of sub surface water to the ‘freezing front’ via
suction causing segregated ice to form leading to ice lens and
pingos
4. Mass movement of the active layer downslope via
Solifluction leading to lobes and terraces
• Other processes such as wind and fluvial action also exist but
are not exclusive to periglacial areas

4. Periglacial areas and Permafrost
• Periglacial literally means ‘edge’ of glacial.
• They are found on the fringes of polar environments
• They contain permanently frozen ground (Permafrost)
• During the brief warmer summers the surface of the
ground thaws
• Periglacial environments are not permanently covered by
ice.

5. Remember how climate changes slowly
POLAR
CONDITIONS
WARMER
CONDITIONS

6. Permafrost
• Within permafrost there are three layers the
top layer is the active layer as it melts and
freezes with summer and winter temperature
changes
• Beneath this is the permafrost zone where
temperatures are too cold to ever melt and
then there is the unfrozen ground due to the
geothermal gradient of the planet

7. Distribution
• Periglacial distribution is straight forward
• FOUND on the fringes of polar regions
• In-between polar and boreal conditions
• Sub Arctic conditions

8. Frost Action – Ice wedges
• Freeze thaw action is one the most important parts of
Periglacial and glacial activity.
• We know this as frost shattering
Explanation
• In extremely low temperatures the ground contracts and
cracks develop
• During the summer meltwater fills these cracks
• In the winter they expand by 9% making them able to hold
more water in the summer.
• This cycle continues

9. Ice Wedge Polygons - >>WATCH<<

10. Ground Ice Features
• Ice wedge polygons
• Downward narrowing masses of
ice that are between 2 to 3 metres
wide at the base and extend below
the ground surface up to 10
metres
Explanation
• Formed by the refreezing of the
active layer during winter causing
soil to contract and cracks open.
• During the melting of the summer
the cracks fill up with meltwater
and sediment then refreeze the
following winter which will widen
and deepen the crack

11. Patterned Ground - Explanation
• They are formed by a series of movements resulting from frost action
• Frost push (caused by hydrostatic pressure) propels the stones upwards,
whilst frost heave causes stones to migrate outwards to form circles
• The up doming of the circle created by the heaving mean that larger stones
roll outwards due to gravity leaving finer sediment in the centre
• As a result stone polygons are elongated into stone nets and stripes which
has a clear relationship between the type of patterned ground and slope angle
• Beyond 30 degree angle patterned ground can no longer form and rock
avalanches may occur

12. Rock Stripes

13. Frost Heave - >>WATCH<<

15. Pingo Formation - >>WATCH<<

16. Pingos
Description
•Ice-cored hills with a height between 30 to 70 metres and a
diameter between 100 to 500 metres
•Most pingos are circular in shape.
•Large ones usually have exposed ice at their top and the
melting of this ice often forms a crater.
•Sometimes the craters are filled with water forming a lake.
Explanation
•The freezing of water in the upper layer of soil creates ice
lens and leads to the expansion of ice
•The growth of the ice core forces up the overlying sediments,
causing dilation cracks, once the ice core is exposed it melts
causing the top of the pingo to collapse forming a crater.

17. Two types of
Pingos occur
• Open System
– Hydraulic pingos (E. Greenland) found
in the discontinuous zone of permafrost
or valley floors.
– Freely available groundwater is drawn
towards expanding ice core so the pingo
grows from beneath the ground

18. Pingos
• Closed System
– Hydrostatic pingos
(Mackenzie delta type)
associated with low lying
flat areas in zones of
continuous permafrost.
– Form from downward
growth of permafrost,
often after a small lake is
enclosed with sediment

19. Water under
the ground is
under
pressure and
is forced up to
the ice front
(ice lens)
causing it to
freeze and
expand the ice
Formed on the site of a
lake infilled with
sediment. meaning the
ground is insulated,
water collects beneath
the sediment. In the
winter the sediment
freezes, and expands.
This confines the water
and increases pressure.
It then freezes and
expands, pushing the
sediment above it
upwards forming a
mound. During the
summer the ice core
melts causing the
mound to cave in on
itself leaving a dip.

20. Frost Shattering
• Freeze–thaw weathering puts pressure on any cracks in
rocks and can shatter them
• Whilst this is not unique to periglacial areas it does occur
with greater severity than elsewhere and the features it
produces are important.
– Block fields
– Scree or talus slopes

21. Blockfields
• Caused by in situ freeze thaw action

22. THE ROLE OF MASS MOVEMENT
Periglacial landforms and Processes

23. Mass Movement
• Comes in two types mainly
• Frost Creep
• Very slow form of movement, material moves downslope
by just a few cms per year even on steeper slopes
• Solifluction – Occurs in regions with permafrost during the
summer the active layer melts forming a mobile water
saturated layer
• This can create stone banked or turf banked lobes on
slopes of 10 – 20 degrees
• On more gentle slopes terraces or benches occur
• The resulting deposits collect at the bottom of the
periglacial valleys and are known as ‘head’ or coombe rock
• The rocks themselves shows downslope orientation and
both angular and sub angular shapes

24. Solifluction
• This is the slow downhill flow of saturated soil.
• It is common in periglacial environments
• It is where the active top layer provides enough water to
allow flow to occur.
• As saturated soil slumps downhill during the summer it
forms solifluction lobes

25. Solifluction in the Cairngorm
• A number of features of the Cairngorm
environment contribute to active solifluction:
– frequent freeze-thaw cycles
– saturated soils and regolith (loose soil covering rock),
after snow melt and heavy rainfall
– frost-susceptible materials, with significant contents
of silt and clay
– extensive regolith across a range of slope angles

26. Asymmetric Valleys
• Differential rates of Solifluction and frost creep lead to one
side of the valley being significantly steeper than the
other.
• For instance in the northern hemisphere south facing
slopes are more exposed to the sun and so thaw more
frequently thus increasing soil moisture and promoting
mass movement, leading to less steep slopes

27. THE ROLE OF SNOW
Periglacial landforms and Processes

28. Nivation
• This localised process occurs when both
weathering and erosion takes places
around or beneath a snow patch
• It is common in periglacial areas and
leads to nivation hollows which form at
the base of slopes and can initiate the
formation of cirques at times
• It is geomorphic activity enhanced by
snow that persists into the melt season

29. THE ROLE OF WIND AND MELTWATER
RIVERS
Periglacial landforms and Processes

30. Wind Action
• Due to periglacial areas generally suffering from
extreme aridity due to moisture being locked up in ice,
the lack of flora means that wind can play a large role
• During the Pleistocene Ice ages deposits of fine silt and
sediment formed extensive outwash plains (Sandurs)
• These sediments were blown southwards and deposited
as loess over large areas of Europe and N. America
which formed soils of high agricultural potential
• Similarly the winds of the Gobi desert are blowing fine
material to the loess plateau in N. China (So therefore
not unique to periglacial areas

32. Role of Meltwater
• Water erosion is highly seasonal occurring in
spring or summer
• Due to melting of the active layer this leads to
short periods of high discharge
• This causes typically braided rivers due to the
high amount of material carried during higher
discharge
• This though is not unique to periglacial regions
and can be seen on many rivers in mountainous
areas which suffer high discharge

33. RELICT PERIGLACIAL FEATURES
Periglacial landforms and Processes

34. • Periglacial features can form distinctive relict forms when the climate
begins to warm
• In Paraglacial conditions (Rapidly changing landscapes which were once
periglacial but now moving towards non glacial) after the rapidly melting
permafrost a thermo-kast landscape can occur containing large surface
depressions and irregular shaped lakes
• In areas of the UK it is only comparatively recently that many of the
mysteries features have been credited as periglacial often by comparing
and surveying areas of present day periglaction (Principle of
Uniformitarianism)

35. Questions:
• Explain 2 ways in periglacial processes have contributed
to upland landscapes (6)
• Assess the contribution of periglacial processes to upland
landscapes (12)