Periglaciation

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,
palsas 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

9. Ice Wedge Polygons

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
• 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
• This term covers a range of features including:
– Circles, Nets ,Polygons, Steps and Stripes
• 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
• This provides the basis for all patterns.
• 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. Frost Heave

13. Think about it.
• Climate changes winter to summer
• During a freeze the top layer freezes
• This makes water particles within the
soil freeze
• Ice expands by 9% when frozen
• Water feeds this from below
• Forcing the top layer upwards

14. How Ice Lens form

15. Rock Stripes

16. Pingo Formation

17. Pingos
•Ice-cored hills with a height between 30 to 70 metres and a
diameter between 100 to 500 metres
•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.
•Most pingos are circular in shape.
•Smaller pingos tend to have a curved top.
•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.

18. 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

19. 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

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
– Tors
– Scree or talus slopes
– Pro-talus ramparts
– Rock glaciers

21. THE ROLE OF MASS MOVEMENT
Periglacial landforms and Processes

22. 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

23. 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

24. THE ROLE OF SNOW
Periglacial landforms and Processes

25. 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

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

27. 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

29. 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

30. RELICT PERIGLACIAL FEATURES
Periglacial landforms and Processes

31. • 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)

32. Possible Relict Periglacial Landforms found in
the UK
Landform Feature
Ice Wedge Polygons Banks of R. Till near Etal
Northumberland
Patterned ground Scotland (Still active) on the Glyders
Pingos Vale of Llanberis
Block Fields (Found above 1000m) Cairngorms and Snowden
Tors Gritstone Tors, Pennines
Screes (Active and relict) Slopes of wastewater and Honister
Pass
Solifluction College Valley Northumberland
Coombe Rock Solifluction Berwyn Mountain valleys, Wales
Asymmetric Valleys Surry and on the Ri8ver Exe, Devon
Nivation Hollows Base of Berkshire Downs
Loess Deposits Parts of East Anglia