Here are the key periglacial processes likely occurring around the glacier shown in Figure 2:
- Frost shattering of rock producing scree slopes at the base of valley sides due to repeated freezing and thawing.
- Solifluction occurring on valley sides within the active layer, transporting fine material downslope and leaving lobes and terraces.
- Nivation occurring in hollows beneath snowpatches on north-facing slopes, deepening the hollows through frost action and meltwater erosion.
- Patterned ground such as stone stripes forming in better drained areas subjected to freeze-thaw cycles.
- Fluvial erosion by meltwater streams flowing from the glacier, causing erosion and leaving braided
1. Learning destination: understand what
permafrost, frost heave, groundwater
freezing, nivation and solifluction are and
what landforms they create
Routes: Identify, describe and explain the
formation of nivation hollows, ice wedges,
patterned ground, pingos and solifluction
lobes
2. What glacial feature does this Wordsworth poem
describe?
“As a huge Stone is sometimes seen to lie
Couched on the bald top of an eminence;
Wonder to all who do the same espy,
By what means it could thither come, and whence;
So that it seems a thing endued with sense:
Like a Sea-beast crawled forth, that on a shelf
Of rock or sand reposeth, there to sun itself”
W Wordsworth 1807 The Leech Gatherer
3. Areas that experience a cold climate, with
intense frost action and the development of
permafrost
Aka tundra areas
20-25% of the Earth‟s surface is periglacial, e.g.
northern North America and Russia above the
Arctic Circle
Experience conditions close to glacial (near an
ice sheet e.g. Greenland). Peri = near.
Consistently below 0 degrees celsius.
Temporally close to glacials (e.g. Highland
Scotland)
Very cold climate with distinctive landforms
May exhibit temperate climates today
4. Where are periglacial environments?
• High altitudes – around ice masses in mountain ranges. Also in
high altitude plateau areas e.g. the Tibetan plateau and Bolivian
plateau
• High latitudes e.g. northern Asia, North America and northern
Europe
• Continental interiors – due to continentality, e.g. Siberia, central
Asia
5. Permanently frozen ground
Impermeable
Subsoil temperatures must remain below zero for
2 years or more for permafrost to develop
The extent, depth and continuity of the
permafrost layer varies through time according
to fluctuations in climate
During summer, when air temperatures are
above freezing, the surface layer thaws to form
an active layer up to 4m deep.
The active layer gets easily waterlogged due to
frozen ground beneath so will easily flow if there
is a gradient - solifluction
6. Continuous – found in coldest regions (mean
below -5) e.g. the Arctic where there is little
thawing even in summer. Affects soil and rock to
a depth of 700m in Canada and twice that in
Siberia
Discontinuous – found in slightly warmer regions
where freezing conditions do not penetrate to
such great depths (20-30m). Discontinuous due
to breaks around rivers, lakes and the sea.
Patches are frozen.
Sporadic – mean annual temperatures are around
or just below freezing, so permafrost appears
only in isolated spots
7.
8.
9. Define the term „periglacial‟ – 2 marks (also
in June 2011)
Explain the annual changes in the active
layer above the permafrost – 4 marks
15. Provides a great deal of erosive material in
glaciers, so already studied
In periglacial areas, screes develop at the
foot of slopes due to frost shattering
On relatively flat areas, extensive spreads of
angular boulders are left, known as
blockfield or felsenmeer (sea of rocks)
E.g. the Glyders, North Wales
19. Results from the direct formation of ice
crystals in the soil as it starts to refreeze
On freezing, fine-grained soils expand
unevenly upwards to form 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, expanding by 9% as they do so.
By repeatedly freezing and thawing over
time, these ice crystals and lenses heave
stones upwards in the soil.
20. In areas where temperatures fluctuate
between 0 degrees and -4 degrees C, the
frost heaving and subsequent thawing is able
to sort material to form patterned ground.
The larger stones move outwards down to
the very low slopes of smaller domes because
of their weight.
On gentler slopes stone polygons are
created, but where the ground is steeper
(greater than 6 ̊) the stones are dragged
downhill by gravity into more linear
arrangements known as stone stripes.
27. Freezing of water in upper layer of soil
where permafrost is thin or discontinuous
leads to the expansion of ice within the soil
This causes the overlying sediments to heave
upwards into a dome-shaped feature known
as a pingo
Less than 50m in height, 0.5km across, found
in sandier soils = open-system or East
Greenland type
28. Closed-system pingos or Mackenzie type pingos
are more typical of low-lying areas with
continuous permafrost
On the site of small lakes, groundwater can be
trapped by freezing from above and by the
permafrost beneath as it moves in from the
lakeside
Subsequent freezing and expansion of trapped
water pushes the overlying sediments into a
pingo form
If the centre collapses it may infill with water to
form a small lake
Over a thousand of these pingos have been
recorded in the Mackenzie delta (Canada)
29.
30. Draw 3 diagrams:
1. Formation of an open-system (East
Greenland) type pingo
2. Formation of a closed-system (Mackenzie)
type pingo
3. A ruptured pingo
31.
32. Draw a labelled sketch to show
characteristics of a pingo and suggest an
explanation for its formation – 7 marks
36. Refreezing of the active layer during winter
causes the soil to contract and cracks open up on
the surface
During melting the following summer, the cracks
open again and fill with meltwater and its
associated fine sediment, which helps to
partially fill the crack
Repetition widens and deepens the crack to form
an ice wedge up to 1m wide and 3m deep
A near polygonal pattern is produced on the
surface, similar to frost heave polygons
Forms ice wedge polygons
40. Occurs mainly between north and east facing
slopes beneath patches of snow in hollows
Frost action below snow which involves
freeze-thaw and solifluction and meltwater
Freeze-thaw disintegrates underlying rock
During spring thaw, weathered particles
moved downslope by meltwater and
solifluction
Leads to nivation hollows which may be the
start of corrie development
43. Summer thaw in the active layer releases a
lot of meltwater
Water cannot percolate downwards due to
frozen ground so it saturates the soil
It reduces internal friction between particles
making the soil mobile
The soil flows even on slopes of only a few
degrees
Leaves behind rounded tongue-like features
forming terraces on the side of valleys –
solifluction lobes
44.
45.
46. Stepped features below vegetation, pushed
forward and rolled under like Caterpillar
truck
Where vegetation is sparse, stones heaved to
the surface are pushed to the front of the
advancing lobe and form a small stone bank
at the front of the lobe
Many parts of southern Britain experienced
these conditions during the Quaternary ice
age and these deposits, which filled in
valleys are known locally as head (coombe in
chalky areas)
47.
48. Periglacial areas are often open and sparsely
vegetated. This means that erosion by water
and wind can be high.
Water erosion is seasonal, occurring in
mainly spring and summer when the active
layer melts.
This can bring short periods of high discharge
in rivers bringing high levels of fluvial
erosion.
Drainage is braided due to high amounts of
debris being carried by meltwater streams.
49.
50. Unobstructed winds reach high velocities
Cause erosion through abrasion
They dislodge fine, unconsolidated materials.
Result in grooved and polished rock surfaces
and in stones shaped by the wind, called
ventifacts
Fine material of outwash plain is picked up
and carried long distances
It is deposited elsewhere as areas of loess
Loess is found in many parts of North
America and Eurasia, just south of the
Pleistocene ice sheet limit
51.
52.
53. Outline periglacial processes likely to be
occurring around the glacier in Figure 2 – 5
marks