Lateral
moraine
Medial moraine
Glacial snout
Braided streams
Photo 2:
•= Ice wedges polygons + thermokarst lakes
Photo 3:
•Collapsed Pingo – closed system
Photo 4:
•Patterned Ground – Stone Circles
Some useful links in Periglaciation:
http://www.fettes.com/Cairngorms/periglacial_Holocene.htm
http://www.mapcruzin.com/arctic_refuge/permcycl.html
Where are Peri-glacial Enviornments?
•High Latitudes areas - eg Alaska
•“Tundra” Regions
•High altitude temperate latitudes - eg Alps
/ Andes
•Covers approx. 20% of earth’s land
surface
•They are the areas found close to
(peripheral) glaciers
Permafrost
The thermal condition of the soil
and rock. Temperatures
below 0ºC persist over at least 2
consecutive
winters and the intervening
summer - I.e the ground is frozen
PERMAFROST
Permafrost
•Covers 20-25% of Earth’s surface - eg:
•Siberia
•Northern Canada
•Alaska
•China
Types of Permafrost:
•Continuous
•Discontinuous
•Sporadic (isolated)
•Thickness ranges from several metres >
500m (eg Siberia)
Periglacial Processes:
1. Frost Shattering
Frost Shattering
Frost Heave: a) Frost Pull, b) Frost Push
Frost Cracking
2. Weathering
Freeze-Thaw
Salt-Weathering
Carbonation
3. Mass Movements
Frost Creep
Solifluction – ground NOT frozen
Gelifluction – where ground is frozen
1.Frost Action Processes:
Dominant set of processes in periglacial
environments is freeze-thaw cycles. This operates
Most effectively where the temperature oscillates
around the freezing point.
Frost Wedging
• Sometimes called “frost-shattering”
• Mechanical (physical processes) caused by the
expansion of water in cracks of rock (9%)
Frost Creep
• Very slow mass movement – through freezing =
heaving upwards perpendicular to the slope and
then thawing = clasts sink down vertically due to
gravity
Frost Heave
•Frost Pull = occurs when a stone adheres to ice within a freezing
active layer and is drawn upwards as the ground heaves
•Frost Push / Heave = since stones have a lower specific heat
capacity, they heat up and cool down faster than the surrounding
soil (a bit like continents heat up and cool down quicker than
oceans). A descending freezing front will therefore move through a
stone more quickly than it will move through the soil on either
side. This means that the soil immediately beneath a stone is likely
to freeze and expand pushing the stone upwards – more quickly
than the surrounding material = leading to sorting
•Involves the displacement of soil and rock underground upwards
towards the surface
•Produces hills – called pingos and mounds called palsas or
thufurs as a core of ice heaves towards the surface
All processes work using
water. Type is affected by
climate and rate by geology.
Processes in the
hydrosphere
Chemical
Biological
Physical / Mechanical
By Freeze-Thaw Action
This process usually happens in
cold, wet areas. Water enters
joints / cracks in rocks and
freezes. As water freezes it
expands, putting pressure on the
joint / crack. The water then
thaws as the temperature rises
above 0°C, releasing the joint /
crack. When the temperature
drops again, the water refreezes
and so on, eventually the rock
breaks off from the pressure.
Rock
structure
(joints):
• Frost
shattering
• Most active where
temperature fluctuate
around the freezing
point
• Water expands by 9%
on freezing cracking
the rocks apart
• EG DARTMOOR
GRANITE
• Salt crystal growth:
• Growth of salt crystals –
eg sodium carbonate in
cracks in rocks – eg
saline water gets into
cracks or rocks and
breaks them down
• Common in coastal areas
Carbonation:
•CO2 is more soluble at lower temperatures – this
can increase the rate of solubility of limestone
(CACO3 – calcium carbonate).
•So in periglacial areas – if there is limestone
rocks – that rate of weathering is often much
greater
•Also if CO2 can be sucked out the atmosphere it
is going to get rid of a greenhouse gas
The importance of FROST ACTION PROCESSES:
The dominant set of processes found in
periglacial areas is frost action - eg FREEZETHAW.
When water freezes it expands by 9% and can
HEAVE the ground - or expand and lift the ground
upwards.
Because periglacial environments are cold by
nature - there is a great deal of frost action
occuring there
Periglacial Processes cont.
4. Nivation
5. Fluvial
6. Aeolian (wind)
Periglacial Case Study Examples:
•Alaska
•Spitsbergen
•Northern Canada
•Northern Norway / Lapland
•Iceland
Solifluction
Definition: Mass movement of soil and regolith affected by alternate freezing and
thawing. Characteristic of saturated soils in high latitudes, both within and beyond
the permafrost zone.
A number of features of the Cairngorm environment contribute to active solifluction:
•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 angles
Solifluction adds detail to the terrain underfoot. Small-scale, active landforms include lobes
and sheets (Sugden, 1971) and turf-banked terraces. The latter reflect also the action of
wind in stripping and shaping the vegetation mat and frequently occur in association with
deflation surface (Gordon, 1993). Ongoing mass movement is also indicated by 'ploughing
boulders' - large blocks that are moving downslope, pushing a rampart ahead of them and
leaving a furrow behind.
Much more striking, however, are the large boulder terraces and lobes that give crenulated
patterns to many granite slopes on the plateau. These steps terminate in stone banks up to
3 m high. These forms are absent from within the limits of Loch Lomond Readvance
glaciers (Sisson, 1979) and so date from this or earlier periods. As delicate features such as
tors have survived beneath ice covers, it is possible that the larger solifluction terraces and
lobes may be of considerable age.
Wind
The Cairngorms experience some of the highest wind speeds of the
British Isles. Gusts over 100 mph may occur several times a year and
the weather station recorded the highest UK wind speed in a gust of 173
mph in March 1986.
Erosion by strong winds creates deflation surfaces. The vegetation, soil
and fine material debris is removed to leave an armoured surface where
large clasts are embedded within a matrix of grit and sand. Remnants of
the former vegetation cover sometimes occur and allow the former
thickness of the regolith to be estimated. Grains of sand and fine gravel
can be observed in motion during strong winds. The resting places of
the transported debris are often unclear but small sand sheets do occur
on the northern flank of Ben Macdui.
Deflation scars are bare patches that result from opening up of the
vegetation. Wind stripes are lines of vegetation that alternate with bare
ground (Bayfield, 1984). Wind crescents are arcuate patches of
vegetated ground.
Ice patches on the snow
result in localised
weathering and erosion
by freeze thaw. This can
lead to small
depressions. Saturated
material may also slump
under gravity - forming a
pro talus rampart.
Snow forms ice
curtains which
are prone to
avalanches
The wet, deep snow on steep
valley sides in the summer
can hit the valley floor with
such force that large areas
can be excavated leaving a
deep plunge pool
Frozen sediments
can be removed by
riverbank erosion
(abrasion,
hydraulic action)
Fluvial
•Frozen sediments are powerful erosive tools.
•Sandhurs show enormous changes in discharge
throughout the year – obviously a higher rate in summer
and spring
•Much of the year the ground is frozen so there is little
runoff – however in summer when there is more melting
there will be more fluvial erosion
Periglacial Landforms:
Blockfields
Rock Glaciers
Solifluction lobes
Asymmetric Valleys
Flattened Summits
Pingos
Loess
Dry Valleys
Tors
Palsas (frost push on peat)
Scree / Talus
Gelifluction Lobes/benches
Nivation Hollows
Pro talus rampart
Soil (stone) stripes
Thermokarst (Lakes)
Sandhurs
Coombe Rock
Ice Wedge Polygons
Involutions
Patterned Ground > 5 types
1.Circles 2.Nets 3.Polygons 4. Steps 5. Stripes
Earth Hummocks (no sorting)
Protalus Rampart
Definition: Unsorted, non-stratified, coarse
angular rock debris forming arcuate low ridges.
Associated with former persistent snowbanks
in shaded sites, commonly at base of corrie
headwalls.
'Protalus rampart' is an overblown title for a simple
landform. It requires the existence of long-lived
snow banks below rock cliffs. Frost weathering
leads to rockfall from the cliff and the blocks roll
down the snow slope to accumulate at its base.
Ballantyne and Kirkbride (1986) describe good
examples from below the Devil's Point and Sròn na
Lairige.
These snow patches
accelerate freeze thaw
(although some studies claim
they prevent it!). Under the
correct conditions they can
develop into full scale glacier
cirques.
NIVATION HOLLOW
PROTALUS RAMPART
PALSAS – A PINGO ON PEAT!
INVOLUTIONS
As water freezes it expands by 9% - repeated
freezing and thawing of the active layer
causes expansion and contraction of the
surrounding material beneath the soil. The
resultant breaking, churning, and mixing of
the soil, rock and sediment is known as
CRYOBURBATION.
This can alter beds of sediment that were
originally laid down horizontally by twisting
and contorting them into folded formations
called INVOLUTIONS.
Thought to have been
exposed by gelifluction
removing the surface
regolith and
subsequently
weathered by freeze
thaw
Note the
surrounding
felsenmeer
Coarse angular blocks on high
summits are a typical consequence
of freeze thaw weathering
BLOCKFIELDS
A common feature of
periglacial landscapes
although not unique to
them
Where a large quantity of frost-shattered rock becomes
mixed with ice, a rock glacier is formed. This can occur
either by:
1. A large supply of rock debris being added to a small
and thin glacier = ice cored rock glacier.
2. The growth of ice within a large accumulation of rock
fragments = ice-cemented
rock glacier.
They tend to have a steep front, sometimes as much as 100m
in height, and they can reach a length of 1km or more. The
presence of ice between rock fragments allows the rock
glacier to deform under its weight and move downslope at
rates of up to 1m per year.
Definition: a glacier whose motion and
behaviour is characterized by a large
amount of embedded or overlying rock
material
A rock glacier may be composed of:
1. Ice-cemented rock formed in talus that is
subject to permafrost.
2. Ice-cemented rock debris formed from
avalanching snow and rock.
3. Rock debris that has a core of ice; either
a debris-covered glacier or a remnant end
moraine.
These are a consequence of intermittent freezing of
interstitial water allowing the erosion by surface
water flow. This process is further increased by
gelifluction on the valley sides during periods of
partial melting. How have they formed?
The melting of segregated and interstitial ice
within the soil above the permafrost table
results in an excess of moisture. This adds
weight, lubricates the particles and moves the
material down-slope. Resistance at the front
of the mass causes the characteristic lobe to
form. These are typically found on gentler
slopes with their long axis parallel to the
slope contour
Tend to form on
slopes of angles
between 10-20
degrees
In valleys experiencing periglacial conditions
gelifluction sheets of material derived from
surrounding slopes can build up to depths of
several metres, and the geliflucted deposit is
referred to as HEAD DEPOSIT.
It usually contains a mixture of fines, sand and
frost shattered stones that have long axes
oriented downslope relecting flow direction. – eg
chalk downs of Southern England. Sometimes
also referred to as COOMBE ROCK.
NORTH FACING
In arctic regions north facing slopes tend to be
frozen all year round whereas the south facing
slopes are more prone to freeze thaw and
solifluction / gelifluction - which removes material
over time by weathering and erosion. Hence the
south facing slope tends to be less steep. Nb South
facing slopes receive more sunlight
SOUTH FACING
Nivation hollows,
gelifluction and deposition
of sediment are all ideas
put forward for the
creation of these features,
which may simply be a
glacial remnant
SANDHUR
Ventifacts > effects of aeolian processes (or wind
erosion). It is thought that powerful wind systems blew off glaciers –
so wind action was therefore significant in periglacial areas to carve
out rocks such as the one here. Lots of finer particles were also taken
by wind and deposited 100s miles away = LOESS.
Ice Wedges, Polygons, and Pingos
As the arctic soil freezes and thaws over many hundred years, it is cracked and buckled
to create ice wedges, polygons, thermocarst lakes, and pingos. This next fewpage
includes:
Steps of the cycle
Animation of the cycle
Steps of the cycle:
There are a number of ways that polygons, arctic lakes, and pingos form. Here's one
way this cycle works:
A cut-away view of the tundra in
summer. The active layer is thawed.
Winter cold causes the soil
to shrink, and cracks to
form. The active layer is
frozen, so it acts just like
the permafrost soils
beneath it.
During warm spring days,
water seeps into the cracks. It
freezes and expands when it is
chilled by the still-frozen soil.
The frozen water forms
wedges of ice in the soil.
In summer, the active layer and the
tops of the ice wedges melt.
Each winter, cracks form again in
the same places...
and each spring, additional
water enters and enlarges the
ice wedges as the freezing
water expands.
This cycle of crack, melt, and
freeze continues to enlarge the
wedges year by year...
until the soil above the wedges is
pushed up, forming ridges. If you look
down from above, these ridges create
a blocky pattern on the ground, called
polygons.
If the ice is exposed, a wedge may
begin to melt.
You can clearly see the ice which has cleaved apart the soil in
this exposed profile.
As more ice is exposed, the ice
wedge and the active layer melt
lower...
until a pond begins to form.
The pond water holds heat from
the summer sun, so the active
layer melts deeper beneath the
water.
Seen from above, these
lakes (called thermocarst
lakes) can become longer in
one direction when
prevailing winds blow
waves against the downwind shore.
The soil buckles and cracks above the ice wedges, causing
these polygons to form . Thermokarst lake.
Such THERMOKARST
topography is often initiated by the
removal of vegetation by man or
fire. This allows the surface to be
exposed to the full variation of
seasonal temperature variations,
especially in continental areas. The
sun’s radiation (especially in
spring and summer) thaws out the
ice wedges and active layer in the
ground forming these lakes.
Is a general term
referring to
topographyic
depressions due to
the thawing of ground
ice. It is characterised
by extensive areas of
irregular, hummocky
ground interspersed
with waterlogged
hollows. Large lakes
are called alases
A closer view of arctic polygons. These are about 70 feet
(20 meters) across, although polygons may be as small as
10 feet (about 3 meters) across.
Ice wedges
Intense cooling and contraction of the permafrost in winter may
cause polygonal patterns of cracks to form. In summer the
cracks fill with meltwater and some loose material and, upon
refreezing the following winter, the crack will be enlarged. Such
ice wedges may extend to a depth of 3m and reach 1m in width
at their surface.
Ice wedge polygons differ from those formed by frost heave in
that they are larger (30m diameter) (compared with 1-5m) and
their edges are slightly higher than their centres (the edge of the
ice deforms the adjacent sediments), whereas frost heave
polygons are domed. The larger polygons are found where the
winter temperature is below –20C. Ice wedges which are 1-2m
wide and 8-10m deep can take up to 100 years to form.
The rims on an ice wedge are formed when expansion of
sediment during autumn freezing causes material to be
pushed upwards as it is forced against the more resistant ice
wedge.
If the ice wedges melt, they become filled with sediment to
form ICE WEDGE CASTS – eg East Anglia
Frost Cracking
•Water seeps into cracks in the active layer (the surface of the
ground / soil which thaws in the summer) up to a metre or
more downwards.
•This water freezes and then cracks
•It cracks because ice has less tensile strength than
permamently frozen ground around and below it
•The repeated cracking in summers then winters – together
with the addition of new ice the following autumn leads to the
creation of ICE WEDGES (imagine an icicle underground) or
SEGREGATED ICE
•Ice wedges (sometimes called ICE WEDGE POLYGONS)
are preserved until the climate changes (eg gets warmer) and
are replaced by ICE WEDGE CASTS = fine sediments
washed and blown into the cracks in the ground
The lake side may break down,
causing the lake to drain or it could fill
up with sediment.
Without its insulating cover of water,
the active layer begins to refreeze.
In winter, the surface freezes over a
thawed remnant of the active layer.
The very wet soil continues to
freeze within the permafrost layer,
even in summer.
As the unfrozen area continues
to contract, the unfrozen water is
squeezed under great pressure.
Eventually, the water is under
such pressure that it pushes
upward (the direction of least
resistance)...
until the unfrozen water collects
under the root mat, and freezes,
creating a pingo.
Closed system
pingo
If the root mat cracks open
enough to expose the ice, the
pingo top begins to melt.
Water collects in the soil and
freezes to form segregated ice.
This is less dense than the
surrounding material and rises
to the surface, creating these
spectacular features which can
be 10’s of metres high and 1km
in diameter
Open System:
Develop where a body of segregated ice is enlarged by groundwater
flow. Instead of forming from trapped groundwater surrounded by
permafrost, the open system model involves groundwater under
artesian pressure moving through the permafrost to continually feed
a centre of expanding ice that domes up overlying sediment.
Often found in discontinuous zone of permafrost where groundwater
is able to circulate more easily through the sub surface and rock
Closed System:
Water collects in the soil and freezes to
form segregated ice. This is less dense
Usually form from the isolation
progressive
infill and
than theand
surrounding
material
and rises to
disappearance of a small
thelake.
surface, creating these spectacular
Refer to animation
features which can be 10’s of metres high
and 1km in diameter
As the ice core continues to melt,
the pingo collapses further.
Continued melting over many
years removes most traces of the
pingo.
When the soil on a pingo cracks open, and
the ice core is exposed, the pingo begins to
melt and break up.
If conditions are right, the
cycle will begin again.
Much controversy exists over the formation of
patterned ground.
1. Some authors feel it is the result of segregated ice
bulging the central turf, causing surface material to
roll to the edges.
Soil may crack under the huge temperature
variations in many periglacial environments. The
process may be increased by the presence of ice
wedges forming in these cracks.
2. It is also hypothesised that ice lenses form
underneath the stones which have a greater
thermal conductivity (they get cold faster) and
these push the stones to the surface.
Patterned Ground
Patterned Ground > 5 types
1.Circles 2.Nets 3.Polygons 4. Steps 5. Stripes
Patterned Ground can be further classified by whether or
not it exhibits particle size sorting.
Sorted patterned ground – is characterized by the
separation of stones (pebbles and boulders) from finer
material on the surface so that the stones are organized
into circles, nets, polygons, steps or stripes. Frost heave
is a key process in the creation of sorted patterned
ground as it separates stones from finer material.
•Frost Push and Frost Pull = a key process in patterned ground
formation
Since stones have a lower specific heat capacity than finer
sediments, they heat up and cool down faster than the surrounding soil
(a bit like continents heat up and cool down quicker than oceans). A
descending freezing front will therefore move through a stone more
quickly than it will move through the soil on either side.
Frost Push
As the freezing front will also penetrate beneath a stone relatively
quickly – finer material underlying the stone will expand pushing the
stone upwards.
Frost Pull
The top of the stones become frozen as the freezing plane (front) moves
downwards through the soil, which pulls the stone upwards with it as it
expands.These processes lead to sorting of the clasts (stones) =
patterned ground.
PATTERNED GROUND
Definition: An array of small-scale, geometric features
found at the surface of a regolith that has been disturbed by
frost action. The group includes circles, polygons, and nets,
which normally occur on level or gently sloping surfaces, and
steps and stripes which are found on steeper gradients. Both
sorted and non-sorted varieties are recognized. The sorted
varieties are typically outlined by coarse, stony material, and
so are termed 'stone circles', 'stone polygons', 'stone nets',
'stone steps', and 'stone stripes'. The origin of patterned
ground involves a complex interaction of several
geomorphological processes, including frost sorting, frost
heaving, and mass movement.
The edge of
the polygons
mark the
position of the
ice wedges
During the spring when thawing begins in the active
layer, the stone stays in its uplifted position because
fine sediments collapse into the cavity beneath the
stone.
As stone have a lower specific heat capacity
Than finer sediments the freezing plane descends
Through stones more quickly and so you get frost push
Under the stones – pushing them upwards towards the
surface.
When the stones are brought to the surface: circles, stripes, polygons,
steps or stripes are formed depending on:
-concentration of stones
-Amount of moisture
-Slope angle
-Operation of slope processes
Earth Hummocks – NO SORTING
If no sorting occurs on patterned ground – a common landform is the
earth-hummock = circular mounds of vegetation that form an irregular
pattern of hummocks over the surface, and they arise where frost
heaving is concentrated into discrete areas under the ground. They
can range in size from a few metres to several metres in height
Central bulge
Here it is clear how the segregated ice core rises up due
to FROST PUSH, bulging the ground and causing the
surface rocks to move under gravity to the sides.
FROST HEAVE stones rise up
from under the
ground
FROST PUSH land rises and
stone roll to the
outside due to
gravity
Soil Stripes