WHAT ARE PERIGLACIAL PROCESSES?

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

QUICK QUESTION… What glacial feature does this Wordsworth

poem describe?

“As a huge Stone is sometimes seen to lieCouched 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 shelfOf rock or sand reposeth, there to sun itself”

W Wordsworth 1807 The Leech Gatherer

WHAT ARE PERIGLACIAL AREAS? 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

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

PERMAFROST 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

3 TYPES OF PERMAFROST 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

EXAM QUESTIONS – JUNE 2010 Define the term ‘periglacial’ – 2 marks

(also in June 2011) Explain the annual changes in the active

layer above the permafrost – 4 marks

THE ANSWERS…

Describe the distribution of permafrost shown in Figure 3 – 4 marks

June 2012

MARK SCHEME JUNE 2012

PERIGLACIAL PROCESSES

FREEZE-THAW ACTION (FROST

SHATTERING)Blockfield

Felsenmeer

FREEZE-THAW ACTION (FROST SHATTERING) 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

FROST HEAVEPatterned ground

Stone polygons

Stone stripes

FROST HEAVE 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.

FROST HEAVE CONT… 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 ) L the stones are dragged downhill by gravity into more linear arrangements known as stone stripes.

Describe the patterned ground shown in Figure 2 and explain its formation – 6 marks

MARK SCHEME…

GROUNDWATER FREEZING

Pingos

GROUNDWATER FREEZING 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

PINGOS 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)

TASK Draw 3 diagrams:1. Formation of an open-system (East

Greenland) type pingo2. Formation of a closed-system

(Mackenzie) type pingo3. A ruptured pingo

EXAM QUESTION – JAN 2012 Draw a labelled sketch to show

characteristics of a pingo and suggest an explanation for its formation – 7 marks

MARK SCHEME

GROUND CONTRACTION

Ice wedges

Ice wedge polygons

GROUND CONTRACTION 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

ICE WEDGE POLYGONS

ICE WEDGE DEVELOPMENT

NIVATION Nivation hollows

NIVATION 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

SOLIFLUCTIONSolifluction lobes

SOLIFLUCTION 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

SOLIFLUCTION LOBES 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)

WATER AND WIND ACTION

(AEOLIAN PROCESSES)

WATER… 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.

WIND… 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

AN EXAM QUESTION TO TEST YOU ON

ALL OF THE PROCESSES…

EXAM QUESTION – JUNE 2011 Outline periglacial processes likely to be

occurring around the glacier in Figure 2 – 5 marks

MARK SCHEME