Periglacial Landforms (Edexcel A Level Geography)

Periglacial Landforms

• The major process that contributes to the production of a periglacial landforms is frost-action

• This leads to vast plains of permafrost with low-growing, marsh vegetation and exposed rocks

• Typical landforms found within a periglacial landscape are:

  • Permafrost

  • Loess

  • Solifluction lobes and terracettes

  • Ice wedges and ice lenses

  • Patterned ground

  • Blockfields/felsenmeer

  • Thermokarsts

  • Pingos

Loess

• Derived from the German word for 'loose', loess is fine, mineral-rich, windblown material

• Mainly created by wind, but also through glacial action

• As glaciers grind bedrock to a fine powder, called rock flour, meltwater streams carry this to the end of the glacier

• It is this sediment that becomes loess

• Loess can range in thickness from a few centimetres to over 90m

• Unlike most soils, loess is pale, loosely packed and crumbles easily

Blockfields or felsenmeer

• In mountainous/alpine regions, extensive freeze-thaw weathering of the bedrock leaves broken, angular fragments of rock strewn across the landscape

• These areas are subject to intensive, repeated cycles of freezing and thawing

Solifluction lobes and terracettes

• Solifluction is the downward movement of rock and soil under gravity, resulting in lobed-shaped features called solifluction lobes

• Occurs during the summer melt period, when the permafrost's active layer becomes saturated with meltwater and 'slips' downslope

• Terracettes are formed when saturated soil freezes and expands, which forces the soil to shift (heave) upwards towards the surface

• During the spring/summer melt, the soil dries and collapses back vertically

• Each cycle of frost heave and thaw moves the soil downslope, slowly forming a terraced environment

Ice wedges and ice lenses

• Ice wedges form when cracks in the surface fill with summer meltwater and freeze during the winter

• Temperatures have to remain low for cracks to form initially but also to prevent evaporation of water during the melt phase

• Continued freezing and thawing cycles, increase the size of the ice wedges each year

• Ice lenses begin to form when moisture in the soil pools and freezes

• Ice lenses grow with subsequent thawing and refreezing forming a lens-shaped block of ice

• As ice lenses increase in size, they cause soil heave, patterned ground and pingos

Patterned ground

• The ordered pattern is created through the sorting of sediment, stones and ice wedges

• Shapes include polygons, circles, and stripes 

• The repeated freezing, heaving and thawing of the active layer produces the pattern

• Initially freezing sorts material from the rock, and when thawing occurs, redistributes the rock particles into a system of shapes

• Frost heave then pushes larger stones to the surface, which due to its uplift, moves the stones sideways

• Smaller particles are removed via meltwater or wind, which leaves the larger material lying on top of ice wedges, which in turn, marks the polygon pattern

• The sloping ground and gravity, force rocks to move downhill forming elongated stone stripes instead of polygons or circles

Thermokarsts

• Thermokarsts result from melted ground ice settling unevenly to form marshy ground of hummocks and hollows

• Found mostly in the flat, lowland plains of the Arctic

Pingos

• Found in the Arctic and sub-Arctic region

• These landforms can reach heights of up to 90m

• They have a core of ice and are surrounded on the outside by green vegetation 

• There are two forms of pingos:

  • Closed system

  • Open system

• Closed-system

  • Form in areas of continuous permafrost with a lake on the surface

  • Lake sediments act as an insulator to the ground beneath, which remains unfrozen, and the permafrost layer

  • Liquid water is contained in this unfrozen ground/talik

  • When the lake retreats, the ground is no longer insulated and the residual water freezes into a core/lens

  • As the permafrost advances, it squeezes the talik and pushes the ice lens and lake sediments towards the surface

  • During the summer the ice lens may melt and collapse, leaving a hollow, called an ognip, that fills with water

• Open-system
  

  • Form in areas of discontinuous permafrost

  • Groundwater is forced through gaps in the permafrost

  • Water rises, accumulates and freezes in the active layer of permafrost, to form an ice lens

  • As the groundwater continues to feed the ice lens, the surface domes to form a pingo

Case Study - Tundra of Northern Canada

Characteristics of Periglacial/Tundra Environments

• 3 types of tundra, sharing similar conditions, are found worldwide:

  • Arctic tundra 

  • Antarctic tundra

  • Alpine tundra

• In Canada, the Arctic tundra can be found in Yukon, the Northwest Territories, Nunavut, north-eastern Manitoba, northern Ontario, northern Quebec and northern Labrador

• The landscape of the Canadian tundra varies due to its location and ranges from large flatlands to rocky mountains

• Closer to the polar permanent ice, the tundra changes into a flat landscape of ice and snow

• During the warmer months, snow and soil above the permafrost melt, creating lakes, streams, rivers and wetlands

• The landscape in the summer is barren, rocky, wet, and dotted with vegetation

• During the winter, the tundra is barren and rocky, with no trees, and snow covered

• As the tundra freezes, the wind blows snow against the mountains, hard-packing the snow into ice sheets

• The permafrost prevents trees from deep rooting and therefore, unable to withstand harsh conditions and winds

• This keeps the landscape looking barren