Periglacial Landforms

Impermeable, permanently frozen ground

Covers approx 20% of earth surface

Three types:

• Continuous: Coldest! Mean annual temp = -5°C to -50°C
  • no plant life
  • e.g. Artic Tundra
• Discontinuous: Mean annual temp = -1.5°C to -5°C
• Sporadic: Mean annual temp = 0°C to -1.5°C
  • Can sustain trees

Above permafrost = ACTIVE LAYER --> Seasonally thaws and is associated with mass movements

Distinct and often symmetrical shape found in soils subjected to intense frost action.

• Polygons and circles
• Stripes on steeper slopes

Exact formation unknown, but suspected:

• Repeated freeze thaw cycles smooth out irregularities and odd shaped piles
• ice sorting
• differential frost heave
• solifluction
• effect of vegetation

"Flowing Soil"

The movement downwards under gravity of thawed soil over frozen ground. The liquid limit in the soil is exceeded causing it to flow - the speed of movement will depend on the slop angle

Seasonal Variability

• Winter - water freezes in soil causing it to exapnd

• Spring - Melts and flows downhill

A landscape of hummocks and wet hollows, resulting from subsidence caused by the melting of permafrost.

May be caused by:

• Broad climatic changes
• Local environment changes

A pingo (also called a hydrolaccolith) is a mound of earth-covered ice

An ice core is formed by the accumulation and freezing of water under pressure

Causes overlying sediment to rise forming a mound

Two Types:

• Open-system: source of water is distant + elevated
• Closed-system: source of water is local + pingo arises becaue of expansion of permafrost