Periglacial Environments: a cold climate, typically near glacial regions. The periglacial environment is a cold climate, often marginal to (next to) the glacial environment, and is subject to intense cycles of freezing and thawing
Permafrost Environments: where the ground is frozen for more than two years in a row
Continuous Permafrost: a continuous sheet of frozen material.
Discontinuous Permafrost: summer sun can melt the permafrost for several weeks or months. It may be that only the upper layer of the ground melts and lower layers remain frozen.
Sporadic Permafrost: Occurs at margins of periglacial environments and is usually very fragmented and only a few metres thick
Periglacial Environments
– These environments are found close to glacial environments, but can extend for hundreds, or even thousands of kilometres from active glaciers.
– They are characterised by two main features: PERMAFROST (continuous and discontinuous) and INTENSE FREEZING AND THAWING.
– The active layer (talik) is that part of the ground (the upper layer), that will potentially thaw during summer and thus be prone to biological processes.
Periglacial Processes
There are four periglacial processes that you must be able to use and link to the formation of periglacial landforms.
The first three processes are UNIQUE to periglacial environments – they therefore produce a distinctive landscape!
1. Frost heave: the concentration and cracking of rapidly freezing soils in which ice wedges form, as well as patterned ground.
2. Suction: the migration of sub-surface water to the ‘freezing front’, which causes the formation of segregated ice leading to the formation of ice lens and pingos.
3. Solifluction: the mass movement of the saturated active layer downslope, largely by gravity, which leads to lobes and terraces.
4. Frost shattering (freeze-thaw): the nine percent expansion of water upon freezing, which forms block fields and screes.
5. Wind erosion: high winds disturb sediment, which can build up in certain areas to create loess deposits.
Periglacial Landforms
Nivation Hollow
The combined action of freeze-thaw weathering and meltwater erosion in sheltered areas results in the gradual deepening and creating of a hollow. They are micro-meso scale.
Blockfields
These are meso-macro scale landscapes, created on bare rocky outcrops, where freeze-thaw weathering breaks the surface layer up over time.
Ice Wedges and Patterned Ground
Frost heave results in the ground contracting and cracking. These cracks can fill with water during summer months and later freeze to create ice wedges. As they become more extensive, they can form polygonal patterns on the ground.
Pingo
The freezing of the upper layers of the soil, where permafrost is thin, leads to the expansion of ice within the soil (ice lenses). This causes the overlaying sediments to heave upwards into a dome-shaped feature, which is less than 50m in height, called a pingo.
Solifluction Lobes
As saturated soil (active layer) slumps downhill during summer it forms solifluction lobes.
Loess
Strong winds pick up large amounts of fine material and redeposit it far away from its source as loess.