Periglacial Environements Flashcards
What are periglacial environments?
Areas that are not glaciated but exposed to the extremely cold conditions
Location of periglacial environments
High altitudes and latitudes
What is the active layer?
A thin layer on top that thaws in winter and melts in summer, between 30-200 cm thick
What is permafrost like?
Contains varying amounts of ice which binds everything together. Can be up to 1500 cm thick and covers 25% of exposed land in the northern hemisphere e.g. Northern Russia tundra, Alaska and Canada.
Risks of permafrost
Causes change within ecosystems and infrastructure (roads and pipes) left vulnerable to erosion when melted. Thawing permafrost could possibly cause rock avalanches. Permafrost contains methane when frozen so after it melts it releases the greenhouse gas which contributes to climate change.
What is continuous permafrost?
Has no gaps
What is discontinuous permafrost?
Has gaps
What is sporadic permafrost?
Has pockets
What’s the active layer like?
Summer temperature is sufficient to melt the surface layer of permafrost, can be very mobile. Varies in thickness depending on latitude and vegetation cover
What is the talik?
Any unfrozen material within the permafrost zone
Periglacial environment example (Zugspite)
Highest peak of Wetter-stein and highest in Germany, Bavaria - Alps, northern edge. 2,962m above sea level, rock type = limestone, age of rock = Triassic rock
What is Scree?
Happens at the bottom of steep slopes where freeze-thaw occurs
What is Felsenmeer?
Exposed rock surfaces that have been broken by frost action. A covering of angular shattered rock on flat and high altitudes areas
What is solifluction?
The slow, downslope movement of fine, textured soils. The active layer thaws and excess water reduces friction so AL descends down the slope. Lobate shaped debris masses form. Round features form terraces
What is a nunatak?
An exposed rock summit of a ridge (not covered by snow) which undergoes heavy freeze-thaw/frost shattering due to proximity of ice. Found in ice fields or glaciers
Frost heave process
1) As active layer starts to re-freeze , ice crystals begin to develop and increase the volume of soil and cause upward expansion of the soil surface
2) Within the fine grained material there are larger particles which, because of their lower specific heat capacity, heat up and cool quicker than the surroundings
3) The soil immediately beneath the stone is likely to freeze and expand before the other material, pushing the stone upwards until it reaches the surface
4) On small domes, the larger particles roll downhill, sorting the material forming polygons or striped patterns
Ice wedges process
1) Water gets into the cracks in stone, freezes and expands which makes the cracks bigger because ice occupies more space than water)
2) When it melts more water is allowed inside, repeating this cycle every year. Usually 1m wide and 2-3m deep. No larger otherwise the material surrounding the crack is likely to cave in on itself
Closed system pingos processes: (Mackenzie delta)
1) A frozen lake with sediment on the floor insulates the ground beneath from the cold, allowing talik to exist
2) Permafrost advances from below during cold periods allowing unfrozen water to turn to ice
3) Pressure increases and sediment is pushed up creating a mound
4) Ice cores melt during summer causing the centre to cave in and create a dip
Open system pingos processes
1) Valley bottoms and areas of discontinuous permafrost
2) Active layer unfrozen in summer, surface water can infiltrate into the ground from above
3) Active layer freezes from surface down. This starts to freeze water in the talik trapped between freezing active layer and permafrost creating ice lenses
4) Crack appears where the surface ruptured
5) Water migrated to these lenses and upon contact freezes, swelling the size of the lends
Open system refers to how the water from the outside gets into the system
What a pingos?
Dome shaped hill. 500m diameter and 50m high caused by a seasonally changing active layer
