Periglacial processes Flashcards
What areas do periglacial areas widely include? 4
- Permafrost.
- Some seasonal temperature variation - the mean temperatures for at least some period in the summer rise above 0ºC;
- Where freeze-thaw cycles dominate the landform creating processes.
- Distinctive ecosystem adapted to the periglacial environment.
What is permafrost?
Permanently frozen ground where soil temperatures have remained below 0 °C for at least 2 years
What is continuous permafrost?
Summers are so cold that there is only a very superficial surface melting of the ground.
1,500 metres depth.
Mean annual temperature: -40C.
Active layer depth - 0.5m.
What is discontinous permafrost?
Slightly warmer areas.
Islands of permanently frozen ground separated by small pockets of unfrozen less cold areas.
Slightly warmer zones due to proximity of surface water e.g. rivers and lakes.
Mean annual temperature: -6C.
Active layer depth - 1.5.
What is sporadic permafrost?
Mean annual temperature : -1C.
Summer temperatures reach several degrees.
Isolated pockets of permanently frozen ground remain below the surface.
Active layer depth - 3m.
What is the active layer?
Summer temperatures sufficient to melt the surface layer of permafrost.
Varies in thickness.
What is talik?
Any unfrozen material within the permafrost zone.
What happens when you progress from the Poles regarding permafrost?
Continuous, discontinuous, none.
Depth will shrink.
Active layer will increase.
How are nivation hollows formed?
Snow falls into small depressions.
Accumulates - firn - neve.
Weathering - freeze-thaw - weakens back rock.
Erosion from meltwater can wash out sediment.
Weathered particles move downslope by soil creep and solifluction.
Processes combined - nivation.
Can form corries.
What is frost heave and what landforms does it make?
The upward dislocation of soil and rocks by the freezing and expansion of soil water.
Patterned ground - sorted material.
Gentle slopes- stone polygons.
Slopes exceeding 6 degrees - stone stripes.
What is frost push?
Cold penetrates the soil.
Large stones chill more rapidly than soil.
Water below the stones freezes and expands.
The stones are pushed up.
What is frost pull?
Ice creeps downwards from the surface.
Growth of ice crystals and the drying of soil on the lower part pulls the stones in a more vertical movement.
What is left as a result of freeze-thaw?
Periglacial areas - screes at the slope foot.
Flat areas - extensive spreads of angular boulders - blockfield/felsenmeer.
What is solifluction and what does it form?
Active laws thaws in the summer.
Excessive lubrication reduces the friction.
Even 2 degree slopes move downhill.
Forms solifluction sheets/lobes - tongue-like features.
Terraces on the sides of the valleys.
Widespread in southern Britain - Quaternary ice age.
What is groundwater freezing and what does it form?
Thin/discontinuous permafrost.
Water seeps into the upper layer and freezes.
Ice expands - causes a dome shape.
Forms pingos.
What is ground contraction and what does it form?
Ground refreezing in the winter contracts the soil.
Surface cracks open up.
Summer melting - cracks open again and fill with meltwater.
Sediment in the meltwater fills the cracks.
Repeated process opens the crack - ice wedge.
1m wide and 2-3m deep.
Causes ice-wedge polygons on the surface.
What is water action?
Mainly summer - meltwater.
High river discharge - more fluvial erosion than expected.
Braided drainage - due to high debris.
What is wind action and what does it form?
High velocities.
Abrasion and dislodges the fine materials in an area.
Ventifacts - stones shaped by the wind.
Polished rock surfaces.
Fine outwash material picked up, carried and deposited elsewhere - extensive areas of loess.
E.g. North America.
England - loess deposits depth - 2m e.g. brick-earth deposits.
China - 300m depth.
