5. Periglacial landscapes, processes and deposits Flashcards
What does periglacial mean?
Domain of frost climate
● Strict sense: effects of ground frost
● Broader sense: also other processes influenced by frost climate (e.g. loess formation)
What is permafrost?
Rock or soil frozen for at least 2 years.
Dry permafrost → little geomorphic effect; e.g. cold bedrock.
What is the active layer of the permafrost?
freezing/thawing cycles
What is cryoplanation?
Formation of flat land surfaces under the influence of periglacial processes
Disintegration of solid rock into coarse congelifracts → boulder fields (e.g. Scottish Highland) without erratics (the boulders
are formed in situ and not brought here by glaciers!)
What is a rock glacier?
- In high mountains
- Tongue-shaped frozen debris masses
- Ice inside, but not glacier ice
- Movement due to slow deformation of ice core, up to 3 m/a.
What is cryoturbation?
Cryo = ice, turbation = deformation
What does different grain sizes and different water content mean?
different rates of freezing
What is solifluction?
Downslope (2º enough!), slow creep of soil over permafrost
High water saturation of the active layer → reduction in shear strength → flow
What are frost fissures and ice wedges?
Ice wedges:
rapid freezing of dry soil
→ soil contraction, cracks in polygonal pattern
→ water enters in thaw period and may re-freeze
→ cracks cannot close
What is an epigenetic ice wedge?
In already existing permafrost;
Younger than the surrounding material;
Crack in the centre, do not grow downward
New wedges down in cracks in the centre of older wedges
What is a syngenetic ice wedge?
Grow parallel with sediment accumulation
Oldest ice at the bottom
Looks like a reverse Christmas tree where triangles haven’t been erased
What is an anti-syngenetic ice wedge?
When erosion removes sediment
They grow downward
Oldest ice is on the outside
Gets deeper each time, but also thinner
What can cause patterned ground?
Polygons and/or sorted polygons (stone rings)
Development of ice wedges (they develop in a certain geometric way)
Periglacial freeze-thaw processes
Stone rings by ice lenses
What is a pingo?
Eskimos for “small hill”
Single ice-cored hillocks with a round base up to 1200 m diameter, height up to 100 m, steep slopes.
Ice core with soil around.
Typically occur on flat surfaces.
What is a talik?
Unfrozen soil
