Frost and Wind Flashcards
What is the peri-glacial concept?
Processes in cold-but not glacial environments, more subtle than glacial processes
What’s more common in Britain? Glacial processes or peri-glacial processes?
Peri-glacial processes
What are para-glacial processes? Give an example
Non-glacial processes greatly affected and conditioned by glaciation or deglaciation.
e.g. sediment transfer process may greatly increase after deglaciation if a slope is unstable after ice-retreat.
What’s the difference between peri-glacial processes and para-glacial processes?
Peri: cold but non glacial
Para: non-glacial but affected by glaciers
What is cryotic ground?
Ground with a temperature below 0
What is permafrost?
Ground that remains below 0 for at least 2 consecutive years
What is seasonally cryotic ground?
Ground that undergoes seasonal thawing and freezing
Describe the general typical effect of frost weathering.
Rocks often fracture along pre-existing weaknesses, this can cause rock disintegration and create fine material that then settles to leave a coarse top layer
What is the difference between macrogelivation and microgelivation?
macro: produces larger clasts
micro: produces finer debris
What types of rocks are more susceptible to microgelivation?
smaller debris –> Micaceous rocks (commonly igneous and metamorphic)
What types of rocks are more susceptible to macrogelivation?
larger debris –> massive schists, gneisses, granulites
What are the main 4 processes by which micro and macrogelivation take place?
Splitting
Flaking
Granular disintegration
Comminution
What is solifluction?
Slow downslope movement of soil under seasonal thawing and freezing.
What is frost creep?
Repeated swelling and resettling of soil/sediment
What is gelifluction?
Slow saturated flow during the thawing of ice rich soil
What is plug-like flow?
Localised sliding within clay rich soils due to thawing and melting
Name three types of solifluction.
Frost Creep, Gelifluction, Plug-like flow
What are block-deposits?
A surface cover of boulders with little or no fine material in the gaps
What is the difference between autochthonous blockfields and allochthonous blockfields?
auto –> result of weathering of rocks that were already there
allo –> glacial deposits weathered
What is the general 3 stage process of blockfields forming?
macrogelivation
then solifluction (moving downslope)
then immobilisation (no fine material to move boulders)
What age are blockfields usually?
Can be relic features from the Neogene protected by glaciers or caused by weathering during glacial periods in the Quaternary
What are debris-mantled surfaces and slopes?
Poorly sorted stony surfaces with a mix of larger clasts and a fine matrix (fine sediment)
What is a diamict?
A poorly sorted deposit
What is a tor?
A residual section of bare bedrock on high ground
What are the two possibilities for explaining the formation of tors?
- Preferential deep weathering of densely jointed bedrock
- Removal of regolith around hard rock by solifluction and frost weathering
What is relic-patterned ground?
terrain with surface patterns defined by micro-relief rocks, vegetation cover and fine and coarse debris.
What are the two types of relic patterned ground? What causes them?
Sorted: differential frost heave
Unsorted: same as sorted but without a concentration of clasts.
What are solifluction landforms?
Landforms on gentle to moderate slopes, often occur on larger hills/mountains but terminating at a steep rise or step
What are solifluction sheets?
A continuous top layer of frost-weathered deposit over bedrock - successive sheets can look like stairs
What are solifluction lobes?
Lobate extensions of sheets on steeper gradients, can override sheets on downslope ends
What are talus deposits?
deposits at the bottom of steep rock walls - predominantly through rockfalls
What is a frost related cause of rock falls?
Macrogelivation
What are 3 types of talus deposits?
Sheets - uniform delivery of the debris.
Cones - concentrated or funnelled in certain spots.
Coalescing cones - cones that intersect laterally.
What are deflation surfaces? What causes them?
Surfaces with almost all vegetation and loose sand stripped away - carpeted with fine gravel and flat lying boulders.
- Caused by strong wind
What are deflation scars? What causes them?
Patches of bare ground in vegetated terrain
- Caused by needle ice action and wind erosion
What are wind stripes?
Selective wind erosion on plateaux surfaces, stripes of vegetation and bare ground perpendicular to dominant wind direction
What are wind polished boulders? What do they tell us?
Wind erosion on bedrock and boulders caused by transfer of KE to rock particles over a long time
- can evidence wind direction
What is debris flow activity? What are the two types?
Rapid downslope flow of poorly sorted debris when it’s mixed with water.
Either Hillslope debris flow (usually initiated by a landslide) or valley confined which is usually initiated by water pressure in sediment.
What does alluvial mean?
Alluvial refers to the stuff left behind by running water.
Why are most alluvial landforms paraglacial?
Because most of the sediment carried in upland rivers is reworked glacial sediment.
What are alluvial river fills?
Deposits of sediments in a river
What are river terraces?
major steps in a valley side corresponding to previous river flow
What are alluvial fans?
low gradient fans caused by tributary streams that end in one trunk valley
