Periglacial Processes and the Formation of Associated Features Flashcards
In summer, what does the energy balance cause?
It becomes positive, and causes an active layer which varies from a few cm to 3m.
How much of the Earth is permafrost?
25%, including 50% of Canada and 70% of Alaska.
What are the factors affecting the permafrost, apart from climate, temperature and moisture availability?
Proximity to water body
Slope angle and orientation
Character of ground - rock and soil types
Vegetation cover can insulate ground
Snow cover can delay freezing process
What are the 4 main processes operating in permafrost areas?
Expansion of water by 9% on freezing - causing frost shattering
Contraction and cracking of freezing soils - resulting in ice wedges and frost heaving
Migration of subsurface water to the freezing front by suction - causes segregated ice and pingos.
Mass movement through solilfluction creating lobes and terraces.
What is an ice wedge polygon and how is it formed?
Frost cracking created areas of irregular polygons 5-30m in size. When the active layer thaws, ice wedges form as water flows into cracks and FTW occurs.
What is patterned ground and how is it formed?
Frost push propels stones upwards and frost heave causes stones to migrate out into circles. The up-doming effect in the centre of the circles means the larger stones get rolled outwards. Cannot form on a 30 degree slope.
What are ice lenses and how are they formed?
Water may build up in soil that is frozen when water migrates to the freezing front.
How large are pingos?
30-70m high and 100-500m wide. Can be conical or elongated.
How are pingos formed?
Growth of an ice core forces up the overlying sediments causing dilation cracks. Once the top of the core is exposed out the surface it melts, causing the top of the pingo to collapse. This formed a crater to fill with meltwater and sediments.
How is an open system (hydraulic) pingo formed?
Found in discontinuous zone or valley floors.
Groundwater is drawn towards the ice core where it freezes, increasing the size of the core, growing it from below the ground
How is a closed system (hydrostatic) pingo formed?
Only in continuous zones.
Formed from the downward growth of permafrost, after a lack is enclosed with sediments. Loss of insulators lake allows permafrost to advance, trapping and freezing the water with hydrostatic pressure.
What are Block Fields?
A frost weathering feature - accumulations of angular ,frost-shattered rocks which pile up on flat plateaus. They form in situ, creating by frost heaving of bedrock and FTW.
What are Tors?
A frost weathering feature - With crown hill tops stand out, where more resistant areas of rock occur.
What are scree slopes?
A frost weathering feature - rock fragments fall and accumulate at slope base.
What are protalus ramparts?
A frost weathering feature - snow accumulates at the base of a cliff and cushions the rocks that fall, and pushing them to the front of the snow patch. Once the snow melts you are left with a rampart up to the cliff.
