Periglacial Landforms Flashcards
Stone polygons/stripes /patterned ground formation
(Frost heave) Ice crystals can form when active layer refreezes which increases the volume of the soil and causes an upward expansion . Once they reach the surface they roll down edges of mounds and form circles.
If slope - lines
Polygon if mounds are close
Stone cools and warms faster so ground around it freezes faster than rest pushing stone up
Stone polygon/stripes / patterned ground description
Circles/ lines of stones
Can be angular polygon shape or elongated stripes downhill
Nivation hollows description
Hollows in slope often north facing
Formation of nivation hollows
When layers of snow build up and don’t melt for a long period of time often as north facing. Freeze thaw weathering below patch and downslope movement of sediments out of hollow in summer meltwater causes deepening by erosion
Description of solifluction lobes
Rounded tongue like features
It’s the slumping downslope movement of rock and soil material
Form of mass movement over land
Often forms terraces on side of valley
Formation of solifluction lobes
Areas of discontinuous permafrost - subsoil doesn’t thaw
When the active layer melts it releases a lot of meltwater and it can’t percolate so saturates soil.
The soil then begins to flow even on gentle slopes
What type of permafrost is an open system pingo formed from
Discontinuous
What type of permafrost is a closed system pingo formed from
Continuous
Description of pingos
Can be open or closed systems
Dome shaped feature and is ice cored
Formation of a closed system pingo (Mackenzie type)
Areas of continuous permafrost where there’s a lake at surface, lake insulates the ground, area beneath is unfrozen. When lake dries ground no longer insulated so permafrost advances. Water collects in centre of unfrozen ground and eventually freezes to create a core that pushes ground above upwards
Formation of a open system pingo ( East Greenland type)
Areas of discontinuous permafrost.
Groundwater forced up through gaps between areas of permafrost, water collects together and freezes,
Leads to an expansion of ice within the soil and causes overlying sediments to heave upwards into dome shaped feature
Description of ice wedge polygons
Cracked ground
Polygonal shapes On surface - ice wedge polygons
Wedges of ice and sediment
Formation of ice wedge polygons
- Temperatures drop low in winter and ground contracts and cracks form in permafrost ( frost contraction)
- when temperatures increase in spring active layer thaws and meltwater goes into cracks and sediments
- water freezes into cracks ( ice wedges)
- frost contraction following years can reopen cracks in same place splitting ice wedge and more water and sediment seep In and freeze, widening ice wedge
What are loess
Fine material can be picked up by wind and carried long distances to be deposited elsewhere as extensive areas of loess
