Periglacial Landforms Flashcards
Open-system Pingos
Discontinuous permafrost
Surface water infiltrates into the upper layers of the ground and freezes
Pressure forces water upwards, increasing the size of the ice core
Ice core expands, leading to increased pressure and forcing sediment up into a dome
Closed-system pingos
Continuous permafrost
Lakes fill with sediment, insulating the ground and creating open talik
Reduced insulation allows permafrost advance, bulging the ice core
Ognips
In summer, when ice cores melt the pingo collapses
Ruptures from the pressure can cause warm air to enter the pingo, collapsing it
Ice lenses
Pockets of ice form due to differential freezing
This draws in water and freezing, causing expansion
Alasses
Thawing of ground ice causing sinking
Depressions fill with water
Gelifluction lobes and slopes
Increase of water volume in pores enables material to move downhill due to gravity
Different rates of movement cause lobes to form
Ice wedge polygon
Winter ground contraction causes cracks to develop
Water seeps into the crack and freezes, widening it
Ridges of ice and stones around the polygon due to frost heave, with the centres lower and filled with water
Asymmetrical valley
Aspect means there are varying rates of mass movement on one side of the valley to the other (South-facing receive more sunlight)
Involutions
Cyroturbation - ground freeze-thaw means it never settles into its original position
Leads to churning of active layer
Blockfields
Frost shattered stones and boulders
Found on mountain tops and plateaus
Patterned ground
Stones are brought to the surface through frost heave
Heavier stones roll outwards, leaving finer material in the middle
Tors
Magma forced upward, forming a batholith of granite
Overlying rocks are removed, revealing granite beneath
Freeze-thaw causes cracks within the granite
Blockfields may form around the Tor
