Periglacial Landscapes Flashcards
Define permafrost
Frozen ground which remains frozen all year round for at least two consecutive years.
Found at high altitudes and latitudes
What is the active layer
Thin layer of soil above the permafrost
Permafrost can reach….km deep
1.5
Give a typical feature of a periglacial area
Ice wedge polygons
Permafrost covers…% exposed land surface in the Northern Hemisphere
25
What is talik
Unfrozen ground within a periglacial area
What is continuous permafrost
No gaps - found where the mean annual temperature is colder than - 5ºC
Arctic circle
What is discontinuous permafrost
Widespread and some gaps - mean annual temperature is -1ºC to -5ºC
What is sporadic permafrost
Isolated + small areas - mean annual temperatures are just below zero
Define periglacial areas
used to be places at or near ice sheets/glaciers. Now associated with permafrost
Not covered by snow and ice all year round
Why do permafrost regions contain seasonal wetlands
The active layer in the summer becomes boggy marshes - permafrost prevents melted water draining downwards
Why does the temperature of the permafrost increase with depth
Lower altitudes, increased distance from the cold air, closer to the heat at the centre of the Earth
Distinguish the terms periglacial and permafrost
Periglacial = associated with areas of permafrost but also includes areas of unfrozen ground, whereas permafrost is only areas of frozen ground
What is frost-heave
Small-scale upwards displacement of soil particles as a result of the freezing and expansion of water in the active layer, just below the ground surface
What is frost creep
When soil particles on a slope show a dominant movement downhill under gravity. Particles are raised perpendicular to the ground surface by frost heave and are dropped down further vertically due to gravity on thawing
Repeated cycles can cause particles to ‘creep’ downslope
What is ground ice
develops when a supply of water exists and freezes to form a core of ice which can force sediment upwards towards the surface
What is solifluction
The downslope movement of rock and soil particles due to gravity, including processes such as soil creep, mudflows and landslides.
Gelifuction refers specifically to soil flows in periglacial regions which occur when the active layer thaws and moves downslope under gravity, over the permafrost.
What are ice wedges and how are they formed
Narrow surface ridges of irregular pentagons
Extremely low temperatures - cracks develop.
Meltwater falls into these cracks in the summer and freezes in the winter (expanding to form ice wedges).
What are pingos and how are they formed
Mounds of earth-covered ice up to 70m high
Form on a site of a lake that has generally been filled with soil
In the summer, the ice core melts and the centre may collapse
What are blockfields and felsenmeers and how are they formed
Extensive frost shattering bedrock consisting of broken u angular fragment of rock
Subjected to repeated cycles of freezing and thawing. More likely to occur in moderate rather than extreme conditions
What are solifluction lobes
Small scale, tongue-like platforms that slip slowly downhill
The downslope movement of soil and rock in response to gravity in a periglacial environment - significant summer melting areas.
