Periglacial Processes, Landforms And Landscapes Flashcards
What is a periglacial
The cold environment on the margins of glaciers
What are the characteristics of a periglacial landscape
Non-glaciated
Characterised by periods of extreme cold, dry condtions
Frequent freeze-thaw
Permafrost
What are periglacial areas often referred to
The tundra
What is the tundra? (vegetation)
A area with treeless vegetation of dwarf shrubs, sedges and grasses, mosses and lichens
Why is the vegetation so small in the tundra
Hindered by mean annual temperature of less than 3C and minimum temperatures as low as -50c
Reduced sunlight for part of year (small growth period)
Why is the growth of plants season so short in glacial/Periglacial
There are only a few days in which the temperature is above 6*c which is the minimum needed for photosynthesis
Where does nivation take place
Below patchestof snow of bare rock (slight depressions in the ground)
Usually on north and east facing slopes in NH where snow less likely to melt (stays for long time)
Where does nivation typically occur
On the north and east facing slopes (less sun so less the likely the snow will melt)
What does freeze-thaw and chemical weathering do?
Cause the rock underneath the snow to disintegrate (fall apart/ degrade/ erode)
What happens when the snow melts in spring (solifluction)
Weathered particles are moved downslope by meltwater and solifluction creating solifuciton lobes
What does the repetition and weathering and solifluction do with snow?
Formation of a nivation hollow which when enlarged can be the beginning of a corrie (cirque) in some areas.
What are solifluction sheets/lobes
Rounded, tounge like features often forming terraces in the sides of valleys
How does rate of flow vary with solifluction
Vary with climatic conditions, slope and vegetation cover but usually move 1-10cm a year
How does solifluction lobes occur
Excessive lubrication when the active layer thaws in summer this reduces friction between between the particles (able to move over each other more easily). Even on a slope as shallow as 2* the active layer can bgin to move downslope
what creates patterned ground? (Process)
Frost heave
What is the first step of frost heave
Active layers starts to re-freeze when temperature drops ice crystals begin to develop
What do ice crystals cause in the soil
Increase the soil volume and cause an upwards expansion of the soil surface (uplifting)
What does fine-grained material cause in the process of patterned ground
Causes the soil to expand unevenly producing small domes on the surface
What can be found within fine-grained material
Stones (coarse material)
How do stones cuse frost heave
They warm up and cool faster
Therefore the penetrating cold passes through the stones faster
This means the soil beneath the stone is likely to freeze and exapnd (9% larger than the original size)
Repeated freeze-thaw causes the crystls to HEAVE up until they reach the surface.
How dose material get semi-sorted in patterned ground
On small domes Large stones roll down the slope of the domes into the depressions between domes effectively sorting the material and creating a pattern of interchanging coarse and fine material
how does slope steepness affect patterned ground
on gentler slopes the pattern takes the form of stone polygons or circles
On steeper ground (more than 6*) the stones move downhill forming STONE STRIPS
what is an ice lens
where moisture accumulates in the soil and has frozen
as it expands it will push the land above it upwards
Some may become exposed
how does a ice lens grow
capillary movement through frost susceptible soil causing the ground to heave and sometimes crack
what is a PINGO
a dome shaped mound of a layer of soil over a large core of ice
what can be found at the core of a pingo
an ice lens of varying sizes
what is the surface layer like on top of a PINGO
often topped with vegetation
surface can also contain cracks as a result of ground swelling
what 2 types of basic PINGO are there
open system type
closed system type
what is an open system PINGO
the water that forms the ice lens comes from outside the system (above ground)
what is a closed system PINGO
water required for the ice lens formation is contained within the area the Pingo forms
what causes groundwater movement and capillary action
hydraulic pressure
where can open system pingos be found
east-Greenland
what are closed system pingos often referred as
MacKenzie type
why are closed system pingos called Mackenzie type
Mackenzie delta in northern Canada where over 1000 PINGOS have been recorded
what can happen in Pingos if the ruptures become too large
the ground cracks exposing the ice lens this can melt the ice causing the pingo to collapse leaving a RUPTURED PINGO
this can form a lake
and a raised edge = rampart
what process occurs in the Rampart of a ruptured Pingo
solifluction
what is the collapsed pingo known as
OGNIP
What is an ice wedge
A crack in the ground formed by a narrow or thin piece of ice that measures up to 3-4m in length at ground level and extends into the ground for several meters.
How does ground contraction cause ice wedges
Refreezing of active layer in winter causes the ground to contract
Cracks open up on the surface
During melting the cracks reopen and fill with melt water
Meltwater contains fine sediment that also fills the crack
This process repeats itself
Widening and deepening the crack to from an ice wedge
What does the birds eye view of an ice wedged area look like
Ice wedge polygons
What is permafrost
Permanently frozen ground where sub soil temperatures remain below 0 for at least 2 consecutive years
What is permafrost a good indicator of
The main periglacial regions
Where is permafrost found today
Tundra regions in high latitudes
Low latitudes at high altitudes
What % of earths land surface has experienced permafrost
20-25% experienced permafrost or extreme frost activity
What are the 4 types of permafrost
Continuous
Discontinuous
Sporadic
Isolated
What is continuous permafrost
The sub soil is constantly frozen with no thawing
What is discontinuous permafrost
permafrost occurring in some areas beneath the exposed land surface throughout a geographic region where other areas are free of permafrost
What is sporadic permafrost
Found when mean annual temperature is just below 0ºC and the summer temperatures reach several degrees above but isolated pockets of permanently frozen ground remain below the surface.
What is isolated permafrost
less than 10% of the surface has permafrost under it.
What is the active layer
Upper part of the ground
Regularly thaws is summer
Highly mobile - due to freeze thaw and melt water saturation
On slopes the active layer will move downslope due to gravity
what are loess deposits?
deposit of wind-blown silt that blankets large areas of the continents. It is often light brown in colour
