Why are the following factors crucial in understanding periglacial processes and the resulting landforms? Flashcards
Nature of material (texture, organic content….)
Overall…
Colour changes albedo variation and amount of incoming radiation reflected (10% to 30%). Specific heat (how much heat is required to increase a certain volume by a certain amount) and thermal conductivity (how quickly heat will move through something). Infiltration and evaporation rates (moisture affects thermal properties).
How wet or dry a material is may affect albedo (wet = dark)
Determines how much water can get in via infiltration and evaporation
Water = heat
Nature of material (texture, organic content….)
Ice wedge polygons
What are they?
Ice-wedge polygons are archetypal polygonal patterns that are feasibly the most ubiquitous feature of ground ice in the top 2–3 metres of this permafrost (Christiansen et al., 2016), particularly in areas where the permafrost is shallow and the topography is flat (Cable et al., 2016., Frost et al., 2018).
Nature of material (texture, organic content….)
Ice wedge polygons
How are they formed?
The thermal contraction theory of wedge growth, suggested by Leffingwell (1915., Gell, 1978), states that ice wedges are produced as an outcome of soil between cracks in the ice shrinking and enabling the infiltration of meltwater in spring (Fortier and Allard 2005., Opel et al., 2018).
This requires severe ground frost in winter, predominantly enabled via a combination of low ambient temperatures (at least -10oC) and a thin snow cover (Wolter et al., 2018).
An inclined freezing front penetrates fastest beneath these cracks, causing any coarser clasts to be “pulled up” due to thermal conductivity. Over centuries to millennia of repeating this process, it eventually leads to the growth of a wedge-shaped ice body as the soil above the ice is pushed up, forming ridges (Mackay 1984).
Nature of material (texture, organic content….)
Ice wedge polygons
How does nature of material (texture, organic content….) effect?
In a study by Steedman (2014) investigating the impact of ice wedge degradation on vegetation composition in the Mackenzie Delta region…
The influence of albedo changes this then has on the positive feedback of furthering ice wedge degradation, given reflectivity of water is considerably lesser than that of tundra vegetation (Weller and Holmgren, 1974., Steedman, 2014). Further to this, Jorgenson et al. (2006) proposes the accumulation of water in degrading ice wedge troughs increases ground temperatures and promotes further degradation.
Aspect and local relief
Overall…
Aspect affects input of radiation.
In northern hemisphere if you’re in a south facing = as much as 4x more incoming radiation.
Aspect affects input of precipitation and snow drifting (wind bearing slopes)
Altitude affects ground temperature
Slope angle controls snow and runoff (steep slope = less now and rapid runoff) (gradual slope = more snow and more infiltration)
Since permafrost reacts to small imbalances, relief has strong affect (including asymmetry)
Aspect and local relief
Rock glaciers
What are they?
It can form when ice and snow melt on the surface of a talus slope, infiltrate down through the rocks, and then freeze at depth.
The result is a mass of rocks that are cemented together by ice.
Aspect and local relief
Rock glaciers
Real world example…
(Barsch, 2007)
994 active rock glaciers in Swiss Alps
Water and moisture
Overall…
Affect specific heat, heat flux, rate of freeze, depth of thaw, basal thaw etc.
Running water gives thermal erosion (constant replenishing warm relative to frozen permafrost).
Standing water insulates against low air temperatures, and is a heat store (heat isn’t being replenished but will still remain warm, 2-3m deep won’t freeze to bottom, water is densest at 4oC)
If diameter>pf depth then no permafrost beneath water
Water and moisture
Pingos
What are pingos?
(Mackay, 1998)
‘Perennial, intrapermafrost, ice-cored hills, typically conical in shape, that can grow and persist only in a permafrost environment’
Commonly found in periglacial areas that are characterised by permafrost and a seasonally changing active layer (AMAP, 2011).
Water and moisture
Pingos
Pingos can be classified on the basis of origin (genesis) into what 3 types?
Hydrostatic (formerly ‘closed system’)
Hydraulic (formerly ‘open system’)
Polygenetic
Water and moisture
Pingos
Pingos form through what?
(Burr et al., 2009)
They develop through pressurized groundwater flow mechanisms to form massive ice-cored mounds which are covered by an overburden of 1-10m
Water and moisture
Pingos
How do Hydrostatic Pingos form?
Closed-system (hydrostatic) pingos are generally found in lowland areas where permafrost is more continuous.
As these lakes fill with sediments from meltwater, the surrounding permafrost advances and squeezes the unfrozen sediments below the lake.
When the lake itself is frozen, the water in the underlying sediments causes the surface to dome upwards creating the pingo.
If the dome cracks, the ice core may melt leading to a collapse of the pingo and a pond forming in the central crater.
(Burr et al., 2009)
Snow cover
Overall…
Snow insulates ground from low temperatures, and adds moisture
Don’t need a lot of snow to make a significant impact- Permafrost does not grow if snow>40cm
1.50m snow provides total insulation
Snow cover
Palsas
What is a palsa?
A palsa is a peaty permafrost mound between 1m and 7m in height and less than 100m in diameter containing a core of alternating layers of segregated ice and peat or mineral soil material (ACGR, 1988)
Usually occur in bogs and wetlands
Most documented palsas occur in Finland, Sweden, Norway, Iceland and Canada.
Snow cover
Palsas
How do Palsas form?
When snow cover is locally so thin that winter frost penetrates sufficiently deeply to prevent summer heat from thawing it completely. The surface of the mire is then raised somewhat by frost processes.
During succeeding winters frost penetrates still deeper, the process of formation accelerates and the hump shows further heaving due to the freezing of pore water and ice segregation. As the surface rises, the wind becomes ever more effective in drying the surface peat and keeping it clear of snow.
When the freezing of the palsa core reaches the till or silt layers at the base of the mire, the mature stage of palsa development begins.
Vegetation
Overall…
Variety of vegetation (lots of colours, more/less moisture, organic material etc)
Vegetation acts as vital insulator (trap air and the thermal conductivity of air is low) (protect the ground from cold air temperatures and prevent the loss of heat outwards).
Vegetation influences infiltration, snow retention, and evapotranspiration
Vegetation
Patterned ground
What is Patterned Ground?
What are the 5 main types?
Ground showing patterns of stones, usually in the shape of polygons
- Circles
- Polygons
- Nets
- Steps
- Stripes
Flat -> steep
(Washburn, 1956)
Vegetation
Difference between sorted and non-sorted patterned ground
(Hjort, 2006)
Sorted patterned ground is defined by alternation of fine
and coarse soil material, whereas non-sorted
patterned ground is formed by microrelief and/or vegetation differences
Vegetation
Patterned ground
For example…
Stripes are features with a striped pattern oriented down the steepest available slope.
Sorted stripes are formed of parallel stony lines whereas non-sorted stripes are a set of vegetated and relatively bare ground lines
Proximity to water body
Overall…
Regional climate variability in Maritime Arctic means being near the sea the climate is relatively mild and so has lots of and long freeze thaw cycles.
Small temperature extremes (winter frost penetration slight: summer slaw slow)
Landscape features produced include rapid freeze thaw weathering and shattering, block fields, small patterned ground features.
Proximity to water body
What are the series of controls on polar coastal processes?
Short term marine factors (freezing, sea and beach ice; energy of wind/ wave/ tide/ current.
Short term terrestrial factors (geology, topography, permafrost rivers, terrestrial debris supply).
Long term factors (plate tectonics, climate change, glacio eustacy and isostacy)
Proximity to water body
Distinctive polar coastal factors
- Sea level change
- Available coastal sediment
- Coastal permafrost
- Macro forms are dominated by glacio-eustatic submergence.
Recent glacio-isostatic rebound is giving widespread emergence with raised beaches.
Climate change will reinforce submergence. - Beaches fed by mass movement (thermokarst flows?), talus slopes and rivers.
Very highs sediment availability may explain high deposition (and erosion) rates.
This may be a kind of coastal paraglaciation. - Permafrost is widespread in cliffs, beaches
Also in the offshore zone if sea level is rising or the coast eroding
Adds thermal erosion to normal mechanical processes (thermoabrasion)
May help to explain annual recession rates of 10m-30m a year.
Proximity to water body
How do tides and currents impact coasts?
Most polar coast is micro tidal (<2m range).
This means that although there is not a lot of tidal energy, what there is is concentrated over a restricted zone.
Tides essential in growth of beach ice.
Tides break the bond between sea ice and coast during thaw.
