Permafrost Flashcards
Permafrost is…
ground below 0 for 2+ years
Periglacial
things affected by freeze thaw
Doesn’t have to include permafrost (Edmonton dominated by freeze/thaw but we don’t have permafrot)
Active Layer
Top layer that seasonally thaws
Where max temp crosses 0 degrees
Base of permafrost is…
where temp crosses back to 0
Depth of zero amplitude
- where min and max temps meet
- above is affected by seasonal temp changes
- below is affected by geothermal gradient
Latitudinal distribution
moving (cooling) towards the poles
Elevational distribution
lapse rate, more permafrost higher up because of colder temps the higher up
mediated by aspect
continuous permafrost
90% of ground underlain by permafrost
extensive discontinuous
50-90% of ground underlain by permafrost
sporadic discontinuous
10-50% ground underlain by permafrost
what we have in northern parts of provinces (the rest are in the territories)
Talik
a zone in a permafrost region, without permafrost
Degree Day (DD)
difference on a given day from the mean temp in either DDfreeze (below mean) or DDthaw (above mean)
Wedging
prying apart of Earth’s materials due to growh of ice
Blockfield
felsenmeer
low gradient accumulation of cracked bedrock due to excessive ice wedging
Rock Glaciers
- alpine permafrost
- accumulation of coarse material on a slope with interstitial ice or ice core
- moves by ice creep
frost heave
displacement of materials due to growth of an ice lens with materials
Earth hummocks caused by …
tundra tussocks
persistent frost heave
Stone stripes
linear patterns of sorting on periglacial slopes
due to frost heave
frost creep
downslope movement of sediment due to frost heave and thaw settling
gelifluction
slow flow of saturated material moving over permafrost
solifluction lobes
slow downslope movement of material due to frost creep and gelifluction
frost pulling
clast stuck in frozen ground and pulled up as frsot heaves, sediment fills void below, so net up-pulling when thawing
frost susceptibility determined by
grain size (3% silt or more is susceptible) and long and slow freezing for ice lens growth
difference between frost boil and sorted stone circles
coarse ring - sorted stone
finer center - frost boil
Open-system pingo
migration of water downslope from below permafrost and in taliks at the base of a hill
discontinuous permafrost regions
Closed-system pingo
water aggregates from a water source below or internal of the hill
continuous permafrost regions
thermal contraction cracking
frost cracking
thin crack appears due to cooling and contraction of medium, ice wedges freeze below active layer and persist in permafrost
requires rapid cooling, doesn’t happen every winter
peatlands and permafrost
high insulators in the summer - keep hot air out
great thermal conductors - move heat from gorund into air in winter
great for permafrost resilience
peatland distirbution similar to _______ permafrost distibution
sporadic and extensive discontinuous
palsa and peat plateuas similarities
ice covered land forms in peatlands, segregated ice growth causes them, drier peat due to further from water table
palsa and peat plateau difference
palsa - hill
pp - plateau, flat, much wider
thermokarst
landform associated with deformation of permafrost, caused by quick surface disturbance or slow climate change
only occur where excess-ice, – caves, sinkholes, karst lakes, etc
retrogressive thaw slump
backwards erosion into a slope after surface disturbance of ice rich ground
positive feedback of exposed pfrost, thaw, mass mvmt, exposed pfrost, etc
active layer detachment slide
shallow slope failure, translateral movement downslope sliding along base layer
due to climate change or surface disturbance
mitigating permafrost thaw
thermosiphons (heat exchangers to cool ground in winter), avoiding permafrost, building on stilts, avoiding ground disturbance, gravel pads (allows for convection and no excess ice)
thermosiphons
have a liquid with low boiling point at bottom, draws in heat from ground, and evaporates out, upwards and into the air
