Permafrost 2 Flashcards
Thermal offsets=
offsets between air, surface, and ground temp
eg
- mean annual air temp= -2C
- mean annual surface temp= +1C
- mean annual permafrost temp= -1C
T/F
if the average ground surface temp is >0C then there likely won’t be any permafrost present in that location
false
permafrost is resilient! It can still be present
what are 2 strong controls on the global distribution of permafrost?
- latitudinal: move toward poles= cooling
- elevational: lapse rate –> lower temp at elevation –> alpine permafrost
- elevation is mediated by aspect (more pfrost on N facing slopes)
Continuous permafrost=
90% of ground underlain by permafrost
- mean annual temp less than -6C
- ground temp less than -2C
extensive discontinuous permafrost=
50-90% of the ground is underlain by permafrost
- mean annual temp -2 to -6C
- ground temp above -2C
Sporadic Discontinuous permafrost=
10-50% of the ground is underlain by permafrost
- mean annual temp -2 to -0C
- ground temp 0 to -1C
Why is there rarely 100% permafrost cover, even in continuous permafrost zones? There are always patches
because these patches are insulated by ice, or a big body of water like a lake or river, so the ground underneath does not freeze
Talik=
zone within a permafrost region without permafrost
- present under lakes usually
What is the frost index model?
an equation that sums up all freezing degree days and thawing degree days in the year, and predicts where permafrost might be based on this.
Where FI= 0.6 or greater, predicts presence of permafrost
It’s pretty accurate!
frost wedging=
prying apart of earth materials by the growth of ice (b/c of volumetric expansion of water when it freezes)
T/F
frost wedging only happens with water
false!
can be with things like salt (eg in the UK!)
scree slopes and talus cones = presence of ___ wedging/ shattering and ___ (high or low) ice flux
frost
low
rock glaciers are a characteristic feature of alpine ___
permafrost
rock glaciers=
accumulations of coarse material on a slope with interstitial ice (ice in pore spaces) and/or a core of massive ice (eg a buried glacier)
Mt. Athabasca has a rock glacier- explain how it formed
sediments broke off from the peak and accumulated in the cirque below. The pore spaces filled with ice and now it’s a flowing rock glacier!
= Hilda rock glacier
rock glaciers primarily move by:
ice creep
ie internal deformation of ice
how quickly do rock glaciers typically move?
very slowly ~cm per year
frost heave=
process of displaying material by growth of an ice lens with earth materials. Displacement occurs perpendicular to the freezing front. VERY slow process
earth hummocks (aka tundra tussocks) are like ____ ___ but at a bigger scale. They’re formed by:
frost heaves
formed by persistent frost heaves
Stone stripes=
linear patterns of sorting that appear on some periglacial slopes due to frost heaves
- pebbles heaved up, then they fall one way or the other
Frost creep=
when frost heave lifts a particle, which then falls down into a different position due to gravity when the ice melts.
repeat this many times= significant movement!
Gelifluction=
slow flow of saturated earth materials overlying permafrost
- the top of pfrost is effectively impermeable, so materials accumulate there at the bottom of the active layer. There is a low shear strength, so it “flows” slowly
Solifluction Lobes=
landform produced by slow downslope movement of debris by combined frost creep and gelifluction
