Permafrost 2

Question 1

Thermal offsets=

Answer 1

offsets between air, surface, and ground temp

eg
- mean annual air temp= -2C
- mean annual surface temp= +1C
- mean annual permafrost temp= -1C

Question 2

T/F

if the average ground surface temp is >0C then there likely won’t be any permafrost present in that location

Answer 2

false

permafrost is resilient! It can still be present

Question 3

what are 2 strong controls on the global distribution of permafrost?

Answer 3

1. latitudinal: move toward poles= cooling
2. elevational: lapse rate –> lower temp at elevation –> alpine permafrost
   - elevation is mediated by aspect (more pfrost on N facing slopes)

Question 4

Continuous permafrost=

Answer 4

90% of ground underlain by permafrost
- mean annual temp less than -6C
- ground temp less than -2C

Question 5

extensive discontinuous permafrost=

Answer 5

50-90% of the ground is underlain by permafrost
- mean annual temp -2 to -6C
- ground temp above -2C

Question 6

Sporadic Discontinuous permafrost=

Answer 6

10-50% of the ground is underlain by permafrost
- mean annual temp -2 to -0C
- ground temp 0 to -1C

Question 7

Why is there rarely 100% permafrost cover, even in continuous permafrost zones? There are always patches

Answer 7

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

Question 8

Talik=

Answer 8

zone within a permafrost region without permafrost
- present under lakes usually

Question 9

What is the frost index model?

Answer 9

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!

Question 10

frost wedging=

Answer 10

prying apart of earth materials by the growth of ice (b/c of volumetric expansion of water when it freezes)

Question 11

T/F
frost wedging only happens with water

Answer 11

false!
can be with things like salt (eg in the UK!)

Question 12

scree slopes and talus cones = presence of ___ wedging/ shattering and ___ (high or low) ice flux

Answer 12

frost
low

Question 13

rock glaciers are a characteristic feature of alpine ___

Answer 13

permafrost

Question 14

rock glaciers=

Answer 14

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)

Question 15

Mt. Athabasca has a rock glacier- explain how it formed

Answer 15

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

Question 16

rock glaciers primarily move by:

Answer 16

ice creep
ie internal deformation of ice

Question 17

how quickly do rock glaciers typically move?

Answer 17

very slowly ~cm per year

Question 18

frost heave=

Answer 18

process of displaying material by growth of an ice lens with earth materials. Displacement occurs perpendicular to the freezing front. VERY slow process

Question 19

earth hummocks (aka tundra tussocks) are like ____ ___ but at a bigger scale. They’re formed by:

Answer 19

frost heaves

formed by persistent frost heaves

Question 20

Stone stripes=

Answer 20

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

Question 21

Frost creep=

Answer 21

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!

Question 22

Gelifluction=

Answer 22

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

Question 23

Solifluction Lobes=

Answer 23

landform produced by slow downslope movement of debris by combined frost creep and gelifluction