Permafrost 4

Question 1

Does thermal contraction cracking happen every winter? What does it require?

Answer 1

No!

requires:
- rapid cooling
- high magnitude cooling (big diff in temp)

Question 2

Describe what happened when the thaw lake in Illisarvik was experimentally drained in 1978. What did they observe?

• cracks were __-__cm wide
• Initial thermal contraction crack was __-___, but in subsequent years it was reversed (ie_____..)
• ice wedge growth rate was __cm laterally each year

Answer 2

purpose= see what happened to newly exposed saturated sediments

• Thermal contraction cracks appeared & ice wedges started to grow after the first winter

3-20cm
top-down
ie. grew from bottom and propagated up
3

Question 3

After 12 years, what did they observe in the drained thaw lake?

Answer 3

no more ice wedge growth after 12 years! Because of insulated veg and snow –> lots of vegetation started growing, which insulated the ground esp from very cold winter air temp. Veg also traps snow= more insulation

Question 4

After 20 years of observation is Illisarvik, how big were the ice wedges?

Answer 4

max 2m high –> not that big

Didn’t answer how we get the massive ice wedges

Question 5

Ice wedge growth ceases, largely due to:

Answer 5

insulation of the ground from cold winter air by vegetation and snow

Question 6

How do we get massive ice wedges?

Answer 6

This can happen when more layers of sediment are being deposited at the site of the ice wedge. The original ice wedge keeps moving up with the permafrost, and that’s how it becomes huge!
= syngenetic permafrost

Question 7

Syngenetic permafrost=

Answer 7

aggradation of permafrost keeps up with a vertically aggrading surface

eg. this is how ice wedges become huge

Question 8

Epigenetic permafost=

Answer 8

permafrost that formed through lowering of the permafrost base in previously deposited sediment

Question 9

T/F
the oldest ice in north america is in an ice wedge, not a glacier

Answer 9

true!
~700ka

Question 10

______ have high organic C soils, where the organic material may be at various stages of decomposition

Answer 10

peatlands

Question 11

What are the thermal properties of peat when it’s frozen (winter) vs dry (summer)?

Answer 11

dry (summer): almost a perfect insulator (low thermal conductivity)= insulates the ground from warm summer air temps

frozen (winter): higher thermal conductivity = very efficient at transferring heat from the ground to the air (temp of frozen ground is transferred to even colder air)

Question 12

T/F

Peatlands contribute to permafrost resilience

Answer 12

true!

• insulates: diurnal temp swings in the summer are muted when peat is present

Question 13

What factor is especially important in maintaining permafrost near the southern boundary of it?

Answer 13

Peat!
Permafrost probably wouldn’t exist here if there was no peat. Therefore, disturbing the surface here = bad news for permafrost :(

Question 14

Palsas and peat plateaus=

Answer 14

ice=cored landforms in peatlands, formed by growth of segregated ice

Question 15

What is the difference between palsas and peat plateaus?

Answer 15

Size

palsas= 10s of m wide
peat plateaus= laterally extensive over 100s of m

Question 16

How do palsas and peat plateaus form? How long can they last?

Answer 16

The surface is raised above the local water table, in turn drying peat= lower thermal conductivity

Therefore, they can persist for 1000s of years!

Question 17

Karst=

Answer 17

landforms associated with dissolution of rick, especially carbonates (eg caves, sinkholes)

Question 18

Thermokarst=

Answer 18

landforms associated with thermal degradation of permafrost
*Only occurs where excess ice is present (ice rich grounds)

Question 19

What are the 2 causes of thermokarsts:

Answer 19

1. surface disturbance (eg remove peat/ expose ice) –> alters ground thermal regime, even if the climate is stable
   = relatively fast process
2. climate warming –> slow process

Question 20

T/F

you need climate warming to initiate thermokarsts

Answer 20

false
surface disturbance is actually a much faster way to initiate thermokarsts

Question 21

What causes methano-genesis in arctic enviro lakes?

Answer 21

thaw of sub-lake permafrost

Question 22

There is a thaw lake cycle. Describle this cycle.

Answer 22

1. bare ground
2. ice wedge develops
3. disturbance= thermokarst initiated
4. formation of thaw pond

This pond can either
a) be a stable long-term lake
b) drain

a1) eventually drains and becomes bare ground again, restarting the cycle

b1) drains
b2) permafrost reaggrade
b3) ice wedges develop, restarting the cycle

Question 23

Retrogressive thaw slumps are a very obvious indicator of ___

Answer 23

thermokarsts

Question 24

retrogressive thaw slump=

Answer 24

backward erosion into a slope after an initial disturbance of ice-rich ground

Question 25

Retrogressive thaw slumps have:
- an arcuate (curved) head scarp which forms a little ___
- a much shallower __-__ zone for thawed + saturated debris

Answer 25

cliff
run-out

Question 26

Why might you see polygonal shaped ground near retrogressive thaw slumps?

Answer 26

This means the ground is ice-rich, which is needed for thermokarsts like retrogressive thaw slumps

Question 27

Active layer detachment slide=

Answer 27

shallow slope failures: translational movement downslope along the base of the active layer

Question 28

Would an active layer detachment slide have a big head scarp?

Answer 28

No, because it’s a shallow movement