Permafrost and Preglacial Environments

Question 1

Define preglacial environment

Answer 1

• Those that are cold but not glacial

- Characterised by seasonal/perennial frozen ground conditions

Question 2

Define Freeze-thaw

Answer 2

• Processes drive geomorphic change on land surface

- Driven by seasonal or dismal temperatures varying around 0 degrees

Question 3

Define permafrost

Answer 3

• Soil or bedrock that is perennially frozen over long timescales (over 2 years and to considerable depth)
• Characterised by significant accumulation of frozen water in soil and sediment

Question 4

How much of earths surface is affected by permafrost and freeze thaw processes?

Answer 4

• Permafrost affects 26%

- Freeze thaw processes affect 36%

Question 5

Where is temperature lowest?

Answer 5

• Temp is lowest close to the surface and increases with depth

Question 6

How does temp control permafrost thickness?

Answer 6

• Mean annual surface temp, ground conductivity and geothermal heat flux
• Exceptions occur under thermal disturbances – e.g. water bodies and climate change response time

Question 7

How does surface albedo play a role in temp?

Answer 7

Dark vegetation absorbs more short-wave solar radiation and thus increases temp

Question 8

Why is frozen ground significant?

Answer 8

• Drives changes in mechanical and hydrological properties of ground
• Highly susceptible to changes in climate surface conditions - most permafrost exist at temps below 0
• Permafrost stores GHGs - as it defrosts, the gases are being released
• Melting permafrost releases large quantities of fresh water into rivers and oceans - increasing sea level rise

Question 9

Outline polar permafrost

Answer 9

• Polar permafrost - occurs in high latitudes with cold temp

- 82% of Alaska, 50% of Canada

Question 10

Outline Alpine permafrost

Answer 10

• Occurs due to cold temp in high altitude areas

- Mainly on Tibetan Plateau, European Alps and Rockies

Question 11

Outline subsea permafrost

Answer 11

• Its extent is not well known

- Either low temp of subsea or remnant of past colder conditions

Question 12

Define isotherm

Answer 12

A line on a map connecting points having the same temperature at a given time or on average over a given period

Question 13

Define sporadic permafrost

Answer 13

Patches of permafrost existing below 1 degree isotherm

Question 14

Define taliks

Answer 14

Unfrozen regions within or below permafrost

Question 15

Describe hydrology in permafrost regions

Answer 15

• Groundwater flow restricted by frozen ground
• Infiltration is restricted
• Rapid run off because permafrost retards percolation

Question 16

Define gelifraction

Answer 16

The mechanical breakup and churning of rock or soil due to repeated freezing and thawing of water within its cracks

Question 17

How is segregated ice formed?

Answer 17

Migration of water to freezing front by suction causes formation of segregated ice, allowing further growth of ground ice

Question 18

What are involutions?

Answer 18

• Forms when ice-rich ground thaws
• Disruptions of sedimentary structure
• Often used as diagnostic for past permafrost conditions
• Permafrost/preglacial ground ice features

Question 19

What are ice wedges?

Answer 19

• V-shaped bodies of ground ice formed from cracking and expansion during freeze-thaw cycles
• Permafrost/preglacial ground ice features

Question 20

What is an alas?

Answer 20

• Small irregular shaped thaw lakes and depressions
• Caused by the melting of massive ground ice
• Permafrost/preglacial ground ice features

Question 21

What are ice wedge polygons

Answer 21

• Form when ice wedges join up
• Currently, millions of square km of earth’s surface
• Permafrost/preglacial ground ice features

Question 22

What are pingos?

Answer 22

• Ice cored mounds up to 50m high and 500m in length
• Top of mound often becomes cracked as ping grows
• Two types
  1) Hydrostatic (closed system)
  2) Hydraulic (open system)
• Ground ice feature

Question 23

What is patterned ground?

Answer 23

• Characteristic feature of both permafrost and periglacial environments;
• Cryoturbation processes sort active-laer sediments by texture
• Precise mechanisms poorly known, but thought to be some form of convectional rotation
• Sorted circles and polygons on flat land
• Stone garlands and stripes on sloping ground

Question 24

What are the 4 key processes of mass wasting in preglacial environments?

Answer 24

1) slope fracture
2) gelifraction
3) creep and flow processes
4) nivation
- Range of landforms result
- Pronival ramparts, ploughing boulders and rock glaciers