L3: Permafrost

Question 1

How much permafrost is about?

Answer 1

More than 24% of exposed land surface in northern hemisphere
Another 20% was active periglacial in Pleistocene
Compared with 10% Earth’s land surface currently glacial
And 30% Earth’s land surface glacial in Pleistocene

Question 2

If the climate changes, the permafrost moves…

Warming =

Cooling =

Answer 2

Moves South

Moves North

Question 3

What does ‘paraglacial’ mean?

Answer 3

Period where a lot of peraglacial activity went on

Question 4

What does ‘permafrost’ mean?

Answer 4

A thermal condition/ state of soil or rock (whether or not ice is present) that freezes (i.e falls below 0oC) one winter and remains frozen through the following summer and into the next winter.

Question 5

Why do we get permafrost?

Answer 5

It is a ground temperature the reflects and balance between heat gain and loss.

In summer net heat gain, surface warming, downward transmission.

In winter heat loss, surface freezes, transmitted down.

Question 6

What processes happen with seasonally frozen ground?

Answer 6

Over the year freezing is max in later winter, thaws in spring from surface downwards.

That thaw will reach all the way down = no permafrost (frozen ground isn’t surviving from one winter to the next).

Question 7

What processes happen with two sided freezing above permafrost?

Answer 7

Where we’ve got permafrost… something very different happens in freezeback

In the freezeback not only is there freezing from the surface down but freezing from the permafrost table up- eventually freeze completely.

Question 8

What is the active layer?

Answer 8

The layer that freezes and thaws in summer.

Question 9

What is talik?

Answer 9

Below max depth of permafrost is unfrozen material.

Also exists within permafrost (often involves water and that’s what drives processes)

Question 10

Micro-scale factors affecting permafrost distribution

Distribution: Soil and Rock

Answer 10

Albedo variation (colour difference) (10% to 30%)
Exposed ground surface will warm up faster 
Specific heat (how much heat is required to heat up a certain volume of something by a certain amount) and thermal conductivity (how quickly it heats up or cools)
Infiltration and evaporation rates (moisture affects thermal properties, wetter = warm up differently).

Question 11

Micro-scale factors affecting permafrost distribution

Distribution : Moisture and Water

Answer 11

Affect specific heat, heat flux, rate of freeze, depth of thaw, basal thaw etc.
Running water is warm and gives thermal erosion
Standing water (more than 2-3 m) insulates against low air temperatures, and is a heat store
Water body insulates ground beneath its centre to a depth equal to its diameter
If diameter>pf depth then no permafrost beneath water

Question 12

Micro-scale factors affecting permafrost distribution

Distribution : Relief and Aspect

Answer 12

Aspect affects input of radiation
Aspect affects input of precipitation and snow drifting
Altitude affects ground temperature
Slope angle controls snow and runoff
Since permafrost reacts to small imbalances, relief has strong affect (including asymmetry)
Permafrost top/base parallel ground surface

Question 13

Micro-scale factors affecting permafrost distribution

Distribution: Surface terrain type

Answer 13

Vegetation acts as vital insulator
Vegetation influences infiltration, snow retention, and evapo- transpiration
Vegetation, micro-relief and permafrost interact strongly but subtly
Snow insulates ground from low temperatures, and adds moisture
Permafrost does not grow if snow>40cm
1.50m snow provides total insulation
Glaciers thus insulate underlying ground
A temperate (“warm”) glacier base is at pressure melting point
Polar (“cold”) glaciers are just below 0oC at base