Periglacial 1: landforms and processes

Question 1

What are periglacial environments?

Answer 1

Cold non-glacial environments

Question 2

What are periglacial environments characterised by?

Answer 2

Continuous freezing and thawing of landscapes in conjunction with seasonal climate variations

Question 3

What is permafrost?

Answer 3

any part of the ground that has been frozen for 2 consecutive years plus

Question 4

What is not necessary for permafrost but is commonly found near it?

Answer 4

Common to have water/ice present but its not necessary for defining permafrost environments because they are defined as a thermal state and not a physical or material state

Question 5

Describe the structure of permafrost areas from top to bottom

Answer 5

Active layer
Supra-permafrost talik
Intra-permafrost talik and closed talik

Question 6

What is a supra-permafrost talik?

Answer 6

an unfrozen part of the ground in a permafrost environment that resides above or a the boundary between the permafrost layers and the active layers

Question 7

What is an intra-permafrost and a closed talik?

Answer 7

Intra-permafrost talik is an unfrozen part of the ground well below the boundary between the active layer boundary. A closed talik is similar but is usually a lot smaller and so is also surrounded completely by permafrost

Question 8

What are the 3 types of permafrost layer defined by coverage of permafrost?

Answer 8

Continuous = pervasive permafrost that comprises 90-100% area of the ground
Discontinuous = Continuous permafrost that is broken up by taliks meaning that the ground is only made up of 90-50% permafrost. 
Sporadic = isolated blocks of permafrost that comprise 10-50% of the ground area

Question 9

Outline the distribution of permafrost across the earth’s surface

Answer 9

Underlies 26% of the earth’s surface. It is commonly found in mountain and alpine environments

Question 10

Describe the relationship between permafrost distribution and latitude

Answer 10

The permafrost layer increases with distance from the equator

Question 11

Describe the thermal regime of the permafrost layer

Answer 11

The temperature increases with depth to a point and the starts to increase after an undefined point

Question 12

Explain the permafrost thermal regime

Answer 12

The temperature at the surface is controlled by the sun’s radiation that obviously has a bigger impact at the surface/shallower depths but then the temperature at the bottom of the permafrost layer has a greater influence of the geothermal heat flux

Question 13

What defines the boundaries of the permafrost layer?

Answer 13

Where the temperature starts to exceed 0 degrees celsius at both the surface and base. Anything in between is the permafrost layer

Question 14

What is ground ice?

Answer 14

Ice formed in freezing or frozen ground

Question 15

Where might ground ice be particularly prevalent?

Answer 15

In sporadic permafrost layers

Question 16

What are the two types of ground-ice?

Answer 16

1. Pore ice = forms within the pores of the ground and cements the ground matrix
2. Segregated ice = bodies of pure ice that form by migration of liquid water in to freezing surfaces.

Question 17

Where does segregated ground ice normally occur?

Answer 17

Usually occurs where unfrozen water exists nearby and permafrost aggrades

Question 18

What are the different forms of ground ice, which is most common?

Answer 18

1. Ice lenses (most common)

2. Massive ice beds

Question 19

What are ice lenses?

Answer 19

Thin horizontal beds of ice

Question 20

What are massive ice beds?

Answer 20

What the tin says - massive bodies of ice

Question 21

What are the 3 ways that massive ice beds are formed?

Answer 21

1. convergence of ice lenses in to one body
2. water in a talik will be closed off and formed in to a massive body of ice under hydrostatic pressure
3. Burial of glacier ice that survives underground

Question 22

What are Pingos?

Answer 22

Conical domes of deformed ice

Question 23

How are pingos formed?

Answer 23

1. Lake underlain by talik
2. Lake drains and exposes talik
3. Permafrost layer accumulates on top of the new lake floor
4. Hydrostatic pressure forces water to move upwards as the talik is forced to shrink
5. Water in the talik has been forced up enough above the surface and to form a massive ice bed

Question 24

What are collapsed pingos?

Answer 24

The ice cores within a pingo thaws and collapses leaving the bump to collapse and therefore leaving a circular rimmed crater behind

Question 25

What are palsas?

Answer 25

Essentially pingos that form under peat environments. An ice lense does not experience thawing during summer because of peat layer above which acts as an insulator. The lense over successive seasons will grow and expand (heave)

Question 26

What differentiates palsas from pingos?

Answer 26

They are usually not as amplified in shape and size.

Question 27

Describe the shape and size of palsas

Answer 27

1-10m high, low relief, circular rim

Question 28

What are ice wedges?

Answer 28

Downward-facing wedges in the permafrost layer of pure ice

Question 29

How are ice wedges formed?

Answer 29

Thermal cracking of permafrost layer during winter allows meltwater to trickle down the cracks during the summer seasons. During the next winter season the meltwater will then freeze against the cold surrounding permafrost layer. Over time, the wedge will weaken the layer and consequently the process will repeat to increase the size of the crack and consequently the ice wedge.

Question 30

What are ice wedges polygons and how are they formed?

Answer 30

There will be a collection of ground cracks arranged in a polygon shape across a landscape that will allow ice wedges below this polygon to form. The ice wedges will form around these polygon sides. The soil within the arrangement of the polygons on the surface will then slump down where it might then be infilled by a lake

Question 31

What are ice wedge clasts?

Answer 31

The infilling of melted ice wedges with sediment after the ice wedges melt.

Question 32

What are ice wedge clasts evidence of?

Answer 32

Where former annual mean air temperature was <6 degrees celsius as this is the level for continuous permafrost which would be ideal conditions for these ice wedges to form. Since then they have melted to allow the clasts to form

Question 33

What are thermokarst landforms/landscapes?

Answer 33

These are landscapes where the ground has failed across a region underlain by ground ice that has since slumped and the ground that was underlain by ground ice has not slumped thereby revealing where the ground ice is

Question 34

What has been happening in the Arctic related to thermokarst landscapes?

Answer 34

The arctic has been warming and so has made thermokarst landscapes more prevelant and visible

Question 35

What are the two types of soil based on frost action?

Answer 35

1. frost-susceptible = ice lenses formation is common through ice segregation
2. non-frost-susceptible = pore ice is only frost that can form in these sol types

Question 36

What determines whether the soil is frost-susceptible or not?

Answer 36

Size of voids in soil - function of grain size distribution. If silt content is 10% or more then this will facilitate capillary water flow between sand particles. This increased water flow will allow more water to be present and therefore more ice to exist in the layers

Question 37

What is the silt content likely to be in frost-susceptible soils?

Answer 37

greater or equal to 10%

Question 38

What is frost heave?

Answer 38

the upward and outward movement of the ground surface due to the freeze/thaw process of ice in the sol

Question 39

What is a large influence upon frost heave?

Answer 39

Frost-susceptibility of the ground/soil

Question 40

What does frost heaving permit?

Answer 40

down slope movement and formation of surface features and landforms (e.g. pingos and ice wedges)

Question 41

What are the two types of frost weathering?

Answer 41

Microgelivation = small scale breakdown of sediment by freezing that occurs in pores and formation of ice lenses 
Macrogelivation = breakdown in to angular clasts through inter-joint freezing

Question 42

What are two landforms that can occur as a result of frost-weathering?

Answer 42

Frost shattered bedrock = breakdown in to alligned sections of bedrock (looks like bread)
Blockfields = detatched rocks from block that were previously from the block as the block moves toward the surface.

Question 43

How can sediment be sorted in to patterns as a result of frost heave?

Answer 43

Ground heave forces coarse sediment out the ground and allows fine material to simultaneously subside down in to the ground. The coarse sediment does not subside back down because it is too coarse as it rolls down the hills of the mounds produced in these patterns

Question 44

What sort of sediment patterns can be produced?

Answer 44

circles, stripes, ovals, steps

Question 45

What is solifluction and how does it occur

Answer 45

slow downslope movement of soil due to freeze thawing of water logged ground following heave and creep of the ground