Murray, T.,2008, Permafrost and periglaciation in J.Holden (Ed), An Introduction to Physical Geography and the Environment. Pearson Education Ltd: Essex (Chapter 17)

Question 1

Periglacial environments are defined as

Answer 1

“those that are cold but non-glacial, regardless of their spatial proximity to glaciers”.

Question 2

What drives geomorphic change in periglacial environments?

Answer 2

Freeze thaw processes- distinctive geomorphological features are produced as a result.

Question 3

Permafrost refers to…

Answer 3

soil or bedrock that is perennially frozen over long time scales (>2 years).

Question 4

Permafrost usually contains ice within pore spaces- this causes

Answer 4

slow movement of the ground itself through expansion and contraction processes.

Question 5

Air temperature usually exceed what temperature during summer in permafrost zones?

Answer 5

0oC- a thin unfrozen layer (the active layer) can be present at the ground surface even when there are frozen layers below this.

Question 6

Freezing/thawing are important because

Answer 6

they drive changes in ground mechanical/hydrological properties- result in a volume change of the ground.

Question 7

Frost heave is

Answer 7

the vertical lifting of the soil surface.

Question 8

Most of the Earth’s permafrost exists at temperatures just a few degrees below 0oC, this means that…

Answer 8

it is highly susceptible to changes in climate/surface conditions.

Question 9

Alpine permafrost occurs because of

Answer 9

low temperatures at high altitudes, e.g Tibetan Plateau.

Question 10

Subsea permafrost occurs where permafrost is found…

Answer 10

beneath the sea- occurs as a remnant of past colder temperatures and rising sea levels which drown frozen ground.

Question 11

Continuous permafrost

Answer 11

laterally continuous permafrost broken only beath lakes, rivers, glaciers and other thermal disturbances.

Question 12

Discontinuous permafrost

Answer 12

not laterally continuous and it varies from 1 to 10 m or more in thickness.

Question 13

Transition between the two zones of continuous permafrost and discontinuous permafrost often occurs at…

Answer 13

the treeline at the mean annual air temperature of the -6 to -8oC isotherm (line of equal temperature).

In both zones the ground is subject to annual and sometimes diurnal freeze thaw close to the surface- this forms the active layer.

Question 14

What are taliks?

Answer 14

Unfrozen zones within with permafrost are known as taliks- open if they are in contact with the active layer and closed if they are completely surrounded by permafrost.

Question 15

Fundamental changes in ground properties occur when the active layer freezes:
Ground mechanical properties

Answer 15

E.g density, heat capacity, thermal conductivity and saturated hydraulic conductivity.

Question 16

Fundamental changes in ground properties occur when the active layer freezes:
Electrical properties

Answer 16

E.g electrical conductivity

Question 17

Temperatures measured in permafrost boreholes are typically lowest close to

Answer 17

the ground surface, excluding the active layer, and increase with depth, reaching the melting point at the base of the permafrost.

Question 18

The main controls on permafrost thickness are…

Answer 18

The mean annual surface temperature
Ground conductivity
The geothermal heat flux

Question 19

Surface albedo also plays a role in determining permafrost thickness

Answer 19

Dark vegetation cover may absorb more short wave solar radiation and thus increase local ground temperature.

Question 20

The ground diffusivity and the temperature fluctuation frequency control

Answer 20

the depth to which surface temperature fluctuations are propagated.

Question 21

Large quantities of carbon are stored in permafrost and so

Answer 21

if their is a change in the distribution of frozen ground and the thickness of the active layer may result in the release of large amounts of greenhouse gas.

Question 22

The grounds temperature profile can be used

Answer 22

to extrapolate past surface conditions.

Question 23

As permafrost melts, this carbon has the potential to be converted rapidly to

Answer 23

methane and hence cause climate warming in a positive feedback.

Question 24

A gas hydrate is a

Answer 24

crystalline solid in which molecules of gas are combined with molecules of water.

Question 25

The hydrate of methane is stable at

Answer 25

high pressures and low temperatures and so occurs commonly in ocean sediments with smaller amounts in permafrost regions.

Question 26

Increases in temperature or decreases in pressure may result in the hydrate

Answer 26

becoming a mixture of gas and ice or water.

Question 27

Groundwater movement within permafrost regions is often restricted by

Answer 27

the presence of frozen ground that acts as a barrier to flow.

Question 28

At temperatures significantly below 0oC the hydraulic conductivity of the ground is

Answer 28

greatly reduced, exerting a retarding influence on groundwater flow. A freezing active layer can restrict aquifer recharge and water flow.

Question 29

In some regions seasonal freezing of the active layer does not reach the depth of the permafrost, allowing

Answer 29

groundwater flow through a residual thaw layer above the permafrost confined below the upper frozen part of the active layer.

Question 30

River regimes in periglacial regions are typically

Answer 30

very seasonal with large discharges resulting from the melt of winter snow cover during spring.

Question 31

Permafrost retards

Answer 31

downward percolation, runoff is often rapid following a snowmelt or rainfall event.

Question 32

Small rivers in periglacial regions flow only during

Answer 32

the summer- despite cold winters major rivers flow all year round under ice cover.

Question 33

The more peaked runoff characteristics of smaller rivers result in

Answer 33

a high sediment transport rate compared with rivers with similar total discharges but which have discharge more evenly distributed during the year.

Question 34

Seasonal icings are

Answer 34

mounds of ice that form in topographic lows during winter in locations where groundwater reaches the surface.
Common features downslope of warm-based glaciers.

Question 35

Seasonal icings are essentially

Answer 35

where return flow (a component of saturation-excess overland-flow) occurs and freezes.

Question 36

Seasonal icings may occur

Answer 36

either below or above the ground surface and in river channels that freeze to their beds.

Question 37

Candle ice consists of

Answer 37

vertically orientated crystals of over 1 m in length.

Question 38

Cold climate environments develop distinctive geomorphology because of three basic processes:

Answer 38

The 9% expansion of water on freezing which causes frost shattering and in turn adds to scree development
The contraction and cracking of rapidly freezing soils which forms ice wedges and polygonally shaped surface features.
The migration of water to the freezing front by suction which causes the formation of segregated ice.

Question 39

Permafrost and periglacial features form distinctive relict forms, collectively known as…

Answer 39

thermokarst because of their similarity to karst (cavernous limestone).

Question 40

Thermokarst features are important in

Answer 40

reconstructing past climate and the extent of former glaciers.

Question 41

Thermokarst features form in

Answer 41

cold but non-glaciated terrain and are thus found at the margins of glaciers.

Question 42

Segregated ice

Answer 42

very large lenses of ice may slowly build up in soil that is frozen from migration of water to freezing front in permafrost regions.

Question 43

Massive ice

Answer 43

where the bands of segregated ice are thick.

Question 44

Intermediate grain sizes, such as silt, have the greatest potential to form

Answer 44

segregated or massive ice within the ground and are most susceptible to ice heave.

Question 45

When ice rich ground thaws what often forms?

Answer 45

Involutions- they are disruptions to the sedimentary structure of the ground and these features are often used as a diagnostic for past permafrost conditions.

Question 46

The melting of massive ground ice also affects

Answer 46

ground surface topography and produces thermokarst consisting of small irregularly shaped thaw lakes and depressions known as alas, which form when these thaw lakes drain.

Question 47

Ice wedges are

Answer 47

V-shaped bodies of ground ice up to 1.5 m in width that can extend some 3-4 m into the permafrost

Question 48

Ice wedges develop because

Answer 48

at low temperature (

Question 49

The ice wedge creates

Answer 49

a weakness that tends to reopen annually as the ground contracts and hence the ice wedge grows.

Question 50

Pingos are…

Answer 50

ice cored mounds up to 55m high and 500m in length which forms in permafrost zones- can be conical or elongated and they contain some segregated ice and a core of massive ice described as a lens.

Question 51

Hydrostatic pingos

Answer 51

Caused by doming of frozen ground as a result of freezing of water expelled during talik elimination and the growth of permafrost beneath a former lake or other water body.

Question 52

Hydraulic pingos

Answer 52

Form at the foot of slopes and result from the inflow and freezing of groundwater seeping from upslope.

Question 53

The melting of the ice core of a pingo forms

Answer 53

a central depression with sediment ramparts, sometimes termed a pingo scar.

Question 54

Palsas are

Answer 54

1-10m high, that form in peat and permafrost zones.

Question 55

Palsas form where

Answer 55

Snow is thin or discontinuous and have a core of segregated ice generated through suction of unfrozen water migrating to the freezing front.

Question 56

The lack of snow in Palsas formations…

Answer 56

allows the ground to freeze to a greater depth than the surroundings and this ice then survives the subsequent summer, insulated by the peat above.

This topography creates a positive feedback as snow is more likely to blow off, resulting in even deeper freezing depths.

Question 57

Frost blisters are

Answer 57

Small ice-cored mounds that develop over a single winter as a result of groundwater that freezes and uplifts the ground surface

Question 58

Four types of processes cause mass wasting in periglacial environments:

Answer 58

Slopes evolve owing to fracture
Debris
Solifluction flows (especially likely to occur in regions underlain by permafrost)
Creep processes and nivation ( the localized erosion of a slope caused by a combination of frost action, gelifluction, frost creep and meltwater flow)

Question 59

During the summer, the active layer…

Answer 59

melts forming a mobile water saturated layer.

Question 60

Slow creep of the active layer occurs by;

Answer 60

Frost creep- occurs because freezing expands the soil normal to its surface but thawing results in settlement vertically resulting in a net downward movement.
Gelifluction- the slow creep of water saturated material.

Question 61

Snow avalanches may move

Answer 61

significant volumes of rock debris.

Question 62

Periglacial slope processes result in a range of landforms particular to periglacial slopes
Protalus (or pronivial) ramparts are…

Answer 62

linear mounds of coarse sediment that form a small distance from the base of a slope.

Question 63

Periglacial slope processes result in a range of landforms particular to periglacial slopes
Ploughing boulders…

Answer 63

can also be seen on slopes in periglacial regions- the boulders move slowly downslope, leaving a trough upslope and forming a prow of sediment downslope.

Question 64

Rock glaciers typically consist of

Answer 64

angular debris and have the form of a small glacier.

Question 65

Many permafrost regions are characterised by

Answer 65

extreme aridity and are defined as polar deserts.

These regions there is abundant evidence for the transport of material by wind and for erosion by abrasion of the wind blown material.

Question 66

Dust clouds are abundant in permafrost regions

Answer 66

material is deposited when the wind velocity drops or when precipitation falls, forming a silt deposit known as loess.

Question 67

Ground ice processes

Answer 67

1. Pore ice
2. Frost heave
3. Sorting

Question 68

1. Pore Ice

Answer 68

As water freezes - 9% volume change

Pore ice fills pores between soil particles

Question 69

2. Segregation Ice

Answer 69

As sediment freezes, water can be attracted to the freezing front and form bands or layers of clear ice (segregation ice)
This can result in up 30% volume increase
Results in FROST HEAVING

Question 70

3. Sorting

Answer 70

Repeated freeze-thaw cycles and heave leads to differential upward movement of coarse material due to frost pull and frost push.

Question 71

Why does the ground become patterned during sorting?

Answer 71

Thus a circular movement is established and the ground becomes patterned.
Stones move upwards and fines move downwards.

Question 72

Earth Hummocks

Answer 72

“A hummock (mound) having a core of silty and clayey mineral soil which may show evidence of cryoturbation”

Question 73

Cryoturbation

Answer 73

= mixing and churning of soil resulting from cycles of freeze and thaw. Disturbs layers into folds and injections known as involutions.

Question 74

Ground Ice: Palsas

Description

Answer 74

Relatively small vegetated mounds, normally formed in peat along the southern edge of the permafrost zone (discontinuous). They are composed of peat and ice.

Question 75

Solifluction

Answer 75

Downward movement of material in response to freeze- thaw cycles

– Creep (autumn)
– Gelifluction (spring)

Question 76

Ground Ice : Pingos

Description

Answer 76

Roughly circular, ice-cored hills

Question 77

Ground Ice : Pingos

Two main types

Answer 77

Hydrostatic and Hydraulic

Question 78

Ground Ice : Pingos

Form on

Answer 78

Thin or discontinuous permafrost

Question 79

Hydraulic Pingos

Answer 79

Water flows beneath the ground (aquifer), but where it flows out onto the surface, it freezes, and pushes up the overlying sediment.

Question 80

Pingo Remnants

Answer 80

1. Pingos continue to grow until the surface of the pingo cracks
2. Cracks allow the sun to melt the ice within and the pingo collapses
3. Ramparts all that remain of the Pingo

Question 81

Ground Ice : Pingos

Ground ice type =

Answer 81

= intrusive ice

Question 82

Segregation ice

Answer 82

As sediment freezes, water can be attracted to the freezing front and forms bands or layers or clear ice (segregation ice)

Question 83

Controls on segregation ice-

Answer 83

a) Moisture- needs sufficient water to be attracted to the freezing front
b) Grain size- needs silt sized particles- frost susceptible
c) Rate of cooling
d) Variations in material and micro topography can cause differential frost heave

Question 84

Cryoturbation

Answer 84

Mixing and churning of soil resulting from cycles of freeze and thaw.
Disturbs layers into folds and injections known as involutions.

Question 85

Ice Wedges- The more severe the cooling…

Answer 85

The denser the polygons

Question 86

Ice wedge casts

Answer 86

When ice melts, cast fills in with sediment

Question 87

Segregated ice lenses

Answer 87

Relatively small vegetated mounds, normally formed in peat along the southern edge of the perafrost zone (discontinuous). They are composed of peat and ice.