3.1.4.4 Periglacial Landforms

Question 1

Periglacial landscapes aren’t glaciated but what are they still exposed to

E.g

Answer 1

Very cold conditions with intense frost action + permanent,y frozen ground (permafrost)

E.g tundra areas like northern Russia and Canada, Alaska

Question 2

What’s permafrost

3 types

Answer 2

Soil, rock or sediment that has been permanently frozen for at least 2 consecutive years

Continuous
Discontinuous
Sporadic

Question 3

Where is continuous permafrost found

Answer 3

In coldest regions, deep into surface layers where there’s hardly any melting of upper most layer

Question 4

Where does discontinuous permafrost occur

Answer 4

In slightly warmer regions, where ground isn’t frozen as deeply (still 20-30m deep)

Question 5

Where is sporadic permafrost found

Answer 5

Where mean annual temperatures are around freezing point

Question 6

What does sporadic permafrost occur in

Answer 6

Isolated spots

Question 7

Describe an active layer

Answer 7

When summer temps are above freezing, the surface layer thaws from the surface downwards to form an active layer

Question 8

Why is an active layer often saturated

Answer 8

As meltwater can’t infiltrate downwards as permafrost is impermeable

Question 9

What’s talik’s

Answer 9

Unfrozen layer beneath/within permafrost

Question 10

7 periglacial landforms

Answer 10

Patterned ground
Ice wedges
Pingos
Blockfields
Solifluction lobes + sheets
Terracettes
Thermokarst

Question 11

What can produced patterned ground

What’s the main process

Answer 11

Repeated cycles of freezing + thawing of the active layer

Main proces involved is frost heave

Question 12

What does frost heave form on the surface

Answer 12

Small domes

Question 13

What’s frost heave

Answer 13

As the active layer starts to refreeze, ice crystals begin to develop
This increases the soil volume + causes an upward expansion of the soil surface

Question 14

Why is the soil immediately. Beneath a stone likely to freeze + expand (patterned ground)

Answer 14

As stones in fine-grained material have lower specific heat capacity so heat up + cool down faster than surrounding finer material.
The cold penetrating from the surface passes through the stones faster than through surrounding material

Question 15

What does the soil beneath a stone do as it freezes + expands before other material

Answer 15

It pushes up the stone until it reaches the surface, meaning a range of features can form

Question 16

2 patterns formed by frost heave

Answer 16

Circles

Stripes

Question 17

2 shapes on flat ground

Answer 17

Circles

Polygons

Question 18

What shape is created by permafrost frost action

Answer 18

Steps

Question 19

5 patterned ground shapes

Answer 19

Circles
Nets
Polygons 
Steps
Stripes

Question 20

How are ice wedges formed

Answer 20

In low temperatures the ground contracts + cracks develop

During summer, meltwater fills these cracks + freezes in the winter to form ice wedges

Question 21

How do ice wedges increase in size

Answer 21

Repeated freezing + thawing

Question 22

What does frost heave cause to form which ponds may from between in summer

Answer 22

Narrow surface ridges

Question 23

What do ice wedges begin as

Answer 23

Cracks less than 5cm

Question 24

What pattern does the ground produce when it contracts

How big are they

Answer 24

Ice wedge polygons

Larger than stone polygons, 15-30m wide, but can reach 100m

Question 25

Whats a pingo

Answer 25

Rounded hill up to 90m high and 800m wide

Question 26

What do pingos often look like

Answer 26

Often green + vegetated on outside with a core of solid ice

Question 27

Where are pingos thought to form

Answer 27

On the site of a lake gradually infilled with sediment

Question 28

What may happen to the pingo in the summer

Answer 28

Part of the ice core will melt + centre may collapse

Resembling a volcanic crater that may fill with water

Question 29

How do ‘closed’ pingos form

Answer 29

1. Lake infills with sediment insulating ground below. Liquid water is trapped in talik between lake sediment + permafrost
2. Water freezes as climate cools to form ice core. Ice expands due to hydrostatic pressure increase and talik is squeezed. Lake sediment is pushed up to form a pingo

Question 30

What are blockfields

What are they repeatedly subjected to

Answer 30

Periglacial landscapes with extensive frost-shattered bedrock (broken up angular rock fragments)

Repeated freezing + thawing

Question 31

What does solifluction involve

Where is it most likely to occur

Answer 31

The downslope movement of rock + solid material due to gravity in a periglacial environment

Occur in areas where summer melting is taking place and there’s a reasonably thick + saturated active layer

Question 32

What are formed where solifluction occurs on slopes around 1-20*
Describe them

Answer 32

Solifluction sheets

Have a smooth surface + can extend over 100m across a slope

Question 33

What will form where slopes have a steeper gradient of 10-20*
Describe them

Answer 33

Solifluction lobes

Have a tongue like look that extends downslope + can be up to 50m in width + 5m high

Question 34

What are terracettes

Answer 34

Small periglacial features often referred to as ‘sheep tracks’ as they look like long, narrow pathways running horizontally alongside a slope

Narrow steps often 20-50cm high and only tens cm wide that run parallel to slopes contours

Question 35

How do terracettes form

Answer 35

In winter soil freezes + expands
In summer particles melts + goes downwards

Particles shifting upwards + downwards create steps in hillsides

Soil creep usually occurs on the slopes of about 5* and produces them

Question 36

2 processes that help produce terracettes

Answer 36

Frost heave

Soil creep

Question 37

What is thermokarst

Answer 37

Depressions in the ground surface resulting from ice melting within permafrost

Question 38

What can cause thermokarst as well as just temperature change

Answer 38

Human activity warming surface layers of permafrost