Patterned ground

Question 1

Describe the formation of patterned ground?

Answer 1

• Particles of different sizes in the active layer are sorted by frost heave
• Frost heave causes more stones to rise to the surface while finer material moves downwards. This is because stones have a lower specific heat capacity than finer sediments and therefore heat up and cool down more quickly.
• As a result, when the freezing front (the boundary between frozen and unfrozen soil) moves through the active layer in autumn it will move through a stone more rapidly, causing the top of the stone to be frozen to underlying material, which pulls the stone upwards as it expands. Once brought up to the ground surface, stones are organised into different shapes.
• The doming of the ground by frost-heave causes stones brought to the surface to roll outwards (frost-thrust), leaving finer material in the central raised area.

Question 2

Which process rearranges soil surface sediments into a range of patterned shapes?

Answer 2

Repeated freeze-thaw cycles rearrange soil surface sediments into a range of patterned shapes including circles, nets, polygons, steps and stripes.

Question 3

What is the impact of repeated freeze-thaw cycles rearranging soil surface sediments into a range of patterned shapes?

Answer 3

It leads to differential expansion and movement of material by the process of frost-heaving and frost-thrusting.

Question 4

When does frost-heaving occur?

Answer 4

Frost heaving occurs when the freezing of moisture into ice crystals within the ground creates upward movement of soil.

Question 5

When does frost-thrusting occur?

Answer 5

Frost-thrusting occurs when the freezing of moisture into ice crystals within the ground creates a lateral movement.

Question 6

Why is frost-heaving more pronounced than frost-thrusting?

Answer 6

Frost- heaving is more pronounced than frost-thrusting because there is less resistance from the overlying ground surface.

Question 7

Give some factors which influence the type of patterned ground that forms?

Answer 7

• The number of stones and their composition/colour.
• The amount of moisture
• The slope angle

Question 8

How does the number of stones and their composition/colour influence the formation of patterned ground?

Answer 8

It influences the formation of patterned ground because stones heat up and cool down at different rates than finer material does.

Question 9

How does the amount of moisture influence the type of patterned ground which forms/

Answer 9

The amount of moisture influences how much expansion there will be in a soil when it freezes.

Question 10

How does the slope angle influence the type of patterned ground which forms?

Answer 10

There is a clear relationship between the characteristics of patterned ground and the slope angle.