Glaciation - Unit 6

Question 1

What is permafrost?

Answer 1

Frozen ground that remains frozen all year for atleast 2 consecutive years

Question 2

What percentage of the Earth’s landscape contains permafrost?

Answer 2

25% of exposed land

Question 3

What does the mean annual ground temperature need to be for permafrost to occur?

Answer 3

Below 0ºC

Question 4

How deep can permafrost be?

Answer 4

1500m

Question 5

What is the active layer?

Answer 5

Top layer of soil that thaws in summer and freezes in autumn

Question 6

What 3 ways can ground ice exist?

Answer 6

1- Pore ice
2- Needle ice
3- ice lenses

Question 7

Where does pore ice develop?

Answer 7

In pore spaces between soil/sediment particles where liquid water can accumulate and freeze

Question 8

What does needle ice consist of?

Answer 8

Narrow ice silvers that are up to several cm long

Question 9

Where does needle ice form?

Answer 9

In moist soils when temperatures drop below freezing overnight

Question 10

When do ice lenses form?

Answer 10

When moisture, mixed within soil or rock, accumulates in a localised zone. They usually run parallel to the surface

Question 11

What are ice wedges?

Answer 11

• Downward narrowing masses of ice

- They are 2-3m wide and 10m deep

Question 12

Describe the formation of ice wedges

Answer 12

• Crack forms in ground during winter
• Temp increases in summer so ice melts and fills crack
• Temp decreases in winter again so water refreezes and ice expands
• Process continues each year, causing ice wedge to continue increasing in size

Question 13

What is patterned ground?

Answer 13

The surface of periglacial areas, characterised by presence of ground materials arranged in symmetrical and geometric shapes

Question 14

Describe the formation of patterned ground

Answer 14

• Ground freezes from surface downwards, causing ground to expand
• Moisture in ground begins to freeze & rise, forming an ice lens
• As ice lens expands, it pushes stones above it as they have a lower SHC than the ice lens
• Stones are raised due to cryostatic pressure (pressure exerted when ice expands) = frost heave
• Mound formed
• When ice thaws, regolith (loose material) falls into the gap beneath stones, preventing it from dropping back
• Process repeats until stones are raised high enough to break through surface of ground
• Once on surface of the mound, stones slip, slide or roll to the base to form patterns

Question 15

What is regolith?

Answer 15

Loose material covering solid rock

Question 16

What is frost heave?

Answer 16

Upward dislocation of soil and rocks by the freezing and expansion of soil water

Question 17

What are pingos?

Answer 17

• Ice-covered hills

- They are 3-70m high and 30-1000m wide

Question 18

Describe the formation of a closed system pingo

Answer 18

• Lakes form in summer and freeze in winter
• Unfrozen lake water and sediment beneath ice acts as an insulator for underlying ground
• Prevents ground freezing, results in talik
• During prolonged periods of cold, permafrost will advance & encroach an overlying talik
  7- Liquid contained within talik will freeze, causing an ice lens
  8- As ice lens grows, it will exert cryostatic pressure & rise upwards, displacing overlying lake
  9- The sediment that was once at the bottom of the lake now covers the raised ice lens

Question 19

What is a thermokarst?

Answer 19

A land surface characterised by very irregular surfaces of marshy hollows and small hummocks formed as permafrost thaws

Question 20

What is a thermakarst lake?

Answer 20

A body of freshwater formed in a depression by meltwater from thawing permafrost

Question 21

What is frost weathering?

Answer 21

A collective term for several mechanical weathering processes induced by stresses created by the freezing of water into ice

Question 22

What is a blockfield?

Answer 22

A surface covered by large, angular rocks. They are a product of freeze thaw weathering, e.g. Snowdonia

Question 23

What is a scree slope?

Answer 23

A slope of loose rock debris at the base of a steep incline or cliff

Question 24

Describe the formation of a scree slope

Answer 24

• FTW occurs
• Weathered materials fall to bottom of slope through mass movement
• Over time, debris will accumulate at the base of the slope angle

Question 25

How does a protalus rampart form?

Answer 25

• Forms in a similar way as a scree slope but shape is different
• Scree lands on the ice & slides down the base of the ice
• Accumulates in the mound
• When ice melts, this accumulation of scree is left

Question 26

What does solifluction mean?

Answer 26

Soil flow

Question 27

What are head deposits?

Answer 27

Materials that have been weathered and then subject to mass movement downslope by solifluction

Question 28

Describe the process of soil creep and the formation of terracettes

Answer 28

• Active layer freezes & expands upwards parallel to the slope
• As it thaws, gravity pulls it vertically downslope, forming terracettes

Question 29

Describe the formation of dry valleys

Answer 29

• Meltwater is released at end of a glaciated period
• Permafrost is impermeable so warter doesn’t infiltrate
• Huge quantities of meltwater carve out deep, steep, V-shaped valleys
• When permafrost thaws, meltwater infiltrates, leaving behind a dry valley

Question 30

Describe the formation of loess plateaux

Answer 30

• During autumn and winter, melting is reduced
• Flow of meltwater down rivers is greatly reduced
• Large parts of formerly submerged floodplains dry out and are exposed to wind

Question 31

What is the periglacial action of wind?

Answer 31

Loess deposits

Question 32

What is periglacial action of water?

Answer 32

Dry valleys