4.3: Periglacial processes and their distinctive landforms and landscapes

Question 1

Define Periglacial

Answer 1

The term periglacial is used to include all non-glacial cold climate areas with a high range of different high latitude and high altitude environments which may or may not contain glaciers

Question 2

Present Distribution of Periglacial Landscapes

1. How much of the earths landscape experiences periglacial conditions today?
2. Name 3 locations

Answer 2

1. Around 20% of the earth’s surface experiences periglacial conditions
2. It is largely in the northern hemisphere in areas such as siberia, northern scandinavia, northern canada and alaska

Question 3

Define Permafrost

Answer 3

Permafrost refers to soil and rock that remains frozen as long as temperatures do not exceed 0 degrees C in the summer months for at least 2 consecutive years

Question 4

Name the 3 types of permafrost

Answer 4

1. continuous
2. discontinuous
3. sporadic

Question 5

Define Continuous Permafrost

Answer 5

It forms in the coldest areas of the world where mean annual air temps are below -6C. It can extend downward 100’s of metres

Question 6

Define Discontinuous permafrost

Answer 6

More fragmented and thinner than continuous permafrost

Question 7

Define Sporadic permafrost

Answer 7

occurs at the margins of periglacial environments and is usually very fragmented and only a few metres thick; it often occurs in hillsides or beneath peat

Question 8

Define Sporadic permafrost

Answer 8

occurs at the margins of periglacial environments and is usually very fragmented and only a few metres thick; it often occurs in hillsides or beneath peat

Question 9

What is the active layer of permafrost?

And how deep can it be?

Answer 9

1. In summer, the energy balance is positive, which causes overlying snow and ice to melt and produce a seasonally unfrozen layer above the permafrost called the active layer
2. It varies in thickness from a few centimetres to around 3m

Question 10

Name 3 factors that influence the distribution and character of permafrost

And how

Answer 10

1. Climate as temperature and amount of moisture available determine the presence or absence, depth and extent of permafrost

On a local scale:

2. Proximity to water bodies: lakes are relatively warm so remain unfrozen throughout the year with a deep active layer
3. Slope angle and orientation influence the amount of solar radiation and therefore melting, freeze-thaw and wind
4. Character of ground surface (different rocks and soil types) can determine the degree and depth of permafrost. For example, dark compact rocks absorb a greater amount of solar radiation
5. Vegetation cover can insulate the ground from temperature extremes
6. Snow cover can slow the freezing process in winter and in spring, delay the thaw and development of the active layer

Question 11

Define Nivation and describe its affects

Answer 11

The effects of snow on a landscape. These include abrasion and freeze-thaw.

Furthermore, melted snow triggers mass movements such as solifluction and slope wash. These processes may produce the shallow pits known as nivation hollows. In time, these hollows may trap more snow and may deepen further with more nivation so that cirques or thermocirques are formed.

Question 12

Define Frost Heave

Answer 12

The upward dislocation of soil and rocks by the freezing and expansion of soil water.

Frost push occurs when cold penetrates into the ground. Large stones become chilled more rapidly than the soil. Water below such stones freezes and expands, pushing up the stones.
Frost pull can alter the orientation of a large stone causing it to stand upright. This occurs when ice creeps downwards from the surface. The growth of ice crystals on the upper part and the drying of the soil around the lower part cause the stone to be pulled into a more vertical inclination.

Question 13

Define Freeze-thaw weathering

Answer 13

Freeze-thaw weathering occurs when rocks are porous (contain hole) or permeable (allow water to pass through). Water enters the rock and freezes. The ice expands by around 9%. This causes pressure in the rock until it cracks. Repeated freeze-thaw can cause the rock to break up.

Question 14

Define Solifluction

Answer 14

Solifluction is the flowage of water-saturated soil down a steep slope. Because permafrost is impermeable to water, soil overlying it may become oversaturated and slide downslope under the pull of gravity

Question 15

What are Ice Wedge Polygons?

And how are they formed?

Answer 15

• Unique to periglacial environments
• The process of frost cracking creates irregular polygons - 5-30 metres across
• They are usually found on valley floors
• When the active layer thaws, ice wedges can begin to form as water flows down into the cracks, it subsequently freezes and contracts, which means the ice wedge can build up over time
• Larger ice wedges usually have a tapering shape 1 - 2 m wide and up to 10m deep, extending down into the permafrost

Question 16

What is patterned ground?

How are they formed?

Answer 16

• It is the general name for features including circles, nets, polygons, steps and stripes
• Unique to the periglacial environment
• They are formed from a series of movement resulting from frost action
• Frost push propels the stones upwards, whilst frost heave causes the stones to migrate outwards to form circles, which provides the basis for each of the patterns
  The doming of the circles created by the heave means that larger stones roll outwards as a result of the gravity, while finer sediments retain central
• As a result of mass movement stone polygons are elongated into stone nets and stripes, with a clear relationship between slope angle and the type of patterned ground

-If a slope gradient is beyond 30 degrees patterned ground features no longer form and rock avalanches may occur instead

Question 17

What are Pingos

How are they formed

Answer 17

• They are unique to periglacial landscapes
• They are ice core mounds 30 - 70 metres high and 100 - 500 metres in diameter
• They can be conical or elongated
• The growth of an ice core forced up the underlying sediments causing dilation cracks
  Once the ice core is exposed at the surface it melts causing the top of the pingo to collapse forming a crater, which may be filled with meltwater and sediments

Question 18

What is frost shattering?

Answer 18

freeze-thaw weathering puts pressure on any cracks in the rocks and shatters them

Question 19

Define Frost creep

Answer 19

Is a very slow form of mass movement - material moves downslope by just a few centimetres per year, even on steeper slopes

Question 20

Define Loess

Answer 20

a wind blown deposit of fine-grained silt or clay in glacial conditions

Question 21

1. When does water erosion occur in a glaciated landscape?
2. What does glacial meltwater carry with it?

Answer 21

1. Water erosion in periglacial areas is highly seasonal, occurring mainly in spring and early summer when surface snow and ice and the active layer melt leading to short periods of very high meltwater stream discharge
2. debris

Question 22

1. What is the role of wind in forming glacial landscapes?
2. Where is it happening today?

Answer 22

1. deposits of fine silt-sized sediments formed in extensive outwash plains can be blown by wind to other areas forming soils of high agricultural potential
2. gobi desert to the loess plateau in northern china