3. Periglacial landscapes

Question 1

What is a periglacial landscape?

Answer 1

A landscape that is covered in permafrost that has seasonal temperature variations, where freeze-thaw cycles dominate geomorphic processes

Question 2

What is permafrost?

Answer 2

Perennially frozen ground overlain by an active layer

Question 3

What is an active layer?

Answer 3

The near surface in a periglacial environment which seasonally freezes and thaws

Question 4

Where can periglacial environments be found?

Answer 4

High latitude areas eg Alaska
Continental interiors eg Siberia
Low latitudes with high altitudes eg Andes

Question 5

What % of Earth’s land surface is covered in periglacial landscapes?

Answer 5

25% (estimated another 25% has also experienced previous periglacial conditions)

Question 6

What geomorphic processes are important in periglacial landscapes?

Answer 6

Frost heave
Freeze thaw
Ground ice formation

Question 7

Describe freeze thaw:

Answer 7

Cause by seasonal fluctuations in temperature
The mechanical weathering process caused by water in cracks in rocks to freeze and expand, resulting in rocks breaking into smaller particles

Question 8

Describe frost heave:

Answer 8

The downslope displacement of soil particles that results from cycles of freeze-thaw

• Stones w finer material heat/cool down quickest as have lowest specific heat capacity
• As temperatures fall water beneath the stones freeze and expand, pushing stones upwards to the surface
• Ground ice can also push fine material upwards producing a domed surface

Question 9

Describe the formation of ground ice:

Answer 9

During summer melting, water percolate into sub-surface geology where it accumulates below the water table
During winter thus freezes and expands between 9-10%, forcing ground surface to be pushed upwards

Question 10

Where can periglacial landforms be found?

Answer 10

They can be a feature of current periglacial periods or fossil features in more temperate regions eg UK

Question 11

What landforms are associated with periglacial environments?

Answer 11

Patterned ground
Pingos
Blockfields

Question 12

What is patterned ground + example?

Answer 12

The collective term for a number of small-scale features of periglacial environment
Eg Barrow, Alaska

Question 13

How is pattern ground formed?

Answer 13

Frost heave forces largest stones towards surface which the move radially under gravity, down the domed surface to form a network of stone polygons 1-2 metres in diameter

Question 14

What is a stone garland?

Answer 14

Elongated polygons that form on a slope

Question 15

What is a stone stripe?

Answer 15

Occurs on slopes of over 60 degrees where stone polygons lose they shape

Question 16

What are pingos?

Answer 16

Rounded ice cored hills that can be up to 90m in height and 800m in diameter

Question 17

What are the two types of pingo?

Answer 17

Open system

Closed system

Question 18

Describe open system pingos:

Answer 18

Common in east Greenland, found in areas of discontinuous permafrost
Develop in valley bottoms
Growth of the ice core is hydraulic

Question 19

Describe how open system pingos are formed:

Answer 19

Water seeps from higher-surrounding areas to low-lying areas by gravity (forms a talik)
Talik freezes and expands, pushing overlying ground surface upwards

Question 20

Describe closed system pingos:

Answer 20

Found in the MacKenzie Delta, Canada, found in areas of continuous permafrost
Develop beneath lake beds where supply of water is from immediate local area
Growth of the ice core is hydrostatic

Question 21

Describe how closed system pingos form:

Answer 21

Groundwater beneath the lake is trapped between the permafrost below and the frozen lake above, causing it to be insulated and thaw = melted
The saturated talk is compressed by the expanding ice and is under hydrostatic pressure
When lake eventually drains, talik is no longer insulated so freezes and expands, pushing ground surface upwards

Question 22

What are blockfields?

Answer 22

Large amounts of freeze-thaw action results in large amounts of scree - in flat areas expansive angular boulders form blockfields

Question 23

What is solifluction?

Answer 23

In summer, large areas of meltwater in upper layers of permafrost cannot be drained away which causes lubrication of the soil and causes ground movement over slopes

Question 24

What has happened to periglacial landforms as temperatures have risen?

Answer 24

Patterned ground has been colonised by vegetation eg Leedon Tor in Dartmoor is covered in grasses
Pingos collapse when ice cores thaw leaving a circular depression = ognip Eg Llanberis, North Wales