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Geography > Periglacial Processes, Landforms And Landscapes > Flashcards

Periglacial Processes, Landforms And Landscapes Flashcards

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1
Q

What is a periglacial

A

The cold environment on the margins of glaciers

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2
Q

What are the characteristics of a periglacial landscape

A

Non-glaciated
Characterised by periods of extreme cold, dry condtions
Frequent freeze-thaw
Permafrost

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3
Q

What are periglacial areas often referred to

A

The tundra

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4
Q

What is the tundra? (vegetation)

A

A area with treeless vegetation of dwarf shrubs, sedges and grasses, mosses and lichens

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5
Q

Why is the vegetation so small in the tundra

A

Hindered by mean annual temperature of less than 3C and minimum temperatures as low as -50c
Reduced sunlight for part of year (small growth period)

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6
Q

Why is the growth of plants season so short in glacial/Periglacial

A

There are only a few days in which the temperature is above 6*c which is the minimum needed for photosynthesis

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7
Q

Where does nivation take place

A

Below patchestof snow of bare rock (slight depressions in the ground)
Usually on north and east facing slopes in NH where snow less likely to melt (stays for long time)

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8
Q

Where does nivation typically occur

A

On the north and east facing slopes (less sun so less the likely the snow will melt)

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9
Q

What does freeze-thaw and chemical weathering do?

A

Cause the rock underneath the snow to disintegrate (fall apart/ degrade/ erode)

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10
Q

What happens when the snow melts in spring (solifluction)

A

Weathered particles are moved downslope by meltwater and solifluction creating solifuciton lobes

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11
Q

What does the repetition and weathering and solifluction do with snow?

A

Formation of a nivation hollow which when enlarged can be the beginning of a corrie (cirque) in some areas.

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12
Q

What are solifluction sheets/lobes

A

Rounded, tounge like features often forming terraces in the sides of valleys

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13
Q

How does rate of flow vary with solifluction

A

Vary with climatic conditions, slope and vegetation cover but usually move 1-10cm a year

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14
Q

How does solifluction lobes occur

A

Excessive lubrication when the active layer thaws in summer this reduces friction between between the particles (able to move over each other more easily). Even on a slope as shallow as 2* the active layer can bgin to move downslope

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15
Q

what creates patterned ground? (Process)

A

Frost heave

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16
Q

What is the first step of frost heave

A

Active layers starts to re-freeze when temperature drops ice crystals begin to develop

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17
Q

What do ice crystals cause in the soil

A

Increase the soil volume and cause an upwards expansion of the soil surface (uplifting)

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18
Q

What does fine-grained material cause in the process of patterned ground

A

Causes the soil to expand unevenly producing small domes on the surface

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19
Q

What can be found within fine-grained material

A

Stones (coarse material)

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20
Q

How do stones cuse frost heave

A

They warm up and cool faster
Therefore the penetrating cold passes through the stones faster
This means the soil beneath the stone is likely to freeze and exapnd (9% larger than the original size)
Repeated freeze-thaw causes the crystls to HEAVE up until they reach the surface.

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21
Q

How dose material get semi-sorted in patterned ground

A

On small domes Large stones roll down the slope of the domes into the depressions between domes effectively sorting the material and creating a pattern of interchanging coarse and fine material

22
Q

how does slope steepness affect patterned ground

A

on gentler slopes the pattern takes the form of stone polygons or circles
On steeper ground (more than 6*) the stones move downhill forming STONE STRIPS

23
Q

what is an ice lens

A

where moisture accumulates in the soil and has frozen
as it expands it will push the land above it upwards
Some may become exposed

24
Q

how does a ice lens grow

A

capillary movement through frost susceptible soil causing the ground to heave and sometimes crack

25
Q

what is a PINGO

A

a dome shaped mound of a layer of soil over a large core of ice

26
Q

what can be found at the core of a pingo

A

an ice lens of varying sizes

27
Q

what is the surface layer like on top of a PINGO

A

often topped with vegetation
surface can also contain cracks as a result of ground swelling

28
Q

what 2 types of basic PINGO are there

A

open system type
closed system type

29
Q

what is an open system PINGO

A

the water that forms the ice lens comes from outside the system (above ground)

30
Q

what is a closed system PINGO

A

water required for the ice lens formation is contained within the area the Pingo forms

31
Q

what causes groundwater movement and capillary action

A

hydraulic pressure

32
Q

where can open system pingos be found

A

east-Greenland

33
Q

what are closed system pingos often referred as

A

MacKenzie type

34
Q

why are closed system pingos called Mackenzie type

A

Mackenzie delta in northern Canada where over 1000 PINGOS have been recorded

35
Q

what can happen in Pingos if the ruptures become too large

A

the ground cracks exposing the ice lens this can melt the ice causing the pingo to collapse leaving a RUPTURED PINGO
this can form a lake
and a raised edge = rampart

36
Q

what process occurs in the Rampart of a ruptured Pingo

A

solifluction

37
Q

what is the collapsed pingo known as

A

OGNIP

38
Q

What is an ice wedge

A

A crack in the ground formed by a narrow or thin piece of ice that measures up to 3-4m in length at ground level and extends into the ground for several meters.

39
Q

How does ground contraction cause ice wedges

A

Refreezing of active layer in winter causes the ground to contract
Cracks open up on the surface
During melting the cracks reopen and fill with melt water
Meltwater contains fine sediment that also fills the crack
This process repeats itself
Widening and deepening the crack to from an ice wedge

40
Q

What does the birds eye view of an ice wedged area look like

A

Ice wedge polygons

41
Q

What is permafrost

A

Permanently frozen ground where sub soil temperatures remain below 0 for at least 2 consecutive years

42
Q

What is permafrost a good indicator of

A

The main periglacial regions

43
Q

Where is permafrost found today

A

Tundra regions in high latitudes
Low latitudes at high altitudes

44
Q

What % of earths land surface has experienced permafrost

A

20-25% experienced permafrost or extreme frost activity

45
Q

What are the 4 types of permafrost

A

Continuous
Discontinuous
Sporadic
Isolated

46
Q

What is continuous permafrost

A

The sub soil is constantly frozen with no thawing

47
Q

What is discontinuous permafrost

A

permafrost occurring in some areas beneath the exposed land surface throughout a geographic region where other areas are free of permafrost

48
Q

What is sporadic permafrost

A

Found when mean annual temperature is just below 0ºC and the summer temperatures reach several degrees above but isolated pockets of permanently frozen ground remain below the surface.

49
Q

What is isolated permafrost

A

less than 10% of the surface has permafrost under it.

50
Q

What is the active layer

A

Upper part of the ground
Regularly thaws is summer
Highly mobile - due to freeze thaw and melt water saturation
On slopes the active layer will move downslope due to gravity

51
Q

what are loess deposits?

A

deposit of wind-blown silt that blankets large areas of the continents. It is often light brown in colour

Geography (103 decks)

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