Systems and Processes: Flashcards
Glacial budgets:
- Considers the balance between the inputs and outputs. Glacier is divided into 2 zones: The accumulation zone and the ablation zone.
Accumulation zone: inputs exceed the outputs and shows the net gain of ice over the course of a year
Ablation zone: outputs are greater than inputs. Where there is a net loss of ice during the year.
Equilibrium Line = the boundary where gains and losses are balanced.
Mass balance varies due to seasons. In summer ablation will be highest due to rapid melting and during winter more snowfall so there will be more accumulation than ablation.
Historic patterns of ice advance and retreat:
Alternating cold and warm periods have led to ice advance and ice retreat during the last 800,000 years.
‘Little Ice Age’ from 1500 - 1850 was when global temps were cooler than the present day. Ice advanced.
Over next hundreds of years climate warmed and since 1980’s many of world glacier’s have experienced considerable shrinkage. Due to Global Warming.
For example the Swiss Glacier Monitoring Network currently notes that 86 out of 95 glaciers observed are retreating, 6 are stationary and 3 are advancing.
Warm and Cold based glaciers:
PMP - at ground surface under normal atmospheric pressure melting point of the ice is 0 degrees. Under pressure, the melting point is lower.
Warm based glaciers:
- Mild areas.
- In summer temps exceed 0 degrees meaning melting will occur. And at the glaciers base the temperature of the ice reaches pmp during the year. Meltwater will act as lubricant which will mean more basal sliding. This results in erosion of the bedrock. And then material will be later deposited.
Cold Based Glaciers:
- Associated with polar environments
- Both winter and summer temps well below freezing, no surface melting. Little/no basal sliding so any movement will be solely internal deformation, as a result little erosion of the bedrock.
Geomorphological processes:
Weathering:
- Frost action
- Nivation
Ice movement:
- Internal deformation
- Rotational
- Compressional
- Extensional
- Basal sliding
Erosion:
- Plucking
- Abrasion
- Transportation
- Deposition.
Weathering:
(frost action)
Frost shattering weathering (freeze-thaw):
1) Water seeps into cracks and pores within the rock
2) When temps fall below 0 degrees water turns to ice and expands by about 9%
3) Exerts stress on the rock enlarging the cracks.
4) Process is repeated a number of times, until chunks of rocks are broken away.
5) Pile of scree ends up at the foot of the slope.
The effects of frost action on the landscape:
- Forms blockfields.
- Accumulation of scree
- Frost heave.
What is Nivation?
Nivation is a collective term for processes involving snow and ice that cause erosion. Nivation hollows are created by nivation processes, which is where snow gathers in small depressions and eventually this erodes into a hollow full of snow. Nivation hollows are the beginnings of Corries.
Internal deformation:
2 mechanisms of internal deformation are …
Intergranular movement (sugar): Individual ice crystals slip and slide over each other, the ice crystals within the glacier tend to orientate themselves in the direction of ice movement and this allows them to slide past eachother.
Intragranular movement:
Individual ice crystals fracture due to glacier’s mass and the influence of gravity. Gradually the mass of ice deforms and moves downhill in response to gravity.
What is compressional flow?
○ Compressional Flow: When ice hits a shallower gradient, friction causes the ice to
slow down, build up and compress. This causes ice to get thicker.
What is extensional flow?
Extensional Flow: When ice meets a steep downhill gradient (usually when going
over a hill), gravity forces the ice to increase in velocity. Friction causes the ice to
thin out and extend, causing deep cracks called crevasses.
What is rotational slip?
○ Rotational Slip: Compressed ice becomes trapped in a hollow, but gravity causes
it to continue to move downwards. Meltwater assists in moving the glacier in a
rotational movement, causing it to continually erode the hollow
What is Basal sliding?
Basal Sliding: Glacier sliding over the bedrock. This is due to meltwater providing
lubrication for the glacier to move.
Controlling factors in ice movement:
Gravity - encourages ice to move downhill.
Friction - Friction exerted by the ground on the ice has to be overcome.
Mass of the ice - Heavier the ice more potential energy it has to move.
Meltwater - lubricates the base of the glacier, enabling it to slip downhill.
Temperature of the ice - depends on the amount of meltwater produced.
What is plucking?
Rocks attached to bedrock or sides become frozen to the glacier. When
the glacier moves, the rocks are pulled ( plucked) from the landscape, leaving a
jagged surface.
What is Abrasion?
Abrasion: A sandpapering effect caused by small rocks embedded within the
glacier rubbing on bedrock. Usually leaves a smooth surface with scratches called
striations.
Glacial transportation?
Transport material from mountainous areas onto adjoining lowlands. Can be carried in 3 ways:
1) Supraglacial - material carried on top of the ice.
2) Englacial - Once supraglacial material, now carried within the ice.
3) Subglacial - material carried beneath the ice.
Water on top of the glaciers may lead to fluvial transport.
