EQ2- What Processes Operate Within Glacier Systems Flashcards
What are the inputs into the glacier system
Direct precipitation - form of snowfall which is compacted to form glacial ice
Avalanches from mountains - massive downhill movement of snow and ice which can be triggered by heavy snowfall, steep slopes and vibrations
Wind deposition - strong winds blow snow onto the glacier
What are the stores and flows which operate in the glacier system
Main stores of snow and ice - may be seasonal variations in the size of these stores
Flows - processes like evaporation , sublimation , meltwater flow and glacial movement are flows of energy and material
What are the outputs which operate in the glacier systems
Water : results from melting close to the glaciers snout
Ice shelves : the ice front extends over water and calving occurs where chunks of ice break off to form icebergs
Evaporation and sublimation also occurs
Explain the process of dynamic equilibrium in the glacier system
The boundary between the accumulation zone (inputs) and the ablation zone (outputs)
The equilibrium line will move depending on the state of the glacier
Explain how energy effects the operation of glacier systems
A glaciers mass combines with the force of gravity to generate potential energy
The energy is converted to kinetic to allow the glacier to move and carry out the process of erosion ,transportation and deposition
Explain how feedback loops effect the operation of glacier systems
Negative feedback loops regulate systems to restore dynamic equilibrium
Positive feedback enhances and speeds up the process
Both feedback loops occur in glacial systems
Define accumulation
Define abaltion
Is where there are inputs into the glacial system
The outputs in a glacial system
Explain the factors that cause variations in the rate of accumulation
Accumulation varies with climate
Accumulation rates increase when there is high levels of precipitation, low average temperatures, low levels of insolation and strong winds
Strong winds at high altitudes causes snow to be blow into hollows
Highest rates of accumulation is found at high altitudes on slopes facing away from the sun (less insolation)
As temperatures are low and other losses like sublimation are low, meltwater is likely to refreeze
Explain the role of feedback loops in the variations in the rate of accumulation
Positive feedback amplify change
If a glacier has a positive mass balance , there will be an increase in ice albedo
Causes a further reduction in temperature , increasing accumulation and initiating a cycle where the glacier will continue to grow and advance
What is a positive mass balance
What is a negative mass balance
When accumulation is greater than ablation , the glacier advances
When ablation is greater than accumulation, the glacier retreats
Explain the factors that cause variations in the rate of ablation
Rate of ablation varies with climate
Found further downslope so temperatures will be higher and melting occurs
Snow is lost to glacial meltwater and evaporation/sublimation
In polar regions large ice shelves extend over water, calving can occur when ice breaks off to form and iceberg. High rates of ablation means large masses of ice can be lost at one
Explain the role of feedback mechanisms with the factors which cause variations in the rate of ablation
Negative feedback is about trying to restore a dynamic equilibrium
When ablation is higher than accumulation , negative feedback operates to try and restore balance
For example high rates of ablation causes increased snowfall due to negative feedback
What are the processes in warm based glacier movement
Moves by both basal slip and internal deformation
What are the processes in cold based glacier movement
Move only by internal deformation
Explain the process of basal slip in glacial movement
Occurs in warm based glaciers
Occurs when the base of the glacier reaches pressure melting point
Meltwater is present and acts as a lubricant allowing the glacier to move quickly over the bedrock
Accounts for 75% of warm based glacier movement
Explain the two processes of enhanced basal creep and regelation as processes of basal slip in warm based glaciers
Basal creep occurs over a large bedrock (greater than 1m wide)
When the glacier and the bedrock meet there is increased pressure and makes the ice plastically deform and engulf the bedrock
It very slowly moves over it and takes its shape
Regelation occurs over a small obstacle (less than 1m wide) when the meeting of the glacier and bedrock causes pressure
This causes heat and the base of the glacier melts to form glacial meltwater to act as a lubricant to move over the obstacle.
The meltwater refreezes further downslope where there is less peessure
Explain the process of internal deformation and how it effects glacial movement
Accounts for 100% of the cold based glacier movement and 25% of warm based glacier movement.
This occurs when the weight of the glacier and gravity (shear stress) cause the ice crystals to deform
The glacier moves downhill very slowly
Explain the two processes of internal deformation and how it causes glacier movement
Inter- granular movement is when individual crystals slip and slide over each other causing movement downhill
Intra- granular movement is when individual crystals become deformed due to stress of ice and moves downhill gradually.
Explain the processes of extensional and compressional flow in basal slip and how it effects warm based glacier movement
Extensional flow is at the head of the glacier where there is GPE
This makes ice move quickly causing tension and ice to fracture and slip downwards
Forms seracs
Compressional flow occurs when the fast moving ice pushes down of slower ice and compresses it.
The high pressure causes the ice to fracture into layers, causing transverse crevaces to form.
Explain the process of surges in basal slip and how it causes warm based glacier movement
When a glacier advances substantially up to 200m per day
The most common cause is enhanced basal sliding triggered by the build up of meltwater
In Iceland geothermal energy and subglacial bed deformation (glacier moves over rock) is a cause of surges
How does ice move in response to the factor of lithology (rock type)
In temperate zones movement is faster over impermeable rock than permeable, as basal meltwater is retained
If the bedrock is permeable meltwater would be able to percolate and it is prone to bed deformation
How does ice move in response to the factor of altitude
Altitude effects the temperature and precipitation inputs
The greater the precipitation the lower the temperature.
High snowfall leads to greater accumulation and faster movement
How does ice move in response to the factor of gravity/gradient (slope)
Gravity and gradient is directly related to flow
Gravity encourages ice to move, the steeper the gradient the greater the pull of gravity
How does ice move in response to the factor of ice temperature
Colder ice moves slower than warmer ice as it does not deform as easily and is more stuck to the bedrock
