Topic 2 - EQ2 - Glaciation (Mr W) Flashcards
How does entrainment enable erosion?
Entrainment helps move out the plucked stones from the ground and then abrasion (erosion) can occur
What role does water have in the transportation of glacial material?
In temperate environments, water flows on top of glaciers leading to fluvial transport. Meltwater may flow through crevasses or holes in the ice transporting material into and down below the glacier. Meltwater also carries material beneath temperate glaciers.
What is the difference between till and fluvio-glacial debris?
Till - Deposited directly by glacier ice
Fluvio Glacial Debris - Deposited by glacial meltwater
What are ice marginal environments?
Environments at the edge of glacial ice. Glacial and fluvio-glacial processes occur.
What are proglacial environments?
Environments at the front of a glacier, dominated by fluvio-glacial processes
What are periglacial environments?
Environments near glaciers. Dominated by freeze-thaw processes.
What are active landscapes?
Landscapes which currently experience glaciation and glacial landform development
What are relict landscapes?
Landscapes not currently characterised by glaciers but feature fossilised glacial landforms.
What are the main stores in a glacial system?
Snow and ice
How do the stores in a glacial system vary?
Summer causes melting and so smaller stores, winter snowfall causes the stores to grow. Global warming in the past 30 years has led to diminishing stores and diminishing glaciers.
What are the three main inputs into the glacial system?
- Direct precipitation in the form of snowfall which compacts into high density clear glacial ice over years
- Avalanches from mountains above
- Wind deposition of snow
What is the equilibrium line in a glacier?
The line that marks the boundary between the accumulation zone and the ablation (output) zone. As the balance of inputs versus outputs shifts the equilibrium will move up or down the glacier.
What is the role of energy in a glacial system?
A glacier’s mass combines with gravity to general potential energy. As the glacier moves potential energy is converted to kinetic energy. Kinetic energy enables the glacier to carry out erosion, transportation and deposition.
What is the main output in a glacial system? What are some other minor outputs?
- Water resulting from melting is the main output
- Chunks of ice breaking off when glacial system extends over water to form icebergs (calving)
- Evaporation of meltwater
- Sublimation
What are the 5 main transfers of energy and material?
- Evaporation
- Sublimation
- Meltwater flow
- Internal deformation
- Basal slippage
Where are the transfers and flows of energy and material most and least pronounced?
- Most pronounced in more temperate environments (as greater seasonal variations in temp above and below 0°C)
- Least pronounced in the world’s coldest environments (e.g. Antarctica)
What do negative feedback loops do for glacial systems?
They regulate systems to establish balance and equilibrium
What do positive feedback loops do in a glacial system?
They enhance and speed up processes promoting rapid change
What is the fundamental cause of ice movement?
Gravity. Ice moves downslope from high to low altitude.
What does the process and rate of glacier movement depend upon?
Temperature of the ice and whether the ice melting point is reached. Ice depth lowers the melting point and so most temperate glaciers reach the pressure melting point and so have meltwater lubricating the glacier allowing it to move quicker.
How do temperate glaciers move? What is the split in causes of movement?
By both basal slip (75%) and internal deformation (25%)
What is the general process of basal slippage?
Occurs when the base of the glacier is at the pressure melting point (pmp), which means that meltwater is present and acts as a lubricant, enabling the glacier to slide more rapidly over the bedrock.
What is enhanced basal slip caused by?
Obstacles on the valley floor
What do large obstacles (>1m) cause?
A process called regelation creep . Which is an increase in pressure which causes the ice to plastically deform around the feature and then refreeze on the down glacier side of the obstacle.
What do smaller objects (<1m wide) do?
Help enhance basal slip by adding a little more pressure.
What is extensional flow?
When ice moving quickly (due to gravitational force because of the steepness of valleys at the head of some glaciers) fractures into layers due to the tension caused by such movement, these layers then slip downwards (extensional flow).
What are surges?
Short lived substantial glacial advances
What are some causes of glacial surges?
- Earthquakes
- Volcanic/geothermal activity causing increased meltwater
- Subglacial bed deformation (when glaciers move over weak rock and the sediment beneath deforms moving the glacier along with it)
What percentage of polar (cold based) glacier movement is down to internal deformation?
100%
What are the two movements that work together to cause movement via internal deformation?
- Intra granular movement
- Inter granular movement
What is intra granular movement (internal deformation)?
Where individual ice crystals become deformed due to the intense stresses within the ice, due to the great mass of the glacier, and so gradually the mass of ice deforms and moves downhill in response to gravity.
What is inter granular movement (internal deformation)?
Where individual ice crystals slide over each other causing the glacier to move.
What is the fundamental cause of ice movement?
Gravity. Ice moves downslope from higher to lower altitudes as the weight of the snow and ice exerts and increasing downslope force.
What does the process and rate of glacier movement depend on?
Glacier movement greatly depends on the temperature of the ice and whether the melting pressure point is reached. Increased ice depth fractionally changes the melting point to a new point, the pressure melting point. Most temperate glaciers reach the pressure melting point and so produce a great deal of meltwater which lubricates and increases the rate of movement (basal slip). Temperate (warm based) glaciers thus move quicker than cold based glaciers which are frozen to the ground and rely on internal deformation.
What are the 7 major factors affecting ice movement?
- Lithology
- Altitude
- Gradient (gravity)
- Ice Temperature
- Ice thickness (size and mass)
- Mass balance
- Feedback mechanisms
Why is lithology important in controlling ice movement?
- Temperate zone glaciers move quicker over impermeable surfaces is faster because meltwater is retained, instead of percolating, so the glacier can keep moving due to basal slippage
- Easily eroded and ‘weak’ rocks are more prone to bed deformation and temperate zone glaciers move quicker over deformable sediment, because as the sediment deforms under the weight of the glacier it moves along the ice above
Why is altitude important in controlling ice movement?
Higher altitudes mean more precipitation and lower temperatures, and so accumulation is greater, therefore there is more mass to the glacier which means faster movement.
Why is gradient important controlling ice movement?
Gravity encourage ice movement, the steeper the gradient, the greater the pull of gravity is and thus the faster the ice movement.
Why is ice temperature important in controlling ice movement?
In some environments (e.g. Antarctica) it is so cold that the ice is frozen to the bed and there is no basal slippage and only internal deformation can occur which means the glacier moves slowly compared to glaciers in more temperate environments which have meltwater due to the pressure, and crucially the higher temperatures.
Why is ice thickness (ice size and mass) important controlling ice movement?
- The heavier the ice the more force needed to overcome increased friction
- When ice is at least 50m thick plastic flow begins, so greater thickness creates more pressure which often causes melting at the base
- Size of ice mass can also affect the rapidity of its response to change
Why is mass balance important controlling ice movement?
If there is a greater rate of ablation, then there is more meltwater, this causes faster movement as basal slippage increases
Why are feedback mechanisms important controlling ice movement?
Positive: the increased movement caused by the existence of meltwater at the base can generate increased frictional heat therefore there is even more melting and an increase in the rate of basal slip
Negative: ice thickness may increase pressure melting and basal slip, but in turn the melting will reduce ice thickness and reduce melting and basal slip.
What is erosion in glaciers?
The removal of weathered material by glacial ice, erosional processes include plucking, abrasion, crushing and basal melting
What does abrasion do to the rock bed of a glacier?
Abrasion by individual stones leads to micro features like chatter marks and striations. Abrasion by rock flour polishes the underlying rocks (sand polishing).
What is the erosional process of plucking in a glacier?
Plucking (or quarrying) occurs when meltwater freezes part of the underlying bedrock to the base of a glacier. Any loosened rock fragments are then plucked away as the glacier subsequently moves forward. Plucking’s importance as a process of eroisoon is very dependent on rock type and the incidence of pre-existing joints.
What is entrainment (in reference to glaciers)?
When small fragments are trapped/entrained in the glacier by basal ice freezing around them and applying sufficient drag to pull them along. And so, abrasion only happens because of entrainment, the dragging of small rock fragments.
What is the link between entrainment and erosion?
Plucked stones became entrained in the basal layer of the glacier and as the glacier moves abrasion occurs. Entrainment is fundamental in erosion.
What is SUPRAGLACIAL debris?
Material falling from hillsides being washed or blown on to the glacier from the surrounding land (also includes atmospheric fallout like volcanic ash).
What is SUBGLACIAL debris?
Material eroded from the glacier bed and valley walls (or material frozen to base from subglacial streams)
What is ENGLACIAL debris?
Material that has worked its way through the glacier or ice sheet
