EQ2 (2.4/5/6) Flashcards
What factors lead to ice movement?
- Gravity
- Altitude
- Ice Temperature
- Ice thickness
- Lithology
- Mass balance
- Feedback cycles
How does altitude cause ice movement?
The greater the altitude the lower the temperature. This leads to more melting occurring and more meltwater.
Why does gravity cause ice movement?
The gradient causes the ice to be pulled down the slope - the larger the mass, the faster the velocity.
How does ice temperature cause ice movement
Higher the temperature the more meltwater, therefore the more ice movement
How does Ice thickness cause ice movement?
When ice is over 50m thick, plastic flow begins, meaning ice moves faster.
How does lithology cause ice movement?
Movement is faster over impermeable surfaces as basal meltwater is retained - aiding slippage.
How does feedback mechanisms cause ice movement?
Increase meltwater will increase basal slip, which increases friction and therefore increases meltwater.
Define supra-glacial?
Material or liquid found on top of the glacier
Define sub-glacial
Material found at the bottom of a glaicer
Define englacial
Material found within a glacier
What is the difference between till and fluvio-glacial debris?
Till is deposited by glacial ice
Fluvio-glacial debris is deposited by glacial meltwater
Define ice marginal
Environment at the edge of the glacial ice where a combination of glacial and fluvioglacial processes occur.
Define pro glacial
Environments located at the front of a glacier
Define Periglacial
Environments near glaciers and dominated by freeze-thaw processes, but not characterised by moving ice.
What is an upland landscape?
Landscapes found at higher altitudes
What is an lowland landscape?
Landscapes at a lower altitudes
What is an active landscape?
A landscape currently being glaciated
What is a relict landscape?
A landscape that had formerly had glaciers
What are the inputs into a glacial system?
- Precipitation
- Strong winds (can blow snow)
- Avalanches (which are triggered by vibrations, steep slopes and heavy snowfall)
What are the two zones in a glacier?
Accumulation and ablation zomes
What is the accumulation zone?
The area where inputs into the glacier exceed outputs out of a glacier
What is an ablation zone?
An area where outputs of a glacier exceed the inputs into a glacier
What is dynamic equilibrium?
The point in which inputs are equal to outputs.
If the glacier is in a state of balance, the equilibrium will shift
What role does energy have in a glacial system?
A glacier has high potential gravitational energy at high altitude. This is converted into kinetic energy as it moves down a slope. This allows a glacier to carry out processes of erosion, transportation and deposition.
What are the main stores in a glacial system?
- Snow & Ice
What are feedback loops?
Positive feedback loops - meltwater, increased slippage, more meltwater
- White snow, very reflective, further cooling = more precipitation
What are different flows/transfers in the glacial system?
Evaporation, sublimation, meltwater flow
- More pronounced in warmer environments
- Less active in colder environments
What are outputs in a glacial system?
- Water occurs at the glacier’s snout
- Ice fronts that extend over water may break off forming ice-bergs - this is called calving.
- Evaporation and sublimation acts as an output.
What is entrainment?
Small rock frat,ents are trapped (entrained) by basal ice freezing around them and applying sufficient drag to pull them along.
What are two ways glacial movement can take place?
Basal slippage and internal deformation
What is basal slippage?
Occurs at the base of the glacier where pressure melting point is reached. This means that meltwater is present and acts as a lubricants, enabling the glacier to slide more rapidly over the bedrock.
What are two types of glaciers?
- Temperate (warm-based) glaciers
- Polar (cold-based) glaciers
What are two methods of polar glacier movement?
- Basal slippage (Basal slip)
- Internal deformation (internal flow)
How do polar glaciers move?
100% internal deformation
How do temperate glaciers move?
- Basal slippage (75%)
- Internal deformation (25%)
What are 3 types of Basal slippage?
- Enhanced basal creep & regelation creep
- Extensional & Compressional flow
- Surges
What is basal slippage?
The base of the glacier is at the pressure melting point, which means meltwater is present. This acts as a lubricant, enabling the glacier to slide more rapidly over the bedrock.
What is the difference between enhanced basal creep and regelation creep?
Enhanced basal creep - bedrock obstacles > 1m wide
Regelation creep - bedrock obstacles <1m wide
What is enhanced basal creep?
Large obstacles (>1m) cause an increase in pressure, which leads to ice plastically deform around the feature.
What is regelation creep?
Smaller obstacles (<1m wide) create a lowered localised pressure melting point (PMP), causing increased levels of meltwater, which refreezes once past the obstacle, as the PMP increases.
What is extensional flow?
At the top of the glacier, the gravitational pull is strong. This increases the velocity of ice movement, leading to more tension. This causes the ice to fracture in to thick layers. The layers slip downwards - this is called extensional flow.
What is an example of extensional flow?
Séracs
What is compressional flow?
Lower down the glaciers, ice is moving slowly, due to the reduction in gradient. This leads to faster ice arriving pushing down on the slower ice compressing it. The high pressure causes the ice to fracture and layers slip forward - this is compressional flow.
What are two examples of surges?
- geothermal activity: seismic and volcanic activity
- subglacial bed deformation
Describe how geothermal activity causes surges?
Seismic and volcanic activity can cause increased levels of meltwater, causing surges - move up to x100times faster.
What is an example of surges?
Volcanic activity can affect glacial speed in Iceland.
What is subglacial bed deformation?
(Marbles on the floor)
- Weak rock on the surface can be deformed, moving the ice on top of ice along with it.
What is internal deformation?
The deformation of ice crystals, causing the glacier to move downslope very slowly.
What are 2 types of internal deformation (internal flow)?
- Inter-granular movement
- Intra-granular movement
What is inter-granular movement?
Individual ice crystals slip and slide over EACHOTHER.
What is intra-granular movement?
Individual crystals become deformed due to stresses exerted by glacier’s mass, under influence of gravity. This leads to gradual movement downhill.
