OCR A Level GL - 4 OCR A Level GL 2.1c Glacier Types and Movement Flashcards
How does glacial ice form?
Snow falls on previously fallen snow, many layers build up and the bottom layers are compacted squeezing air out, turning into granular snow and firn and then glacial ice
What is firn/névé?
Compacted granular ice that forms where snow is deeply buried.
What is the density of fresh snow?
0.05 g/cm3
What is the density of firn/névé?
0.4 g/cm3
What is the density of glacial ice?
between 0.83 and 0.91 g/cm3
What is diagenesis?
the process whereby fresh snow, over time, under compaction, becomes glacial ice.
How long does it take for glacial ice to form?
between 30-40 years in high altitude locations up to 1,000 years in high latitude locations
What are the two main types of glaciers?
- Valley glaciers 2. Ice sheets
What are the characteristics of valley glaciers?
They follow the course of existing river valleys Typically between 10-30km in length
What are the characteristics of ice sheets?
They are the largest accumulations of ice Defined by extending more than 50,000km2 Antarctica and Greenland are the only 2 ice sheets
What is the pressure melting point?
The temperature at which ice is on the verge of melting
What are the characteristics of warm-based glaciers?
- High altitude locations e.g. Alps and Rockies 2. Steep relief 3. Basal temperature at or above pressure melting point 4. Rapid rates of movement (typically between 20-200m/year)
What are the detailed warm-based glacier characteristics
Warm-based glaciers occur in temperate areas e.g. western Norway and southern Iceland Small (hundreds of metres to a few kilometres in width) There is summer melt Meltwater lubricates the glacier, leading to more movement (20 - 200m per year) and consequently more erosion, transportation and deposition All ice in warm-based glaciers is at or above pressure melting point because of the warmer atmospheric temperature, the weight of ice and the effect of geothermal heat at the bed Warm-based glaciers are associated with basal processes such as basal sliding. These promote more rapid ice flow and lead to the development of specific features such as striations and the formation of subglacial landforms (e.g. drumlins) and glaciofluvial features (e.g. eskers).
What are the characteristics of cold-based glaciers?
- High latitude locations e.g. Greenland and Antarctic 2. low relief 3. Basal temperature below pressure melting point and so frozen to the bedrock 4. Very slow rates of movement (only a fewm/year)
What are the detailed characteristics of cold-based glaciers?
Cold-based glaciers occur in polar areas, e.g. the Arctic and Antarctic. They are large, cover hundreds of square kilometres. They occur in areas of low precipitation and little snow. Therefore, there are low levels of accumulation and little to no melting as the ice stays very cold All ice in cold-based glaciers is below pressure melting point. There is very little meltwater and therefore, slow movement (only a few metres/yr). The glacier is often frozen to the bed of the glacier, meaning less erosion, transport and deposition. Cold-based glaciers have limited landscape impacts.
How does gravity influence the movement of glaciers?
it is the fundamental cause of glacial movement
How does gradient influence the movement of glaciers?
the steeper the gradient of the ground, the faster ice will move
How does thickness of ice influence the movement of glaciers?
thickness influences the basal temperature and therefore the pressure melting point, which influences movement
How does internal temperature of ice influence the movement of glaciers?
It determines the type of movement Internal Deformation OR Basal Sliding This will affect the speed of movement
How does glacial budget influence the movement of glaciers?
a positive budget causes glacial advance
What are the two mechanisms by which internal glacial ice moves?
- break apart (creating crevasses)
- internal deformation
Which part of the glacier moves the fastest?
centre of a glacier at the surface
What are the characteristics of the rigid zone in a glacier?
- Found in the upper zone of a glacier
- Ice is solid, brittle and breaks
- Crevasses form
What are the characteristics of the zone of plastic flow in a glacier?
- Found in the lower zone of a glacier, where ice is under pressure
- . Ice will deform and behave more like a plastic
What is basal sliding?
the act of a glacier sliding over the bed due to meltwater under the ice acting as a lubricant
What 3 types of basal sliding?
- Slippage
- Creep
- Bed deformation
What is slippage?
a circular motion that can cause ice to move away from the back wall of a hollow
What is creep?
a slow, downward movement of loose rock and soil down a gentle slope
What is bed deformation?
the movement of soft sediment or weak rock beneath a glacier.
When is bed deformation most effective?
beneath temperate glaciers as the underlying sediment and rock are saturated with water
Give a named example of the importance of basal sliding in glacial movement?
Franz Josef glacier in New Zealand -which is a warm based glacier that moves approximately 300m per year, and 45% of its movement is from basal sliding
What are the 2 types of internal deformation?
- Intergranular flow
- . Laminar flow
What is intergranular flow?
When individual ice crystals re-orientate and move in relation to each other
What is laminar flow?
where individual ice crystals move along layers within the glacier, often within layers of annual accumulation
Give a named example of glacial movement by internal deformation
The Meserve glacier in Antarctica moves only 3-4m per year and 100% of this movement is by internal deformation.
What is extending flow?
It is when ice moves over a steep slope and it is unable to deform quickly enough so fractures and creates crevasses. The leading ice pulls away from the ice behind it which has yet to reach the steeper slope
What is compressing flow?
It is when the gradient reduces and ice thickens. The following ice pushes over the slower moving leading ice, on planes of movement, which are all at different angles
