1c. Different types of glacier and movement Flashcards
How is glacial ice formed?
- snow fall remains frozen throughout year
- fresh snow fall on top, low density, feathery texture
- new snowfall compresses previous layers (neve), forcing out air, becomes higher density ice
- if ice survives one summer, its called firn
- further compaction by snow forms glacial ice (process called diagenesis)
What colour is glacial ice and why?
bluish because of the lack of air in the ice
How long does it take for glacial ice to form?
40-1000 years
What is an ice sheet? (size?)
large accumulations of ice extending 50,000km²
Where are the only 2 current ice sheets?
- Greenland
- Antarctica (13.6 million km²)
What is a valley glacier?
Glacier confined by valley walls, between 10-30km in length
Characteristics of warm-based (temperate) glaciers?
- high altitude locations
- steep relief
- basal temperature at or above pressure melting point (creates layer of meltwater, reducing friction, helps movement)
- rapid rates of movement
Impact of warm-based glaciers on the landscape?
- rapid rates of movement cause erosion/erosional landforms
- ablation produces meltwater, causing glacio-fluvial landforms
Characteristics of cold-based (polar) glaciers?
- high latitude locations
- low relief
- basal temperatures below pressure melting point so frozen to bedrock (slow movement plucks valley floor)
- very slow rates of movement, few metres per year
Impact of cold-based glaciers on the landscape?
Limited impact, not very dynamic glaciers
Diagram of glacier temperature profiles
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What’s the most important difference between warm and cold based glaciers?
Relationship between the basal temperature and the pressure melting point
Glacial movement: factors that influence movement?
- Gravity
- Gradient
- thickness of ice (influences basal temp & pressure melting point)
- glacial budget (+=advance)
- internal temp of ice
What is the rigid zone of the glacier?
where ice is brittle and breaks, shown as crevasses
What is the zone of plastic flow?
where, under pressure, the ice deforms and behaves more like plastic
Why do the sides and base of glaciers move slower than the middle and top?
- ice may have been frozen to sides and valley floor
- obstructions - friction
Basal sliding: which type of glacier? how does it happen?
- warm based (temperate) glacier
- basal temp is above pressure melting point, thin layer of meltwater exists between glacier and valley floor, reduces friction
What 3 mechanisms does basal sliding consist of?
- slippage
- bed deformation
- creep/regualtion
Basal sliding: slippage?
Ice slides over valley floor as the meltwater reduces friction between the base of glacier and valley floor (any friction can create more meltwater)
Basal sliding: creep or regelation?
- When ice deforms under pressure due to obstructions on valley floor - Spreads around/over obstruction before refreezing when pressure is reduced
Basal sliding: bed deformation
When the ice is carried on saturated bed sediments that move along with the glacier (high pressure)
Internal deformation: what type of glacier? What type of relief does it happen on?
- cold based (polar) glaciers
- only occurs on a slope
Internal deformation: what two types of flows and how do they work?
- inter-granular flow = movement of individual ice crystals in relation to each other
- laminar flow = movement of individual layers within the glacier
Internal deformation: how does it create crevasses?
- when ice moves over a steep slope, it can’t deform fast enough so it fractures - forms crevasses
- forms slip planes
Internal deformation: how does an extending flow create crevasses?
- down slope, leading ice pulls away from ice behind it that hasn’t reached the slope yet
Internal deformation: compressing flow
- when gradient reduces, ice thickens and pushes over slower moving leading ice
