Ice formation and movement Flashcards
What is a snow line?
Permanent snow over in the upland areas - the lower edge is called the snow line.
What conditions causes a snow line?
Colder climate - more precipitation falls as snow.
Shorter summers - less time for the winter snow to melt.
What happens to the snow line as the climate continues to deteriorate?
It moves down the slope.
Where can a snow line be found in the world?
Sea level in Greenland, but 6,000 m on the equator.
No permanent snow cover on the British Isles - however scientists estimate that if the Scottish mountains were 200-250m higher, there would be.
Northern hemisphere - snow line has a higher altitude on the south side than the north side.
What is firn/neve and what is the explanation for the formation of it?
Snow initially falls as flakes.
Snow accumulates - compression by the upper layers gradually turns the lower layer into a more compact form - firn.
Meltwater then seeps into the gaps, freezes, and further compacts the mass.
As more snow falls, more air is squeezed out of the lower snow by the weight of the upper layers.
20-40 years, a mass of solid ice develops.
The mass changes colour from white (indicating air) to a blueish colour (little air).
This is the ice that begins to flow downhill as a glacier.
High density - 0.8.
What is a temperate (alpine) glacier?
What types of movement are used?
Likely to erode?
+ EXAMPLE.
Melt in the summer - release huge amounts of meltwater. Acts as lubricant - reduces friction.
Move by basal flow, extending/compressing flow, creep and surges.
MAINLY move by basal slippage - PMP raises temperature through pressure and friction - meltwater.
More likely to erode, transport and deposit material.
EXAMPLE: Franz-Joseph glacier, New Zealand.
What are polar (cold based) glaciers?
Movement?
Likely to erode?
+ EXAMPLE.
Temperature is permanently below OC - no melting.
Internal flow.
Little movement and erosion.
EXAMPLE: Greenland and Antarctic.
What are the characteristics of ice?
Great rigidity and strength - low-tensile strength.
Under steady pressure it behaves like a plastic, mouldable body.
Under sudden pressure it’ll break apart.
What is the upper zone of a glacier?
What is the lower zone of a glacier?
The upper zone - ice is brittle, breaking apart to form crevasses.
The lower zone - steady pressure.
Meltwater from the pressure and from friction from the bedrock - more rapid, plastic flow.
What is PMP?
Pressure melting point.
The melting point of the ice is raised slightly by increased pressure.
E.g. ice will melt at -1C rather than 0C.
Basal ice is more likely to melt at temperatures close to OC (PMP).
Relevant to TEMPERATE glaciers only.
What is internal flow/division?
Ice crystals orientate themselves in the direction of ice movement.
Allows ice crystals to slide past one another.
Where the ice movement is fast enough, crevasses may develop.
This is a main feature of a polar glacier - no meltwater.
Only move 1-2cm per day.
What is basal slippage?
Temperate glaciers only.
If the glacier moves over the bedrock, this can raise the temperature of the base ice through friction.
The lower (basal) ice can then melt, and act as a lubricant.
2-3m movement per day.
Can pick up material - can be used to erode its bed.
What is compressing flow?
Occurs when there is a reduction in the gradient of the valley.
Leads to ice deceleration and a thickening of ice mass.
Ice erosion is maximum here.
OPPOSITE to extended flow.
What is extended flow?
Occurs when the valley gradient becomes steeper.
The ice accelerates and becomes thinner - with crevasses.
Less ice erosion here.
OPPOSITE to compressed flow.
What is regulation flow/creep?
Obstacle encountered - pressure increases.
Stress builds up ice behaves like plastic - flows round/over the obstacle.
The lower the temperature the greater the pressure that is needed.
