Enquiry question two Flashcards
Describe the glacial system
What is the zone of equilibrium and what factors affect it?
The area on the glacier where there is a balance between accumulation and ablation
Depends on:
- the rates of accumulation or ablation
- the time of year/season
- glacial retreat occurs when ablation > accumulation
- glacier increases if accumulation > ablation
What processes contribute to accumulation and ablation?
accumulation
snowfall
avalanches
wind blown snow
hoar frost
ablation
windblown snow off glacier
avalanching off glacier
sublimation - ice -> water vapor without being water first
calving - breaking off of ice chunks from the glacial snout
How are moraines formed?
As the glacier advances it pushes debris in front of it
When it retreats it leaves it as a mound
As it advances again, it forms a new mound
These are moraines
How does impact on the environment depend on the speed of the glacier
Faster = more likely to impact and transform the landscape
Slower = less likely to impact it
How do glaciers erode the ground?
As glaciers move, they pick up debris
Which helps erode the base and the sides
Like sandpaper
Describe the terms on this graph and why it changes
Positive regime: occurs when accumulation > ablation
the result of seasonal changes, inputs outweighing outputs and long term change as a result of cooling climatic factors
Negative regime: occurs when ablation > accumulation
CASE STUDY The Athabasca Glacier - Canadian Rockies
Warm based
Located between the Banff and Jasper NPs
Remnants of much larger Cordilleran ice sheet - covered much of N America
Retreats between 1-3m a year - begun to speed up
Since 1750 (end of little ice age) it has retreated by 2km
Retreat can be tracked by the push moraines, (found in front as material that is bulldozed in the winter and left behind in summer)
Now believed to retreat up to 5m pa
What are the fundamental causes of ice movement
-Gravity
-Accumulate mass in upper portion and ablate in lower portion
-Ice in acc. zone builds up, the weight of it builds up downslope pressure —> known as shear stress
What do glaciers do regardless of whether it is advancing or retreating?
Moving downslope due to gravity and shear stress
What factors are involved in the speed of movement?
- degree of imbalance
- gradient between the zones of accumulation and ablation
What is basal sliding & which type of glacier does it occur in
Occurs when there is meltwater - from weight of ice decreasing the pressure melting point - beneath the glacier acting as a lubricant so the glacier can move - (slippage)
Warm based glaciers
What is basal creep & regelation creep
Occurs when a glacier moves over an obstacle
The increased localized pressure decreases the pressure melting point, causing meltwater to form, acting as a lubricant for the ice to move up and over it
What is internal deformation
Top ice layer moves faster due to less friction
What is ICE CREEP
the deformation of ice under the stress of movement due to changes in slope angle or ice thickness (creating crevasse like features at the surface)
What does an increased and a decreased gradient do?
Increased - the glacier accelerates causing ice faulting called extensional flow
Decreased - causes ice to slow down and compress leading to faulting in the ice where crevasses close up - compressional flow
basal creep images
What are crevasses
cracks that form in glacier ice when the glacier is put under too much pressure for it to deform by flowing
eg intensive stress caused by stretching if the glacier is speeding up as it flows down the valley
crevasses can also be caused by the ice flowing over bumps or steps in the bedrock
Types of crevasses
What is subglacial bed deformation
As glaciers flow over soft sediments, the movement of the ice above results in the sediments below being ground down and dragged along the direction of flow bc it is softer the glacier may speed up
this can account for 90% of forward ice movement
what factors impact the rate of movement and what are glacial surges
What are the different types of glacial erosion
ABRASION - physical weathering and grinding of a surface through friction and impact by material carried in water, or ice
PLUCKING - the process of particle detachment by moving glacial ice
basal ice freezes in rock surface cracks
as the body of the glacial ice moves, material around the ice in the cracks is pulled and plucked out
QUARRYING - an extreme form of plucking, creating steep and angular rock cliff faces
FRACTURE AND TRACTION - occurs due to the crushing effect of the weight of the moving ice over the rock
if water gets into the cracks created, then it can aid the plucking process
DILATION - occurs when the removal of weight from above reduced the pressure on the bedrock, causing it to adjust and crack and fractures open up
MELTWATER EROSION - since the water is under hydrostatic pressure, the meltwater can dissolve minerals and carry these away especially in limestone
What is glacial debris entrainment and the types?
it us the incorporation of debris onto or into the glacier
supraglacial: occurs at the surface of the glacier - washed down material, rocks plus ash from volcanoes in iceland
can make the glacier top look dirty
subglacial: occurs underneath a glacier or ice sheet
this material can get lodged and begin to deform the land and the ice
englacial: material which has worked its way down through the glacier
describe glacial sediment transportation
in ice sheets —> most material is transported subglacially via the basal layer
valley glaciers —> more englacial and supraglacial debris due to erosion at the sides
the rocks come into contact with each other, they are worn down like fluvial attrition
: . sediment movement is horizontal and vertical
meltwater also helps move it along
WHAT ARE THE FOUR GLACIAL PROCESSES
WHAT ARE THE FOUR GLACIAL PROCESSES
WHAT FACTORS AFFECT THE RATES PF GLACIAL EROSION AND MOVEMENT
WHAT FACTORS AFFECT THE RATES PF GLACIAL EROSION AND MOVEMENT
