Why and how different glaciers move

1. Glacier Movement
Lower Sixth

2. What we’ll learn today
• The mechanisms that cause glaciers to move

3. How they Move
• The fundamental cause of ice movement is
gravity
• Glaciers flow downslope because they
accumulate mass (ice) in their upper portions
(from precipitation and from wind-blown snow)
and ablate (melt, sublimate and calve ice
bergs) in their lower portions.
• As the ice in the accumulation zone builds up
over time the weight of it builds up a
downslope pressure (Known as Shear Stress)
• This increases as the slope angle increases
and once it is greater than the resisting forces
the glacier moves downward

4. • This forward
movement continues
regardless of whether
the glacier is
advancing or retreating
as seen below:

5. The different types of Glaciers
• The only factors to consider in the speed is degree of
imbalance and the gradient between the zones of
accumulation and ablation.
• WARM wet based glaciers experience greater snowfall in
winter and faster ablation in the summer therefore the
imbalance between them is greater so the glacier moves
down the slope more rapidly to maintain equilibrium
• COLD based glaciers have slower rates of accumulation
and even slower ablation rates therefore the ice moves
more slowly

6. Glacial System Diagram

7. Movement occurs in different ways
• Basal Sliding
• Occurs when there is meltwater beneath the glacier acting as a lubricant
so the glacier can move (called slippage) (Warm based glaciers)
>>WATCH<<

8. WARM BASED GLACIER
Move by basel slip and internal deformation
POLAR GLACIER
Move only by internal deformation
SURGES
Glaciers can advance up to 100 x
there normal rates they are usually
caused by enhances basal creep due
to a build up of meltwater at the ice-
rock interface
INTERNAL DEFORMATION
The weight of the glacier
causes ice crystals to deform
so the glacier moves slowly
downslope
Or individual layers of the
glacier move forward
BASEL SLIP
Glaciers can slide because ice melts under
pressure, resulting in a film of water acting as
a lubricant
CREEP AND REGELATION
Enhanced basal creep is best for
causing ice to deform around
large debris deposits, such as
boulders.
Regelation slip is the process of
melting and refreezing of ice
over small deposits
EXTENSIONAL AND
COMPRESSIONAL FLOW
Over steep slopes basal sliding
increases and ice accelerates
and thins (extensional)
Over shallow slopes basal slip
slows and ice thickens
(Compressional flow)

10. Internal Deformation
• Ice under stress from movement deforms this is called ICE
CREEP and results from ice thickness increases or
changes in slope angle
• Where the ice creep can’t respond quick enough ice
faulting occurs which can create crevasse like features
at the surface
• When gradient increases = the glacier accelerates
causing ice faulting extensional flow
• Decreased gradient – decreased acceleration of ice
causing the ice to compress which leads to faulting in the
ice where crevasses close up

11. Regelation Creep
• >>HERE<<

12. Extensional and Compressional Flow

13. Crevasses
• Transverse crevasses form across a glacier in a region where the speed is
increasing, which causes stretching in the direction of glacier flow. They fan
across the glacier, common in the accumulation zone and near steepening
slopes
• longitudinal crevasses (parallel) to flow form in the direction of a glacier flow, and
where ice slowly
spreads out sideways to cover a larger area. Commonly found near the
terminus of glaciers

15. Sub Glacial Bed Deformation
• When a glacier moves over relatively weak or
unconsolidated rock and the sediment itself deforms under
the weight of the glacier moving it is called Sub Glacial
Bed Deformation
• Locally this can account for up to 90% of forward ice
movement
• Further help on glacial movement can be found
>>HERE<<

16. Velocity of Glacier Ice
• Overall warmer glaciers move faster than colder ones due
to basal sliding and internal deformation. Even greater
speeds can be achieved when the glacier moves over
deformable sediment.
• There are a number of factors that can impact upon the
rate of movement:
– Altitude - (Affects temp + Precipitation)
– Slope - (Angle of slope affects flow)
– Lithology - (Impacts upon basal sliding and potentially Sub
Glacial Bed Deformation
– Size - affects the rapidity of response
– Mass Balance - Affects the equilibrium of the glacier and whether
its advancing or retreating

17. Velocity
• The highest velocities occur during glacial surges where at
times the glacier collapses when the mass ad slope of ice
build up to critical levels within the accumulation zone
• These are rare events and only occur in about 4% of
global glaciers but ice can race forward at up to 100 times
normal velocity

18. Using graph paper draw the glacial movements to compare:
Glacier Movement
GLACIER COUNTRY BASAL SLIDING (%) INTERNAL DEFORMATION (%) ICE THICKNESS (%)
Aletsch Switzerland 50 50 137
Tuyuk Su Kazakhstan 65 35 52
Salmon Canada 45 55 495
Upper Athabasca Canada 75 25 322
Lower Athabasca Canada 10 90 209
Blue USA 9 91 26
Vesl-Skautbreen Norway 9 91 50
Meserve Antarctica 0 100 80
1. Basal sliding against internal deformation
2. internal deformation against thickness
• what relationships if any are there?

19. ANSWER
0
20
40
60
80
100
120
basal sliding
internal deformation

20. Now using the same dataset can you work out the mean, median
and mode of each?
Glacier Movement
GLACIER COUNTRY BASAL SLIDING (%) INTERNAL DEFORMATION (%) ICE THICKNESS (%)
Aletsch Switzerland 50 50 137
Tuyuk Su Kazakhstan 65 35 52
Salmon Canada 45 55 495
Upper Athabasca Canada 75 25 322
Lower Athabasca Canada 10 90 209
Blue USA 9 91 26
Vesl-Skautbreen Norway 9 91 50
Meserve Antarctica 0 100 80

21. What are the mean, median and mode and
why would we use it?
• Mean
– This is the average and makes use of all numbers and gives a simple overview of the whole dataset
– It works best when numbers have a fairly narrow range
– When there are anomalies (significantly Higher or lower numbers) it may not be useful
• Median
– This is the middle value when ranked smallest to largest
– Not affected by extremes
• Mode
– Easiest measure of central tendency can be used for categorical data (Data divided into groups
(e.g.Race, gender etc)
– Mean and median can only be used for ordinal data (statistical data)
– Not affected by extremes
– Can have no modal value if all data only appears once (Or more than one)
(All of these are very easy to work out using excel spreadsheets)