3.1.4.3 Geomorphological Processes Flashcards
2 ways the rigid upper layer of ice travels
Uniformly
Quickest
2 ways the plastic lower layer ice travels
None uniformly
Slowest at base
Why are glaciers slower st valley walls and base
Friction
What movement doesn’t exist in cold base glaciers
Basal slip
What’s the main movement in cold based glaciers
Internal flow
When does internal flow occur
Occurs when ice crystals orientate themselves in the direction of the glaciers movement and slide past each other
3 stages to internal flow
Jumble of ice crystals
Ice crystals align under pressure
Ice crystals now slide over one another
Why do ice crystals align in internal flow
Pressure
7 movements in warm based glaciers
Basal flow/slippage Regelation slip Creep extending flow Compressing flow Surges Rotational flow
When does basal sliding occur
When the overlying ice’s weight + friction. With bed and sides cause ice to melt
Encourages ice to move as it isn’t frozen to its base + meltwater acts as lubricant
What causes the ice to melt at the bottom of the glacier for basal flow
Pressure and friction
What 2 processes help basal flow
Regelation slip
Creep
What happens in regelation slip
Obstacles to the ice flow (small<1m) create added pressure on the ice as it begins to move over them ;causing melting which aids the passage of ice over the obstacle
What happens on the upside of the glacier in regelation slip
PMP decreases so it’s warmer and ice melts (higher pressure)
What happens on the downside of the glacier in regelation slip
PMP increases
So it’s colder
Water refreezes (lower pressure)
What are overcome by creep
Larger items
What happens in creep
The ice acts like plastic and moulds itself around the obstacle as the ice crystals change shape/deform
What’s creep all due to
Stress concentrations around larger obstacles on the bedrock floor
When does compressing flow occur
Where there’s a reduction in gradient of valley floor
What happens to the ice in compressing flow
Ice decelerates
Thickening of ice mass
What’s at it’s maximum in compressing flow
Ice erosion
When does extending flow occur
When the valley gradient become steeper
2 things the ice does in extending flow
Accelerates
Becomes thinner
What’s at it’s minimum in extending flow
Erosion
When do surges occur
When an excessive build up of meltwater under the glacier leads to ice moving forward rapidly
Who are surges a hazard to
People living in the glacial valley below the snout
How much can surges move the glacier by in a day
250-300m
Where does rotational flow occur
Within the Corrie, the birthplace of many glaciers
What happens in rotational flow
Ice moving downhill can pivot about a point producing a rotational movement
What combines with pivot water movement in rotational flow
What does this lead to
Pressure
Leads to greater erosion and an over deepening of the Corrie floor
What can happen in extending flow due to higher velocity
The surface ice can break and crack
Which flow has the most gravitational force
Extending flow
Which temperature at he base causes faster ice movement
Why
Warm
More meltwater which lubricates base
Why does ice move slower if the base is cold
Ice is frozen to bed rock and there’s more friction
What bedrock floor gradient causes ice to move faster
Why
Steeper
Greater pull of gravity
What time of year do glaciers move fastest at
Why
Summer
More meltwater lubricates ice
What thickness of ice causes ice to move faster
Why
Thicker
More potential energy but more force is needed to overcome friction
What geology causes ice to move faster
Why
Impermeable rock
As more meltwater stays on rocks base and lubricates it
Why do glaciers move slower with permeable rock
As meltwater goes into rocks and doesn’t stay on surface so less lubrication
How much friction causes ice to move faster
Less friction
Why does ice move slower with more friction
As more ice is in contact with bed and valley sides
What causes the ice in a glacier to move at different rates as it moves through a valley
The fractional drag between ice and rock
What happens as the sides and base of a glacier move slower then the centre surface ice
The ice cracks producing crevasses on the surface
2 other ways crevasses form
Where extending flow occurs (ice sped up)
Where the valley widens/ glacier spreads onto a plain
Why do crevasses form when there extending flow or widening
As the surface ice is unable to adjust rapidly enough to extra stresses by basal slip/internal flow
5 types of crevasses
Crevasses at margins (sides) Longitudinal crevasses Transverse crevasses Di radial splaying crevasses Bergschrund (large crevasses)
Why do crevasses at margins form
As frictional drag between the ice and rock of the valley sides causes the margins to move slower then the centre
What angle to crevasses open up at margins compared to old ones
New open up At an angle to the margin
Old ones may be bent/rotated round in direction of the glacial flow
When do longitudinal crevasses occur
When the glacier spreads out laterally as the valley widens so there are stresses in the ice
How do stresses in the ice act when forming longitudinal crevasses
What position do crevasses open up in
At right angles to the margins so crevasses open up parallel to the glacier margins
When do transverse crevasses occur
When a glaciers gradient steepens and extending flow occurs
What shape are transverse crevasses upglacier
Why
Convex shaped
As the ice moves faster in the centre than the sides
When do transverse crevasses close
When compressing flow occurs (gradient reduces)
Where do di radial splaying crevasses splay out
In the glacier snout region from the spreading out of ice into a lobe
What angles do di radial splaying crevasses also open up at to the direction of stresses
Right angles
What’s the bergschrund like
We’re is it
A big semi circular crevasse
at the back of a glacier
How is a bergschrund formed
By the tension caused by ice pulling away from the ice attached to the back wall
