2.A5 Different processes explain glacial movement and variations in the rates Flashcards
The fundamental cause of glacier movement is what and why, what does this increase?
Gravity, why? May be due to the greater rates of accumulation in the accumulation zone causing further pressure on weight on snow and increasing downwards slope. This is known as shear stress and increases the slope angle and therefore moves away from the zone of accumulation. This is different depending on temperate or polar glaciers.
Which zone has a quicker rate of movement and why?
Ablation due to the difference in the amount of temperature and snowfall, melting usually occurs and a lack of direct snowfall leading to a net loss of ice.
Warm-wet temperate glacier movement -
Experience greater input in winter and outputs in the summer. The overall imbalance between the two zones is greater so the glacier move downslope more rapidly to maintain the equilibrium and slow ice movement. Also the movement of warm based glaciers can be from either internal deformation or basal sliding rather than cold based who can only move by internal deformation.
Cold polar glacier movement -
This experiences slower rates of ice movement due to the rates of accumulation and especially ablation resulting in a smaller gradient between the equilibrium.
Basal slippage -
Only found in temperate glaciers and not cold based due to polar being frozen to the cold base. This relates to the presence of meltwater beneath the glacier. The process of the basal slippage and the meltwater acts as a lubricant reducing friction with the entrained debris and regulation creep allow the glaciers to slide over the bed.
Regulation creep -
Occurs only with temperate glaciers along with basal slippage.
This is where the
basal ice deforms under pressure when encountering obstacles (rocks) it increases with pressure when applied over the obstacles also increases the result of melting under this pressure. After passing the obstacle the pressure is decreased and refreezes. This overall increases the meltwater from decreasing the pressure melting point as the water acts as lubricant and the pressure water melts at is reduced.
Internal deformation -
Cold based glaciers are unable to move through basal sliding. Due to their basal temperature being below the PMP. When the slope gradient is increased there is acceleration of extensional ice flow, found common in the zone of ablation due to the steepness and gradient. Its main cause is gravity and the pressure in the accumulation zone depending on the mass of the glacier (previously discussed)
A number of other factors also affect the rate of movement these can include -
Altitude,
slope, lithology, size and variations in mass balance) with
both positive and negative feedback in the system.
What causes the highest velocity of a glacier?
Glacier surge, Where the flow instabilities and result in a dramatic increase of glacier velocity.
Altitude in the velocity of a glacier -
The higher potential energy gained from height can increases glacier movement from the main primary factor being put into play of gravity. However, tend to be mostly cold-based so can only move through internal deformation.
Mass balance - of glacier velocity. Comparison of the mass balances.
Areas of accumulation have slower rates of movement compared to areas of ablation. This also affects whether the glacier is advancing or retreating.
Slope - in glacier movement
Steeper sloped valley glaciers have higher rates of flow.
Lithology - in glacier velocity
Lithology influences bed topography, for example easily erodible rocks can create deformations which may slow down the rate of glacier movement especially in polar glaciers as temperate can experience regulation creep lowering the PMP where the pressure of the debris can cause melting acting as lubricant.
