PHYSICAL GEOGRAPHY
GLACIATION
, TOPIC ONE - HOW CAN GLACIATED LANDSCAPES BE VIEWED AS SYSTEMS?
TOPIC ONE A - GLACIATED LANDSCAPES CAN BE VIEWED AS SYSTEMS
WHAT ARE GLACIATED LANDSCAPES
Glaciated landscapes are those parts of the earth’s surface that have been shaped, at least in part, by the action of glaciers
They include those places that are currently occupied by glaciers, in both high latitude locations (such as Antarctica and
Greenland) and high altitude locations (such as the Rocky Mountains and the Himalayas)
They also include those places that were glaciated in the past, such as Northern Britain
Glaciated landscapes contain many distinctive landforms produced by the erosional and depositional action of glaciers
A glacier forms when snow accumulates over time, turns to ice, and begins to flow outwards and downwards under the
pressure of its own weight.
In polar and high-altitude alpine regions, glaciers generally accumulate more snow than they lose from melting,
evaporation, or calving. If the accumulated snow survives one melt season, it forms a denser, more compressed layer called
firn. The snow and firn are further compressed by overlying snowfall, and the buried layers slowly grow together to form a
thickened mass of ice.
There are three general types of glaciers: alpine or valley glaciers, ice sheets, and ice caps
The development of a glaciated landscape over time can be viewed within a systems framework
A system is a set of interrelated objects comprising components (stores) and processes (links) that are connected together
to form a working unit or unified whole
Glaciated landscape systems store and transfer energy and material on time scales that can vary from a few days to
millennia (thousands of years)
The energy available to a glaciated landscape system may be kinetic, potential, or thermal
- It is this energy that enables work to be carried out by the natural processes that shape the landscape
The material found in a glaciated landscape system is predominantly the sediment found on valley floors in upland areas as
well as in glacial lowlands
THE COMPONENTS OF OPEN SYSTEMS
Glaciated landscape systems are open systems. This means that energy and matter can be transferred from neighbouring
systems as an input
It can also be transferred to neighbouring systems as an output
In system terms, a glaciated landscape has:
Inputs
Including kinetic energy from wind and moving glaciers, thermal energy from the heat of the Sun and potential energy from
the position of material on slopes; material from deposition, weathering and mass movement from slopes and ice from
accumulated snowfall
Outputs
As glaciers melt and retreat they lose energy and deposit debris and rock fragments, known as moraine and till. Meltwater
also flows through the glacier and exits the snout from the zone of ablation.
Many of the world's largest rivers originate in glacial landscapes, for example the Ganges, Indus and Yangtze. They may
carry vast quantities of pulverised rock ranging in size from glacial rock flour in suspension to outwash plains of sand, gravel
and boulders.
Including glacial and wind erosion from rock surfaces; evaporation, sublimation, and meltwater
Processes
The key processes at work in the glacial system are those of weathering, erosion, transportation and deposition. The
amount and rate of weathering and erosion depends on a range of factors including the temperature, local geology, slope
gradient, velocity and weight of the glacier, its thickness and the size of its load. Much of the erosion is dependent upon
movement of the ice mass. This can occur in a number of ways depending on the type of glacier (warm-based or
cold-based)
Erosion is dependant on the movement of ice mass:
, ● Basal sliding
- Occurs only in warm glaciers where temperatures are such that significant meltwater lubricates the
contact between the base layers of glacier ice and the bedrock. The meltwater occurs either as a result
of internal tunnels transferring it via surface moulins (vertical tunnels), or increased pressure as the
basal ice encounters resistant bedrock, which may reach the pressure melting point that causes basal
ice to melt.
● Internal deformation
- Occurs predominantly in cold glaciers where gravity and the pressure of ice in the accumulation zone
causes ice crystals to slide over each other in a series of parallel planes in a ‘crumpling’ deformation.
This can result in deep crevasses at the surface.
● Extensional flow
- Where the gradient becomes steeper the ice moves faster ‘stretching’ the ice mass and becoming
thinner through a series of fractures which form crevasses at right angles to the direction of flow.
● Compressional flow
- Where the gradient becomes less steep or the ice encounters a major obstacle the ice mass slows,
backs up, crevasses close and there are thrust fractures as the ice mass compresses. The increased
thickness of ice exerts greater pressure on bedrock and can result in more extensive pressure erosion.
Main erosional processes at work within the glacial system
● Abrasion
- Rock fragments and debris carried by the glacier scrape the rock below/adjacent to the ice flow in the
valley with which it has contact leaving striations (scratches) in the bedrock and incorporating the
eroded rock into the ice mass, from where it can cause erosion subsequently.
● Plucking
- Meltwater flowing along the base of the glacier freezes to the bedrock, fragments of which are ripped
out by the moving glacier.
● Rotational scouring
- As layers of rock debris accumulates on the surface of a glacier from valley sides, over successive
winters it becomes embedded within the compressed ice. Bands of slowly rotating frozen rock are then
scraped over the bedrock as the glacier moves downhill.
As coastal and fluvial systems, weathering also plays a key role in the glacial landscape
● Nivation
- Hollows form under the emerging glacier as a result of the freeze-thaw cycle and mass wasting. Over
time these may enlarge and start to form corries (see erosional landforms below).
● Frost action
- An umbrella term for freeze-thaw processes where meltwater percolates into cracks and freezes
causing fissures to expand under pressure of ice and, with repeated cycles, shatter the surrounding
rock.
● Pressure release / Dilation
- Where the variable weight of glacier ice on top of bedrock can cause fractures to open up, expand and
extend deeper.
SYSTEM FEEDBACK IN GLACIATED LANDSCAPES
When a system’s inputs and outputs are equal, a state of equilibrium exists within it
In a glaciated landscape, this could happen when the rate at which snow and ice is being added to a glacier equals the rate
at which snow and ice is being lost from glacier by melting and sublimation; as a result the glacier will remain the same size
When this equilibrium is disturbed, the system undergoes self regulation and changes its form until equilibrium is restored
This is known as dynamic equilibrium, as the system produces its own response to the disturbance. This response is an
example of negative feedback
GLACIATED MASS BALANCE
The glacier mass balance, or budget, is the difference between the amount of snow and ice accumulation and the amount
of ablation occurring in a glacier over a one year time period
The majority of inputs occur towards the upper reaches of the glacier and this area, where accumulation exceeds ablation,
is called the accumulation zone
Most of the outputs occur at lower levels where ablation exceeds accumulation, in the ablation zone
, The two zones are notionally divided by the equilibrium line where there is a balance between accumulation and ablation
The annual budget of a glacier can be calculated by subtracting the total ablation for the year from the total accumulation
A positive figure indicates a net gain of ice through the year, increasing the volume of ice and allowing the glacier to
advance or grow. The equilibrium line will, in effect, move down the valley.
A negative figure indicates a net loss of ice through the year. In this situation ablation exceeds accumulation and the glacier
will contract and retreat up-valley, along the equilibrium line
If the amount of accumulation equals the amount of ablation the glacier is in equilibrium and therefore remains stable in its
position
There will often be seasonal variations in the budget with accumulation exceeding ablation in the winter and vice versa in
the summer
It is, therefore, possible that there will be some advance during the year even if the net budget is negative and some retreat
even when it is positive
Even when in retreat, the ice in a glacier may move forwards across the equilibrium line under gravity, so it can appear that
a retreating glacier is actually advancing
Due to changes in weather conditions from year to year, the mass balance of a glacier is not constant, but can vary quite
considerable over time
Climate change can cause changes over longer-term time scales
GLACIATION
, TOPIC ONE - HOW CAN GLACIATED LANDSCAPES BE VIEWED AS SYSTEMS?
TOPIC ONE A - GLACIATED LANDSCAPES CAN BE VIEWED AS SYSTEMS
WHAT ARE GLACIATED LANDSCAPES
Glaciated landscapes are those parts of the earth’s surface that have been shaped, at least in part, by the action of glaciers
They include those places that are currently occupied by glaciers, in both high latitude locations (such as Antarctica and
Greenland) and high altitude locations (such as the Rocky Mountains and the Himalayas)
They also include those places that were glaciated in the past, such as Northern Britain
Glaciated landscapes contain many distinctive landforms produced by the erosional and depositional action of glaciers
A glacier forms when snow accumulates over time, turns to ice, and begins to flow outwards and downwards under the
pressure of its own weight.
In polar and high-altitude alpine regions, glaciers generally accumulate more snow than they lose from melting,
evaporation, or calving. If the accumulated snow survives one melt season, it forms a denser, more compressed layer called
firn. The snow and firn are further compressed by overlying snowfall, and the buried layers slowly grow together to form a
thickened mass of ice.
There are three general types of glaciers: alpine or valley glaciers, ice sheets, and ice caps
The development of a glaciated landscape over time can be viewed within a systems framework
A system is a set of interrelated objects comprising components (stores) and processes (links) that are connected together
to form a working unit or unified whole
Glaciated landscape systems store and transfer energy and material on time scales that can vary from a few days to
millennia (thousands of years)
The energy available to a glaciated landscape system may be kinetic, potential, or thermal
- It is this energy that enables work to be carried out by the natural processes that shape the landscape
The material found in a glaciated landscape system is predominantly the sediment found on valley floors in upland areas as
well as in glacial lowlands
THE COMPONENTS OF OPEN SYSTEMS
Glaciated landscape systems are open systems. This means that energy and matter can be transferred from neighbouring
systems as an input
It can also be transferred to neighbouring systems as an output
In system terms, a glaciated landscape has:
Inputs
Including kinetic energy from wind and moving glaciers, thermal energy from the heat of the Sun and potential energy from
the position of material on slopes; material from deposition, weathering and mass movement from slopes and ice from
accumulated snowfall
Outputs
As glaciers melt and retreat they lose energy and deposit debris and rock fragments, known as moraine and till. Meltwater
also flows through the glacier and exits the snout from the zone of ablation.
Many of the world's largest rivers originate in glacial landscapes, for example the Ganges, Indus and Yangtze. They may
carry vast quantities of pulverised rock ranging in size from glacial rock flour in suspension to outwash plains of sand, gravel
and boulders.
Including glacial and wind erosion from rock surfaces; evaporation, sublimation, and meltwater
Processes
The key processes at work in the glacial system are those of weathering, erosion, transportation and deposition. The
amount and rate of weathering and erosion depends on a range of factors including the temperature, local geology, slope
gradient, velocity and weight of the glacier, its thickness and the size of its load. Much of the erosion is dependent upon
movement of the ice mass. This can occur in a number of ways depending on the type of glacier (warm-based or
cold-based)
Erosion is dependant on the movement of ice mass:
, ● Basal sliding
- Occurs only in warm glaciers where temperatures are such that significant meltwater lubricates the
contact between the base layers of glacier ice and the bedrock. The meltwater occurs either as a result
of internal tunnels transferring it via surface moulins (vertical tunnels), or increased pressure as the
basal ice encounters resistant bedrock, which may reach the pressure melting point that causes basal
ice to melt.
● Internal deformation
- Occurs predominantly in cold glaciers where gravity and the pressure of ice in the accumulation zone
causes ice crystals to slide over each other in a series of parallel planes in a ‘crumpling’ deformation.
This can result in deep crevasses at the surface.
● Extensional flow
- Where the gradient becomes steeper the ice moves faster ‘stretching’ the ice mass and becoming
thinner through a series of fractures which form crevasses at right angles to the direction of flow.
● Compressional flow
- Where the gradient becomes less steep or the ice encounters a major obstacle the ice mass slows,
backs up, crevasses close and there are thrust fractures as the ice mass compresses. The increased
thickness of ice exerts greater pressure on bedrock and can result in more extensive pressure erosion.
Main erosional processes at work within the glacial system
● Abrasion
- Rock fragments and debris carried by the glacier scrape the rock below/adjacent to the ice flow in the
valley with which it has contact leaving striations (scratches) in the bedrock and incorporating the
eroded rock into the ice mass, from where it can cause erosion subsequently.
● Plucking
- Meltwater flowing along the base of the glacier freezes to the bedrock, fragments of which are ripped
out by the moving glacier.
● Rotational scouring
- As layers of rock debris accumulates on the surface of a glacier from valley sides, over successive
winters it becomes embedded within the compressed ice. Bands of slowly rotating frozen rock are then
scraped over the bedrock as the glacier moves downhill.
As coastal and fluvial systems, weathering also plays a key role in the glacial landscape
● Nivation
- Hollows form under the emerging glacier as a result of the freeze-thaw cycle and mass wasting. Over
time these may enlarge and start to form corries (see erosional landforms below).
● Frost action
- An umbrella term for freeze-thaw processes where meltwater percolates into cracks and freezes
causing fissures to expand under pressure of ice and, with repeated cycles, shatter the surrounding
rock.
● Pressure release / Dilation
- Where the variable weight of glacier ice on top of bedrock can cause fractures to open up, expand and
extend deeper.
SYSTEM FEEDBACK IN GLACIATED LANDSCAPES
When a system’s inputs and outputs are equal, a state of equilibrium exists within it
In a glaciated landscape, this could happen when the rate at which snow and ice is being added to a glacier equals the rate
at which snow and ice is being lost from glacier by melting and sublimation; as a result the glacier will remain the same size
When this equilibrium is disturbed, the system undergoes self regulation and changes its form until equilibrium is restored
This is known as dynamic equilibrium, as the system produces its own response to the disturbance. This response is an
example of negative feedback
GLACIATED MASS BALANCE
The glacier mass balance, or budget, is the difference between the amount of snow and ice accumulation and the amount
of ablation occurring in a glacier over a one year time period
The majority of inputs occur towards the upper reaches of the glacier and this area, where accumulation exceeds ablation,
is called the accumulation zone
Most of the outputs occur at lower levels where ablation exceeds accumulation, in the ablation zone
, The two zones are notionally divided by the equilibrium line where there is a balance between accumulation and ablation
The annual budget of a glacier can be calculated by subtracting the total ablation for the year from the total accumulation
A positive figure indicates a net gain of ice through the year, increasing the volume of ice and allowing the glacier to
advance or grow. The equilibrium line will, in effect, move down the valley.
A negative figure indicates a net loss of ice through the year. In this situation ablation exceeds accumulation and the glacier
will contract and retreat up-valley, along the equilibrium line
If the amount of accumulation equals the amount of ablation the glacier is in equilibrium and therefore remains stable in its
position
There will often be seasonal variations in the budget with accumulation exceeding ablation in the winter and vice versa in
the summer
It is, therefore, possible that there will be some advance during the year even if the net budget is negative and some retreat
even when it is positive
Even when in retreat, the ice in a glacier may move forwards across the equilibrium line under gravity, so it can appear that
a retreating glacier is actually advancing
Due to changes in weather conditions from year to year, the mass balance of a glacier is not constant, but can vary quite
considerable over time
Climate change can cause changes over longer-term time scales
