EQ2

Question 1

What factors control the rate of glacier movement?

Answer 1

Altitude, gravity/gradient (slope), ice temperatures, ice thickness (size and mass), lithology, and mass balance (e.g. rate of ablation.

Question 2

How does lithology (different rock types and their characteristics) affect the rate of glacier movement?

Answer 2

In temperate zones, movement is faster over impermeable surfaces, because basal meltwater is retained - aiding slippage. However, if bedrock is permeable then the meltwater may be able to soak away (percolate), slowing the movement of a glacier. Furthermore, easily eroded rocks (e.g. sandstone, heavily fractured metamorphic rock) are more prone to bed formation and warm-based glaciers can reach great velocities when they move over deformable sediment.

Question 3

How does altitude affect the rate of glacier movement?

Answer 3

-Affects the temperatures and precipitation inputs.
-The greater the precipitation and lower the temperature, the greater the chance of supply of snow and ice, and an increase in mass balance.
-Higher snowfall leads to greater accumulation and faster movement.

Question 4

How does gravity/gradient (slope) affect the rate of glacier movement?

Answer 4

-Slope can be directly related to flow - steeper slopes lead to faster speeds.
-Gravity encourages ice to move - and the steeper the gradient, the greater the pull of gravity.

Question 5

How does ice temperature affect the rate of glacier movement?

Answer 5

-Colder ice moves more slowly as it does not deform as easily, and it stays stuck to bedrock more.
-In some environments, e.g. Antartica, ice is so cold that it’s frozen to bedrock. So polar glaciers move more slowly than temperate glaciers.

Question 6

How does ice thickness (size and mass) affect the rate of glacier movement?

Answer 6

-Size can affect the rapidity of response.
-Mass balance, which affects the equilibrium of the glacier and also whether it is advancing or retreating.
-When ice is 50m thick plastic flow begins, so greater thicknesses create more pressure in the ice which causes faster movement.
-The heavier the ice (i.e. the greater its mass), the more force is needed to overcome increased friction caused by extra weight.

Question 7

How does mass balance (e.g. rate of ablation) affect the rate of glacier movement?

Answer 7

-Mass balance, which affects the equilibrium of the glacier and also whether it is advancing or retreating.
-Rate of ablation - the more meltwater there is, the faster the movement as basal slippage increases.

Question 8

Explain the role of feedback cycles in affecting the rate of movement of glaciers:

Answer 8

The rate of movement varies not only between glaciers, but also over time for individual glaciers, as a result of changes in inputs and feedback cycles. For example, an increase in basal meltwater will increase basal slip, which could promote a positive feedback cycle by generating increased frictional heat and therefore a further increase in the rate of basal slip. Alternatively, negative feedback can occur, e.g. an increase in ice thickness may increase pressure melting and basal slip so the ice moves faster, but in turn this will reduce ice thickness and therefore lead to reduced pressure melting and basal slip.

Question 9

What is sublimation?

Answer 9

The change from the solid state (ice) to gas (water vapour) with no intermediate liquid stage (water).

Question 10

What is the accumulation zone of a glacier?

Answer 10

Where there is a net gain of ice over the course of a year. Here glacial inputs exceed outputs.

Question 11

What is the ablation zone of a glacier?

Answer 11

This is where there is a net loss of ice during a year. here outputs exceed inputs.

Question 12

What are the inputs in a glacier system?

Answer 12

-The main input is direct precipitation in the form of snowfall. As this snow is increasingly compacted over many years, it turns from low-density white ice crystals (snowflakes) to high-density clear glacial ice.
-Avalanches from mountainsides.
-Wind deposition - strong winds at high altitudes blow snow onto the glacier.

Question 13

Explain the stores/components in a glacial system?

Answer 13

-The main stores are snow and ice.
-There may be seasonal variations in the size of these stores (particularly in more temperate regions, where there can be significant winter snowfall and summer melting).
-Over the last 30 years or so, the stores of many of the world’s glaciers have shown a decline in mass, which has been attributed to climate change and global warming.

Question 14

What are the outputs in a glacial system?

Answer 14

-The main output is water, which results from melting close to the glacier’s snout (where temperatures are higher).
-Where the ice front extends over water (e.g. ice shelves in Antartica), huge chunks of ice may break off to form icebergs. This process is called carving.
-The processes of evaporation and sublimation also act as outputs.

Question 15

What is meant by the term ‘dynamic equilibrium’ in a glacial system?

Answer 15

Many physical systems move towards a state of dynamic equilibrium, where landforms and processes are in a state of balance. In a glacial system, the equilibrium line marks the boundary between the accumulation zone (glacial inputs) and the ablation zone (glacial outputs). If the glacier is in a state of balance - where inputs equal outputs - the equilibrium line will remain in the same place. As this balance shifts, the equilibrium line will move up or down the glacier (hence the term ‘dynamic’ equilibrium).

Question 16

What role does ‘energy’ have in a glacial system?

Answer 16

A glacier’s mass combines with the force of gravity to generate potential energy. As the glacier moves, this movement is converted into kinetic energy, which enables the glacier to carry out the process of erosion, transportation - and ultimately deposition. Meltwater facilities the conversion of the potential energy into kinetic energy (work).

Question 17

What are flows/transfers of a glacial system?

Answer 17

There are many flows and transfers of energy and material. These include processes such as evaporation, sublimation, meltwater flow and the process of glacial movement (internal deformation and basal sliding). Flows and transfers are ore pronounced and active in warmer environments (where there are significant seasonal variations in temperature). In the world’s coldest environments, such as Greenland and Antartica, glacial systems are less active.

Question 18

Do feedback loops occur in a glacial system?

Answer 18

Positive and negative feedback loops are significant aspects of all geomorphic systems:
-Negative feedbacks regulate systems to establish balance and equilibrium.
-Positive feedbacks enhance and speed up processes, promoting rapid change.
Both positive and negative feedbacks occur in glacial systems.

Question 19

Is the glacial system an open system?

Answer 19

Think of a glacier as an open system - with inputs from, and outputs to, other systems (such as the hydrological system).

Question 20

What is the glacial mass balance?

Answer 20

-Whether a glacier is growing or shrinking, depends on the balance between accumulation and ablation. The year-to-year change in this ice budget is known as the mass balance of the ice. It’s calculated by dividing the glacier into two zones: the accumulation zone and the ablation zone.
-The mass balance varies over the course of a year. Ablation is at its highest during the summer (due to rapid melting of the ice). However, during the winter, higher amounts of snowfall and limited melting result in accumulation exceeding ablation.

Question 21

How does gravity cause the movement of ice?

Answer 21

The fundamental cause of ice movement is gravity. Ice moves downslope from higher altitudes to lower areas either on land or at sea level. As the ice mss builds up over time in the accumulation zone, the weight of the snow and ice exerts an increasing downslope force due to gravity (known as shear stress). Shear stress increase as the slope angle increases and, once the shear stress is great e ought to overcome the resisting forces of ice strength and friction, the glacier pulls away and moves downward from the zone of accumulation. The momentum of the ice’s movement towards the ablation zone prevents further build-up, thereby maintaining the glacier at a state of dynamic equilibrium with the slope angle. This forward movement of glacial ice towards the margins/snout, occurs regardless of whether the glacier as a whole is advancing or retreating.

Question 22

How does the process and rate of glacier movement depends on the temperature and the pressure melting point of the ice?

Answer 22

The process and rate of glacier movement will depend on the temperature of the ice and whether the pressure melting point is reached. At the surface of the glacier the melting point is 0ºC, but with increased ice depth the melting point is fractionally lowered by the pressure of the overlying ice.
-Most temperate (warm-based) glaciers reach the pressure melting point, and therefore produce a great deal of meltwater, which lubricates and increases the rate of movement by a number of processes collectively known as basal slip.
-Polar (cold-based) glaciers are too cold to reach the pressure melting point, meaning that they are frozen onto the bedrock and movement only occurs by a process called internal deformation.

Question 23

What different movement processes occur at temperate and polar glaciers?

Answer 23

-At temperate (warm-based) glaciers, they can move by both basal slip and internal deformation. The basal slip can account for up to 75% of glacier movement, compared to internal deformation only accounting for 25% of glacial moves,ent in warm-based glaciers.
-At polar (cold-based) glaciers, they move only by internal deformation.

Question 24

What is basal slippage (basal slip)?

Answer 24

This occurs when the base of the glacier is at the pressure melting point, which means that meltwater is present and acts as a lubricant, enabling the glacier to slide more rapidly over the bedrock. Basal slip can be further subdivided into several processes: enhanced creep, regelation creep, extensional flow, compressional flow, and surges.

Question 25

What is enhanced basal creep and regulation creep?

Answer 25

-Enhanced basal creep - Basal slip is enhanced by obstacles on the valley floor. A large bedrock obstacle (>1m wide) causes an increase in pressure, which makes the ice plastically deform around the feature (creep).
-Regelation creep - Smaller obstacles (<1m wide) will cause pressure-melting, increasing ice movement by basal slip. The ice freezes on the down glacier (lee) side of the obstacle. The process of melting under pressure and refreezing is known as regelation.

Question 26

What is extensional and compressional flow?

Answer 26

-Extensional flow - Over steep slopes, the rate of basal slip will increase and the ice will accelerate and thin. This is known as extensional flow. It accelerates due to there being a strong gravitational potential force pulling the ice downwards. When ice moves more quickly there’s more tension, causing the ice to fracture into thin layers. The layers then slip downwards.
-Compressional flow - Over shallower slopes, basal slip slows and the ice decelerates and thickens. This is known as compressional flow. The faster ice from the head of the glacier pushes down on the slower ice and compresses it. The higher pressure causes the ice to fracture into layers, and the layers slip forwards.

Question 27

What are surges?

Answer 27

In these short-lived events a glacier can advance substantially, moving up to 100 times faster than normal. They have various causes (e.g. earthquakes/seismic activity), but the most common is enhanced basal sliding triggered by the build-up of meltwater at the ice-rock interface, such as after geothermal/volcanic activity.
It can also be caused by subglacial bed deformation, which occurs locally when a glacier moves over relatively weak or unconsolidated rock. The sediment itself can deform under the weight of the glacier, moving the ice ‘on top’ of it along with it. Locally this process can account for up to 90% of the forward motion of glacier ice, often in poly thermal outlet glaciers as in Iceland.

Question 28

How does internal deformation (internal flow) occur?

Answer 28

Internal deformation occurs through:
-Intra-granular movement - Where individual ice crystals become deformed or fractured due to the intense stresses within the ice (as exerted by the glaciers mass under the influence of gravity). Gradually, the mass of the ice deforms and moves downhill in response to gravity.
-Inter-granular movement - Where individual ice crystals slip and slide over each other.

Internal deformation occurs in both polar and temperate glaciers, and the movement is estimated to be up to 1-2cm a day.

Question 29

Glacial processes:

Answer 29

Erosion, entrainment, transport, deposition.

Question 30

Distinguish between the following term: supraglacial, englacial, subglacial.

Answer 30

-Supraglacial - Sources include material falling from hillsides being washed or blown onto the glacier from the surrounding land, plus atmospheric fall-out such as volcanic ash (a common feature on Icelandic glaciers).
-Englacial - This is material that has worked its way down through the glacier or ice sheet.
-Subglacial - Sources include material eroded from the glacier bed and valley walls, material frozen to the base from subglacial streams.

Question 30

Distinguish between the following term: supraglacial, englacial, subglacial.

Answer 30

-Supraglacial - Sources include material falling from hillsides being washed or blown onto the glacier from the surrounding land, plus atmospheric fall-out such as volcanic ash (a common feature on Icelandic glaciers).
-Englacial - This is material that has worked its way down through the glacier or ice sheet.
-Subglacial - Sources include material eroded from the glacier bed and valley walls, material frozen to the base from subglacial streams.

Question 31

Distinguish between till and fluvial-glaical debris:

Answer 31

Till is sediment deposition directly by glacier ice. Fluvio-glacial debris is deposited by glacial meltwater.

Question 32

Distinguish between ice marginal, proglacial and periglacial:

Answer 32

-Ice marginal - Environments at the edge of the glacial ice where a combination of glacial and fluvioglacial processes occur.
-Proglacial - Environments located at the front of a glacier, ice cap or ice sheet and dominated by fluvioglacial processes.
-Periglacial - Environments near glaciers and dominated by freeze-thaw processes, but not chart reprised by moving ice.

Question 33

Distinguish between upland and lowland landscapes:

Answer 33

-Upland glacial landscapes - are those at higher altitudes in hills and mountains.
-Lowland glacial landscapes - are those at lower altitudes on valley floors ad coastal plains.

Question 34

Distinguish between active and relict landscapes:

Answer 34

-Active glacial landscapes - Currently experience glaciation, active glacial processes and landform development.
-Relict glacial landscapes - Are not currently characterised by glaciers but feature fossilised glacial landforms due to past glaciation.

Question 35

How can glaciers be classified according to the temperature of their base?

Answer 35

Temperate (warm-based) and Polar (cold-based) glaciers
Glaciers can be classified according to the temperature of their base.
1. In warm-based glaciers, the base is warmer than the melting point of ice. It’s warmer because of heat from friction caused by the glacier moving, or because of geothermal heat from the Earth. The ice at the bottom of the glacier melts, and the meltwater acts as a lubricant, making it easier for the glacier to move downhill. Ice at the surface also melts if the temperature reaches 0 degrees Celsius, and meltwater moves down through the glacier, lubricating it even more. Lots of movement means lots of erosion.
2. In cold based glaciers, the base is cold so there is very little melting. The ice is frozen to the base of the valley, so there’s very little movement. There’s hardly any melting at the surface either, even in the summer. This means that cold-based glaciers don’t cause very much erosion at all.

Question 36

How fast do glaciers move?

Answer 36

-Polar glaciers move almost exclusively by internal deformation, so their movement is slow (as are their rates of erosion and sediment transfer). Greenland’s Jakobshavn Glacier moves unusually quickly; polar glaciers generally move only a few metres a year. Canada’s Saskatchewan Glacier (see Figure 3B) is more typical of glacier speeds.
-With temperate glaciers, internal deformation combined with basal slip results in greater movement and higher rates of erosion and sediment transfer. Temperate glaciers move at between 2 and 200 metres a year (with, for example, the Mer de Glace in the French Alps moving at about 70 metres a year - like Canada’s Saskatchewan Glacier).

Question 37

Explain the role of water in the transportation of glacial material:

Answer 37

Water, as well as ice, has an important role in the transportation of material. In temperate environments, water flows on top of glaciers - leading to fluvial transport. This water may flow down crevasses or holes in the ice (moulins), and thus transport material into and beneath the glacier. Temperate glaciers also have meltwater streams flowing under the ice, which carry material to the glaciers snout and beyond.

Question 38

What are the two main types of glacial erosion?

Answer 38

Abrasion and Plucking.

Question 39

What is glacial deposition?

Answer 39

The deposition of sediment transported by the ice occurs when it melts - mainly in the ablation zone close to the glacier’s snout. Here the sediment on - and in - the ice simply melts out. Water may then carry the sediment further away from the ice, sometimes over distances of many kilometres.

Question 40

How does abrasion occur due to a glacier?

Answer 40

-Abrasion occurs because of entrainment - ice includes angular frost-shattered material, which scours the landscape. Large rocks carried below the ice often scratch the bedrock to form striations or scratches.
-Abrasion by individual class (stones), which leads to micro-features such as striations and chatter marks.
Additionally rock flour (grade sizes under 0.1 mm in diameter) polishes the underlying rocks by ‘sand paper’ action.

Question 41

How does plucking occur due to a glacier?

Answer 41

-Plucking or quarrying occurs when meltwater freezes part of the underlying bedrock to the base of a glacier. Any loosened rock fragments are then
‘plucked’ away as the glacier subsequently slips forward.
-Plucking is often referred to as glacial quarrying.
Quarrying is a two-stage process with the initial widening of the joints by fracture and the subsequent entrainment of any loosened material. The importance of plucking as a process is clearly very dependent on rock type and the incidence of preexisting joints.

Question 42

Glacial transportation:

Answer 42

Glaciers act like giant conveyor belts, which transport material from mountainous areas onto adjoining lowlands. Material can be carried in three ways:
* Supraglacial - mainly weathered material carried on top of the ice (see Figure 2).
* Englacial - formally supraglacial material, but now buried by fresh snowfall and carried within the ice.
* Subglacial - material carried below the ice, which is dragged and pulverised by the overlying glacier.
Water, as well as ice, has an important role in the transportation of material. In temperate environments, water flows on top of glaciers - leading to fluvial transport. This water may flow down crevasses or holes in the ice (moulins), and thus transport material into and beneath the glacier. Temperate glaciers also have meltwater streams flowing under the ice, which carry material to the glacier’s snout and beyond.

Question 43

Landform evidence:

Answer 43

The landforms created by glacial processes differ in upland and lowland areas. Upland areas are characterised by erosional landforms, such as corries, glacial troughs and hanging valleys. Lowland areas tend to have more depositional landforms, such as outwash plains and glacial till deposits. The presence of boulder clay in East Anglia and along the Holderness coast tells us that these are areas of glacial deposition that represent former outwash plains. Corries, tarns and glacial troughs found in the Lake District provide evidence that glaciers were active in that area.

Question 44

How does fracture and traction occur due to a glacier?

Answer 44

Fracture and traction occur as a result of the crushing effect of the weight of moving ice passing over the rock and variations in pressures lead to freezing and thawing of the meltwater (basal melting), which aids the plucking process.

Question 45

How does dilation occur due to a glacier?

Answer 45

Dilation occurs as overlying material is moved, causing fractures in the rock parallel to erosion surfaces as the bedrock adjusts to the unloading.

Question 46

How does meltwater erosion occur due to a glacier?

Answer 46

Meltwater erosion can be both mechanical (similar to Aluvial erosion, except that the water is under hydrostatic pressure) and chemical, whereby glacial meltwater can dissolve minerals and carry away the solutes, especially in limestone rocks.

Question 47

Glacial deposition:

Answer 47

Glacial deposition occurs when material is released from the ice at the margin or the base of a glacier. Deposition may occur directly on the ground (ice contact) or sediments may be released into meltwater. Deposition mechanisms include: release of debris by melting or sublimation of the surrounding ice, lodgement of debris by friction against the bed, deposition of material from meltwater, and disturbance and remodelling of previously deposited sediments.