Glaciated Landscapes And Change EQ2

Question 1

What is the accumulation zone of a glacier?

Answer 1

The area where there are inputs into the glacial budget

Question 2

What is the ablation zone of a glacier?

Answer 2

The place where there are outputs from the glacial budget

Question 3

What is dynamic equilibrium and the line of equilibrium?

Answer 3

• Dynamic equilibrium is where the accumulation and ablation levels of the glacier are equal or balanced
• The line of equilibrium is the line that separates the accumulation zone from the ablation zone. If a glacier is in dynamic equilibrium this line does not move

Question 4

What feedback loops operate in a glacial system, and how do they help to maintain equilibrium?

Answer 4

• Positive feedback loops occur and help to speed up processes. For example meltwater helps glaciers to move more
• Negative feedback loops also occur and help to maintain dynamic equilibrium. For example the meltwater from the glacier reduces the size of the glacier

Question 5

What processes increase the accumulation of a glacier?

Answer 5

• Direct snowfall increases the snow and ice mass in the glacier as fresh snow is compacted over time to create clear glacial ice
• Avalanches bring a huge mass of snow, ice and rock into the ablation zone which are also compacted into the glacial layers
• At high altitudes, strong winds blow snow into the head of the glacier which is then compacted into the glacier

Question 6

How does the process of glacial ablation happen?

Answer 6

• The main output is melting which happens close to the snout of the glacier
• Ice mass is also lost through both sublimation and evaporation on the surface of the glacier
• Ice calving also creates icebergs from the glacier where the glacier meets the sea/ocean

Question 7

What factors cause variation in the rate of accumulation?

Answer 7

• Accumulation occurs when there are high levels or precipitation and low average temperatures as there is a greater input into the glacier and less ablation
• Accumulation also increases when there are strong winds, as more snow and ice are blown into the glacier, and low levels of insolation (solar radiation)
• Greater accumulation occurs at higher altitudes and poleward facing slopes
• Positive feedback cycles also occur as greater mass balance increases the albedo effect which lowers temperatures and increases snowfall

Question 8

What factors cause variations in rates of ablation?

Answer 8

• Greater ablation occurs when there are higher average temperatures and lower levels of precipitation as there are greater levels of melting
• If glaciers are near bodies of water then ablation is increased as huge chunks of the glacier may fall into the water as ice shelves
• Increased levels of snow and ice in the accumulation zone also increase rates of ablation, as more of the glacier moves into the ablation zone which means more glacial mass is lost. This is an example of a negative feedback cycle

Question 9

How do temperate (warm based) glaciers move?

Answer 9

These glaciers move by both Basal slip and internal deformation

Question 10

How do polar (cold based) glaciers move?

Answer 10

They move only by internal deformation

Question 11

What is basal slip?

Answer 11

• The process that accounts for 75% of all glacial movement in temperate glaciers
• It occurs when glaciers meet an obstacle on the glacial slope. At the obstacle the glacier increases pressure, thereby reducing the pressure melting point to below 0 and causing the glacier to melt
• The meltwater that is present acts as a lubricant allowing the glacier to slip over the obstacle

Question 12

What is regelation creep?

Answer 12

• When basal ice deforms under pressure when encountering obstacles under 1m wide
• The Ice Will then increase up the glacier and reform in a plastic state to flow over the obstacle

Question 13

What is extensional flow?

Answer 13

• At the steep head of the glacier there is a strong gravitational force which pulls the ice downwards
• This Ice then moves quickly, around 2m a day and fractures into transverse crevasses that are 50m thick. Further down the glacier the ice is thicker (200m) and moves slower (0.5m a day)
• This movement is known as extensional flow.

Question 14

What is compressional flow?

Answer 14

• The fast ice that moves by extensional flow from the head of the glacier pushes into slower ice at the base of the glacier and compresses it
• The pressure that builds up causes the ice to crack into layers which then slip forward

Question 15

What is internal deformation?

Answer 15

Intra-granular movement:

• Where individual ice crystals become deformed and fractured due to intense stress within the ice from the glacier’s mass and 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

Question 16

When do glacial surges occur?

Answer 16

• The can occur as a result of volcanism and geothermal energy which melts the ice at the ice rock interface and so allows the glacier to move rapidly due to the large amounts of meltwater that is created
• Tectonic activity can also lead to surges as weak rock can become saturated with meltwater, allowing for the glacier to easily slip over the rock

Question 17

How does lithology control the rate of glacial movement?

Answer 17

• In temperate glacial zones, movement is faster over impermissible rock as the meltwater is unable to permeate away allowing it to be retained and aid slippage
• Easily eroded rocks (sedimentary/heavily fractured metamorphic rocks) allow temperate glaciers to move more quickly over them. This is because there is more deformable sediment

Question 18

How does altitude control the rate of glacial movement?

Answer 18

• At higher altitudes there are lower temperatures and higher levels of precipitation
• This increases accumulation and increases the glacial mass balance
• A larger mass balance increases glacial movement

Question 19

How does gravity/gradient control the rate of glacial movement?

Answer 19

• Gravity encourages glaciers to move, and the steeper the gradient the greater the gravitational pull
• Steeper slopes lead to faster movement speeds

Question 20

How does ice temperature control the rate of glacial movement?

Answer 20

• In some areas e.g. Antarctica, glacial ice is so cold that it freezes to bedrock
• This means that it either moves very slowly or doesn’t move at all
• Colder Ice does not deform as easily which further reduces it speed

Question 21

How does ice thickness control the rate of glacial movement?

Answer 21

• The greater the thickness of the ice, the more pressure is created which in turn causes faster movement
• The heavier the ice, the more force is needed to overcome increased friction caused by the extra weight

Question 22

How do feedback mechanisms control the rate of glacial movement?

Answer 22

Positive feedback:
-Increased basal meltwater will increase basal slip which increases frictional heat which produces more meltwater and increase the rate of basal slip

Negative feedback:
-Increased ice movement increases friction and so increases ice melting which reduces ice thickness and ice mass

Question 23

How do erosion and entrainment combine to alter glacial landscapes?

Answer 23

• Erosion removes weathered (weakened) material by glacial ice through plucking, abrasion, crushing and basal melting
• Entrainment is where small rock fragments are trapped/entrained by basal ice freezing around them and applying force that is sufficient to pull them along

Question 24

What is supraglacial, englacial and subglacial debris?

Answer 24

Supraglacial:
Debris that is transported in the ice surface. This debris comes from material that has fallen from hillsides or that has been blown or washed onto the glacier

Englacial:
Rock debris that is transported within the ice. It has worked its way down from the top

Subglacial:
Rock debris that is transported at the base of the glacier. This includes material that has been eroded from the glacial bed and valley walls and material that was frozen to the base of subglacial streams

Question 25

What is the role of water in the transportation of glacial material?

Answer 25

• Temperate glaciers have water flowing both on top of them and underneath them which help to carry glacial material to the glacier’s snout
• Water May flow down crevasses or holes in the ice (moulins), thus transporting material into and beneath the glacier

Question 26

What are Till and Fluvio?

Answer 26

• Till is sediment deposited directly by glacial ice

- Fluvio is sediment deposited by glacial meltwater

Question 27

What are Ice marginal glacial environments?

Answer 27

Environments at the edge of glacial ice where a combination of glacial and Fluvio-glacial processes occur

Question 28

What are proglacial environments?

Answer 28

Environments located at the front of a glacier, ice cap or ice sheet that are dominated by Fluvio-glacial processes

Question 29

What are periglacial environments?

Answer 29

Environments near glaciers that are dominated by freeze-thaw processes, but not characterised by moving ice