Glaciated Landscapes and Change EQ3

Question 1

What are the main processes of glacial erosion?

Answer 1

• Frost shattering (freeze thaw)
• Pressure release
• Plucking
• Crushing and fracturing
• Abrasion

Question 2

How do glacial erosional processes contribute to the development of corries?

Answer 2

1. A pre-glacial hollow is enlarged by nivation (freeze-thaw and removed by snow melt)
2. Snow accumulates in the hollow (alimentation), compression occurs (firm) until formation of glacial ice
3. Having reached a critical depth (>30m), the corrie is now loaded with large amounts of debris and driven by steep gradients and large inputs of snow. The cirque glacier starts to move by rotational slip and ice moves out in a rotational manner, eroding the floor by plucking and abrasion.
4. Frost shattering in the bergshrunel leads to an accumulation of debris at the base which then becomes entrained by the ice and is used ro erode the cirque floor.
5. At the front of the cirque where the pressure and thus erosion are reduced, there is a rock lip. This may be added to later by moraine deposition and and in some cirques it helps to retain a tarn

Question 3

How are aretes formed?

Answer 3

• Aretes are narrow knife edged ridges between two corries.
• They are formed when the back wall of two corries are eroded by plucking, abrasion and freeze-thaw weathering
• As the back walls erode, the corries erode towards eachother which eventually creates tge narrow ridge

Question 4

How are pyramidal peakes formed?

Answer 4

-Pyramidal peaks occur when corries erode their back walls by abrasion and plucking. In this cass it occurs with three or more corries on a single mountain top

Question 5

How are U-Shaped valleys formed?

Answer 5

• Form When narrow V-shaped river valleys are eroded by an advancing glacier
• Most erosion is done by plucking and abrasion

Question 6

How are truncated spurs formed?

Answer 6

• Truncated spurs are steep and rocky sections at the side of a trough that jut into a U-shaped valley
• These are formed when the ends of pre glacial interlocking spurs are eroded by the much less flexible and more powerful glacier

Question 7

What are hanging valleys and how are they formed?

Answer 7

• A small tributary V-shaped or U-shaped valley high above the main glacial trough floor often with a waterfall
• They are eroded by a smaller and weaker glacier that that of the main valley which means that they erode to a far shallower depth. Misfit rivers left behind are what form waterfalls

Question 8

What are ribbon lakes and how are they formed?

Answer 8

• Long narrow lakes along the floor of a glacial trough
• They occur when areas on The Valley floor experience greater erosion from either there being the confluence of two glaciers, or there being weaker rock at that part of The Valley
• Sometimes moraine can be created which dams the lake

Question 9

How are Roche moutonnés formed?

Answer 9

• At the upstream (stoss) end of the bedrock, increased pressure is caused by the resistance of the outcrop
  
  • This causes localised pressure build up, causing the pressure melting point of the glacier to fall, causing localised melting
    
    • Meltwater causes basal slip an the glacier erodes the outcrop by erosion. Entrained rock moves with the glacier, causing striations and chatter marks
• On The downslope (lee) side, reduced pressure causes the meltwater to freeze, and so the ice freezes to the rocky outcrop
  
  • As the glacier moves, the frozen rock is then plucked and entrained with the glacier
    
    • The rock places by the glacier leaves behind a jagged surface

Question 10

How are crag and tails formed?

Answer 10

• Underlying geology plays an important part in their formation
• They are formed when a large slab of resistant rock (a cragg) stops the flow of a glacier
• The Ice is then forced to move and erode around the rock where there is less resistant rock
• Material that is directly in the lee of the obstruction is protected by the cragg. This material can’t be eroded and so forms a gently sloping tail of deposited material

Question 11

What are knock and lochon landscapes?

Answer 11

• The name given to glacially scarred lowland areas
• These landscapes have alternating Roche moutonées ([knock] more resistant rock) and eroded hollows containing small lakes ([lochons] less resistant rock)

Question 12

Can corries be used to show past ice moment and extent, and are there any issues with using them?

Answer 12

-Corries can be used to show past movement but not extent

• In Britain and the northern hemisphere, most corries are orientated between the northwest and southeast, with most being northeast facing, which indicates the direction of ice movement
• As a glacier moves it turns large till rock fragments (clasts)in the direction of glacial movement. Till fragment analysis can be used to measure the orientation of a large sample of clasts, indicating glacial direction

-Although Most corries have a northern orientation, anomalies can occur

Question 13

Can glacial troughs be used to show past ice moment and extent, and are there any issues with using them?

Answer 13

• Glacial troughs can show extent but not movement
• On some U-shaped valleys it is possible to see a trimline, which indicated the height and extent to which the glacial trough was filled with ice. Below this there is evidence of glacial abrasion
• However, tributary glaciers and steeper gradients impact the thickness of the glacier which in turn impacts the height of the glacier and therefore the trim line in The Valley

Question 14

Can Roche moutonnees be used to show past ice moment and extent, and are there any issues with using them?

Answer 14

-They can show movement but not extent

• The stoss end always points upslope and therefore indicated the direction which the glacier moves from
• Striations are always formed parallel to iceflow and so always show the direction of glacial travel

-However, striations only show local movement unless there is an extensive exposed area of bedrock and they can be hard to see

Question 15

Can crag and tails be used to show past ice moment and extent, and are there any issues with using them?

Answer 15

• They can be used to show movement but not extent
• The Gail of the crag (made from deposited sediment) is deposited parallel to ice flow and shows the direction the glacier travelled in
• However, crag and tails only show glacial movement at a very local level where the more resistant cragg is

Question 16

Can ground moraine be used to show past ice moment and extent, and are there any issues with using them?

Answer 16

• It can be used to show extent but not movement
• If ground moraine was deposited over a large area then we can determine that there was a large glacier. If there is a small amount of ground moraine, then we can determine that it was a small ice mass

Question 17

Can terminal moraine be used to show past ice moment and extent, and are there any issues with using them?

Answer 17

• It can show extent but not movement
• As it is deposited at the maximum extent of the glacier, it can be used to show the extent of glacial movement

-However, as glaciers advance and retreat constantly, it could be mistaken for push and recessional moraine and therefore may not show maximum extent

Question 18

Can erratics be used to show past ice moment and extent, and are there any issues with using them?

Answer 18

• They can show both extent and movement
• The extent can be shown by the size of the erratics. Larger erratics (16,000 tonnes) can demonstrate a large mass of ice
• The movement can be worked out by establishing the source of the erratic. This can be done by matching the geology of the erratic to another landform, therefore determining the source of the ice. E.g. volcanic material from the Alison Craig in the Firth of Clyde have been found 250km south on the Lancashire plain

Question 19

What are drumlins?

Answer 19

Drumlins are rounded mounds formed parallel to ice flow, with a broad upstream end and a tapered downstream end

They can be found in: the Ribble Valley (Lancashire), the Eden Valley (Cumbria) and Northern Ireland

They are an example of equifinality, as we don’t quite know how they were formed

Question 20

What are the two theories of how drumlins are formed?

Answer 20

The Boulton-Menzies theory:

• Suggests that a drumlin is formed by deposition in the lee of a slowly moving obstacle in the deforming layer
• The obstacle of bedrock or thermally frozen material forms the core of the drumlin, and ground moraine is plastered around it

The Shaw theory:

• All drumlins were formed by subglacial meltwater in floods, causing irregularities to form in the river bed
• These irregularities were subsequently moulded into drumlins and streamlined by the advancing ice

Question 21

What are the two types of till?

Answer 21

Lodgement till: Spread onto The Valley floor beneath the ice by glaciers

Ablation till: Dropped by a glacier as it melts. The till is mainly deposited close to the snout as this is where most ablation happens. The glacier drops debris as the ice around the debris melts

Question 22

What are the different types of moraine?

Answer 22

Lateral moraine:

• A ridge of moraine along the edge of a Valley floor
• Exposed rock on The Valley side is weathered and fragments fall down on to the edge of the glacier
• This is carried along The Valley and deposited where the ice melts; parallel to ice flow

Medial moraine:

• A ridge of moraine down the middle of The Valley floor that occurs when two glaciers converge
• Material is carried and deposited when melting occurs; parallel to ice flow

Terminal moraine:

• A ridge of moraine extending across The Valley at the furthest point the glacier reached
• Advancing ice glaciers carry moraine forward and deposits it at the point of maximum advance when the glacier retreats

Recessional moraine:

• A series of ridges running cross The Valley behind the terminal moraine
• Each recessional moraine indicates a standstill during ice retreat, they show the cycle of advance and retreat

Push moraine:
-A ridge of moraine with stones tilted upwards. Any moraine material at the glacial snout will be pushed forward during this advance

Question 23

What are kames and how are they formed?

Answer 23

• They form on the ice surface

- They consist largely of sand and gravel deposited by streams in the final surges of a glacial period

Question 24

What are Kane terraces and how are they formed?

Answer 24

• They result from the infilling of a marginal glacial Lake

- When the ice melts, the Kane terrace is left as a ridge on the vale side

Question 25

What are Kame deltas and how are they forme?

Answer 25

• Smaller features that form when a stream deposits material on entering a marginal lake
• It forms small, mound like hills on The Valley floor

Question 26

What are crevasse kames and how are they formed?

Answer 26

Small hummocks deposited on The Valley floor as a result of sediment deposited in a surface crevasse

Question 27

What are eskers and how are they formed?

Answer 27

• They are long, narrow sinvous (winding or meandering) ridges of Fluvio-Glacial sand and gravel
• They form when glaciers retreat and the subglacial streams, that meandered, deposit the debris at a consistent rate, forming ridges

Question 28

How are kettle holes/kettle lakes formed?

Answer 28

• As the glacier retreats, calved chunks of ice remain in the out wash plane
• Meltwater starts to flow over the ice, covering the deposits in Fluvio-Glacial debris
• Eventually, The ice melts and the debris subsides to form a depression, which often fills with meltwater to form a kettle lake

Question 29

Can kames be used to show past ice extent and movement, and are there any issues with using them?

Answer 29

• Kames can show both extent and movement
• Since kame terraces occur at both sides of a glacier, they can show the rough extent of a glacier
• Kame terraces form parallel to ice flow and the ice margin and show movement of a glacier
• However, in a relict landscape, Kame terraces could be mistaken for deposition landforms such as lateral moraine
• Kame terraces could also be susceptible to human interference

Question 30

Can eskers be used to show past ice extent and movement, and are there any issues with using them?

Answer 30

• Eskers could be used to show ice direction, as meltwater and ice flowed in a similar direction
• However, we have assume that meltwater and ice flowed in a similar direction

Question 31

Can sandur be used to show past ice extent and movement, and are there any issues with using them?

Answer 31

• As the edge of the sandur marks the extent of glacial outwash, we can assume that that is where the greatest extent of the glacier was
• However, sandur is vulnerable to erosion, weathering and human interference

Question 32

Can meltwater channels be used to show past ice extent and movement, and are there any issues with using them?

Answer 32

-Meltwater channels can be used to reconstruct ice movement, as we can assume that the meltwater channel flowed in the same direction as ice flow

However, we have to assume that meltwater and ice flowed in similar directions