Lesson 5

Question 1

What are the 3 circumstances under which glaciers generally deposit their load?

Answer 1

• When the velocity is reduced
• When they become overloaded with debris
• When ablation increases

Question 2

Why do glaciers deposit their load when velocity is reduced?

Answer 2

As the glacier slows down, it has less power to move material

Question 3

Why do glaciers deposit their load when they become overloaded with debris?

Answer 3

The glacier tends to drop things

Question 4

Why do glaciers deposit their load when ablation increases?

Answer 4

The glacier starts melting, leading to material in it being dropped

Question 5

What is glacial till?

Answer 5

Debris underneath the ice

Question 6

What is the transport of glacial till like?

Answer 6

It can be transported hundreds of miles to areas with different geology

Question 7

What is supraglacial debris?

Answer 7

Glacial debris carried on top of the glacier

Question 8

Where does most supraglacial debris come from?

Answer 8

Freeze-thaw action

Question 10

What is englacial debris?

Answer 10

Glacial debris located within the glacier

Question 11

What is subglacial debris?

Answer 11

Glacial debris located at the bottom of a glacier

Question 12

What are erratics?

Answer 12

Debris carried by glacier which is made up of a different type of rock to the bedrock it now rests upon

Question 13

How are erratics carried?

Answer 13

Supraglacially

Question 14

Explain the formation of erratics:

Answer 14

• Rock debris falls onto the glacier due to freeze-thaw or plucking of valley sides
• It is then transported on/in the glacier
• It is deposited when ablation increases, so it can no longer carry the weight

Question 15

How can you tell where erratics have come from?

Answer 15

Geology
e.g. erratics found in boulder clay in Northumberland have travelled from Scandinavia

Question 16

Processes of glacial deposition
What is lodgement till?

Answer 16

Subglacial material that becomes lodged in the glacier bed

Question 17

Give an example of a landform formed by lodgement till:

Answer 17

Drumlins

Question 18

Processes of glacial deposition
What is ablation till?

Answer 18

Material dumped by a melting glacier that is no longer able to carry debris

Question 19

Give an example of a landform formed by ablation till?

Answer 19

Terminal moraine

Question 20

Processes of glacial deposition
What is deformation till?

Answer 20

Where weak bedrock is moved by the glacier as it turns to sediment

Question 21

Give an example of deformation till:

Answer 21

Rock flour

Question 22

Processes of glacial deposition
What is flow till?

Answer 22

When high meltwater content causes glacial debris to flow during deposition
Also produces rock flour

Question 23

Lodgement Till
When does it form?

Answer 23

When subglacial debris gets stuck or ‘lodged’ in the bed

Question 24

Lodgement Till
Where can it occur within the ice?

Answer 24

Anywhere, generally occurs where subglacial load is high and therefore the erosive ability of the ice is reduced

Question 25

Lodgement Till What are some characteristics?

Answer 25

Compared to ablation till: - More rounded - Less angular - Elongated and orientated to the flow of ice (geology of rocks face the same way)

Question 26

What can both lodgement and ablation till form?

Answer 26

Large flat till plains like the ones found in East Anglia and Minnesota

Question 27

Ablation Till What causes it?

Answer 27

The melting of ice around the debris

Question 28

Ablation Till What sort of sediments does it usually come from?

Answer 28

Supraglacial sediments, derived from freeze-thaw eroded material

Question 29

Ablation Till Where is debris carried?

Answer 29

Into the ablation zone and deposited towards the snout of the glacier

Question 30

Ablation Till What are some characteristics?

Answer 30

Compared to lodgement till: - More angular (less altered by abrasion) - Less spherical - Less compact - Reduced amount of glacial flour

Question 31

Flow Till Due to the high meltwater content, how is material deposited?

Answer 31

Material flows during deposition With so much small material, it can act like a fluid

Question 32

Flow Till How is material carried?

Answer 32

Usually supraglacially

Question 33

Flow Till What are some characteristics?

Answer 33

- Finer - More angular, less spherical - Has evidence of sorting

Question 34

Name the different types of moraines: 6

Answer 34

- Drumlins - Lateral moraines - Medial moraines - Terminal moraines - Recessional moraines - Hummocky moraines

Question 35

What type of features are moraines?

Answer 35

Ice contact features

Question 36

Drumlins What type of till are they primarily made of? What size are they? How do they show ice direction?

Answer 36

1. Primarily made of lodgement till 2. 10-50m high and 200-2000m long 3. They are stoss and lee features - the steeper, blunt end is the stoss end

Question 37

Drumlins How are they formed?

Answer 37

Drumlins form through the deposition of glacial till beneath the glacier. As ice moves over the till, it shapes it into a streamlined mound

Question 38

Drumlins Where are they found?

Answer 38

- They are often found in swarms, forming a basket of eggs topography - They are typically found in lowland areas, often regularly spaced

Question 39

Drumlins What is the elongation ratio about?

Answer 39

The elongation ratio is used to measure the shape: length of drumlin -------------------------- = elongation ratio maximum width Greater elongation suggests a more powerful ice flow

Question 40

Lateral moraines Where do they form?

Answer 40

A lateral moraine forms along the sides of a glacier

Question 41

Lateral moraines How do they form?

Answer 41

As the glacier scrapes along, it tears off rock and soil from both sides of its path This is left at the side of the glacier, forming a lateral moraine

Question 42

Medial moraines Where do they form?

Answer 42

Where 2 tributary glaciers come together

Question 43

Medial moraines Why are they generally not preserved after ice retreats?

Answer 43

They are generally features found on the surface of the ice, consisting of rock that has fallen from a rock wall where the glaciers converged. Due to them being thin and surficial, they are rarely preserved after ice retreats.

Question 44

Terminal moraines What do they mark?

Answer 44

The maximum limit a glacier advanced

Question 45

Terminal moraines How are they formed?

Answer 45

As the glacier accumulates, debris accumulates at the snout. As the glacier ablates, ablation till is added to this snout. When the glacier retreats, the terminal moraine is left behind as a prominent feature.

Question 46

Terminal moraines How is their shape significant?

Answer 46

They mirror the shape of the ice margin at the time of deposition

Question 47

Recessional moraines Where do they form?

Answer 47

They form behind the terminal moraine

Question 48

Recessional moraines How do they form?

Answer 48

Debris accumulates during short-lived phases of glacier advance or a standstill disrupting the general pattern of glacier retreat They may form on a yearly basis in some locations

Question 49

Hummocky moraines How do they form?

Answer 49

Used to be thought it was due to ice stagnation (ice wouldn't move and would drop all its debris without moving when it melted) however its now believed they are polygenetic landforms, forming over multiple ice ages

Question 50

Hummocky moraines What do they look like?

Answer 50

A chaotic pattern of small, irregular mounds, that are typically mounded in shape.

Question 51

Name the ice-marginal moraines

Answer 51

- Lateral - Medial - Terminal - Recessional - Hummocky All linear in topography except for hummocky which are non-linear

Question 52

Give an example of a location with drumlins

Answer 52

Drumlin Belt, Ireland

Question 53

Give an example of a location with lateral moraines

Answer 53

Langdale

Question 54

Give an example of a terminal moraine

Answer 54

Valparaiso moraine

Question 55

Give an example of a recessional moraine

Answer 55

Some in Langdale valley

Question 56

Give an example of hummocky moraines

Answer 56

Coire a'Cheud-chnoic