unit four

Question 1

where can rock debris be transported or entrained in a glacier ? (4)

Answer 1

1. the surface (supraglacial debris)
2. within the glacier (englacial debris)
3. at the base of the glacier (subglacial debris)
4. at the front of a glacier (proglacial debris)

Question 2

describe supraglacial debris

Answer 2

found on the surface of the glacier, this is where frost shattered, avalanche and other debris fall onto the glacier, the material is angular and unsorted

Question 3

describe subglacial debris

Answer 3

found at the base of a glacier, small debris can be entrained by basal ice freezing, while large boulders can be entrained by deformational flow and transported by traction. some materials can be plucked where regelation takes place around the bedrock

Question 4

describe englacial debris

Answer 4

found within the glacier, they occur as ice moves forming crevasses where debris can fall into the cracks or be carried by meltwater and trapped within the glacier

Question 5

describe erratics

Answer 5

different rock types to the bedrock they sit on.

Question 6

why is there so much subglacial debris found at the snout of a glacier?

Answer 6

it is in the zone of ablation so it always has a negative mass balance. outputs are larger than inputs and so more debris are visible as the ice will constantly be reducing, exposing debris on the surface

Question 7

what flow type does ice that flows over an increasingly steep gradient have?

Answer 7

extensional flow due to internal stress. this can result in supraglacial debris falling down crevasses and becoming englacial debris

Question 8

what flow type does ice that flow over a decreasing gradient have?

Answer 8

compressional flow due to internal stress, resulting in sub/englacial material being moved towards the surface becoming supra-glacial debris

Question 9

how do supraglacial debris become englacial debris?

Answer 9

via extensional flow, they fall into crevasses and become englacial debris

Question 10

how do englacial debris become supraglacial debris?

Answer 10

via compressional flow, they move towards the surface due to internal stress

Question 11

What are deposits deposited directly by a glacier called?

Answer 11

Glacial deposits

Question 12

What are deposits deposited by glacial meltwater called?

Answer 12

Fluvioglacial deposits

Question 13

What are some examples of landforms formed by glacial deposits?

Answer 13

Drumlins, terminal moraines, recessional moraines, lateral moraines, medial moraines, push moraines

Question 14

What are some examples of landforms formed by glacial meltwater (fluvioglacial)?

Answer 14

Eskers, Kames, Kame terraces, kettle holes, kettle lakes, varves

Question 15

Where can fluvioglacial (glacier meltwater) landforms be found?

Answer 15

Landscapes called sandur‘s or outwash planes

Question 16

Where can glacial ice landforms be found?

Answer 16

Till planes

Question 17

Describe what glacial deposits tend to be composed of

Answer 17

Unsorted, unstratified debris containing rock fragments of all shapes and sizes ranging from boulders to small clay sized particles, they’re called glacial till or sometimes boulder clay

Question 18

Where is lodgement till formed?

Answer 18

Subglacially

Question 19

How is lodgement till formed?

Answer 19

It’s plastered onto the underlying surface by the glacier above, where friction between the debris and the bed is greater than the drag produced by the ice moving over it. This is common where there is a large amount of subglacial debris or slow moving ice

Question 20

Describe lodgement till

Answer 20

A mix of rounded boulders in a matrix of sand, mud, and clay. Due to the pressure involved this till tends to be compacted and then often forms drumlins

Question 21

Describe how ablation till is formed

Answer 21

This material is deposited from supra-glacial, englacial and sub glacial debris due to the process of ablation. Meltwater may remove some of the finer clay leaving only the larger ones

Question 22

Describe ablation till

Answer 22

poorly stratified, compacted and unsorted till that is often more angular in nature than lodgement till

Question 23

Where is ablation till mainly formed?

Answer 23

At the snout of a glacier

Question 24

What is deformation till?

Answer 24

When a glacier re-advances over an area of previously deposited till, the sediment can be folded or faulted.

Question 25

Describe the appearance of deformation till

Answer 25

Well compacted and contains many different rock types. The patterns reflect the stresses involved in its formation

Question 26

What is a moraine?

Answer 26

A moraine is an accumulation of glacial debris deposited by a glacier or left behind as a glacier retreats.

Question 27

What are the two categories of moraines?

Answer 27

Subglacial or ice marginal

Question 28

What are till planes?

Answer 28

Glacial moraines can cover large areas of land producing extensive, relatively flat areas called till planes

Question 29

What are drumlins?

Answer 29

Elongated hills streamlined in the direction of ice flow and composed largely of glacial deposits.

Question 30

What till are drumlins composed of?

Answer 30

Lodgement till

Question 31

What does ‘basket of eggs topography’ mean?

Answer 31

They describe drumlins, which are found in groups and often appear to look like a basket of eggs from above

Question 32

What do glacial deposits tend to be composed of?

Answer 32

Unsorted, unstratified debris containing rock fragments of all shapes and sizes from boulders to small clay size particles

Question 33

What is the deformational theory for drumlins formation?

Answer 33

When a glacier moves over an obstacle at the base of a glacier, till is plastered around it. This happens when there is a large amount of subglacial debris. The lodgement till then becomes streamlined into the elongated tear drop shape as the glacier flows over it

Question 34

What is sorting?

Answer 34

The arrangement of rock fragments into similar sizes. They can be well sorted, moderately sorted or very poorly sorted

Question 35

What does stratification mean?

Answer 35

The layering of similar sized clasts, when there are clear layers, the sediment is stratified and when there are no clear layers the sediment is unstratified

Question 36

How do sediment clasts become more round?

Answer 36

As a result of attrition, where during movement collisions occur removing the shaper edges

Question 37

How can you tell how far of a distance rock has traveled?

Answer 37

How rounded or angular it is. The rounder the more distance it has travelled