Lesson 11: Glacial Deposition

Question 1

Define lodgement

Answer 1

This occurs beneath the ice when subglacial debris becomes stuck on the glacier bed. It occurs when the friction between the subglacial debris and the bed becomes greater than the drag of ice over it

Question 2

Define ablation

Answer 2

This process refers to debris being dumped as the glacier melts and thaws. It can include supraglacial, englacial and subglacial material

Question 3

Define deformation

Answer 3

This is a less-common process associated with weak underlying bedrock, whereby the sediments are defined by the movement of the glacier

Question 4

Define flow

Answer 4

Occurs if high meltwater content causes the glacial debris to creep/slide or flow during deposition

Question 5

Define moraine

Answer 5

Accumulation of glacial debris, whether it is dumped by an active glacier or left behind as a deposit after glacial retreat

Question 6

What are the 2 types of moraine?

Answer 6

Subglacial
Ice-marginal

Question 7

Define subglacial moraine

Answer 7

formed beneath the glacier

Question 8

Define ice-marginal moraine

Answer 8

formed along the margins of a glacier

Question 9

Decribe lateral moraine

Answer 9

Exposed rock on the valley side is weathered and fragments fall below onto the edge of the glacier, creating a ridge. This is then carried along the valley and deposited when the ice melts. Parallel to ice flow

Question 10

Describe medical moraine

Answer 10

When two valley glaciers converge, two lateral moraines combine to form a medial moraine. Material is transported and deposited when the ice melts. Parallel to ice flow

Question 11

Describe recessional moraine

Answer 11

These represent a stand-still during ice retreat. There appear like a series of ridges running across the valley behind the terminal moraine. A good indication of ice advance and retreat

Question 12

Describe terminal moraine

Answer 12

A ridge of moraine extends across the valley at the point of maximum advance, before the glacier retreats

Question 13

Define drumlin

Answer 13

An oval or ‘egg-shaped’ hill made up of glacial till and aligned in the direction of ice flow

Question 14

What size do drumlins vary between?

Answer 14

30-50 metres high and 500-1000 metres long

Question 15

How do drumlins usually occur?

Answer 15

Usually occur in clusters or ‘swarms’ on flat valley floors or lowland plains and forming ‘basket of eggs’ topography

Question 16

Why is there controversy over drumlin formation?

Answer 16

-Some have a rocky core with sediment moulded around it.
-Some partly consist of fluvial sediments as well as glacial till, suggesting that meltwater played a part in their formation

Question 17

Example of drumlins

Answer 17

Drumlin field, Honister Pass, Lake District

Question 18

Define till plains

Answer 18

A flat plain consisting of glacial till that has been deposited

Question 19

Define ablation till

Answer 19

Often more angular clasts as they are not ground down, and also the matrix of clay or silt-size particles (rock flour)

Question 20

Define lodgement till

Answer 20

Relatively rounded clasts because of the grinding that occurs at the ice bed interface, set within the matrix of clay or silt-sized particles (rock flour)

Question 21

What can lodgement till be remoulded into?

Answer 21

Streamlined flutes (known as swarms when in groups)

Question 22

Describe erratics

Answer 22

Lone depositional feature
Of a different geology to the bedrock thy ‘sit’ on

Question 23

How much can erratics weigh?

Answer 23

Up to 16 000 tonnes

Question 24

Example of an erratic? How far was it carried?

Answer 24

Canadian Rockies to plains of Alberta by the Cordilleran Ice Sheet
300km