GP1: Erosion & Transport Processes

Question 1

4 variables of erosion

Answer 1

Glaciological, substratum, topographic, temporal

Question 2

what are substratum characteritstics?

Answer 2

the material below the glacier

Question 3

What are temporal variables?

Answer 3

duration of glaciation or other processes in other variables of erosion

Question 4

What are 3 glaciological variables?

Answer 4

basal shear/driving stress
subglacial water pressures and drainage configuration
thermal regime (erosion can only happen if the glacier is warm enough to move)

Question 5

What affects the substratum of the glacier foundation?

Answer 5

structure, lithology, joint distribution, degree of weathering

Question 6

What are the two types of material that can underlay a glacier?

Answer 6

sediments or bedrock

Question 7

If sediment are underneath a glacier then what can affect its strength?

Answer 7

thickness, composition, structure and permeability

Question 8

What is more likely to be eroded - sediments or crystaline bedrock?

Answer 8

bedrock

Question 9

What are the two scales of topographic variables?

Answer 9

Small-scale = roughness of the bed at a specific point
Large-scale = locations of large ice masses, valley shape and size, depth an overall accumulation rate

Question 10

What are the two types of subglacial erosion?

Answer 10

Abrasion

Plucking/quarrying

Question 11

What is evidence of abrasion happening?

Answer 11

Presence of striae on rocks.

Question 12

How are striae caused through abrasion?

Answer 12

scoring of particle debris embedded in a glacier upon a specific rock

Question 13

What can striae also indicate regarding the glacier?

Answer 13

ice flow-axis direction

Question 14

What can happen to striae as you move downglacier and how?

Answer 14

They become wider and smoother because they are reworked that makes them blunter which then translates in to wider and smoother striae.

Question 15

What can sand do to the surface of a rock it flows over?

Answer 15

It can smooth it through a sandpaper effect

Question 16

What does plucking/quarrying involve?

Answer 16

Water at the bed can seep in to fractures in the bedrock where it can refreeze which can the pluck bits of the bedrock out of the bed as the glacier moves and then carry it with the glacier as it moves down glacier.

Question 17

What can we use today to see how this would have happened in the past?

Answer 17

Downslope rock faces that have clearly had parts of them ripped out

Question 18

What happens to erosion if the glacier bed is frozen to its base?

Answer 18

No abrasion or plucking can happen which means erosion is close to zero. However, plucking can still occur just at a much slower rate due tot he force generated by internal deformation as the glacier continues to move internally.

Question 19

What happens when unlithified/soft sediment beds are eroded?

Answer 19

quick process whereby depositon and erosion happen almost instantaneously to each other. This happens because the bed is easily deformable. The process dominated a lot of the glacial processes in Great Britain and has now created many relic cirque glaciers

Question 20

How can we determine how material was transported in the past?

Answer 20

By looking at its morphology today

Question 21

What are the supraglacial debris entrainment mechanisms for valley glaciers?

Answer 21

Avalanches and freeze-thaw weathering can cause material to fall off on to the glacier

Question 22

What are the supraglacial debris entrainment mechanisms for ice caps and ice sheets?

Answer 22

Nunataks and volcanic ash

Question 23

What are nunataks and how can they contribute to debris entrainment?

Answer 23

Ridges that stick out the top of ice bodies

Question 24

What is the process of frost-wedging?

Answer 24

freezing and then melting cycles of moisture in between rocks. The freezing causes the rock to expand 9% that places stress upon the rock that may cause it to break

Question 25

What are two requirements for freeze-thaw weathering to happen?

Answer 25

temperate regions so that the cycle of temperatures can happen and enough saturation within rock to supply enough moisture

Question 26

What differentiates debris at the base of a glacier to anywhere else in the glacier?

Answer 26

At the base there is as much as 75% debris content

Question 27

What are 3 implications of the high debris content at the base of a glacier?

Answer 27

1. ice is slowed down in motion as the rheology has been changed 2. erosion rates increase 3. increases the chances that material will be transported large distances from original position which can provide interesting information about transport (e.g. saunton sands)

Question 28

How is regelation an entrainment mechanism?

Answer 28

this is where the glacier is forced to melt on the upside of an obstacle due to increased pressure against it and then refreeze on the leeside. During this process ice can infiltrate in to subglacial sediments where it can then form part of the glacier

Question 29

How is englacial thrusting an entrainment mechanism?

Answer 29

Where basal debris can be elevated to englacial positoin by compressive deformation near the glacier margins.

Question 30

When could englacial thrusting happen?

Answer 30

1. during rapid glacier readvances 2. where wet based ice decelerates against cold-based ice 3. where ice flows against a topographic barrier that favours debris being forced in to ice

Question 31

How can a nunatak cause entrainment?

Answer 31

material is transported down on the downslope side (relative to ice flow direction) and as the glacier flows around a nunatak it will accumulate material from the side and bed. The material collected from all sources will then accumulate as a wedge entrained within the ice

Question 32

What is active transport?

Answer 32

basal transport zone where abrasion and crushing can happen and thereby rework sediments

Question 33

What is passive transport?

Answer 33

supraglacial and englacial transport of particles with little to no modification. This means the end material remains angular.

Question 34

What type of moraine can occur as a result of passive transport? and how?

Answer 34

Medial moraines - these are moraines that form on the surface or within the valley

Question 35

What are the 3 types of medial moraine can occur as a result of passive transport?

Answer 35

Lateral moraine - confluences of ice streams that meet together and Ablation dominant - ice melts and material therefore gets concentrated then transported on the surface Avalanche - transient, isolated concentrations of debris from large, low-frequency rockfalls