GP2: Deposition and Glacial Sediments

Question 1

What are the 3 ways of categorising sediments based on deposition process?

Answer 1

Glacigenic - generated directly by ice
Glacifluvial - eroded then carried by meltwater channels
Gravitational mass movement - downflow movement of material through effect of gravity

Question 2

What are the two divisions of glacigenic deposits?

Answer 2

Primary (till)

Secondary (reworked till)

Question 3

Where are primary glacigenic deposits deposited?

Answer 3

ice-interface or subglacial traction zone

Question 4

Describe the style of primary glacigenic

Answer 4

unsorted mixture of clast sizes known as a diamict

Question 5

What is the other name for primary deposits?

Answer 5

Till

Question 6

What can support the till deposits?

Answer 6

a matrix of well sorted fine material or a matrix of clasts.

Question 7

What can we infer about the clasts within a clast matrix that is supporting a till based on their shape?

Answer 7

Whether they are subglacial or supraglacial in origin

Question 8

What are secondary glacigenic deposits comprised of?

Answer 8

reworked primary till as a result of gravity stream flows

Question 9

What might be responsible for reworking primary glacigenic deposits?

Answer 9

meltwater floods or land collapses

Question 10

What aids distinction of secondary from primary glacigenic deposits and how?

Answer 10

Because secondary deposits have been reworked they are usually sorted more than primary ones.

Question 11

What is the overriding factor that affects sediment transport potential for glacifluvial deposits?

Answer 11

the amount of glacial water - greater amount of water the greater sediment transport potential

Question 12

What is a key feature of temperate regions that affects sediment transport potential?

Answer 12

Seasonal variations - warmer seasons means greater ablation which means more sediment transport in summer

Question 13

What makes glacifluvial deposits easy to identify?

Answer 13

Well sorted

Question 14

What are the two types of glacifluvial deposit?

Answer 14

Plane-bed

Cross-laminated facies

Question 15

What produces plane-bed deposits?

Answer 15

fine sized sediment deposited on to flat sandy stream beds under a calm marine environment

Question 16

What produces cross-laminated facies?

Answer 16

migration and vertical accretion of channel current ripples.

Question 17

What are the two types of glacifluvial transport?

Answer 17

Suspension (within an R-channel)

Bedload (along the bed)

Question 18

What affects the rate of sediment transport for glacifluvial transport?

Answer 18

Sediment availability and characteristics of water flow

Question 19

What are the two aspects of water flow that affect the rate of sediment transport for glacifluvial transport?

Answer 19

Flow competence (largest particle flow can carry)
Flow capacity (total quantity of available sediment that can be transported)

Question 20

What is the overriding influence upon flow competence and flow capacity for water flow characteristics that affect glacifluvial sediment transport?

Answer 20

Velocity and discharge

Question 21

What are the two drainage types of a glacier that affect method of sediment transport?

Answer 21

Distributed drainage systems (can access large expanses of the bed but have limited flow velocities)
Channelised drainage systems (reverse of drainage)

Question 22

What are the two types of mass movement that are most common for glaciers?

Answer 22

rockfalls and flows

Question 23

What are the 3 types of fall deposits?

Answer 23

talus/scree
solifluction
debris flows

Question 24

What are talus/scree slopes?

Answer 24

generated by frost-wedging causing material to fall down the steep slope. The material then forms a diamict at the base that also forms a fan shape. The talus diamict differentiates from a glacial diamict because of the levle of sorting that occures.

Question 25

What is solifluction?

Answer 25

downslope movement of water-saturated sediment due to receurrent freezing and thawing of the ground with seasonal variation.

Question 26

How can you observed solifluction from above?

Answer 26

The appearance of ‘lobes’

Question 27

What environment are solifluction deposits a key characteristic of ?

Answer 27

Periglacial

Question 28

What are debris flows?

Answer 28

gravitational flowage of sediment-water mixtures caused by flash floods or glacial lake outburst floods.

Question 29

What do debris flows lead to in terms of sediments they affect?

Answer 29

Homogenisation - cement mixer effect

Question 30

What is the product of a debris flow at the end?

Answer 30

A large sheet of sediment

Question 31

What can happen when debris flows occur in quick succession?

Answer 31

Geomorphological channel flow specifically for more flows that occur soon after

Question 32

What is the feedback between sediment sorting and transport?

Answer 32

Sediment transport sorts sediments based on size usually (large then small) of which the sorting then increases the permeability of some deposits. more sorting means more permeabiltiy means greater ability of the water to sort sediments.

Question 33

What affects the shape of clasts in sediment transport?

Answer 33

erosion processes and lithology

Question 34

What affects the roundness of clasts in sediment transport?

Answer 34

varies with fracture and transport mechanisms but is therefore largely a product of subglacial or supraglacial origin

Question 35

What affects texture of clasts in sediment transport?

Answer 35

Striae on the clast instantly means subglacial transport. If the clast is linear and parallel then this also means there is stability in the system

Question 36

What do wear patterns tell us about sediment transport?

Answer 36

Asymmetry in wear is characteristic of subglacial transport

Question 37

What does fabric of clast tell us about sediment transport?

Answer 37

product of multiple clasts - i.e. if clasts are orientated the same (imbircation) then this tells us the flow direction.