The characteristics of glaciofluvial deposits

Question 1

How do the sediments laid down by meltwater contrast with till deposits associated with glacial deposition?

Answer 1

The sorted and stratified sediments laid down by meltwater contrast markedly with the unstratified till deposits associated with glacial deposition.

Question 2

Rock debris can be entrained and transported by meltwater streams flowing where in relation to the glacier?

Answer 2

Rock debris can be entrained and transported by meltwater streams flowing supraglacially (on the glacial surface), englacially (within the glacier) and subglacially (beneath the glacier).

Question 3

Where is rock debris deposited by meltwater?

Answer 3

Rock debris is deposited either supraglacially, englacially, subglacially or in a proglacial environment.

Question 4

Define the term proglacial?

Answer 4

Proglacial - The zone adjacent to a glacier snout or ice-sheet margin.

Question 5

Give some reasons why the distinctive characteristics of glaciofluvial deposits develop?

Answer 5

• The fluctuating nature of meltwater discharge: transportation is usually greater in the warmer summer months, due to ice melt and may stop entirely during the winter. The high-velocity, turbulent discharges associated with summer ablation result in meltwater streams with the competence and capacity to transport large volumes of rock debris
• The physical constraints of the meltwater channel which may vary from constricted subglacial tunnels to extensive braiding.

Question 6

How do environments of glaciofluvial deposition vary?

Answer 6

• In ice-contact environments, the meltwater may deposit its material subglacially, englacially or supraglacially
• In proglacial or outwash environments, the meltwater may deposit its material either at or beyond the ice-margin

Question 7

Ice-contact glaciofluvial streams may be under how many meters of ice?

Answer 7

Ice-contact glaciofluvial streams may be under hundreds of meters of ice and therefore under great pressure and moving at high velocity.

Question 8

Outwash material has been carried by meltwater for longer periods than ice-contact deposits have been. What is is the impact of this on clasts?

Answer 8

As a result clasts will be:
- More rounded due to attrition
- Smaller, as meltwater at lower discharges has less energy than ice
- Better sorted, as velocity falls, the largest particles will be deposited first
- Stratified vertically with layers that reflect diurnal (daily), seasonal and annual sediment accumulation

Question 9

How do the characteristics of outwash vary with increasing distance from the ice front?

Describe the characteristics of outwash in each zone?

Answer 9

The characteristics of outwash will vary with increasing distance from the ice front in a series of zones:
- A proximal zone exists, where particles are large, reflecting the high discharge of meltwater as it exits the glacier.
- Beyond lies the medial zone, where particle size is not as coarse and clasts are more rounded than in the proximal zone, reflecting increased transportation
- The distal zone, here outwash is better sorted, with smaller and more rounded particles than in the other zones.

Question 10

Why do glaciofluvial deposits vary over short distances?

Answer 10

Glaciofluvial deposits vary over short distances in response to fluctuations in discharge.