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Geography - Glaciers > Unit 4a > Flashcards

Unit 4a Flashcards

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1
Q

How do glaciers move/transport the entrained (picked up) rock debris?

A
  • flowing ice body (glacial transportation)
  • flowing meltwater (fluvial transportation)
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2
Q

What are the 4 locations where entrained debris can be picked up?

A
  1. supraglacial debris = transported on the surface of the glacier (fluvial/glacial)
  2. englacial debris = transported within the glacier (fluvial/glacial)
  3. subglacial debris = transported at the base of the glacier (fluvial/glacial)
  4. proglacial debris = transported away from the front of the glacier (fluvial only)
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3
Q

What is supra glacial debris? What are the characteristics of the material?

A

where frost shattered, avalanche and other debris falls onto the glacier from the valley side, material is angular and unsorted

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4
Q

What is subglacial debris? What are the characteristics of the material?

A

Small debris accumulated by basal ice freezing, where large boulders can be entrained by deformational flow. Some debris can be plucked from where regelation takes place around irregular bedrock

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5
Q

What is englacial debris and what are the characteristics of the material?

A

occurs as the ice moves at variable speeds forming crevasses where debris can fall into the cracks or be carried by meltwater and trapped within glacier

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6
Q

What are erratics?

A

these are different rock types to the bedrock that they sit on.

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7
Q

What is extentional flow and what does it result in terms of debris?

A

Ice that flows over an increasingly steep gradient will experience internal stress, results in supraglacial debris falling into crevasses and becoming englacial debris

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8
Q

What is compressional flow and what does it result in terms of debris?

A

Ice that flows over a decreasing gradient will experience external stress, resulting in sub/englacial debris moving towards the surface becoming supraglacial debris

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9
Q

What 6 glacial landforms are formed due to glacial ice?

What landscape will these landforms be found on?

A

Drumlins, Terminal morraine, Recessional morraine, Lateral morraine, Medial morraine and Push morraine

Till Plain

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10
Q

What 6 glacial landforms are formed due to meltwater?

What landscape will these landforms be found on?

A

Eskers, Kames, Kame terraces, Kettle holes, Kettle lakes, Varves

Sandur/Outwash Plain

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11
Q

What is glacial till known as in the U.K?

A

Boulder Clay

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12
Q

What is lodgement till and how does it form?

A

This till is plastered on the underlying surface by the glacier above.
This happens when the friction between the debris and the bedrock is greater than the drag created by the glacier
forms subglacially

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13
Q

What are the characteristics of lodgement till?

A
  • unsorted, unstratified
  • till is comprised of debris ranging from large boulders to a fine matrix of sand, silt and clay
  • till is compacted (due to pressure)
  • more rounded
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14
Q

What is ablation till and how does it form?

A

this material can be deposited from sub, en and supra glacial debris due to process of ablation
sometimes meltwater can carry away finer material, leads to more angular debris.

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15
Q

What are the characteristics of ablation till?

A
  • unsorted and unstratified
  • contains larger material and smaller cobbles, but NO fine material
  • till is poorly compacted
  • clasts are angular
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16
Q

What is deformation till and how does it form?

A

if glacier advances over an area of previously deposited till, underlying sediment can be folded/faulted
till tends to be well compacted, contains different rock types
the patter of till will reflect the sheer stress involved with its formation

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17
Q

What is a moraine?

A

an accumulation of glacial debris deposited by a glacier or left behind as the glacier retreated

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18
Q

How can a moraine be categorised?

A

subglacial or ice- marginal (formed on the edges)

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19
Q

What are till plains?

A

glacial moraine can cover large areas of land, producing extensive flat area of land
(typically 50m thick, above there may be other depositional landforms)

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20
Q

What is a drumlin?

A

an elongated hill, streamlined in the direction of ice flow, composed of glacial deposits (lodgement till)

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21
Q

What is a cluster of drumlins known as?

A

a basket of eggs

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22
Q

What are the conditions needed for drumlins to form?

A

glacier has to have a high concentration of sediment, high amount of meltwater is also needed

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23
Q

What is the process called that forms drumlins in the subglacial sediment?

A

sub - glacial sediment deformation

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24
Q

What are the two theories of drumlin formation?

A

The fluvial theory
The deformational theory

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25
What does the fluvial theory suggest on how drumlins are formed?
drumlin formation is due to: - sub-glacial meltwater flooding which deposits fluvioglacial material - these deposits are then streamlined after the subglacial flood by glacial ice - additional till to form elongated mounts
26
What does the deformational theory suggest on how drumlins are formed?
(more widely accepted) 1. sediment beneath the glacier gets saturated with meltwater 2. glacier then becomes in contact with something that is more resistant, glacier can no longer carry sediment (lodgment till) 3. glacier will deposit material which starts to mold and sculpt the landscape beneath it
27
What are the ice marginal landforms?
Moraines
28
What is lateral moraine?
Near the head of the valley glaciers supraglacial debris is often in concentrated bands, on EITHER SIDE of the glacier
29
What is medial moraine?
when the supraglacial debris is often concentrated bands in the MIDDLE of the glacier
30
How does lateral moraine form?
formed from freeze-thaw weathering/rockfall/avalanche plucking from within the glacier can also influence
31
How is medial moraine formed?
two moraines join together and force the sediment into the centre happens in the CONVERGENT zone
32
Where are terminal moraines found?
(end moraines) mark the furthest advance of a glacier
33
How do terminal moraines form?
debris is deposited at the firthest point the glacier has reached the upside valley is Steeper than the down side When formed by a valley glacier, tend to form a smaller crescent shaped ridge across the valley
34
What is an example of a terminal and lateral moraine?
Bylot Island Glacier CANADA
35
How do terminal moraines form? (How does the debris reach the snout of the glacier)
Glacial deposition occurs constantly at the snout, transported to this point as the glacier flows downslope At the zone of ablation (end) of glacier is in a state of negative mass balance, so the glacier is losing mass through ablation
36
How do terminal moraines form? (How does the debris accumulate)
the debris accumulates, if the glacier remains stationary for a number of years glacier = in a state of equilibrium (supports the debris being deposited)
37
How do terminal moraines form? (How is the debris left behind, when the glacier retreats)
glacial deposition occurs constantly at the snout as the glacier melts, the debris (sub, en and supra glacial) is deposited as ablation till
38
What is the ablation till that forms the terminal moraine like?
poorly sorted and compacted not stratified and angular in nature
39
What is a push moraine?
- form when glacier advances over existing moraine, act as a bulldozer pushing the moraine into a new ridge - cause the clasts of the moraine to orientate themselves vertically
40
How are medial moraines formed, in terms of the sediment?
(a ridge of moraine down the middle of the valley floor) - when two valley glaciers converge, two lateral moraines combine to form medial - material is carried and deposited when melting occurs - PARALLEL TO ICE FLOW
41
What is a recessional moraine?
(formed the exact same manner as terminal) they just represent a location where the glacier paused for a long time during a retreat - deposits ablation till
42
What does glacial sediment consist of?
rock debris entrained within glacier, does experience much change, due to its fixed position in the ice = angular shape
43
What is the exception to glacial sediment?
subglacial debris, due to abrasion, can be eroded and worn away as its dragged over the bedrock below
44
How does rock flour form? What type of debris is it?
when both subglacial clasts and bedrock abrade each other, it produces a fine powder found in glacial debris
45
What does fluvioglacial sediment consist of?
can be deposited sub, supra or englacial, referred to as ice-contact fluvioglacial deposits transported by meltwater
46
What is a proglacial deposit?
when it is deposited beyond the snout (ahead of the glacier)
47
What is the difference between how sorted and stratified glacial/fluvioglacial debris is?
fluvioglacial = well sorted = stratified (debris is layered, the heaviest boulders are dropped first) Glacial = poorly sorted = unstratified (not much erosion, dumped)
48
What is the difference in the shape of debris between glacial/fluvioglacial debris?
fluvioglacial = rounded, usually eroded glacial = angular because the debris is mostly plucked, little to no erosion
49
Why are fluvioglacial deposits imbricated whereas glacial deposits aren't?
fluvioglacial deposits experience alignment, because the water pushes the debris in one direction there is non in glacier, as there is no meltwater transporting the debris
50
What is glacial debris that is deposited called?
glacial till
51
What is fluvioglacial debris that is deposited called?
fluvio deposits
52
What is meant by sorting of debris?
the arrangement of rock fragments (clasts) into similar sizes (poorly sorted = clasts vary in size well sorted = clasts of a similar size)
53
What is meant by stratification?
the layering of similar size clasts (when there are no clear layers, sediment = unstratified)
54
What is meant by the shape of debris, what can influence this?
the degree of roundness of the clasts occurs due to attrition mature clasts = rounded (travelled a long distance immature clasts = angular (transported short distances)
55
Where can fluvioglacial deposition take place?
by meltwater on or under the glacier (ice- contact) or by meltwater flowing away from the glacier (proglacial)
56
How can ice contact features be deposited?
subglacial or supraglacial
57
What are eskers?
- long sinuous ridges of sand, gravels and pebbles deposited by meltwater streams/rivers flowing through sub or en glacial tunnels
58
What is an example of an esker?
Munro Esker, Ontario
59
How do Eskers form? (how does the process of deposition begin)
- begins when a subglacial meltwater channel becomes obstructed - this leads to a rapid decrease in the velocity of the water, letting deposition begin
60
How do eskers form? (what happens when the glacier retreats)
builds up annually, mound of material remains on the landscape
61
How do eskers form? (what do the clasts show about the depositional journey)
the clasts: - often rounded, travelled long distances - due to attrition and abrasion - clear sorting and stratification (because seasonal temp variations lead to variations in meltwater velocity) - larger ones being transported in the summer - clear imbrication (all clasts align in the path with the least resistance)
62
What is a Kame/ Kame Terrace?
both form supraglacially on the surface of a glacier, composed mainly of sand and gravels
63
What is an example of a Kame/Kame Terrace?
East Lothian, Scotland
64
How do Kame/Kame Terrace form? (first stage)
in the zone of ablation, surface meltwater streams pick up and transport supraglacial debris - flow short distances before flowing into depressions on the surface (Kames) or at the edge (Kame Terraces)
65
How do Kame/Kame Terrace form? (how is the debris sorted and stratified)
when the meltwater stream flows into a depression the flow velocity will drop, letting the debris be deposited - the supraglacial velocity varies seasonally, larger clasts transported in warmer months -... leads to sorting and stratification
66
How do Kame/ Kame Terraces form? (clasts shape and size)
these clasts are usually angular/subangular - the process that leads to the origin of this debris (rockfall, avalanche) usually produces angular material
67
Why might Kame Terraces possibly contain larger angular fragments? (last stage, without the ice bit)
when the glacier retreats, depressions filled with sediment are gradually lowered to the surface, forming inverted mounds on the ground (disturbing sorting and stratification)
68
What are the three proglacial features?
Kettle holes/Lakes Proglacial lakes and Varves Sandur, outwash plains
69
What are Kettle Holes/Lakes?
Kettle holes are depressions found within the outwash plain located infront of a retreating glacier
70
What is an example of Kettle Holes/Lakes?
The Meres of North Shropshire
71
How do Kettle Holes form?
1. dead ice (carved off and separated from the glacier) There is increased levels of ablation, and there is a negative mass balance 2. Sediment shed from retreating glacier buries the ice blocks, builds up and covers the dead ice 3. due to increased ablation, the ice blocks melt away, causing the sediment to fall in (where the ice melted) = Kettle hole (depression)
72
How do Kettle Lakes form?
the first three stages are the same as Kettle Holes - permeable rock is needed to be able to fill the kettle hole - precipitation can fill creating a Kettle Lake (creates an aquifer = ground water supply)
73
How do proglacial lakes form?
- meltwater streams in front of a retreating glacier will cause depressions at the front of the glacier or where recessional moraine dam the water - proglacial lakes will fill with sediment as the stream velocity will slow upon entering the still water of the lake - isn't a permanent feature
74
How do proglacial varves form?
sediment that will begin to fill these lakes will form alternating annual layers of fine clay/silt and coarse sand and gravels are known as varves
75
How do varves fluctuate between the seasons?
Summer = increased melting = more meltwater means that there is more course sediment that is deposited Winter = decreased melting and more inputs, sediment may be dissolved, when water freezes over that sediment is deposited
76
What does the thickness of the varves show?
shows the seasons + average temperatures of the year
77
What are Sandur (Outwash plains)?
flat landscape formed by fluvioglacial deposits in front of a retreating ice sheet - these landscapes are dominantly composed of sands and gravels deposited by flowing water

Geography - Glaciers (8 decks)

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