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Glacial Landscapes Unit 4 Flashcards

1
Q

What is the definition of supra glacial debris?

A

Transported on the surface of the glacier

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2
Q

What is the definition of englacial debris?

A

Transported within the glacier

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3
Q

What is the definition of sub glacial debris?

A

Transported at the base of the glacier

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4
Q

What is extensional flow?

A

When ice flows over an increasingly steep gradient and experiences internal stress, resulting in crevasses

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5
Q

What is compressional flow?

A

When ice flows over an increasingly decreasing gradient causing it to experienced internal stress, crevasses close

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6
Q

What are glacial deposits?

A

Debris deposited directly by a glacier

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7
Q

What are fluvio-glacial deposits?

A

Debris deposited by glacial meltwater

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8
Q

What is the typical composition of glacial deposits?

A

Unsorted and unstratified

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9
Q

What is Lodgement till?

A

This is formed subglacially and is plastered onto the underlying surface by the glacier above where friction between the debris and the bed is greater than the drag produced by the ice moving over it.

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10
Q

What are the characteristics of Lodgement till?

A

It’s common where there is a large amount of subglacial debris or slow moving ice. It is often a mix of rounded boulders in a matrix of sand mud and clay due to the pressure involved. This still tends to be compacted and often forms drumlins.

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11
Q

What is ablation till?

A

It is sometimes referred to melt-out till this material is deposited from sub to en to supra glacial debris due to the process of ablation

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12
Q

What are the characteristics of ablation till?

A

It tends to be poorly compacted and sorted and unstratified. in some cases meltwater may remove some of the finer particles such as rock flour leaving only the larger ones. this is often more angular in nature than lodgement till that may have been dragged so glacially leading to a greater degree of rounding from abrasion.

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13
Q

What is deformation till?

A

If a glacier read advances over an area of previously deposited till, the underlying till sediment can be folded or folded.

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14
Q

What are the characteristics of deformation till?

A

Deformation till tend to be well compacted and contain many rock types. The patterns in the till will reflect the sheer stresses involved in formation.

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15
Q

What is Moraine?

A

Moraine is an accumulation of glacial debris deposited by a glacier or left behind as the glacier retreats. Moraines can be categorised between either sub glacier or ice marginal ( formed on the edges)

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16
Q

What is a till plain?

A

Glacier moraine can cover a large area of land producing an extensive relatively flat area known as a till plain

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17
Q

What are the characteristics of till plains?

A

Till plains typically have 50 meter thickness of till (ground moraine), above which there may be other depositional landforms

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18
Q

What is a Drumlin?

A

A drumlin is an elongated hill streamlined in the direction of ice flow and composed largely of glacial deposits. Most geographers agree that drumlins are composed of lodgement till.

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19
Q

What is the size and scale of drumlins

A

They can measure up to 50 m to several kilometres in length, and a few metres to 100 m in height

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20
Q

Where do drumlins form in relation to a glacier?

A

Drumlins form beneath the glacier (subglacial)

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21
Q

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

A

Subglacial sediment deformation– the moulding and sculpting of sediment by the flow of the glacier

22
Q

What are the current theories of Drumlin formation?

A

The fluvial theory and the deformational theory

23
Q

What is the fluvial theory of Drumlin formation?

A

The fluvial theory suggested that drumlin formation is due to subglacial meltwater flooding which deposits the fluvioglacial material. these deposits are then streamlined after the subglacial flood by the glacial ice with additional till to form the elongated mounds

24
Q

What is the deformational theory of Drumlin formation?

A

When a glacier moves over an obstacle at the base of the glacier, till is plastered around it. This happens when there is a large amount of subglacial debris. The lodgement till subsequently becomes streamlined into the elongated ‘teardrop’ shape as the glacier water flows over it. This theory is more widely accepted by geographers

25
What is lateral moraine?
Lateral meine is found at the size of the glacier and is a product of freeze thaw weathering occurring on the side of mountains which loosens the rocks and causes rockfall onto the side of the glacier or it can be caused by mass movement for example an avalanche.
26
What are the debris characteristics of lateral moraine?
The debris is more jagged and angular
27
How is medial moraine formed?
It is formed when valley glaciers merge – the confluence of two valley glaciers (two lateral moraines merge)
28
What are terminal moraines?
Terminal Moraines mark the furthest advance of a glacier. Debris is deposited at the furthest point at which the Glacier reaches.The Up-Valley side is usually steeper than the down-valley side. When formed by a valley glacier they tend to form a small crescent shaped ridge across the valley.
29
What is a recessional moraine?
Recessional moraine are formed in exactly the same manner as a terminal Moraines but in this case, they represent a location where the glacier pauses for a considerable time during its retreat depositing ablation till. They are always found behind the terminal moraine.
30
What are push moraines?
These form when a glacier advances over an existing moraine. The glacier will act as a bulldozer to push the moraine into a new ridge. This process will cause the clast in the moraine to orientate themselves vertically.
31
What is meant by the sorting of rock?
The arrangement of rock fragments (clasts) into smaller sizes
32
What is meant by the stratification of sediment?
The layering of similar size clasts
33
What is meant by the shape of the sediment?
The degree of roundness of the clasts. Rounding of clasts occurs as a result of attrition, whereby during movement collisions occur removing the sharper edges.
34
What are eskers?
Eskers are long sinuous (winding) ridges of sons, gravels and pebbles deposited by Mount water streams/rivers flowing through subglacial and sometimes on glacial, tunnels. They can be up to 20 m high, 3 km wide and 100 km long in extreme cases.
35
How are Eskers formed?
-running water a high velocity due to hydrostatic pressure transports a large quantity of sediment which become rounded due to extensive attrition -Fluctuating velocity due to seasonal variations in melt water enable deposition to occur with stratified layers of different size clasts -Some theories suggest that the tunnel may become blocked, stopping the flow of water allowing rapid deposition -A retreating glacier, then exposes the esker/landform deposit
36
What is imbrication?
It is when the clasts align themselves in the direction of flowing water as the water will push on the flat face and flip them over so that they downstream
37
What is a named example of an esker?
The Munro Esker near Munro Lake in northern Ontario formed from the retreat of the Laurentide ice sheet at the end of the Devensian, it is 250 km long and almost 5 km wide in places.
38
How are Kames and Kame terraces formed?
They are formed supraglacially on the surface of the glacier. In the zone of ablation, surface melt water streams will pick up and transport super glacial debris – sands and gravels. These streams will flow into lakendepressions on the surface of the ice upon which the flow velocity will drop and the debris will be deposited. If the lake is at a glacier edge, a Kame Terrace will form, whereas away from the edge, a Kame will form. The ice then melts and the mound of debris is left behind leaving a Kame.
39
Why will the clasts in Kames/Kame terraces be quite angular in shape?
They have not been eroded as they stay stationary/in the same place on the ice with limited to no attrition as it is wind blown or from avalanches
40
Why do clasts on the Kames/ Kame terraces show clear sorting and stratification?
Meltwater drops heavier rocks first when it loses energy
41
Explain why Kame terraces contain larger angular fragments
They’re more likely to occur on valley sides which are prone to mass movement – avalanches and rock falls on the ice margin
42
What is a named example of Kames and Kame terraces?
The east Lothian area of Scotland contains many Kames and Kame terraces. These features are typically up to 20 m high and 200 m in length and were formed during the retreat of the ice at the end of the Devensian glaciation
43
What are kettle holes and kettle hole lakes?
Kettle holes are depressions found in the outwash plane (sandur) located in front of a retreating glacier. When these depressions are filled with water they are called Kettle-hole Lakes. They form where blocks of stagnant or dead ice calve from the front of the glacier.
44
How are kettle holes formed?
-Blocks of ice are left behind by the retreating glacier -Sediment is shed from retreating glacier and buries the ice blocks -Ice blocks melt away and the sediment collapses forming depressions -Groundwater sometimes fills the kettles if the water table is high enough or the hole is deep enough , they can also be filled with rainwater dependent on the mix of sediment if it is permeable or impermeable
45
What is a named example of kettle holes and kettle lakes?
The Meres of North Shropshire, there were formed at the end of the Devensian glaciation when the ice sheet retreated. Hundreds of small Kettle Hole depressions and lakes were formed. This area also contains some particularly large Kettle-hole lakes such as The Mere, Cole Mere and White Mere, which are over 300 m across.
46
What are pro glacial lakes?
They are found in front of a retreating glacier when melt water streams will cause lakes to form in depressions in front of the glacier or wear a recessional Moraines dam the melt water. These pro glacial or ice margin lakes will fill with sediment as the stream velocity will slow upon entering the Still water of the lake.
47
What is a varve?
Above is the alternating annual layers of fine clay/silt and coarser sand/gravel from the sediment that begins to fill the lakes. Coarse sand/gravel layers are formed in the summer/spring due to the high rates of ablation causing more water meaning that the streams will have more energy Fine silt/clay layers are formed in the winter as they are suspended in the water and settle due to less energy because of less melt water
48
How are Varves used?
They can be useful to geographers in the UK as the layers can give them an idea how long it took the glaciers in the UK to retreat completely – age of Lake
49
What is a sandur (outwash plains)?
The flat landscape formed by Fluvioglacial deposition in front of the retreating ice sheet is known as a sandur or outwash plain. These landscapes are dominantly composed of sand and gravel deposited by flowing water, but may also contain other fluvioglacial landforms.
50
What is an example of an outwash plain?
Some of the most impressive sandur/outwash plains can be found in Iceland such as Skeidararsandur covering 1300 km² – the largest sandur in the world

Geography (4 decks)

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