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Advanced Geomorphology > Chapter 9 > Flashcards

Chapter 9 Flashcards

1
Q

Glacier

A

A mass of ice on land that formed by the accumulation of snow.

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2
Q

Where do glaciers form?

A

They form at high elevation (alpine glaciers) and high latitude (continental glaciers)

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3
Q

What happens when a glacier gets big?

A

When glaciers get big enough they start to move.

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4
Q

Continental Glaciers

A

These domes of ice move as they collapse down and outward under their own weight.

  • land beneath the ice is depressed
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5
Q

Differences in flow velocity in a glacier

A

Slowest at the bottom, fast at the top. Typically top center.

A glacier will advance at different rates depending on the season.

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6
Q

Seasonal changes for glaciers means…

A

Means differences in temperature. In winter there will be snow that accumulates and the glacier grows in size.

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7
Q

Glacier in the summer

A

In summer, precipitation may include more rain. The glacier may also melt.

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8
Q

Melt water’s effect on glaciers

A

The presence or absence of melt water will affect how fast and how far a glacier moves.
changggeeee ?????
Sometimes on the surface of a glacier, where the ice is moving at different velocities, there is tension (tensions stress).

The ice being a solid with then crack.

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9
Q

What does melt water have that ice doesn’t

A

Heat and mobility

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10
Q

Meltwater affect on glaciers

A

Melt water on the surface of a glacier is able to enter the glacier by way of the crevasses or cracks on the surface. This melt water (which has heat and mobility) is able to create tunnels in the ice.

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11
Q

Two types of glacier

A

Depending upon conditions at the base of the glacier, especially the presence of meltwater, there are two types of glaciers:

  • COLD BASED GLACIER
  • WARM BASED GLACIER
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12
Q

COLD BASED GLACIER

A

The ice is frozen to the underlying bedrock.

(The glacier deforms as it moves. The bottom is slow, the top is fast.)

Average ice velocity is slow.

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13
Q

WARM BASED GLACIER

A

The ice is NOT frozen to the bedrock beneath it.

(The ice does not deform internally. Instead it slides slides along as a single mass on a layer of melt water. Average velocity is faster.)

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14
Q

Formation of an alpine glacier

A
  1. One this glacier reaches a critical size it will begin to flow downhill. The sediment will be eroded with the ice..

Sediment at the base of the ice is set in motion (eroded) by the ice; it moves with the ice, beneath it (subglacial mode of transport).

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15
Q

zone of accumulation (see diagram)

A

higher part of the glacier (above firn line) where there is a net increase in snow and ice

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16
Q

zone of ablation (see diagram)

A

lower part of the glacier (below firn line) where there is a net loss of snow and ice

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17
Q

3 ways of sediment transport

A

Subglacial

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18
Q

What happens to sediment during SUBGLACIAL TRANSPORT in a glacier?

A

As the sediment moves, its texture remains mostly unchanged. This sediment is more or less encased in ice and does not “react” with other hard surfaces.

Where the piece of sediment is in contact with the underlying bedrock, there is more weathering and erosion. At contact, the moving sediment abrades against the bedrock creating very fine sediment.

As the sediment is worn down more of it is in contact with the bedrock. Due to increased friction the sediment stops moving.

As the ice continues to movie it pushes the sediment so that it rolls over exposing a new sharp edge to the bedrock.

This process may repeat itself over and over until the large piece of moving sediment has many flat surfaces or facets.

Facets may also be covered in straight scratches or striations that form when small pieces of sediment are caught between the moving rock and the bedrock.

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19
Q

Sediment created in a glacial environment by frost action and abrasion consists of ______

A

two sizes.

This bimodal sediment includes large, angular pieces resulting from frost action and much smaller pieces from abrasion.

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20
Q

Regelation

A

The way that a glacier moves around an obstacle by melting and refreezing.

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21
Q

Nature of glacial ice

A
  • Glacial ice is very much in a state of transition. Which it is a solid it is very close to being a liquid.
  • It forms at 0°c and more or less remains there. It will melt where pressure is applied.
  • This also means that ice will “flow” even though it’s a solid.
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22
Q

Roche Moutonnet Formation.

PHOTO

A
  1. At 1 ice encounters an obstacle it cannot move. The ice slows down and pressure increases. The ice here then melts.
  2. At 2 the solid ice eventually slides forward and around the obstacle. At the same time meltwater moves down and around the obstacle.
  3. At 3 the meltwater is now down at the lee-side of the obstacle. Here, under lower pressure the meltwater re-freezes.
  4. The bedrock at the lee-side of the obstacle is physically weathered creating more angular rock fragments.
  5. The end result is the formation of a ROCHE MOUTONNET
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23
Q

Roche Moutonnet

PHOTO

A

An asymmetrical stream streamlined erosional bedrock feature. With a smooth, gently sloping up ice side (often covered in striations) and a steep angular lee side.

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24
Q

Striations

A

Striations are are straight, long (<10 m), shallow (<1cm) engraving or scratched in the bedrock caused by the passage of a rock embedded in the base of a glacier.

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25
Q

Striations are good indicators of…

A

Striations are very good at indicating ice flow direction,

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26
Q

Chattermark or Friction Crack Formation PHOTO

A

Instead of the ice going around the rock fragment (regelation) or eroding the rock fragment once again, it is possible that the bedrock may break from shear stress.

If this happens the bedrock is broken (physically weathered) such that a friction crack or “chatter mark” is formed

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27
Q

Chattermark or Friction Crack

A

These are crescent shaped “holes in the bedrock that can be concave up-ice or concave down-ice.

(asymmetrical shape in cross-section)

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28
Q

Drift

A

All glacial sediment whether deposited by solid ice or meltwater.

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29
Q

Glacial erosional features

A 
Roche Moutonnet
Friction Crack (ChatterMark)
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30
Q

Till

A

Glacial sediment deposited exclusively by solid ice.

Till is often made up of large, angular rock fragments (>5cm). That are the product of frost action and much smaller grains (<1mm) that are created by abraision.

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31
Q

Modes of Glacial Transport

A
  1. Supraglacial (on top)
  2. Englacial (inside)
  3. Subglacial (beneath)
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32
Q

Glacial Deposition

A

Deposition takes place when the ice melts or when the ice can no longer move the sediment.

This last mode of deposition can take place beneath the glacier.

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33
Q

Deposition beneath the glacier

A

If there is a high enough concentration of sediment at the base of the glacier the ice may not be able to move it. Eventually the ice will detach from the sediment, leaving it behind as it continues to flow forward.

Till may also be deposited in and around irregularities in the bedrock. (Till deposited in this way is Lodgement Till)

34
Q

Lodgement Till

A

Very dense, often very hard, contains all the original grain sizes it has when it was in transport and it often has an “internal fabric” created by the ice as it passes after deposition. This internal fabric may include alignment of some rock fragments or grooves left in the surface of the till.

35
Q

Balance/Imbalance in a glacier

A

When the edge or toe of a glacier remains in place that means that there is a balance between the solid ice that is flowing forward due to gravity and the ie that is melting.

36
Q

Formation of Ablation till

A
  1. At A the glacier is warm-based (not frozen to the bedrock) because of pressure melting.
  2. At B the glacier is cold-based (it is frozen to the bedrock) because the glacier is thinner, pressure is less and cold air temperatures can penetrate into this thinner, less insulated ice.
  3. At C: as the ice at the edge of the glacier slows down, it is pushed by the faster ice behind it. This causes ice and sediment to move up and way from the bedrock.

As a result of all this movement, sediment is carried onto the ice (supra-glacial), in the ice (englacial) and beneath the ice (subglacial) is concentrated at the edge of the glacier (C).

37
Q

Ablation till

A

Till deposited at the edge of a glacier.

  • Not compressed (not dense) nor hard like lodgement till.
  • Often has been reworked by meltwater and gravity so that the finer gain sizes have been removed.
38
Q

Both lodgement till and ablation till have a _________ structure

A

massive structure. There is little or not time to rework the sediment as it is deposited.

39
Q

Edge of the ice sheet….

A

The edge of an ice sheet, especially one that is in overall retreat, is dynamic and can be irregular in shape and move forward and backward at different times and places.

40
Q

Till Plain

A

Area large area of land covered in till. They often have irregular or hummocky topography. (Their surface is often irregular with lots of small highs and lows that are a result of uneven deposition and the formation of kettles)

41
Q

Factors affecting the formation of hummocky topography (kettles)

A

Different rates of ice released by the glacier will also affect topography as they melt.

As a glacier melts it may leave blocks of ice stranded on the ground in front of it. This ice block may be completely or partially buried by sediment (till) from the glacier.

When this ice block melts a basin or depression is left behind.

If his basin fills with water it is a kettle lake.

42
Q

Factors affecting the formation of hummocky topography (kettles)

A

As a glacier melts it may leave blocks of ice stranded on the ground in front of it. This ice block may be completely or partially buried by sediment (till) from the glacier. When this ice block melts a basin or depression is left behind.

(If this basin fills with water it is a kettle lake.)

43
Q

Drumlin

A

An asymmetrical teardrop shaped hill composed of till that is deposited beneath an advancing ice sheet.

(lodgement till)

44
Q

Moraines

A

Long, linear ridges of till deposited at the margin of an ice sheet when it stopped.

As the ice continues to move forward it melts and releases sediment. Moraines mark the edge of the glacier.

(ablation till)

45
Q

Terminal Moraine

A

Marks the furthest advance of the ice sheet.

46
Q

Recessional Moraine

A

This marks a time and place where the ice stopped and deposited sediment during its retreat.

47
Q

Lateral Moraine

A

This marks the side of a glacier.

48
Q

Medial Moraine

A

This occurs when two glaciers merge and the lateral moraines also merge to form a single moraine within the ice.

49
Q

Types of Moraine

A

Terminal
Recessional
Lateral
Medial

50
Q

Esker

A

A long linear ridge of sediment deposited by meltwater in tunnels at the base of the glacier.

51
Q

Kame

A

A mixture of sediment deposited at margin of an ice sheet where meltwater and gravity have concentrated the sediment.

These are often larger, taller hills of poorly sorted sediment.

52
Q

?????

A

As a result the ice may be pushed up reducing friction and allowing the ice to flow faster. If this meltwater is able to flow along the base of the glacier it can move sediment and create such things as

53
Q

Greenland Glaciers (photo)

A

(a) “river of ice” confined to a fjord.

In Greenland the melting of ice around the margins of the ice sheet is significant. It has accelerated recently because of more meltwater on the ice sheet. As this meltwater finds its way to the base of the glacier the ice beings to move faster. Faster ice often turns into thinner ice which breaks apart easier and it begins to float at the coast.

The end result is a sudden, dramatic retreat of the ice margin.

54
Q

Ice Margins- Retreating Ice Sheet

A

Photo: Gently sloping, thin ice

- More affected by underlying bedrock topography.

55
Q

Ice Margins- Retreating Ice Sheet

A

Photo: Gently sloping, thin ice
- More affected by underlying bedrock topography.

An ice sheet that is retreating will sometimes experience a local re-advance. This creates an irregular ice margin.

56
Q

Relationship between ice thickness and base conditions.

A

Where ice is thinner cold based conditions are more likely because of exposure to the atmosphere.

Where ice is thicker there is more likely to be warm-based conditions because of the insulating effects of ice and the geothermal gradient.

57
Q

When a glacier reaches the ocean (photo)

A

Upon reaching he ocean the ice begins to float and melt.

The ice will also break apart to create icebergs.

The rise and fall of sea level with tides will help to break the ice.

(A) While sediment may be released from the entire glacier, more is released from the base of the glacier.

(B)
Sediment is also carried by icebergs and eventually deposited as they melt.

58
Q

Glacial Lake Deposits - Summer conditions (photo)

A

During the summer the surface of the lake is ice free. Water and sediment enter the lake but only the coarser sediment (i.e. silt) settles to the bottom.
(silt in suspension does not settle???? to the bottom.)
This creates a coarser grain, lighter colours summer lay on the lake bottom.

59
Q

Glacial Lake Deposits - Winterr conditions (photo)

A

during the winter, the lake is covered in ice. Water in the lake is isolated and circulates very little. Now the finest sediments (i.e. clay, organic material) carried in suspension are deposited created a fine grained, dark coloured winter layer.

60
Q

Glacial Lake Deposits - Summer AND winter conditions (photo)

A

With the passage of each year alternating summer and winter layers, are deposited in the lake (rhythmites).

During the summer, in addition to sediment and meltwater, pieces of glacial ice is transported into the lake. This glacial ice often carries sediment, some of it coarse, which drops into the lake when the ice melts.

The presence of large drop stones in finer summer and winter layers makes these deposits VARVES which are exclusive to a glacial lake environment.

61
Q

Paraglacial

A

Cold environments that persist after a glacier is gone.

62
Q

Periglacial

A

Cold environments that do not always experience freezing conditions.

63
Q

Canada’s landscape is a mixture of both

A

paraglacial environments and periglacial environments.

64
Q

Feature most commonly associated with paraglacial and periglacial landforms.

A

The most common feature associated with these environments is permafrost. Permafrost is ground that has been frozen for at least two years.

Much of the permafrost in the northern hemisphere is “fossil perfmafrost”, which is the product of conditions - like the last ice age - that no longer exist.

65
Q

Permafrost on sea floor

A

Permafrost on the sea floor is confined to more shallow, coastal areas where it was created when sea level was lower. All permafrost has an active layer.

66
Q

What helps control the thickness of the active layer is:

A
  1. VEGETATION COVER

2. SNOW COVER

67
Q

Vegetation cover and active layer thickness

A

Short dense vegetation is an insulator that prevents melting

68
Q

Snow Cover and active layer thickness

A

A covering of snow is also an insulator that will protect permafrost.

69
Q

Snow Cover and active layer thickness

A

A covering of snow is also an insulator that will protect permafrost, keeping it from melting and it may trap heat, preventing it from forming.

70
Q

Permafrost on hillside

A

The active layer can move once it forms. Gravity then creates a variety of land forms - lobes and parallel ridges - in this periglacial environment.

In the northern hemisphere, a north facing slope will be colder as it gets less sunlight. More snow will accumulate and persist longer on this slope. Here, as the base of the snow pack there is repeated freeze thaw cycles which physically weather the bedrock.

71
Q

Nivation hollow??

A

Gravity, and perhaps some meltwater, erodes and transports this sediment to create a shallow depression in the hillside called a nivation hollow on this slope.

72
Q

Patterened ground

A

These are regular, repeating patterns in sediment that are caused by freeze-thaw cycles.

73
Q

Patterned ground: circles

A

defined by a raised edge. (about 1 m wide)

74
Q

????

A

This mixing in the form of convection currents is the result of repeated expansion and contraction cause by freeze-thaw cycles. At the surface, the larger grains are pushed further to form a ridge (A)

75
Q

Pingo

A

A large ice cored hill.

76
Q

Formation of a pingo

A

Pingos form in two ways… as:

  1. Open systems
  2. Closed systems
77
Q

?

A

In a layer of sediment, ice forms at some point underground. (A)
One the ice forms, more water is drawn to it. This additional water, sometimes in the form of water vapour freezes to the ice and the original ice grows in size. As the ice grow it pushed up the ground above it, creating a pingo.
The ice inside the pingo contains little to no sediment. As it forms the ice excludes the sediment, pushing it away and maximizing uplift.

Cracks open on the surface as expansion continues. Eventually, as the pingo grows its surface cracks and openings in the vegetation appear. this arrows water and heat in that will melt the ice core and cause the pingo to collapse.

78
Q

Vegetation on Pingos

A

Pingos are covered in vegetation that insulates the ground and protects the ice core.

79
Q

Closed systems for pingos

A

In a closed system, pingos form when a lake drains.

Permafrost beneath a lake occurs at greater depthe because of the heat holding capacity of the water.

Once the lake is drained, the exposed ground beneath the lake freezes - the surface of the permafrost rises.

Water between the lake bottom and the surface of the permafrost is trapped. It eventually freezes to form ice that pushes the ground up.

80
Q

Permafrost - why importance

A
  • it is a major feature in the Canadian landscape.
81
Q

Sources of liquid water in a glacial environment

A
  • Meltwater - rain, melting snow or melting ice
    pressure melting in the glacier.
    arguably, a geothermal gradient could be contributing to melt.
    Meltwater itself can contribute to more melting.
82
Q

How does liquid water affect behavior or….

A

Liquid at the base of a glacier - warm based glacier most likely. IF you have enough meltwater you get an esker.

Advanced Geomorphology (10 decks)

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