Glaciation

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  • Created by: Chloe
  • Created on: 17-10-16 18:56

Glacier Formation

A glacier forms when snow accumulates and doesn't melt during the summer months. Once the snow has been around for a year without melting it is called firn. An accumulation of firn forms a glacier.

Accumulation - Increase in the volume of snow.
Ablation - Decrease in the volume of snow.
Glacial Budget - Difference between ablation and accumulation.

Glaciers retreat in the summer due to the ammount of ablation exceeding the amount of accumulation caused by an increase in temperature.

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Factors affecting glaciated landscapes

What are the factors which affect glaciated landscapes?

  • Aspect - North facing slopes are cooler as they recieve less of the suns energy meaning there is more accumulation on the north facing slopes and more ablation on the south facing slopes.
  • Relief - Steep slopes mean that snow doesn't have a chance to settle and flows down the mountain.
  • Altitiude - Higher altitude means it is colder therefore there is more accumulation and less ablation.
  • Climate - Fluctuations causes more or less snow to fall, disturbing the equilibrim.
  • Geology - Permeable rocks enable snow to be absorbed into the ground meaning snow doesn't settle on the surface and compress to form a glacier.
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Why do glaciers move?

Why do glaciers move?

  • Gravity - Causes movement downhill.
  • Gradient - Steeper gradient causes a glacier to move faster.
  • Ice thickness - Influences basal temperature and pressure melting point.
  • Ice temperature - Allows ice to move relative to other ice.
  • Glacial budget - A positive budget causes the glacier to advance.

Pressure melting point 
The temperature at which ice is on the verge of melting.

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Warm and Cold - based glaciers

Warm-based glacier:

  • High altitiude
  • Mid latitude
  • Steep relief
  • Basal temperature is at or above pressure melting point
  • High accumulation
  • High melting point
  • Melt water accumulates at the base, allowing it to move easily.

Cold-based glacier:

  • High latitude
  • Lower altitude than warm-based glaciers
  • Low relief
  • Below pressure melting point so base frozen to the bedrock.
  • Move only a few m per year.
  • No melt water at base meaning it doesn't move as easily.
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Glacier Movement

Basal sliding:
The base moves due to the temperature of the base.
Warm-based glaciers move by basal sliding due to the creation of meltwater.
Slipage - Ice moves over the valley floor due to meltwater reducing friction between the base of the glacier and the valley floor.
Creep or regelation - Ice deforms due to obstacles on the valley floor, spreads over obstacle and refreezes over it.
Bed deformation - Ice is carried by saturated bed sediments. It is like it is moving on roller skates.

Internal deformation
Interglacial flow - Individual ice crystals re-orientate.
Laminar flow - Movement of separate layers of ice in the glacier.
Cold-based glaciers move by internal deformation as they are unable to move by basal sliding.
If the relief is steep, the glacier can't deform quick enough to move over the obstacles, causing the base to shatter, forming crevasses.

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Extending and compressing flows

Extending - Ice pulls away from the ice behind which hasn't reached the steeper slope.
Compressing - Ice thickness and flowing ice pushes over the slowing-moving leading ice.

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Weathering processes

Weathering - Physical or chemical processes alter the material.

Freeze-thaw - Water enters cracks in rocks, freezes and expands. Ice melts, travels further down the rocks, freezes and expands again. This process keeps occuring, eventually causing the rock to break up.
Frost shattering - Existing water in the rock pores freezes and expands causing the rock to break up.
Pressure release - Overlying ice melts, resulting in the underlying rock expanding and freezing due to the decline in pressure.

Oxidation - Minerals react with oxygen, becoming soluble and the structure is destroyed.
Carbonation - Carbonic acid reacts with CaCO3 producing calcium bicarbonate.
Solution - Material dissolves in acidic water.
Hydrolysis - Rock materials and water react, producing materials such as clay.
Hydration - Water added to rock minerals creating large, new minerals.

Tree roots - Roots grow in cracks, topples over exposing rock and soil to weathering.
Organic acids - Decomposition of plant and animal litter, causing soil to be acidic.

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Weathering + Erosion

Rock fall - Rocks detach and fall when slopes are greater than 40 degrees.
Sudes - Internal structure of slope is weakened.

Erosion:

Plucking - Meltwater seeps into valley floor cracks, freezes, becomes attached to the glacier. Glacier advances, pulling pieces of rock away.
Abrasion - Rocks on the bottom of the glacier scrape along the valley floor breaking it up and removing material.
Nivation - Ice grows into underlying rock. Area od roc losens, and its dragged away by the glacier.

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Transportation

Supraglacial - Material carried along surface of glacier.

Englacial - Debris, previously supraglacial which gets covered by accumulation.

Subglacial - Debris on base caused by plucking or abrasion.

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Deposition

Lodgement till - Material deposited by advancing ice.
Ablation till - Material deposited by melting ice.

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Glacial Landforms

Corrie -

  • Snow accumulates on slope
  • Ice grows into rock (nivation)
  • More accumulation
  • Mass increases, causing it to move down hill
  • Takes the rock with it
  • Leaving a hollow
  • Rotational movement of material causes plucking, making it steeper.
  • Debris from plucking and weathering helps to abrade the hollow making it deeper

Arete - 

  • Two corries back to back

Pyramidal peak - 

  • 3 or more corries back to back on a mountain
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Glacial Landforms

Corrie -

  • Snow accumulates on slope
  • Ice grows into rock (nivation)
  • More accumulation
  • Mass increases, causing it to move down hill
  • Takes the rock with it
  • Leaving a hollow
  • Rotational movement of material causes plucking, making it steeper.
  • Debris from plucking and weathering helps to abrade the hollow making it deeper

Arete - 

  • Two corries back to back

Pyramidal peak - 

  • 3 or more corries back to back on a mountain
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U shaped valleys

As the glacier moves out of the corrie it causes the valley shape to change from a v to a u.

As the glacier moves through the valley due to gravity, processes such as plucking and abrasion occur, causing the valley to deepen and widen.

Glaciers can't flow past interlocking spurs, so instead cut through them, forming steep truncated spurs.

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Hanging Valleys

Tributary valleys feed into the main valley.
The main valley erodes quicker than the tributary valley, leaving the tributary valley higher up. This is called a hanging valley.

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Truncated Spurs

Cut-off rounded areas of land, formed when a glacier cuts through interlocking spurs.

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Roche Moutonnees

Roche moutonnees:

  • Indicates directoin of ice flow.
  • When there is a band of resistant rock, the glacier moves over it.
  • Abrasion occurs creating a smooth layer of rock.
  • Meltwater flows down the other side, seaping into the cracks in the rocks and freezes.
  • Plucking occurs creating a rough edge.
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Ribbon Lakes

Occurs when there are different types of rock, some are less resistant than others.

Less resistant rock erodes more quickly than resistant rock, creating a hole.

Glacier melts, leaving behind a lake.

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Striations

Show direction of glacier movement

Ice passes over resistant rock, localised pressure melting on the up-valley side. The area is smoothed by and streamlined by abrasion. 

Striations are grooves or scratches made by subglacial material.

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Chatter marks

Grooves in the resistant rock because there is more meltwater, meaning material has more movement within the glacier.

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Glacial deposition

Ablation till:

  • Eratics
  • Morraines - Terminal, lateral, medial
  • Boulder clay - Unstratified material depositied by a glacier.

Fluvioglacial:

Ice contact:

  • Eskers
  • Kames
  • Kettle holes

Prolonged

  • Varves
  • Outwash (sandurs)
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Periglacial

  • Pingos
  • Ice wedges
  • Patterned ground
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Fluvioglacial Features

  • Kame deltas - Material deposited at the edge of a glacier.
  • Eskers - Form when meltwater from the base of a glacier deposits material. Looks the same as a medial mrraine, however eskers have stratified layers unlike morraine.
  • Kettle holes - Lump of ice is left behind by a glacier, stratified sediment left behind by meltwater builds up around it. Ice melts, leaving a hole behind. The hole eventually is filled in with water, forming a kettle lake.
  • Varves - Sediment layers which are deposited in lakes.
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Periglacial Landforms

  • Patterened ground - General term for small-scale features of periglacial environments.
  • Pingos:
    Open system: 1. Water collects in the valley bottom within an area of talik.
    2. When the temperature falls the talik becomes frozen, it expands, pushing the surface up into a dome.
    Closed system: 1. Water from lakes seeps into talik.
    2. Temperature falls, talik surrounded by advancing permafrost.
    3. Talik freezes, expands, pushes the surface into a dome.
    4. Ice melts, depression forms, called an ognip.
  • Talik - Unfrozen ground.
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Periglacial Landforms

  • Patterened ground - General term for small-scale features of periglacial environments.
  • Pingos:
    Open system: 1. Water collects in the valley bottom within an area of talik.
    2. When the temperature falls the talik becomes frozen, it expands, pushing the surface up into a dome.
    Closed system: 1. Water from lakes seeps into talik.
    2. Temperature falls, talik surrounded by advancing permafrost.
    3. Talik freezes, expands, pushes the surface into a dome.
    4. Ice melts, depression forms, called an ognip.
  • Talik - Unfrozen ground.
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