glaciated landscapes - knowledge

What % of earth is covered by glaciers

10%

When was the last glacial maximum

21,000 years ago, 32% of these earth was covered

Ice cap v ice sheet

<50,000 km² (vakaajokull, Iceland) = ice cap

>50,000km² (Greenland, Antarctica) = ice sheet

Where is freshwater stored

90% stored in cryosphere

What happens if all ice melted

Sea level rise by 70 m

What’s the cryosphere

All frozen parts of the planet

Inputs - open glacial system

• Energy - thermal (sun), kinetic (movement of the glacier) and potential (position on slope)

• Matter - snowfall (precipitation), avalanching, wind deposition (wind blown snow), debris from mass movement and weathering

Outputs - open glacial system

• Energy - thermal (e.g. evaporation)

• Matter - meltwater, ice (carving of iceburgs into lakes/oceans), evaporation, sublimation and debris

Throughputs - open glacial system

• Stores - ice, water and debris

• Flows - ice, water and debris

Positive balance

Glacier is gaining mass (normally during the winter)

Negative balance

Glacier is losing mass (during the summer)

Dynamic equilibrium

A glacier system in equilibrium where inputs (accumilation) = outputs (ablation) - self regulated

Glacier mass balance

1. Accumilation zone

2. Positive balance

3. Equilibrium line

4. Negative balance

5. Ablation zone

How does glacial ice form

• New snow compresses and compacts the layer beneath, air is removed - low density snow now high density

• Known as diagenesis, takes 40-1000 years

• True glacial ice found around 100m down, very pure blue colour

Valley glaciers (warm based)

• Confined by valleys, follow course of river valley

• May be outlet glaciers from ice sheets or fed by Corrie glaciers

• 10-30km long

• Alps, rockies and Andes

Ice sheets (cold based)

• Accumilation extending more than 50,000km²

• 96% of world ice, only found in Antarctica, Greenland (thickest ice 4,700 m)

• Ice sheets previously covered most of Europe

Warm based glacier

• High altitude locations, steep relief

• High accumulation and ablation

• Basal temperatures at or near pressure melting point

• Melt water created as temperatures reach pressure melting point at base of ice

• Rapid rates of movement – mobile glacier = erosion (20-200m/year)

• Basal slippage occurs

Cold based glacier

• High latitude locations with low relief

• Ablation and accumulation is limited

• Basal temperatures below pressure melting point (no melt water and basal slippage)

• Glacier is frozen at the bed, therefore little movement and little erosion or deposition

• Slow rates of movement, temperatures below 0°

• Internal defamation

Glacial budget - influencing glacier movement

A positive budget (net accumulation) causes the glacier to advance

Gravity - influencing glacial movement

Fundamental cause of movement of an ice mass

Gradient - influencing glacier movement

The speed of the gradient of the grand surface, the faster the ice will move if other factors are excluded

Thickness of ice - influencing glacier movement

Influences basal temperature and the pressure melting point

Internal temperature- influencing glacier movement

Allow movements of one area of ice relative to another

Internal deformation - Latimer flow

1. Movement of each layer within the glacier

2. Will occur faster depending on the gradient and position of the glacier

Inter-granular flow - internal deformation

Individual grains of ice slip, move in relation to each other, re-orienting themselves

Internal deformation- example

Moves 3-4 M/year at its equilibrium line, 100% of this is movement

Where is Latimer flow found

Cold based glaciers

Where is basal sliding

Warm based glaciers

Creep and regelation - basal sliding

1. Direction of movement due to gravity

2. Pressure build up, causes localised pressured melting

   Ice deforms under the pressure, spread around block ‘plasticly’

3. Meltwater flows around the block then refreshes when normal pressure returns

Slippage - basal slippage

1. Direction of movement due to gravity

2. Reduces friction between base of glacier and bedrock

3. Friction creates meltwater, as it reaches pressure melting point, allowing it to move more

Bed deformation - basal sliding

1. Direction of movement due to gravity (gentle gradient)

2. Carry’s the ice by saturated bed sediments, water under high pressure

3. Referred to as on ‘ ice skates ‘

Examples - basal sliding

Franz josef, New Zealand - moves 300 M/year, warm based

Salman, Canada - 45% of movement due to basal sliding, could be up to 90%

Extending flow

When ice moves down a slope quickly, fractured ice accelerates forward becoming thinner

Compressing flow

When the gradient is reduced, the ice slows and becomes thicker

Extending and compressing flow

1. Extending flow, Bergschrund and Crevasses

2. Slip plane

3. Compressing flow

4. Extending flow, Crevasse and Seracs (ice blocks or steep faults)

5. Surface of ice breaks and cracks because of higher velocity

6. Compressing flow

7. Pressure bulges as compressing flow begins

Wind - physical factors influencing landscapes

• Erosional, transportation, deposition - a moving force

• Acts upon fine material deposited by ice or meltwater

Precipitation amount - physical factors influencing landscapes

• Main Input of snow, sleet and rain

• High Lattitude = precipitation may be low

• High altitude = high precipitation

• Antarctica means precipitation = 4.5 mm/year

Structure of geology - physical factors influencing landscapes

• Properties of rock types, jointing, bedding and faulting

• Angles of rocks influences valley profiels and permeability of rock type

Latitude - physical factors influencing landscapes

High Lattitude have cold dry climates with low variation in precipitation

Altitude - physical factors influencing landscapes

High altitudes have higher precipitation but, higher temperatures = more melting

Relief - physical factors influencing landscapes

Steeper the relief, the greater fource of gravity = more energy for a glacier to move down the slope

Aspect - physical factors influencing landscapes

• Face away from the sun = low temperatures and melting (below 0c for longer) - opposite for facing toward the sun

• Will effect the mass balance and the shape of the landscape

Lithology of geology - physical factors influencing landscapes

• Physical and chemical composition of rocks

• More strong rocks are resistant to erosion, weaker are vulnerable to decay (at low temperatures)

• Strong rocks form glaciated landscapes (arêtes, pyramidal peaks)

Temperature - physical factors influencing landscapes

• If temperatures above 0c ice will start to become a output system

• High altitude have significant areas 0c + temperatures

• High Lattitude temperature doesn’t really rise above 0c

Seasonal distribution of precipitation - physical factors influencing landscapes

• Jasper, precipitation = 25mm in January (snow), 100mm in June (ice)

• Little seasonal change in Antarctica

• Greater seasonal change, more varied mass balance

Geomorphic process

Rock changing processes

Weathering - geomorphic processes in landscapes

Decay and disintegration of rocks at or near the earths surface

Mass movement - geomorphic processes in landscapes

• Forces acting on a slope material exceed forces trying to keep the material on the slope

• Most significant on steep slopes

• Adds debris to glaciers providing a tool for abrasion

Erosion - geomorphic processes in landscapes

Occurs as glaciers advance in upland areas

Deposition - geomorphic processes in landscapes

• Glaciers deposit when there capacity to transport the material is reduced

• All deposits are known as drift

• Divided into till (material from ice)

• And outwash (material from meltwater)

Transportation- geomorphic processes in landscapes

Divided into supraglacial, englacial and subglacial

Freeze-thaw - physical weathering

• Water enters cracks and expands by 10% when it freezes, causes pressure causing rock to split

• More frequent fluctuations in temperatures around 0c = more effective

Frost shattering - physical weathering

• At low temperatures water trapped in pores freezes and expands

• Creates stress and rock disintegrates to small pieces

Pressure release - physical weathering

• Weight of overlaying ice in a glacier is lost due to melting

• Underlying rock expands and fractures Parallel to the surface

• Significant as granite is known for its strength

• The parallel fractures are called pseudo-bedding planes

Other bits for physical weathering

• Temperature may stop these processes

• No chemical alteration occurs

Oxidation - chemical weathering

• Some minerals in rocks react with oxygen (in air or water)

• Iron is susceptible to this and becomes soluble under extremely acidic conditions and the structure is destroyed

• Often attacks iron-rich sediments that bind sand grins together in sandstone

Carbonation - chemical weathering

Water combines with dissolved carbon dioxide which reacts with calcium carbonate in rocks (limestone) to make calcium carbonate (solvable)

Solution - chemical weathering

• Salts are solvable in water, iron is only solvable in acidic water PH3

• Any process where mineral dissolves in water is known as solution - there are mineral specific processes

Other information for chemical weathering

• Water contacts rock and dissolves some of the minerals in the rock

• Chemical reactions happen when temperatures increase - 10c increase leads to 2.5x increase in reactions

• Rain/snowfall can become slightly more acidic

Tree roots -biological weathering

• Grow in cracks and places pressure

• Many expose rocks and make them susceptible to weathering

Organic acids - biological weathering

• Produced during decomposition causing soil water to become more acidic and react with minerals (chelation)

• Blue-green algae produces a shiny film of iron and magnesium oxide on rocks

Other bits - biological weathering

May be affected by low temperatures so may have limited significance

Rock fall - mass movement

• Slopes of 40 degrees +, rocks may become detached through physical weathering, can happen in minutes to seconds

• Fall to the foot of the slope under gravity

• Transport processes may remove this/can axumilate as a straight, lower angled scree slope

Slides - mass movement

• May be linear with movement along a slip plane (fault/bedding) are also known as slumps

• May occur due to steeping or undercutting of valley sides due to erosion at the base of the slope under gravity (adding to the downslope fources)

• Common in weak rocks (clay) which becomes heavier when wet, adds to downslope forces

Other bits - mass movements

• Forces acting on a slope, material exceed forces keeping material up

• Most significant on steep slopes

• Adds debris to glaciers providing a tool for abrasion

Other bits - erosion

Occurs as glaciers advance in upland areas

Plucking - erosion

• Happens when meltwater is in joints in the rocks of the valley floor

• Freezes and attaches to the glacier, as moves pulls the rock with it

• Effective at base of glacier as weight of ice may produce meltwater

• Significant when bedrock is highly jointed (allows water in)

• Known as quarrying

Plucking - erosion

1. Meltwater enter crack in the water

2. Meltwater freezes and separates rock from bedrock

3. As the glacier moves the block of rock freezes to the ice and is ‘plucked’ out

Abrasion - erosion

• When the glacier moves, debris embedded in the side which scours the surface rocks, wearing them away (like sandpaper)

• The debris is course will scrape, scratch and grove the rock

• The fine material will smooth and polish the rock

• Debris will go fine creating rock flour which is responsible for the white look glacier meltwater streams

Abrasion - erosion

1. Angular rock debris are embedded in the base and sides of the glacier

2. As the glacier moves, the rock in the base of the ice scrape against the bedrock - sand paper effect

3. After ice has melted, smooth rock is left behind, often with striations (scratches in the rock surface)

Ice thickness - factors effecting erosion

• Increased thickness of ice = increased pressure placed on debris = increased abrasion

• Too much ice will cause too much pressure = increased friction, reduction in movement

• Thickness tends to be 100-200 M

Debris size and shape - factors effecting erosion

• Debris exerts large pressure downwards compared to there weight

• Larger the debris the more useful

• Angular debris is also useful as the pressure is on one bit of he bedrock

Presence of basal debris - factors effecting erosion

• Ice can’t erode itself

• Rate increases when more debris is present, movement of the glacier may slow due to too much friction

Hardness of particles and bedrock - factors effecting erosion

• Most effective when hard debris is moved across a soft bedrock

• If the bedrock is resistant, a little abrasion will occur

Removal of fine debris - factors effecting erosion

• To maintain high rates of abrasion, rock flour needs to be removed so that larger debris can abrade the bedrock

• Mainly done by meltwater

Movement of debris to the base - factors effecting erosion

• Abrasion doesn’t just wear down bedrock but also erodes the debris

• Debris needs to be replenished if abrasion is to remain effective

Sliding of basal ice -factors effecting erosion

• Abrasion requires sliding to ensure rocks move across the surface

• High rates of sliding more potential for erosion as more debris is able to move across the bedrock

Basal water pressure - factors effecting erosion

• A layer of meltwater is vital for sliding and abrasion

• If the water is under pressure, the glacier is buoyed up, low pressure and erosion

Emblemton and king 1968 - factors effecting erosion examples

Mean annual erosion for active valley glaciers is bettween 1000-5000 m³

Glacier d’argentere - factors effecting erosion example

Ice 100m thick flowing 250 m/year, eroded a marble plate at up to 36 mm/year

Bolton 1974 - factors effecting erosion example

• Measured rock plates beneath the breiömerkurjökull glacier, Iceland

• Found ice 40m thick, basalt eroded 7mm/year, marble 3mm/year

• Ice had velocity 9.6m/year, increased to 15.4m/year as erosion of marble increased to 3.75 mm/year though ice was 8m thicker

• Suggests velocity is more important than thickness

Supraglacial

• Debris carried on top of/ surface of a glacier

• Comes from weathering and rockfall

Englacial

• Debris within the ice

• Possibly supraglacial covered by snowfall, fallen into crevasses or sunk into the ice due to pressure melting

Subglacial

• Debris emmbedded into the base of the glacier from plucking and abrasion

• Could have continued down through the ice as former englacial debris

Deposition information

• Glaciers deposit when there capacity to transport the material is reduced - due to ablation during times of retreate

• all deposits are known as drift

Lodgement till

• Deposed by advancing ice, due to downward pressure by thick ice

• Subglacial debris may be pressed into valley floor and left behind

• Enhanced pressure melting

• Drumlins are the main land form

Ablation till

• Deposited by melting ice, form stagnet / retreating glaciers (durning a warm period / the end of glaciation events)

• Most glacial deposition land forms are due to this

Angular / sub-angular in shape (deposition)

Embedded in ice and no further erosion processes (particularly meltwater which could make the rock smooth)

Unsorted depositon

• All deposits are deposed together (dosen’t matter the size and weight )

• When water deposits it losses energy and deposits in a size based way

Unstratified deposition

Glacial till dropped in mounds and ridges rather than layers - typical of water-borne deposits

Formation of Corrie - early stage of glacier

1. Freeze-thaw action

2. Fresh snow

3. Debris removed by meltwater stream

4. Surface thaws in the summer

Starts with nivation of a small hollow, overtime they enlarged and contain more snow, compresses into glacial ice

Formation of corrie - during glaciation

1. Frost-shattering above glacier

2. Bergschrund crevasse

3. Plucking

4. Frost-shattering

5. Abrasion

6. Flow path of ice

7. Rotational flow

8. Corrie lip

Formation of glacier - during glaciation

• Ice acquires a rotational movement under its weight

• Causes plucking of the back wall, increase steepness

• Debris allows the hollow to deepen

• Thinner ice can’t erode so a higher lip is left

• Lip may contain moraine deposited by the ice as it moves out of the corrie

Formation of corrie - post-glacial

1. Headwall

2. Tarn (dammed by rock lip)

3. Rock lip (threshold)

Corrie may become filled with water forming a small circular lake / tarn

Arêtes

• Narrow steep-sided ridge between 2 corries described as knife edged (very thin)

• Striding edge, each side are 200-300 m high (almost vertical) - can walk one person at a time

Pyramidal peak

• Where 3+ corries develop around a hill or mountain top and there back wall retreat - remaining mass will form a pyramidal peak

• Example is weisshorn Switzerland

Truncated spur

Erosion of the valley to create the parabolic shape, the base flattens/ cuts into the v shaped valley

Hanging valley

Deferential erosion between a smaller glacier joining a larger glacier, where the smaller one connects to it higher up as can’t erode as much so appears to be hanging

Rock step

Are less eroded and more resistant because the glacier was ‘younger’ and had less mass so the glacier couldn’t erode the resistant rock (found just after corries)

Roche moutonnee

More resistant rock (an igneous intrusion), that have been smooth/rounded up-valley and a steep, jagged down-valley