Linkage between General Climate & Glacier snout behaviour
Factors controlling glacier response over time
Relaxation/ response time – time interval between change of input & the achievement of new equilibrium
Amplification factor – small change in mass balance initiate large change at the glacier terminus
Specific mass balance characteristics – damp down minor climatic oscillations
Steady state situation – glacier remain at zero for many years & glacier dimension remains constant
Glacier Morphology
Response to climate
Distance between snout & accumulation Area – contributes to fluctuations due to climate
Narrow valley glacier – more time to respond than ice cap
On Land – Glacier Responds by expanding/ withdrawing snout
Extension – more surface area exposed to ablation
Fjord – difficulty in achieving equilibrium, continue to advance until spread out & increase cross sectional area exposed to melting & calving
Mass Balance Changes
Minor oscillations – direct response to annual climate oscillations
Major advances/ retreats – indirect/ lagged, significant long term changes
Direct response – short term mass balance change
Negative mass balance – reflected in 1 season
Positive mass balance change – may not be reflected by several seasons
Climatically induced snout retreats – more rapidly than climatically induced snout advances
High Accumulation, Low Ablation – interrupts retreat
Glacier Activity – influences velocity of kinematic waves
Very active Glaciers (Western Side of New Zealand) – responds directly to climatic oscillations
Sluggish glaciers (eastern side) – greater time lag
Compute response tie of Glaciers (e.g. Berendon Glacier in British Columbia by Nye)
Glacier Length
Height of Glacier Surface above mean sea level
Slope of surface
Mass Balance data
Mathematical models – Assumes
- Climatic fluctuations are small
- Any effects caused by changes in the quantity of melt water at the base can be ignored
- Changes in the temperature of ice (and thus the relation of stress to strain rate) can be ignored
Glacier mass balance change – measureable
Predictable
Surge behaviour
Surge – snout advance
Have a cycle of activity
Not climatically induced
Prolonged storage of surplus mass – until critical stage of instability or threshold reached
Attainment of critical stage is predictable
Wavelength & amplitude of surge cycle – shorter for small valley glaciers
Variations over days & weeks – related to ablation rates & meltwater discharge
Short-lived advances interrupting overall period of retreat – rapid responses to minor climatic oscillations
Little ice Age – 1500 -1920
Alpine climatic fluctuations from
Records of vineyards
Fruit growing, settlement history
Cereal growing, ease of ocean travel aspect of individual dated settlement sites
Vegetation studies – pollen analysis, lichenometry, studies of changing tree-line altitude------information on climatic fluctuation
Archaelogical & pedological investigation – information on recent climatic fluctuations
Technique – radio – carbon dating
Indicator of severity of Icelandic climate – sea ice off Icelandic coasts
Radiometric dating, palynology, dendrochronology….lichnometric technique
Prediction of glacier Behaviour – numerical model experiments of Climap Project, NCAR project
Sunday, August 16, 2009
Saturday, August 15, 2009
Spatial Distribution of Glaciers
Current glacierization
Areal Extent of Glaciers
Flint: - Importance of knowledge of Glacier Volumns – appreciate the importance of glacierization
Glacier volume – by radio-echo sounding
Degree of Inundation of land surface by snow & ice
Degree of Glacierization – percentage of land surface covered at the end of Balance
Year,
Data Plotted on a grid instead of a map
Degree of relief by ice
- Morphological variable within a landscape system
- Index of the intensity or type of glacial or nival processes operating upon the bedrock base
Detailed movement of snow & ice thickness – radio echo sounding profile
Continuous data concerning ice surface altitude & form, ice thickness, sub-ice bedrock relief
Applied in Greenland, Arctic Canada & Antarctica
Factors influencing the current distribution of snow & ice
Precipitation
High Evaporation rate, low annual precipitation, negative net precipitation
High altitude west coast environment – extremely heavy precipitation
Glaciologically influence as precipitation in the form of rainfall – contributes little to glacier mass
Nivometric coefficient – index of snow effectiveness
- ratio of snowfall (in water equivalent) to total annual precipitation
Nivometric coefficient – > 1 low precipitation
less suitable for glacial growth suitable for prolonged glacial survival
Medium Nivometric coefficient – high precipitation
Marginal from point of view of glacierization
Nivometric coefficient < 1 – high precipitation
Temperature
Mean summer temperature
Relationship between regional temperature characteristics & glaciarization
Latitute
Ice cover zone
Frost rubble zone climatically contolled systems
Tundra Zone
Altitude
Independent parameter at regional & local scale. Fundamental control over climatic parameters & hence on glacier distribution
Altitudinal zonation of mountainous area
Glacial/ Nival
Sub nival
Alpine
Sub Alpine
Upto sea level in high laltitude
High altitude in low latitude
Relief
Surface relief
Breath of an individual summit determines whether or not a glacier can be supported
Glaciation level
Partsch – brucker method of defining this limit
Snow fence effect – jaggered mountain scenary in baffin island in trapping snow &
allowing cirque glacier to develop lower than normal altitudes
mass balance – position of snout
morphology of channel – precise location of channel
shape ratio: ratio of elevation to area – and over 600m
roughness index: geometric properties of surface
high dissected topography – inhibit glacierization
Aspect
Orientation of ground surface with respect to incoming solar radiation (local scale)
Little control at regional/ larger scales
Distance from nearest ocean
Independent variable – influencing
Regression analysis
Glacier Inertia
Ice caps & ice sheets – out of equilibrium with their climatic environment devoid of relationship between morphological parameters as altitude, aspect & relief
Regression graphs are used to pot relationships – eg . Between altitude of glaciations level for Norway & ocean distance – Chorlton & lister
Areal Extent of Glaciers
Flint: - Importance of knowledge of Glacier Volumns – appreciate the importance of glacierization
Glacier volume – by radio-echo sounding
Degree of Inundation of land surface by snow & ice
Degree of Glacierization – percentage of land surface covered at the end of Balance
Year,
Data Plotted on a grid instead of a map
Degree of relief by ice
- Morphological variable within a landscape system
- Index of the intensity or type of glacial or nival processes operating upon the bedrock base
Detailed movement of snow & ice thickness – radio echo sounding profile
Continuous data concerning ice surface altitude & form, ice thickness, sub-ice bedrock relief
Applied in Greenland, Arctic Canada & Antarctica
Factors influencing the current distribution of snow & ice
Precipitation
High Evaporation rate, low annual precipitation, negative net precipitation
High altitude west coast environment – extremely heavy precipitation
Glaciologically influence as precipitation in the form of rainfall – contributes little to glacier mass
Nivometric coefficient – index of snow effectiveness
- ratio of snowfall (in water equivalent) to total annual precipitation
Nivometric coefficient – > 1 low precipitation
less suitable for glacial growth suitable for prolonged glacial survival
Medium Nivometric coefficient – high precipitation
Marginal from point of view of glacierization
Nivometric coefficient < 1 – high precipitation
Temperature
Mean summer temperature
Relationship between regional temperature characteristics & glaciarization
Latitute
Ice cover zone
Frost rubble zone climatically contolled systems
Tundra Zone
Altitude
Independent parameter at regional & local scale. Fundamental control over climatic parameters & hence on glacier distribution
Altitudinal zonation of mountainous area
Glacial/ Nival
Sub nival
Alpine
Sub Alpine
Upto sea level in high laltitude
High altitude in low latitude
Relief
Surface relief
Breath of an individual summit determines whether or not a glacier can be supported
Glaciation level
Partsch – brucker method of defining this limit
Snow fence effect – jaggered mountain scenary in baffin island in trapping snow &
allowing cirque glacier to develop lower than normal altitudes
mass balance – position of snout
morphology of channel – precise location of channel
shape ratio: ratio of elevation to area – and over 600m
roughness index: geometric properties of surface
high dissected topography – inhibit glacierization
Aspect
Orientation of ground surface with respect to incoming solar radiation (local scale)
Little control at regional/ larger scales
Distance from nearest ocean
Independent variable – influencing
Regression analysis
Glacier Inertia
Ice caps & ice sheets – out of equilibrium with their climatic environment devoid of relationship between morphological parameters as altitude, aspect & relief
Regression graphs are used to pot relationships – eg . Between altitude of glaciations level for Norway & ocean distance – Chorlton & lister
Glacier Morphology
Ice dome - convex surface slope of ice dome
Thinner ice – steeper slope to flow
Thicker ice – lesser surface slope
On horizontal bed, h = -/2h.s
h. = 11m
s = horizontal distance from margin in metres
Ice sheet
Valley glacier
Ice shelf
Dome of 10-50 km size
Precipitation increases with increasing altitude to summit
Dome of continental size
Increase of precipitation with altitude occurs only when near the periphery
Outlet glacier – peripheral zone of ice dome marked by radiating pattern of ice dome extending deyond dome margin within ice dome they occupies a depression & distinguished by a zone of rapidly moving ice bordered by crevasses ….ice stream
Longer glacier + gentler gradient
Greenland no mountain range, gentler gradient
Ice shelf
Models of developing principles of ice creep
Sheer cliff rising 30m above sea level
Flat surface
Accumulation
Flat upper surface
Land glaciers
Bottom freezing
Highest near the seaward edge & decreases inward
Ablation
Calving & bottom melting
Glaciers constrain by topography
Ice field
Level area of ice
Distinguished from the cap because no domelike shape
Difficult distinction between
Mountain icefield and non equilibrium ice cap
St. Elias Mountain Area, North America
Valley glaciers
Originates in icefield or cirque
Radiates from main massif, dendritic pattern simpler than rivers
Tributary glaciers joins main glacier
Hubbard glacier – 120km long
Usual size – 10-30km
Freed from constrained of valley forms piedmont lobes
Altitude high relative to size
Cirque glaciers
Accumulation from drifting snow, rigourous than larger adjacent glaciers
Plan shape of isolated cirque glacier favours strong convergent flow above EL & divergent flow below
Ice apron – thin masses of snow adhering to mountain sides
Ice fringes – bordering a coastline
Surface Ice Forms
Sastrugi – dunes of hard packed snow elongated in the direction of prevailing wind
Steeper Ice sheet Periphery
Crevasse
Surface feature related to glacier movement
Splaying crevasse
Chevron crevasse
Traverse crevasse
Life of crevasse is limited
Extensive crevassing – convex long profile
Foliation – banding in ice
Alternative layers of white bubbly ice & bluish ice
Thinner ice – steeper slope to flow
Thicker ice – lesser surface slope
On horizontal bed, h = -/2h.s
h. = 11m
s = horizontal distance from margin in metres
Ice sheet
Valley glacier
Ice shelf
Dome of 10-50 km size
Precipitation increases with increasing altitude to summit
Dome of continental size
Increase of precipitation with altitude occurs only when near the periphery
Outlet glacier – peripheral zone of ice dome marked by radiating pattern of ice dome extending deyond dome margin within ice dome they occupies a depression & distinguished by a zone of rapidly moving ice bordered by crevasses ….ice stream
Longer glacier + gentler gradient
Greenland no mountain range, gentler gradient
Ice shelf
Models of developing principles of ice creep
Sheer cliff rising 30m above sea level
Flat surface
Accumulation
Flat upper surface
Land glaciers
Bottom freezing
Highest near the seaward edge & decreases inward
Ablation
Calving & bottom melting
Glaciers constrain by topography
Ice field
Level area of ice
Distinguished from the cap because no domelike shape
Difficult distinction between
Mountain icefield and non equilibrium ice cap
St. Elias Mountain Area, North America
Valley glaciers
Originates in icefield or cirque
Radiates from main massif, dendritic pattern simpler than rivers
Tributary glaciers joins main glacier
Hubbard glacier – 120km long
Usual size – 10-30km
Freed from constrained of valley forms piedmont lobes
Altitude high relative to size
Cirque glaciers
Accumulation from drifting snow, rigourous than larger adjacent glaciers
Plan shape of isolated cirque glacier favours strong convergent flow above EL & divergent flow below
Ice apron – thin masses of snow adhering to mountain sides
Ice fringes – bordering a coastline
Surface Ice Forms
Sastrugi – dunes of hard packed snow elongated in the direction of prevailing wind
Steeper Ice sheet Periphery
Crevasse
Surface feature related to glacier movement
Splaying crevasse
Chevron crevasse
Traverse crevasse
Life of crevasse is limited
Extensive crevassing – convex long profile
Foliation – banding in ice
Alternative layers of white bubbly ice & bluish ice
Thursday, August 13, 2009
Glacier System
Input & Output
Mass Balance
Input/output relationships of ice firn, snow
Water equivalent (a amount of water instead of melted)
Accumulation
` Direct precipitation
Ablation
Surface melting
Basal & internal melting
Evaporation
Wind deflation
Calving
Mass Balance relationships
Season Spatial Variation Mass Balance Character
Autumn snow accumulation at Snow mass increasing
higher altitudes – ablation of Ice mass decreasing
ice continues at lower altitudes Total Mass constant
Winter Snow accumulates over whole Snow mass increasing
glacier, little ablation Ice mass Constant
Total mass increasing
Spring Snow Accumulating at Snow mass constant
higher altitudes. Ablation of Ice mass constant
winter snow at low altitudes total mass constant
Summer Little snow accumulation Snow mass decreasing
Except at high altitudes Ice mass decreasing
Ablation over much of glacier Total Mass Decreasing
(snow at higher altitude firn & ice
at lower altitude)
Difference between accumulation & ablution for a whole year – net balance
Balance year – interval between the time of minimum mass in one calendar year & time of minimum mass in the following year
Positive net balance – gain of ice & snow
Negative net balance – loss of ice & snow
Zero Net Balance- winter & summer balance are equal
Relationship to climate
Climate on ablation – melting
Adiative
Heat exchange with the air in contact with glacier
Efficacy of solar radiation on melting – albedo of glacier surface
Fresh snow – 0.6 – 0.9
Later season – 0.2 – 0.4
Heat exchange between air & glacier surface
Conduction of heat from air to ice (enhanced in windy conditions)
Condensation of water vapour on glacier surface results in release of latent heat
Rain =/= melting
Schytt – correlation between mass surface temperature & total ablation
Effect on glacier movement
Movement of glacier = F(input & output)
Characteristics
Input & output magnitude
Spatial distribution on a glacier
Energy input decreases – from maritime to continental climate
from temperate to high latitude
greater the amount of energy required - greater is mass loss in equilibrium line
distribution of total amounts of accumulation & ablation on a glacier also affects the discharge of ice
Glacier in humid area – more active than glaciers in dry area
Temperate - polar latitudes
Latitudinal decline in activity
Movement within a glacier
Continuous movement
Longitudinal dimension – maximum discharge at equilibrium line & decreases down glacier from it
Vertical velocity – accumulation zone, buries any stone above equilibrium line
Ablation zone, stone emerges due to ice melting
Nye: compressive flow – reduction in forward velocity
Extending flow – longitudinal stress more tensile than over burden pressure
Transverse direction
Channel slope – amount & nature of friction
Sheet flow – confined to any valley, base friction only
Stream flow – confined in rock valley
Channel – maximum flow at centre
Velocity reduction at margin
Velocity change with depth – not common
Periodic movements – f(long term, short term fluctuations of climate)
Research scope of glaciologists
Direct response
- Variations effect glaciers wholly
- Climatic detoriation, glaciers thickens (every part)
- Stable adjustment
- Thick or thin slightly in response to change
Until new equilibrium profile is reached
- Unstable adjustment
Initial change triggers charge which increases with time
Stable – extending flow
Unstable – comparing flow
Kinematic waves – means by which the effects of fluctuations is net mass balance are transmitted down the glacier
Bulge moves faster than ice on either side – amorainic rock would move ice faster than normal area
Surges – ice travels downglacier at speeds far above mormal
Consists of
- A wave of thickening ice subjected to compressive flow
- A zone of high velocity ice with intensely fracture ice behind the wave crest
- A zone of tension or extension where the ice is thinning
Slope graph following surge
Periodicity of surge
Causes
High velocity
Trigger mechanism
Variables affecting glacier movement
Independent variable – climate & nature of relief
Dependant variable – size & morphology of glacier
Independent variables
Geothermal environment
Permeability & geothermal heat eaffect glacier flow
Volumn & type of debris contained within glacier
Climate
High solid precipitation totals & high ablation values – rapid rate of flow
Initial high snow temperature, effect of warming by summer percolation of meltwater closer to mlting, creep processes are rapid
Warm ice flowing fast generates heat by deformation near base & by basal sliding
Regional relief & slope forms
Steepness of bedrock slope down affects velocity localised high velocity, icefall
Irregularities of bedrock floor
Whether glacier ice ends in land or calves in water
On land – snout thins/ thicks near snout, flow decreases near snout
On water – calving
Profile of glacier – its relationship to land
Dependant variables
Glacier morphology (Ahlaman)
Mass Balance
Input/output relationships of ice firn, snow
Water equivalent (a amount of water instead of melted)
Accumulation
` Direct precipitation
Ablation
Surface melting
Basal & internal melting
Evaporation
Wind deflation
Calving
Mass Balance relationships
Season Spatial Variation Mass Balance Character
Autumn snow accumulation at Snow mass increasing
higher altitudes – ablation of Ice mass decreasing
ice continues at lower altitudes Total Mass constant
Winter Snow accumulates over whole Snow mass increasing
glacier, little ablation Ice mass Constant
Total mass increasing
Spring Snow Accumulating at Snow mass constant
higher altitudes. Ablation of Ice mass constant
winter snow at low altitudes total mass constant
Summer Little snow accumulation Snow mass decreasing
Except at high altitudes Ice mass decreasing
Ablation over much of glacier Total Mass Decreasing
(snow at higher altitude firn & ice
at lower altitude)
Difference between accumulation & ablution for a whole year – net balance
Balance year – interval between the time of minimum mass in one calendar year & time of minimum mass in the following year
Positive net balance – gain of ice & snow
Negative net balance – loss of ice & snow
Zero Net Balance- winter & summer balance are equal
Relationship to climate
Climate on ablation – melting
Adiative
Heat exchange with the air in contact with glacier
Efficacy of solar radiation on melting – albedo of glacier surface
Fresh snow – 0.6 – 0.9
Later season – 0.2 – 0.4
Heat exchange between air & glacier surface
Conduction of heat from air to ice (enhanced in windy conditions)
Condensation of water vapour on glacier surface results in release of latent heat
Rain =/= melting
Schytt – correlation between mass surface temperature & total ablation
Effect on glacier movement
Movement of glacier = F(input & output)
Characteristics
Input & output magnitude
Spatial distribution on a glacier
Energy input decreases – from maritime to continental climate
from temperate to high latitude
greater the amount of energy required - greater is mass loss in equilibrium line
distribution of total amounts of accumulation & ablation on a glacier also affects the discharge of ice
Glacier in humid area – more active than glaciers in dry area
Temperate - polar latitudes
Latitudinal decline in activity
Movement within a glacier
Continuous movement
Longitudinal dimension – maximum discharge at equilibrium line & decreases down glacier from it
Vertical velocity – accumulation zone, buries any stone above equilibrium line
Ablation zone, stone emerges due to ice melting
Nye: compressive flow – reduction in forward velocity
Extending flow – longitudinal stress more tensile than over burden pressure
Transverse direction
Channel slope – amount & nature of friction
Sheet flow – confined to any valley, base friction only
Stream flow – confined in rock valley
Channel – maximum flow at centre
Velocity reduction at margin
Velocity change with depth – not common
Periodic movements – f(long term, short term fluctuations of climate)
Research scope of glaciologists
Direct response
- Variations effect glaciers wholly
- Climatic detoriation, glaciers thickens (every part)
- Stable adjustment
- Thick or thin slightly in response to change
Until new equilibrium profile is reached
- Unstable adjustment
Initial change triggers charge which increases with time
Stable – extending flow
Unstable – comparing flow
Kinematic waves – means by which the effects of fluctuations is net mass balance are transmitted down the glacier
Bulge moves faster than ice on either side – amorainic rock would move ice faster than normal area
Surges – ice travels downglacier at speeds far above mormal
Consists of
- A wave of thickening ice subjected to compressive flow
- A zone of high velocity ice with intensely fracture ice behind the wave crest
- A zone of tension or extension where the ice is thinning
Slope graph following surge
Periodicity of surge
Causes
High velocity
Trigger mechanism
Variables affecting glacier movement
Independent variable – climate & nature of relief
Dependant variable – size & morphology of glacier
Independent variables
Geothermal environment
Permeability & geothermal heat eaffect glacier flow
Volumn & type of debris contained within glacier
Climate
High solid precipitation totals & high ablation values – rapid rate of flow
Initial high snow temperature, effect of warming by summer percolation of meltwater closer to mlting, creep processes are rapid
Warm ice flowing fast generates heat by deformation near base & by basal sliding
Regional relief & slope forms
Steepness of bedrock slope down affects velocity localised high velocity, icefall
Irregularities of bedrock floor
Whether glacier ice ends in land or calves in water
On land – snout thins/ thicks near snout, flow decreases near snout
On water – calving
Profile of glacier – its relationship to land
Dependant variables
Glacier morphology (Ahlaman)
Saturday, August 8, 2009
GLACIER ENVIRONMENT: CONTROL
Kierman: controls of Glacial Environment
• Glacier Variables – ice temperature, glacier morphology, glacier consaint, glacier gradient, glacier movement & velocity, ice thickness, glacial processes
• Bedrock variables:- lithology, structure, orogenic & tectonic history, bedrock preparation, glacial sediment
• Topographic variables:- periglacial topography, contemporaneous topography, post glacial topography
• Temporal variables:- duration of glaciation, number of glacial stages
Source
Murray Gray: GeoDiversity Valuing & conserving Aboitic Nature
• Glacier Variables – ice temperature, glacier morphology, glacier consaint, glacier gradient, glacier movement & velocity, ice thickness, glacial processes
• Bedrock variables:- lithology, structure, orogenic & tectonic history, bedrock preparation, glacial sediment
• Topographic variables:- periglacial topography, contemporaneous topography, post glacial topography
• Temporal variables:- duration of glaciation, number of glacial stages
Source
Murray Gray: GeoDiversity Valuing & conserving Aboitic Nature
GLACIER ICE
Glacier Components
Ice
Air
Water
Rock Debris
ICE CYSTALS
Ice
Weak & can easily be made to slip on planes parallel to basal plane
Water is a substance which is less dense when solid (ice)
International Association of Scientific Hydrology
- minimum 10 types of solid precipitation
Correlation between wind speed & snow Density
Wind speed = snow density
Rime Ice –
- formed when supercooled water droplets strike a cold solid object & freeze on impact
- whitish appearance because of entrapped air bubbles
- accumulates in cool, humid conditions on surface which are most exposed to wind, important in cool maritime glacial environment
Superimposed Ice
- formed when water comes in contact with cold glacer surface & freezes
- air temperature above or at freezing point
- ice source in polar continental areas like northern
- water from rain or melting of previous wintrs snow cover
Transformation
Firn – snow which is survived a summer melt season & has begun the transformation to glacier ice
Density > 0.4 MG m-3
Temperature
Heat derived from
§ surface
§ base (geothermal heat Flux)
§ internal friction
Warm Ice Close to pressure melting point
Cold Ice Below pressure melting point
Pressure melting point- the temperature at which water freezes diminishes under additional pressure (@ 1 degree per 140 bars)
Cold Ice
Firn formed at temperature so low there is little or no surface melting in summer
Cold ice form is related to cooling of surface layers of a glacier by winter wind
Warm Ice
Formed whenever there is sufficient heat to rise the temperatures to pressure melting point
Basal Heat Sources raises temperature of basal ice
- Ice is thick
- Surface temperature is high
- Ice velocities are high
- Accumulation is high & moderate
Presence of Basal Ice at Pressure melting point
Water is present at the ice/rock interface
Ice movement Mechanisms
Time Lapse Photography – reality of glacier flow
Bucking of glacier ice (snot of storstrom glacier, droning Louise land
Demonstration of glacier flow
Internal Deformation
Deforms in response to stresses setup within its ice mass by the force of gravity
Any point within the glacier subjected to uniaxial compressive stress as a result of overlying ice
- Hydrostatic pressure
- Shear stresses
Hydrostatic pressure – same in all directions related to weight of overlying ice
Shear Stress – related to weight of ice
Surface slope of glacier
t = p g h sin a
t = shear stress
p = density of ice
g = acceleration due to gravity
h = thickness of glacier
a = slope of upper surface
Creep
Deformation of ice in response to stress
Mutual displacement of ice crystals relative to each other
Glens flow law – applied to glaciers by Nye
E = A t^n
E = strain rate
A = constant f (Temperature)
T = effective shear stress
N = exponent with a mean value 3
Fracture
Ice creep cannot adjust sufficiently rapidly to the stresses within the ice & as a result the ice fractures & movement takes place along plane
Basal Sliding
Enhanced basal creep
Pressure melting
Slippage over a water layer
Enhanced basal creep
Glaciers flow over large obstacles
Determines the direction of flow in ice
Pressure melting
Ice moves through series of bumps
Ice melts & freezes according to minor difference in pressure caused by obstacles
Regelation ice
Enhanced basal creep – efficient for large obstacles
Inefficient for small ones
Pressure melting – efficient for small obstacles
Slippage over a water layer
Role of other materials on glacier ice
Rock debris
Estimate 0.05% of total volumn of glacier ice varies to 8%
Sudden increase of glacier weight can increase flow rate of glacier locally
Air bubbles
Explodes with cracking sounds
Atmospheric debris
Dust & salts
Friday, August 7, 2009
Glaciers & Landscape
Glacial Studies – two dimensions
- Glacier Dynamics – Glaciology
- Glacier Form – Glacial Geomorphology
Glacier Systems
-systems approach
Input (Mass & Energy) Output (Mass & Energy)
Glacier Water Vapour Water Ice Rock Detritus Heat Precipitation Rock Detritus Gravity Solar Radiation Geothermal Heat
Two Subsystems –
- Accumulation
- Ablation
Equilibrium Line (Threshold)
Other Thresholds –
- Glacier Bedrock
- Glacier Atmosphere
Response time – glaciers experience a change of input
Lag before the response becomes discernible at snout
Glacier economics
Balance between rates of input, throughout output
Feedback mechanism
Negative feedback- effects of a change of input are damped down or eliminated
Positive feedback – change is exaggerated or propagated
Scale Awareness
Ideas of Tricart, 1965
Model examples (understanding schemes)
Ice Sheet or Ice Cap
Valley Glacier 
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