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)