GLACIER ICE

Glacier Components

Ice Crystals

Air

Water

Rock Debris

ICE CYSTALS

Ice Crystal Characteristics

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 Canada & arctic Siberia

- 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 Greenland)

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

Boulder results in increased strain

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