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Supraglacial & Englacial Flow Summary (Englacial Flow summary…
Supraglacial & Englacial Flow Summary
Englacial Flow summary
Arborescent network of englacial conduits = predicted by shreve & rothlisberger
Conduits
grow with depth
coalesce as larger grow
at expense of smaller ones
Most surface meltwater
enters glacier via moulin/crevasses
is routed rapidly to the bed
Flow varies
Accumulation area
percolation & seepage
Ablation area
seepage & moulins
Runoff increases downglacier
resulting in a more efficient drainage system
Seasonal evo
Runoff increases downglacier
-->
resulting in more efficient drainage
through ice vs snow
Seasonal evolution supraglacial drainage
Early season
- percolation through snow after winter
slower
Later
- water routed quicker
bare ice exposed
'flashier' hydrologically
In essence
Lotsa snowcover, slow flow
low magnitude, damped
slowly varying surface runoff
from snow-covered areas
Exposed ice, fast flow
High magnitude, flashier
Diurnally peaked surface runoff
from exposed-ice areas
Removal snow cover from ablation area in summer
critically impacts surface runoff
Slow drainage & dynamics
Slow drainage --> softens ice ∴ influencing ice flow
Englacial flow theory
Conduits assumed to be full
∴ at hydrostatic pressure
Reality - not always full
= f ( melt cycle & water flux )
∴ May be at atmos pressure, especially near terminus (> dynamic)
Flow direction water @ atmos pressure
If no ice
solely f( gravity ) i.e. topog
Reality: heavy ice overburden
∴ f ( hydrostatic pressure ) i.e. gravity & ice above
∴ Water can flow uphill against topog gradients
Water
fluxes vary
seasonally
diurnally
Pipes often filled 3 - 4 pm
but not full earlier
Rothlisberger study water pressures
Small decrease water flux
requires
greater reduction in conduit cross-sectional area
Smaller x-sectional area --> Restricts water flow --> Requires increase in water pressure
Inverse relation water flux & pressure
hence larger conduits grow @ expense of smaller