Supraglacial meltwater routing
Supraglacial meltwater flow
= meltwater routing @ glacier surface
surface conditions = critical
snow cover vs exposed ice?
debris cover?
thermal regime?
strongly influences nature of glacial runoff
Meltwater routing over ice
= Fast
- Meltwater flows via sheetflow to supraglacial streams
- Water travels quickly in streams
∴ little potential for meltwater storage
Surface travel time = f (distance to moulins & crevasses)
Meltwater channels have
low roughness thus facilitate v fast flow
Meltwater routing through snow/firn
= Slow via percolation
Snow acts like porous aquifer / sponge
Delays delivery of water elsewhere
Initially, melt refreezes & warms snowpack
Vertical flux = f ( permeabiliy & obstruction by ice layers )
Lateral flow at surface
--> occurs in water table within snowpack / firn
Supraglacial streams
Fast flowing ~1 - 5 m/s (faster than rivers)
Various scales (cm to km)
Flow for tens km at high elevations where
gradients = high
crevasses/moulins = infrequent
Majority water travel time over ice
= sheetflow from place of melt to nearest stream
Surface condition implications
Runoff response to melt varies
--> thus snowline retreat during melt season = important
Snow covered areas
= slow response
Exposed ice areas = rapid routing
Rapid flow across ice to quickly enter internal drainage system
Provided entrance points e.g.crevasses/moulins
Snowline Position
Snowline retreats during melt season
Implication glacial runoff timing:
Snowpack removal via ablation
Facilitates FASTER routing of melt later in season
Takes less time for water to reach englacial system
Snowpack = slow portion
When max melt rate?
Between 1 - 3 pm in afternoon