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Supraglacial (Meltwater sources (1. Surface meltwater (Dominates most…
Supraglacial
Meltwater sources
1. Surface meltwater
Dominates most glacial systems
Equivalent to large fluvial flood
Melt of ice & snow
2. Basal melt
= generated by
friction & geothermal heat
Anomalies
:
subglacial volcanic eruptions
very high flow rates
3. Groundwater
usually v small portion
4. Precipitation
Precipitation significance varies with region
i.e. in parts of Norway, precip = signif contributor
Typical
melt rates
Surface
up to 10cm / day
Basal
~ 1 cm/yr (alpine)
Groundwater
V small - few estimates
Precip
significance depends on region
Energy sources surface melting
Solar radiation
~71%
~
insolation
= f (cloud cover / albedo)
Sensible heat
21%
= heat conducted to surface
f (air temp + turbulence [wind])
Latent heat
8%
= heat provided by condensation
f ( vapour pressure; turbulence )
Precipitation
f ( raindrop temp thus v INEFFICIENT )
Albedo
Critically influences energy available for melting
Albedo = f (snow & debris cover)
e.g. Barnes Ice Cap
debris = enhancing melt
snowling receding
ice pretty grey
Variability surface melt
Lapse rate = important
(air temp & vapour pressure)
Melting ceases @ high altitudes
Highest melt
during summer (temp)
in areas of exposed ice (α)
@ lowest altitude
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
Vapour pressure
Dry atmos --> easier for water evap
--> more conducive to melt
Where surface melt goes ?
Surface melt either:
Runs off edge
Enters glacier