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Thermal Zones of Ice Mass (Percolation Zone (Meltwater percolates…
Thermal Zones of Ice Mass
Thermal Zonation of Ice Mass
(Benson, 1962)
Can divide ice mass into distinct thermal zones
Dry snow zone
No surface melt (air temp too low)
Percolation Zone
Ice melts in summer
+ meltwater
percolates through snowpack
Soaked Zone
Whole snowpack
saturated
with meltwater
Dry Snow Zone
No surface melting even in summer
Rare
- Only found at:
Centre of large ice sheets e.g. AIS
Extreme altitudes in Asia/Alaska
Greenland
Arguably has no dry snow zone anymore
2012 - melt occurred across whole of greenland
Equilibrium line
Below ELA
All snow from that year / winter MELTS
No snow survives / persists past summer
= altitude @ which there is no net annual mass ∆
boundary between firn & ablation area
Dry snow zone line
= line above which
no surface melt occurs
Percolation Zone
Summer melting occurs
Meltwater refreezes @ depth (completely)
Refreezing releases latent heat
∴ warms snowpack more
Meltwater percolates
preferentially through weaknesses (cracks/pipes) in snowpack
However, large parts snowpack still very cold
if snowpack not warm enough
--> won't lose mass
Greenland melt
Melt extent increasing as global temps increasing
Ablation zone
= characterised by
net mass loss
over a given year
Exposed ice present @ glacier surface
at end melt season
All snow inputs have melted by end of summer
5 Zones
Dry snow zone
Percolation zone
Wet snow zone
Superimposed ice zone
Ablation zone
Thermal zone distribution
All 5 zones found in Antarctic IS
(& parts of GrIS?)
Temperate (warm) glaciers
Composed of only wet snow & ablation zones
lack dry snow/percolation zones
Superimposed Ice Zone
Lotsa meltwater
Melt percolates down to
previous summer ice surface
Potentially refreezes
Mean
snow ρ
Autum snowpack ~23% denser vs Spring
Parry et al 2007
Wet snow line
altitude @ which all snow from previous year = raised to melting point
a.k.a. saturation line
3. Wet Snow (Soaked) Zone
All snow deposited in previous winter
= raised to melting point by end summer
i.e. Whole snowpack raised to melting point
Features: ice lens / pipe formation
Moving downglacier
Increasing proportion of snowpack
= raised to melting point
Freezing
1 g water
releases sufficient latent heat to raise 160g snow by 1°C