Leverett Study
Leverett Glacier Study Sole 2013
600 km2 catchment derived from inSAR surface DEM
GPS sites extend ~ 100 km from margin
Measure:
Ice velocity
Temperature
Melt discharge @ proglacial river
Ice lowering
Study
period
Summer 2009 - 2010 = perfect experiment
2009
2010
warm summer
average summer temps
signif positive temp anomaly
in bounds of temp predicted for 100 yrs from now (IPCC)
∴ assess dynamic response to climate scenario
2010 Melt discharge
Double that of 2009
Much more sustained
Despite similar peak melt in 2009
Velocity vs Melt Q
2009 Lower Sites
Beginning
melt season
Ice accelerates
Peak melt season
Velocity drops back down to background velocity
Why?
Drainage system evolves
Becomes channelised/efficient
∴ No longer pressurised by system
2009
vs 2010
Spring faster 2010 vs 2009
Greater melt produced in 2010
∴ Higher speedup wrt winter velocity
2010 Velocity Speedup
(% wrt winter)
Occurs earlier 2010 vs 2009
More pronounced
Propagates higher upglacier
Ice Melt vs Acceleration
% velocity speedup correlates with ablation
Leverett take-home
Faster summer velocities during warmer years
(@ land-terminating outlet glacier ice sheet)
Land-terminating outlet glacier on NW Greenland
Problem
Assumed winter velocities = constant
They were not
Winter slowdown observed
Autumn velocities = slower than expected background velocities
Cause Winter Slowdown
After big melt seasons
Much more efficient drainage developed
Low pressure channels extend much further upglacier into ice sheet
∴ Pronounced Autumn slowdown
Summer melt season → essentially 'preconditions' glacier for Autumn slowdown
Annual velocity implications
After high melt season
winter velocities = reduced wrt background velocity
∴ Annual velocity ~balanced out by autumn slowdown
Annual velocity
= f(...
Dictated by winter displacement
(if it can balance summer speedup)
Leverett velocities almost balanced
Winter velocity correlates w late summer melt
Summer velocity correlates w melt
Net Velocity Effect
2009 vs 2010
Speedup in high melt summer
= balanced by subsequent winter slowdown
∴ Annual average velocities do not differ
If anything, slower annual velocities in 2010
as winter slowdown overshot ∴ ↓ annual velocity
Winter variability = critical to annual displacement