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