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High Mountain Asia Glaciers (Austfonna Glacier, Svalbard (Cause? (No…
High Mountain Asia Glaciers
GMB
Zones
Accumulation
ice forms (snow falls, compacts & preserved)
Ablation
melting
Equilibrium line altitude separates 2 zones
Equilibrium
line altitude
Elevation at which accumulation = ablation
ice formation = melt
Glacier Mass Balance
Glaciers flow downslope ∴ preventing:
Accumulation zone thickening
Ablation zone wasting away
∴ Glacier flow = important control glacier shape
Since ice transported between zones
Length Response to Climate Δ
Climate warms - glacier shortens
Climate cools - glacier shortens
∴ Glacier shape adjusts - but how ?
- E.L. Δ
Equilibrium
line Δ
Climate warms
∴ Glacier retreats
Why ?
More ablation (melt)
Less accumulation
ELA moves to higher elevations
Climate cools
Glacier advances i.e. length increases
n.b. Delay / lag exists
Terminus mvmt lags temp cooling
Glaciers must build up snout/driving stress sufficiently
--> before glacier advances forward
Mtn Glacier Thickness Δ
In response to changes in:
Surface mass balance (SMB)
Flow rate
Thickness change rate
ΔH/ΔT = (Qin-Qout) / L + b
Q = (depth averaged flow rate) x thickness
b = local surface mass balance
Austfonna Glacier, Svalbard
Dynamic thinning
on one portion of glacier terminating near sea
Acceleration
of terminus
No velocity Δ upglacier
Cause?
No associated Δ surface melt
∴ Something else must be causing acceleration
'Dynamic' Thinning
Thinning due to terminus accelerating
Qin > Qout --> Thinning
i.e. Change to Qin > Q out balance
Not change to SMB term (melt/freeze)
Inferring
SMB (b)
b = - (Qin - Qout) / L
Infer from
Equation
Flux change in glacier
Thickness change
Glacier length
Inferring SMB in reality
Geographic data on glacier used
Datsets divided into sections of given area for:
Ice thickness
Velocity
Average SMB in each section calulated
Calculate all fluxes in + out
Then use equation
b = - (Qin - Qout) / L
Glacier length
& Climate
Temp not directly related to glacier length
∴ 1. Must interpret length Δ with caution
2. Consider natural variability before inferring climate change
i.e. variability independent of climate (weather etc)
Must determine natural length variability for that glacier
Climate Δ alters SMB & velocities
--> both of which alter thickness