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Ice Shelf Buttressing (Unconfined ice shelf (Nothing but oceans @ sides -…
Ice Shelf Buttressing
Unconfined
ice shelf
Nothing but oceans @ sides - unconfined
Little speedup of grounded zone
if part/all of ice shelf removed
i.e. will not affect upstream ice sheet significantly
e.g. Erebus Ice Tongue
∴
All driving stress transmitted to grounding zone
Confined
ice shelf
Ice shelf confined in embayment
Embayments have sidewalls which
provide extra support to grounding zone
∴ Sidewalls support some driving stress of ice shelf
Ice shelf thinning can cause speed up inland
e.g. Pine
Island
Ice shelf thinning
Grounding zone speedup can drive retreat of grounding line
= induced by increased 'pulling' at g.l. by ice shelf
i.e. ice shelf 'yanks' on grounded ice
Problem: force should depend on g.l. depth only
regardless of ice shelf thickness
Enter: geographical setting
Removal of ice from confined ice shelf
Removes some ' back stress '
∴ Ice @ grounding line flows faster
May trigger unstable g.l. retreat
Since resistance to driving stress is reduced
Backforce/ Buttressing
Any force exerted which resists driving stress
Some driving stress taken up by:
i.e. stress sidewalls (lateral) & ice rises (basal)
∴ Reducing 'tug' at grounding line
Thomas, 1979
Marine Ice Retreat Model
Varying responses to melting
Confined & foredeepened
Significant retreat
(Deepens inland
with buttressing)
1. Buttressing removal
speeds up g.l. retreat
2. Retreat g.l. to deeper bed
since depth g.l. ∝ flow upstream
∴ greater buttressing required to stabilise
Confined & oceanward deepening
Only a little retreat
Despite lotsa melting & buttressing removal
-->
Shallower g.l. encountered on retreat
∴ Requires less backstress for stability
Hence did not retreat far
Unconfined
Little reatreat
All driving stress transmitted to grounding zone
Response to ice shelf removal
= f (geographical setting of ice shelf)
i.e. Confined or unconfined ice shelf (by topog)
Determines whether ice shelf removal affects ice sheet significantly or not
Ice tongues
= perfectly unconfined
∴ all driving stress transmitted back to grounding line
e.g. Drygalski ice tongue on Ross Ice Shelf
Most ice shelves = confined
embayed
pinned to raised areas of bed
Confinement
Lateral forces influence flow
i.e. mountains / slow flowing ice sheet / ice rises
(undersea mountains)
Things which exert basal stress
e.g. Pine Island ice shelf g.l. changing rapidly
--> mtns/stagnant ice = confining
Melt = faster
where underside of ice = steeper