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Deforming Bed Implications (Reconstructions IS & soft beds…
Deforming Bed Implications
Reconstructions IS & soft beds
Reconstructed ice extents differ greatly
Depending on nature of bed (rigid or deformable?)
Deformable bed → glacier flows faster
∴ has flatter, lower profile
∴
Wider thinner ice sheet if soft bed
e.g. Laurentide IS, Boulton (1985)
Ice extent
from moraines
Fit glacial geology + isostatic rebound curves
better
Geomorphological Effects
Sediment accumulations
e.g. Fluting, drumlins, moraines
Form where deformation rate ↓ downglaicer
[Where spatial gradients in sed def rates exist]
i.e.
Glaciers cannot evacuate
large
sediment volume it has generated
LGM
Sediment deformation
facilitated fast flow
Over 80% ice masses were probs underlain by deformable sediments
Sediment bed role
Can
protect
underlying landscapes
Glacier motion 1
Motion = sum of
Internal deformation
Basal sliding
Subglacial sediment deformation
Internal deformation
= well modelled
Basal sliding & subglacial sed def
still poorly understood
Glacier motion 2
Internal deformation
= slow, generally steady process
Short term variations glacier motion driven by
i.e. Basal sliding & subglacial sed def
Basal motion variations
= intimately related to subglacial water pressures
All motion components
1° through role of
basal water pressures
Closely related to water flow through/beneath ice
Experimental
Till Flow Law
How ?
Put till in pressure units
Add water
Expose to given pressure
Aim
Try to find relation btwn driving stress + strain rate
Issue
Is this representative of nature ?
vs under ice, undisturbed sediment