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

i.e. Glaciers cannot evacuate large
sediment volume it has generated

[Where spatial gradients in sed def rates exist]

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

All motion components

1° through role of
basal water pressures

Closely related to water flow through/beneath ice

= intimately related to subglacial water pressures

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