MTID Paleoclimate

1
MT/ID Paleoclimate

• Complex pattern!
• More detailed than modern weather stations and
  SNOWTEL sites!

2
Glacier flow

• Without the flow of ice, life as we know it
  would be impossible.
• Observed since 1700s
• Quantified Glens Flow Law
• ? Atn strain rate is proportional to shear
  stressn
• A f(Temp) 7x10-18 to 7x10-15 (at 0C)
• n f(crystallinity?) 1.5-4.2, use 3?
• V kT3

3
What is Flow?

• Mode
• Brittle
• Ductile
• Character
• Homogeneous
• Inhomogeneous
• Shear
• Pure
• Simple

4
What is Flow, really?

• Slip (planar)
• External
• Internal - intragranular
• Creep (intergranular)
• Phase change (recrystalization)

5
Planforms of observed flow

• Stakes across glacier
• Resurvey across time

6
Observed flow Plan and profile

• Plan View
• Parabolic
• Septum (ice streams)
• Profile
• Exponential
• Non-zero at the bed

7
Modes of profile flow

• Total Velocity
• Internal Velocity
• Laminar
• Sum of processes
• Basal Slip
• Not if frozen to bed
• Bed Deformation
• If not rock

8
Observed bed deformation

• Inferred from structures in till
• Measured from markers emplaced in basal sediment
  and recovered

9
Structures of glaciers

• What structures do you see here?Grinnell
  Glacier
• Lenses, layers, fractures
• How do they form?

10
Schematic mountain glacier

• Plan View
• Cross-section

11
Schematic mountain glacier

• Detailed section
• Terminus

12
Example Malaspina Glacier

• Note accommodation of Malaspina and Agassiz
  glaciers into increasing space
• Longitudinal compression

13
Brittle Deformation - Crevasses

• Long observed
• Results from rapidly-applied stress
• Form many distinctive patterns

14
Mechanics of Crevassing

• Observed patterns relate observed strain directly
  to the mechanics of stress couples

15
Crevasse Examples

• Depth lt10m
• Tensional and marginal
• Terminal splays
• Complex systems

16
Crevasse Examples
17
Icefalls
18
Icefalls
19
Unsteady Flow I

• Flow is NOT constant
• Varies with season (snow load increases strain
  rate)
• Varies with bed resistance f(water)?
• Varies unpredictably!