Glacial II Flow and Process

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Glacial II Flow and Process
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Specific Mass Budget

• Point mass budgets measured with ablation stakes
• End of summer to EOS
• Uses old snow/firn/ice as a marker

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Specific Mass Budget trends

• Accumulation often increases slightly with
  increasing altitude.
• _at_ ELA, bn 0
• Ablation increases rapidly with decreasing
  altitude below the ELA.
• Why?

EQUILIBRIUM LINE ALTITUDE
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Snowlines

• Indicator of mass balance
• Short-term
• Firn line
• Highest firn line
• Long-term
• ELA

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Snowlines

• Glaciation Threshold
• Cirque floors
• Highest lateral moraines
• Toe-headwall altitude ratio
• Accumulationarea ratio

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Controls on Snowlines I - Latitude

• Latitude temperature (treeline)
• Highest near equator
• Latitude ? precipitation (snowlines)
• Saddle near equator
• Weak gradients (lt1 m/km)

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Controls II - Continentality

• Lowest near moisture source
• Higher inland
• Strong gradients
• Up to 10 m/km

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Spatial Resolution

• Humlum (1985)
• West Greenland
• Local data are consistent
• Needs no smoothing
• High resolution!

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MT/ID Paleoclimate

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

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Observed Flow Plan and Profile

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

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Modes of Profile Flow

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

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Observed Bed Deformation

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

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Brittle Deformation - Crevasses

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

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Crevasse Examples

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

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Unsteady Flow - Surges

• Many glaciers (10) surge
• Stagnant for years
• Increase in thickness
• Surge!
• Decouple from the bed?
• Surface fracturing
• Thrusting?

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Surging Terminus
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Summary of Flow Process I
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Summary of Flow Process II
t1 bar
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Glacier Bed Processes

• Most important processes happen out of sight
• Deformation (internal, bed)
• Erosion
• Deposition
• Processes are a function of
• Thermal regime
• Behavior of ice
• Behavior of bed material

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Observed Ice Core Temps

• Greenland
• Shallow warm bulge
• Tbed lt 0C
• Antarctica
• Shallow warm bulge
• Tbed 0C
• Reflects temperature change with time
• LIA, Hypsithermal

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Thermal Regime

• Critical to processes!
• Warm wet-based
• Cold dry-based
• ?ice lt ?water, therefore
• Pressure increase forces melting point decrease
  PMP
• -0.7C/km of ice
• Because PMP lt 0C, heat is trapped at the bed of
  warm ice
• Warm ice thick, fast, temperate or heated

Pressure Melting Point
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Pressure Melting
melt
melt

• For ice at PMP
• Movement increases pressure, thus melting, on the
  up-ice side of an obstruction
• Movement away from the obstruction causes
  freezing on the down-ice side regelation

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Effects of Pressure Melting

• High pressure is experienced on the upice side of
  an obstruction.
• Pressure melt results
• Water migrates around/through obstacle
• Regelation occurs in low pressure zone

MELT
REFREEZE
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Erosion by Plucking

• Regelation incorporates loose bed material into
  basal ice plucking

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Abrasion

• Plucked material is available to wear away the
  bed abrasion

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Abrasion Features / chattermarks
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Polish

• Typical of similar hardness (bed vs. tool) and
  fine load ( sandpaper)

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Erosion and Deposition

• Erosion
• Plucking vs. abrasion
• Effect of pressure
• Effect of velocity
• Deposition
• Lodgment vs. meltout

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The Subglacial System

• f(distance) downice
• Water increases to the terminus
• Debris decreases below the terminus