Glaciers

1
Glaciers

• Lecture Outline
• Localization of glaciers
• Classification of glaciers
• Mass budget of glaciers
• Movement of glaciers
• Glacier hazards and resources

2
Localization of Glaciers

• Definitions
• Glacier body of ice formed from the compaction
  and recrystallization of snow that shows evidence
  of past or present movement

3
Localization of Glaciers

• Definitions
• Snowline elevation above which a net
  accumulation of snow occurs
• Fquilibrium line (firn line) separates
  accumulation zone from ablation zone

4
Localization of Glaciers

• Definitions
• Older firn revealed by increasing dust content
  superimposed sediment

5
Localization of Glaciers

• Definitions
• Equilibrium line not firn line where meltwater
  from acc. Zone flows into ablation zone and
  refreezes (superimposed ice

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Localization of Glaciers

• Relationship between latitude and elevation of
  snowline

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Localization of Glaciers

• Localizations of centers during Pleistocene when
  snowline intersected earths surface
• Keewatin
• Labrador

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Classification of Glaciers

• Morphological classification
• Ice sheets
• Broad, unconfined masses
• Generally flow in radial pattern from one or more
  central ice domes
• Only partially affected by underlying bedrock

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Classification of Glaciers

• Subtypes of ice sheets
• Continental larger than 25,000 km2
• Ice caps smaller than 25,000 km2
• Plateau glaciers Highland ice sheets
• small, central nourishment areas on high plateau
• Tongue-like outlet glaciers along margins
• Numerous nunataks

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Classification of Glaciers

• Subtypes of ice sheets
• Continental larger than 25,000 km2
• Antarctica
• Greenland

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Classification of Glaciers

• Subtypes of ice sheets
• Continental larger than 25,000 km2
• Antarctica
• Greenland

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Classification of Glaciers

• Subtypes of ice sheets
• Continental larger than 25,000 km2

13
Classification of Glaciers

• Subtypes of ice sheets
• Ice caps smaller than 25,000 km2

14
Classification of Glaciers

• Subtypes of ice sheets
• Plateau glaciers
• Small, central nourishment areas on high plateau
• Tongue-like outlet glaciers along margins

15
Classification of Glaciers

• Subtypes of ice sheets
• Plateau glaciers Highland ice sheets
• small, central nourishment areas on high plateau
• Tongue-like outlet glaciers along margins

16
Classification of Glaciers

• Subtypes of ice sheets
• Plateau glaciers Highland ice sheets
• Small, central nourishment areas on high plateau
• Tongue-like outlet glaciers along margins
• Juneau Icefield
• 4000 km2 of ice
• 30 outlet glaciers
• JIRP since 1946

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Classification of Glaciers

• Alpine glaciers
• Valley
• Cirque
• Piedmont

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Classification of Glaciers

• Textbook subtypes of valley glaciers
• Ice streams
• Reticular glaciers
• Outlet glaciers
• Alpine glaciers
• Cliff reconsituted glaciers
• Wall-side glaciers
• Cirque glaciers
• Apron glaciers

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Classification of Glaciers

• Textbook subtypes of lowland glaciers
• Piedmont glaciers
• Expanded foot glaciers
• Fringing glaciers
• Stagnant glaciers

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Classification of Glaciers

• Examples of valley glaciers

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Classification of Glaciers

• Examples of valley glaciers

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Classification of Glaciers

• Examples of valley glaciers

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Classification of Glaciers

• Examples of valley glaciers

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Classification of Glaciers

• Thermal (geophysical) classification of glaciers
• Warm ice (formerly temperate)
• Found outside temperate regions
• Ice is at pressure melting point upper 10m may
  freeze in winter
• Find ice worms on warm ice but not cold ice
• lt 1 mm diameter, 3 mm long
• Live in snow, firn
• Need temperature at 0oC. burrow if sunny

25
Classification of Glaciers

• Thermal (geophysical) classification of glaciers
• Warm ice (formerly temperate)
• Most important source of heat usually latent
  heat transferred upon freezing and condensation
• Each gram of water that freezes releases enough
  heat to raise temperature of 160 grams of ice by
  1oC.
• Condensation of 1 gram of vapor releases enough
  heat to melt 7.5 grams of ice
• 13-15m cold surface layer on Seward Glacier was
  raised to 0oC in first 10 days of summer melt
  season

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Classification of Glaciers

• Thermal (geophysical) classification of glaciers
• Warm ice (formerly temperate)
• If impermeable glacier ice is exposed at surface
  meltwater will runoff and not add heat
• In some subarctic glaciers of Scandanavia
• warm is found in accumulation zone (where firn
  absorbs meltwater)
• cold ice is found in ablation zone (where
  meltwater runs off

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Classification of Glaciers

• Thermal (geophysical) classification of glaciers
• Warm ice (formerly temperate)
• If basal ice is at pressure melting point
  additional heat will create meltwater
• Important in basal sliding, surges, basal erosion

28
Classification of Glaciers

• Thermal (geophysical) classification of glaciers
• Cold (polar) ice
• Thin active layer
• Little water generated cannot warm-up ice inside
  glacier

29
Classification of Glaciers

• Thermal (geophysical) classification of glaciers
• Cold (polar) ice

30
Classification of Glaciers

• Facies classification
• In accumulation zone
• Dry-snow facies cold snow and old snow with
  little melting
• Percolation facies some melting but not enough
  to percolate through snowpack, freeze and raise
  temp. to pressure-melting point
• Soaked facies lot of meltwater capable of
  percolating through snowpack and raising temp. to
  pressure melting point
• Superimposed ice
• In ablation zone
• Glacier ice

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Classification of Glaciers

• Facies classification

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Classification of Glaciers

• Equivalent glacier classes

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Mass Budget of Glaciers

• Accumulation processes
• Direct precipitation rain, snow, rime ice
• Superimposed ice
• Avalanching

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Mass Budget of Glaciers

• Measure thickness (in snowpit) of accumulation
  above previous summers ablation surface

35
Mass Budget of Glaciers

• Construct test pit profile
• Density
• Free-water content
• Ice structures

36
Mass Budget of Glaciers

• Construct test pit profile
• In JIRP test pits and movement surveys repeated
  each year

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Mass Budget of Glaciers

• Ablation processes
• Melting
• Evaporation
• Wind deflation
• Calving

38
Mass Budget of Glaciers

• Measure ablation with stakes bored into firn/ice
• Rates vary widely
• 8 mm/h during summer in French Alps
• 12 m for entire summer in Scandanavia Alaska

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Mass Budget of Glaciers

• Climatic controls on ablation
• Net downward radiation (longwave shortwave)
• Affected by albedo of glacier surface
• New snow 0.6 to 0.9
• Glacier ice 0.2 to 0.4
• Conductive heat exchange (sensible heat) between
  air and ice
• Ineffective unless wind removes chilled layer of
  air next to glacier
• Warm rain can be important

40
Mass Budget of Glaciers

• Climatic controls on ablation
• Latent heat transfer
• Condensation (600 cal/g) and freezing (80 cal/g)
  release heat
• Evaporation (600 cal/g) and melting (80 cal/g)
  absorb energy

41
Mass Budget of Glaciers

• Climatic controls on ablation
• Radiation is most important esp. in continental
  climates
• Varies with season, time of day, latitude, cloud
  cover, aspect, humidity
• In Sweden radiation accounts for 75 of ablation
  in June but only 30 in August

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Mass Budget of Glaciers

• Annual mass budgets
• Positive budget glaciers advances, thickens,
  covers larger area
• Negative budget retreat, thins, shrinks in area

43
Mass Budget of Glaciers

• Annual mass budgets
  glacier movement
• Whether a glacier advances or
  retreats depends on
• Net balance AND
• Rate that mass transfer of ice
  occurs from
  accumulation zone
  to ablation zone by glacier
  movement
• Continental glacier will have smaller
  accumulation AND smaller ablation
• Maritime glacier will have large accumulation AND
  large ablation ? will move faster with more
  erosion

44
Mass Budget of Glaciers

• Longer term mass budgets
• Positive budget glaciers advances, thickens,
  covers larger area
• Negative budget retreat, thins, shrinks in area

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Mass Budget of Glaciers

• Longer term mass budgets
• Positive budget glaciers advances, thickens,
  covers larger area
• Negative budget retreat, thins, shrinks in area

46
Mass Budget of Glaciers

• Longer term mass budgets
• Positive budget glaciers advances, thickens,
  covers larger area
• Negative budget retreat, thins, shrinks in area

47
Mass Budget of Glaciers

• Can correlate energy budget with glacier mass
  budget Wolken 1999 thesis
• Measured
• Net shortwave radiation
• Net longwave radiation
• Latent heat flux
• Sensible heat flux
• Net shortwave gt ½ total

1935 (top) and 1981 (bottom)
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Mass Budget of Glaciers

• Can correlate energy budget with glacier mass
  budget Wolken 1999 thesis

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Mass Budget of Glaciers

• Can correlate energy budget with glacier mass
  budget Wolken 1999 thesis

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Mass Budget of Glaciers

• Contrast in behavior of glaciers in adjacent
  valleys

51
Mass Budget of Glaciers

• What happens to mass budget when massive debris
  flow is deposited on glacier?

52
Movement of Glaciers

• Rates
• Temperate glaciers few cm/day
• If steep 0.3-0.5 to 3-6 m/day
• Surging glaciers
• Greenland 40 m/day
• Alaska up to 80 m/day
• Rates depend on degree to which driving force of
  new mass gt resisting force of lower

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Movement of Glaciers

• Rates
• Accumulation zone moves faster in winter
• Ablation zone moves faster in summer
• Not steady, uniform flow pulsating, spasmodic

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Movement of Glaciers

• Rates of movement
• Glacier moves fastest at center near surface

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Movement of Glaciers

• Rates of movement
• Glacier moves fastest at center near surface

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Movement of Glaciers

• Rates of movement
• If frozen to bed (cold ice)
• With warm ice at base substrate is rigid
• With warm ice and substrate is not frozen and not
  bedrock

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Movement of Glaciers

• Rates of movement

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Movement of Glaciers

• Mechanisms of glacier movement
• Rotation of ice crystals past each other (A)
• Downslope movement of water between ice crystals
  ? elongates ice crystals

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Movement of Glaciers

• Mechanisms of glacier movement
• Slippage of glacier over bedrock ( C ) enhanced
  if substrate is deformable (i.e., not bedrock)
  and saturated
• Internal slippage (D) esp. near terminus (thrust
  planes)
• Slippage along basal planes of ice crystals (E)

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Movement of Glaciers

• Mechanisms of glacier movement
• Basal slippage varies in importance

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Movement of Glaciers

• Hypothesis of movement
• Weight of glacier can be resolved into two
  components
• One perpendicular to bed s ?gz cosa
• One parallel to bed t ?gz
  sina
• When t lt s ice block is stable
• If a or z increases t increases
• When t gt s glacier deforms and moves downhill
  faster

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Movement of Glaciers

• Hypothesis of movement
• Kinematic hypothesis assumes ice moves in fashion
  similar to viscous fluid
• Flow lines

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Movement of Glaciers

• Hypothesis of movement
• With kinematic hypothesis
• Ice movement in accumulation zone is away from
  sidewalls more material added to sides than to
  center (avalanches, snowdrifts)
• Ice movement in ablation zone opposite radiation
  causes faster ablation near sidewalls

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Movement of Glaciers

• Hypothesis of movement
• Plastic flow hypothesis
• Assumes that glacier ice behaves as a plastic or
  pseudo-plastic body with critical yield stress of
  1 bar 1 kg/cm2
• Three types of movement
• Plastic flow need t gt s (sop need critical
  thickness, z)
• Block slippage along bed
• Internal slipping along faults

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Movement of Glaciers

• Hypothesis of movement
• Plastic flow hypothesis

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Movement of Glaciers

• Hypothesis of movement

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Movement of Glaciers

• Hypothesis of movement
• Compressive flow
• Extending flow

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Movement of Glaciers

• Crevasses
• Usually lt 30 m deep
• From differential ice movement where elastic
  limit is exceeded
• Types

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Movement of Glaciers

• Crevasses
• Types

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Movement of Glaciers

• Crevasses
• Transverse

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Movement of Glaciers

• Foliation
• Gulkana Glacier, Alaska

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Movement of Glaciers

• Foliation
• Vaughn Lewis Glacier, Alaska

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Movement of Glaciers

• Wave bulges ogives
• Vaughn Lewis Icefall, Juneau Icefield

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Movement of Glaciers

• Wave bulges and ogives
• Vaughn Lewis Icefall, Juneau Icefield

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Movement of Glaciers

• Ogives
• Vaughn Lewis Icefall, Juneau Icefield

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Movement of Glaciers

• Wave bulges ogives
• Below Vaughn Lewis Icefall, Juneau Icefield

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Movement of Glaciers

• Hypothesis of movement
• Effect of small obstructions at base of glacier
• Melting of warm ice on up-glacier side
• Re-freezing on down-glacier side

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Movement of Glaciers

• Hypothesis of movement
• Compressive flow in ablation zone can lead to
  thrust faults

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Movement of Glaciers

• Movement of ice sheets

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Movement of Glaciers

• Movement of coastal glaciers

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Glacier Hazards Resources

• Hazards
• Calving glaciers ? icebergs (e.g., Columbia
  Glacier)

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Glacier Hazards Resources

• Hazards
• Advancing ice
• e.g., during Little Ice in Alps, Caucasus,
  Karakorum, Norway
• Surging glaciers

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Glacier Hazards Resources

• Hazards
• Advancing ice
• e.g., during Little Ice in Alps, Caucasus,
  Karakorum, Norway
• Surging glaciers

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Glacier Hazards Resources

• Hazards
• Ice avalanches (e.g., Mt. Huascaran in Peru, 1970)

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Glacier Hazards Resources

• Hazards
• Glacial lake outburst floods (GLOFs)

86
Glacier Hazards Resources

• Hazards
• Glacial lake outburst floods (GLOFs)

Post-GLOF
Pre-GLOF
87
Glacier Hazards Resources

• Resources water supply from glaciers of the Wind
  River Range
• Largest concentration of glaciers in American
  portion of Rockies 50 covering 17 mi2
• Altithermal (7000-4000 BP) probably melted all
  ice
• Glaciers re-formed during Audubon advance (3000
  BP)

88
Glacier Hazards Resources

• Resources water supply from glaciers of the Wind
  River Range
• Ice advance during Little Ice Age (1400-1750)
• Dinwoody Glacier 1.3 mi2 with terminus at 11,000
  ft. elev.
• Pronounced retreat in 1930s and 1950s
• Repeat photography 1935 vs. 1988

1935 (top) and 1981 (bottom)
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Glacier Hazards Resources

• Resources water supply from glaciers of the Wind
  River Range
• Use stereo zoom transferscope to compare
  elevation of Dinwoody Glacier surface on stereo
  aerial photo pairs 1958-1983
• Contour those data Dinwoody lost avg. thickness
  of 77 feet

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Glacier Hazards Resources

• Resources water supply from glaciers of the Wind
  River Range
• Use radar to find remaining thickness of ice
• 50 of ice lost 1958-1983
• 50 of 1983 ice lost by1994

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Glacier Hazards Resources

• Resources water supply from glaciers of the Wind
  River Range
• Use radar to find remaining thickness of ice
• 50 of ice lost 1958-1983
• 50 of 1983 ice lost by1994
• W.E. lost is
• 8 of avg. annual runoff
• 30 of the September-October runoff (when other
  sources of runoff are lacking)