1. Unit 3 – Gradational Processes
Glacial Processes
Unit 3 – Gradational Processes
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2. Glacial Processes Types of Glaciation Mass Balance Temperature Motion
Water
Erosion
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3. Types of Glaciation Continental Alpine
Enormous sheets of ice, up to 2km thick, that carve and rework land masses
Responsible for most of the features we see in Canada
Niagara escarpment, Great Lakes, hills in Peterborough area, bump with the Shneiders sign (401 before Guelph), Oak Ridge Moraine…
Alpine
Smaller scale and still occurring in many high elevation areas
Temperature is cold enough that snow does not melt during the summer, the accumulated snow gradually turns to ice, forming an alpine glacier
Many in the Western Cordillera and Innuition Mountains

4. Glacial Landscapes Laurentide and Cordilleran Ice Sheets (18 kaBP)
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5. Introduction: Glacial Landscapes
Late 20th century distribution of glacial ice is shown in Fig 7.3
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6. Late Wisconsinan Glaciation in Canada
Consider the last glaciation
Decay of the Laurentide Ice Sheet (Fig 7.9)
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7. Late Wisconsinan Glaciation in Canada
Great Lakes region
note the changes in ice position and the drainage
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8. Late Wisconsinan Glaciation in Canada
Prairie region
Ice positions, drainage
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9. Late Cenozoic Glaciations
Depositional Feature
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10. Glacial Landscapes: Models
Movement of ice inferred from streamlined features (Fig 7.8)
note Keewatin and Quebec spreading centres
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11. Glacial Landscapes: Models
Erosion Zone
Transition
Active Zone
Wastage Zone
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12. Late Cenozoic Glaciations
Theory for the cycles of glacial periods:
Milenkovich Cycles
Causes
Climate Change is required to generate the conditions needed to produce large ice sheets in the mid-latitudes
for example at the height of the last glaciation, global temperature was ~6oC cooler than the 20th century average
at the time and spatial scales in question there are several causes: mainly tectonics and orbital forcing
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13. Late Cenozoic Glaciations
Causes
Tectonics (slow gradual change)
Movement of large land masses into both polar regions (albedo effects)
Closing of the Arctic ocean (ocean and albedo effects)
Mountain building (uplift)
Gradual removal of carbon dioxide from the atmosphere by chemical weathering processes on land
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14. Late Cenozoic Glaciations
Causes
Tectonics (slow gradual change)
due largely to tectonics and weathering there was a slow and gradual cooling through the Tertiary
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15. Late Cenozoic Glaciations
Causes
Orbital Forcing
The Earths orbit around the Sun varies in its eccentricity, also the Earths axis changes in its angle of tilt and ‘wobbles’
These changes cause the Earth to receive different amounts of radiation from the Sun at the time scales of tens of thousands of years
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16. Late Cenozoic Glaciations
Causes
Orbital forcings cause variations in temperature that operate at the time scales of tens of thousands of years, they are superimposed on climate changes caused by other factors
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17. Glacial Processes: Mass Balance
Dobbin Bay, Ellesmere Island, Nunavut,
July 2000
Accumulation and Ablation Zones
Equilibrium Line
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18. Mass Balance Alpine and Continental Ablation and Accumulation Zones
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19. Mass Balance Accumulation Processes Snowfall
Rainfall (freezes in glacier)
Condensation
Drifting Snow and Snow Avlanches (in alpine environments)
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20. Mass Balance Ablation Processes Dobbin Bay Melting Evaporation
Sublimation
Streams
Calving
Dobbin Bay
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21. Mass Balance
Mass Balance is the budget between accumulation and ablation
May be determined for a part of a glacier or the entire glacier
For the whole glacier:
when positive: glacial advance
when negative: glacial retreat
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22. Mass Balance Techniques Direct Measures Indirect Measures
Snow and ice stakes
Cores, trenches, surveying
Indirect Measures
Remote Sensing
Aerial Photography
Satellite Imagery
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23. Mass Balance Global warming???
Global Data from National Snow and Ice Data Center
State of the Cryosphere
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24. Mass Balance
Bhutan Example
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25. Glacial Processes: Ice Temperature
Temperature (Thermal Regime)
Importance of ice temperature
Influences Motion and Erosion
Controls on Ice Temperature
Surface Air Temperature
Snowfall
Geothermal Heat
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26. Ice Temperature Basal Thermal Regime Cold Based or Polar Glaciers
Ice at the bottom of the glacier
Melting Point is depressed at high pressures
Cold Based or Polar Glaciers
Basal Ice is frozen to bed
Warm Based or Temperate Glaciers
Basal Ice is at or near the pressure melting point
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27. Glacial Processes: Motion
Ice Velocities are Variable
between several metres to hundreds or thousands of metres per year
influenced by several variables
ice thickness
slope
ice temperature
water
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28. Motion Glaciers move in response to stress where
Shear Stress (τ)
τ = ρgh sinβ
where
τ = basal shear stress
ρ = density of ice
g = acceleration due to gravity
h = ice thickness
β = slope of ice surface
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29. Motion Stress causes the ice crystals to deform and recrystallize
crystals slide (glide) past one another
This process of motion is called Creep
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30. Motion Mechanisms Creep Sliding Enhanced Basal Creep Regelation
Basal Slip
Bed Deformation
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31. Motion Sliding Enhanced Basal Creep
creep rate increases around bed obstacles because:
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32. Motion Sliding Regelation
net transfer of ice downslope due to melting and refreezing of basal ice around bedrock obstacles
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33. Motion Sliding Basal Slip Bed Deformation slipping of basal ice on bed
aided by liquid water at the bed
Bed Deformation
Materials in the bed may deform and carry the glacier along
more common when bed is comprised of non-frozen saturated sediments
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34. Motion Extending and Compressive Flow extending (accelerating flow)
compressive (decelerating flow)
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35. Motion Surging Sudden increase in velocity to potentially km per year
may occurs where ice is warm based
may be related to an increase in the amount of basal water
reduces friction: causes basal slip
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36. Motion Crevasses and Structures
Crevasses may develop where the ice fractures
ablation zone
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37. Glacial Processes: Water
Water influences motion and erosion processes
Water is more important in ablation zones (particularly for temperate ice)
Supraglacial
Englacial
Subglacial
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38. Glacial Processes: Erosion
Erosional Processes
Abrasion (scour)
Plucking (quarrying)
Fracturing
Meltwater
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39. Glacial Erosion: Abrasion
Abrasion rate is influenced by:
basal sliding velocity
high velocity = higher abrasion
frequency, size, and hardness of the clasts
a relatively small number of large, angular, hard clasts are most effective
the efficient removal of fine materials (silt) by meltwater at the bed
abundant fine material reduces contact with the bed
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40. Glacial Erosion: Abrasion
Distribution of Abrasion?
Evidence of abrasion: striations and related forms
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41. Glacial Erosion: Plucking
Plucking (quarrying)
pressure distribution at bed (Fig 5.7)
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42. Glacial Erosion: Plucking
Plucking (quarrying)
on up ice side of obstacle (b) there is scour and abrasion and partial melting
on down ice side of the obstacle (c) there is freezing of water (thus regelation) and the erosion of broken fragments in a process called plucking (quarrying)
the clasts may be entrained into the ice (frozen in) or moved by meltwater
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43. Glacial Erosion: Plucking
Evidence of Process
basal ice (regelation ice) often has a high debris content
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44. Glacial Erosion: Plucking
Evidence of Process
variety of landforms result from plucking (stoss and lee forms)
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45. Erosion and Ice Temperature
Erosion most effective under warm ice, there is very little or no abrasion under cold ice
Distribution of erosion may change with changes in temperature
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46. Glacial Processes Entrainment: How is debris incorporated into ice:
debris may be picked up (entrained) in basal ice as regelation occurs
materials can be thrust up into the ice when subglacial cavities fill with water
in alpine environments materials may be deposited on the ice and move into the glacier through crevasses and moulins
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47. Glacial Processes Transport Materials may be carried (transported)
at the bed or within the basal ice (subglacial environment)
within the glacier (englacial environment)
on the surface of the glacial (supraglacial environment)
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48. Glacial Sediments (Deposits)
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49. Glacial Deposits Depositional Environments Glacial Till
Glaciofluvial deposits
Glaciolacustrine, Glaciomarine deposits
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50. Depositional Environments
Materials may be deposited
beneath the glacier (subglacial)
at the margin or on the surface of the glacier (supraglacial)
as the ice melts out (e.g. englacial materials deposited at bed)
into bodies of water near the ice
into stream channels draining the ice
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51. Depositional Processes:
Glacial Till
Till may be deposited beneath an actively sliding glacier through a process called Lodgement (Lodgement Tills)
Till may be deposited as ice melts out producing Melt Out Tills (Ablation Tills)
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52. Glacial Till
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53. Depositional Processes
Materials may be deposited
by glacial ice directly
by flowing water
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54. Glacial Deposits: Glaciofluvial
Glaciofluvial (or fluvioglacial or outwash) sediments are materials that have been transported and deposited by glacial meltwater streams
These streams may be subglacial, supraglacial or proglacial
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55. Glaciofluvial Deposits
What are the general characteristics of glaciofluvial materials?
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56. Glaciofluvial Deposits
What are the general characteristics of glaciofluvial materials?
sand and gravel
moderately well sorted (can vary)
stratified (beds, laminations, structures that indicate deposition by flowing water)
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57. Glaciolacustrine and Glaciomarine
deposition of glacial sediments in a lake (standing water)
Glaciomarine
deposition of glacial sediments in a sea (standing water)
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58. Glaciolacustrine and Glaciomarine
Environment of Deposition (Figs 5.10, 5.11)
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59. Glaciolacustrine and Glaciomarine
Materials are delivered to the lake or sea by:
streams draining the glacier
glacial ice melting in the water body
icebergs that carry materials out into the lake or sea
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60. Glaciolacustrine and Glaciomarine
Characteristics of Glaciolacustrine and Glaciomarine sediments
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61. Glaciolacustrine and Glaciomarine
Characteristics of Glaciolacustrine and Glaciomarine sediments
mixtures of coarse and fine material near the glacier
on the lake or sea bed, far removed from the glacier, the materials are fine grained, well sorted and stratified (layered)
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