Paths of Glacial Transport

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Paths of Glacial Transport

• Supraglacial all the way
• Supraglacial to englacial to supraglacial
• Subglacial all the way
• Subglacial to englacial to supraglacial
• Which path will have the greatest effect on
  abrasion of transported clasts?

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Types of Glacial Deposits

• Drift all deposits in any way related to
  glaciation.
  
• Till unstratified drift carried and deposited by
  the ice.
  
• Stratified drift water has played a role in
  deposition. Types are
  
• Glaciofluvial by meltwater streams
• Glaciolacustrine in glacial lakes
• Glaciomarine in the ocean

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Types of Till - Processes

• Subglacial lodgment till
• Melt-out till - either subglacial or
  supraglacial
  
• Flowage - flow till
• How would these deposits differ?

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Lodgment TillMechanisms

• Direct plastering at the base of the glacier
• Due to
• 1) frictional drag over irregularities in the
  substratum (especially if rock)
  
• 2) Release of debris by pressure-controlled
  melting
  

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Characteristics of Different Types of Till
An Assignment How do tills differ with respect
to

• Thickness
• Abrasion of clasts
• Compaction
• Grain size distribution
• See Figure 11.12

• Fissility
• Jointing
• Shapes of clasts
• Fabric of clasts
• See Figure 7-9

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Note The following figures are useful for the
discussion of depositional landforms as well as
many figures in the textbook Figure 16.4,
Figure 7-5, Figure 10-14, Figure 12.2, Figure
8.52, Figure 164, Figure 17-6
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Depositional LandformsMoraines

• Some moraines have ridgelike form others do not.
  Among those that do not, ground moraine is the
  most common form. It occurs as flat to rolling,
  hummocky terrain. In many areas, the sediment is
  predominantly lodgment till overlain by ablation
  till. In some areas, bedrock hills may protrude
  through the ground moraine.

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Depositional Landforms Moraines (cont.)

• Another variety of moraines without ridgelike
  form is disintegration moraine. This is a
  moderately rugged terrain of chaotic mounds and
  pits (kames and kettles) formed by the
  downwasting of stagnant ice. The sediments are a
  mixture of ablation till, glaciofluvial deposits,
  and glaciolacustrine deposits.

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Depositional LandformsMoraines (cont.)

• Most other moraines have ridge-like form. Common
  moraines in alpine terrain are lateral moraines
  and medial moraines. The former are formed along
  valley sides below the equilibrium line. Why
  would that be? They are most prominent where the
  valley is not too restrictive. Debris may be
  from within the glacier due to lateral flow or
  may be mass-wasted.How would the latter be
  related to slope aspect?

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Depositional LandformsMoraines (cont.)

• Medial moraines form from the merger of two
  valley glaciers and their lateral moraines.
  Traced downglacier, medial moraines often merge
  with a cover of ablation till resting on the ice.
  Medial moraines are rarely preserved when the
  ice melts. Why would that be?

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Depositional LandformsMoraines (cont.)

• End moraines are built around the margin of a
  glacier. The terminal moraine marks the
  outermost advance of the glacier during a
  particular glacial stage. There can be only one
  terminal moraine. Recessional moraines mark the
  stabilized ice margin during a period of
  punctuated recession of the glacier.

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Interlobate Moraine

• Interlobate moraines are formed along the common
  margin of two adjacent lobes. Such moraines are
  often very prominent.

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End MorainesProcesses of Formation

• Movement of debris-laden ice to snout.
• Requires glacier in equilibrium
• Lowering of ablation cover.
• Squeezing out saturated substrata.
• Ice push

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End MorainesOther Considerations

• May contain stratified drift
• Prominence also related to
• Grain size of till more prominent if
  coarser-grained
  
• Age younger moraines less eroded
• May be discontinuous due to
• Erosion by meltwater
• Lack of sufficient debris in the ice

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Streamlined FormsFlutings

• Streamlined glacial forms are oriented with the
  long direction parallel to glacial flow.
  Flutings are ridges up to 10 m high and less than
  a km long. They are formed by squeezing of
  substratum materials into cavities on the
  downglacier end of embedded boulders. Figure 12.2

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Streamlined FormsDrumlins

• Elliptically elongated hills parallel to flow
  direction.
  
• Dimensions of long.
  
• Blunt end upglacier, tapered downglacier.
• Composed mostly of till, but may have core of
  bedrock, waterlaid material (deformed)
  
• Usually located several miles back from ice
  margin in clusters. Why? Figure 7-5

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Drumlins - AssignmentHow do they form?
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Glaciofluvial DepositsProcesses of Deposition

• Deposition either in contact with the ice or some
  distance beyond the ice (proglacial)
  
• Processes of fluvial deposition most common
• Sometimes flow is in tunnels or other openings in
  the ice where water may be under pressure.