Glaciofluvial Deposits Distinguishing Characteristics

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Glaciofluvial DepositsDistinguishing
Characteristics

• Clasts rounded
• Usually unimodal grain size (fines removed)
• Bedding, some rather crude
• Often cross-bedded
• Grain-to-grain contact
• Imbrication possible, may reveal flow dir.

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Ice-Contact LandformsConsiderations and
Characteristics

• Ice on at least one side
• Extreme range and abrupt changes in grain size
• Clasts less abraded than in proglacial deposits
• May include bodies of till
• Slumping common

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Glaciofluvial LandformsKame Terraces

• Short, narrow benches along valley wall of
  glaciated valleys.
• Surface often pitted with kettles.
• Accumulations of streams that flowed between
  glacier and valley wall.
• Ice usually stagnant.
• Left as terraces when ice melted. Fig. 8.52

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Glaciofluvial LandformsKames

• Moundlike hill.
• Formation may be as sediment is deposited in
  crevasses in or on the surface of stagnant ice.
• Or, where small deltas or fans build against the
  ice.
• Debris collapses to form mound when ice melts.
• May be found in kame-and-kettle moraines.

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Glaciofluvial LandformsKettles

• Basin where ice block was surrounded by
  sediments.
• Occur singly or in groups. Figure 10-14

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Glaciofluvial LandformsEskers

• Long, narrow commonly sinuous ridges.
• May connect downvalley with deltas.
• Overall trend parallels the direction of ice
  flow.
• May climb over low ridges. How can it be?
• Slumping may occur along sides.
• Mostly sand gravel, but with lenses of till.

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Glaciofluvial LandformsEskers (cont.)

• They are deposits of streams in tunnels.
  Probably stagnant ice
• Can you reconstruct what it was like when the
  glacier was forming?

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Proglacial LandformsCharacteristics

• Composed of outwash coarse-grained deposits of
  streams beyond the ice margins.
• Usually the deposits of braided streams.
• Well-sorted to poorly-sorted.
• Many variations in grain size, but generally a
  decrease downstream.
• Silt, clay minor or absent.
• Rounding of clasts, especially boulders and
  cobbles.

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Outwash FeaturesOutwash Plains vs. Valley Trains

• Considerable lateral extent
• Usually in lowlands
• Banked against end of glacier
• May be fan-shaped

• Confined by valley walls
• Long and linear or sinuous

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Pitting and Terracing of OutwashPitting is
common in the upper reaches of outwash deposits.
It is probably the result of ice blocks carried
by outburst floods.Terraces are formed as the
stream cuts down through its own deposits, as in
most other stream terraces.Assignment How do
you relate terrace formation to the glacial
cycle?
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Glaciolacustrine FeaturesGlacial Lakes

• In erosional basins cirques (tarns), rock basins
  in glacial troughs, etc.
• Behind moraines
• Kettle lakes
• Any more?

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Glacial-Lake Sediments

• Delta coarse sediments, steep cross- bedding
• Bottom deposits mostly silt and clay usually
  laminated, may be varved. What are varves?
• May include dropstones
• Shore features wave-cut cliffs, beach deposits,
  etc.

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Glaciofluvial DepositsProcesses of Depositon

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

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Glaciofluvial DepositsDistinguishing
Characteristics

• Clasts rounded
• Usually unimodal particle size (fines removed)
• Bedding, some of it rather crude.
• Often cross-bedded.
• Grain-to-grain contact.
• Imbrication possible may reveal flow direction

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Glaciofluvial LandformsIce-Contact Landforms

• Ice on at least one side.
• Extreme range and abrupt changes in grain size.
• Clasts less abraded than in proglacial deposits.
• May include bodies of till.
• Slumping common.
• Types based on surface form related to genesis.

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Outwash FeaturesOutwash Plains vs. Valley Trains

• Considerable lateral extent.
• Usually in lowlands.
• Banked against end moraine or glacier
• May be fan shaped.
• Figure 16.4
• Figure 7-5

• Confined by valley walls
• Figure 8.52

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Outwash FeaturesPitting and Terracing

• Pitting common in upper reaches of outwash
  deposits. Probably the result of ice being
  carried by outburst floods.
• Terraces formed as the stream cuts down through
  deposits, as in most other stream terraces.

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Glaciolacustrine FeaturesGlacial Lakes

• In erosional basins cirques (tarns), rock
  basins, etc.
• Behind moraines. Figure 10-14
• Kettle lakes.

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Glaciolacustrine FeaturesGlacial-Lake Sediments

• Delta coarse sediments, steep cross-bedding.
• Bottom deposits mostly silt and clay usually
  laminated may be varved with dark clayey winter
  layer and silty summer layer.
• May be dropstones.
• Shore features wave-cut cliffs, beach deposits,
  etc.

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Types of Glacial Deposits

• Drift all deposits in any way related to
  glaciation.
• Till vs. Stratified Drift Figure 8-3
• Till unstratified drift carried and deposited by
  the ice
• Stratified Drift water plays a role in
  deposition
• Glaciofluvial transportation and deposition by
  meltwater streams.
• Glaciolacustrine deposition in glacial lakes.

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Types of TillProcesses of Formation

• Subglacial lodgment lodgment till
• Melt-out processes melt-out till
• Flowage flow till

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Lodgment tillFigure 11.3

• Direct plastering at base of glacier.
• Due to 1) Fractional drag over irregularies in
  bedrock.
• 2) Release of debris by pressure- controll
  ed melting.
• What are the properties of lodgment tills?

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Melt-Out Till

• Surface englacial debris released by summer
  melting.
• Basal melting due to geothermal heat.

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Flow Till

• Subglacial flow, under pressure, into basal
  cavities.
• Supraglacial material released by melting
  flows down snout of glacier.