Glacial Erosion Ice Push

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Glacial ErosionIce Push

• Glacier acts as bulldozer,may push limited amount
  of debris into ridge known as
• ICE-PUSH MORAINE.

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Glacial ErosionAbrasion

• Grinding by transported grains of silt and
  larger sizes.
• Effects polish, striations, grooves.
• Embedded fragments shared these features as
  well as facets.

Longitudinal glacier flow
Debris particle paths
Diverging ice flow
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Glacial ErosionAbrasion

• Evidence
• Polish, striations, grooves, facets (on clasts)
• Done by different sizes of embedded debris
• Rock flour
• Seen as cloudiness or milkiness in glacial
  meltwater.
• Direct measurement
• Rates of a few mm/yr
• SLIDES

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Glacial ErosionAbrasion

• Influencing Factors
• Adequate amount of basal debris
• Replenishment of basal debris
• High rate of basal sliding
• Adequate thickness to apply pressure
• Hardness of embedded debris
• Angularity and size of embedded fragments

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Glacial ErosionAbrasion

• Replenishment of Debris

Longitudinal glacier flow
Movement towards glacier bed equal to amount
of basal melting
Path taken by particle
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Glacial ErosionPlucking (Quarrying)

• Pulling out large blocks of rock along fractures.
• May be dragged free or refrozen to base of
  glacier (regelation).

GLACIER Flow
Preassure-induced Melting
Refreezing
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Glacial ErosionPlucking

• Fractures
• Created by theglacier by draggingembedded
  fragmentschattermarks

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Glacial ErosionPlucking

• Other Mechanisms for Rock Fracturing
• Freeze-thaw
• Unloading
• Including by the glacier when it recedes.
• Earthquakes and other deformation

9
Glacial ErosionFeatures Produced by Ice Sheets

• Whalebacks streamlined, abraded hills oriented
  parallel to ice flow. Dimensions height 1 to
  10 m length 1 m to several km. Surfaces often
  striated.

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Glacial ErosionFeatures Produced by Ice Sheets

• Formation of Whalebacks

Fast erosion
Flowing ice
Little erosion beneath stagnant or slowly moving
ice
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Glacial ErosionFeatures Produced by Ice Sheets

• Rock drumlins have the profile of true drumlins
  (steeper end upglacier) but are composed of
  bedrock. Dimensions height up to 50 m length
  up to several km

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Glacial ErosionFeatures Produced by Ice Sheets

• Rock drumlins
• 1. May occur in drumlin fields with true
  drumlins.
• 2. May have survived because they are composed
  of more resistant rocks.
• 3. May have been preglacial hills overridden and
  smoothed by glacier.

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Glacial ErosionFeatures Produced by Ice Sheets

• Roches moutonees are streamlined bedrock hills
  with the steep end downglacier.
• Polish and striations on upglacier side indicate
  abrasion there.
• Downglacier side eroded by plucking is steep and
  irregular.
• Dimensions are similar to those for whalebacks
  and rock drumlins.

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Glacial ErosionFeatures Produced by Ice Sheets

• Characteristics of Roche Moutonees

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Glacial ErosionFeatures Produced by Ice Sheets

• Negative Relief Features
• Megagrooves are parallel streamlined depressions
  with about the same dimensions as the
  positive-relief features.
• Rock basins are wider and less streamlined their
  occurrence usually coincides with more easily
  eroded rock.

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Glacial ErosionFeatures Produced by Ice Sheets

• Rock Basins

gabbro
slate
0
80 km
diabase sills
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Glacial ErosionFeatures of Alpine Areas

• The largest and otherwise most significant
  glacial landform of alpine areas is the glacial
  trough.
• Longitudinal profiles of glacial troughs are
  steep in their upper parts and are also stepped
  and are commonly stepped.
• Paternoster lakes may occupy the floors of the
  steps.

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Glacial ErosionFeatures of Alpine Areas

• Glacial Steps

Riegels
Riegels
Basins
Riegels
Basins
Basins
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Glacial ErosionFeatures of Alpine Areas

• Glacial Troughs
• Transverse profiles are said to be U-shaped but
  vary in actual shape.

V-shaped
ParabolaW/2D
Semi-circleW/2D1
W/2D1
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Glacial ErosionFeatures of Alpine Areas

• Features Associated with Troughs
• Truncated spurs
• Result of straightening valley.
• Hanging valleys
• Greater erosion in main valley leaves
  discordant relationship.
• Commonly marked with waterfall.

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Glacial ErosionOther Glacial Troughs

• Fiords (sometimes fjords)
• Lower part occupied by arm of sea.
• Formed by outlet glacier
• Finger Lakes type trough in soft rocks.

Basin
Threshold
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Glacial ErosionAlpine Feature - Cirque

• Half-bowl shaped scoup just below highest
  mountains.

Headwall
Snowline
Threshold
Basin
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Glacial ErosionAlpine Areas - Cirques

• Probably originate as nivation hollows.

Protalus Rampart
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Glacial ErosionAlpine Areas - Cirques

• Expand into cirque as glacier forms and advances.

Bergsrund
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Glacial ErosionAlpine Areas - Cirques

• Cirque Aspect
• NE aspect in Northern Hemisphere favors
• 1) Protection from sun
• 2) Receives wind-driven snow

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Glacial ErosionAlpine Features

• Aretes sharp-crested ridge dividing two
  glaciated areas
• Cols low areas through ridges such as
  aretes often passes
• Horns jagged peak that survived erosion

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Glacial ErosionAmounts

• Area Erosion (in ft)
• Canadian Shield 10-50
• Scandinavia 80
• New England 10-15
• Valleys, B.C. 200
• Yosemite 650
• Finger Lakes 1400