Glacial Modification of Terrain

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Glacial Modification of Terrain
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Objectives of the Unit

• Understand processes of glacial modification of
  terrain
• Learn about types and formation of Glaciers
• Analyze periglacial (zone indirectly influenced
  by glaciers) environment and ice age.

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Unit Outline

• Impact of Glaciers on the Landscapes
• Glaciation past and present
• Types of Glaciers
• How Glaciers Form

• 5. Continental Ice Sheets
• 6. Mountain Glaciers
• 7. The Periglacial (zone indirectly influenced by
  glaciers) environment
• 8. Are we still in Ice Age
• 9. Focus Study Antarctica

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1. Impact of Glaciers on the Landscapes

• Glaciers occur when there is net accumulation of
  snow
• Grinding by moving ice impacts overwhelmingly
• 7 of erosion is by glaciers

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2. Glaciation past and present

• Record is approximate and incomplete
• Pleistocene Glaciation
• Impact only of recent Ice Age
• Many parts of continental terrain have been
  imprinted by Pleistocene events
• Started gt1.8 million years ago
• Glaciation and retreat alternated
• Last major retreat took place 9,000 years ago
• Period since last glacial stage is Holocene Epoch
• Refrigerated high altitude and high latitude
  areas covering 1/3 earth

• Periglacial process impacts
• Landscape effected because of periglaciation, sea
  level changes, crustal depression and pluvial
  development
• Periglacial processes (erosion and deposition)
  affected 20 of earth mass
• Periglaciation zone zone indirectly influenced
  by glaciation
• Worldwide lowering of sea level during each
  episode of Pleistocene glacial advance
• Weight of ice resulted in lowering of 4,000 ft.
  Canada and N Europe are still in isostatic
  rebound.
• Pluvial developments increased rainfall that
  resulted in lakes where they were not present
• Contemporary Glaciation
• Ice covers 10 of the Earth now
• (96 is Antarctica and Greenland)

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Pleistocene Glaciation
Figure 19-1(c)
Figure 19-1(b)
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3. Types of Glaciers

• Movement and impact of ice depends on the
  quantity of ice and environment
• Two types of Glaciers
• Ice Sheets
• Mountain Glaciers

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3 a. Continental Ice Sheet

• Ice sheet An immense blanket of ice in non-
  mountainous areas that completely inundates
  terrain e.g.. Antarctica and Greenland
• Outlet Glacier A tongue of ice around the margin
  of an ice sheet that extends between rimming
  hills to the sea

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3b. Mountain Glaciers

• Two types
• Icefield An unconfined sheet of ice in high
  mountain areas
• AlpineIndividual glaciers that develop in high
  mountain areas
• Icefield glacier An unconfined sheet of ice in
  mountains
• Valley glacier Long narrow river of ice
• Piedmont glacier Valley glacier extended over
  flat land and beyond
• Alpine glacier Glacier in mountain crest line
• Cirque glacier small glacier that does not move
  down-valley

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Alpine Glaciers
Figures 19-6 and 19-7
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4. How Glaciers form

• Need certain circumstances and right combination
  of temperature and moisture
• Balance of accumulation and ablation is critical
• Accumulation incorporates snow
• Ablation by melting and sublimation

• Changing of snow to ice
• Firn (Neve) packed snow granules. Snow granules
  ½ density of water
• Equilibrium line where accumulation and ablations
  offset each other
• Two portions one for accumulation zone and other
  for ablation zone

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Snow to Ice
Figure 19-8
Snow changes to ice by compression and
coalescence From snowflake to granular form and
to Neve and Glacier Ice
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4. How Glaciers form(cont)

• Glacial movement
• Orderly unlike fluvial
• Under pressure it deforms not break
• Flow is often erratic as all parts of the glacier
  do not move at the same rate
• If confined in the valley center moves faster
  that sides as in streamflow

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4. How Glaciers form(cont)

• Erosion by Glaciers controlled by Volume and
  speed of glacier by the process of plucking and
  abrasion
• Plucking Quarrying action pried out and dragged
• Abrasion(jumping and bouncing and rolling and
  sliding) results in polishing in resistant rocks
  and digging and groves in soft rocks
• Erosion results in angular and rugged landscape
  in mountainous areas

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4. How Glaciers form(cont)

• Transportation by glaciers
• Glacier Flour rock ground to fine texture like
  talcum powder
• Most typical component of glacial load
• Picked up from bottom and carried along an narrow
  zone
• Alpine glacier might carry mass wasting material
  on top of ice
• Transportation speed varies based on slope,
  season and variations in accumulation
• Flowing water transports waters to many glaciers

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4. How Glaciers form(cont)

• Deposition
• US Midwest got most productive soils from Canada
• Drift all material carried and deposited by
  glaciers
• Till rock debris deposited by moving or melting
  ice with no meltwater flow and re-deposition
• Glacial erratic Outsized boulder included in the
  glacial till which may be different from bedrock
• Deposition by meltwater
• Glaciofluvial deposition at the margins of the
  glaciers and can extend to periglacial zone
• Deposition and redeposition
• Subglacial streams issuing from ice, depositing
  debris
• Meltwater from glaciers picks up material already
  deposited and re-deposited else where
• Redeposition is common by melt water

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Glacial Till
Figure 19-13
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Glacial Erratic
Figure 19-14
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5. Continental Ice sheets

• 2. Erosion
• Result in an undulating surface
• Scoured knobs, scooped out depressions, bare
  rocks and lakes dominate
• Erratic and inadequately developed stream
  patterns
• Creates U-shaped valleys
• Roche Moutonnee Bedrock hill over-ridded by
  moving ice
• Erosional effects further modified by
  depositional debris

• Most extensive that reshaped 1/5th of Earths
  land surface
• Development and flow
• Except for Antarctica, developed in subpolar and
  midlatitude locations then spread in all
  directions
• Initial flow in preexisting channels followed by
  erosion by ice accumulation

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Ice Sheet Deposition

• Moraine largest conspicuous rising topography
• Till plain irregular undulating surface formed
  from uneven deposition
• of glacial till Esker Long sinuous ridges
• Drumlins Low elongated hills Kettles
  Depressions in a moraine

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5. Continental Ice sheets (contd)

• 4 Glaciofluvial features.
• Stratified drift drift sorted while flowing
• Outwash plain smooth flat alluvial apron
• Valley train A lengthy deposit at valley bottom
• Esker long sinuous drift
• Kame steep or conical hill from stratified
  drift

• 3. Deposition
• Till plain irregular undulating surface formed
  from uneven deposition of glacial till
• Moraine largest conspicuous rising topography
• Kettle Depression in a moraine
• Drumlin Low elongated hill

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Growth of a Terminal Moraine
Figure 19-20
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6. Mountain Glaciers

• They do not reshape as much as ice sheets
• Development and flow
• Downslope along existing valley or channel
• Alpine glaciers are in sheltered depressions near
  head of stream valley

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• Erosion by mountain Glaciers
• Cirque broad glacial head of glacial valley
• Arate narrow serrated spine of rock
• Col pass or saddle ridge when adjacent cirque
  are cut back
• Horn steep sided pyramid rock
• Tarn small lake in depression
• Glacial trough valley with straight course and
  changing gradient
• Paternoster Lakes sequence of small lakes
• Hanging valley tributary glacial trough with
  bottom higher than principal trough it joins

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Cirques
Figures 19-26 and 19-27
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Glacial Trough
Figure 19-33
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Glaciated Valleys
Figures 19-32 and 19-34
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7. The Periglacial Environment

• gt20 of Earth from periglacial environment,
  mostly from Pleistocene epoch. These are in high
  altitude or high latitude
• Patterned ground a. frost action, b. Role of ice
  in geomorphology
• Pro-glacial Lake formed because of obstruction by
  glaciers are temporary

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Mountain Landform Development
Figure 19-28
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Moraines in Mountains
Figure 19-36
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7. Are we still in an Ice Age

• Many theories of glaciation and deglaciation
• Variation in intensity of solar radiation
• Shifting earths axis or variation in
  eccentricity of earths orbit
• Changes on CO2 in atmosphere
• Changes in position of continents and oceanic
  circulation
• Some combine various factors
• Question remains are we still in post or
  interglacial period
• Many glacier began to readvance in 1960s and 1970
• Weather changes have been unfavorable

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Focus Study Antarctica

• 98 glacier
• Bedrock floor irregular and deeply buried, below
  sea level in some places
• 2 section with trans-Antarctic mountains

• Few dry interior valley (3 parallel)
• Influences the world environment in terms of sea
  level, ocean temperature, circulation pattern,
  nutrient content of the ocean and atmospheric
  circulation
• If melted sea level would rise by 73 m.