Landforms Geography

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Landforms Geography
Glaciers
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Glacial Geomorphology

• Development of a glacier
• Types of glaciers
• Glacial landforms
• History of glaciers
• What causes glaciation?
• Impact of global climate change on glaciers
• Periglacial processes and landscapes

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Development of a Glacier

• Glacier slowly moving mass of dense ice formed
  by gradual thickening, compaction, and refreezing
  of snow water over time
• After summer melt, some snow left over
• With weight and partial melting, snow turns to
  Firn, crunchy transition from snow to ice
• Further compaction, ice crystals align, become
  dense glacial ice which flows slowly downslope
• At least 40-m thick to become glacier

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Glacial Mass Budget

• Glacial input Snow
• Glacial output ice, meltwater or water vapor
• Zone of Accumulation top of glacier where temps
  are cooler - input gt output
• Zone of Ablation lower part of glacier where
  temps are higher output gt input
• Equilibrium line point on glacier where input
  output

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Glacial Formation
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Glacial Mass Budget
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Glacial Mass Budget
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Glacial Movement

• Glaciers move through internal deformation
• Interior of glacier like malleable plastic

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Glacial Movement
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Glacier Types

• Mountain Glaciers
• Ice Cap Continuous sheet of ice covering entire
  landscape
• Ice Field Buries all but tallest mountains
  can be very thick
• Alpine Glacier Flows down valleys away from
  high country
• Cirque - Bowl-shaped depression on mountain flank
  due to glacial erosion snow source

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Alaskan Glaciers
Hubbard Glacier
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Continental Glaciers

• Huge ice masses covering a large part of a
  continent or large island also called ice
  sheets
• More than 3000 m deep in places
• Covers most of Antarctica and Greenland
• Weight of ice presses lithosphere down into
  asthenosphere, called isostatic depression

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Continental Glaciers
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Glacial Landforms

• Rock debris picked up by glaciers, transported
  in direction of movement deposited
• Glacial erosion
• Glacial Abrasion scratch and gouge bedrock
• Glacial Striations caused by glacial abrasion
• Glacial Grooves deep striations
• Glacial Plucking boulders ripped from ground by
  glacier deposited by retreating glacier, called
  Glacial Erratics

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Glacial Erosional Landforms

• Roche Moutonnée rounded hill, gradual on side
  toward direction from which glacier comes

Glacial Erratic
Glacial Striations
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Alpine Erosional Landforms

• Glacial Erosion
• Cirque bowl-like feature on mountain flanks
• Tarn small lake in bottom of cirque
• Arête narrow, steep ridges between cirques
• Horn mountain with 3 or more arêtes at summit
• Glacial Trough u-shape valley eroded by glacier
• Hanging Valley side trough above main trough
  possible waterfall

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Alpine Erosional Landforms
Cirque
Horn Matterhorn
Glacial Trough
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Glacial Depositional Landforms (Till)

• Glacial Till sediment directly deposited by
  glacier many particle sizes
• Moraine winding ridge formed by till at the
  front or side of glacier Moraine types
• Lateral along former edges of glacier
• Terminal along front of former glacier
• Recessional formed as glacier recedes
• Medial between 2 glaciers
• Ground irregular deposition as glacier recedes

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Glacial Depositional Landforms (Till)
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Glacial Depositional Landforms (outwash)

• Glacial Outwash sediments deposited by water
  out under a glacier as it melts forms Outwash
  Plain, flat feature in front of former glacier
• Kame large mound deposited near glacier front
• Esker winding ridge from water flowing in
  tunnel through ice under glacier
• Kettle Lake big ice block fallen off glacier
  front is buried by outwash, melts later forming
  lake

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Glacial Depositional Landforms
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Glacial Depositional Landforms
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History of Glaciation

• As early as 2.3 B years ago, ice covered much of
  Earth, and off and on since then
• Most important Ice Age was Pleistocene Epoch, 1.8
  M years ago till 10K years ago
• Glacial period when glaciers expand from poles
  cooler temps, lower sea level,
• Interglacial period when glaciers recede
  warmer temps, higher sea level

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Pleistocene Glaciations

• Named for southern extent of ice sheet in North
  America
• Nebraskan 1 million yrs ago
• Kansan 625 K yrs ago
• Illinoisan 300 K yrs ago
• Wisconsin 35 K to 10 K yrs ago
• Laurentide Ice Sheet eastern North America
• Cordilleran Ice Sheet western North America

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Maximum Extent of Pleistocene Glaciation
30 of earths surface covered by ice sheets
(Only 11 coverage today)
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Oxygen Isotopes
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Evidence of More Glaciations?

• Ice core samples suggest more than the known 4
  glaciations show more cool, glacial periods
• Oxygen isotopes O-16 O-18 both in water, but
  O-18 evaporates more in warmer climate, so ratio
  of O-16 to O-18 in ice cores can indicate
  relative warmth of climates over 1 million yrs
  ago!

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Great Lakes
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Causes of Glaciation

• Summer temp (melting) is key to glaciation
• Possible Factors1. Variations in solar
  radiation (dust, sunspots)
• 2. Reduced carbon dioxide (escaping heat)
• 3. Increased volcanic activity (reflective dust)
• 4. Variations in Earth-Sun geometry (axial tilt,
  shape of orbit, rotation)
• 5. Plate Tectonics

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Milankovitch Theory

• Dominant theory of causes of glaciation, based on
  Earth-Sun geometry
• Orbital eccentricity strongly elliptical orbit
  puts Earth farthest from Sun in summer, cooling
  it
• Tilt obliquity Earths tilt varies from 22.1º
  to 24.5º - less tilt means lower angle Sun and
  less insolation at poles, thus cooler summers
• Orbital precession wobbles of Earths axis -
  North Pole may point toward Sun at farthest point
  of orbit, creating a cool summer

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Milankovitch Theory
Orbital Eccentricity
Axial Tilt
Orbital Precession
When three factors coincide, high probability of
glaciation
Glacial Geomorphology Processes and Landforms
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Climate Change and Glaciers

• Since mid-1800s glaciers have been receding, both
  alpine and continental
• Alps, Parts of Andes, Mt. Kilimanjaro melting
• Thousands of sq miles of Antarctica Greenland
  ice sheet lost over last 30 years due to warming
• Melting area of Greenland has increased rapidly
  since early 1990s

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Climate Change and Glaciers
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Climate Change and Glaciers
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Periglacial Processes and Landscapes

• In near-glacial environments constant
  freeze/thaw cycle effects on landscape
• Permafrost ground that is permanently frozen
• Continuous poleward of -7ºC mean annual
  isotherm all surfaces frozen exp under water
  avg 400 m thick, up to 1000 m thick
• Discontinuous poleward of -1ºC mean annual
  isotherm thinner than continuous, esp. on south
  facing slopes

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Extent of Permafrost
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Permafrost Processes

• Active Layer soil that melts refreezes daily
  or seasonally as thin as 10 cm in continuous
  permafrost, up to 2 m thick in discontinous
• Dramatic warming in arctic is making active layer
  much thicker releasing tons of CO2
• Talik body of unfrozen ground within
  permafrost, e.g. under a lake, important for
  movement of groundwater