Introduction

• Definition
  
  • A thick mass of ice that originates on land from the accumulation, compaction, and recrystallization of snow
    
  • What makes glaciers unique is their ability to move.
    
  • Due to sheer mass, glaciers flow like very slow rivers.
    
• Location
  
  • Occupy 10% of Earth’s surface
    
  • Primarily located in polar regions (Antarctica & Greenland)
    
  • But found on every continent
    
  • Form above the snow line
    
• Formation
  
  • New layers form each year
    
  • Weigh of overlying layers compresses buried layers
    
    • Snow recrystallizes – looks like sugar
      
    • Snow begins to grow, air pockets decrease
      compacts & becomes very dense
      
    • After 2 winters => FIRN
      
  • Firn
    
    • Generally 16x the size of a snow crystal
      
    • ½ as dense as water
      
    • Increase in size as the overburden increases
      
    • Over time, grows to form even larger crystals
      
    • Forms glacial ice
      
• Movement
  
  • When ice sheet thickness > 18 meters, the ice sheet:
    
    • Deforms
      
    • Flows
      
  • Movement slower at base than at top
    
  • Advance and retreat
    
  • Surge
    
  • Two basic types of movement
    
    • Plastic flow
      
      • Occurs within the ice
        
      • Under pressure, ice behaves as a plastic material
        
    • Basal slip
      
      • Entire ice mass slipping along the ground
        
      • Most glaciers are thought to move this way by this process
        
  • Rates of movement
    
    • Average velocities vary considerably
      
    • Rates of up to several meters per day
      
    • Some glaciers exhibit extremely rapid movements called surges
      
  • Budget of a glacier
    
    • Accumulation + loss = glacial budget
    • If accumulation exceeds loss (called ablation), the glacial front advances
    • If ablation increases and/or accumulation decreases, the ice front will retreat
      
• Features
  
  • Crevasses
    
    • Cracks in the surface of the glacier
      
    • Caused by movement
      
  • Moraines
    
    • Long, dark bands of debris
      
    • Visible on the top of the glacier
      
    • Medial Moraines
      
    • Lateral Moraines
      

Types of Glaciers

• Ice
  
  • Ice Sheets, Ice Shelves, Ice Caps, Ice Streams/Outlet Glaciers, and Ice fields
    
• Glaciers
  
  • Mountain Glaciers, Valley Glaciers, Piedmont Glaciers, Cirque Glaciers, Hanging Glaciers, and Tidewater Glaciers.
    
• Ice Sheets
  
  • Greenland and Antarctica
    
  • 50,000 square kilometers
    
  • Antarctica
    
  • 4200 meters thick in some areas
    
  • Covers nearly all of the land features except the Transantarctic Mountains
    
• Ice Shelves
  
  • Occur when ice sheets extend over the sea, and float on the water
    
  • Thicknesses: few 100 m to 1000s of meters
    
  • Retreating ice shelves may provide indications of climate change
    
• Ice caps
  
  • Mini ice sheets
    
  • form primarily in polar and sub-polar regions that are relatively flat and high in elevation
    
• Ice Streams and Outlet Glaciers
  
  • Ice streams are channelized glaciers
    
  • Flow more rapidly than the surrounding body of ice
    
• Ice Fields
  
  • Similar to ice caps
    
  • Flow is influenced by the underlying topography
    
  • Typically smaller than ice caps
    
• Mountain Glaciers
  
  • Develop in high mountainous regions
    
  • Often flow out of icefields
    
  • The largest mountain glaciers are found
    
    • Arctic Canada & Alaska
      
    • the Andes in South America
      
    • the Himalayas in Asia
      
    • Antarctica.
      
• Valley (alpine) glaciers
  
  • Commonly originate from mountain glaciers or ice fields
    
  • Flows down a valley from an accumulation center at its head
    
  • Look like giant tongues
    
  • May be very long
    
  • Can reach sea level.
    
• Peidmont
  
  • Occur when steep valley glaciers spill into relatively flat plains
    
  • Spread out into bulb-like lobes.
    
• Cirque Glaciers
  
  • Named for the bowl-like hollows they occupy (cirques)
    
  • Found high on mountainsides
    
  • Tend to be wide rather than long.
    
• Hanging Glaciers
  
  • Also called ice aprons
    
  • Cling to steep mountainsides
    
  • Wider than they are long
    
  • Common in the Alps
    
• Tidewater Glaciers
  
  • Flow far enough to reach out into the sea
    
  • Responsible for calving numerous small icebergs
    

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Glacial Landforms

• Glacial Erosion
  
  • Glaciers erode the land in two ways
    
    • Plucking – lifting of rocks
      
    • Abrasion
      
      • Rock flour (pulverized rock)
        
      • Glacial striations (grooves in the bedrock) Glacial Landforms
        
• Landforms
  
  • Glacial Valleys
    
  • Fjords
    
  • Pater noster lakes
    
  • Cirques
    
  • Tarns
    
  • Arêtes
    
  • Horns
    
• Glacial Deposits
  
  • Glacial drift – refers to all sediments of glacial origin
    
  • Types of glacial drift
    
    • Till – material that is deposited directly by the ice
      
    • Stratified drift – sediments laid down by glacial meltwater
      
  • Landforms made of till
    
    • Moraines - layers or ridges of till
      
      • Lateral moraine
        
      • Medial moraine
        
      • End moraine – terminal or recessional
        
      • Ground moraine
        
    • Depositional features
      
      • Outwash plain, or valley train
        
      • Kettles
        
      • Drumlins
        
      • Eskers
        
      • Kames
        
  • Landforms made of stratified drift
    
    • Outwash plains (with ice sheets)
      
    • Valley trains (when in a valley)
      
      • Broad ramp-like surface composed of stratified drift deposited by meltwater leaving a glacier
        
      • Located adjacent to the downstream edge of most end moraines
        
      • Often pockmarked with depressions called kettles
        
    • Ice-contact deposits
      
      • Deposited by meltwater flowing over, within, and at the base of motionless ice
        
      • Features include
        
        • Kames
          
        • Kame terraces
          
        • Eskers

Ice Ages

• Have occurred throughout Earth’s history
  
  • Began 2 to 3 million years ago
    
  • Division of geological time is called the Pleistocene epoch
    
  • Ice covered 30% of Earth's land area Ice Ages
    
  • Four major stages recognized in North America
    
    • Nebraskan
      
    • Kansan
      
    • Illinoian
      
    • Wisconsinan
      
• Effects of the last Ice Age
  
  • Forces migration of animals and plantsIce Ages
    
  • Changes in stream courses
    
  • Rebounding upward of the crust in former centers of ice accumulation
    
  • Worldwide change in sea levelIce Ages
    
  • Erosion and deposition
    
  • Climatic changes
    
• Some possible causes of glaciation
  
  • Changes in oceanic circulation
    
    • Thermohaline Current (AKA deep ocean circulation patterns)
      
  • Variations in Earth’s orbit
    
    • The Milankovitch hypothesis
      
      • Shape (eccentricity) of Earth’s orbit varies
        
      • Angle of Earth’s axis (obliquity) changes
        
      • Earth’s axis wobbles (precession)
        
      • Changes in climate over the past several hundred thousand years are closely associated with variations in the geometry of Earth’s orbit
        
  • Changes in oceanic circulation
    
    • Disruptive factors
      
      • Earth heats up
        
      • Ice at polar caps melt
        
      • Increases amount of fresh water in oceans
        
      • Decreases density of sea water
        
      • Thermohaline /deep ocean currents can’t form
        
      • Thermohaline circulation belt slows, stops, or moves towards the equator
        
      • Climate not moderated
        
      • Poles freeze, start of new ice age?
        

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