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Glaciers Glaciers Presentation Transcript

  • Glaciers and Periglacial Landforms Processes and Landforms Paleoclimatology
  • Overview
    • Glaciers
    • Glacial Processes
    • Glacial Landforms Periglacial Landscapes
    • The Pleistocene
    • Paleoclimatology
  • Objectives
    • Describe the different forms of glaciers in terms of the similarity of their formation and differences in spatial extent
    • Explain the interrelationships between the processes of glacier formation, and those of glacial motion
    • Relate glacial motion to the geomorphological themes of erosion, transportation and deposition, and describe the landforms associated with each
    • Identify various glacial landforms and describe the processes that created them
    • Describe the features and processes of periglacial landscapes
    • Describe some of the significant features of the Pleistocene
    • Identify major sources of climatic variability and explain how they contribute to climate change
  • Glaciers
    • Definition: A large mass of ice, flowing across the land under the influence of gravity and their own weight
    • Types
      • Alpine glaciers: Mountain glaciers, follow drainage patterns
        • Snowfield: area above snowline which provides ice for glaciers
        • Cirque glaciers: glaciers originating in basins of accumulated snow
        • Valley glaciers: several cirque glaciers merge into a greater downstream flow
        • Piedmont glaciers: after leaving the mountain slopes, several valley glaciers can merge into a larger flow across the landscape
        • Tidal glaciers: occur if a glacier reaches the sea. Large pieces of ice can break off forming ice bergs
      • Continental glaciers: continuous expanses of solid ice that subsume broad landscapes, including drainage systems and surrounding peaks
        • Ice sheets
          • cover entire continental masses
            • Antarctica (90% coverage)
            • Greenland (81% coverage)
          • ice mass can achieve depths of 2000 – 3000 meters
          • actual landmasses can be isostatically depressed below sea level
        • Ice caps
          • covers an area less than 50,000 sq. km. and typically has a circular shape
        • Ice fields
          • Ice fills elongated valleys along mountain ranges
  • Glacial Processes
    • Formation
      • Zone of Accumulation: area above snowline where snow exists year-round
      • Snow accumulates in basins and becomes compacted under its own weight
        • Snow becomes firn (compacted, granular snow)
        • Firn becomes glacial ice (exhibits strata from accumulation)
    • Mass Balance
      • Above the snow line, in the Zone of Accumulation, mass is added to the glacier
      • Below the snow line, the glacial ice can melt, sublimate, deflate in the wind, or break off the main glacier
        • Ablation or Waste are terms used to describe these losses
        • Zone of Ablation: the area below snowline where mass is lost from the glacier
      • Mass balance refers to the rate of accumulation compared to the rate of ablation
        • Positive balance: accumulation greater than ablation; glacier advances
        • Negative balance: ablation exceeds accumulation; glacier retreats
        • With current climate change, the world’s glaciers are largely in retreat
        • When rates of accumulation and ablation are equal, glacial movement continues to occur, but there is no net advance or retreat
    • Glacial Movement
      • Simultaneous sliding and oozing motion
      • Frictional movement
        • glacial ice rubs against bedrock on the sides and bottom of the valley
        • Abrasion and Plucking (erosional process)
        • Lateral and medial moraines (transportation features)
      • Plastic movement
        • glacier moves faster internally than along frictional edges
        • Causes cracks (crevasses) to form on the surface
      • Surges
        • Glaciers have been known to move several meters in one day
        • requires either large accumulations of mass, or lubricating meltwaters along the sides and bottoms
  • Glacial Landforms
    • Erosion
      • Plucking
      • Abrasion
    • Transportation
      • Surface load
      • Suspended load (englacial transport)
      • Along margins
    • Deposition
      • Occurs as a result of ablation
      • Melting and outwash sort transported material by mass and texture
        • Larger objects deposited in situ
        • Smaller sediments carried out by outwash
    • Erosional Features of Alpine Glaciers
      • Modified upslope drainage
        • U-shaped valleys
        • Horns
        • Ar ê tes
        • Cirques
        • Hanging valleys
        • Tarns and paternoster lakes
        • Fjords
    • Depositional Features of Alpine Glaciers
      • Glacial Drift
        • Deposits of transported material (cobbles and finer sediment)
          • Stratified drift: deposited by melt waters, sorted by size
          • Glacial till: unsorted material deposited in place by ice
      • Moraines
        • Deposition of glacial till by retreating glaciers
        • Rapid ablation causes till to be dispersed over a surface, creating a ground moraine or till plain
        • Slowing retreats (punctuated by periods of equilibrium) concentrate deposits of till
          • terminal moraines mark the farthest extent of glacial advance
          • recessional moraines mark periods of slowing retreat during periods of general retreat
    • Features of Continental Glaciation
      • Erosional features
        • deranged drainage
        • roche moutonn é e
      • Depositional features
        • Terminal and recessional moraines
        • Till plain, outwash plain
        • Eskers
        • Kettles
        • Kames
        • Drumlins
  • Periglacial Landscapes
    • Features of Subarctic and Polar (tundra) climates that are not directly related to glaciation
    • Processes
      • Physical weathering
      • Mass movement
      • Climate
      • Soil
    • Features
      • Permafrost
      • frost action
      • ground ice
    • Permafrost
      • develops after soil and rock have been below freezing for at least 2 consecutive years
        • Independent of moisture content of the soil
        • snow cover insulates the ground, preventing heat loss
      • Continuous and Discontinuous Zones of permafrost
        • Continuous Zone
          • Permafrost occurs everywhere, continuously, throughout this region
          • Occurs pole-ward of the –7 o C mean annual temperature isotherm
        • Discontinuous Zone
          • Occurs equator-ward of the –7 o C mean annual temperature isotherm
          • Permafrost becomes patchy and disconnected, becoming sparser at lower latitudes (mixed landscape of cryotic and noncryotic soil)
          • Patches occur on slopes facing away from the sun (North slopes in N. Hemisphere), cold soil, or areas not blanketed by snow
      • Permafrost behavior
        • Active layer: exposed to daily and seasonal freezes and thaws
          • active layer thickens with increases in temperature
        • Thawing releases carbon dioxide into the air
        • Taliks
          • areas of noncryotic soil within areas of continuous permafrost
          • taliks form links with groundwater, permafrost disrupts these links
    • Ground Ice and Frozen Ground
      • Refers to frozen subsurface water
        • Pore Ice
        • Lenses and Veins
        • Segregated Ice
        • Intrusive Ice
        • Wedge Ice
      • Frost Action
        • expansion of water as it freezes creates physical forces
          • Shatters rock, creating block fields or felsenmeer
          • perturbs the soils
            • Frost heaving
            • Frost thrusting
            • cryoturbation
            • Ice wedging
      • Landforms
        • Pingos: frozen injected artesian water, forming a circular mound, sometimes up to 60 m in height
        • Palsas: Mounds of peat with ice lenses (1 – 10 m)
        • Patterned ground: heaving and thrusting of the soil sorts the particles according to texture, with accumulations in wedge cracks, forming polygonal patterns on the ground
      • Hillslope Processes
        • Active layer becomes saturated with water during thaw cycles, and a slow downhill flow can occur
        • solifluction, gelifluction
      • Thermokarst landscapes
        • Formed from melting ground ice with poor drainage
        • cave-ins, bogs, depressions, standing water and small lakes
        • not related to carbonated Karst topography
  • The Pleistocene
    • 1.8 million to 10,000 years ago
      • Ice sheets and glaciers covered 1/3 of Earth’s surface
      • Periglacial regions occupied another 40%
    • The longest prolonged cold period in Earth’s history
      • Ice Age: period of prolonged cold marked by significant periods of glacial advance
        • glacials: 90,000 years
        • interglacials: 10,000 years
      • Pleistocene included 18 glacials
    • Features
      • Formation of the Great Lakes
        • Drainage systems enlarged by glacial action
        • Two periods of advance and retreat
      • Charging of the Great Plains Aquifer
      • Land Bridges
        • Lower temperatures caused more of Earth’s water to be tied up in ice
        • Sea levels were 100 meters lower than today
        • Exposed land, linking several continents, allowing for movement of species, especially humans
          • Bering Straits Land Bridge
          • England and France
          • Australia, New Guinea and Indonesia
      • Paleolakes
        • Advance of glaciers caused an advance of polar conditions, subpolar lows and polar jet stream, bringing wetter conditions further south
          • Pluvials
          • Interpluvials
        • Much of the American Southwest exhibited large lakes that are now dry
  • Paleoclimatology
    • The study of past climates and their change over time
      • Ice cores
      • Ocean sediments
      • pollen records
      • correlation of coral productivity to sea-level changes
    • Humans evolved during the coldest parts of Earth’s history
    • Recent Fluctuations
      • Medieval Warm Period: 800 – 1200
      • Little Ice Age: 1200 – 1350, 1800 - 1900
    • Mechanisms of Climate Change
      • Variations in Earth-Sun relations
        • 100,000 year cycle in variation of the shape of Earth’s orbit
          • 17.7 million km variation in Earth-Sun distance
        • 26,000 year cycle in precession
          • affects axial parallelism
        • 40,000 year cycle in axial tilt
          • varies between 22 o and 24 o
      • Solar variability: variation in solar output
      • Tectonics: movement of continents between latitudes
      • Atmospheric factors
        • Volcanic eruptions
        • Fluctuations in CO 2 content
      • Oceanic Circulation
        • Formation of the Isthmus of Panama 3 million years ago altered the patterns of ocean currents, area of upwelling, and distribution of hot and cold ocean waters