Glacial Processes

Basic summaries of ice formation, ice movement, and weathering.

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  • Glacial Processes
    • Ice movement
      • Internal deformation- Cold based glaciers move 1-2cm/day mainly by internal deformation. Ice crystals orientate themselves in the direction of ice flow, allowing them to slide past one another.
      • Basal slippage- Pressure and friction  increase temperature, causing basal ice to melt, the melt water acts as a lubricant allowing ice to move 2-3cm/day (mainly temperate glaciers).
        • Regelation- Ice melts under high pressure upwards of an obstacle, acting as a lubricant for more ice to pass over, and refreezes under lower pressure on the downstream side of the obstacle, creating a regelation layer.
      • Extending flow- Steep gradient makes ice flow faster and become thinner and more spread out. Less erosive.
      • Compressing flow- gentle gradient makes ice flow slower and become thicker and less spread out. More erosive.
    • Ice formation
      • Layers of snowfall compress lower snow and force out air to form neve. Eventually forming ice. Mleting and refreezing of old snow can assist the process.
    • Weathering
      • Freeze thaw- Most effective when temperature fluctuates around 0°c, water in cracks in rock expands by 9% when frozen, causing rock to shatter. More active in periglacial environments than polar.
      • Abrasion- Angular, frost-shattered rocks below glacier sandpaper the bedrock, and can form striations indicating direction of ice movement.
      • Plucking- Angular, frost shattered rocks are pulled out of the bedrock by meltwater refreezing around them. Common downslope of obstacles where lowered pressure causes refreezing.
  • Extending flow- Steep gradient makes ice flow faster and become thinner and more spread out. Less erosive.

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