Glacial Systems & Landscapes: Periglacial Processes & Landforms

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  • Glacial systems & landscapes: Periglacial processes & Landforms
    • Permafrost = permanently frozen ground w/ top layer that melts (active layer)
      • 20-25% Earth's land
      • Continuous = all ground frozen
        • Mean annual temp = below -5 to form
      • Discontinuous = patches are frozen
        • Mean annual temp = below 0 to form
    • Mass movement
      • Temp above 0 = active layer melts but meltwater can't drain
        • Active layer = waterlogged & heavy = flows easily
          • Flow called solifluction, occurs wherever gradient
      • Solifluction lobe = when one bit of soil = faster than soil around it
        • E.g. if its on steeper ground = flows further = tongue shape
      • Can also occur through freeze thaw
        • Soil = frozen = expands = soil forced upwards at right angles to slope
          • Ground thaws = soil move vertically down
            • As a result, soil ends up further down slope
    • Ice wedges formed by frost contraction
      • 1.Temp drops = ground contracts = cracks
      • 2. temp increase = active layer thaws = meltwater seeps into cracks
      • 3. Permafrost's still frozen so water freezes
      • 4. Re-open another year = splitting ice wedge more
    • Patterned ground
      • By frost heave or frost contraction
      • Frost heave = water underneath stones freezes = force stone upwards
        • Once forced up they roll down the mounds that have formed
          • They form circles/polygons around them
      • Frost contractions = ground crack in polygon shapes = filled with stones = polygon patterns on surface
    • Periglacial Landforms
      • Pingos
        • Conical hill = ice core
        • Open system
          • Discontinous permafrost
          • Groundwater forced through gaps & collects together & freezes = core of ice = push ground upwards
        • Closed  system
          • Continuous permafrost
          • Forms when lake on surface
          • Lake insulates ground beneath = remains unfrozen
            • Lake dries up = permafrost advances around unfrozen ground = water collects in centre
              • Eventually water freezes = ice core = push ground above upward
      • Blockfields
        • Expanses of loose rocks
        • Formed in place by frost shattering of bedrock
      • Terracettes
        • Vegetation interrupts soil moving downwards (frost creep)
        • Flat area builds up behind obstruction
      • Thermokarst
        • Ice in ground melts = ground collapse & holes form
          • Become filled with water = uneven, marshy

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