periglacial environments

• No permanent ice covering but very cold 

  • Modern tundra
  • Southern England during glacials ]

   
• Periglacial regions have permafrost:

  • Permanently frozen soil or bedrock
  • Only top layer melts in summer and waterlogs soil 
  • Weathering (physical and chemical) mainly in melted layer 
• Main weathering is freeze thaw. 

  • Repeating cycle 
  • Freeze thaw increases fluid pathways so increases chemical weathering rates 
  • Produces scree slopes
• Frost heave:

  • Brings stones to surface 
  • Water in soil and mud freezes and expands pushing stones up 
  • When it thaws more mud replaces ice under stones supporting them 
  • Cycle repeats 
• Ice wedges:

  • Formation due to freeze thaw of thermal expansion and contraction 
  • Similar shape to desiccation cracks 
• Patterned ground:

  • Ice wedges continue to grow and creates a pattern on surface 
  • Similar to desiccation cracks 
• Solifluction:

  • In summer top layer of waterlogged soil moves downhill by solifluction 
  • Comes to a stop in hollows and leaves solifluction lobes (head deposits)
  • Creates deposits with grains aligned downslope 
• Dry valley:

  • Created in periglacial conditions where permeable bedrock freezes and water flows over it 
  • When the climate warms water infiltrates into bedrock leaving a dry valley 
• Dartmoor tors formed by freeze thaw in periglacial conditions 
• Wind erodes deposits:

  • Low rainfall in polar regions 
  • Areas below ice sheets are rocky deserts 
  • Wind erosion of grains on rock - creating undercutting