Periglacial

• What are periglacial landscapes

  • Periglacial usually refers to areas that:

  o   Have permafrost (frozen ground >1 year)

  o   Intense frost action and bare ground for some of the year

  o   Freeze and thaw cycles dominate the landform creating processes

  • Which have distinctive ecosystems adapted to periglacial environments
  • Lasting geomorphic impact of past glaciation on post-glacial landscapes
  • Areas such as these account for around 25% of the world’s total land area
• Temperature and Periglacial landscapes

  • Temperature is a main driver of periglacial environments
  • Periglacial climates are impacted by seasonal temperature variations, as well as snow cover and vegetation
  • Snow and vegetation can insulate the ground and form a buffer layer that can reduce the amplitude of the seasonal temperature variations in soil
• Frost and the Ground

  • The atmospheric temperature is in constant energy exchange with the ground
  • This leads to different layers of soil conditions: the active layer, which sits above the permafrost table, an isothermal permafrost layer and below that frost free soil DRAW
  • The active layer is the surface layer that freezes and thaws with the seasons, the thickness of this layer is determined by the frequency and magnitude of thawing
• Permafrost interactions with soil

  • Permafrost is soil, regolith or bedrock that is below 0˚ in cool temps
  • The layer of permafrost is absent both under water and forests
  • In a level area, as you move from a bare environment to a forest environment with lakes and trees, the thickness of the active layer increases while the presence of permafrost decreases DRAW
  • In mountain permafrost, periglacial processes are common above the treeline. Dependent on the orientation of the slope,
  • polar facing = more permafrost
  • equatorial facing = less permafrost
• Frost Processes

  • Frost wedging – the thermal expansion of water in cracks leads to it widening, overtime as water melts and is replaced and then frozen again a vertical ice wedge network is created in the rock
  • Frost heave – Soils containing water expand when frozen, moving soil upward. This freezing can upheave coarse sediments
  • Patterned ground – Dynamics of seasonal thaw/freeze actions in the active layer leads to a variety of patterned grounds, such as stripes, circles or polygons
  • Solifluction – slow downslope movement of soil in cold regions due to freezing and thawing
• Periglacial mountain erosion

  • Frost cracking and frost creep lead to debris covered layers and smoothing of the landscape with convex slopes
• Rock Glaciers

  • Require steep terrain
  • Contain ice in their cores, and have a variation of flow rates
  • The accumulation of rock debris from periglacial mountain erosion provides the material for rock glaciers
• Permafrost Thaw

  • Increases the risk of soil slumping
  • Thermokarst are a characteristic landform of thawing in ice rich regions. They are irregular pits and depressions developed by thaw settlement