68-74 GEOGRAPHY

Periglacial Processes and Distinctive Landforms

Periglacial Environments

  • Definition: Periglacial refers to climate conditions and landscapes near glaciers during the Pleistocene and all non-glacial cold climate areas with high latitude and altitude.

  • Characteristics of Periglacial Climates:

    • Intense frosts in winter and snow-free ground during summer.

    • Average annual temperatures range from 1°C to -4°C.

    • Daily temperatures below 0°C for nine months and below -10°C for six months.

    • Rarely rise above 18°C in summer.

    • Low precipitation (under 600 mm/year).

    • Frequent cycles of freezing and thawing, causing melting of interstitial ice.

  • Current Distribution:

    • Approximately 20% of Earth's land surface experiences periglacial conditions.

    • Locations include Siberia, northern Scandinavia, Canada, and Alaska.

Past Distribution

  • During the Pleistocene, about 33% of the world was periglacial, extending to southern France, northern Italy, and the Balkans.

  • Southern Britain experienced periglacial conditions without ice coverage.

  • Currently, between 21% and 24% of Earth's surface has permafrost, predominantly in Canada and Alaska.

  • Notable that the area of permafrost is declining due to climate warming.

Factors Influencing Permafrost

  • Main factors affecting permafrost distribution include:

    • Climate: Determines presence, depth, and extent of permafrost.

    • Local Factors:

      • Proximity to water bodies contributes to depth of active layer.

      • Slope angle and orientation affect solar radiation exposure and melting.

      • Ground surface characteristics influence permafrost depth.

      • Vegetation cover insulates ground, affecting temperature extremes.

      • Snow cover can delay freezing and thawing processes.

Key Concepts

  • Permafrost: Soil and rock that remains frozen; classified into:

    • Continuous: Found in coldest regions (mean annual air temperatures below -6°C).

    • Discontinuous: Thinner and fragmented.

    • Sporadic: Occurs at periglacial margins, very fragmented.

  • Active Layer: Top layer of soil that melts in summer and freezes in winter.

Periglacial Landforms Formation Processes

  • Major Processes:

    • Frost Action: Leads to frost-shattering, forming block fields and screes.

    • Cracking of Freezing Soils: Ice wedges forming, and frost heaving creates patterned ground.

    • Migration of Water: Subsurface water moves to freezing front, forming segregated ice.

    • Mass Movement: Active layer moves downslope via solifluction.

Distinctive Landforms

  • Ice Wedge Polygons: Formed by frost cracking, resulting in irregular polygons typically on valley floors.

  • Patterned Ground: Includes circles, nets, polygons, formed by frost push and heave.

  • Pingos: Ice core mounds that can cause collapse once exposed and melt - classified into:

    • Open System: Grows from below in discontinuous permafrost.

    • Closed System: Forms in continuous permafrost due to overlying sediments.

Role of Frost and Weathering in Periglacial Environments

  • Frost Shattering: Increases rock fragmentation and formation of:

    • Block Fields: Angular, frost-shattered rocks.

    • Tors: Resistant rock areas on hills.

    • Scree/Talus Slopes: Fragments collecting at the base of cliffs.

    • Pro-talus Ramparts: Created at the base of snow patches from fallen rocks.

  • Mass Movement:

    • Frost Creep: Slow material movement downslope.

    • Solifluction: Downsloping movement of saturated soil during summer melt.

Effects of Nivation, Wind, and Meltwater

  • Nivation: Weathering and erosion around snow patches leading to nivation hollows.

  • Wind Action: Wind moves a lot of fine sediment, seen during Pleistocene and ongoing processes in desert areas.

  • Water Erosion: Seasonal erosion with short periods of high discharge follow spring thaw.

Relict Periglacial Features

  • Changes in climate can create distinctive relict landforms like thermokarst landscapes and other features attributed to former periglacial conditions. This highlights the geographic distribution and evidence of past glaciation.