Glaicers

• Glaciers

  • In the recent past, glaciers have covered more than 1/3 of Earths surface. Currently they cover 10% of land mass
  • A glacier is a large perennial accumulation of ice, snow and sediment that originates on land and moves down slope
  • Outputs of glaciers = ablation, sublimation, ice calving
• Types of Glaciers


  • Ice sheets- large glaciers covering lass masses e.g. Greenland and Antarctica. If all the ice melted in these ice sheet, then sea level would rise by 66m
  • Ice shelves – Sheets of ice floating on water and attached to land. E.g., the ross ice shelf which contain enough water for 5m of sea level rise
  • Alpine glaciers – small glaciers occurring at high elevations
  • Different types of alpine glaciers:
  • Cirque glacier – found up high, bowl like depression
  • Valley glacier – extends down the mountains into a valley
  • Piedmont glacier – extends into a flatter area
• Glacier movement


  • Constrained by valley walls, and experience friction on all sides
  • Glaciers slid over valley beds by basal slip (meltwater at the base, warms up, melting ice allowing it to slid easier) and internal flow (deformation of ice crystals inside glacier – similar to creep)
  • Wet bottom glaciers - Water flows along base of the glacier, basal sliding, ice slips over meltwater slurry
  • Dry bottom glaciers - Cold base is frozen to substrate, movement is by internal plastic deformation of ice
• Glacial erosion

  • Incorporation- A process where rocks or sediments are incorporated into the glacier, such as plucking
  • Plucking- Refers to when a glacier loosens and lifts rock fragments off underlying bed rock and into the base of the glacier DRAW
  • Abrasion- The mechanical erosion of a bedrock surface by sediments incorporated into a glacier
  • Fracturing- Pressure from ice and abrasion can lead to high shear stress and cause fractures
  • Striating – Grinding and scratching of sediments trapped in ice onto a bedrock pavement
• Alpine Glacier- Erosional features

  o   U shaped valleys

  o   Cirque

  o   Arete

  o   Horn

  o   Hanging valley

  o   Truncated spurs

  o   Lower valleys experience a higher rate of erosion – drops off (see hanging valleys)

  o   Fjords - deeply eroded coastal glacial valleys, sea level rises to flood the valley

  • Contain sills at the front which are glacial sediments left behind
• Glacial sediments


  • Sediment is deposited as a result of glacial erosion
  • Position of sediment release could be subglacial, along margins or at the terminus
  •  Moraines- landforms from accumulation of till (lateral, medial, terminal)
  • Erratics
• Proglacial environments

  • Water drains from melting glaciers and forms river systems, usually braided with high sediment supply, rivers will join back up and deposit large amounts of sediments in an outwash plain
  • Over distances a transition is made to fluvial processes
• Paraglacial

  • Paraglacial refers to changes in sediment yield as a result of the presence, and retreat of glaciers and are on the rise
  • End moraines form at the terminus of the glacier, terminus glaciers form at the farthest edge of flow
  • Recessional moraines form as retreating ice stalls
  • Ground moraine – is till left behind by a rapidly retreating ice
  • Kettle holes and lakes form from dead ice
  •   Eskers- long, sinuous ridges of sand and gravel deposited by meltwater streams
• Consequences of glaciations

  • Re shaping of landscapes – paraglacial forms
  •   Sea level changes due to ice melt
  • Subsidence and isostatic rebound
  • Drainage – also mega flooding depending on melt rate
  • Ice sheets interact with atmospheric-ocean systems and change weather patterns depending on their melt