Fluvio-glacial and periglacial landforms

• Fluvio-glacial landforms

  • Produced by meltwater from glaciers
  • Meltwater is released from glaciers during short, seasonal periods of melting but mostly during deglaciation
• What is a kame?

  An accumulation of partially sorted material found at the front of a melting glacier
• Two types of Kames

  • Delta kames -> During glaciation: A hill or hummock composed of stratified sand deposited by glacial meltwater
  • Kame terraces -> After glaciation: Ridges of material running along the edge of the valley floor - similar to a lateral moraine but composed of rounded outwash deposits instead of angular sediment
• How are delta kames formed

  In one of three ways:

  • Englacial streams emerge at the snout and lose energy, depositing their sediment load
  • Supraglacial streams deposit material when entering ice marginal lakes. This is because it loses energy as it enter a static body of water
  • Debris filled crevasses collapse during periods of glacial retreat depositing the debris
• How are kame terraces formed?

  • Supraglacial streams form on the edge of the glacier as ice melts when in contact with the valley sides due to friction
  • These streams on the edge of the glacier pick up and carry lateral moraine which is deposited on the valley floor when the glacier retreats
• Stratified

  Sediment arranged into clear and distinct layers
• Fluvio-glacial landforms

  Kames

  Eskers

  Outwash planes
• What is an esker?

  A long, sinous (curving) ridge of stratified sediment deposited by glacial meltwater
• Delta Kames


  Formed during glaciation
• Terraced Kames


  Formed after glaciation
• How is an esker formed?

  • Subglacial streams carry huge amounts of debris under pressure in confined tunnels
  • As meltwater emerges at the snout, deposition occurs when the pressure is released
  • As the snout retreats due to deglaciation, the point of deposition gradually moves backwards up the valley
  • Some eskers are beaded: the ridge shows variations in height and width, with the tallest and widest parts due to periods when the rate of retreat slowed
• Esker during glaciation

  A sub glacial stream with sediment
• Esker after glaciation


  A ridge of deposited sediment which indicates the position of the sub glacial sediment
• What are outwash plains?

  • A flat expanse of fluvio-glacial sediment in the proglacial area - the area in front of the snout of the glacier
  • Typically drained by braided streams - rivers divided by numerous small islands and channels
• How do outwash plains form?

  • Meltwater streams gradually lose energy as they enter lowland areas beyond the ice front and they deposit their load
  • The largest material is deposited nearest the ice front and the finest material is deposited furthest away
• Periglacial

  Places near or on the edge of ice sheets: Areas with...

  • Permafrost: land that has been frozen solid for 12 months of more overlain by an active layer
  • Seasonal temperature variation
  • Freeze-thaw cycles which dominate geomorphic processes

  Periglacial landscapes are found in high latitude areas eg. Alaska

  They cover 25% of the earths surface
• periglacial landforms

  Patterned ground

  Pingos

  Ognips
• Permafrost environments

  • Characterised by a lack of precipitation and extremely low temperatures
  • Cold and dry climate > no accumulation
  • Generally too arid to support glacial conditions
• Continuous permafrost

  When summers are too cold so there is only a very superficial melting of the ground. Mean annual temperature below -5° all year
• Discontinuous permafrost

  Found in slightly warmer areas so there are islands of permanently frozen ground separated by small pockets of unfrozen less cold areas. Mean annual temperature between -1° and -5°
• Sporadic Permafrost

  Found when mean annual temperature is just below 0° and summer temperature several degrees above, but there are isolated pockets of permanently frozen ground
• What is patterned ground?

  A collective term for a number of fairly small scale features of a periglacial landscape including stone polygons, stone garlands and stones stripes
• What are stone polygons?

  Circle of stones surrounding a small dome-shaped area of ground 1-2m in diameter
• What is a stone garland?

  Found on slopes of 3-50 degrees - more elongated oval shaped formation
• What is a stone stripe?

  Found on slopes steeper than 60 degrees where the polygons lose their shape, leaving a line or stripe of stones
• How does patterned ground form?

  The process of frost heave occurs in the active layer

  • Stones underground cool down faster than the surrounding soil - they have a lower heat capacity
  • As temperatures fall, water beneath the stones freeze and expands by 10% > lifts the stones upwards in the soil
  • Repeated frost heave cycles pushes the stones upwards
  • Eventually the stones reach the surface which is domed due to the soil that has been pushed up above the stones
  • The stones move down the dome by gravity > forms a stone polygon - depending on the steepness of the slope is what pattern is formed
• Active layer

  The melted surface layer above permafrost that forms in summer
• What is a pingo

  A rounded ice-cored hill that can be as much as 90m high and 800m in diameter. There are two types: open system and closed system
• How do open-system pingoform?

  Water is supplied from elsewhere

  • These form in the bottom of valleys where water from the surrounding slopes collects due to gravity
  • This water freezes and expands by 10% which forces the overlying surface material up into a dome shape
• How do closed system pingosform?

  Water is already in there eg. a lake

  • These develop beneath lake beds when the supply of water is from the immediate local area
  • Permafrost grows during cold periods, trapping groundwater beneath the lake ( talik ) between the frozen lake above and permafrost below
  • This talik eventually freezes forcing up the overlying sediment into a dome shape
• Talik

  Unfrozen ground within permafrost
• What is an ognip?

  The remnants of a pingo: A rampart surrounding a circular depression
• How does an ognip form?

  Ognips form when pingos collapse. This happens when temperatures rise and the ice core thaws.

  Therefore a rising climate leads to the formation of ognips