Glacial Morraine

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Lateral Morraine - Description

  • With the eventual melting or retreat of glacier, such accumulations of moraine appear as hummocky, linear embankments running along the valley sides parallel to the ice movement.
  • They are unsorted, unstratified, angular material in clay
  • Examples:
    • Cwm Idwal in Wales
    • Tasman Glacier in New Zealand
    • Athabasca Glacier in Canada (1.24m high, 1.5km long).
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Lateral Morraine - Formation

  • Derived from loose weathered rock that moves down valley sides and is gradually fed onto the glacier below. The combination of this load supply and the movement of the glacier creates lines of debris that gradually become part of the moving body of ice.
  • When the ice has melted/retreated material falls onto the valley sides and floor. It may slump or erode after this.
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Medial Morraine - Description

  • Often made up of only one metre or so of coarse stony debris. The material is largely supraglacial and central and so rarely gives rise to landforms in post glacial times.
  • They are unsorted, unstratified, angular material in clay
  • They mark the confluence of two glaciers vallies and lie parallel to the direction of flow.
  • They are less defined towards the snout.
  • Generally between one and 30m high and one and 20km long. Between 50-100m wide.
  • Examples:
    • Kaskawesh in Yukon, USA. 1km wide moraine, narrowing to 60m.
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Medial Morraine - Formation

  • Formed when two glaciers meet.
  • The two lateral moraines that converge subsequently flow as one in the middle of the enlarged glacier (+explain lateral moraine formation).
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Terminal Morraine - Description

  • Mark the maximum advance of a glacier and the boundary between glacial and proglacial landscapes.
  • From a plan view, they are typically arc-shaped.
  • Consist of a ridge of material (or several mounds/hummocky hills) stretching across a valley.
  • Elongated at right angles to the direction of ice advance
  • Often steep-sided, particularly the ice contact side (20-30 degrees, distal slope is 10-20 degrees), and reach heights of 50-60 meters.
  • There is only one per glacier.
  • They are typically 30-60 meters high.
  • They are perpendicular to the valley floor and glacier direction. Sometimes it creates a dam creating a proglacial ribbon lake.
  • They are often crescent shaped, moulded to the form of the snout.
  • They are formed from unsorted, unstratified, angular material in clay.
  • Examples:
    • Cape Cod – North East USA.
    • Cromer Ridge, Norfolk – 8km wide, 9 meters high.
    • The Franz Loset glacier in NZ. Highest recorded at 430 meters.
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Terminal Morraine - Formation

  • When ice melts and the material it has been carrying is deposited. This is why they contain a range of unsorted material, from clay to large boulders.
  • Occurs when the glacier has a positive mass balance causing it to advance – boulder clay is pushed along the glacier snout and forms a pile.
  • The glacier retreats due to a now negative mass balance, leaving the pile of unsorted, unstratified and angular debris as a ridge.
  • The height is determined by how long the ice remains stationary at the maximum point.
  • It may be weathered by freeze thaw action or slump in post glacial times.
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Recessional Morraine - Description

  • Also forms parallel to the glacier snout (right angles to ice flow)
  • Proglacial areas may have more than one recessional moraine
  • They will be positioned between the snout and terminal moraine
  • Sediment it consists of tends to be unsorted, unstratified, angular and in clay
  • Smaller and less steep than terminal moraine as snout is less steep when retreating
  • Can be from 0.5-100km long, 20-500m wide and 3-50m high
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Recessional Morraine - Formation

  • As the glacier retreats, it is possible for a series of moraines to be formed along the valley, marking points where the retreat halted for some time – this is recessional moraine.
  • The halt is usually due to a climate change
  • (+formation exactly as terminal moraine above)
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