Physical Geography

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Cirques/Corries

Formaton:

  • Snow falls and collects in a hollow high up on the mountainside
  • Freeze thaw weathering around the hollow causes the surrounding rock to disintegrate
  • The debris is washed away when snow melts and the hollow becomes bigger
  • As more snow falls and collects in the hollow it is compressed and becomes glacial ice
  • Erosion and weathering by abrasion, plucking and freeze-thaw action makes the hollow bigger
  • Gravity causes ice to move in a rotational direction, this is known as rotational slip and this causes ice to pulll away from the backwall
  • Plucked debris from backwall causes further erosion through abrasion 
  • The debris is deposisted at the lip
  • These processes create a rounded armchair shape with a steep backwall
  • A circular lake known as a tarn forms in the hollow
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Ice Movement

Regelation Slip:

  • Works best over smaller objects
  • On the upglacier side of anobstacle increased pressure causes the basal ice to melt locally
  • Meltwater allows ice to slip over an obstacle
  • The water then refreezes due to reduced pressure
  • This is called the relegation layer

Compressional Flow:

  • This is when the velocity increases and glacier increses in density
  • Below the ELA (Equilibrium Line Accumilation) ice from the upper valley pushes against the down valley
  • This happens where slope gradient 
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Ice Movement 2

Creep – occurs when ice meets an obstacle and leads to pressure melting on upstream side which aids flow. Meltwater refreezes on downstream side.

Extending-compressing flow – where the gradient is steep, the glacier moves faster and thins (extending flow) leading to reduced erosion but where the gradient is gentle, the glacier moves slowly and thickens (compressing flow) leading to increased erosive power.

Surges – glacier moves forward very rapidly (maybe 300 metres in a day) due to the build up of sub-glacial meltwater or perhaps large rock avalanches near the source. Surges may happen every 50 – 100 years.

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Glacial Trough/U-Shaped Valley

Description:

  • A glaciated valley often characterised by steep sides and a flat bottom, resulting primarily form erosion by strongly channelled ice.
  • E.g. Valley of Lauterbrunnen, Switzerland

Formation:

  • Ice occupies a former river valley
  • The ice removes the interlocking spurs
  • This is through the processes of abrasion and plucking at the base especially and 'bulldozing' as material is pushed out the way
  • Thus, the valley is widened and deepened
  • Presense of extentional and compressional flow leads to varieies of depth
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Drumlims

Descrpition:

  • Astmmetrical elongated mounds of glacial deposits
  • Basket of Eggs topography
  • Longer than wide
  • Long axis parrallel to ice movement
  • Steeper stoss side
  • Gentler lee side
  • 50-60 metres high
  • 25-600 metres wide

Formation:

  • The most widly accepted view is that drumlins were formed when ice became overloaded with material, reducing its capacity
  • The reduced capacity may be due to the melting of ice or reduction in velocity
  • Once the material has been deposited it is mouled and streamlined by later ice movement
  • This is similar to a rouche mountonee without a plucked face
  • OR [Evans] = Subglacial deformed masses of pre-existing sediment to which more sediment is added
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Kames

Description:

  • Mounds of fluvioglacial sediment
  • Rounded mounds/hills
  • Undulating mounds of ill-sorted material that collapses as ice melts
  • Width - 50m Height 3m - 5m

Formation:

  • Hollows on the surface of a melting glacier would fill up with sediment and then gradually go down to lower levels as the ice melts
  • This forms a mound on the ground surface
  • These collapse when the ice melts
  • Kame terrances are formed when a gap between the valley side and the ice margin is filled with glaciofluvial deposits, leaving behind a terrance when the ice melts
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Kettle Holes

Description:

  • Diameter - 5m to 100m
  • Depth - 1m to 5m

Formation:

  • Formed when a glacier is melting and a piece of ice is isolated from the rest of the glacier
  • It is buried by outwash debris
  • It subsequently melts and the resulting subsidence causes a small hollow in the outwash plain
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Eskers

Description/Formation

  • Winding/sinvous ridges of often course sands and gravels that are deposited by meltwater as it flows in channels beneath
  • These channels are called Subglacial meltwater channels
  • Three types - Sharp crested, multiple crested, broad crested
  • Material is carried in these steams
  • As the energy of the stream decreases material is deposited
  • Large particles are deposited first until all material is deposited
  • When the glacier melts the esker is exposed

E.g. Kemb Hills, Scotland

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Meltwater Channels

ONLY EROSIONAL LANDFORM

Formation:

  • Form as a result of the original course followed by a river before glaciation may be blocked by ice or as an overflow from a proglacial lake
  • Large amounts of meltwater had a lot of energy to erode and carve out deep gorges, that today are occupied by streams too small to have created valleys
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Braided Streams/Eyots

What are they?

  • Seasonal variation in meltwater discharge lead to fluctuations in the sediment load
  • Excess material is deposited during times of lower discharge and many obstruct flow leading to braiding

E.g. River Eyra, Iceland

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