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Glaciated landscapes 6 (kettle holes (which may contain lakes can form on…
Glaciated landscapes 6
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proglacial streams
transport a lot of sediment, but their high variable discharge means that sediment can be deposited within the channel resulting in braided streams
in summer the streams have a high discharge and are debris laden, but in winter the discharge is lower. meaning sediment is deposited in the channel to form channel bars breaking the flow of the stream
kettle holes
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the dead ice becomes buried by outwash material. once the dead ice has finally melted the overlying sediment forms a depression - filled with a lake
pro-glacial lakes my form at the ice front from melt water damned by end moraine if the lakes overflow the moraine flooding occurs
eskers
result from the deposition of material carried by subglacial and englacial meltwater streams during the glacial period
the streams are sediment laden due to flowing under hydrostatic pressure. the subglacial, englacial streams flow within tunnels
deposition occurs when pressure is released as meltwater emerges at the glacier snout. as the glacier snout retreat, the point of deposition gradually moves backwards to leave an exposed sinuous ridge of material on the valley floor where the meltwater steam was previously
some eskers are beaded with beads of greater size most likely to occur when the rate of retreat slowed
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nivation - term which covers a collection of geomorphic processes which can occur under a permanent show patch high up in the mountains
enlargement of hollow by freeze-thaw and carbonation. debris is transported by running meltwater at the base
there is N/E facing hollow debris collects at the front of hollow can form a protalus rampart ( a depositional land-form of periglacial origin)
ice needles
in the summer water percolate into the ground. in the winter the ground nearest to the surface freezes to form ice lenses between the layers of soil or ice needles
the ice lenses or needles draw in water from the surrounding sediment by capillary action. frost heave causes an increase in soil volume, and so there is an upward expansion of the soil surface
this causes a domed surface, frost heave is most significant in fine grained material which is sufficiently porous to allow capillary actions and the growth of ice lenses
stone polygons - ice beneath rocks expands due to capillary action, (stones low specific heat capacity means they cool faster) when thawing occurs sediment fills and eventually stones will rise to the surface. once they reach the surface they will roll outward due to the uneven terrain
pingo formation
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groundwater rises to the surface under artesian pressure, ice lens forms and the ice freezes + expands push terrain upwards
the ice lens is rising due to meltwater rises + displaces sand sediments if exposedby the sun ice lens will melt and pingo will collapse. this depression can be filled by meltwater forming an ognip