Cold environments

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  • Created on: 10-01-13 09:19

Fluvioglacial processes

Deposition
Melting ice produces melt water with a clarge capacity for carrying debris. water under pressure has high velocity and is extremely tubulent allowing of transportation of larger material. creating deep subglacial valleys filled with potholes.
Material sorted as velocity decreases and load is deposited. Can also be stratified as a result of seasonal variations in flow.
Features of FLuvioglacial deposition:
Eskers -
  long ridges of material formed in direction of ice advance.
              winding (sinuous) form, 5-20m high
              consist of sorted coarse material e.g coarse sands and gravel
              often stratisfied (layered)
deposits made by subglacial streams. cosinderable hydrostatic pressure allows for large load and short uphill distances.
Kames: mounds of  fluvioglacial material deposited at the front (snout) of a stationary/melting glacier and then often collapses when glacier retreats.
Kame terraces: similar to kames but form on along the sides of the glacier, deposits of melt water streams flowing between the ice and valley side.

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Fluvioglacial processes

Outwash plains: foudn at glacier's snout, created by sorted material deposited by mealtwater streams, coarsest material closest to glacier, finer material (e.g clay) carried some distance before being deposited also layered vertically due to seasons.
meltwater streams crossing plain are braided, channel choked with coarse material marked by seasonal variations in discharge.
Kettle holes: form on outwash plain, small depressions filled iwth lakes or marshes, formed from blocks of ic washing onto plain and metling forming small lakes. overtime can form peat.
Varves:  lakes on fringe of ice, layers of seasonal deposition, one layer is known as a varve. coarser, light-coloured layer is spring and summer deposition when mealtwater at peak (larger layer) thinner darker and finer silt settles during autumn and winter as discharge decreases. varves indicate age of lake and past climate conditions.

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Proglacial processes

Periglacial areas - areas not actually glaciated but exposed to very cold conitions and intense frost action developing permanently frozen ground (permafrost) e.g tundra in northern canada and high mountain areas e.g the alps.

Permafrost:  subsoil temperatures remain beloq zeo for at least 2 consecutive years. currently covers a quarter of the earth's surface. Summer temperatures thaw surface layer downwards called the active layer  thinkness dependent on local conditions but up to 4m.
Continuous permafrost: found in coldest regions (e.g Siberia) , deep surface layers permafrost can be as deep as 1,500m, in summer months barely any melting.
Discontinuous permafrost: regions slightly warmer, ground not frozen to as great a depth around 20-30m below surface max 45m. also gaps in permafrost under rivers, lakes, sea.
Sporadic permafrost: Where annual temperatures are around freezing point. permafrost occurs in isolated spots, local climate prevents thawing of soil during the summer.

Solifluction: active layer thaws in summer, friction reduced through lubrication between soil, gentle 2 degree slopes enough for soil movement downhill creating sheets or lobes tounge-like features forming on terraces at side of valley.

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Proglacial processes

Freeze-thaw action (frost shattering)
Temperatures rise during day and drop below freezing at night during winter, water enters cracks in rocks and freezes overnight, overtime crack widens as ice expands due to pressure, crack widens and eventually pieces begin to break off. creating material at the base known as scree.

Nivation: occurs beneth hallows filled with snow. particually north and east facing slopes (prevailing winds) freeze-thaw and chemical weathering operate under snow disintergrating underlying rock, weathered particles moved downslope and over time nivation hollows are formed which forms the beggining of a Corrie.

Frost heave: action of stones and other material rising from the ground, due to soil around and under the stone freezing faster than surronding area due to stone's heat capacity. can create patterned ground and on gentler slopes can form stone polygons but on steeper slopes (exceeding 6 degrees) stones move downhill to fomr stone stripes.

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Proglacial processes

Groundwater freezing
where permafrost is thin or discontinuous, water seeos into upper layers and freezes, expansion causes overlaying sediments to ehave upwards into a dome shaped feature. rising as high as 50m. named open sysem or east greenland type.
low lying areas with continuous permafrost: small lakes and groundwater trapped by freezing, pushing up overlayingg sediments into a closed syem pingo or Mackenzie type. e.g Mackenzie delta in northern Canada.

Ice wedges: refreezing of active layer cause soil to contract. cracks open in surface, and are filled in summer process repeats widening and deepening to form an ice wedge which can beomce 1m wude and 2-3m deep can produce ice-wedge polygons

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Ice formation and movement.

Compressing flow: reduction in gradient of valley floor leading to ice deceleration and thickening of the ice mass. ice erosion is at its maximum
Extending flow: valley gradient becomes steeper. ice accelerates and becomes thinner, leading to reduced erosion.
Basal flow (sliding/slippage): friction occurs as glacier moves over bedrock, lower ice under pressure creting meltwater which acts as lubricant, enabling ice to flow more rapidly.
Syrges: exessive build up of meltwater under glacier creating rapid ice movement, up to 250-300 m in one day. repreent hazard to people living below snout.
Internal flow: ice crystals orientate themselves in direction of glacier movement and slide past each other. surface ice moves faster, crevasses develop, internal flow is main feature of the flow of polar glaciers, no meltwater means they're frozen to their beds.
Creep: stress builds up within glacier, ice behaves with pasticity and flow, occurs when obsticles are met.
Rotational flow: occurs within the corrie, ice movign downhill pivots around a point, producing rotational movement. this and increased pressure within rock hollow leads to greater erosion and over-deepening of the corrie floor.

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Glacial erosion + Corrie landforms

Abrasion: material glacier is carrying rubs away at valley floor and sides like sandpaper.
Coarser material leaves scratches on rock called striations, debris involved with abraison worn down by proccess into fine material called rock flour.
Plucking:
glacier freezing onto rock outcrops then pulling away from mas of rock taking fragments with it. Found at base of glacier, pressure and friction result in melting of ice also in well joined rocks and where freeze that has occured leaving a jagged landscape.

Corries: armchair saped rock hollow with steep back wall and over deepened basin with a rock lip. containing small lake (tarn). mainly found on north east facing slopes, reduced insolation allows more snow accumulation. Origionally due to Nivation.
Aretes: when two corries develop in an area back to back, eg Striding Edge - Helvellyn creating a narrow, steep-sided ridge between the hollows.
Pyramidal peak:  when three or more corries develop back to back, often with very sharp appearence due to frost shattering.

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Glacial troughs and associated landforms.

Glacial trough: glaciers flow in pre existing valleys, combination of large amout of meltwater and subglacial debris means more erosion power, so straightens valley and turns it fromV-shaped to U-shaped valleys. e.g Great Langdale Valley
Hanging valleys: smaller tributary glacier meets the main, triutary has less erosion power thus is higher up than main valley. (e.g Valley of Church Beck Lake district)
Trucated spurs: interlocking spers formed by rivers turned into trucated spurs by erosion.
Roches moutonnees:  rocks effected by glaciation leaving an upstream side polished by abraison and downstream side made jagged by plucking.
Subglacial: under the glacier
Englacial: middle of ice
supraglacial: top of ice

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