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Glaciation-Topic 2 (Glacial Mass Balance (The relationship between the…
Glaciation-Topic 2
Glacial Mass Balance
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Accumulation (inputs)- comes in the form of precipitation, rockfalls, avalanches and blown snow.
Ablation (Outputs)- comes in the form of iceberg calving, meltwater and sediment and evaporation
The mass balance is the nett difference been the accumulation and ablation.The point where these are equal is known as the equilibrium point . An area of accumulation occurs at the top of the glacier in areas above the equilibrium line ( a positive mass balance). Areas below the equilibrium line are areas of ablation( a negative mass balance)
If the total glacier has a negative mass balance the a glacier will shrink while if a glacier has a positive mass balance it will be expanding. As a glacier expands or shrinks the equilibrium line will constantly change position moving up or down the glacier.
Glacial Proceses
Abrasion- individual class (stones) submerged in the glacier rub against the bedrock creating marks and etchings
Plucking- the removal of fractured bed rock when ice moves over and the rock freezes to the bottom of the glacier being ripped from the bedrock.
Fracture and traction- the crushing effect of the weight of the ice causes the bedrock to deform and fracture under the immense pressure
Meltwater Erosion- either via means of physical eruption or via the chemical process due to carrying of acidic sediments causing chemical erosion
Glacial Movement
Basics
Snow fall in the accumulation zone makes the glacier deeper near the top of the glacier and the extra wight at the top causes the ice to be pulled down and along towards the zone of ablation
The fundamental cause of ice movement in a glacier is due to gravity. The wight of the ice is forced down hill by gravity with the ice having huge amounts of potential energy especially at higher altitudes. This energy and gravity then cause a glacier to move
Velocity Of a Glacier
warm based glaciers move far faster than cold based glaciers as the meltwater acts as a lubricant and reduces the friction (basal sliding)to the surface while in a cold based glaciers the ice is frozen to the ground and therefore there is much more resistance
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Movement Processes
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Regelation Creep/slip
occurs when basal ice deforms under pressure where encountering obstructions such as rock steps, the high pressure melts the ice which when flows over obstacle refreezes in the power pressure
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Glacial Debris
types of debris
Supraglacial
Debris transported on the glaciers surface. Sources include falling ,material from valley sides and atmospheric fall out such as volcanic ash (commodity feature in iceland)
Subglacial
Debris transported beneath the glacier. Sources include deformed/eroded bedrock and englacial debris
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