Glaciation-Topic 2
The formation Of Glacial Ice
Types of Ice (Stages)
Snowflakes- Snow falls which is made out of ice crystals and air (90% air)
Granular Snow-More snow falls and compacts onto the snow below forcing the air out (50% air)
Firn- the compacted granular snow that has not yet been compacted into glacial ice but is becoming more compressed (20-30% air)
Glacial Ice- Fully compacted by pressure and turns to glacial ice (only 10% air)
The compression to granular snow and the firn takes a very short time sometimes only days in areas of high precipitation but to turn into glacial ice from firn can take anywhere from 20 years to 150 years in the poles
Glacial Mass Balance
The relationship between the gains and losses off the ice store in the glacial system.
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 Movement
Glacial Proceses
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
Altitude - effects amount of precipitation and therefore energy
Slope/gradient
Glacial Size
Geology/ Litholophy
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
Movement Processes
Enhanced basal creep
Regelation Creep/slip
whereby basal ic deforms around irregularities on the underlying bedrock surface
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
Internal Deformation
Intergranular Flow
Laminar Flow
when individual ice crystals deform and move in relation to each other
When there is movement of individual layers within a glacier
Glacial Debris
types of debris
Supraglacial
Subglacial
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)
Debris transported beneath the glacier. Sources include deformed/eroded bedrock and englacial debris
Englacial: debris transported in a glacier