Topic 2 - Glaciation EQ2 Flashcards
What are glaciers, what type of system are they?
persistent body of dense ice that is constantly moving under its own weight
- are open systems with inputs and outputs
Outline and explain the inputs of glaciers?
- precipitation in the form of snowfall is the man input, it is increasing compacted over many years forming high-density clear glacial ice
- avalanches from steep mountain sides (specifically with poleward aspect)
- wind deposition - strong winds at high altitudes blow snow onto accumulation zone
Outline and explain the stores within glaciers?
Main stores are snow and ice, which vary seasonally specifically in more temperate regions (where there can be significant winter snowfall and summer melting)
Outline and explain the flows/transfers within glaciers?
processes such as evaporation, sublimation, meltwater flow and glacial movement
- more pronounced and active in warmer environments
Outline and explain the types of feedback loops?
Positive feedback loops - enhance and speed up processes, promoting rapid change
Negative feedback loops - regulate systems to establish balance and equilibrium
Explain the dynamic equilibrium of glaciers?
Equilibrium line marks the boundary between accumulation zone and the ablation zone - will remain in place if inputs equal outputs
- equilibrium line moves up or down the glacier when balance shifts
Outline and explain the ouputs of glaciers?
- main output is meltwater, result of melting close to glaciers snout (where temps are highest)
- calving - when ice extends over water, it causes huge chunks of ice to break off
- processes of evaporation and sublimation
Outline and explain glacial mass balance?
Wether a glacier is growing or shrinking depends on the balance between accumulation and ablation - changes yearly
- ablation is greatest in summer and accumulation is greatest during winter
Explain the accumulation zone of glaciers?
where there is a net gain of ice over the course of a year (inputs exceed outputs)
- if accumulation exceeds ablation it leads to positive mass balance, the glacier advances
Explain the ablation zone of glaciers?
where there is a net loss of ice over the course of a year (outputs exceed inputs)
- if ablation exceeds accuulation it leads to negative mass balance, the glacier retreats (and potentially dies)
Explain how the climate affects how a glacier works and the landforms it creates?
- cooler climate results in thicker ice which moves faster and advances - erodes and transports more vigorously
- warmer period causes glacier to shrink so the ice becomes thinner and retreats - less erosion and transport of debris (deposits more)
Outline and explain how a positive feedback loop can enhance accumulation?
gain of ice increases surface albedo further lowering temperatures and leading to more snowfall - glacial mass increases
Outline how glaciers move?
Their movement is dependent on the temperature of the ice (determines wether PMP is reached) if meltwater is present then they will move by processes called basal slip - otherwise by internal deformation
Explain how temperate glaciers can move?
By basal slip - Melting point at surface of the glacier is 0 degrees, but due to pressure of overlying ice it is lowered - temperate glaciers meet PMP so meltwater produced which lubricates bedrock and glacial base, increasing rate of movement
- can also move by internal deformation
Explain how polar glaciers can move?
PMP is not met due to temperatures being too cold - glaciers are frozen to the bedrock which prevents movement through processes like basal slip
- move instead by internal deformation
Explain the process of basal slip?
Occurs when the base of the glacier is at the PMP, means that meltwater is present and lubricates the base - enables the glacier to slide rapidly over bedrock
- can be subdivided into other processes (eg surges, creep and regelation)
Explain how the process of creep and regelation enhances basal slip?
Basal slip is enhanced by obstacles on the valley floor, large obstacles (over 1m) causes increase in pressure - so ice plastically deforms around the feature (creep), small obstacles cause PMP to be met - enhances basal slip
- ice refreezes on downward (lee) side of obstacles - process known as regelation
Explain how the process of extending and compressing flow enhances basal slip?
Over steep slopes, rate of basal slip increases and the ice accelerates and thins (extending flow) over shallower slopes basal slip slows and the ice decelerates and thickens (compressing flow)
Explain how the process of surges enhances basal slip?
- various causes for example earthquakes
- most common is enhanced basal slip triggered by the build up of meltwater at the ice-rock interface
Explain how polar glaciers move?
Internal deformation - occurs when the weight of glacier ice and gravity causes ice crystals to deform - glacier moves downslope very slowly
Explain the effects of different sized obstacles in creep and regelation?
- Obstacles larger than 1m causes an increase in pressure, which make the ice plastically deform around the creep
- obstacles smaller than 1m cause pressure-melting which increases ice movement by basal slip
Explain how internal deformation occurs in depth - give both types of movements?
- Inter-granular movements, where individual ice crystals slip and slide over each other
- intra-granular movements, where individual ice crystals become deformed or fractured (due to stresses within ice) - mass of ice deforms and moves downhill
Explain subglacial bed deformation?
Occurs locally when a glacier moves over relatively weak or unsolidated rock - sediment can deform under weight of glacier, moving the ice on top along with it
Outline 4 factors which affect the rate of glacial movement?
- altitude
- gradient of slop
- presence of meltwater
- ice thickness
