glacial processes Flashcards
what is plucking?
the glacier freezes onto and into rock outcrops
as the ice moves away it pulls pieces of rock
this mainly occurs at the base of the glacier where jointed rocks have been weakened by freeze-thaw action
plucking leaves a jagged landscape
what is abrasion?
the material in the glacier is rubbing away at the valley sides and floor
scratches may be left known as striations
if the debris is very fine it is called rock flour
how does the presence of basal debris affect rates of glacial abrasion?
pure ice is unable to carry out abrasion of solid rock and so basal debris is an essential requirement
rate of abrasion increases to produce friction which slows down rate of movement
how does the debris size and shape affect rates of glacial abrasion?
particles embedded in the ice exert a downward pressure proportional to their weight
large debris more effective in abrasion
angular debris is more effective as pressure is more concentrated into one area
how does the relative hardness of particles and bedrock affect rates of glacial abrasion?
abrasion is most effective when hard resistant rock debris at the glacier is moved across a weak, soft bedrock
if bedrock is resistant there is little abrasion
how does the ice thickness affect rates of glacial abrasion?
the greater the thickness, the greater the pressure exerted on the basal debris and the greater rate of abrasion
beyond a certain thickness, the pressure becomes too great and there is too much t
friction
how does the basal water pressure affect rates of glacial abrasion?
the presence of a layer of meltwater at the base of the glacier is vital if sliding and therefore abrasion takes place
if the water is under pressure, perhaps because it is confined, the glacier can be buoyed up, reducing pressure and erosion
how does the sliding of basal ice affect rates of glacial abrasion?
determines if abrasion can take place
abrasion requires basal sliding to move the embedded debris across the rock surfaces
the greater the rate of sliding, the more potential there is to erode
how does the movement of debris to the base affect rates of glacial abrasion?
abrasion wears away both bedrock and basal sliding
debris needs to be replenished if the abrasion is to remain effective
how does the removal of fine debris affect rates of glacial abrasion?
to maintain high rates of abrasion, rock flour needs to be removed so that the larger particles can abrade the bedrock
this is mainly done by meltwater
what is nivation?
A complex process that is thought to include a combination of freeze-thaw action, solifluction, and chemical weathering
what is rockfall? (transportation)
weathered debris falls under gravity from exposed rock above the ice down onto the edge of the glacier
what is avalanches? (transportation)
these often contain rock debris within the snow and ice that moves under gravity
what is debris flow? (transportation)
in areas of high precipitation and occasional warmer periods, melting snow or ice can combine with scree, soil and mud
what is aeolian deposits (transportation)
fine material carried and deposited by wind, often blowing across outwash deposits
