basal sliding and internal deformation Flashcards
what do warm based glaciers mainly move by
basal sliding
when will basal sliding occur
when basal temperatures are at or above the pressure melting point, generating a thin layer of meltwater between the glacier and the valley
what three mechanisms does basal sliding consist of
creep, slippage, or bed deformation
what is slippage
when the ice glides over the valley floor due to meltwater reducing friction
what is creep
when ice deforms, in a rather similar way to how plastic would, under increased pressure from an obstruction on the valley floor
what is bed deformation
when ice is carried by saturated sediments on the valley floor over a gentle gradient
what is an example of a glacier that moves frequently
the Franz Josef glacier in New Zealand moves around 300m per year
why do cold based glaciers never move by basal sliding
cold based glaciers never move by basal sliding because the basal temperature is always below pressure melting point
how does ice in a warm based glacier deform compared to ice in a cold based glacier
ice at 0 degrees deforms 100x faster than ice at -20 degrees
how do cold based glaciers move
internal deformation
what are the two aspects of internal deformation
intergranular flow
laminar flow
what is intergranular flow
when individual ice crystals move and reorientate around eachother
what is laminar flow
the movement of layers within an ice sheet- often layers of annual accumulation
what is fundamentally required for internal deformation
a gradient- internal deformation can only take place where there is at least some slope
give an example of an ice sheet that moves by internal deformation and how much does this move by every year
the merserve glacier in antarctica only moves by 3-4 m every year and this is entirely by internal deformation
