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SUMMARY:The pressure melting point of ice and Jakobshavn's fast flow - Dr 
 Mauro Werder (University of Bristol)
DTSTART:20140424T130000Z
DTEND:20140424T140000Z
UID:TALK51471@talks.cam.ac.uk
CONTACT:Rosie Williams
DESCRIPTION:Jakobshavn Isbrae and many other outlet glaciers of present an
 d past ice sheets lie in deep troughs which often have several overdeepene
 d sections.  The subglacial drainage system of such glaciers is heavily in
 fluenced by two effects caused by the pressure dependence of the melting p
 oint of water.  The melting point decreases with increasing water pressure
 \, this enhances wall-melt in downward sloping channels and diminishes wal
 l-melt in upward sloping channels.  Thus the first effect is the well know
 n shutdown of channels on steep adverse bed slopes of overdeepenings and t
 he associated high water pressure/low effective pressure.  The second effe
 ct is a 2D effect and has not received much/any attention so far: the orie
 ntation of a channel will be deflected from the direction of the (negative
 ) hydraulic potential gradient (which drives the water flow) towards the s
 teepest slope of the bed.  This leads to the enhanced formation of side ch
 annels dipping into the trough at about a 45° angle.  This efficient conn
 ection between the margin and the trough equalizes the hydraulic potential
  and increases the water pressure in the trough even further.\n\nI investi
 gate these two effects with the 2D subglacial drainage system model GlaDS 
 using Jakobshavn Isbrae as an example.  I compare model runs with the pres
 sure melt term disabled and enabled.  With the term disabled the main chan
 nel situated in the trough is continuous and produces a large depression i
 n the hydraulic potential and consequently high effective pressure in the 
 trough (1-2MPa). Conversely\, with the term enabled the main channel becom
 es discontinuous on steep adverse bed slopes and many side channels form o
 n the margins of the trough.  This leads to a hydraulic potential in the t
 rough which is higher than in the surrounding area and consequently the ef
 fective pressure is low (0-1MPa).\n\nLow effective pressure leads to reduc
 ed basal drag and thus to more basal sliding.  This work suggests that the
  pressure dependence of the melting point of water may be one of the leadi
 ng causes for the fast flow of Jakobshavn Isbrae and other glaciers in dee
 p troughs.\n
LOCATION:British Antarctic Survey
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