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SUMMARY:The pressure melting point of ice and Jakobshavn Isbrae's fast flo
 w - Dr Mauro Werder\, University of Bristol
DTSTART:20140423T153000Z
DTEND:20140423T163000Z
UID:TALK52214@talks.cam.ac.uk
CONTACT:Neil Arnold
DESCRIPTION:Jakobshavn Isbrae and many other outlet glaciers of present an
 d past ice sheets lie in deep troughs which often have several over deepen
 ed sections.  The subglacial drainage system of such glaciers is heavily i
 nfluenced by two effects caused by the pressure dependence of the melting 
 point of water.  The melting point decreases with increasing water pressur
 e\, this enhances wall-melt in downward sloping channels and diminishes wa
 ll-melt in upward sloping channels.  Thus the first effect is the well kno
 wn shutdown of channels on steep adverse bed slopes of overdeepenings and 
 the associated high water pressure/low effective pressure.  The second eff
 ect is a 2D effect and has not received much/any attention so far: the ori
 entation of a channel will be deflected from the direction of the (negativ
 e) hydraulic potential gradient (which drives the water flow) towards the 
 steepest slope of the bed.  This leads to the enhanced formation of side c
 hannels dipping into the trough at about a 45° angle.  This efficient con
 nection between the\nmargin and the trough equalizes the hydraulic potenti
 al and increases  the water pressure in the trough even further.\n\nI inve
 stigate these two effects with the 2D subglacial drainage system model Gla
 DS using Jakobshavn Isbrae as an example.  I compare model runs with the p
 ressure melt term disabled and enabled.  With the term disabled the main c
 hannel situated in the trough is continuous and produces a large depressio
 n in the hydraulic potential and consequently high effective pressure in t
 he trough (1-2MPa). Conversely\, with the term enabled the main channel be
 comes discontinuous on steep adverse bed slopes and many side channels for
 m on the margins of the trough.  This\nleads to a hydraulic potential in t
 he trough which is higher than in the surrounding area and consequently th
 e effective pressure is low\n(0-1MPa).\n\nLow effective pressure leads to 
 reduced basal drag and thus to more\nbasal sliding.  This work suggests th
 at the pressure dependence of the melting point of water may be one of the
  leading causes for the fast flow of Jakobshavn Isbrae and other glaciers 
 in deep troughs.
LOCATION:Scott Polar Research Institute\, main lecture theatre
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