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SUMMARY:Pattern formation in permafrost - Dr Lucas Goehring\, BP Institute
DTSTART:20080424T103000Z
DTEND:20080424T113000Z
UID:TALK11512@talks.cam.ac.uk
CONTACT:Anne Alexander
DESCRIPTION:Polar regions of both the Earth and Mars are host to a surpris
 ing variety of surface patterns\, which form in soils which are permanentl
 y frozen (permafrost).  These patterns form\, in large part\, due to the c
 omplex interactions between soil\, ice\, and in some cases\, liquid water.
   This talk will focus on two such common geomorphologies: polygonal terra
 in\, and patterned ground. Polygonal terrain occurs in areas of ice-satura
 ted permafrost which see large temperature variations over the year.   The
  winter cooling creates a large strain in the ice component\, leading to f
 racture.  These cracks remain open for some time\, and snow and detritus c
 an fall into them.  In the summer\, when it warms\, the cracks heal\, but 
 there is a net addition of material.  Over thousands of annual cycles\, th
 e crack networks can thus grow and develop into beautiful regular polygons
 \, which cover vast areas of circumpolar terrain.  Patterned ground relies
 \, instead\, on instabilities that occur during the freezing of water-rich
  permafrost\, which leads to horizontal variations in ice content.  These 
 variations cause differential frost heave\, as areas that accumulate more 
 ice are forced to expand more to accommodate it.  When the ice melts\, the
  soils deflate\, but they do not return completely to their original state
 .  Over many cycles\, repeated heaving can churn up the active layer of pe
 rmafrost in a convection-like way.  This leads to landscapes covered with 
 gently undulating stripes\, as if from a giant's plough\, or sorted circle
 s of stones.  I will report on recent field observations\, from Antarctica
  and Greenland\, which attempt to study the rates at which these processes
  occur.  I will also discuss further plans for experiments to investigate 
 these intriguing pattern formation problems.  \n\n\n\n\n
LOCATION:Open Plan Area\, BP Institute\, Madingley Rise CB3 0EZ
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