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SUMMARY:Particle size segregation and spontaneous levee formation in geoph
 ysical mass flows - Nico Gray (Manchester)
DTSTART:20111104T160000Z
DTEND:20111104T170000Z
UID:TALK33044@talks.cam.ac.uk
CONTACT:Dr Ed Brambley
DESCRIPTION:Hazardous geophysical mass flows\, such as snow avalanches\, d
 ebris-flows and pyroclastic flows\, often spontaneously develop large part
 icle rich levees that channelize the flow and enhance their run-out. Measu
 rements of the surface velocity near an advancing flow front have been mad
 e at the United States Geological Survey (USGS) debris-flow flume\, where 
 10m$^3$ of water saturated sand and gravel are allowed to flow down an 80m
  chute onto a run-out pad. In the run-out phase the flow front is approxim
 ately invariant in shape and advances at almost constant speed. By trackin
 g the motion of surface tracers and using a simple kinematic model\, it wa
 s possible to infer bulk motion as incoming material is sheared towards th
 e front\, over-run and shouldered to the side. At the heart of the levee f
 ormation process is a subtle segregation-mobility feedback effect. Simple 
 models for particle segregation and the depth-averaged motion of granular 
 avalanches are described and one of the first attempts is made to couple t
 hese two types of models together. This process proves to be non-trivial\,
  yielding considerable complexity as well as pathologies that require addi
 tional physics to be included.\n
LOCATION:MR2\, Centre for Mathematical Sciences\, Wilberforce Road\, Cambr
 idge
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