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SUMMARY:Wetting in Granular Flows: Debris Flows &amp\; Ice Avalanches - Dr
  Barbara Turnbull\, University of Nottingham
DTSTART:20130614T120000Z
DTEND:20130614T131500Z
UID:TALK45284@talks.cam.ac.uk
CONTACT:Dr Henry Burridge
DESCRIPTION:There are many cases of geophysical granular flows where fluid
  mediates the grain contacts: here we focus on two of them ranging from fl
 uid volume fractions of hundredths of a percent to 60%.\n\nFirstly we focu
 s upon the hazard posed by avalanches of rock & ice. These can arise from 
 collapsing glacier séracs\, rock-faces previously stabilised by permafros
 t or the activity of an ice-capped volcano. The extraordinary mobility of 
 the extreme event at Karmadon\, Russian Caucasus\, in September 2002 broug
 ht such ice-bearing flows into sharp focus. Here\, we explore the hypothes
 is that localised melting within such ice-bearing flows may significantly 
 alter the dynamic characteristics compared to a classical dry granular she
 ar flow. Building sandcastles on the beach as children\, we relied on the 
 mechanical strength of moisture coating the sand grains to hold our struct
 ures together. Furthermore\, when we ice skate it is in fact a microscopic
  ‘pre-melted’ water film between blade and ice that allows us to glide
  over the surface. So\, when considering the granular mechanics of ice\, c
 an we expect these two phe- nomena to interact? The dynamical effects of m
 elting processes that lead to wetted particle surfaces are here investigat
 ed in a laboratory experiment.\n\nIn contrast\, when we move to higher flu
 id volume fractions\, the flow separates into dry and wet regimes. This ca
 n be seen in debris flows of water\, sediments and rocks and volcanic laha
 rs. In these flows dry rocks collect the front of the flow forming a dry s
 nout that is pushed along by the viscoplastic water/fines mixture in the f
 low’s body. Despite the largest\, most energetic rocks and boulders typi
 cally forming part of the granular snout\, debris flow modelling has been 
 largely focussed on the viscoplastic behaviour in the body\, with relative
 ly little consideration given to the sometimes extreme deviations in predi
 cted impact pressures. Here we discuss a method for characterising these d
 ifferent flow regimes using data from laboratory-scale chute flows of glas
 s bead\, water and glycerol mixtures.
LOCATION:LR3B\, Inglis Building
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