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SUMMARY:Experimental modelling of the Fluid Dynamics of Magma Chambers / B
 uoyancy induced Taylor dispersion - Andrew Gilbert\, BP Institute / Tiras 
 Lin\, BP Institute
DTSTART:20140619T103000Z
DTEND:20140619T113000Z
UID:TALK52904@talks.cam.ac.uk
CONTACT:Catherine Pearson
DESCRIPTION:Experimental modelling of the Fluid Dynamics of Magma Chambers
  \n\nDetermining whether magma chambers convect is of importance for volca
 nologists and geologists alike. The reason why some solidify to form pluto
 ns and others erupt is still uncertain. This study has done mathematical a
 nd experimental modeling of a simple analogue basaltic magma chamber to de
 termine the conditions under which convection occurs. The experimental set
  up used is a tank heated from below and cooled from above\, separated int
 o porous and fluid layers with thermal and image data taken. Various regim
 es are possible\, including regimes in which the particles forming the por
 ous layer become entrained into the convecting fluid. Textural analysis of
  plagioclase aspect ratios in igneous bodies has also been done to determi
 ne the solidification histories of various igneous intrusions. \n\nBuoyanc
 y induced Taylor dispersion\n\nWe consider the turbulent mixing that occur
 s due to the injection of a small constant volume flux of dyed salty fluid
  at the top of a long narrow tank tilted at an angle from the vertical. Us
 ing dye and a light attenuation technique\, the evolution of the reduced g
 ravity can be extracted throughout the tank\, which is initially filled wi
 th fluid of lighter density. The injected fluid mixes vigorously with the 
 fluid that initially occupies the tank\, and a mixed region of turbulent f
 luid slowly propagates through the tank due to the unstable density gradie
 nt that is set up along the length of the tank. The evolution of the mixin
 g region along the length of the tank can be described as a diffusive proc
 ess using Prandtl’s mixing length theory\; the tilt causes a shear flow 
 that enhances the effective diffusion\, in a way analogous to Taylor dispe
 rsion for turbulent pipe flow. We show that the solutions to the correspon
 ding nonlinear turbulent diffusion equation match well with our experiment
 al profiles throughout the range of tilt angles tested (0-45 deg.)\, and t
 hat the profiles of reduced gravity along the length of the tank take on a
  self-similar form. Across the width of the tilted tank\, a density gradie
 nt is formed throughout the mixed region of dense fluid\; we develop a mod
 el for the cross-tank profiles of velocity and reduced gravity based on th
 e Navier Stokes equation and the advection-diffusion equation\, and show g
 ood agreement between our model and our experimental data.
LOCATION:Open Plan Area\, BP Institute\, Madingley Rise CB3 0EZ
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