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SUMMARY:Marginal stability of explosive volcanic columns - Guillaume Carra
 zo
DTSTART:20090409T103000Z
DTEND:20090409T113000Z
UID:TALK17831@talks.cam.ac.uk
CONTACT:John Maclennan
DESCRIPTION:Explosive volcanic eruptions eject dense\, hot\, multi-phase j
 ets which can exhibit several behaviours. The evolution of these flows in 
 the atmosphere crucially depends on the rate of entrainment of surrounding
  air into the jet\, on the dynamics of the particles within the jet and on
  the thermal exchanges between the particles and gas. If the entrainment a
 nd the heating of atmospheric air within the jet is important\, the densit
 y of the volcanic mixture can become smaller than the one of the atmospher
 e and the jet forms a buoyant eruption column. Otherwise\, the jet natural
 ly collapses producing pyroclastic density currents. The study of the erup
 tive deposits of the Montagne Pelée volcano (Martinique\, F.W.I) shows th
 at these different dynamic behaviours often follow one another during a si
 ngle eruption. However\, the theoretical predictions for a column collapse
  are in disagreement with field data. A new model of turbulent entrainment
  of surrounding fluid within the flow is presented to reconcile both. Obse
 rvations of historical eruptions also reveal that a third dynamical regime
  exists in which the volcanic jet separates into a buoyant rising part and
  a denser collapsing part. Two experimental studies are presented to inves
 tigate this particular regime and the stability of the buoyant rising part
 .
LOCATION:Harker 2 seminar room\, Department of Earth Sciences
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