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SUMMARY:Frontal Dynamics of Powder Snow Avalanches
DTSTART:20121011T171500
DTEND:20121011T181500
DTSTAMP:20260916T120422Z
UID:cfeab814e3638ccb5dab79ccb04ebe0b4b32575ea114128c785797be
CATEGORIES:Conferences - Seminars
DESCRIPTION:Michel Louge\, Professor\, Sibley School of Mechanical and Aer
 ospace Engineering\, Cornell University (http://www.ece.cornell.edu/louge/
 ).\nAbstract:\nWe analyze frontal dynamics of dilute powder snow avalanche
 s sustained by rapid blow-out into the head. Such material injection arise
 s as a weakly cohesive snow cover is fluidized by the very pore pressure g
 radient that the particle cloud induces within the snowpack. We model clou
 d fluid mechanics as a potential flow consisting of a traveling source of 
 denser fluid thrust into a uniform airflow. Stability analysis of a mass b
 alance involving snow cover and powder cloud yields relations among scouri
 ng depth\, head height\, frontal speed\, mixed-mean density and impact pre
 ssure when the avalanche achieves a stable growth rate. We compare predict
 ions with field measurements of powder snow avalanches carried out at the 
 Vallee de la Sionne (Switzerland)\, show that powder clouds cannot reach s
 teady frontal speed on a uniform snowpack with constant cloud width\, and 
 derive a criterion for cloud ignition. Because static pressure is continuo
 us across the mean air-cloud interface\, and because shear stress is negli
 gible\, the relatively small frontal acceleration is insensitive to local 
 slope\, but instead arises from a deficit of flow-induced suction pressure
  in the wake. We calculate how far a powder cloud travels until its mixed-
 mean density becomes stable\, and show how topographic spread can hasten i
 ts collapse.
LOCATION:GC A331 http://plan.epfl.ch/?lang=fr&room=gca331
STATUS:CONFIRMED
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