Abstract
ABSTRACTParticle size, particle speed and airflow speed have been measured in the powder snow clouds of avalanches to investigate the suspension and transportation processes of snow particles. The avalanches were artificially triggered at the Lautaret full-scale avalanche test-site (French Alps) where an ultrasonic anemometer and a snow particle counter were setup in an avalanche track for measurements. Relatively large particles were observed during passage of the avalanche head and then the size of the particles slightly decreased as the core of the avalanche passed the measurement station. The particle size distribution was well fitted by a gamma distribution function. A condition for suspension of particles within the cloud based on the ratio of vertical velocity fluctuation to particle settling velocity suggests that the large particles near the avalanche head are not lifted up by turbulent diffusion, but rather ejected by a process involving collisions between the avalanche flow and the rough snow surface. Particle speeds were lower than the airflow speed when large particles were present in the powder cloud.
Highlights
As a dry-snow avalanche descends a mountain slope, a powder snow cloud develops and covers a dense flowing core when avalanche speed is >∼10 m s−1 (Hopfinger, 1983)
Physical modeling of the powder snow avalanche was first based on analogies with a gravity current driven by the difference in density between a fluid containing suspended particles and the ambient air (Beghin and others, 1981; Beghin and Olagne, 1991)
Fukushima and Parker (1990) introduced the particle entrainment/settlement process and indicated that the powder cloud rapidly developed and flowed down the slope as a gravity current as long as turbulent energy was high enough to entrain particles from the snow surface and maintain them suspended in the air
Summary
As a dry-snow avalanche descends a mountain slope, a powder snow cloud develops and covers a dense flowing core when avalanche speed is >∼10 m s−1 (Hopfinger, 1983). Well-developed dry-snow avalanches generally show layered structures: a dense-flow layer, a fluidized (saltation) layer and a powder (suspension) layer from bottom to top (Issler, 2003; Gauer and others, 2008). They are often referred to as mixed-motion avalanches or mixed powder snow avalanches. Fukushima and Parker (1990) introduced the particle entrainment/settlement process and indicated that the powder cloud rapidly developed and flowed down the slope as a gravity current as long as turbulent energy was high enough to entrain particles from the snow surface and maintain them suspended in the air (self-ignition).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
