Frontal dynamics of powder snow avalanches

Abstract

[1] We analyze frontal dynamics of dilute powder snow avalanches sustained by rapid blow-out behind the front. Such material injection arises as a weakly cohesive snow cover is fluidized by the very pore pressure gradient that the particle cloud induces within the snowpack. We model cloud fluid mechanics as a potential flow consisting of a traveling source of denser fluid thrust into a uniform airflow. Stability analysis of a mass balance involving snow cover and powder cloud yields relations among scouring depth, frontal height, speed, mixed-mean density, and impact pressure when the frontal region achieves a stable growth rate. We compare predictions with field measurements, show that powder clouds cannot reach steady frontal speed on a uniform snowpack with constant cloud width and derive a criterion for cloud ignition. Because static pressure is continuous across the mean air-cloud interface and deviatoric stresses are negligible, frontal acceleration is insensitive to local slope, but instead arises from a deficit of flow-induced suction in the wake. We calculate how far a powder cloud travels until its frontal mixed-mean density becomes stable, and show how topographic spread can hasten its collapse.

Seismo-acoustic energy partitioning of a powder snow avalanche

“…The location of infrasound and seismic energy radiation along the avalanche path presented in this study, is in agreement with the hypothesis that infrasound is produced by the power cloud and with the dynamical evolution of a PSA in terms of an eruption current (Carrol et al, 2013). They showed that the powder cloud formation is strongly enhanced by the narrowing of the avalanche path, while it is limited by the path spreading in the initiation and deposition area.…”

“…They showed that the powder cloud formation is strongly enhanced by the narrowing of the avalanche path, while it is limited by the path spreading in the initiation and deposition area. Our seismic and infrasound array observation, clearly shows that while seismic energy is radiated as an elongated source all along the avalanche path, the infrasound signal is radiated mostly from the powder cloud, that develops only within the narrow avalanche channel and is missing in the wider starting and deposition areas (Carrol et al, 2013).…”

Dynamically consistent entrainment laws for depth-averaged avalanche models

“…There is only indirect, yet suggestive observational evidence for eruption from videos and profiling radar measurements. Louge et al (2011) andCarroll et al (2013) recently suggested a similar mechanism for the dilute front of fast dry-snow avalanches or powdersnow avalanches and obtained erosion depths compatible with observations. However, some details appear to need further study, in particular the relation to the pressure distribution in the avalanche head obtained by McElwaine (2005) for non-eroding powdersnow avalanches and the rapid dilution of the eroded snow.…”

Maximum Solid Phase Concentration in Geophysical Turbulent Gas‐Particle Flows: Insights From Laboratory Experiments

“…They include dust storms (e.g., Goudie & Middleton, 2001), powder snow avalanches (e.g., Carroll et al, 2013), and volcanic biphasic suspensions such as conduit flows, buoyant plumes, or pyroclastic density currents (e.g., Bonadonna et al, 2011;Carazzo & Jellinek, 2012;Dufek, 2016;Gonnermann & Manga, 2007). They include dust storms (e.g., Goudie & Middleton, 2001), powder snow avalanches (e.g., Carroll et al, 2013), and volcanic biphasic suspensions such as conduit flows, buoyant plumes, or pyroclastic density currents (e.g., Bonadonna et al, 2011;Carazzo & Jellinek, 2012;Dufek, 2016;Gonnermann & Manga, 2007).…”

“…Turbulent dilute mixtures of gas and solid particles are found in various geophysical contexts. They include dust storms (e.g., Goudie & Middleton, 2001), powder snow avalanches (e.g., Carroll et al, 2013), and volcanic biphasic suspensions such as conduit flows, buoyant plumes, or pyroclastic density currents (e.g., Bonadonna et al, 2011;Carazzo & Jellinek, 2012;Dufek, 2016;Gonnermann & Manga, 2007). The concentration of particles controls the dynamics of these mixtures by changing their density and in some cases their thermal energy (Valentine & Sweeney, 2018).…”