Environmental Engineering Reference
In-Depth Information
Figure 2.5.
Different types of snow observed in avalanche deposits. (a) Block of wet snow
(size: 1 m). (b) Slurry of dry snow including weak snowballs formed during the course of the
avalanche (the heap height was approximately 2 m). (c) Ice balls involved in a huge avalanche
coming from the North face of the Mont Blanc (France); the typical diameter was 10 cm. (d)
Sintered snow forming broken slabs (typical length: 40 cm, typical thickness 10 cm)
any fluid-mechanics approach for modeling rapid mass movements and have given
impetus to extensive research combining laboratory and field experiments, theory,
field observation, and numerical simulations [ANC 07a, PUD 06].
A number of experiments on snow have been done in the laboratory. Authors
such as Dent and Lang [DEN 82] and Maeno [MAE 93] have measured the velocity
profile within snow flows and generally deduced that snow generates a non-Newtonian
viscoplastic flow, whose properties depend a great deal on density. Transposing these
laboratory results to real avalanches is not clearly reliable due to size scale effects
and similarity conditions. Furthermore, given the severe difficulties inherent to snow
rheometry (sample fracture during shearing tests, variation in the snow microstructure
resulting from thermodynamic transformations of crystals, etc.), properly identifying
the constitutive equation of snow with modern rheometers is out of reach for the
moment. More recently, Ancey and Meunier [ANC 04c] showed how avalanche-
velocity records can be used to determine the bulk frictional force; a striking result
is which the bulk behavior of most snow avalanches can be approximated using a
Coulomb frictional model. Kern
et al.
[KER 04, KER 09] used outdoor and field
experiments to measure shear-rate profiles inside snow flows to infer rheological
properties; this clears the way for precise rheometrical investigations of real snow
avalanches.
Since there are little sound field or laboratory data available on the basic
rheological processes involved in avalanche release and flow, all avalanche-dynamics
