Dimensions of dry snow slab avalanches from field measurements

Abstract

[1] Dry slab avalanches release by a sequence of propagating fractures. In this paper, I provide field measurements of the important length parameters resulting from fractures for hundreds fallen slabs including depth, length, and width. The field data show wide variations in these parameters. Probability plots of all dimensions (length, width, and depth) suggest they approximately obey log normal probability density functions. Given slab dimensions, two applications are considered on the basis of the field data. These applications are: (1) Estimates of total fracture energy consumed around the perimeter of the slab are given, where it is presumed fracture is mostly mode I, and along the base (weak layer) of the slab, where shear fracture (mode II and III) is expected. For average characteristic dimensions, the analysis suggests that energy consumed on the perimeter is somewhat less than in the weak layer. Even though fracture energy around the perimeter is expected to be higher than in the weak layer, the larger area fractured in shear at the base of the slab compared to area fractured in tension around the perimeter results in a comparable amount of total energy needed around the perimeter. (2) Approximate estimates of avalanche mass for average characteristic dimensions based on slab depth D (the only length possibly known prior to avalanching) are made. The mass is considered related to destructive potential and simple guidelines are given to estimate mass in relation to D with validation by considering concurrent size and estimates of D by mountain guides.

Dry snow slab quasi‐brittle fracture initiation and verification from field tests

“…A measurement of short critical length implies only an unstable snow pack without the potential size of the avalanche expected taken into account. McClung [2008] has given estimates of how avalanche volume and destructive potential increase as D increases.…”

Long-term avalanche hazard assessment with a Bayesian depth-averaged propagation model

“…However, the procedure chosen is highly speculative. A more realistic description of the release conditions, including the most recent developments concerning the size distribution of snow avalanches (McClung, 2009) could easily be included in our framework.…”

Influence of snow cover properties on avalanche dynamics

“…For agglomerates, the strength of an agglomerate is expected to depend on the bonding mechanism as discussed by [Mishra and Thornton, 2001]. Indeed, the densification during tumbler rotation (Figure 4.7) plays a role since fracture toughness of snow depends on density [Bazant et al, 2003;McClung, 2009]. Hapgood et al [2007] observed that the extent of consolidation depends on the intensity of agitation in the tumbler and resistance of the granule to deformation.…”