## Mechanisms of slab avalanche release and impact in the Dyatlov Pass incident in 1959

We show how a combination of irregular topography, a cut made in the slope to install the tent and the subsequent deposition of snow induced by strong katabatic winds contributed after a suitable time to the slab release, which caused severe non-fatal injuries, in agreement with the autopsy results

Johan Gaume

2021

### Introduction

• During the night of February 1, 1959, nine Russian hikers died under unexplained circumstances during a skiing expedition in the northern Ural Mountains.
• The group had decided to set up their camp on the slope of the Kholat Saykhl (Fig. 1a); the name means “Dead Mountain” in the local Mansi language.
• Something unexpected happened after midnight that caused expedition members to cut the tent suddenly from the inside and escape towards a forest, more than 1 km downslope (Fig. 1b), without appropriate clothes, under extremely low temperatures, and in the presence of strong katabatic winds induced by the passing of an arctic cold front.
• A Last picture of the Dyatlov group taken before sunset, while making a cut in the slope to install the tent.
• C Configuration of the Dyatlov tent installed on a flat surface after making a cut in the slope below a small shoulder.
• Snow deposition above the tent is due to wind transport of snow

### Methods

• Problem formulation for the analytical model of delayed avalanche release.
• We assume a plane strain problem with a cut in a curved slope, with a planar slope-parallel weak layer of angle α, thickness d at the depth h described by a parabolic equation: where h0 is the depth of the weak layer at the cut (x = 0), hc is the constant depth of the weak layer at the upper straight portion of the slope $$\left( {x \ge l_{\mathrm{c}}} \right)$$, lc is the distance from the cut to the point on the slope where the slope surface becomes parallel to the weak layer.
• The choice of the parabolic slope approximation has been based on the following considerations.
• It reflects a smooth uphill steepening of the slope.
• It leads to a second-order Euler–Cauchy differential equation with a simple analytical solution.

### Results

• Around 100 m above the tent, there is a shoulder which separates a rather flat plateau and a steeper slope below (Fig. 2a).
• This slope consists of 4–6 m high steps (Fig. 1c and Fig. SF2) and the tent was installed below one of them, where it was easier to make a cut in a locally flatter slope.
• The choice of the tent location was likely driven by the fact that the larger scale shoulder would protect them from the strong winds.
• As we show below, this choice of location could have contributed to the accident: small scale topographic variability resulted in a locally steep weak snow layer while the larger shoulder contributed to significant wind-driven snow accumulation above the tent, eventually leading to an instability

### Conclusion

• Significant progress in snow and avalanche research over the past two decades has allowed better understanding of avalanche dynamics and of the processes related to snow-slab avalanche release.
• These developments include a snow slab with a spatially variable thickness and its evolution due to sintering of the wind-transported snow, which affects the instability of a buried weak snow layer.
• Our numerical simulation of the impact of a snow avalanche on a human body constrained by an obstacle combines advanced elastoplastic constitutive models with large-deformation dynamic numerical analysis (MPM) and biomechanical modeling of the human body.
• This opens new perspectives for research on the effects of snow avalanches on human health and safety

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