Analysis of the Durrand Glacier Avalanche Accident

Durrand Avalanche Report page 28
5. The La Traviata couloir, where the fatal accident occurred, is a steep, wind-loaded, 310
metre long shallow gully with a 37° upper slope where the avalanche started. All the
avalanche reference books and other sources consulted warn that couloirs such as this
have a high probability of being potential sites of avalanche activity. According to the
references, the specific features of this couloir that were indicators of high avalanche
hazard are:
(a) The slope steepness. Avalanche accidents most commonly occur on slopes of 31° to 35°;
this one is even steeper at 36° to 37°.
(b) Lee slope build-up and cross-slope loading. Most avalanches occur on slopes where
winds cause snow to accumulate and build-up to form dense and potentially dangerous
snow slabs. In this case, more than a metre of additional snow was present in the gully.
(c) A convex upper slope. At such places of convex curvature, a snow slab resting on a
persistent weak layer would be in tension due to the difference in the rate of snow creep
above and below the break in slope. A skier crossing over such a convex slope is more
likely to trigger a release compared to other slopes.
(d) Relatively smooth underlying terrain (scree in this case). This would not provide the
anchors that a more rocky slope would have, and means that the slope would have a
relatively small surface roughness depth. Compared to more rocky slopes, it would be
more prone to slide with lesser amounts of snow.
(e) Connectivity to an area of shallow snow. In such areas, the weight of a person skiing over
into the more shallow snowpack can set off a skier remote triggered avalanche. This is
more likely to happen if the snow slab rests on a persistent weak layer, such as a layer of
faceted crystals, as was the case at Durrand.
6. By taking his entire party up the La Traviata couloir at the same time, the guide was
unnecessarily exposing his group to a higher avalanche risk, and not following generally
accepted safety procedures described in the avalanche references consulted. Specifically,
the following features or actions increased the avalanche risk and the risk generally to the
group.
(a) The presence of the whole group in the couloir at the same time. This exposed the entire
party to avalanche hazard, and reduced the number of potential rescuers available. It also
meant that a rescue would likely involve the difficult task of tracking down several
transceivers buried in a small area. Finally, the large group size meant that a greater weight
of skiers (surcharge) was present on the unstable snow slab, especially at the convex top of
the couloir, and on the thinner snowpack above.
(b) The presence of a terrain trap at the base of the La Traviata couloir. The abrupt change in
slope caused rapid deceleration and deposition of snow, allowing an initial 310 metre long
moving snow slab in the gully to cascade over itself and form a deep, 65 to 85 metre long
debris deposit. This deeply buried many of the victims and greatly decreased their
chances of survival.
(c) The location of the guide some distance ahead of his group. This did not allow him to track
their progress and well-being, or immediately notice that a large avalanche had occurred.
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