Analysis of the Durrand Glacier Avalanche Accident

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Executive Summary On January 20, 2003, seven of 21 ski tourers under the leadership of Mr. Ruedi Beglinger, a Swiss-trained mountain guide, owner and chief guide of Selkirk Mountain Experience Ltd., and member of the Association of Canadian Mountain Guides (ACMG) and the Canadian Avalanche Association (CAA), died when they were buried by a large (Size 3-4) avalanche in the Durrand Glacier area, 35 km north northeast of Revelstoke, B.C., Canada. Guide 310 m (1017 feet) 37° upper slope Durrand Glacier Chalet Uphill track June 19, 2003 Figure 1: looking east at the site of the fatal avalanche accident in the La Traviata couloir. For several weeks prior to the accident, warnings of the presence of a widespread persistent weak layer of faceted crystals in the winter snow pack, and an overlying snow slab that could produce large avalanches, were being widely reported in public avalanche bulletins issued by the Canadian Avalanche Association, and the Avalanche Control Section of Parks Canada at Rogers Pass. The Canadian Avalanche Association’s private data exchange system (InfoEx) was also warning of the hazard; however, Selkirk Mountain Experience did not subscribe to InfoEx and therefore was not able to obtain this detailed, daily information on avalanche hazard. After the accident, all nine snow profiles dug in the vicinity of the fatal avalanche by investigators, and other tests, confirmed the widespread presence of the persistent weak layer and overlying snow slab. This means that the dangerous avalanche conditions in the Durrand glacier area should have been detected in standard snow profiles, and by doing stability tests, as described in the Canadian Avalanche Association’s Observation Guidelines and Recording Standards for Weather, Snowpack and Avalanches (2002). Copyright: no part of this report may be reproduced without the written permission of the author.
Executive Summary page 2 The destination chosen for this fatal ski tour first required going down into the narrow valley of Cairns Creek, and then up to a sub-alpine area called Swiss Meadows. This part of the route required crossing potentially high risk and unavoidable avalanche terrain on the south face of Tumbledown Mountain during a period of considerable avalanche hazard. The overall slope of this face is about 38° to 40°, which, statistically, is within the most common range of slope angle where avalanches occur. An avalanche occurring on this face would carry skiers down over bluffs or through gullies and into the terrain trap at the confined bottom of the Cairns Creek valley. From Swiss Meadows, the group originally intended to go up low-angled and relatively safe slopes to the summit of Fronalp Peak, as shown on Selkirk Mountain Experience’s guiding map. Instead, they toured up below the west ridge of Tumbledown Mountain on a route that was so close to the base of the slope that it was subsequently overrun by the avalanches that occurred later that day. 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 such couloirs 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. This would not provide the anchors that a more coarse, rocky slope would have, and means that the slope would have a relatively small surface roughness depth. Compared to other areas, this slope 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 snow pack 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. Copyright: no part of this report may be reproduced without the written permission of the author.
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Analysis of the Durrand Glacier Avalanche Accident

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