Analysis of the Durrand Glacier Avalanche Accident

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Durrand Avalanche Report page 29 (d) The remote location of the accident site and poor weather conditions. This did not allow outside rescuers to arrive at the accident scene until nearly an hour after the avalanche happened, at which point all but one of the totally buried victims had been recovered, and were dead. (e) The lack of the most efficient equipment to find and dig out buried victims. Specifically, the group did not all have dedicated avalanche probes and full-sized, robust shovels. 7. The September 23 rd , 2003 Coroner’s Inquiry report on the Durrand accident has numerous errors and omissions and does not, in our opinion, fulfill the objectives of a coroner’s inquiry report, as described in the British Columbia Coroner’s Act and related documentation. Specifically, the Coroner’s Inquiry report does not establish the full body of facts that led up to this accident, and therefore does not allow a thorough set of recommendations, to prevent a reoccurrence, to be developed. Some of the errors and omissions are as follows: (a) The location of the accident site is erroneously reported as being 25 km north of Revelstoke, when in fact it is 35 km north northeast of Revelstoke. The Universal Transverse Mercator (UTM) grid location is also not correctly stated. (b) The report inconsistently reports the steepness of the slope, and does not give the correct elevation of the starting zone (crown). (c) The report does not say anything about what was done by the guide to evaluate snow stability in the weeks prior to, or on the day of, the accident. (d) There is no mention of what instructions the guests received with regard to dealing with an avalanche, or conducting an avalanche rescue, especially one with so many buried victims. (e) There is no comment on the destination and route finding choices that were made by the guide. Specifically, there is no mention that the group had to cross the high risk face of Tumbledown Mountain before even getting to the La Traviata couloir, and that they toured up so close under the west ridge of Tumbledown Mountain that their uphill track was subsequently overrun by the avalanches that occurred later the same day. (f) There is no description of how the guide’s route finding decisions, and other actions, compare with commonly accepted principles for traveling safely in avalanche terrain, as described in numerous textbooks and other literature on the subject, including the Association of Canadian Mountain Guide’s training manual. (g) There is only a brief mention of the rescue efforts, and no description of how the remote location, poor weather conditions, deep burial, large number of buried transceivers, and available probes and shovels affected the rescue efforts, and how efficient those rescue efforts were. 8. A Coroner’s Inquiry report is limited in scope and cannot establish fault or censure anyone who may bear responsibility for an accident. By relying on the Coroner’s Inquiry report, not conducting its own thorough investigation of this accident, and not considering taking disciplinary action against its member, the Association of Canadian Mountain Guides is not following its own Code of Ethics, and standards common to many professional organizations in Canada. This lack of action does not, in our opinion, encourage safe operating standards, or serve the best interests of the winter recreation industry, society as a whole, or the ACMG itself. Copyright: no part of this report may be reproduced without the written permission of the author.
Durrand Avalanche Report page 30 9. The fatal slide was most likely a skier-remote triggered Size 3-4 slab avalanche involving at least 19 000 tonnes of snow. It most likely occurred as a result of the following sequence of events: (a) Early winter snow and weather conditions which produced a deep seated layer of unstable faceted snow resting on a rain crust. (b) Deposition of an initial layer of new snow, without much wind, on the facet layer. This protected the facet layer, and prevented it from being destroyed by wind. This was followed by further deposition of wind-driven snow, which would have formed a cohesive, dense snow slab. In areas of lee slope build-up in the La Traviata couloir, the snow resting on the weak facet layer was up to 260 cm deep. (c) The widespread presence of the persistent weak facet layer, which allowed a slide, once it started, to propagate over a very large area. It is important to recognize that there must be a weak layer of snow to begin with, otherwise it would be physically impossible for an avalanche to start and propagate out into more distant snow. (d) In the La Traviata couloir itself, the wind-deposited snow may have been deep enough to support the weight of the skiers ascending the slope, and did not initially trigger a release. (e) As the lead skiers crossed over the convex roll at the top of the La Traviata couloir, they crossed onto a much shallower snowpack, where the weight of the skiers relative to the weight of snow was much greater, and the snowpack was not capable of supporting their weight. This may then have caused the surface snow slab to collapse into the underlying weak (faceted) snow, which would explain the “whumpf” that was heard, and adjustment of the snowpack that was noticed. snow slab weak layer old snow ' Frank W. Baumann 1. stress 2. Whumpf! 3. propagation 4. fracture 5. AVALANCHE! frictional force Fig. 22: Probable triggering mechanism of the fatal La Traviata avalanche. The weight of skiers above the crown caused a thin snow slab resting on an unstable facet layer to collapse. This collapse created a flexural wave that propagated into the deeper, winddeposited snow at the top of the couloir, where it set-off the fatal avalanche. Copyright: no part of this report may be reproduced without the written permission of the author. force of gravity shear force normal force
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Analysis of the Durrand Glacier Avalanche Accident

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