Analysis of the Durrand Glacier Avalanche Accident

Durrand Avalanche Report page 7
(e) When new snow started to fall on December 10, winds were light, and the faceted crystals
were left intact, and were then covered by the new snow that fell between December 10
and 27 th (including 40 cm between December 25 th and 27 th ). The preserved facet layer is
believed to have formed the failure plane on which many subsequent avalanches, including
the ones in the Durrand Glacier area, ran.
F. History of wind activity in the Columbia mountains
1. Winds are an important element that factor into the formation of avalanche hazard. Winds
take snow from windward slopes and deposit them on downwind, or lee, slopes. This may
cause a build-up of snow (lee slope deposition) to occur in some areas, such as below
ridges or in couloirs. The greater the wind speed, the more lee slope deposition occurs,
and the denser is the slab that is formed. The wind direction and terrain determines on
which slopes, or aspects, lee slope deposition occurs. Note that lee slope deposition may
occur, and produce avalanche hazard, even during clear weather when no snow is falling.
2. According to Larry Stanier’s report to the Coroner, significant winds (those with velocities of
more than 25 km/h) were reported on eight separate occasions between January 1 and 19
on the InfoEx system by ski operations in the Northern Selkirks. Moderate winds are those
with wind speeds of between 26 and 40 km/h, and strong winds are those with wind
speeds of greater than 40 km/h. The significant wind events noted were as follows:
Date Wind Description
Jan 2 Strong southwest winds.
Jan 3 Strong south and southwest winds.
Jan 4 Moderate southwest winds.
Jan 7 Strong southwest.
Jan 8 Moderate northwest.
Jan 12 Moderate west.
Jan 19 Moderate to strong southwest.
Table 1: General description of winds, North Columbia mountains, January 2 to 19, 2003.
3. The La Traviata couloir, where the fatal avalanche occurred, faces approximately
southwest, and the snow pillows and wind rolls present indicate that it would most heavily
be loaded by southeasterly winds that blow across the southerly face of Tumbledown
Mountain. In this specific case, the snow profiles recorded immediately after the accident,
show that a considerable amount of lee slope build-up occurred. Specifically, it was found
that snow in the La Traviata couloir (2475 m elevation) was up to 260 cm deep. By
comparison, a 148 cm depth of snow was recorded in a sheltered study plot at Durrand
Chalet (1940 m elevation), and windward slopes above the La Traviata couloir only had
about 50 cm of snow.
Copyright: no part of this report may be reproduced without the written permission of the author.