UAC Releases Pierre Slide Investigation Photos
Details from avalanche investigators offer sobering insight into tender snowpack, and consequences
Investigators from the Utah Avalanche Center today visited the scene of Jamie Pierre’s fatal avalanche accident at Snowbird on Sunday. The investigation remains in progress, but the Center released more details on the tender conditions of the snowpack and four photos—two from the accident scene, two from a slide Pierre and his partner triggered remotely in getting to the South Chute zone where Pierre was caught and carried. (See the UAC report HERE.) — Tim Mutrie
Additional details from today’s investigation, from the UAC:
Weather & Avalanche History:
The weak snow structure has been well documented over the last few weeks. Here is the time line.
Oct 5-6: Significant storm produced 1 to 1 1/2′ feet of snow. Warm weather melted much of this snow but some did linger on the more northerly aspects. The melt-freeze process in early October produced a stout crust. This crust varies in thickness depending on aspect. It’s thicker on east and northeast slopes, thinner on the more due north. Colder subsequent weather deteriorated this snow forming large grained facets below this crust, especially on the northerly aspects.
Oct 15 & Nov 1: Oct 15 had a small storm with a two week colder clear period which faceted this snow above the melt freeze crust. Nov 1 had another small storm whose snow also deteriorated rapidly to facets. It is these two events that, combined, form the weak layer that is causing the collapsing and avalanches.
Nov 5: Around a foot of low density snow fell. This gave us the first hint on how the previous snow would behave. On Oct 6 a skier triggered a small slab avalanche in Collins Gulch. The weak layer was the faceted snow from Oct 15 & Nov 1. On Oct 7, another skier triggered avalanche was reported. During Oct 8-11, numerous reports were coming in of backcountry travelers experiencing collapsing of the snowpack, including THIS one from the Peruvian Gulch which illustrates the poor structure.
Nov 12: A storm rolled in producing 5-9″ of dense snow. A ski touring party in Gad Valley was experiencing collapsing and remotely triggered to small avalanches.
Nov 13: The second portion of the storm brought another 5 to 10″ of snow with wind. With all the previous observations and the new storm snow, the Utah Avalanche Center rated the danger at Considerable and possibly High if snowfall kept up harder then expected. (Nov 13 Advisory)
The fatal avalanche had the same snowpack structure as that of all the collapsing and other avalanche activity over the week of Nov 6 through Nov 11.
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