UPDATE to avalanche incident investigation on Elk Mountain, Glacier National Park, Montana as reported by Erich Pietzsch.
A full incident report will follow in the next few days. We are providing this information so backcountry travelers are aware of the conditions that led to this avalanche incident.
The avalanche occurred on the afternoon of Wednesday, January 8, 2013. The following day (January 9) a team of 3 avalanche specialists and a district ranger from the U.S. Forest Service, the U.S. Geological Survey, and Glacier National Park along with a member of the party involved traveled to the scene of the incident. The scene was located along the main south side of Elk Mountain along the southern edge of Glacier National Park, Montana. Lack of visibility, moderate to strong winds, and substantial new snow limited our ability to access and document the entire accident site. However, with a member of the part accompanying us, we were able to access a lower part of an avalanche crown. Based on conversation with the party, there were actually two separate avalanches that occurred at two separate times but in adjacent gullies. We investigated the snowpack along the lower edge of the avalanche that did not involve the party. However, this avalanche was witnessed by a member of the party earlier in the day.
Investigating the crown proved a bit difficult due to new snowfall and snow loading at the crown. The avalanche occurred on a south-southeast facing slope on the south side of Elk Mountain in an area locally known as “The Backstrap” and funneled into a gully. The average slope angle of the starting zone was approximately 35 degrees and the alpha angle was 32.5 degrees. Avalanche dimensions were also difficult to determine due to conditions, but the crown face depth appeared to range from 12 to 36 inches deep and the avalanche was approximately 145 feet wide and ran approximately 1400 vertical feet. The crown was located at approximately 7200 feet in elevation and the toe of the debris was around 5800 feet. The caught skier was carried approximately 800 vertical feet. US classification of the avalanche is SS-ASu-R4-D2-I. We found six to ten inches of new snow that had fallen by late morning of January 9. This new snow covered up a substantial portion of both the avalanche crown and the debris. We performed a snow profile along the crown as well as multiple Extended Column Tests (ECTs). Our extended column tests resulted in propagation of a fracture just above an ice crust. At the location of the crown we investigated, we found about a one meter (39 inches) wind slab sitting on top of this weak layer. The weak layer appeared to be a layer of small facets sitting on top of this ice crust. This ice crust may potentially be a sun crust that formed on January 3. The weather and snow conditions leading up to this incident produced wind slabs, sometimes very sensitive, sitting on top of a variety of layers including crusts and facets. More detailed information will be available in the full incident report. Be safe.