Skier Triggered Slide in Hell Roaring (Out of Bounds)
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22 Dec 2009
Recently received a report of a single skier triggered avalanche in the Hell Roaring Basin outside of the Big Mountain Ski Area. This slide was triggered just to skiers right of a rock convexity on a southeast facing slope. The slope averaged 38 degrees and was slightly dished below the roll over. The fracture line varied in depth with the trigger point at 53 cms (21") below the surface. The slide was approximately 36 meters (120') near the starting zone and flared to approximately 44 meters (150'). The deposition on the road ranged from 165 cms (66")to 250 cms (100"). The slide slid approximately another 60 meters (200') below the road and the total slide path was approximately 138 meters (450').
The bed surface was on two different layers, the lower bed surface was an old faceted layer that had since rounded and stiffened to a pencil hardness the upper bed surface was the Thanksgiving melt freeze/ice crust. Initial observations seemed to indicate that the slide triggered on the Thanksgiving melt freeze ice and stepped down to the old faceted layer on the rock roll.
This is a preliminary report and hopefully can give more details after the individual is interviewed.
Tony Willits
Flathead National Forest
12/24/2009 |
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