Avalanche Investigation

From today's advisory:

Yesterday, Mark, Eric, Karl and I joined folks from Bridger Bowl to investigate the avalanche that killed a snowboarder on the west side of the range two days ago.  Although the slide was only 50 feet wide, it was a three foot thick hard slab of windblown snow that broke on a 40-45 degree slope and pulled even more slabs off its flanks.  The crown depth tapered quickly from a whale-sized drift of snow on its southern edge to a thin slab only inches deep mid-gully.  Thick drifts are all over the place, but in most cases are bonded to the old snow surface.  This slide was triggered near the top of the path and funneled debris through small, but not insignificant trees over 1,300 vertical feet.  The victim was carried 1,100 feet downhill and came to rest with his head under 5 feet of dense debris.  The load of windblown snow from the weekend was a heavy burden.  Large loading events do not need a persistent weak layer for avalanches to occur.  This avalanche broke on small grains of lighter density snow which happened to be the weakest layer in the snowpack. Although the snowpack investigation yielded no surprises, standing at the top of the path was gut wrenching. The terrain on the west side of Bridger Bowl is steep, serious and unforgiving.  All slopes lead into trees, steep gullies or over cliffs.  Most of the wind whales are bonded into place and are not cracking or avalanching.  But as the two snowboarders found out on Monday, there are still some that can be broken free, especially at its thinner edges where fractures can propagate under the meatiest slab.   Given the tricky nature of analyzing these slopes, plus the fact that the winds have not died down, I’m rating the avalanche danger MODERATE on all slopes today.

More pictures and video at www.mtavalanche.com