Snowmobile triggered avalanche off Blue Lakes Road

Avalanche triggered on Feb 21, 2011 when two snowmobiles were on the same slope attempting to free a stuck snowmobile. Slab was composed of all of the storm snow that accumulated Feb 16 through Feb 19. Slab failed on small facets above the January 13 rain crust and stepped down to small facets and rounds at the base of the rain crust that was the ultimate bed surface in this event. Jan 30 snowfall had been removed from this area by strong east winds prior to the Feb 16 snowfall.

A small portion of rocks/cliff band is protruding from the bed surface near the point where snowmobile tracks enter the avalanche from the northwest side. There is still a very deep snowpack around these rocks. HS below the bed surface >2.5m. This avalanche did not fail to the ground as some initial reports had indicated. The slab was thinnest (around 3 feet on the northwest end (flank) where the trigger likely occurred and much thicker (up to 8 feet) at the southeast flank of the avalanche. There were no snowmobile tracks around or near the southeast flank indicating that the point of initiation most likely occurred near the shallow end of the slab and around the rocks where the slab was thinnest and the easiest place to trigger from.

There are crowns from numerous natural avalanches in this area in similar terrain on similar aspects at similar elevation. The crowns for these avalanches were in the 1 to 3 foot range and most likely occurred during the widespread natural avalanche cycle on Friday Feb 18.