20100121 Happo North Avalanche

I was not there to observe this avalanche, however an account and pictures were emailed to me. No one was buried, although people down slope were almost caught. The debris pile was 200cm deep.

Skier triggered, Size 2. Crown wall 100cm deep. Sliding surface probably the melt freeze crust from 20100111.

The area is at about 1050m, north aspect, probably about 32 degrees. Almost no trees with steep rollovers onto a summer road.

Weather and snowpack structure: We had a bout 100cm of storm snow in the last week or so sitting above the last MFC. Previously stability had been Good. On 20100120 temperatures started to rise rapidly with a high of +9C recorded at 800m. Overnight and then on the morning of 20100121 there was moderate rain that slowly turned to sleet then snow.

My guess is that the additional water content in the snowpack added weight which was too much for the interface between the slab and melt freeze crust that had weakened due to the warmth. It is unlikely that there was enough rain to penetrate 100cm down to the sliding surface. The skier triggered the slide after jumping of a small terrain feature.

Reality check: this avalanche was more than enough to bury and kill a person and it is in an area that is very easily accessed and sometimes skied by people with no avalanche rescue equipment at all.