Human-triggered avalanches, Hillman’s Highway & Gulf of Slides, 2018-3-10

On Saturday, March 10, 2018, two separate avalanche incidents were reported. During the previous 2 days, 14.5″ of snow was deposited at Hermit Lake from a nor’easter and the upslope snowfall that followed. This storm was accompanied by moderate winds that rose to the 60’s mph the afternoon before. Saturday’s advisory called for 4.5″ more snow with increasing wind shifting slightly to the NW. Avalanche danger was rated Considerable in Hillman’s Highway, along with Left Gully and the Headwall forecast zones.

Around mid-day, a party of three talked with a snow ranger on duty who advised that low visibility and continued wind loading made their plan to travel into Hillman’s Highway unwise. The party hiked to Hillman’s and entered the 75′ wide couloir onto a 15-20 degree section of the otherwise steeper runout. Soon after the party returned to the courtyard and reported that everything the snow ranger had cautioned against had played out. Two were struck by debris, knocked down, and carried downslope. Fortunately, much of the energy of the debris flow was absorbed by boulders and holes from a warm spell which reduced our snowpack substantially. When the threat of natural avalanches occurring is elevated, the risks are as well. The natural avalanche that occurred in Hillman’s Highway was much larger and would likely have been unsurvivable.

The same day a party of two skiers set a skin track near the middle gully in the Fingers area of Gulf of Slides, in sparse trees. As the terrain steepened, they began to boot along the left edge of the gully next to the trees. The snow was loose and dry with “no shearing and bonding felt okay”. The first skier had been to this area many times and stayed out of the gully as they made their way towards the rollover near the top. They had spread themselves out as they moved up the slope but paused as they reached the rollover because “something felt wrong”. In moments, the slab failed a “couple hundred feet above” the party and hit both skiers. The first skier was carried but, being on the edge of the gully, he escaped the main flow of debris while the other skier clung to a nearby bush. The skier that was carried turned his beacon to search and could not locate a signal of his partner, who was still above him. Shortly after the caught and carried skier texted for help on his cell phone, the pair made contact and eventually were able to call off the rescue response. The skier who held onto the bush lost his poles while the skier who was carried lost all his equipment though eventually recovered one ski.

Later conversations with the skiers in Gulf of Slides revealed a debate as to whether or not they triggered the slope. They considered it likely that they did not trigger the slope, but rather that it had avalanched naturally. From our perspective, the trigger is relatively unimportant in this instance. If the avalanche had not released while ascending, it is possible that they could have made it to the top and triggered the slope on the way down. In that case, much more of the slab could have been above them with more serious consequences likely. After some reflection, looking at weather data and reading the avalanche advisory, the triggering skier admitted that “overconfidence due to personal experience” in that particular area led him to ignore the obvious red flags that existed due to the snow and weather conditions that day. After the period of warm weather and ice crust which had dominated recent ski conditions, it seems likely that the scarcity heuristic was in play as well. The call of fresh powder is hard to ignore sometimes but it is important to remember that good luck can play a role in good outcomes like this one and luck is one thing no one can count on.