Turnagain Pass

Yesterday the weak facets near the base of the snowpack showed their teeth and two snowmachiners had very close calls.  On the Seattle Creek Headwall a slope (that had been previously high marked and skied) was triggered just as the as snowmachiner that climbed it turned to travel back down. The rider tried to pull his airbag but was unsuccessful and was completely buried except for a hand sticking out.  He was quickly rescued by his party but his sled was not located.  In Lynx Creek a snowmachiner triggered a slope just after he crested the hill but was not caught. Snowmachiners in both locations remarked that there were no signs that the snowpack was unstable and in both cases there was already tracks on the slope. Many other skiers and riders enjoyed the mountains yesterday without incident. All these factors are characteristic of deep persistent slab, low probability of triggering but high consequences if you do find the wrong spot. The slab in Seattle Creek was reported to be 4-6′ deep and the avalanche in Lynx 1-3′ deep. This type of avalanche is often triggered in a thin part of the slab, near rocks or on the edge of the slab. These can also be triggered by multiple skiers/boarders and/or snowmachines on, near or under slopes. It may be the 3rd or 10th or 25th track that tips the balance. Observers have found weak faceted snow at the base of the snowpack across the area from Seward to Girdwood. However, another tricky part of the equation is that although this set-up is fairly widespread it is also variable making some slopes safe to ride and others very dangerous. The take away from the avalanches yesterday is that weak snow with a deep slab on top is poor snowpack structure and may remain suspect for days to come. Temperatures above freezing in the Alpine and direct sunshine may also make these slabs more easy to initiate.  All of this has to be a factor in decision making this weekend.  Remember signs of instability are not always present and slabs may break once you are well out onto them. As always practice safe travel protocols, be aware of other parties in the area, choose terrain wisely, carry rescue equipment and don’t let the sunshine cloud your judgment. 

Seattle Creek avalanche. Photos: Chad Aurentz

Lynx Creek avalanche. Photos: Mark Guess

Snowpack near the Lynx Creek avalanche shows hard snow over soft weak snow near the ground. Photo: Travis Rupp

In addition to deep persistent slab avalanches there are a few other avalanche concerns to pay attention to today. All of these concerns could be a hazard seperately or once initiated, trigger a larger persistent slab deeper in the snowpack. Warm temperatures and direct sunlight may also play a factor in all of these concerns. We have reached the time of year. The sun is out and affecting the snow in terrain on the Southern half of the compass. A small crust was observed forming on Thurday on steep southerly slopes. Pay attention to changing conditions!

Wind Slabs: Old stubborn wind slabs may be triggered on leeward slopes. Looked for pillowed or drifted snow, listened for hollow sounds and avoid areas with stiff snow over soft snow. Warming temperatures and direct sunlight may make these slabs easier to trigger.

Loose snow: With 4-8″ of loose snow on the surface over a dense base, watch your sluffs and watch how the sun is affecting the snow around you. These may pack enough punch to push you somewhere you don’t want to go i.e. a terrain trap. 

Cornices: Give cornices wide berth, avoid travel on slopes below them and remember they can break farther back onto the ridge than expected.  If cornices do break and fall they could trigger an avalanche on the slope below.