The last two days have brought warm, sunny spring-like conditions to Turnagain Pass and today will be much the same. After several human triggered avalanches on Tuesday, there were no reported slides yesterday – however, very few people were out. Although the weather is inviting, the snowpack is not. A very poor structure exists currently and is one that will likely persist for the foreseeable future. The set-up is simple: a hard slab 1-3′ thick over weak faceted (sugary) snow on top of a hard bed surface. This is textbook for human triggered slab avalanches.
The slab on top of the weak layer is quite variable due to the strong winds during Monday’s storm. There are portions of terrain that have been scoured to the point of uncovering old tracks (anti-tracks) and areas where a slab thickens from 0 to 30″ over just 10′. These are extreme examples, but my point is – sussing out trigger points and how one triggers an avalanche today. Thin areas of the slab, roughly 1′ or less, are the most likely places for a person to trigger an avalanche. The thicker areas of the slab will take a group of people near each other, such as a large party congregated on a ridgeline, something we call large triggers. Large triggers also include snowmachines – yet our unprecedented lack of snow has kept motorized use closed.
Not only is sussing out trigger points a hard thing to do and a bit too much to gamble on right now, but another thing to consider is the potential lack of obvious signs of instability. Collapsing or whoomphing was widespread two days ago, but less so yesterday. Don’t let an absence of these signs lure you into thinking the snowpack is stable until it is too late. All you have to do is dig in a couple feet and you’ll see for yourself the weak faceted snow that is plaguing the mountains.
Photo and Video – Textbook slab avalanche ingredients:
Windloaded slopes vs. scoured slopes. Avoiding steep windloaded areas is a good strategy right now.
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