Turnagain Pass

Below 2500’ a layer of wet poorly bonded snow is sitting beneath a slab 1-5’ thick, depending on the location. On the Northern side of the Turnagain pass this slab is closer to 5’ thick. Yesterday on Eddies’ South Face several large (D3) avalanches released naturally on this wet layer. Simultaneously several smaller avalanches released sympathetically on adjacent slopes. It was reported that this occurred in one single event during the warmest part of the day, just after 3pm. Several parties all in different locations described a very loud “Canon” sounding collapse and felt the snowpack drop ½ an inch.  

On the far Southern end of Turnagain Pass where this slab is only 1-2’ thick below 2500’, recent activity and collapsing were not observed yesterday. What this means is that there is more stress on this weak layer where the slab is thicker and thus more likelihood of it reaching its critical tipping point. This problem exists on all aspects below 2500’ and could become active even in places where the slab is thinner. At this elevation band it will be important to avoid being on or near large slopes steeper than 35°. Some examples of these slopes are the East Face of Seattle Ridge and the Library near Center Ridge.

*Even thought temperatures are dropping below freezing at night the wet snow below is unable to re-freeze due to the insulating properties of the slab. This problem is likely to persist for a while and will be most active during the warmest parts of the day. 

Close up photo of one of the many avalanches that occured yesterday on Eddies. This one was on a SW apsect. Photo by Laine Parish.

 View of Eddies West Face. Several larger (D3) avalanches occured at a similar elevation band on the South Face, but could not be seen in entirety from the roadside. 

Oblique view of the South aspect of Eddies. Several large (D3) avalanches are out of view from roadside perspective. 

Weak layers of faceted snow buried as deep as 5’ sit on some slopes on North facing terrain in the Alpine.  This set up will not be found everywhere.  Because of this variability, it is especially important to treat this terrain with suspicion.  Assessment of this issue is very difficult.  The best strategy for “managing” this problem is to avoid this terrain for the time being and give those underlying weak layers ample time to adjust to the large loads (3’+ snow/3”+ H20 over the last week) that have been placed on them.  This is a low likelihood/high consequence scenario that requires patience and time.

Moderate ridgetop winds from the Northeast and several inches of new snow could create small isolated wind slabs in the Apline. These wind slabs will likely be small (2-6”) but could be tender if we see 3+ inches of new snow today. Pay attention to the amount of new snow accumulation. Southern aspects have a sun crust that could make a good sliding surface if these wind slabs form today.