Turnagain Pass

Yesterday’s sunny skies revealed what most of us powder lovers do not wish to see after a snowfall event…wind. Monday night and Tuesday morning North and West winds wreaked havoc on much of the terrain around Turnagain, Summit Lake, Portage and the Girdwood Valley. Wind scalloped many snow surfaces, scoured some ridgelines to the rocks and sastrugi was reported on Tincan. Along with the winds, no natural avalanche activity was seen in the Turnagain area, but the Summit Lake region saw several shallow natural wind slab avalanches along with one that appeared to step down into an older weak layer.

For today, our main avalanche concern centers around a person triggering a large persistent slab avalanche up to 2′ or more in depth. Below the storm snow and recent wind slabs (addressed below) sits the Jan 21 buried surface hoar we have been talking about for some time. This layer is roughly 1-2′ below the surface and with recent wind and snowfall adding stress to it, the possibility for a person to tip that balance and initiate a larger slab avalanche is possible. There is also the possibility that a small wind slab or cornice fall could trigger this layer. We are back in a regime where no signs of instability are likely to be present before one of these avalanches releases and snowpit tests become unreliable. Therefore, assessing your terrain and the potential outcome if an avalanche breaking deeper in the pack does occur is key. Are there terrain traps below you? Cliffs? Are your partners watching and rescue ready? As we head into another period of high pressure (after today) keep these things in mind.

Northerly winds creating plumes off of Tincan Proper yesterday morning. (Photos: Jessie Haffener)

Anti-tracks on Tincan 

–

Watch for wind slabs to be lurking intermixed with the variable surface conditions on the steeper slopes. These will likely be shallow, up to a foot thick, and stiff. They should be easy to identify with a rounded shape and hollow feeling. Watch for shooting cracks and places the wind crust becomes thicker. Cross loaded gullies could be a good place to find and trigger a wind slab as winds did blow at all elevations. 

Image below of a shallow wind slab on Tincan yesterday. Small terrain, small avalanche – Large terrain, small to large avalanche with higher consequences.

Above 3,000′ in the Alpine zones, several old weak layers of facets and buried surface hoar sit near the ground and in the mid-pack. This structure is most pronounced in areas with a thin overall snow cover, such as the South end of Turnagain Pass and the Summit Lake area. Recent wind slab avalanches Monday on Fresno ridge (Summit Lake zone) look as if they ‘stepped’ down into older weak layers in the snowpack. This is noteworthy and a reminder not to forget there are lurking old layers that could ‘wake up’ if one hits just the wrong spot.

Pictured below are shallow wind slab avalanches on Southeasterly facing Fresno ridge that looked to have triggered a deeper weak layer and subsequent larger avalanche lower on slope in the trees. (Photo: Jessie Haffener)

–