Turnagain Pass

Yesterday we had two reports of human triggered avalanches in the Turnagain Pass region and one near Summit Lake.  No one was injured.

The avalanche reported near Summit Lake was a slab avalanche that failed on facets over a crust.  The crown was estimated at 11-18″ thick and 80′ wide, with a  40′ vertical run.

Another avalanche was on Sunburst, where an anonymous skier reported triggering a wind slab on a west facing slope.  The avalanche was estimated to be 140′ wide, range in thickness from 1-2′, and ran 100′ vertical.  The bed surface was reported to be a layer of facets.  No one was caught or buried.

The other report was from 2nd Bowl, also known as Jr’s Bowl, off Seattle Ridge.  This snow machine triggered slab avalanche was on a northeast aspect at 2000′ and reported to be approximately 300′ wide, running 600′ vertical.  The crown depth was about 2′ thick and ran on small facets.  It’s important to note that one section of the avalanche triggered avalanches on both sides of the first.  No one was injured.

As snow enthusiasts, it’s incredibly valuable to share these experiences with the community.  We’re grateful to the parties involved for reporting this information, and for the positive outcomes.

Avalanche with trigger point. The middle released first, then the right slide, then the left.  2.4.2020 . Photo J. Davis

Small features can pile debris into terrain traps.  2.4.2020 . Photo J. Davis

Today calls for mostly cloudy skies and temperatures ranging from the 20’s to 32°F.  A trace of snow is possible today with calm to light southwest winds.  With relatively calm and temperate conditions, our snowpack will continue to adjust and settle.  Right now, the structure of the snowpack is fairly similar throughout the Turnagain pass area, but the stability can vary from one slope to the next. Yesterday, we had three reports of human triggered avalanches.

Where wind slabs exist on steeper slopes, it could be easy and likely for a human to trigger an avalanche. With the scope of the advisory area, it’s unreasonable to generalize which slopes have wind effected conditions right now.  This is where your awareness and on-site observation plays a critical role in making wise terrain choices. It’s essential to look for clues where wind slabs are forming, or have already formed.

Signs a wind slab could exist include:

• Pillowed features (see photo below)
• Visual signs of winds depositing snow onto the lee of ridges or gullies
• Scoured exposed areas can indicate loading to the leeward side
• Stiffening of the snowpack
• Rippling on the surface
• Shooting cracks
• Hollow drum-like sounds in the snow

If you encounter these conditions don’t hesitate to adjust your route or plan.  This is a time to choose routes with intention, and dig/test/interpret the snowpack if that’s a skill-set you possess.

If you’re up for some reading, consider Roger Adkins paper discussing decision making and strategic mindset.

Pillowed wind features on SW aspect of Tincan, Hippy Bowl.  2.4.2020 . Photo: H Thamm

Our snowpack structure contains weak layers formed in January, before the storms last week.  Our testing shows these layers are becoming more stubborn but still possible for a human to trigger a large avalanche in these layers 2-3′ down in the snowpack.  Yesterday An observer suspected an avalanche was initiated within one of these layers.  With time and our current warming trend, the chances increase for the top 2′ of snow to consolidate and become more cohesive.  Current and trending warmer temperatures could create a more distinct slab above these weak layers.

Additionally, If a wind slab is triggered, it could step down to initiate one of these layers deeper within the snowpack.

Loose Snow Avalanches:  On steep slopes with unconsolidated snow, watch for easily triggered loose snow sluffs.