Turnagain Pass

Recent Avalanche Activity:
There were several small to medium sized human triggered wind/storm slab avalanches yesterday. There was also evidence of a handful of natural slabs and sluffs occurring mid-storm on 2/7. Several observations were sent in with more detail on yesterday’s activity – check them out!

Sunburst

• One skier triggered soft slab – 18-30″ deep, ~50′ wide and running ~1100 ft. (See Photo below)

Tincan – At least 5, but up to 11, small storm/wind slab pockets remotely triggered by skiers. (See photos below)

• 2 small soft slabs in Tincan Common Bowl (Kitchen Wall) remotely triggered from up track
• 2 small soft slabs on lower south facing rolling terrain below up track, also thought to be remotely triggered
• 1 small wind slab on CFR 
• 1 larger soft slab in Hippy Bowl with several small slabs releasing below the lower rollover

Seattle Ridge

• Several natural storm slabs and sluffing occurring mid-storm

Sunburst skier triggered soft slab (WSW, 3,650′). Thanks to the party for sending in this photo – check out their additional photos with a write up on triggering the slide HERE.

Tincan small soft slabs on the lower south facing rollovers below the common up track (SW facing, 2,500′). *Note the crack extending from one pocket to the other intersecting the ski track. (Photo: Mark Norquist)
 

Tincan’s Hippy Bowl larger soft slab (SW, 3,300′). Note the several pockets below the rollover. These are believed to be remotely triggered from above.

Today’s primary concern – Persisting storm/wind slabs:

There is much uncertainly with how the storm snow is bonding with the pre-existing surfaces. There were areas yesterday (i.e. Tincan) where the new snow was quite active and people were able to remotely trigger avalanches from over 100′ away. Yet on Sunburst, only one slide occurred even though many people were skiing/snowboarding. At elevations around 3,000′ and below surface hoar exists between the old hard crust and the storm snow. Additionally, above 3,000′ there is a facet/crust combination that exists below the storm snow (responsible for the Sunburst slide). The trick is the new snow was still unconsolidated enough yesterday that slides were mainly confined to small pockets. With settlement overnight allowing the new snow to become more of a slab over these persistent grain types, we could see remote triggering again today along with wider propagation and subsequent larger avalanche activity. 

Quick hand pits and keeping an eye out for cracking and collapsing are good ways to assess the new snow/old snow bonding. These clues are hard to get while on the up track so stepping off it now and then may tell you something. To avoid any avalanche issues today you can steer clear of slopes steeper than 30 degrees.

Once again, we are mentioning the deep slab concern that exists at the upper most elevations (above 3-3,500′). This problem has shown signs of inactivity for the time being and the probability of triggering a deep slab is low yet, the consequences are high. It’s possible another load, or just the right trigger (cornice, a person on a thin spot or a large group of people), could initiate a failure in the weak snow at the base of the pack (basal facets) causing a large full-depth slide.

Below is a cross section of the pack at the site of the Sunburst avalanche mentioned above. You can see the basal facets sitting under the pack that are responsible for the lingering deep slab concern.