Learning Lessons

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There have been 4 excursions to ski the Pine Creek Basin area that are close enough in time and location to form an unintentional experiment testing snow stability, holding some variables steady and changing others resulting in differing outcomes. What patterns can be seen?

First, the ski trips:
  • Trip 1, Mike Spencer Pk, 3.5 miles East of Pine Creek, skied 2/3/10, 10AM-3PM, 8400-6800′ skied, N-NE aspect, 4 skiers, 4-6′ snow, sunny AM-overcast/snowing PM, temps 5AM-23, 11AM-39, 5PM-30 (from Pine Creek Basin Snotel @ 6,720′)
  • Trip 2, Stouts Mt, 2 miles West of PC, skied 2/6/10, 10AM-4PM, 8600-6600′ skied, S-SE aspect, 4 skiers, 3-5′ snow, clearing AM-sunny PM, temps 5AM-27, 11AM-37, 5PM-25 (from PCBS @ 6,720′)

 

  • Trip 3, Girls Camp Bowl, .75 miles West of PC, skied 2/6/10, 3PM-6PM, 7200-6600′ skied, NE aspect, 6 skiers, 3-5′ snow, clearing AM-sunny PM, temps 5AM-27, 11AM-37, 5PM-25 (from PCBS @6,720′)

 

  • Trip 4, Girls Camp Bowl, .75 miles West of PC, skied 2/7/10, 11AM-1PM, 6800-6600′ skied, NE aspect, 2 skiers, 3-5′ snow, sunny AM and PM, temps 5AM-14, 11AM-30, 5PM-20(from PCBS @ 6,720′)

 

All of the terrain was of the same basic character; open trees, glades and drainages and of about the same slope angles, ranging from 25-40 degrees.

Second, the tests:
  • Trip 1, 3 pits showed the reactive layer to be buried surface hoar 8-12″ down, sheared Q2 at 7 taps at 37 degrees, sheared Q2 in mid teens taps on 28-31 degree slopes but no propagation in extended column. The over-laying snow was newly fallen, light fluff(no slab)
  • Trip 2, 2 pits showed layers and slabs but no shear by 30 taps. The surface snow was moistening with the days heat and sunlight.

 

  • Trip 3, 1 pit showed reactive layer shearing at 7 taps.

 

  • Trip 4, 2 pits showed reactive layer to be older buried surface hoar about 2′ deep, sheared Q2 at 25 taps

 

Third, the results:

  • Trip 1, 2 laps skied uneventfully, no sluffs, whumps, cracking, no signs of instability
  • Trip 2, 1 lap skied uneventfully, saw new, small wet slides and rollers, beginnings of wet instabilities

 

  • Trip 3, 1 lap skied with 4 skiers triggering slab breakouts with 8-14″ crowns causing 2, 50-70′ wide slides with 200-300′ runout of debris.

 

  • Trip 4, 1 lap skied uneventfully, no signs of new instabilities

 

Fourth, conclusions:

  • Trip 1, reactive layer in snowpack in the RED zone on angles above 35 degrees, in the YELLOW zone on angles less than 32 degrees. The skied terrain was mostly under 35 degrees, the slope was relatively uniform with few rollovers(convexities) and we crossed out of one minor drainage, there was no slab on the reactive layer, just fluffy new snow. The day, although warming turned overcast during the descent with little to no wind. We skied conservative lines based on the tests
  • Trip 2, GREEN zone conditions in our tests but the S exposure and sun quickly warmed the snow and early sign of wet instabilities hurried us along. If we had an advantage, it is that this aspect has already been warmed and cooled several times, somewhat stabilizing the slap and it did not have the buried surface hoar found on the northerly slopes. We did cross around and over rollovers but tried to limit them, we did ski down a drainage that could have proved dangerous as a terrain trap; a little later in the day or a bit warmer and it could have been a big problem. Our route selection could have been better.

 

  • Trip 3, RED zone with this test, slope angles averaging steeper than the first 2 trips, many rollovers and a minor drainage on left side of descent, more skiers, late on a warm day that stressed the reactive layer and it did fail on rollovers in the terrain. The fact that the skiers triggered the slides and were therefore at the top of it and that the slab was relatively thin prevented more serious consequences. They moved to an area of lesser slope angle and fewer convexities and skied out.

 

  • Trip 4, Overnight cold temperatures settled the reactive layer into the GREEN zone on the same slopes as Trip 3. Stayed off the reorganizing snowpack on this slope and left while it was still cold.

 

Fifth, lessons:

  • heed the tests results
  • know the instability

 

  • heed new stress on the snowpack, in this case rapid warming

 

  • avoid convexities and drainages when the tests indicate RED to YELLOW conditions

 

I know looking at these recent, closely spaced trips with differing results and looking for patterns is helping me understand what I do well and what I need to do differently.

Please feel free to make corrections or add observations or call me a knucklehead for that matter!
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9 responses to “Learning Lessons

  1. >knucklehead…Okay, next i want to see a line chart and a pie graph…lol! And to think you only had an hour for lunch today! Great editorlial piece, Turbo! It is helpful to see the basics from several of our recent trips. Nice work.In all seriousness now; this is what i had invisioned this site to be, locals learning from, sharing with, and supporting one another to build a unified, healthy, and safety minded backcountry ski and snowboard community. This is a hot topic, not because any of us are pointing fingers or laying blame to any decisions made, but rather to learn from these events and figure out how they factor in to our backcountry habits. Like Turbo said in a previous comment, "we all want to be safe and come home at night." I hope there hasn't been any offense taken by our desire to try and learn the how's and why's. Collectively we can all contribute to each others success by sharing our thoughts and ideas. Thanks to all of you who have participated on this site and have shared your knowledge, stoke, and information.

  2. >I agree with Dean, Nice job Turbo. I think it covers everything nicely! I feel I have learned a ton from all of this, not just visiting the site but more visiting about it. Reevaluating our practices and observations. It enforces some of our current practices and adds some new ones! This website is a valuable tool and glad to have it thanks to Mean Dean. Now, LET'S GO SKIING! or ice climbing……..

  3. >Um, can I call Dean a knucklehead? Just thought that if the door was open…Scott, thanks for taking the time to help me dig a pit. Thanks for helping me understand what the results ment. I am good at watching you guys do the investigaion work, but it is about time I help carry the load.Justin and Beth, still waiting till we can meet up and do some skiing! Lets make plans soon.

  4. >"In some areas, a buried surface hoar layer one to two feet in depth also persists. This layer failed on the sixth skier to cross an east-northeast facing slope at an elevation of 8,500 feet in the Snake River Range on Saturday". This quote is from today's BT avy 5 PM forecast….

  5. >Great job Turbo!I like having all the info I can get. The Teton Avy forcast doesn't even do as good as job as you. It is nice to see it in the field and then have the results to review and let the conclusions sink in. Thanks a bunch!

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