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Author Topic: It slid last week so it's good…right?  (Read 24949 times)
peteyboy
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It slid last week so it's good…right?
« on: 03/06/14, 07:24 AM »

Hoping to start a knowledgeable discussion about decision making regarding the safety of a slope that has knowingly avalanched during a recent storm cycle on top of a resilient crust.  Here's our recent representative scenario:  New snow on an old crust.  Cold temps throughout.  Known poor bond; as storm total is building, the new snow is gaining cohesion.  Avalanche rating risk is high, all kinds of signs of the layer being highly reactive.  Shooting cracks in the trees, tons of whoomphing, even large remote triggers.  The whole tree of red lights.  We skied (on the very knowledgeable advice of the owner guide of the area we return to every year) a zone where he had ski cut and slid each vulnerable shot earlier in the storm cycle.  But now 40 to 80 or more cm on top of that in less than a week.  Skied every shot with no signs of instability whatsoever.
For our decision making, I wonder about slide activity on a mature crust: how well and for how long/much new snow at what speed/wind/temps can we trust that we won't just have a shallower cohesive new slab on the same poor bond?  Really an issue for when there is rapid reloading like we just had.  I realize that buried surface hoar crystals will be wiped out by avalanching the slope, but the crust remains.  Not looking for mathematical answers, just to generate thought and comment.
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wolfs
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Re: It slid last week so it's good…right?
« Reply #1 on: 03/06/14, 06:44 PM »

Anecdotally, I have had experiences in the Crystal BC where it was areas that had recently slid that were more prone to releasing their most-recent slabs than were areas very nearby that had not slid. Could see slightly buried debris piles beneath such slides as clues. Hypothesis is the smooth scour of the previous slide had made the underside of that slab even less likely to bond to the base, and more able to obey gravity's call when it was separated or tweaked by a ski cut. On the plus side chances are lesser that it would step down to next layer beneath scour. Maybe, subjective on how much "new" slab there is, as to whether a slid slope is safer, or not?
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T. Eastman
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Re: It slid last week so it's good…right?
« Reply #2 on: 03/07/14, 07:59 AM »

A slide can create a slick bed surface for subsequent snow falls.  This is likely why some tracks are frequent performers.
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maximusj
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Re: It slid last week so it's good…right?
« Reply #3 on: 03/07/14, 11:25 AM »

I think that you have to be wary with this... avalanching can (and often does) hit the reset switch, but if a slide occurs on a crust and the next snow event does not bond well to the crust, you are back where you started.

Here is a short discussion from The Avalanche Review. It references a continental snowpack, but the points are valid here as well - there is no silver bullet.

http://www.avalanche.org/moonstone/Forecasting/ResettingtheSnowpack.TAR28.4.pdf
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freeski
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Re: It slid last week so it's good…right?
« Reply #4 on: 03/08/14, 12:43 PM »

The skier triggered slope in Liberty Bowl, reported in the Jan. TRs, did not slide after the next loading event. However the rest of the slide areas along and under that skiers left side wall went natural down to the same crust layer. The path on skiers left, halfway up the the cornice ridge col face, showed an under cut and zig zag  pattern all along side crown wall, indicating deeper layer of rotten snow. That crown ran diaganal to the fall line and down.
« Last Edit: 03/08/14, 01:44 PM by freeskiguy » Logged

two sets of principles. They are the principles of power and privilege and the principles of truth and justice. If you pursue truth and justice it will always mean a diminution of power and privilege. If you pursue power and privilege, it will always be at the expense of truth and justice
C Hedges
freeski
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Re: It slid last week so it's good…right?
« Reply #5 on: 03/08/14, 01:21 PM »

The  storm that triggered the naturals came in warm and ended cold and conditions  were not favorable to surface hoar growth just prior to that storm meaning that either that there was either no sf on the bed surface, any sf  was morphed  or not enough loading had yet occured  to re-trigger a natural on the old bed surface. After the next loading event heli-ski had started and the guides ski cut along the deposition zones close to the wall, no slides and looks like good skiing was had by all. No old crown lines were visible.
« Last Edit: 03/08/14, 04:06 PM by freeskiguy » Logged

two sets of principles. They are the principles of power and privilege and the principles of truth and justice. If you pursue truth and justice it will always mean a diminution of power and privilege. If you pursue power and privilege, it will always be at the expense of truth and justice
C Hedges
freeski
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Re: It slid last week so it's good…right?
« Reply #6 on: 03/08/14, 02:20 PM »

Moral-your life, your risk, your decision. What knowledge do you have, what observations have you made? And still....last Sunday, a young lady asked me if the slope i had just ski cut was safe to ski and i told her that there were.... ''no guarantees''. The ski cut was made on a 40 degree roll, previous two day warming produced some roller balling and crust and now with 1' new, low density snow,with 5'' wind slab, no results. She wisely choose the conservative line in the face of uncertainty. I don't let people differ their risk to me, no matter how much i think i know. How else are they going to make their own calls?
« Last Edit: 03/08/14, 04:15 PM by freeskiguy » Logged

two sets of principles. They are the principles of power and privilege and the principles of truth and justice. If you pursue truth and justice it will always mean a diminution of power and privilege. If you pursue power and privilege, it will always be at the expense of truth and justice
C Hedges
rlsg
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Re: It slid last week so it's good…right?
« Reply #7 on: 03/08/14, 03:21 PM »

Ten four that frsg...
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peteyboy
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Re: It slid last week so it's good…right?
« Reply #8 on: 03/08/14, 11:40 PM »

That's why I feel we got lucky.  But I posted this because I have found this to be a fairly pervasive opinion point of slope safety - much like "it gets skied a lot".
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Charlie Hagedorn
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Re: It slid last week so it's good…right?
« Reply #9 on: 03/09/14, 11:50 AM »

It's clear from inbounds ski area operations that sufficient avalanche control work is capable of rendering normally avalanche prone slopes safe-enough to sustain ski area operations even in deep storm conditions, so it's possible that your guide was correct. Making expert calls is the realm of experts; some will argue that there are no experts.

Caveat skier.
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freeski
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Re: It slid last week so it's good…right?
« Reply #10 on: 03/09/14, 12:20 PM »

Yea but they re-bomb those slopes or ski cut them after a new storm loading event prior to opening the area. Sometimes it slides, sometimes it doesn't. If they, the experts truely knew whether or not a slope was safe, why waste the cash and place even more toxic chemical explosive residue into the enviornment? I think that i have offered factual proof here on tay that some commerical guides, your experts coming out of ski area patrols, hide their client related avy incidents. This creates a false sense that the experts know what they are doing and does not further the goals of education or client safety.
« Last Edit: 03/09/14, 02:18 PM by freeskiguy » Logged

two sets of principles. They are the principles of power and privilege and the principles of truth and justice. If you pursue truth and justice it will always mean a diminution of power and privilege. If you pursue power and privilege, it will always be at the expense of truth and justice
C Hedges
davep
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Re: It slid last week so it's good…right?
« Reply #11 on: 03/10/14, 10:47 AM »

Below is a video of "Employee housing" going big yesterday at Crystal.    I saw large crowns and slides down to the old/bad layer in Niagras/O-Meadows nearby when this terrain opened a few weeks ago.  I didn't notice big crowns in EH.   Did EH slide down to that pre-storm layer, can't say.   Just wanted to point out that this is a slope regularly controlled by experts and people have been skiing it for weeks.  But conditions changed (ie. rain, warm), so yesterday control work produced different results.

http://youtu.be/Yxi8aWWg3n0
« Last Edit: 03/10/14, 10:52 AM by davep » Logged
snoqpass
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Re: It slid last week so it's good…right?
« Reply #12 on: 03/10/14, 03:48 PM »

Yea but they re-bomb those slopes or ski cut them after a new storm loading event prior to opening the area. Sometimes it slides, sometimes it doesn't. If they, the experts truely knew whether or not a slope was safe, why waste the cash and place even more toxic chemical explosive residue into the enviornment? I think that i have offered factual proof here on tay that some commerical guides, your experts coming out of ski area patrols, hide their client related avy incidents. This creates a false sense that the experts know what they are doing and does not further the goals of education or client safety.
Because no "Expert" is going to point at slope in the winter and say it's 100% safe
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rlsg
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Re: It slid last week so it's good…right?
« Reply #13 on: 03/10/14, 05:45 PM »

I've had "experts" tell me a slope was 100 % safe.  I skied it but that was because I thought it was "probably" "pretty" safe.  A few years later up there way north of the boarder at the same place, "experts" were guiding a bunch of folks and a bunch bit it...I assume they were marching fairly close just like on my trip.  No Way any  body knows when a slope is "absolutely" stable;  at best the calculation of somewhere near "low" risk is possible....everybody should be "calculating their own risk" and not leaving this to somebody else, IMHO...
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snoqpass
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Re: It slid last week so it's good…right?
« Reply #14 on: 03/10/14, 07:58 PM »

The use of the word expert in this sport is over used
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Joedabaker
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Re: It slid last week so it's good…right?
« Reply #15 on: 03/10/14, 08:21 PM »

So much for the skier compaction theory ie...Hamburger Hill Chair 6 Crystal.
A few years back there was an eye opening picture of the Moguls under the Glacier chair at Blackcomb where the slope had given out to a similar type avalanche. That is an eye opener when hard pack moguls pull out like a slab avalanche!
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T. Eastman
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Re: It slid last week so it's good…right?
« Reply #16 on: 03/10/14, 10:18 PM »

Quote
So much for the skier compaction theory ie...Hamburger Hill Chair 6 Crystal.
A few years back there was an eye opening picture of the Moguls under the Glacier chair at Blackcomb where the slope had given out to a similar type avalanche. That is an eye opener when hard pack moguls pull out like a slab avalanche!

Such slides occur on a fairly frequent basis, nothing new here...

... read up and don't assume that snow gets better through the season.
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Joedabaker
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Re: It slid last week so it's good…right?
« Reply #17 on: 03/11/14, 06:41 PM »

Such slides occur on a fairly frequent basis, nothing new here...

... read up and don't assume that snow gets better through the season.
I don't see it very often on packed runs maybe you can provide more reading fodder.
Frequently maybe deeper into spring but we got much rain that it accelerated that progression of saturation. Kinda the perfect set up with the crap layer. Often times DOT comes across this in late April or May on their highway opening work.
« Last Edit: 03/11/14, 06:57 PM by Joedabaker » Logged
freeski
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Re: It slid last week so it's good…right?
« Reply #18 on: 03/11/14, 08:57 PM »

With enough explosive force applied, no snow is stable. Take mt. Saint helen's, may 1980, for example. The op said that all the red flags were flying and the guide/ owner said go for it. Why do they want people to differ risk to them but still have a signed liability waiver? It's common to see avy courses bunched up, doing transceiver searches in major avy paths or ski clients at 5 second intervals. Sure the risk may be perceived as low at the time or maybe try and thread the ''trigger point'' needle on a high risk day, but what message does this send to the student or client? It's ok to go against best practice if a guide says it's ok? I guess i just don't understand this behavior and need enlightenment. Why do some guides take clients into avy terrain on high risk days? 
« Last Edit: 03/11/14, 09:13 PM by freeskiguy » Logged

two sets of principles. They are the principles of power and privilege and the principles of truth and justice. If you pursue truth and justice it will always mean a diminution of power and privilege. If you pursue power and privilege, it will always be at the expense of truth and justice
C Hedges
Joedabaker
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Re: It slid last week so it's good…right?
« Reply #19 on: 03/11/14, 10:49 PM »

Ha found it after some searching...
Great example of skier compacted area that pulled out at Blackcomb Heavenly Valley run lookers left of Glacier Basin Chair in May 2008.
It is more dramatic with the cat track and moguls in the picture...strikes home that it can happen even in the most compacted zone.

Many years ago I had seen some spring pull outs at Chinook Pass that were natural which had 3ft crowns and it really gave me an anything can happen feeling.


* heavenly_basin.jpg (25.88 KB, 575x336 - viewed 1245 times.)
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freeski
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Re: It slid last week so it's good…right?
« Reply #20 on: 03/12/14, 08:10 AM »

Lots of miss information floating around. Recent observations for our area,east NC were that no step down had occured during last cycle. I guess the climax avy that left a pile on hwy 20, cutthoat path doesn't count? Or how about the whole wall on Pica peak that lost it's entire snow load,except the hanging cornice. That mass of snow did not step down pica bowl,however.  Watch out for generalized statements based upon generalized observations for a generalized area.
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two sets of principles. They are the principles of power and privilege and the principles of truth and justice. If you pursue truth and justice it will always mean a diminution of power and privilege. If you pursue power and privilege, it will always be at the expense of truth and justice
C Hedges
Jeff_Ward
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Re: It slid last week so it's good…right?
« Reply #21 on: 03/12/14, 06:16 PM »

Lots of miss information floating around. Recent observations for our area,east NC were that no step down had occured during last cycle. I guess the climax avy that left a pile on hwy 20, cutthoat path doesn't count? Or how about the whole wall on Pica peak that lost it's entire snow load,except the hanging cornice. That mass of snow did not step down pica bowl,however.  Watch out for generalized statements based upon generalized observations for a generalized area.
I hate to continue the thread drift but I wanted to address something said by freeskiguy.  I agree that there has been a lot of misinformation floating around but I think we probably disagree on where it is coming from.  When you quote past avalanche forecasts you should be careful to look at when the forecast was put out.  You paraphrase a forecast that stated "no step down had occured [sic] during the last cycle".  That particular forecast was put out on Thursday March 6th, which was well before the last avalanche cycle that caused all of the avalanches you refer to.  I can understand an honest mistake but with your track record I felt obligated to correct your observation.   

For those of you that are wondering what happened with the most current avalanche cycle, I have been out the last three days (Sunday - Tuesday) traveling through a lot of the terrain around Washington Pass to observe these avalanches, including a day with one of the NWAC forecasters.  There was a large natural cycle on Saturday but we observed only three avalanches that were deeper than the recent storm snow.  One large avalanche that has run down to bare glacial ice multiple times this year (north aspect 8,400').  One relatively small pocket on a steep hanging slab on an east aspect near 7,800', and the third avalanche was on a solar aspect that was difficult to assess whether or not it was more than just storm snow.  Not to downplay these large avalanches but considering the weather event that caused them I would have expected more. 

The other avalanches freeskiguy refers to did not step down to the deeper (late Jan/early Feb) layers from what we observed.  They were large but that would be expected considering the amount of storm snow, warm temperatures and the type of terrain these avalanches came out of (very steep, rocky terrain).  Personally, I think NWAC did a good job of forecasting this avalanche cycle.  If you go back and look at the forecast for last weekend it was about as accurate as you could hope considering they have such a large area to forecast for and only one forecaster a day to accomplish that huge task.  I know I'm biased because I work as an observer for NWAC but to have someone imply that professional observers and NWAC forecasters are intentionally giving the public misinformation is very offensive.   

« Last Edit: 03/12/14, 08:37 PM by Jeff_Ward » Logged
freeski
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Re: It slid last week so it's good…right?
« Reply #22 on: 03/13/14, 11:38 AM »

I hate to continue the thread drift but I wanted to address something said by freeskiguy.  I agree that there has been a lot of misinformation floating around but I think we probably disagree on where it is coming from.  When you quote past avalanche forecasts you should be careful to look at when the forecast was put out.  You paraphrase a forecast that stated "no step down had occured [sic] during the last cycle".  That particular forecast was put out on Thursday March 6th, which was well before the last avalanche cycle that caused all of the avalanches you refer to.  I can understand an honest mistake but with your track record I felt obligated to correct your observation.   

For those of you that are wondering what happened with the most current avalanche cycle, I have been out the last three days (Sunday - Tuesday) traveling through a lot of the terrain around Washington Pass to observe these avalanches, including a day with one of the NWAC forecasters.  There was a large natural cycle on Saturday but we observed only three avalanches that were deeper than the recent storm snow.  One large avalanche that has run down to bare glacial ice multiple times this year (north aspect 8,400').  One relatively small pocket on a steep hanging slab on an east aspect near 7,800', and the third avalanche was on a solar aspect that was difficult to assess whether or not it was more than just storm snow.  Not to downplay these large avalanches but considering the weather event that caused them I would have expected more. 

The other avalanches freeskiguy refers to did not step down to the deeper (late Jan/early Feb) layers from what we observed.  They were large but that would be expected considering the amount of storm snow, warm temperatures and the type of terrain these avalanches came out of (very steep, rocky terrain).  Personally, I think NWAC did a good job of forecasting this avalanche cycle.  If you go back and look at the forecast for last weekend it was about as accurate as you could hope considering they have such a large area to forecast for and only one forecaster a day to accomplish that huge task.  I know I'm biased because I work as an observer for NWAC but to have someone imply that professional observers and NWAC forecasters are intentionally giving the public misinformation is very offensive.   


where did i say or imply that nwac was intentionally miss informing the public? Maybe that observation exists within your own bias. Lets deal with the facts like, i did not read that nwac report you say that i paraphased. It is also a matter of public record that the FS took permit action to enforce permitted terrain boundaries for two outfitters in our area. I was a part of that action as well as other safety related conflicts resolution. I stand by my ''track record''.  
« Last Edit: 03/13/14, 12:22 PM by freeskiguy » Logged

two sets of principles. They are the principles of power and privilege and the principles of truth and justice. If you pursue truth and justice it will always mean a diminution of power and privilege. If you pursue power and privilege, it will always be at the expense of truth and justice
C Hedges
Jeff_Ward
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Re: It slid last week so it's good…right?
« Reply #23 on: 03/17/14, 11:39 AM »

where did i say or imply that nwac was intentionally miss informing the public? Maybe that observation exists within your own bias. Lets deal with the facts like, i did not read that nwac report you say that i paraphased. It is also a matter of public record that the FS took permit action to enforce permitted terrain boundaries for two outfitters in our area. I was a part of that action as well as other safety related conflicts resolution. I stand by my ''track record''.  
I'm sorry about making assumptions about what you were referring to.  What you wrote made it sound like the "miss information" was coming from professional observations made in the Washington Pass area.  What information were you referring to?
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Splitter
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Re: It slid last week so it's good…right?
« Reply #24 on: 03/17/14, 08:41 PM »

where did i say or imply that nwac was intentionally miss informing the public? Maybe that observation exists within your own bias. Lets deal with the facts like, i did not read that nwac report you say that i paraphased. It is also a matter of public record that the FS took permit action to enforce permitted terrain boundaries for two outfitters in our area. I was a part of that action as well as other safety related conflicts resolution. I stand by my ''track record''.  

It is just that your track record is so often antagonistic. I am going to agree with you that organizations have made mistakes and even possibly overstepped boundaries intententionally. Members of the public have in the past and will continue in the future to make poor decisions.

If your true goal is education you might consider that at least one person stops hearing your message when it takes the tone of zealous evangelism.
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