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Author Topic: Snoqualmie Pass - Kendall Stumps - 12.31.08  (Read 6026 times)
Stugie
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Snoqualmie Pass - Kendall Stumps - 12.31.08
« on: 01/02/09, 10:49 AM »

We decided to leave the comfort of the terrain we knew well, mostly because with the avy danger as high as it is, these areas are not so comforting.

We decided to stick to lower angles in the trees, and finally decided a quick tour in Snoqualmie would be nice.



I'll skip the hoopla and get to the meat.  We dug a pit on a 30*, S facing slope at about 4500'.  The snowpack was definitely being loaded, and our pit was approx. 7' deep.  Significant layering was a horribly bonded granular layer about 4" down, and then at 2' was a faceted crust.  Also apparent was the crust at or near the ground.  We then dug a rouchblock and it failed at 4" from the touch of my ski.  I then stood and gave one small flex and the block failed at 2'.  Some scary results, even in an area usually considered to be relatively safe.

We skied safe lines through the trees.  Kyle might have some more pics to add, and possibly video of our rouchblock.



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Kyle Miller
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Re: Snoqualmie Pass - Kendall Stumps - 12.31.08
« Reply #1 on: 01/02/09, 12:01 PM »

At least the snowpit was interesting
heres the video


* DSC06086_copy.jpg (112.16 KB, 600x800 - viewed 994 times.)
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Rusty Knees
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Re: Snoqualmie Pass - Kendall Stumps - 12.31.08
« Reply #2 on: 01/02/09, 01:17 PM »

Nice info, you guys.  Thanks for the video, too!  If a picture is worth a thousand, a vid must be worth a mil. 

What will make either the 4" or that 2 foot layer safe?  Does it bond over time? 
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Aaron_Riggs
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Re: Snoqualmie Pass - Kendall Stumps - 12.31.08
« Reply #3 on: 01/02/09, 03:07 PM »

Thanks for the visuals.

What will make either the 4" or that 2 foot layer safe?  Does it bond over time? 

I've been thinking about this too. Aside from a big warmup helping to stabilize the snowpack, the overall weight of new accumulation should help too.

Someone posted a very interesting article or chart on this subject (weight of new accumulation) in the last year about how the deeper the snowpack gets, the less stress a skier puts on a buried layer. I searched for it but could not find it. I would like to read it again if anyone remembers where that post is.
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Stugie
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Re: Snoqualmie Pass - Kendall Stumps - 12.31.08
« Reply #4 on: 01/02/09, 09:28 PM »

What will make either the 4" or that 2 foot layer safe?  Does it bond over time? 

I have no idea for sure.  I think Aaron hit it right in that a big warmup might do the trick.  I would assume that the buried layers might bond with additional pressure from added weight, but I also remember seeing pics of an avy near Snow Lake last year with like an 8' crown.  Slides like that make me think that isn't necessarily a good rule of thumb.

I think that, in light of a good warm-up, a rain might also help with bonding.  The snow on our first layer that slid was just on the verge of rain, but felt more like granuals of sleet/hail.  Fun for skiing, crap for layering and bonding.

*ps* - tough to see in the vid, but the first 'go' is from my one ski barely touching the snowpack.  The second 'go' is after I plant both skis on the block and do a small flex.
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CookieMonster
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Re: Snoqualmie Pass - Kendall Stumps - 12.31.08
« Reply #5 on: 01/03/09, 09:18 AM »

Thanks for sharing the video - this is fantastic information. Question: the first failure was in new snow. Looked like the surface snow didn't quite have enough cohesion to form a soft slab ( but the failure was so fast I couldn't really tell ). What was the shear quality of the second failure? The second layer definitely had enough cohesion to form a soft slab but the shear, while sudden, doesn't look very clean in the video. ( Of course maybe the shear quality doesn't matter because Q1 and Q2 are supposed to have the same relevance for skier triggering. )

Also, do you have ( or can you reconstruct ) a basic profile of the pit ( maybe including hand-hardness, layer thickness, and grain type )? Just basic would be great ... nothing complicated. With clear evidence of high instability ( the NWAC bulletin + your slope side instability tests that revealed significant instability ) why did you choose this terrain? I know there is a lot of theory or proof on the anchoring effects of trees but the trees in the pictures are not really thick enough to prevent avalanching. I understand this was probably a small slope but it certainly looks large enough to produce size 2 avalanches. ( These questions are simple curiosity and not an attempt to second guess! ) Thanks again for taking the time to get outside and bring the information back.
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savegondor
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Re: Snoqualmie Pass - Kendall Stumps - 12.31.08
« Reply #6 on: 01/03/09, 03:53 PM »

At least the snowpit was interesting
heres the video


illustrating why on that day, bc was BAD!!!

SCARY SCARY SCARY.  your vid shows nearly no bonding on those layers.
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Stugie
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Re: Snoqualmie Pass - Kendall Stumps - 12.31.08
« Reply #7 on: 01/05/09, 09:27 AM »

Question: the first failure was in new snow. Looked like the surface snow didn't quite have enough cohesion to form a soft slab ( but the failure was so fast I couldn't really tell ). What was the shear quality of the second failure? The second layer definitely had enough cohesion to form a soft slab but the shear, while sudden, doesn't look very clean in the video. ( Of course maybe the shear quality doesn't matter because Q1 and Q2 are supposed to have the same relevance for skier triggering. )

Sheer quality of the first layer was definitely Q2 (some of my weight was distributed over the first ski, but not all of it - hence the Q2 rating), but the more cohesive layer you refer to was about Q3 - one good flex.

Also, do you have ( or can you reconstruct ) a basic profile of the pit ( maybe including hand-hardness, layer thickness, and grain type )? Just basic would be great ... nothing complicated. With clear evidence of high instability ( the NWAC bulletin + your slope side instability tests that revealed significant instability ) why did you choose this terrain?

Wow, okay.  If it helps, I'll put some grades to my laymen's terms -
We dug a pit on a 30*, S facing slope at about 4500'...our pit was approx. 7' deep.

The pit was about 7' deep on a 30 degree S facing slope at about 4500' elevation.

Significant layering was a horribly bonded granular layer about 4" down, and then at 2' was a faceted crust.  Also apparent was the crust at or near the ground.

The granular snow would obviously fall into being a "c" type crystal, and the layering where it sheared the second time was a layer consisting of "d" type crystals.  Again, this same "d" type was found at depth, near the ground.  A lot of the inbetween layering was "b" type.  Hardness/resistance was finger to a couple fingers depth for most layers except for the faceted crust, that was maybe pencil depth (I didn't have my pocket protector with me, so I'm guessing.)

We then dug a rouchblock and it failed at 4" from the touch of my ski. I then stood and gave one small flex and the block failed at 2'.

Again, laymen's terms for a Q2, and then Q3 shear quality.  Hope that helps.  I thought laymen's terms might be a little easier for people to understand.  I understand a lot of the snow talk, but I'm not formally trained either, so I'm not claiming any kind of expertise in the field.  I'm just out a lot, so I figured my info might be useful.  The isolated slope between a number of trees was used to test our Rutschblock, and not to ski.  Also, don't learn how to spell from me...I was informed I spelled Rutschblock wrong...I have many things to work on!  Cheesy

With clear evidence of high instability ( the NWAC bulletin + your slope side instability tests that revealed significant instability ) why did you choose this terrain? I know there is a lot of theory or proof on the anchoring effects of trees but the trees in the pictures are not really thick enough to prevent avalanching. I understand this was probably a small slope but it certainly looks large enough to produce size 2 avalanches. ( These questions are simple curiosity and not an attempt to second guess! ) Thanks again for taking the time to get outside and bring the information back.

We decided to stick to lower angles in the trees, and finally decided a quick tour in Snoqualmie would be nice.

Low angle, in the trees.  The trees looked liked varying types of conifers and judging from the size, appeared as if they would make suitable anchors, considering the slope we skied was lower angle (maybe 25*?) and further into the trees than that which we dug our pit/Rutschblock on.  I'm sorry my photos do not depict this.  There were a couple of open spots within the trees that might have slid at that angle, but not likely.  You don't know til you go.
« Last Edit: 01/05/09, 09:34 AM by Stugie » Logged

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CookieMonster
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Re: Snoqualmie Pass - Kendall Stumps - 12.31.08
« Reply #8 on: 01/05/09, 03:51 PM »

Thanks for the excellent information. I have been gathering information for on-going work in modeling snowpack instability on the computer. In a different post ( here on TAY ) I indicated that I wasn't sure about the distribution of instability, nor if it was as bad as some people think.

I wasn't taking issue with the NWAC forecast ... I'm trying to understand how instability is actually distributed rather than using rules of thumb from bulletins or individual skier reports. I need the big picture and the most recent cycle has provided lots of information. At first it seems like instability must worsen by elevation but my personal experience, along with reports of extreme instability at low elevations, has disproven this hypothesis.

The NWAC forecast, along with field reports from guides and high-quality information from local skiers such as yourself, has painted a very complex picture of the snowpack and of the distribution of instability across the Cascades. Certainly, despite very high instability in some locations, the trip reports and personal experiences I've had over the past two weeks have left me with many more questions than answers.

For example: I was out one afternoon, in the alpine, in heavily loaded snow and couldn't get results on any slope. Everything about the snow ( from feel and layers ) said that the snowpack should be highly reactive. Yet it was not. The vast differences in the descriptions of instability are interesting. Some people reported remotely triggering very large slides on low angle terrain while other people report very low instability and Q3 shear quality even in areas where instability is otherwise widespread ( such as your report from Kendall Stumps ). Thanks for taking the time, I do appreciate it. The extra information you provide is really helpful.

( Graphic is distribution of avalanche terrain at Chinook Pass. I'd like to find a way to visualize distribution of instability ... rendered over the actual terrain, if you will. Or failing that, I'd like to try and understand why highly unstable snow sometimes goes and sometimes doesn't. The snowpack reports from TAY members contain lots of clues but linking them together is extremely tricky. )


* chinook_pass_avalanche_paths_05.jpg (166.96 KB, 800x674 - viewed 604 times.)
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Stugie
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Re: Snoqualmie Pass - Kendall Stumps - 12.31.08
« Reply #9 on: 01/05/09, 09:41 PM »

That map is really cool...that'd be a sweet additional overlay for google earth!
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andyrew
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Re: Snoqualmie Pass - Kendall Stumps - 12.31.08
« Reply #10 on: 01/05/09, 10:57 PM »

That map is really cool...that'd be a sweet additional overlay for google earth!

No kidding!  Just earlier today I was thinking about how one could generate avalanche starting zones and runouts as an overlay to google earth or google maps using usgs digital elevation model data.  It would be way more useful for trip planning than trying to squint at contour lines on a 7.5' quad, and the DEM data is much higher resolution so you'd be able to see smaller features like benches.  I've got a little experience with the DEM data (it's actually quite simple to parse), but nothing with google maps or earth.  Where'd you get the map of Chinook Pass, CookieMonster?
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CookieMonster
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Re: Snoqualmie Pass - Kendall Stumps - 12.31.08
« Reply #11 on: 01/05/09, 11:55 PM »

I made that map of Chinook Pass with some custom software, DEM data from USGS, and orthographic imagery from University of Washington. The rendering is customized using a variety of graphics tricks. Mostly simple, some complicated. There are other useful and useless research images here:

http://www.scenomics.com/internal/accounts/richardm/avalanche/topics/images_01.htm
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Stugie
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Re: Snoqualmie Pass - Kendall Stumps - 12.31.08
« Reply #12 on: 01/06/09, 08:28 AM »

Holy crap!  So most of this programming jargon is WAY over my head, but I understand how to read the final maps (at least I think I do).  I would be really curious to see Granite Mtn. area and a few others that are pretty prone or reknowned for sliding.  You know Cookie Monster, if you need specific info from snow pits, rutschblocks, etc. for programming this kind of stuff (sheer levels, snow density, etc.), would it be possible to make a simple form we could fill out after some bc outings to help you out?  Charles might even make a link to it or sticky it for you if you wanted and asked him...
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CookieMonster
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Re: Snoqualmie Pass - Kendall Stumps - 12.31.08
« Reply #13 on: 01/06/09, 03:48 PM »

Most of those maps are easy to read so I assume that you're reading them correctly. These maps are great tools for aiding perception of exposure to avalanche terrain. But as a perceptual tool, they have several downsides: for example: non-avalanche terrain does not indicate safe terrain. Second, although the maps provide a very accurate depiction of which slopes are steep enough to avalanche, they don't integrate snowpack information. This is a nasty thorn.

Third, the middle ground terrain is subject to perceptual errors even if fairly absolute maps are provided. These perceptual errors are caused failing to evaluate terrain traps across different spatial scales. So a specific gully is a very specific terrain trap. But in some cases, this small gulley is inside a small valley and the small valley can also be a terrain trap ( even though it's likely to be regarded as a "terrain feature" ). The interaction between several levels of trapping features at multiple spatial scales is very tricky. Should a slope be considered more dangerous because it's directly connected to another very dangerous slope? What about slopes below dangerous slopes?

Mountain guides, and other very experienced mountain travelers definitely know how to read terrain in this manner. It's just very difficult to teach a computer how to do it. There are other issues as well such as line-of-sight traps and whether or not to warn about open slopes.

My earlier posts in this thread, and other posts throughout this messageboard, discuss the importance of using information relevant to the current situation. Information relevant to the current situation is absolutely critical and far more important than data from the avalanche bulletin with respect to decision-making. ( This is a characteristic of Bayesian revision; one piece of data, especially data from a low entropy class, can override all previous data and call for a complete revision of the forecast. Some people believe avalanche forecasting is a Bayesian activity. ) I'd like to be able to use these maps in conjunction with the results of slopeside instability tests and form a big-picture of instability, consequences, and alternate choices.

It would also be interesting to integrate "same day" snowpit data to help fill in blank spots. I'm not quite sure how to visualize the snowpit data graphically. There are many different theories about the spatial validity of a snow pit: some people say "no where else" some people say "slope" and some people say "drainage".

Your suggestions would be helpful indeed. I would also need fairly precise coordinates of the location in UTM and WGS84, such as from a GPS unit.

Also, it should go without saying that all this work is based on several hypotheses. It's not proven, it's not necessarily useful, and I'm not sure the direction it will take this winter.
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