|
|
|
|
|
|
Turns All Year Trip Reports
(1) Viewing these pages constitutes your acceptance of the Terms of Use.
(2) Disclaimer: the accuracy of information here is unknown, use at your own risk.
(3) Trip Report monthly boards: only actual trip report starts a new thread.
(4) Keep it civil and constructive - that is the norm here. |
|
|
|
|
Author
|
Topic: Avalanche Discussion (Read 11713 times)
|
burns-all-year
5Member
Offline
Posts: 98
|
Interesting discussion, but I'm not sure it says very much. The Cookie guy seems adept at tearing down the arguments of others...that seems to be his motivation. Seems to me that this is all just mental masturbation and one-upmanship. Maybe we could actually discuss some real snowpack/avalanche observations that occured in the past few days?
|
|
|
|
|
Logged
|
FAWNING ACOLYTE
|
|
|
garyabrill
Member
Offline
Posts: 488
|
I think you are off base here, Cookie Monster. I think you were the first one to mention the Durrand accident. Earlier I merely mentioned the winter of 2002-3 - as a classic example of snowpacks with persistent weaknesses.
Most recently Matt used La Traviata as such (an example), also. We were discussing persistent weak layers you will note if you read the thread more carefully.
The main point is that persistent weak layers require a different mind set than new snow instabilities because they are triggered and behave differently - in most cases - than new snow instabilities.
The current snowpack has potential to be troublesome and much more so if it snows enough in the near and intermediate future. Numerous trip reports and recent avalanche forecasts support this conclusion.
|
|
|
|
|
Logged
|
|
|
|
Mattski
Member
Offline
Posts: 102
|
Thank you Gary, I agree. My addition about trigger points relates to what you mentioned about the change in behavior of the snowpack with buried surface hoar in relation to trigger points. The Cement Basin avalanche had seven people on the slope and the last person triggered the avalanche on buried surface on a 25 degree slope leading into a 38 degree convexity.
Skykilo references this point, he skied the same area then Hummel followed with different results and consequences. Rudi had a lot of people out on the slope yet it was triggered on a 10 degree slope near the top of the ridge, where the snowpack was shallow enough for Kelly to impact the weak layer.
One of the surprise factors of avalanches class 2 and larger is the size, often catching people on lower angle terrain and propagating much wider than anticipated. I believe knowing the layer exists and results have occurred on it, should be a red flag to not test this when there are possible consequences. When other people ski a slope with these buried weak layers, that can create a negative feedback loop, if other people skied it then it is okay. This is true of early season snowbridges over crevasses as well.
I appreciate this discussion, it opens up awareness to the history that helps us shape our decisions with knowledge gained here.
|
|
|
|
|
Logged
|
|
|
|
skykilo
Member
Offline
Posts: 693
WWW
|
It's not just what you do; it's how you do it. There was a night-and-day difference between how Jason and I "skied" that slope. From personal experience with wet slides I'm effectively 100% sure that I would have been carried in a similar avalanche, had I treated that slope the way Jason did. I'm not sure why you insist that this is related to unpredictable triggering.
You're discussing an experience I witnessed firsthand and I think you're making an unwarranted and inaccurate conclusion. I'm not sure what the utility of that is. I don't think there was anything unpredictable about that particular slide.
My advice to anyone would be to always follow safe travel protocols; approach changes in the terrain, the aspect, and the slope angle with caution; and never trust second- or third-hand observations and conclusions. The situation on Fortress was easily preventable with these prescriptions.
|
|
|
|
|
Logged
|
|
|
|
garyabrill
Member
Offline
Posts: 488
|
Thank you Gary, I agree. My addition about trigger points relates to what you mentioned about the change in behavior of the snowpack with buried surface hoar in relation to trigger points. The Cement Basin avalanche had seven people on the slope and the last person triggered the avalanche on buried surface on a 25 degree slope leading into a 38 degree convexity.
Skykilo references this point, he skied the same area then Hummel followed with different results and consequences. Rudi had a lot of people out on the slope yet it was triggered on a 10 degree slope near the top of the ridge, where the snowpack was shallow enough for Kelly to impact the weak layer.
One of the surprise factors of avalanches class 2 and larger is the size, often catching people on lower angle terrain and propagating much wider than anticipated. I believe knowing the layer exists and results have occurred on it, should be a red flag to not test this when there are possible consequences.
I believe your words "not to test this when there are high consequences" don't mean that one shouldn't test or observe the snow but rather with high consequences one shouldn't bet one's life on the test results - am I right?
We should always observe the snowpack and make appropriate tests - if nothing more than to learn something for future use. But it is a lot different making a snowpack test for academic reasons than it is to make a snowpack test and then to bet your life on the results. When the consequences are high, I think it wiser to play it conservatively. With sufficiently deeply buried weak layers - Persistent Weak Layers - this is especially true. But that doesn't mean that observing the snowpack in a variety of ways isn't best practice. Otherwise one sets one's self up for the situation where one's perception of stability is for good stability when there may actually be isolated locations of instability.
I remember heli skiing once in the north cascades back around 1978. Good new snow and stability semed to be the rule. Then we came upon one particular slope and avalanche path that was 18" of new snow overlying classic depth hoar. Apparently this particular slope had avalanched to the ground early in the winter and then the shallow depth of the snowpack allowed for depth hoar formation. Although this is an unusual situation and in my experience west of the crest, in mid to late winter, unique, it still happened. At that point in my Cascade snowpack career I knew very little about the behavior of depth hoar - although I recognized it as such. Luckily it didn't slide as it was a big slope. In retrospect ( and maybe even at the time as I faintly recall) I believe the reason it didn't avalanche was probably that the overlying new snow wasn't sufficiently cohesive in that particular instance.
When other people ski a slope with these buried weak layers, that can create a negative feedback loop, if other people skied it then it is okay. This is true of early season snowbridges over crevasses as well.
I think that is true even in snowpacks absent persistent weaknesses. There seem to be two good points there: 1) In higher risk avalanche terrain and conditions avalanches can happen, and 2) Just because someone else has skied a slope doesn't mean it it safe.
Sky brings up another good point, that the precise line - micro routefinding - one takes can make a difference. I would just argue that with weak layers like facets and surface hoar in particular, knowing where that line is may be beyond human capability for most of us.
|
|
|
|
« Last Edit: 02/01/09, 08:02 AM by garyabrill »
|
Logged
|
|
|
|
Gregg_C
Member
Offline
Posts: 298
|
"My advice to anyone would be to always follow safe travel protocols; approach changes in the terrain, the aspect, and the slope angle with caution; and never trust second- or third-hand observations and conclusions. "
I could not agree more with Sky, he nailed it precisely. I would emphasis the part about never trusting second-or third-hand observations and conclusions--including this thread. Buried layers?, Ice glazing? In the Cascades! You have got to be kidding. Maybe as a short term issue but very rarely is it a concern over the course of the winter. Our dramatic temperature swings take care of that
I doubt the hundreds of people that were just killing the Baker backcountry yesterday followed this thread. They talked to the ski patrol, "great right side up snowfall with super bonding to the crust" and sniffed out the snowpack for themselves.
I skied 15 days in the Selkirks the winter of the accidents and had a great time. If we listened to half the experts sitting on their computer making conjectures we would have stayed home. One day Troy Jungen and I and others were heading out and got stopped by a CBC film crew. The next day's story was, "Skiers risk death in killer backcountry". No, we told them that sticking to good terrain was the key to a successful and safe trip.
I have the very high respect for the experts on this website who share their knowledge, it just think in this case they are making judgements about the snowpack that don't fit the reality for those of us putting skiis/snowboards to snow.
Here is my advice for anyone wanting to learn about staying safe in the backcountry: Before you spend money on a course, read all the reports and spend time digging pits, just beg someone who has been staying alive for 30 plus years to take you out and teach you how to read terrain and routefind. Perhaps that is simplistic, but it has worked for me. That should be the most important part about avalance safety.
|
|
|
|
|
Logged
|
|
|
|
garyabrill
Member
Offline
Posts: 488
|
In reality persistent weak layers in the Cascades tend not to be as bad or as persistent as in areas farther away from the coast. Still, weak layers here often last for 3 weeks or so (with respect to skier triggering) after snowfall begins - serious snowfall, not the dribble we've seen of late. However, Cascade persistent weak layers seldom disappear completely and usually resurface with heavy loading in the winter or melt cycles in the spring - although these are typically not the situation for skier release. But rules of thumb like,
"Buried layers?, Ice glazing? In the Cascades! You have got to be kidding. Maybe as a short term issue but very rarely is it a concern over the course of the winter. Our dramatic temperature swings take care of that."
are made to be broken. Recall the fatal 15' slab avalanche at the Baker ski area that was most likely (M. Moore) skier! released in February of 1999 or the natural 15-25' slabs of early February 1990.
Along the Cascade east slopes persistent weak layers seem to be the norm all winter long from my experience and the only thing that mitigates avalanche cycles there is the lack of sufficient load - few storms reach the east slopes with heavy enough snowfall to make the weak layers critical - although one certainly did near Washington Pass this January.
Over a long enough period of time - and who knows what that is - the Cascades will have winters like the Rockies and the Rockies will have winters more typical of the Cascades. Almost all of my close calls have been with persistent weak layers - and in the Cascades - since the very early days of my skiing career.
Obviously terrain is the key but a lot of smart and very experienced skiers have been caught while applying a new snow regime mindset to a snowpack with unusual characteristics. Safe terrain parameters shift when conditions shift.
|
|
|
|
|
Logged
|
|
|
|
garyabrill
Member
Offline
Posts: 488
|
Triggered 12-15" slab on 35-40 degree north aspect yesterday near Mt. Baker at 4500'. Propagated 50-60 feet wide and slid on a rough crust with some faceted grains on top of the crust. Do not know if there was any surface hoar involved but it is possible given the location. The recent snow in this location was not cohesive at all so the slab itself was an older and seemingly settled and faceted layer from earlier snows. I noticed the underlying snow in this location immediately before the slab released was harder than in other locations I'd skied and traveled on. I checked at a noticeable convexity and expected a sluff but instead a slab broke at my control line. I don't know any reason the snow should have been harder underneath in this location - as far as I could tell this was a random isolated slab in a situation where 3"-10" sluffs were the norm on steeper slopes. I would note that between 4000' and 5500' the recent snow from Monday was loose, not cohesive, but that underlying this 6-14" of recent snow the older surface was much more variable with wind slabs, settled snow, and warming crusts in evidence, all now somewhat faceted on shady aspects. A harder crust (the bed surface of the slab) generally underlies this structure. Despite the slab I would rate the hazard Moderate (although down to 4000' near Mt. Baker). Still this can't be the only lingering slab.
It clearly was an example of the behavior of persistent weak layers.
I was not at risk in this situation but was surprised by the slab. The lack of cohesiveness with a slab points to a very bad bond in this location. This snowpack would not support much load. Fortunately or unfortunately (depending on one's viewpoint) heavy loads of new snow aren't likely to be in our future any time soon.
It is interesting to note that Canadian forecasts also speak of isolated slabs. As a matter of fact there is good reason to believe that underlying surfaces throughout the west are likely to have a variety of facets, surface hoar, and degenerating crusts because of the long lasting and unusual weather recentlly across the entire area south of northern Canada and west of the Great Plains.
|
|
|
|
|
Logged
|
|
|
|
clozner
5Member
Offline
Posts: 19
|
Gary - If it isn't a secret stash, can you post a map or description of where you were. Headed out this weekend and want to know if this is in the same general vicinity.
Thanks
|
|
|
|
|
Logged
|
|
|
|
garyabrill
Member
Offline
Posts: 488
|
Gary - If it isn't a secret stash, can you post a map or description of where you were. Headed out this weekend and want to know if this is in the same general vicinity.
Thanks
Sorry....
I skied near Mt. Baker again today and my sense for the snow there is that it may be more unstable - certainly weaker bonds and less settled - below treeline than above. I notice my skis slipping more while climbing at the lower elevations (again on north slopes).
Skied north facing above treeline (heavily wind affected), north facing below treeline - better snow, and east facing above treeline - good snow but variable in depth over some older harder windslabs and crusts.
|
|
|
|
|
Logged
|
|
|
|
Gregg_C
Member
Offline
Posts: 298
|
The avy guy goes out and finds an avalanche.  Gary, I am really glad that you found your persistent layers and an avalanche to emphasis the point. Touche. The point I was trying to make with my court jester comments was that it has been the case in the past on this site that people get in a froth over layers. I spent a lot of time in the Canadian Rockies in winter and to me that is a snowpack that has persistent layers. On my list of concerns for the Baker snowpack, (my stomping grounds), layers don't even make the list. More snow, rain events, and the evil snow shoe crowd are what I worry about.
I had an awesome day of backcountry skiing on Saturday in very stable conditions.  I was giving an introductory tour of Baker to Western Freshman and CO skier Louie Dawson and friend Skylar. At the end of the day he commented, "Wow, we could never ski terrain like this in Colorado in mid-winter". Welcome, I said, to the beauties of the Maritime snow pack.
http://picasaweb.google.com/GreggCronn/NoWetAndScrappyHereADayWithTheYoungUnsII#
Thanks for putting up with an avalanche dunce and letting me participate in this learned and impressive discussion. I will now withdraw back into my happy ignorance and let the experts continue.
Good sking to all and if you see a snow shoe clad idiot destroying someone's finely crafted skin track, start beating them with your pole. Maybe that will solve the problem. 
|
|
|
|
« Last Edit: 02/15/09, 05:15 AM by Gregg_C »
|
Logged
|
|
|
|
Lowell_Skoog
Member
Offline
Posts: 1620
WWW
|
"No wet and scrappy here." I love it.
|
|
|
|
|
Logged
|
|
|
|
garyabrill
Member
Offline
Posts: 488
|
The avy guy goes out and finds an avalanche. Gary, I am really glad that you found your persistent layers and an avalanche to emphasis the point. Touche. The point I was trying to make with my court jester comments was that it has been the case in the past on this site that people get in a froth over layers. I spent a lot of time in the Canadian Rockies in winter and to me that is a snowpack that has persistent layers. On my list of concerns for the Baker snowpack, (my stomping grounds), layers don't even make the list. More snow, rain events, and the evil snow shoe crowd are what I worry about. I had an awesome day of backcountry skiing on Saturday in very stable conditions. I was giving an introductory tour of Baker to Western Freshman and CO skier Louie Dawson and friend Skylar. At the end of the day he commented, "Wow, we could never ski terrain like this in Colorado in mid-winter". Welcome, I said, to the beauties of the Maritime snow pack. http://picasaweb.google.com/GreggCronn/NoWetAndScrappyHereADayWithTheYoungUnsII#Thanks for putting up with an avalanche dunce and letting me participate in this learned and impressive discussion. I will now withdraw back into my happy ignorance and let the experts continue. Good sking to all and if you see a snow shoe clad idiot destroying someone's finely crafted skin track, start beating them with your pole. Maybe that will solve the problem.
Cool, Greg C. Mostly stable, I'd agree. But mainly because it hasn't been snowing.
I find Baker a lot like the Monashees, less layering except when there is layering. I worry about people developing bad habits by developing sets of expectations that work - most of the time.
|
|
|
|
|
Logged
|
|
|
|
garyabrill
Member
Offline
Posts: 488
|
Time to get out the shovels. There are some pretty good questions that will need to be asked and an attempt needs to be made to answer them. I guess the scenario with the weak layers is coming out about the best that it can what with warm temperatures and in some areas rain or very wet snow before it really started to turn on. But the rain wasn't all that much and and there should be an upper elevation limit beyond which things may not be as good. It will be interesting also to see if things in the passes and along the east slopes become as stable as in places like Baker and Paradise? It is also nearly March which can make a difference. Finally a real snowstorm, how about that!
|
|
|
|
|
Logged
|
|
|
|
garyabrill
Member
Offline
Posts: 488
|
I skied near Stevens Pass on Friday and did experience a number of whumpfs the largest of which radiated out from my body about 50'. Several of the whumpfs seemed to be on the buried faceted layer near 4300' in elevation, but another, near 4800' was likely on buried surface hoar (didn't whumpf the same way and was more progressive). Like others I believe it seemed more stable above 5000' to 5500' or so and most unstable in a zone above warming effects from last week and below the deeper snow and inversion top at middle elevations.
There are a lot of interesting observations on the Friends site at www.avalanchenw.org under Snowpack Info Exchange/Search Reports that are worth reading. Also Garth's avalanche forecast detailed a number of incidents fairly widespread throughout the area. The weak layers are still there (through Saturday for sure) although some of the incidents may also have been new snow instabilities.
It looks like that at Baker there may have been enough rain and warming Sunday to make skier triggering less likely once this recent rained on surface forms a crust. The weak layers will likely remain but be somewhat strengthened most probably beyond reasonable skier triggering (except when warm or if very heavily loaded. But, thus far, anyway, the passes and east slopes appear to be staying cooler and so could also maintain the weaker structure.
It's been an unusual period for us northwesterners.
Anybody else find anything unusual this past few days?
|
|
|
|
« Last Edit: 03/01/09, 02:23 PM by garyabrill »
|
Logged
|
|
|
|
skierguitarist
Member
Offline
Posts: 292
|
Tumalo Mt. near Mt Bachelor......Friday I witnessed two "no-brainer" new snow/ wind slab slides. Lots of new snow plus high winds ( and so, wind transport... ) yielded loading in the usual suspect areas-- a cornice of 40ish degrees starting zone directly tucked underneath-- and the other on another similarly in degrees steep starting zone (this one has pretty much turned into a "burnished" surface as it releases snow quitie regularly when ever the big dumps arrive)
The slab from under the cornice event occur when one skier hopped off the cornice and stopped in the middle of the slope to see his buddy do the same. The first guy got to see the whole slope expode as his buddy maytaged his way down to near the first guy (who also got hit by the slide...)...Fortuntely both stayed on top (and seemed to not be hurt) and were able to find all there belongings and able to ski to safety. Looked like no awareness of snow stability/ mechanics nor terrain managment protocal. Once again, the clueless servived (or what I percieved to be "clueless".
|
|
|
|
|
Logged
|
|
|
|
Stugie
Member
Offline
Posts: 925
WWW
|
Lots of windslab near crystal in the bc on Friday as well. No releases, but once the sun was out and shining brightly, we also experienced a lot of whumfing and vacated the area (Cement Basin). The settling occured in mostly safe terrain, but the warning signs were apparent and we took note and played it safe moving to other aspects that weren't sun affected.
|
|
|
|
|
Logged
|
"The mountains are not stadiums where I satisfy my ambition to achieve, they are the cathedrals; the houses where I practice my religion." - Anatoli Boukreev
|
|
|
garyabrill
Member
Offline
Posts: 488
|
A word of warning. Test for this layer near Stevens Pass:
Interesting layer found between about 4800' and 5300' on NW through NE aspects. The layer of graupel about 1-1/2" thick and overlying firmer snow is now buried about 24". This layer was responsible for a remarkable number of dry slabs recently. I do not know the age of the layer but find that 10-12" of snow has accumulated since the avalanche cycle. The number of slabs observed was somewhere between a dozen and 2 dozen on angles of 35 degrees and up in mostly gladed terrain. One slab propagated across the head of three small scale gullies typical of the Heather Ridge terrain. Additional slopes were cracked but hadn't released. Ski tests on a couple of the few safe slopes that hadn't slid were unremarkable at about 5300' but additional ski tests and skiing on steep terrain below about 4800' showed good stability. But that may be because the graupel was (or has been moist below that elevation at some point in time. A snowpit at 5100' yielded an easy to moderate shear at 24" and a compression test score of 19 was obtained. But since the overlying layers are just fist and 4F hard the CT result may overstate the stability of the layer. This layer doesn't lend itself to discovery by pole testing and "feel" of the skis. The upper limit of recent slab observations are probably just because of the terrain limitations at Heather Ridge and the weak layer should extend higher. I would be concerned about this layer on steep rolls (where most releases were) on north aspects near Stevens Pass. On sunnier aspects where a buried suncrust underlies recent snows it seems likely that the formation of the suncrust has mitigated this weakness. Those slopes felt stable while dry today.
I've only seen surface hoar act as unstable as this graupel layer has recently shown itself to be and the terrain where the slabs occurred has rarely had more than an occasional slab historically.
|
|
|
|
|
Logged
|
|
|
|
|
Thank you to our sponsors!
|
Contact turns-all-year.com
Turns All Year Trip Reports ©2001-2010 Turns All Year LLC. All Rights Reserved
The opinions expressed in posts are those of the poster and do not necessarily
reflect the opinions of Trip Reports administrators or Turns All Year LLC
|
Turns All Year Trip Reports | Powered by SMF 1.0.6.
© 2001-2005, Lewis Media. All Rights Reserved.
|
Page created in 0.764 seconds with 21 queries.
|
