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01-14-2008, 11:11 AM #1
Terrain management or "poor line" selection as a factor for avalanche avoidance
Erica asked this in a separate thread:
I'll start with the most obvious one and let other's chime in.
Ski lower angle slopes. Most avalanches occur in the 30 to 45 degrees slope angle. Citation here - http://www.dola.state.co.us/dem/publ.../avalanche.htm. More data available in Tremper.
To expand on the above comment, make sure your lower angle slope does not have a higher angle slope that has a lot of snow above it. It is possible for skiers on the lower angle slope to be caught by an avalanche occurring on the higher angle/steeper slope above them
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01-14-2008, 11:22 AM #2Hucked to flat once
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There is a lot of stuff to ski even with a moderate danger rating. I might be fisting the dead horse here, but a good Avi I course would cover this topic really well.
There are a lot of ways to ski in terrain and LL's 1st point is a good one. Another thing to consider is slope aspect (N, S, E, W). Sun and wind can greatly affect snowpack so when something is bad because of these factors, find somewhere to ski where those factors are not present. IE the moderate rating is due to wind loading and the wind was from the west, chances are there are areas to travel/ski that are not east facing that might be safer and completely doable.
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01-14-2008, 11:29 AM #3
I'm not familiar with the east vail chutes, but my guess was that the lines skied are obvious steep gullies/avalanche paths. These are very enticing because of openness and pitch. The criticizers/survivors were likely skiing more meadows/tighter trees on fall lines that didn't drop like an anvil directly into the valley. I apparently like/love doing this today.
looking for a good book? check out mine! as fast as it is gone
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01-14-2008, 11:32 AM #4
Of course this is all generally covered in Avi classes, so thats the best place to go if you really want to learn more.
The main things I think about are:
1) Slope Angle - if its not steep enough to slide you'll be safe. Specifically less than 30% will greatly reduce the risk. Here's the graph demonstrating where most avi's occur:
2) Slide history and evidence - if the area is an active slide path with a history I'd avoid it at time of high danger. Generally if an area is below treeline but is open with no larger trees and steep enough then it probably slides. If a slope has killed others that is noteworthy.
3) Terrain features that are higher risk to slide and/or higher consequence if they do slide. Rollovers/convex slopes (those that get steeper in the middle rather than angle off), terrain traps (for example a gully where even a shallow slide would bury you deeply), cliffs below where you'd get swept off, etc.
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01-14-2008, 11:36 AM #5
To add my $0.02:
Snow depth. ie do shallow points appear in places on the slope? Are they above you, below your line or off to the side? These serve as trigger points and if the slope will slide where will it go? right on top of you or off to another place.
This brings in slope shape: convex or concave? Convex slopes are under tension and somebody skiing right on the roll-over can cause it to release.
A more advanced variable:
History. A lot harder to know. This is where local knowledge comes in. Has it slid recently? Does it have a reputation for sliding a lot (due to shallow areas hidden under the slope or lack of anchors). Is there a crust still in action or has a previous slide taken everything down to ground and allowed a whole new building process to take place? Has there been a sustained cold snap that produced facets etc.Recently overheard: "Hey Ralph, what were you drinking that time that you set your face on fire?"
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01-14-2008, 11:38 AM #6
Another consideration is runout. Should you ski a slope that can slide, what's going to happen if it does. Where will it take you. The consequences if you will. There is a big difference in skiing a line that empties into a giant boulder field, trees or a terrain trap like a low angled gully or depression over skiing a line that has a longer less dramatic runout. Try and think about what your gonna get dragged through if the slope rips out and let that guide you in your risk assessment.
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01-14-2008, 11:39 AM #7
great posts above
id also just add that never base any decision on the result of one test or any one peice of information. The more tests and observations the better.
I can think of more than a few scenarios I would NEVER ski a certain 28* slope even if it is below the 30-45 guideline
of course i have a very low risk threshold.
(im not picking on you LL or smitchell or anyone else, just saying in general)
edit to add:
I also like to think of each of these "rules" more as guidelines. Just remember the answer invariably is "It Depends".
Nothing is 1 Dimensional.
Look for Instabilities rather than Stabilities.Last edited by pechelman; 01-14-2008 at 11:50 AM.
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01-14-2008, 11:43 AM #8
Snow flows like water, so the four things that are always on my mind:
1) What's above me?
2) What's below me?
3) Where am I and where am I going?
4) What's going on around me?
To expand just a touch without writing a book:
1) if something released 3000' feet above me, would I be in a path?
2) a choke, ravine, bend in a chute all make little slides big -does it open up wide, or choke down tight.
3) Am I in danger where I am right now or will I enter danger on this path- am I on the windward or leeward side of the valley, in a ravine, in a trap, approaching a change in slope angle or an obvious wind-loaded pillow area?
4) Any natural activity - where is it, what aspect, what type? What does the snow feel like when I plant my pole - is it unconsolidated sugar, hard crust, hard as a rock?
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01-14-2008, 11:48 AM #9Registered User
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This has been posted before but it's a good watch. Some tips on the human element as well as terrain management.
A Dozen More Turns
A Dozen More Turns is the true story of five close friends, all with extensive avalanche education, who went on a New Year's Day hut trip in Southwestern Montana. A member of the group triggered an avalanche with truly devastating consequences. This film tells this tragic story in an effort to help backcountry enthusiasts re-calibrate their decision-making processes when up on the slopes. Using emotional interviews, science and compelling home video footage left behind by the group, each viewer is left wondering if simply having avalanche education is enough to save our lives in the backcountry. How much are we willing to risk for a dozen more turns?
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01-14-2008, 11:53 AM #10
Wind loading was mentioned above, but I want to emphasize that wind loading can occur at a much higher rate than snow fall during a storm. The 11 foot dump at Tahoe last week had a maximum rate of about 6 inches an hour, but wind can deposit snow at an incredible rate, something like 50 inches in an hour, significantly affecting potential slide areas.
I skied a couple roll overs this weekend that gave me the heebie-jeebies, but I had confidence in the snow stability. It still amazes me how quickly the snowpack stability improves in maritime climates. +1 for sierra cement.
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01-14-2008, 12:07 PM #11
Great info here, take an Avy course. Ski with guides, ask them why they choose a specific route up, run down, etc. I've learned a ton skiing with guides on days with higher avy risk.
A few more thoughts. Once you've committed to ski a line, where are your islands of safety? Where are you going to stop to watch your buddy ski that is going to be safe? Ski one at a time, from island of safety to island of safety. And the runout at the bottom of the slope is huge. Heli/Cat ski runs always open up at the bottom, never funnel into a terrain trap like a gully or creek bed.
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01-14-2008, 12:24 PM #12
Not necessarily off topic but I think heuristic traps are where poor terrain selections begin. In other words, things contribute to a go / no go decision that really should have absolutely no bearing on a terrain assessment or the decision to ski a particular slope. Things like group size, other tracks, sun shining, powder fever, car time to get there, etc etc.
More avalanches occur on slopes that are familiar to the skier than unfamiliar to the skier, which is why I think heuristic traps are critical to understanding this stuff."Buy the Fucking Plane Tickets!"
-- Jack Tackle
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01-14-2008, 12:29 PM #13
When shit is unstable I'll stay on ridgelines keeping myself ABOVE any thing that can break. At that point I'm no longer trying to "ski" and epic line but just trying to travel out as safely as possible.
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01-14-2008, 12:46 PM #14Something about the wrinkle in your forehead tells me there's a fit about to get thrown
And I never hear a single word you say when you tell me not to have my fun
It's the same old shit that I ain't gonna take off anyone.
and I never had a shortage of people tryin' to warn me about the dangers I pose to myself.
Patterson Hood of the DBT's
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01-14-2008, 12:56 PM #15
When people are trapped in slides where all objective factors pointed toward a no-go decision (avy rose, wind loading, prof of poor bonding in the snow, prior natural and human triggered slides in the area, etc) there must be something else at work. The experts call them heuristic traps but they could more broadly be called human nature.
This applies even when people think they are being objective or scientific. When you dig a pit, the pit tends to validate whatever preconceived notions you bring to the slope. If two people dig a pit and one thinks the conditions are sketchy, the pit is going to tell him this. And if the other skier thinks the slope seems solid and safe, the same pit is going to tell him that."Buy the Fucking Plane Tickets!"
-- Jack Tackle
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01-14-2008, 12:57 PM #16
Great points.....the Avy class we took earlier this year was great, lots to think about. I would add that having an escape route in case something does go wrong. Skiing the sides of a route instead of the gut, thus making it a bit easier to perhaps bail if need be.
ROLL TIDE ROLL
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01-14-2008, 01:04 PM #17
Interesting...again.
It's not at all an answer to the good question that was asked, but this thread reminded me of a quote from a venerable Wasatch wizard, forgot his s/n, thai stick or sumpin, who said, in a great wy splitride TR, "Avalanche hazard ratings are relative terms. Best not to search out the hazardous, but rather, the stable. "...[should have ended with 'grasshopper'...]Something about the wrinkle in your forehead tells me there's a fit about to get thrown
And I never hear a single word you say when you tell me not to have my fun
It's the same old shit that I ain't gonna take off anyone.
and I never had a shortage of people tryin' to warn me about the dangers I pose to myself.
Patterson Hood of the DBT's
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01-14-2008, 01:10 PM #18
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01-14-2008, 02:54 PM #19
thanks for the insight everybody. I appreciate it.
and yes, I do need to take a proper Avy course. My mountain rescue avy & snowpack training is getting outdated.
but I have one more question regarding trees in a BC line selection:
generally, is there less risk in skiing a particular line because it has trees? I always thought trees werent necessarily the lesser evil because if a slide did happen, you could get pin-balled through them...??Last edited by erica_z; 01-14-2008 at 03:02 PM.
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01-14-2008, 03:04 PM #20Registered User
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I'd also point out the part (I didn't see it at least) about folks that get suckered into the slides, just because there were already tracks on the given slope.
Remember, it's not always just having someone on the slope, it's more a matter of having someone trigger the sweet spot, that may make it go.
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01-14-2008, 03:04 PM #21Hugh Conway Guest
Also think about the consequences of the slope above you sliding on the approach - either naturally or triggered by another party or by a member of your party triggering it. Don't assume the skin track was set by someone who knew what they were doing.
heuristics = "rules of thumbs" etc. heuristic traps = how your comfortable approximations can dramatically fail.
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01-14-2008, 03:10 PM #22
I'm so glad that the discussion involves heuristic traps/human nature - and I dare say male nature.
I posted this once - SUMMIT FEVER.
Interestingly tomorrow will be a bluebird day. The first day after a big storm event with high winds. Nice weather is forecasted. I'm set to go with a friend of mine who's also quite motivated and want to ski some N faces. Looking at my old debrief I wonder whether I should just not even go? Im not convinced I have the will power to look at the N face of Decker, Trorey, Pattison and NOT ski them. How much of safe touring is recognizing your own failures and tailoring your touring to meet them?
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01-14-2008, 03:11 PM #23Registered User
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3) Terrain features that are higher risk to slide and/or higher consequence if they do slide. Rollovers/convex slopes (those that get steeper in the middle rather than angle off), terrain traps (for example a gully where even a shallow slide would bury you deeply), cliffs below where you'd get swept off, etc.
I am nowhere near experienced enough to say whether this is actually practical knowledge, i.e. that you should choose lines away from trees and protruding rocks.Last edited by bookem; 01-14-2008 at 03:17 PM. Reason: sppeling
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01-14-2008, 03:16 PM #24
Very closely spaced trees can serve as anchors. Trees with foliage that grows right to ground are actually better anchors then trees without vegetation. Generally speaking trees have to be close together enough that fast tree-skiing is difficult for the trees to be good anchors.
Widely spaced trees are not good anchors and can actually serve as weak points in the snowpack. They're also things to hit if you get swept downslope in an avalanche -- as you recognized.
So, as with almost everything to do with avalanches ... it depends.
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01-14-2008, 03:35 PM #25
It doesn't seem like this has been covered yet so I'd add the following:
1. Pick terrain which allows you to make as many assessments as possible in safe spots. Ie I like shallow skin tracks on ridgelines. There's often shallow pockets of snow, little convexities, small rolls, maybe even the holy grail of quick and easy testing, small cornices to drop and bomb slopes. I like doing many quick - and - dirty tests when touring.
2. Know your terrain well. Ideally look at it in summer and keep tabs on snowpack throughout winter. If you're going to a new place, look at maps, google earth, pictures - anything you can get your hands on. Talk to people about the terrain. Of course nothing is a substitute for being there but what if you're there on a clear day in the valley and its cloudy/whited out in alpine?
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