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Punching into crevasses: skis vs on foot
- wolfs
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- markharf
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<br><br>No doubt this is to some extent true, but it's difficult for me to imagine that it makes much difference in real-world terms. How much tension operates in the average snowbridge? How much difference does the specific source of the (bridged) hollow space below make?<br><br>Hmm. I'm not sure that stream undercut bridges and crevasse bridges equate 100%, crevasse bridges have a lot of other factors at work. They aren't melting out nearly as much from below; in many cases they start to fail naturally because the snow bridge is actually being stretched out too far laterally, rather than being ablated and thinned. In that case it's a system under tension, where any piece of the system might fail under your weight and not necessarily the very thinnest part.
<br><br>I'm not clear how the presence of intermediate layers might change the equation of skis = greater safety. <br><br>I also like Sky's analysis, probably because I already believed it true, although I'd not conceptualized it in terms of measurable downward acceleration. Back to that stream-crossing analogy: I've often had the experience of skiing across a thin bridge as it collapses under my skis. If I'm moving fast enough, I make it to the other side. A dull, plodding pace (my special talent) means I fall through.<br><br>Last, although there is no doubt that a heavily-weighted turn exerts more force on that achetypical snow bridge than a more subtle weight shift, it's hard to imagine a turn weighted so emphatically that it corresponded in pounds per square inch to the average plunge-stepper. That's why even big, gorilla-like skiers like myself float along with big grins on our faces, while descending climbers grimace and cuss and posthole all afternoon. <br><br>Of course, I'm willing to be proven otherwise on any or all of the above. <br><br>Enjoy,<br><br>MarkAlso, crevasse bridges tend to have a bunch of odd intermediate layers where you might only partially fail it.
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- powscraper
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- ron j
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<br>Jason, I've skied over cracks maybe as much as half that width and didn't consider it particularly hazardous; I'm sure if I skied as well as (I perceive) you do I would not hesitate to ski that which is pictured (in the shot YOU posted), in the right conditions. As for the pics that Jeffey & Sam posted of you, well, um, ah... It's kinda fun to find yourself being used as an example without your knowledge, isn't it <br><br>... and how 'we' are crazy to be skiing on top of snowbridges. I say 'we' because they used some photos of myself and brother as examples. Here is the picture they used, which they considered insane. I'm interested in what the general BC skier thinks here:
<br>We have done a lot of (uphill) roped glacier travel on skis in the mountie's annual ski GT class. While I agree that arresting a fall is a bit more problematic with skis on, we seem to get by ok. Of course we don't do two person rope teams; that could change the situation considerably. Also on one occasion we descended the glacier roped on skis (which I was definitely not looking forward to). What happened was that the fog had come in and the visibility had diminished to about 10 ft. We had marked the crevasse hazards on the way up with wands but we were not confident everyone would see the hazards in time, swooshing down the glacier on skis in the fog. What we decieded to do was rope up and put our skins on so that everyone could SLOWLY inch their way down with each rope team leader staying in sight of the tail end of the rope ahead. It took a while but I guess it worked ok 'cause we didn't lose anyone <br>That's the only time I've skied downhill roped (if you can call it that) and like others point out I have no interest in improving my roped downhill skiing skills. If I'm going to climb it, I want to (at least start out intending) to ski it. <br> <br>...But then the tradeoff is that on the ascent (assuming you are roped) it may be harder to self-arrest if there is a problem, and on the descent it just isn't practical to ski roped. Or has anyone tried this?
<br>I happen to be quite fond of belayed ski cuts, especially in chutes where there's no exit if it slides, or any other place where a ski cut leaves safety in question. We've gotten so that we can set them up pretty quick with a partner's skis and then the tester can safely literally bomb the hell out of a chute with his or her body by just jumping into it with skis on. The other thing that appeals to me is that once the tester is happy with the results and is ready to ski the slope he/she can have the belayer take out all the loops and knots on the other end of the rope and then ski on down dragging the rope behind (still tied in). If it was a bad call the resue should at least be fairly quick as it is unlikely the rope will be completely buried. <br><br>...Speaking of belay-skiing, do any of you guys set up a belay anchor for doing ski cuts on avy slopes?
<br>Yeah, I'm not sure I'm smart enough to follow all that but is sounds really good to me... and I guess the smaller the crevasse the better. The skis certainly would seem to bridge the smaller crevasses; my biggest concern skiing down is that at the completion of the turn my skis are across the fall line (presumably in line with the typical crevasse) so the bridging effect will be minimal. So, Sky, I guess following your practice and theory of skiing straight down the slope without turning would minimize that risk, eh? <br><br>Let's assume you travel at 10 m/s (~22 miles/hr, a very reasonable skiing speed). If you are above a crevasse opening below a snow bridge that is 2m wide, this gives you about .2 seconds above the abyss. In .2 seconds, gravitational freefall is only (1/2)*9.8(m/s^2)*(.2^2)~1meter. <br>The same analysis for 15 m/s (~33mph) results in a fall of less than 1/2 meter, in which case your speed would certainly carry you over the crevasse, albeit leaving you in a tumble.
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- Matt
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<br><br><br>To continue on the tangent.....Many times I have wished for a rope before ski cutting a slope and kicking cornices. This technique would really open up some mid winter chutes with localized instabilities such as wind loaded entries with no place to "safely" ski cut. I would be a little more concerned if this procedure was used to ski open slopes with a wide spread avalanche concern, but for localized stuff, could be just the ticket.<br><br>Back to the subject......There is always someone or group that think everything, lets call them adventurous skiers, do is crazy. It all comes down to your skill and the level of risk you are willing to accept. Ok......we are taking about UK skiers right.....do they have mountains in the UK? I find it funny they choose that relatively tame picture of a crevasse jump over others I have seen. The skier appears to plan that jump quite well, looks like a great glory shot and a good day at the office.<br>I've heard of people ski cutting a slope roped though not as much here in washington. This isn't a technique I have used, but have definately wanted to in the past. Now that I have my nice 20 meter rope, I'll be using it more often, especially when I have even a remote avi concern. <br>
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<br><br>.....unless your roped up.<br>Can you put me in touch with your 300 lb ski buddy? He sounds like he'd make an outstanding snowbridge tester?perfect for these sultry mid-summer days.
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- Jim Oker
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<br><br>From experience, i can't say which in particular (collapse or punch through) is more prevelant but I can say I've experienced both. One nugget of advice that I'd like to pass on is this: don't stand 2ft behind your partner. In other words, leave some room. It makes a difference, even if it's only 10 feet. Of course if you were on a rope this wouldn't really apply (I assume the rope is tight), in these cases I wasn't. I just think its a good policy even if the best policy is to be a smart climber. The thing is, we're not always as smart as we would like to think. Avi wise it's not a bad idea either. You just never know...<br>Wolfs - is what you're, in essence, whether it is really PSI that matters on wide bridges, or simply total weight? In other words, are most failures on such bridges of the posthole nature, or are they total bridge collapses?
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- Pinch
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- wolfs
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<br><br>That was sort of the gist of my original question. I think it's pretty obvious that being on skis rather than on foot will prevent a lot of falls into stream hollows etc. or in at least some crevasse crossings where what matters is how much weight is put on a section of snow that happens to be the thinnest, and how much surface area that's spanned over. The 'superstition' part is whether that evidence is enough to convince you that 100% of all possible scenarios where a crevasse is bridged with snow are going to be better while you're on skis, better enough to convince you that maybe if you're on skis you don't need to rope up. The exact physics of how some unseeable crevasse crossing happened to fail will be academic to you at the point where you find yourself wedged head down 50 feet deep in the freezer, you just don't want it to happen period.<br>As far as the down part - skiing glaciers roped is so undesirable that I didn't really consider it to be part of the scope of my original question. You either ski the damn thing or you don't, or at least you limit being roped to a small percentage of the descent that seems the worst. Otherwise the whole idea of skiing it is a bust. (I agree though with something that Amar said in the original TR thread that got this rolling - he mentioned that he skied the Inter alright after the incident, but wore his harness. Read the related accident report on cascadeclimbers for why this simple precaution might make all the difference in the world if you DO punch in, so long as you're still findable and alive.)<br>I was originally thinking mostly of 'up'. The 'down' analysis that Sky started in on is relevant too, in that it's something to think about as you cross all the known bridged points.<br>Also: I hope to god that we ARE crazier than the Brits, at least when it comes to skiing. I mean come on, this is the country that produced "Eddie the Eagle"...<br>Maybe for an upcoming TAY gathering, we could have the more adventurous adjunct of our virtual group go down to the lower Coleman or something, and build up a whole series of linked kickers on the edge of crevasses, and mark em up nice with spotting dye and flags and maybe buff up the landing zones a little. It'll be like a backcountry terrain park. Some of us approaching-the-crest-of-the-hill folks might even venture to pop one or two of those if they are nicely prepped ;DWolfs - is what you're, in essence, whether it is really PSI that matters on wide bridges, or simply total weight? In other words, are most failures on such bridges of the posthole nature, or are they total bridge collapses?
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- David_Coleman
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