Ken Roberts - - Ski Backcountry


more . . . on managing crevasse risk on skis

09may1

what's here

see on main crevasse page

unroped travel + crevasse rescue

  • harness -- lots of experienced groups make it a normal practice to put their harnesses on any time they're on a possibly crevassed glacier, even though they have no intention of roping up.

The idea is that if one skier does fall into a (hopefully small) crevasse, then it's much easier for other skiers to at least anchor the faller, possibly haul them out, if the faller is already wearing a harness. Of course it helps if the faller was not the one carrying the rope.

  • helicopter aid -- the chance of serious injury in an unroped crevasse fall is substantial, and might be nearly impossible for the party of skiers to handle without summoning motorized professional help.

  • solo skiers -- On various forums there have been some suggestions about what equipment a solo skier could carry to have the best chance of climbing out of a crevasse. (My own view is that solo skiers should not allow the slightest distraction of mental attention from the task of selecting a tour which has no chance of a crevasse fall.)

roped travel + crevasse rescue

For procedures for roped travel and crevasse rescue, read long detailed descriptions in books (see below under Resources).

Some stray thoughts:

  • skier versus climber, traveling roped on firm snow: If someone punches through, they may pull others off-balance, and the others start sliding and need to arrest. Non-skiing climbers on a glacier normally carry their ice axes in position for self-arrest, while skiers usually prefer to travel upward and downward with each hand holding a ski pole. But ski pole tips are not reliably effective for self-arrest. And the metal edges of the skis don't help when your body is down on hardpack snow getting pulled headfirst by a rope down toward a crevasse. So if skiing while roped together, need to have serious self-arrest "daggers" on your ski poles, or tie at least one ski pole to your pack so you can hold an ice axe in your hand.

  • Hanging upside-down from a rope in a crevasse is a very bad idea. Attaching the rope higher on the body (like to a chest harness) reduces the chance of hanging upside-down. But a higher attachment point also makes it more likely to be pulled off-balance, and getting pulled from the chest makes it more difficult to get your ski edges back "underneath" you when you're sliding after you've been pulled off-balance.

  • Skiing downhill roped, it's very difficult not to allow significant slack in the rope -- which makes punching through into a crevasse much more dangerous and more likely to require a tricky complicated rescue procedure - (also more likely to pull a second skier down into the same crevasse).

  • Crevasse rescue (even when the faller is roped) can be a big tricky mess. It's good to read the details in the books to find out how complicated and tricky the mess can be - (even in ideal weather conditions).

If you're not scared by the complexity, or by the difficulty in executing it successfully by a non-professional group in the emotional and social confusion of a real occurrence, then read it again, and start thinking about different things that could go wrong. Then think about what could go wrong while trying to do it in bad weather.

  • helicopter aid -- a complicated rescue situation with a big crevasse might be very difficult for the party of skiers to handle without summoning motorized professional help.

  • Some skiers tie simple overhand knots in the rope, with the hope that one of the knots will get caught in the lip of the crevasse and help stop the falling and sliding.

  • Two-person party can be very tricky for crevasse rescue even when roped together with best equipment and procedures - (read the books for why).

One 2-person strategy not often mentioned, for glacier sections which do not have very deep crevasses: Keep a long rope between the two, and if one punches down through, make a normal part of initiation of rescue to lower the faller further down into the crevasse until the they reach a point where the faller can anchor to the side of the crevasse (or rest securely without needing to anchor). That takes the tension off the rope, so then the outsider can devote full attention to making a secure outside anchor and other next rescue steps (instead of splitting attention and strength between holding tension on the rope and setting up an anchor). Definitely helps to have a clever communication method to coordinate this "lowering" strategy.

resources

  • book by Martin Volken, Scott Schell, Margaret Wheeler: Backcountry Skiing (Mountaineers, 2007). Lots of helpful details about how crevasses form and procedures for roped travel and crevasse rescue, and some good overall context for skiing on glaciers, but not much specific detail about how to assess the level of crevasse hazard for skiing.

  • book by Andy Selters: Glacier Travel and Crevasse Rescue (Mountaineers, 1990). Well-written book with lots of helpful overall guidance and detailed procedures. Only a couple of pages specifically about skiing -- with some helpful details about that - (including warning of the danger of the "temptation" to "skew the judgment" and assume it must be OK to ski downhill fun and free after successfully climbing up roped together).

  • book by Peter Cliff: Ski Mountaineering (1987). Lots of pages about how crevasses form and procedures for roped travel and crevasse rescue. A couple of good scary stories about big crevasse falls. Half a page of "safe habits" to avoid crevasse falls.

  • websites? I haven't yet found much in English. I'd be very glad for suggestions, including suggestions for detailed helpful resources in other languages.

yet more . . .

probability

Numerical probabilities don't work for risks like this, because

(a) there's so many variations in the situations;

(b) the number of bad events with skiers is so small;

(c) gathering accurate info about exposure time is nearly impossible.

so there is nowhere near a large enough sample to make estimates of numerical probabilities.

But actually we almost know anything like accurate probabilities for decisions we make in life.

risk averseness / tolerance

Instead here's some "qualititative" approach to frequencies of bad events:

(1) sorta like while staying home and surfing the web.

(2) sorta like while driving my car to get me to a ski tour and back -- or other driving I do around home for social and exercise purposes.

(3) tolerate a bit more risk frequency than (2), because doing one of my regular ski tours around where I live is special for me.

(4) tolerate a lot more risk frequency than one of my regular ski tours around where I live, because this tour on this glacier is a once-in-a-lifetime accomplishment for me.

(5) just broke up from ten-year relationship - (nothing seems to matter any more).

I find (2) to be an interesting "benchmark", because driving a car is significantly risky, but most of us choose to do it anyway, even for purposes which are not "necessary".

I understand the reasoning behind (3), but I doubt we have enough data to tell the difference between (2) and (3), and if we aim for (2) in our ski touring we'll likely hit (3), but if we aim for (3) we'll likely hit (4).

I suspect (4) is where lots of Americans are at when they make a week-long ski trip to Europe. The problems I have with it are: (a) really it's not "once-in-a-lifetime", it's once (or twice of more) each year just for skiing, and once or twice or more for risks on trips of other types; and (b) it turns out to be an excuse for not thinking seriously about risk levels at all, and instead either just going along with whatever the group drifts into, or gets led into by some over-confident loud-mouth, or just copying whatever itinerary that some other American groups did in previous years (even if conditions this year are completely different).

I can understand that it's hard to resist falling into attitude (4) once you're in the midst of the trip, but I'm not seeing why some careful analysis and consideration of alternatives could not happen a month or two before starting the trip.

Skiers into (5) are not going to listen to rational arguments anyway, so I'm not going to make them. I do wonder how the presence of people with that kind of risk tolerance influences the statistics of accidents -- especially for solo skiers.

kinds of crevasse-falls

Different kinds of falls into a crevasse could have different consequences:

(1) punch one foot through a snow bridge, but the rest of the body stays on top.

(2) very short fall while roped with little slack, into a crevasse narrow enough to possibly be climbed out of (e.g. with "chimney" climbing techniques)

(3) fall 7-10 feet (2-3 meters) while roped (because the rope was badly managed, or because it was while skiing downhill), into a crevasse narrow enough to possibly be climbed out of (e.g. with "chimney" climbing techniques).

(4) fall unroped into a crevasse narrow enough to possibly be climbed out of (e.g. with "chimney" climbing techniques).

(5) fall 6-10 feet while roped into a wide crevasse (with no way to climb out of it except up the rope).

(6) fall 6-10 feet while roped into a wide crevasse with a tricky overhanging lip from which rescue is possibly only with the best equipment and smartest creative techniques.

(7) fall unroped into a wide deep crevasse.

(8) multiple persons fall into the same wide deep crevasse.

levels of assessment of crevasse risk

(A) good evidence from multiple sources that this section of the glacier is so well "plugged" that unnecessarily risky actions like multiple persons coming together in one spot, or aggressive skiing with substantial impact on the snow could be attempted, without a frequency of bad outcome higher than around frequency (2) or (3) above under "risk averseness / tolerance".

(B) good evidence from multiple sources that this section of the glacier is strongly and thoroughly enough bridged, so that "normal" downhill skiing could be attempted without a frequency of bad outcomes higher than around frequency (2) or (3) above under "risk averseness / tolerance" - (but "unnecessarily" risky actions like multiple persons coming together in one spot could result in higher frequency of bad outcomes).

(C) good evidence from multiple sources that this section of the glacier is strongly enough bridged, so that flat or uphill climbing on skis with skins could be attempted without a frequency of bad outcomes higher than around frequency (2) or (3) above under "risk averseness / tolerance" - (but skiing downhill could result in higher frequency of bad outcomes).

(D) good evidence that "normal" downhill skiing might have a frequency of falling into a crevasses around frequency (3) or (4) above under "risk averseness  / tolerance -- but if a fall did occur it could only be into a crevasse narrow enough to possibly be climbed out of (e.g. with "chimney" climbing techniques) -- because there is good evidence that there are no wider crevasses in this section of the glacier.

(E) evidence that "normal" downhill skiing might have a frequency of falling into a crevasses around frequency (3) or (4) above under "risk averseness  / tolerance -- and if a fall did occur it might be into a crevasse wide enough so it could only be gotten out of with aid of a rope and special equipment and careful procedures.

see also

 

concept words: ski skiing snow skier skiers skis roberts report reports

backcountry mountaineering randonnee rando off-piste tour tours touring route routes

technique: techniques technical theory theories theoretical physics physical biomechanics biomechanical mechanics mechanical model models concept concepts idea ideas