Avalanches
Avalanches are dangerous, take care
By 1999 I had done several avalanche awareness courses, and many other mountaineering and skiing training courses and pretty much thought that I knew how to avoid avalanches.... then I was caught in an avalanche one day while out skiing on Scotland in March on what was really a low risk day. (Though it was of course the 13th!). Fortunately no-one was seriously hurt. But that was when I learned the most important lessons - you can never relax, never think that you are safe, never think you know it all. We did make several small mistakes that day, but the main mistake we made was in just being complacent...
This page has some tips and tricks for dealing with avalanche risk and also links to other useful sites.
Avalanche Assessment Some details of how to assess the risk of avalanche once you are actually out on the slopes.
Equipment What to take to be prepared.
Avalanche Links Some links to other avalanche sites.
but first some scary pictures of what big avalanches can do......
These pictures were taken in Eastern Switzerland in 1999 after a year of particularly bad avalanches. It certainly took massive avalanches do do all this damage, stripping off snow, trees, bushes, grass and even topsoil from an entire hillside. But if you thought snow was always soft and fluffy it's time to think again....
Avalanche Assessment
There are lots of things you need to do before you even leave home, such as getting avalanche and weather forecasts, preparing your route carefully, and even deciding whether to go out or not. Once you're out on the slopes there are further things to do, firstly and most importantly just being observant. What is going on with the snow and the weather? How dangerous does your planned route look? What is the snowpack you are skiing on like? Snow pit & Rutschblock Test
Pretty much every time I am out I'll dig a snowpit to get a feel for what is going on in the snow... this doesn't have to be a rigorously done scientific process like the professional avalanche testers do, but it's a lot better to at least have a look at what hidden horrors you're skiing over rather than just guessing or hoping....
Firstly choose a safe slope to dig your pit on (one where you won't get avalanched!) and ideally one at a similar altitude, angle and slope orientation to the slopes you plan to climb or ski on. Don't just dig one pit, dig several in different places through the course of the day to see how consistent the snow is.
Dig a big pit, ideally down to the ground. If you can't dig down to the ground then at least dig down to a hard stable layer. A shovel really helps here, but you can use an ice-axe. Have a look at the layers in the snow on the back wall of the pit - how consistent are they in terms of hardness, grain size and wetness?. Be aware of sudden changes and really thin layers. An obvious and easy to picture warning sign is a layer of hard packed windslab lying over loose hail (polystyrene balls). It doesn't take much imagination to see this as a dangerous situation, but there are many other things to look for. Digging the snowpit, the isolated slab for the Rutschblock test can be seen at the back.
Once I've looked in the pit I isolate a 1 meter by 1 meter slab at the back of the pit, down as far as any suspect layer that the back wall of the pit has alerted me to. An ice-axe handle is very useful to isolate this block. The skiing and ski-mountaineering convention is often to make the slab larger. However I feel it is better to be consistent and always test a similar sized block and because I do many Rutschblock tests when I'm out winter climbing and don't have a shovel with me to excavate a really big pit, I stick with the 1m by 1m size for all tests.
Once you have isolated the slab at the back of the snowpit, the next stage is testing the isolated slab. The important thing here is to be internally consistent so that over a number of days, months and even years you begin to get a picture of what snow is safe and what is not. After turning back from a winter climb once in Scotland on the basis of a slightly dodgy looking pit and block, I heard others had been avalanched on the same slope a few hours later - that was a very, very useful learning experience.
I use the following release scale. Remember that a slab on a steeper slope will release more easily. So if you're testing on a 20º slope but going to ski a 40º slope take care. I generally add about 1 release level for a 10º increase in slope angle. It's not an exact science though...............
- Slab releases on isolation
- Slab releases as I walk around the side of the pit and/or as I approach from above
- Slab releases on contact with my feet
- Slab releases on resting bodyweight
- Slab releases on downsink
- Slab releases on soft jump
- Slab releases on hard or repeated jump
- No release.
This slab released on first contact with my foot on an easy angled slope (10-15º). Not good.
............and finally the most important bit of any avalanche assessment - bailing out if it looks dubious. Blue sky, perfect snow but we decided to turn around........ .......this was the day when hail (graupel) poured out from underneath a hard slab and just kept on coming......
Equipment
Some notes on equipment to carry and use to mitigate against avalanche hazard. If someone is buried you really have only a few minutes to find them and get them out alive.The three basic, cheapest and most important pieces of kit are a shovel, an avalanche transceiver and a probe. More expensive items of kit, such as self inflating rucksacks and avalungs are not commonly carried yet.
In small groups it is really essential that everyone has all three items. You have no way of knowing who might be avalanched. In larger groups, of six or more, you can begin to carry a bit less kit, but you need to think carefully about how you might split up (maybe for an unforeseen reason) at some point in the day, and if you do both parties need to be safe. It goes without saying that everyone needs their own transceiver.
The shovel really doesn't need much explanation, If your friends are buried under the snow and you are on the surface you will want to dig them out. Again it's wise not to underestimate the power of an avalanche and the effects it has on snow. You might think you can dig snow away easily with your bare hands, but it just will to work in avalanche debris. Even plastic bladed shovels are pretty suspect, and I would certainly recommend a metal blade shovel. Snow is however relatively light, so a large blade, large volume shovel is what you want.
The transceiver is a radio transmitter and receiver used for locating victims who have been buried by an avalanche. A full explanation is not given here as each transceiver varies, but there are two main ways of doing this. With older transceivers a search tends to be done on a grid basis, with newer models its increasingly feasible to walk straight toward the burial. In both case it's very important to use clues to narrow down the search area (A visual scan of the debris for clues, remembering and marking the place where you last saw the victim on the surface). Transceiver searching requires quite a lot of practice because it needs to be done very quickly.
The probe is basically a long collapsible pole used to locate a victim more precisely once the transceiver has located them to within a metre or so. Like the shovel their use is pretty obvious. Push it down using a close grid pattern (20cm or less) until you find the buried victim, just try not to poke their eye out.
A very small point release slab avalanches in the Silvretta group, Switzerland....... and below, a giant avalanche coming off Kan Tengri in the Tien Shan, Kazakhstan.
Avalanche Links
Scottish Avalanche Information Service Scottish Avalanche forecasts and reports, in season.
American Avalanche Association
Canadian Avalanche Association
Ortovox Makers of the most famous Transceivers.
Avalanches are dangerous, take care
Contributions
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