Buried in snow - search and rescue

10 December 2019

Interview with 

Lawrence Jones; Mark Diggins, Scottish Avalanche Information Service; Jim McElwaine, University of Durham

SNOW_SHOVEL.jpg

A snow shovel half-buried in snow.

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Returning briefly to the story of Lawrence Jones, who had just been dragged away by an avalanche and buried in snow...

Lawrence - I think I was something like eight or ten feet down, about twelve minutes or something like that. So quite a long time. I was upside down as well, so when they found me I was in the position of John Travolta, Staying Alive, you know that dance movie he does with his one arm in the air, almost like Superman pointing downwards. Which again wasn't very helpful when they're trying to dig me out and the first thing they do is find my boots. When you're in there you have no idea which way is up or down. So even if you had the ability to try and dig yourself out you wouldn't know which way to go.

Mark Diggins explains to Chris Smith the procedure for the people searching for Lawrence...

Mark - Well firstly I think Lawrence is very lucky to have survived, because statistics show that after ten minutes you've got a 10% chance of survival. So he is very lucky to have survived that depth and for that length of time. It's absolutely critical then that the people on the surface have equipment that enables them to find somebody that's buried. So everybody carries these transceivers, and they both transmit and receive a signal. So when you're skiing around, they were transmitting; but then if someone gets buried, those people on the surface will have to turn the machines to 'receive' so they can find somebody. So they will take you to an area of probably about a metre square or so on the surface. But of course if someone is buried deeply, then on the surface the signal might be the same in a larger area. So then what you really need is an avalanche probe. And these are three metres, so you push those into the snow, and they're actually quite sensitive so you can tell when you've got something that's yielding. And then as soon as you find somebody, you leave the probe in, and then you have to dig down. And the digging down is also extremely tiring because you're talking about a weight of 600 kilos per cubic metre. It's an enormous amount of weight that you have to move very quickly.

Phil - Jim, I want to ask you: I've also heard you can get these backpacks with airbags in, for if you're free skiing for example, that you can activate in the event of an avalanche. Why would that help at all?

Jim - They have several effects, one of which is just to shield you from impacts, which can often do an awful lot of damage. But their main effect is through something called segregation, so they help you end up on the top of the snow. So that means you're less likely to be damaged, you're more likely to be able to breathe, and you're more likely to be seen. Now why is it that they help you stay on the top of the snow? Well it's the same reason that if you have a box of cereal and you shake it around, then the larger lumps of cereal end up on the top; and this is through an effect called kinetic sieving. If you have large particle with lots of small particles moving around it, they can fall through the gaps in between, and they effectively force the large particle up to the top. And in an avalanche, if you put an air bag on, you are acting like a very large particle in amongst these smaller snow grains or blocks of snow, so you've got a very much higher chance of ending up on the top of the snow.

Phil - Does that difference then between your normal size, as a human shape, versus with a big swollen airbag; is that enough increased size to actually bring you way up in the avalanche?

Jim - Yeah. A friend of mine actually did that for their PhD. They put a load of dummies on a slope, half with airbags and half without, and then they blasted the slope. And all of the dummies with the airbags had some part of them on the surface that was visible, whereas I think half of the dummies that didn't have airbags ended up buried deep down in the snow.

Chris - Sounds like a good opportunity to ask you Mark: do you actually detonate avalanches? Because I know in some ski resorts they do do that in order to reduce the risk.

Mark - Yeah. So in many avalanche services, they control the avalanche situation by... if they leave the snow to build up, then you get huge avalanches that may come down and be totally, really destructive. So they have a process whereby they control them. So they will fire charges into start zones so they release avalanches bit by bit, so you don't get a whole mass coming down but you get smaller avalanches coming down.

Chris - And Jim, why would a charge like a shockwave from sound trigger an avalanche?

Jim - So it's surprisingly difficult to actually trigger avalanches with explosives. Normally you want the explosion actually to go off in the air, to fire a shockwave into the surface; and it really can trigger them for the same reason that skiers do, it's just additional loading over an area. But it can take quite a lot of explosives.

Chris - Because I think I've heard it; and also I've seen on James Bond, so it must be true, when the baddie fires a gun and unfortunately that shock is enough to dislodge an avalanche. Is that possible or is that artistic license because it's James Bond?

Jim - That's artistic license. The energy in sound waves is so low that they're never going to trigger an avalanche.

Chris - Jim, I'm disappointed.

Jim - It's a disappointing answer. But the science is the science.

Chris - And just returning to you, Mark: when a person's actually buried... because Lawrence alluded to the fact you don't know what direction's up or what direction's down, but also you've got this enormous amount of weight bearing down on you, you must effectively just be locked in position. You're completely at the mercy of the snow and anyone who comes to dig you out, presumably?

Mark - Yes, you are totally locked in. You cannot move a millimetre. So if you're twisted or in a really awkward position, you're held in that super awkward position. And also as you're breathing, then you slowly encase the snow in front of your face with ice, and so that starts to inhibit your ability to breathe. So it's a bit of a grim prospect.

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