Multiple Avalanches kill 8 in Switzerland

Multiple Avalanches kill 8 in Switzerland

Started by Admin in Avalanche Safety - 20 Replies

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Ir12daveor
reply to 'Multiple Avalanches kill 8 in Switzerland'
posted Jan-2010

Cheers Ise, that clears up a few things in my head.

Admin
reply to 'Multiple Avalanches kill 8 in Switzerland'
posted Jan-2010

Various sources are now reporting the recovery of 3 further fatalities from the Diemtig valley, bringing the total toll for that incident to 7.

No other people had been reported missing.

From The Guardian :-

The victims were in a group of off-piste skiers hit by an avalanche shortly before midday on Sunday, burying two. A second avalanche, about half an hour later, hit the rescue party.

An emergency operation involving eight helicopters from the Swiss air rescue service and 100 rescuers was able to pull nine people from the snow. One man was already dead, and three others died in hospital.

The earlier victims were identified as a German and three Swiss, one of whom was a rescue doctor who had flown in to help.

Rescuers had been unable to search for the remaining skiers yesterday because fog and snow prevented safe access to the area by air or on foot.

Experts had held out little hope the missing three people would be found alive. It was the biggest avalanche death toll in Switzerland since February 1999, when two snow slides swept away several chalets in the canton of Valais, killing 12 people.


Be careful out there...

...heavy snowfall in recent days have prompted officials to warn of a heightened avalanche risk in the Swiss Alps.

The Admin Man

Ise
reply to 'Multiple Avalanches kill 8 in Switzerland'
posted Jan-2010

Admin wrote:
Be careful out there...

...heavy snowfall in recent days have prompted officials to warn of a heightened avalanche risk in the Swiss Alps.



These warnings are going on deaf ears, people on holiday have some bizarre ideas about why and where avalanches occur and how and why snow is unstable.









This slide is at the top of the Orxival drag lift in Grimentz, it's quite small and looks like it was triggered from above by two snowboarders who decided to take a couple of extra turns by walking a few metres up from the lift and then riding down. Neither were equiped, no transceivers, no probes or shovels.

The small slab that detached then hit the piste below, we just arrived as the pisteurs were probing the snow and were ready to assist but they were happy no one had been hit by the slide.

In the final shot you ought to be able to see how badly consolidated the snow is, there seems to be two distinct slabs both of which failed.

None of which is particularly worthy of comment apart from that at the same time as the piste security are probing the snow people are climbing up on the ridge above them and looking over the cornice at the top to the pisteurs below. Simultaneously, about 150m behind us skiers without any equipment are skiing into the Abondance itinerary which was clearly closed. In some bizarre and potentially lethal parody of safe skiing one particular group ski the slope one at time before regrouping below it, the spot they picked would be to within a meter or two the maximally exposed position in the bowl and slides on any the slopes around it would have reached maximum depth exactly where they were stood.

And all day we saw the exact same thing, skiers and boarders without any equipment at all on slopes that were extremely dangerous, moving in groups from 2 or 3 to 7 or 8 only a few meters apart, stopping for a chat in positions of extreme danger or terrain traps.

Edited 1 time. Last update at 06-Jan-2010

Davidof
reply to 'Multiple Avalanches kill 8 in Switzerland'
posted Jan-2010

Interesting photos. You should post them to data-avalanches.org.

It takes a lot of force to trigger a slab. A 100x50x50cm slab may contain a 750 tonnes of snow, a 70 kg (or even 85kg if we take a typical swiss or brit) is nothing in comparison. What probably happens is that there is a localized collapse on a weak layer and that causes a domino effect. But for that to happen there needs to be a weak layer. In the above case either a layer of surface hoar or depth hoar formed by a temperature gradient formed at the interface between the two layers or where there is a crust.

Your photos clearly show another danger. A shallow surface slab, maybe not too nasty, but its weight can take a second more deeply buried slab to create a big slide.

Ise
reply to 'Multiple Avalanches kill 8 in Switzerland'
posted Jan-2010

It's pretty much the prevailing condition locally, one poor layer on top of another. This is a lee slope, actually very slightly off lee, so wind transport is a factor on this particular slope. The layering is similar on other local slopes of the same aspect.

SLF are still giving graphic warnings :

The snow layering is of highly varied structure. In some areas, faceted, weak layers are evident, interspersed with rain crusts up to altitudes of approximately 2500 m. Loosely packed snow lies atop the surface in many areas, in some places accompanied by surface hoar. More deeply embedded layers are inadequately bonded to each other in some regions.


SLF suggest risk is escalating as well, personally I'm supposed to be in the Jura for a few days where SLF don't produce forecasts so I'm going to be interested to see first hand the conditions there.


Dave Mac
reply to 'Multiple Avalanches kill 8 in Switzerland'
posted Jan-2010

davidof wrote:It takes a lot of force to trigger a slab. A 100x50x50cm slab may contain a 750 tonnes of snow, a 70 kg (or even 85kg if we take a typical swiss or brit) is nothing in comparison.


I respectfully question the snow density stated. The weight of a cubic metre of concrete is 2.4 metric tonnes. So, one eighth of that volume might be in the region of 0.3 tonnes.

Given a very low coefficient of friction exiting in a hoar layer, and taking into account the force from a snowboarder would not be a static, but a dynamic force, then you might expect avalanche conditions.

Admin
reply to 'Multiple Avalanches kill 8 in Switzerland'
posted Jan-2010

Dave Mac wrote:
davidof wrote:... A 100x50x50cm slab may contain a 750 tonnes of snow, ...


I respectfully question the snow density stated.


Dave, I suspect David means 100 metres by 50 metres x50cm - or 2500 cubic metres.
The Admin Man

Dave Mac
reply to 'Multiple Avalanches kill 8 in Switzerland'
posted Jan-2010

Admin wrote:
Dave Mac wrote:
davidof wrote:... A 100x50x50cm slab may contain a 750 tonnes of snow, ...


I respectfully question the snow density stated.


Dave, I suspect David means 100 metres by 50 metres x50cm - or 2500 cubic metres.


Dozy me.

Topic last updated on 10-February-2010 at 15:21

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