Ever wondered how avalanche danger levels are set?

20th January 2013, by Abi Butcher

The Swiss Avalanche Institute in Davos issues the avalanche warnings we see across the Swiss Alps

How do ski resorts work out their avalanche warning each day? WTSS web editor Abi Butcher visited the SLF, the Swiss Avalanche Institute in Davos last week, to find out.

Every year, around 25 people lose their lives to avalanches, 90% of which they have triggered themselves. The SLF is working to research how and why avalanches start as well as monitor the conditions for its twice-daily avalanche bulletin on which ski resorts and mountain guides, as well as scores of skiers and snowboarders rely.

The now government-funded Avalanche Institute was founded in 1935 in response to the deaths of soldiers in the Dolomites — more were lost in avalanches than enemy fire, but no one understood how or why avalanches started.

Dr Martin Heggli from the SLF explained: “Though no Swiss soldiers were involved, the Swiss Army became interested, winter tourism was just beginning and Davos seemed the right place because it had the Parsenn cable car, and an easily accessible area on the mountain.”

The first avalanche bulletins were taken from that site, which is now one of the SLF’s 250 measurement stations across the Swiss Alps. Around 90 of the stations are manned, and positioned between 1,000m and 2,000m, the other 160 are unmanned, solar-powered and positioned between 2,000m and 3,000.

The Swiss Army first sent out weekly bulletins, but today’s alert is issued twice daily — at 8am and 5pm in four different languages — and is relied upon by resorts and mountain guides assessing avalanche danger. 

“We assume there are increasing numbers of skiers going off-piste, but the number of deaths has remained constant in the past 20-30 years, if not slightly on the decline,” explained Dr Heggli.”

Some resorts send the SLF information about skier-triggered avalanches, but they are not obliged to. The institute asks all skiers and snowboarders to report an avalanche if they see or trigger one, because it is vital to ongoing research.

“But prevention is crucial, because almost 90 per cent of skier avalanche victims trigger their avalanches themselves,” says Dr Heggli.

As well as studying snow and the structures it forms depending on the surrounding environment, the SLF gathers statistics and records of avalanche activity.

Its statistics on survival rates underline how crucially important it is for skiers to carry and know how to use an avalanche transceiver, as well as shovels and probes. After 15 minutes of an avalanche, a skier or snowboarder has an 80 per cent survival rate. This drops to 40 per cent at 30 minutes — the time it normally takes for an organised rescue team of helicopter and dog to arrive. After 60 minutes, the survival rate drops to 25 per cent.

There are five avalanche warning levels — Low (1), Moderate (2), Considerable (3), High (4) and Very High (5). In the past 20 years, the highest number of avalanche deaths have occurred at Level 3, at 51 per cent. Next is Level 2, which has claimed 30 per cent of the deaths, Level 4 with 13 per cent, Level 1 with 5 per cent and Level 5 at 1 per cent.

Dr Heggli said that when Level 5 is issued ski lifts are normally shut and the deaths would probably have occurred from avalanches on roads or damaging buildings.

But he said it is good news that despite the increase in skiers and snowboarders going off-piste, avalanche deaths remain constant.

“We think this is because of better risk management, better education, higher profile of mountain guides,” he said.

The SLF is sharing its expertise and information with other European avalanche warning services, such as in Slovenia which has a new and relatively inexperienced team of scientists studying avalanches.

“We also do some work in places like Iceland and Chile, for the protection of infrastructure, and we have worked with Russia for the 2014 Sochi Olympics because the area had big avalanche problems,” added Dr Heggli.

For more information on the SLF and to read its avalanche bulletins, visit slf.ch

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• snow
• switzerland
• avalanche
• davos
• off-piste
• off piste
• swiss

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