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planetFear - Articles - The PlanetFear Guide To Avalanche Risks

The PlanetFear Guide To Avalanche Risks

Article by Barry Roberts
Monday 8th March 2010

A gigantic avalanche triggered by serac collapse thunders down to the moraine near Tangnag, in Nepal's Khumbu region. Photo: copyright David Pickford / www.davidpickford.com

Avalanches present the number one danger to skiers, climbers, and ski-mountaineers, and you really don’t want to get caught in one.  These are the three key facts you should probably know:

 

  • Over 150 people each year on average are killed in avalanches with around 100 of these deaths occurring in the European Alps.
  • In 90-95% of cases the victim themselves triggered the avalanche which killed them.
  • Most avalanche accidents happen when the risk was known to be high.

The following story of a young US snowboarder is sadly typical:

The man was boarding with two friends late in the afternoon on the day after a heavy snowfall. They decided to head for an out-of-bounds area, which draws the occasional skier and snowboarder because of the steep terrain and untracked powder. The gullies were clearly marked with signs that say “avalanche area – do not enter.”

Two of them made it out safely. When their friend did not appear, they left immediately to summon help. The third man’s body was found at 7 p.m that evening.

The snowpack was so unstable that searchers feared that their efforts could trigger more avalanches. Five members of the local ski patrol and four others working with two search dogs strapped on snowshoes and headed up the gully in the dark. They had one of the dogs working through the trees and debris on the right side of the gully, while the other worked the right. They were ready to quit and head down when one of the dogs found a scent. The man’s body was buried under about 50cm of snow.

“You can have every type of equipment – transceivers, shovel, probes — but it’s good or bad decision-making that’s going to keep people alive or leave people dead in avalanche terrain,” the rescuers said. “They made some bad decisions.”

 

Before reading on, stop and ask yourself:

 

1. What was the final cause of death?


2. What was the incident spiral that led to the accident?


3. What would you have done differently?

 

 

What Exactly Is An Avalanche?

The Avalanche Handbook defines an avalanche as a falling mass of snow which can contain rocks, soil or ice. Avalanches are caused when an area of snow loses adhesion and slides down the mountain side, possibly carrying you with it or engulfing you in its path. Two different forces are at work here. The force of gravity acting on the mass of snow to try to pull it down the mountain, and friction which is preventing it from sliding away. Since gravity is constant, the trigger for an avalanche is either a reduction in the amount of friction (typically caused by an increase in temperature) or an increase in the force, typically caused by fresh snowfall, wind blowing new snow onto an already laden slope) or (and unfortunately for us) the presence of a skier or climber on the slope.

Avalanches come in various different flavours, depending primarily on the quantity and type of snow released. There are a number of different systems of classification, most of which go beyond the scope of this guide, but the basic differences are laid out below. The key distinction is between a loose slide (where the snow does not bind to itself) and slab (where it falls as a block).

What is common to all types of avalanche is the extraordinary destructive power they can unleash. It may seem surprising that something as delicate as snowflakes can cause so much trouble, but the largest avalanches can bring down over 100,000 tonnes of snow, travel up to 3 kms and can easily flatten large trees and destroy buildings. Most fatalities are caused by dry slab avalanches which travel at around 100-125 kph. Even the slowest - loose wet slides - still travel at around 30 kph. The high mountain airborne powder avalanche is a particularly deadly beast reaching speeds of over 300kph and preceded by a wind that can flatten ancient forests. Not easy to ski out of despite what you see in the movies!

 

For all types of avalanche, the risks are essentially the same:

 

- Burial and suffocation (65% of deaths)

The greatest danger is being buried by the avalanche and suffocating. The snow in an avalanche can set like concrete when it comes to a rest, and the victim or victims can be buried several metres down. Digging the victim out fast is essential.

- Collision with obstacles (25% of deaths)

The power of an avalanche can break bones and limbs. Walkers, climbers and skiers have also been killed when an avalanche (which might otherwise have had only limited effect) has swept them over a cliff or into a crevasse.

- Hypothermia and shock (10% of deaths)

Victims who survive the initial trauma and avoid being completely buried can still die of cold injury in the aftermath of the accident.

 

Overall survival rates are poor. Fewer than half the victims fully or partly buried by an avalanche survive to tell the tale. The next three articles in this series explain how to avoid being one of them.


Essential Kit For Avalanche Survival

You’ll need three essential pieces of kit which should always be carried whenever you travel off-piste. This applies even if it’s just a simple jaunt within the pisted area - plenty people have died within a few yards of the lift system and all too often they lacked one or more of these vital pieces of kit. If you don’t have all three – don’t go off piste.

 

Avalanche Transceiver (ARVA)

The transceiver (or "bleep")is a relatively recent but essential safety device. A transceiver is a small electronic radio transmitter/ receiver. In “normal” mode it emits a steady pulse on an agreed international frequency (457kHz - throw away any older device using a difference frequency). In “search” mode it acts as a radio receiver to detect the signal from another transceiver. The idea is that everyone in the group sets off with their transceivers set to transmit. If anyone gets buried in an avalanche, the others immediately switch their transceivers to search mode and (hopefully) find the victim in time to dig them out. Don't forget that a transceiver needs to be worn under your clothing not slung over the top or carries in your backpack!

Shovel

Finding a victim is not a lot of good unless you have the equipment to dig them out. Skis, poles, snowboards, twigs, bare hands and so on don’t work. You need a shovel. Most skiers carry lightweight plastic shovels with detachable aluminium handles that fit easily into a backpack.

Probe

For detailed searching – or searching for a victim with no transceiver – a probe is your best hope. This is a thin sectional aluminium pole, like a tentpole, which assembles into a 2-3m spike which can be used to “probe” the area to search for the victim.

With avalanche gear perhaps more so than any other area you need to learn and practice its use. The various techniques are covered in the following sections.

Other Stuff That Can Be Useful

Inclinometer

A simple plastic device like an old school protractor for measuring the angel of a slope. Most avalanches happen on slopes of between 30 and 45 degrees so this helps to spot a dangerous slope. Advantages: quick to use and very light-weight. Disadvantages: ski pole test (see later) does just as well.

Avalung

Essentially, this device is a mouthpiece that sucks in air from a wide area of a harness you wear over the top of your jacket. The idea is that it enables you to breathe even when buried in dense snow and thus prolongs your chances of rescue before suffocation. Advantages: if it works, it could save your life. Disadvantages: they can be a bit awkward to wear and their effectiveness depends entirely on getting the mouthpiece into your mouth whilst being avalanched, and before being buried. Sounds tricky?

ABS System

If you are going to be skiing off piste regularly, buying one of these extraordinary devices would seem to be a worthwhile investment - they are now an H.S.E. registered safety product, so effective they have proved at reducing avalanche fatalities. Essentially the ABS system is a pack storing a huge balloon which can be deployed in the event of being avalanched. This means the person being avalanched becomes much lighter than the rest of the sliding snow, and will remain on top of the slide. ABS systems are not at all cheap, but the exceptionally high survival rate of people who have been avalanched whilst wearing them suggests they are a priceless investment for any skier venturing regularly into avalanched-threatened terrain.

Snow Saw

Useful for doing research, digging snow pits, and making snow shelters. Advantages: makes cutting snow much faster. Disadvantages: extra weight to lug around. You hardly ever see anyone carrying these.

Recco or Similar Passive Systems

“passive” tags that are designed to perform a similar function to transceivers. Advantages: lighter, much cheaper (often free if they’re sewn into ski clothing), don’t need batteries, and require no intelligence to use. Disadvantages: you need huge bulky equipment to search for one which few ski-resorts keep and no-one carries off-piste. Effectively useless outside a pisted area and of questionable value within it. There is no record of anyone ever being saved through wearing one of these.


Important note: planetFear advises anyone who is venturing out into the Scottish mountains for the remainder of this extraordinary winter to check the excellent Sportscotland Avalanche Information Service before finalising plans.  

 


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