Avalanches
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They rank alongside earthquakes, flash floods, sharks and
lightning strikes as deadly, unpredictable, unstoppable forces that can
strike at random to maim and kill unsuspecting holidaymakers.
At the other end of the spectrum, the rationalist view of avalanches would
have it that they can be controlled, their risk managed or even eliminated
by a combination of technology and common sense.
The truth lies somewhere between these extremes. For the most part avalanches
are creatures of habit - they start under fairly predictable conditions
and they follow the same tracks year after year. As long as you follow some
basic rules, you need never put yourself at risk.
Most avalanche accidents happen when people ignore these basic rules. The
majority of avalanche deaths among skiers and snowboarders are caused by
the skier or snowboarder themselves or somoeone in their group.
Every so often, however, freak weather conditions change the rules. Either
so much snow falls, or it falls under such unusual weather conditions, that
normally safe slopes become avalanche-prone. These are the big killers,
which come down unexpectedly on villages from slopes which have no history
of avalanching. |
Avalanche types
There are three principal types of avalanche - powder,
wet snow and slab.
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Powder Avalanches
These generally start from a single point, growing as
they progress.
Ever-increasing volumes of powder snow are thrown into the air, flowing
down the slope as a dense cloud. Speeds can reach up to 400 kph (250 mph)
and the shock wave of the approaching avalanche can flatten everything
in its path.
Although rare, especially in Europe, this type of avalanche is extremely
dangerous, battering or choking its victims to death.
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Wet Snow Avalanches
In spring, or whenever it is subjected to elevated
temperatures, snow transforms rapidly. As a result its cohesion and strength
is reduced; wet snow avalanches frequently result.
These generally start from a single point, spreading as they slide. Their
progress is generally slow, unless they encounter steeper terrain or are
funnelled into a gully.
Due to the density of snow carried, these avalanches can be extremely
destructive. Once they stop, they set like concrete; buried victims are
unable to move or breathe.
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Slab Avalanches
Around 75% of all avalanche incidents involving skiers
are due to slab avalanches. The most common cause is wind; snow is carried
over ridges and dropped on lee slopes, building a thick, unstable layer
of dense snow, called wind slab.
This type of avalanche, however, can occur whenever layers of snow do
not cohere strongly, for instance if the intervening surface is smooth,
damp or granular.
The reason that slab avalanches are so dangerous is that the instability
is invisible to the naked eye. It may be buried under a layer of fresh,
inviting powder. But given the right trigger, such as the tracks and weight
of a skier, the top layers of snow fracture right across the slope and
begin to slide over the layers below.
Victims find themselves standing on or below the moving slab, with very
little chance of escaping as it breaks up and carries them down the slope.
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Judging Risk
Reducing Risk
If Caught
Friend Caught
Your chance of survival is greatly increased if you are discovered
quickly. The deeper you are, the worse your situation.
Speed is essential. Two-thirds of fatalities
are due to suffocation, so the chances of survival diminish very quickly
after the first half-hour.
- Make sure the slope is stable after the initial slide.
Stay alert as you search so you are not caught in a second slide.
- Mark the spot where the victim was last seen.
- Carry out a quick search first, then a more detailed
hunt. Shout and use the handle of your pole or the tail of your ski
to probe the snow if you don't have a shovel or avalanche pole. Most
probable areas are at the edges of the slides, or around boulders and
trees.
- If there are several in the group, two should go for
help after a first quick search, the rest carry on searching.
- Once you have located the victim, uncover the face
with all speed.
- Depending on the type of avalanche, injuries are likely
to be suffocation or crushing, as well as hypothermia.
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Transceivers
Using transceivers
Transceivers offer the best chance of rapidly locating buried
skiers. They must be worn by all members of the party, and if your transceiver
is not compatible with that of your colleagues, it is of no use whatsoever.
They must emit a signal at a standard frequency of 457kHz - some older models
in the US operate at a different frequency - these should no longer be used.
Make sure you install new alkaline batteries at the beginning
of each season. You must wear the unit close to your body where it won't be
ripped off in an avalanche. At the start of the day, the group tests all transceivers
to ensure their batteries are strong. They are then left on the transmit setting
throughout the day. If one of the party is taken by an avalanche, the rest switch
to the receiving mode to locate the incoming signal.
Practice is essential before you need to use your transceiver.
When one of your group is buried, it's too late to be reading the searching
instructions.
If the amount of off-piste skiing that you do does not justify
buying your own transceiver, you can hire one for the day in most resorts. In
addition, any ski guide worth his or her fee should be able to provide them
for all their clients for a daily charge.
Searching with a transceiver
First search down the flow line from the last seen point, following
the route as shown.
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Single Search
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Group Search
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Pinpointing the signal
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| Once you have received a signal from the buried transceiver,
turn off all except one receiver. Walk in the direction of the signal until
you reach the point where it is strongest. Turn through 90 degrees and once
again find the place where the sound is strongest. Repeat this process until
you can pinpoint the buried victim precisely. |
Avalanche cords are a second-best
option. On dangerous-looking slopes, you trail a 10-metre cord behind you as
you ski. If you are buried, it is hoped that part of the cord remains visible
on the surface.
Recco transmitters consist
of a chip of material that can be detected under snow by a receiver (the system
is similar to a shop's anti-theft device). They are cheap and light, and can
be attached to your clothing or ski-boots. While better than nothing, their
disadvantage is that the searchers must be equipped with a receiver. In practice
this means waiting for rescuers to arrive and hoping that they carry the necessary
equipment.
New on the market in the last few years, you can also
wear an inflatable vest. This
incorporates a cylinder of compressed air. In the event of an avalanche, you
crack the cylinder, inflating the vest. Not only does its bulk help you to float
on the surface of the slide, but should you be buried, you can breathe the air
from the vest (as long as you can find the nozzle). Nice idea, but remember,
the best plan is not to get caught.
A shovel and first aid kit
should be carried if your off-piste skiing takes you any
great distance from help, as should a reflecting emergency blanket.