By Kingsley Jones, International Mountain Leader
This article was published on the AT Magazine website:
Alps has already claimed its first avalanche fatality
of the season, and before the end of winter there will
be another 250,000 avalanches in this mountain chain
alone, and around the world about 150 people will fall
victim to the 'white death'. In this article we sort
through the myths and arm you with some essential avalanche
avoidance tips, that are as valid on Aonach Mor as they
are on the North Face of Everest. In over 95 percent
of all avalanche accidents, the victim or someone in
the victim's party triggers the slide. Avalanches are
the only natural hazard in the world, that is commonly
triggered by the victim!
you have witnessed an avalanche, you will have very
little idea of their terrifying destructive force, so
here it is in terms you will be more familiar with.
Avalanches have been clocked travelling at speeds of
up to 360 km per hour (225 miles an hour), which is
the top speed of a MacLaren F1 or Ferrari Enzo. Imagine
a line of these supercars, often up to several hundred
metres wide, racing towards you at top speed! A typical
dry snow avalanche travels around 130 km per hour, and
reaches this speed within five seconds after it fractures,
with acceleration similar to a BMW 5 Series. There is
little chance of out skiing an avalanche, let alone
escaping on foot!
force of an avalanche depends a lot on its speed, but
a low speed avalanche of about 20km per hour will generate
enough force (100 kPa) to uproot a mature spruce tree
instantly, that would take a lumberjack armed with a
chainsaw over an hour to fell. A high-speed powder avalanche
can create forces of up to 1000 kPa, which is enough
to move reinforced concrete structures, such as chalets
and bridges. This equates to about 145 psi, which is
five times the pressure of your car tyre. With these
forces avalanche debris is often compacted to the density
let's dispel some of those myths. Noise does not trigger
avalanches, although the idea is a convenient plot device
in movies, so don't worry if Heidi is yodelling in the
valley. Another popular myth is that if you are buried,
you can spit out of your mouth to work out which way
is up and down. Considering that a cubic meter of snow
weighs 250kg (the weight of a fully grown male lion),
so unless you are Geoff Capes, you won't manage to dig
yourself out. Some fatalities have been recovered from
just 10cm beneath the surface.
all this doom and gloom, it's important to state that
you don't need to become a snow scientist to stay safe,
as there are a few general principles and danger zones
in the field that if respected, will save your life.
Avalanches do not strike without warning. They happen
in particular places due to specific combinations of
snow and weather conditions. There are almost always
obvious signs that these conditions exist.
do avalanches occur?
Most avalanches occur on slopes of 30 to 45 degrees,
but large ones can occur on slopes as little as 25 degrees.
You can measure these angles in the field with your
trekking poles by standing one vertically, and the other
horizontally with one tip on top of the vertical pole
and the other end against the snow. If the horizontal
pole handle touches the snow the angle is 45°. If
you have to lower the horizontal pole to half way down
the vertical pole, for the handle to touch the snow,
the angle is just roughly 25°. Over 99.8 percent
of avalanche accidents occur in the backcountry - the
bowls, peaks, and slopes outside of ski areas, where
there is no avalanche control.
do avalanches occur?
Avoiding too much snow science, avalanches occur when
a weak layer in the snowpack can no longer support the
weight of a stronger layer / slab above it. There are
two sets of factors that need to be judged; firstly
how the stronger and weaker layers form, and secondly
how the weight of the stronger layer can be affected.
The layers are mainly formed through temperature differences,
creating different crystal shapes, water contents, and
features such as depth hoar. Unless you get training
in this field, the section on key warning signs below
should suffice to keep you safe. The secondary factor
of weight in the stronger slabs can be judged in the
field. As I said in the opening paragraph, the vast
majority of avalanche victims caused (or someone else
in the group caused) the avalanche that killed them.
You can minimise the group weight on a snowpack by travelling
across areas of risk one by one, rather than as a group
with a high combined weight.
warning signs are there?
The best warning is seeing evidence of recent avalanches.
Don't be lulled into a false sense of security though,
as several avalanches can follow the same route each
season. You may see shooting cracks in the snow, which
is a sign of slab formation. If there is any evidence
of recent high winds or snow drifting, be extra vigilant
as windslab avalanches could occur. Another warning
sign is when the snow collapses in a wide area around
your weight, which indicates a hard slab over a weaker
layer. If there is a forecast for rain on the snow during
your outing, be extremely careful as the weight of water
entering the snowpack can trigger a natural avalanche.
The final common warning sign to look out for are sun
balls. Imagine making a snowball by rolling some snow
down a slope so it accumulates, and that's what a sun
ball looks like. These form naturally by solar warming
causing some snow to slough and fall down the slope,
accumulating as it travels. This is a warning sign of
a large temperature gradient, which can cause instability
in the snow pack.
are the danger zones?
The most dangerous avalanches usually occur on convex
slopes, as there is great stress within the snowpack
as it is bent over the rounded slope. Have a look at
the contours on your map to identify these slopes before
you set off. Leeward (downwind side of a ridge or mountain)
slopes are especially dangerous because wind blown snow
adds depth, creating hard, hollow sounding wind slabs.
A whole mountain may become dangerous during a snowfall
of an accumulation rate of an inch or more an hour,
and if this is forecast it is best to head down the
pub for the day.
should I do before I set off for the hill?
Over 90 percent of avalanche fatalities did not check
avalanche advisory before heading out. These avalanche
forecasts are available on the internet, phone, cable
car stations, tourist offices, and radio reports in
mountain areas. In the UK check out the Scottish Avalanche
Information Service website. Next you should pack your
avalanche safety kit, which includes an avalanche transceiver,
probe and snow shovel. These are essential for everyone
in the team, as in event of an accident, there is a
'golden' 15 minutes to recover a buried victim, before
their survival chances plummet from 93% to 50% after
thirty minutes, 26% after forty five minutes, and 5%
after two hours. Needless to say, with statistics like
this, you need to practise lots or get professional
training. Make sure that you turn off your mobile phone,
as the signal can seriously affect transceivers, and
make sure that you wear your transceiver close to your
body, not in a pocket or rucksack, so it doesn't get
separated from you in event of an avalanche.
should I be aware of on the mountain?
Most natural avalanches occur within a day of heavy
snow fall, so if you are going out keep to non-corniced
ridges or windward slopes. Following an old track does
not necessarily mean a slope is safe, as the wind direction
may have changed. Look out for raised footprints, as
this is a sign of wind scouring and the incidence of
windslab on the mountain will be high. Be aware of the
weather during the day, as rapid changes in wind, temperature
and snowfall cause changes in the snowpack and may affect
stability. Also plan your route to avoid terrain traps,
which are the likely tracks that an avalanche will follow
when triggered. An obvious example of a terrain trap
is a gully, as it acts as a natural avalanche chute.
happens if I am avalanched?
If caught you are caught in a slide, try to get off
the slab or grab a tree as soon as you can, as after
a few seconds it will be impossible due to the rapid
acceleration of the avalanche. Human instinct for survival
will kick in, and you will try and 'swim' to the surface.
Without doing this, you will sink below the surface,
as snow can be up to 90% air, and the human body is
more dense. Three quarters of victims die from asphyxiation
(breathing their own carbon dioxide), and a quarter
of victims die from trauma caused by hitting trees and
rocks on the way down. Only 2 percent live long enough
to die from hypothermia. Due to the asphyxiation concerns,
keep your mouth closed, and don't shout or cry out.
If you stay conscious as you feel the avalanche come
to a stop, it is important to try and protect your head
with your arms to create an air pocket to breathe in.
do the rescuers do?
This is really beyond the scope of this article, which
focuses on how to avoid avalanches in the first place,
but the answer is simple. You cannot rely on the emergency
services to assist, as their call out response time
is often over 20 minutes, so beyond the 'Golden' 15
minutes. If you are avalanched, you are completely reliant
on the equipment and training of your companions. The
key lesson of this is never to travel alone on snow
slopes. This may be a sobering thought, so if in doubt
then get some training. When in the field, call for
assistance anyway as the victims are likely to have
suffered trauma, shock and hypothermia. If you cannot
locate the victims, the rescue teams may bring in trained
searchers and dogs, as our four legged friends can find
a buried victim eight times faster than a 20-person
team equipped with avalanche probes.
We can avoid the vast majority of avalanche accidents
with just a little bit of knowledge. Almost all avalanche
accidents occur to people who are very skilled at their
sport. Despite this expertise, their avalanche skills
usually lag far behind their sport skills. Be very diligent
about your planning before you set out, get avalanche
and weather forecasts, let someone know where you are
travelling, and make sure you go with a friend(s) and
that you are all equipped with avalanche safety kits.
On the hill don't be afraid to change your plans in
reaction to warning signs that you identify, and if
there is any risk identified minimise it by reducing
your impact on the snow pack. You can achieve this by
reducing your group weight, by crossing sections one
by one between islands of safety. Another factor I have
come across increasingly is a willingness by people
to see these safety precautions as a necessary part
of the day, rather than a bit of a drag. The key to
safety is some basic avalanche awareness knowledge.
Good luck, and I wish you a very safe winter in the