By Kingsley Jones, International Mountain Leader
This article was published on the AT Magazine website: Link
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 of concrete.
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
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
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 hills!