Snow as a threat
Kathi, Nadja, Vanesa, Lara
(video)
Welcome
bla bla
Introduction
There the snow lies, white and innocently, and seconds later a destructive avalanche
can roll into the valley. Snow is a contrast of beauty and menace , which contributes to
the fascination of snow. (picture snow)
Facts:. (1. Bild)
Generally there are two types of avalanches, there are powder avalanches, which
consist of dry snow and dense flow avalanches, which consist of compacted, moist
snow. The dense flow avalanches reach speeds of 50-100 km/h. In very steep terrain, a
dense flow avalanche can be transformed into a powder avalanche as it descends,
reaching a velocity of 200-300 km/h.The annual average number of avalanche victims in
the European Alps is around 110 people. 90% of the victims nowadays are winter sport
participants who trigger the fatal avalanche themselves.
But how exactly do avalanches arise?
Formation: (2. Bild)
Avalanches occur on slopes with a gradient steeper than around 30 degrees, the
steeper the slope the higher the risk of an avalanche. If the snow consists only of one
layer, there arise hardly any avalanches. But mostly as a consequence of various
snowfalls, the snowpack consists of several layers. Those layers do all have different
features and especially the surface of the snow is influenced by the weather. Surface
hoar can form, or the snow surface can become otherwise transformed so that the layer
of snow deposited by the next snowfall does not bond sufficiently with the existing cover.
The more different layers there are the more unstable is the snowpack. Fractures form
and get bigger especially near the boundary between two different layers.
Triggering: (3. &4. Bild)
For the avalanche to come off there must be a trigger, something that leads to an
overstressing. This can be heavy snowfall or the temperature. If the upper layers get
warmed up by the sun and slide down the lower layers get under more pressure. Even if
the weak layer underneath the snow slab is capable of carrying the weight of the layers
above, it can remain, for a long time after a snowfall, sufficiently fragile to be fractured
locally by a skier for example. Within a few seconds, large sections of a slope can
become detached with a speed of around 20 m/s and begin to slide down. In this case
usually a snowpack 50 meters wide, 70 meters long and 1/5 meter thick gets released.
This can easily be some dozen truckloads of snow…The slab of snow breaks into pieces
and races towards the valley at quickly gathering speed. The ensuing release of the
entire slab can often bury the person.
Artificial avalanche releases - why? (for the others: "artificial" means, that it's not done
in a natural way)
In winter you may often hear a loud bang in the mountains, ensued by a thunder noise.
Avalanches are getting dynamite-triggered. The aim is to protect avalanche-threatened
areas - at least for a certain time. After explosive applications, the slopes are being
groomed and will be opened for sportsmen.
Avalanches get also dynamite-triggered beyond the skiing areas. For example above
traffic routes or settlement areas.
It's important that avalanches get dynamite-triggered regularly to release small
avalanches. It prevents that a dangerous snow pack can form where a great avalanche
can develop.
Artificial avalanche releases are important for the protection from great avalanches.
(show pictures)
Artificial avalanche releases - how?
There are different possibilities to release avalanches artificially. However, the principle
is the same. Because of the pressure (a force pressing on sth) of the blast, a fracture (a
break) in the snowpack will be caused, so that this part slips off.
Warning
If you want to know how high the avalanche danger is, there is an avalanche situation
report (Lawinenlagebericht) or as the Swiss say, an avalanche bulletin. It is a graphic
representation of the danger levels for avalanches. (show picture) This map always
changes and you can check it out on a website.
But this information is not sufficient if you're up to go skiing in the morning.
You must observe the weather, to examine the snow pack, study the map and estimate
(beurteilen/einschätzen) the local circumstances. For those things, there are avalanchewarning services.
Throughout Europe there are five danger levels:
sluff - Level 1
small - Level 2
medium - Level 3
high - Level 4
very high - Level 5
How to survive an avalanche and ways to be saved:
(Picture)
When someone is blocked in an avalanche the first 10 to 20 minutes are crucial to get
somebody out alive.
After that time most people suffocate, because the airways are blocked or there is too
less oxygen beneath the snow.
Also the difficulty of undercooling gets worse, if it is so cold, like it is under the snow, the
metabolism decelerates. So the person is in need of less oxygen and his chance to
survive rises. An Avalanche is as hard as concrete if it has stopped, so the blocked
ones aren’t able to move a bit.
The faster a person can be saved, the higher are the chances for him to get over it. That
means fast help is essential.
That is the reason why the so-called help of companion is he most important thing. In
that case the companions try to get as close to their friend as possible with their
gadgets. When they are around the person they pick up their soundwaves. It is like a
long stick, with its help you can poke through the snow and hopefully you will feel
something harder than the snow. That might be your friend. And then they begin to dig.
The good thing is, when the avalanche once has been released and comes to standstill,
it is almost safe to go on that slope.
If the blocked person isn’t in possession of an avalanche protection gadget, it is very
difficult for his friends to find him.
(Picture2)
You can get those gadgets in almost every sport shop and it really is useful. Not just for
you, if your friend gets blocked, your chances to find him are much better.
Is there still no way to find him, there are dogs, which are trained to find people under
the snow.
So they need to call the REGA. The REGA is a helicopter, which saves injured or lost
people.
There can be long ways of arrival, so the help of companion is almost always faster than
to wait until the helicopter appears.
The life-saving equipment, gear and education have improved extremely in the last few
years, so fortunately the chances to survive raised.
Anyway the highest priority is to avoid getting blocked in an avalanche.
But what shall we do if we recognize that we have released an avalanche?
There are a few rules, which you should observe.
First you should throw away your sticks, you might get injured or stuck owing to them.
Also you must try to stay on your board or skis and get out sideways.
If you tumble down, it is vital to do swimming moves to stay on the surface.
If the avalanche slows down, you have to build like a hole in front of your mouth and
nose to safe some space for air. Otherwise you will suffocate quickly.
If you are out there on your own and you get blocked, your chances are very bad. When
there are no eyewitnesses, nobody is able to help you. Unfortunately blocked ones are
invisible and can't shout.
Avalanche defence (picture change)
Avalanche defence activities reduce the hazard avalanches pose to human life,
surroundings and property. Without protection against them, living in the Alps would be
impossible. What kind of defence you use depends on the geographic patterns of the
place where you live. There are different techniques how to protect a city against
avalanches. Usually this is about directly intervening with the evolution of the snow pack,
or to lessen the effect of an avalanche once it has occurred.
An active technique is to promote the stabilisation and settlement of the snow pack by
disrupting weak layers, increasing the unity and lessening the amount of snow that can
go with the avalanche. For this is the triggering as my colleague has explained.
Permanent techniques slow, stop, divert or prevent the snow from moving. The most
common structures are:
 Avalanche barriers: these are steel wire meshes, that are extended across the
slope and reach the surface of the snow. The purpose of that is to prevent the
avalanche at the starting zone, so that the movement is restricted and therefore
less harmful. (picture change)
 Avalanche Galleries are a common sights on railroads , where tracks are covered
with those an art of tunnel. The snow can easily go over that gallery and the
railroads are not getting covered with snow.
 In Davos it isn't allowed to build a pitched roof because the snow caps can easily
fall off the roofs and harm people. There are only few roofs that are not horizontal
here. If a slope roof is still wanted, there is the possibility of snow guard devices
that increase the snow retention on roofs.
But one of the most effective ways is the forest. The trees slow the snow down and can
even stop it from moving. Cutting down trees in an avalanche endangered zone it not
very beneficial for the people and the cities.
Last big event
February 1999 is known as the avalanche winter. During 5 weeks over 5 meter of snow
fell down and a strong storm that had occurred set good conditions for avalanches.
Around 1200 avalanches set off and caused 70 deaths. It damaged buildings and the
environment and cost Switzerland a few millions. The valleys were cut off because all of
the roads and railroads were covered in snow. All of the Davoser inhabitants and the
tourists (around 50,000 people) had to stay in Davos for at least a week until the streets
were freed from the snow again.
How does the force of an avalanche actually feel?
Well, one day I was on the slope. The snow was perfect; it was like sugar and went up to
my hips. Suddenly I heard a bump, and that sound means no good.
I looked up the slope and saw a huge avalanche.
The force was incredible, although I was at a safe distance. I was almost able to feel the
power of it.
I was scared of that sight and by the same time amazed how powerful nature can be
and how little and weak we are. I will never forget, what distances also the snow dust
covered.
Sources:
-Book: “Schnee“
-www.slf.ch