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Avalanches

For use with Talking Point worksheets

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Avalanches

Postby TalkingPoint » Sat Dec 31, 2005 7:15 pm

Avalanches

What are they?
Avalanches are large areas of snow which slide down the side of a mountain with tremendous force. They can uproot trees, destroy buildings and kill people. In the last 50 years the number of fatalities due to avalanches has increased noticeably due to the fact that winter sports such as skiing have become much more popular and available. In the USA more than 500 avalanches have been recorded since 1950. The majority of victims are men in their 20s and 30s.

An avalanche consists of three parts. It begins with the "starting zone", which is where the snow cracks as the lower part starts to slide downwards. The second part is called the "track", which is the name of the "road" the avalanche takes as it travels down the mountain. Lastly there is what is called the "runout zone", which is where the avalanche spreads out and comes to a halt.

Where do they occur?
They tend to occur most in the Alpine countries of France, Switzerland, Italy and Austria, but they also occur in other mountainous countries. The USA is ranked fifth in the world for frequency of avalanches. Avalanches tend to occur on slopes that are angled at between 30 and 45 degrees on the north side of mountains. Snow does not often build up on steeper slopes and snow on the south (sunnier) side of mountains is warmed by the sun and therefore melts a little, causing the layers to stick together more efficiently, thus reducing the risk of areas of snow breaking off and causing an avalanche.

Why do they happen?
Many different factors, often in combination, can contribute to causing an avalanche: the weather, the temperature of the air and the snow, how steep the slope is, whether the slope is on the north or south side of the mountain, which way the wind is blowing, what type of land is under the snow itself, and even whether there are many trees on the slope or not! Sometimes it only takes a loud noise to trigger an avalanche. Avalanches often occur as a result of a heavy snowfall, hence one of the riskiest times for avalanches can be the first 24 hours after a snowstorm. Underlying all these causes is, of course, the force of gravity, which simply pulls unstable snow down a mountain.

Sometimes it can be possible to "predict" an avalanche, or at least locate a possible zone for one, but this can be difficult as conditions can change in a very short time. For instance, weather conditions can worsen in the blink of an eye. In frequent avalanche zones the local authorities may even set off an avalanche deliberately (under strictly controlled conditions) in order to avoid a build-up of snow which may threaten a village or tourist zone. In cases like these, explosives may be used to start the avalanche.

How to survive one!
If you have the misfortune to find yourself caught up in an avalanche it is suggested that you try to "swim" through it in an effort to keep yourself near the surface of the snow. If you find yourself buried under the snow, guidelines recommend that you dig away the snow around your head to create a breathing space. They recommend that you do not shout out for help because snow is a good insulator and will muffle the sound of your voice. You are unlikely to be heard and will just tire yourself out with the effort. Above all, it is recommended that you keep calm so that your chances of survival are increased.

Quick Quiz: Read the clues below and write the solutions on a piece of paper. Then take the first letter of each answer and rearrange them to find the hidden word connected with this Talking Point.

1. Avalanches are large areas of snow which slide down the side of a __________ with tremendous force.

2. If you have the misfortune to find yourself caught up in an avalanche it is suggested that you try to "__________" through it.

3. In frequent avalanche zones the local authorities may even set __________ an avalanche deliberately (under strictly controlled conditions) in order to avoid a build-up of snow.

4. Weather conditions can __________ in the blink of an eye.

5. Avalanches tend to occur most in the __________ countries of France, Switzerland, Italy and Austria.

6. In the last 50 years the __________ of fatalities due to avalanches has increased noticeably.

7. Sometimes it only takes a loud __________ to trigger an avalanche.
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