Avalanche Fences Exposed!

31 August 2020

For months of the year they lie beneath deep snow, trapping it so that avalanches can be circumvented.  But when the snow melts, what is beneath is exposed to the world.  In the summer months many visitors scratch their heads at the sight of avalanche fences and wonder what form of sheep or goat they might be designed to contain.

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Their real purpose is often lost to the casual observer: to help keep roads, railways and towns – not to mention the people therein - safe from a sudden, often deadly avalanche.  In places like the Swiss and French Alps, where locals have had to live alongside the threat of avalanches for thousands of years, intricate systems of artificial structures have mitigated the risk of avalanches for almost as long.

Image Credit
Image Credit
Strangely, the purpose of this kind of fencing in mountainous regions is not to stop a snow drift but to cause one.  The fences (usually referred to as snow fences) are positioned so that drifting snow is blown in to a place where it presents the least amount of danger.  By forcing a drift on the side of the mountain, it is then less likely to cover the transport routes below.

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Image Credit
Over many centuries, communities have learned, often to their great cost, where the initiation zones of avalanches are located.  This led to the very human desire to stabilise the snow and it was the idea of a fence which was found to work.  No doubt there was much trial and error but the idea was to help absorb the force of the snow-pack through a system of fences – and to transmit that force to the ground, keeping the snow in its place.

Avalanche fences in Anzere, Switzerland
Snow Fences
Why so many fences?  Often is necessary to build rows on the up and downslope sides of any known failure point.  So if shear failure occurs in one place it is hoped and expected that the fences will limit the resulting potentially catastrophic shift of the mass of snow.

Snow fences near Blaserhutte
9533 Avalanche Fence
Sometimes, these fences are built around a basin.  The snow is forced to drift in the basin and will form a temporary pond in the spring, allowing livestock to be watered half way up a mountain.  Ski resorts will also use these fences to create a greater depth of snow for their guests to enjoy.  Yet when so many fences can be seen positioned directly above a town, such as Honningsvag, Norwayin the picture below then it is safe to assume that they are there to help control any potential avalanche.

IMGP7497 Switzerland Wengen Avalanche Protection Fences
Avalanche fences above Stubaital
A huge amount of time and energy goes in to the construction of these fences.  The mountains of Europe have been covered with them in their current form for over a century, starting with wood and latterly metal versions.  One can only wonder if their arrival led to divisions in local community with one half welcoming the arrival of new technology, the other half bemoaning the latest blot on the landscape.

Avalanche fences
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Whether you see them as a man-made marvel or a panoramic view-spoiler, their efficacy is unquestioned. They have been proven, time after time, to save lives and to reduce maintenance costs.  The National Research Council of the US showed in 1991 that the cost of removing snow mechanically was about 100 more than trapping it with snow fences.  There will never be a true figure for the amount of human lives saved by these fences but it is undoubtedly in the many thousands.

Specialized Engineering Services - Finalist
Specialized Engineering Services - Finalist
Scientific advances have now allowed the fences to become nets in more inaccessible places.

Image Credit
Image Credit
Of course, the snow fence is not a panacea for avalanche avoidance – there is a limit to human ingenuity when it comes to side-stepping the destructive power of nature.  One could even say that, strictly speaking, snow fences do not and cannot guarantee protection from an avalanche. This is because they are not constructed to support as heavy a load of snow that would be ultimately involved in an avalanche.  So, if one comes, it comes but at least the fences will have helped make it less severe than it otherwise could have been.

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(No, this really isn't a set from Thunderbirds. International Rescue is not on its way).
First Image Credit

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