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Anatomy of an Avalanche
BBC Two 9.30pm Thursday 25th November 1999

Flying over Galtür In February 1999, a catastrophic avalanche at Galtür in Austria claimed 31 lives. Over the next six months, Horizon followed a team of scientists as they pieced together the extraordinary chain of events that led to the disaster. The scientists' investigations into the extreme forces of nature responsible for the tragedy are making people re-evaluate their calculations about avalanches.

Computer model before the disaster The picturesque skiing resort of Galtür was considered by everyone to be a relatively safe area. Most years a small avalanche follows the same route, but trickles out safely long before the village. It even has a name: the Wasser-Leiter or Water Ladder. Computer models had indicated that the Wasser-Leiter would never have the power to reach the village, which is over 200m from the base of the mountain. So how the devastating avalanche in February managed to travel so far, in so short a time, was a scientific mystery.

Dissecting the layers of snow Since the disaster, a team of forensic scientists has been painstakingly analysing every aspect of the event. By working out the wind and weather conditions at the time of the disaster, and dissecting every layer of snow, the scientists have meticulously calculated the complex physics underlying this massive avalanche.

Crucial to the analysis was a daring experiment carried out the same month as the disaster itself. This involved scientists building a reinforced concrete bunker, bristling with detection equipment. Above the bunker, a massive avalanche was deliberately set off with explosives. As snow thundered down the mountain, the bunker was completely engulfed in snow, generating a unique set of data.

A cross-section of the inside of the avalanche The results revealed unexpected new information about how avalanches work. Radar allowed scientists to peer inside the avalanche as it was happening, providing information about the way in which snow accumulates, and the effect that different layers of snow have as they churn around inside the massive flow. The results enabled the team to piece together what had happened at Galtür, leading to a greater understanding of how and why the tragedy occurred.

New snow fences being built at Galtür At Galtür changes have already begun. Avalanche hazard zones have been extended and they are taking new precautions, which up to now had never been thought necessary. To prevent avalanches from starting on the mountains, snow fences made of steel are being constructed, and between the village and the slopes a 300m long avalanche dam is planned. New buildings replacing those that were destroyed will be made avalanche-proof, with reinforced concrete walls and no windows on the avalanche side. It is hoped that this combination of precautions will protect the village if another disastrous avalanche should ever happen again.

Programme transcript

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