Galtür Avalanche

On February 23 1999 the worst Alpine avalanche in 40 years. It killed 31 people in the small Alpine village of Galtür, Austria. Three major weather systems originating from the Atlantic accounted for large snow falls totalling around four metres in the area. 'Freeze-thaw' conditions created a weak layer on top of an existing snow pack, further snow was then deposited on top. This, coupled with high wind speeds creating large snow drifts , caused unusually high volumes of snow to be deposited.

The Zones

Like most populated regions of the alps Galtür was hazard zoned according to the perceived risk into red, yellow and green areas.

*Red Zone- No building allowed to be built in this zone; highly vulnerable to avalanches.

*Yellow Zone- Moderate risk; buildings are allowed but must be reinforced to resist avalanche.

*Green Zone- Avalanche safe; buildings are allowed to be built; no reinforcement required.

The Cause

The cause of the avalanches puzzled scientists for a long period of time. Although the area was prone to avalanches, never before had they occurred on such a scale as this, reaching the village. A complex sequence of events led to the hazard: 4000km away, on the 20th of January, an Atlantic storm was forming. Turbulent warm air from the tropics headed north, and, cooling, it swung back towards Europe. This started a series of storms. Combined with cold arctic air coming from the north, there was a very dry, light snowfall exceeding 4m. A massive snowpack formed on the mountains above Galtür. NW winds piled the snow to increasing depths. A melt-crust developed in late January, formed when solar energy thaws the upper snow layers in the day, but it then refreezes at night. At Galtür, it bonded with ice and hence lasted longer than they were generally known to. The resulting powder avalanche contained a central layer scientists were not previously aware existed. Known as the saltation layer, it was primarily responsible for the destruction of buildings.

The Avalanche

The avalanche occurred on February 23 1999 at 16:01 when the frozen layer of snow (melt-freeze-crust) failed. Due to the cold conditions, snow with a very low density (between 50 and 70 kg/m³) was formed. This caused a massive powder avalanche (see Avalanches) travelling at around 186mph (290km/h) down the mountain side. As it travelled down the mountain, the avalanche picked up twice the amount of the initial snow volume of around 170,000 tonnes doubling its size. The avalanche was estimated to contain around 300,000 metric tonnes of snow, it had a height of around 100m (300 ft.) at its leading edge and took only 50 seconds to reach the village. The avalanche went into the green zone destroying seven modern buildings and causing extensive primary and secondary damage as well as burying 57 people. Many people died of asphyxiation from inhaling and sufficating on the aerosol type snow due to its low density.

Aftermath

Soon after the avalanche rescuers began to look for survivors; in 24 hours the rescuers saved 26 people. A rescue dog, Heiko, amply proved the value dogs have in avalanche rescue, saving many lives. The day after the avalanche 31 people were all confirmed dead. Outraged families demanded to know why the avalanche penetrated the supposedly safe zones and devastated Galtur. However, hazard zoning is based nearly entirely on the historical record, and there was no evidence of avalanches travelling so far on this track in the past. Since this disaster there have been renewed efforts to improve avalanche knowledge and forecasting so that hazard zones can be accurately predicted. This is particularly important if land use or climate changes rendering past information less useful. Response has included the extension of the hazard zones, with steel fences constructed on all mountain sides above the village. A 300m avalanche dam directly protects the village.
The avalanche attracted media attention from all over the world mostly due to the magnitude of the rescue operation. It was also profiled on National Geographic's Seconds From Disaster in the episode "Alpine Tsunami".

External links

A transcript of a BBC documentary is excellent and contains information from many experts.
*http://www.bbc.co.uk/science/horizon/1999/avalanche_script.shtml

A complete report on the winter of 1999 in the Swiss alps is available
*http://www.slf.ch/media/winter99-de.html