Galtür Avalanche
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On February 23, 1999 the worst Alpine avalanche in 30 years 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.
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[edit] Weather conditions
The winter of January-February 1999 was particularly severe, with non-stop snowfall in the region accumulating 270cm of snow over the course of 7 weeks. Strong winds of between 80 and 90 km/hour created large snow drifts moving 10-20 tonnes of snow in one hour. On February 6th temperatures rose to 5 degrees Celsius, warm enough to melt the snow. On the 8th temperatures plummeted below zero again making an unusually hard snow layer, the melt-freeze-crust. The snow continued to build up until the melt-freeze-crust layer could not withstand the intense weight of the snow pack, collapsing on February 23rd 1999.
[edit] 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.
[edit] The Avalanche
The avalanche occurred on February 23, 1999 at about 16:00 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 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.
[edit] Aftermath
Soon after the avalanche rescuers began to look for survivors; in 24 hours the rescuers saved 26 people. 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.
[edit] TV
The avalanche attracted media attention from all over the world mostly due to the magnitude of the rescue operation. The avalanche was also profiled on National Geographic's Seconds From Disaster in the episode "Alpine Tsunami".
[edit] External links
A transcript of a BBC documentary is excellent and contains information from many experts.
A complete report on the winter of 1999 in the Swiss alps is available
