Title:The Avalanche Disaster of Galtür in 1999 - The Rescue Operation, Analyses with Recalculation and Countermeasures
Proceedings:Proceedings Whistler 2008 International Snow Science Workshop September 21-27, 2008
- Gebhard H. Walter [ Austrian Federal Service for Torrent and Avalanche Control, Imst, Austria ]
Abstract:On the 23 of February a catastrophic avalanche disaster happened. It took place in the Tyrolean village of Galtür in the Austrian Alps. Heavy snowstorms from the Northwest brought in three periods enormous snow masses. Heavy Wind and additionally massive drift-snow packages causes a powder snow avalanche with an unknown dimension. The two neighboured so called "Outer Wasserleiter-Avalanche" and "Weisse Riefe-Avalanche" buried 60 persons, 31 people were killed. 6 houses were destroyed and 18 damaged. A rescue operation started and because of the locked road only helicopters could reach the valley. Over 12.500 people have been evacuated by 46 helicopters also from the US Army. To analyses the long runout distance and the destructions detailed investigations were done. By field work and helicopter support the avalanchepath were mapped. After the recalculation of the snow masses and avalanche forces simulations with different models were done. The comparison of the more dimensional models (SAMOS 99, SAMOS AT and ELBA) shows that the second starting area in combination with the great snow entrainment played an important role. Immediately after the disaster the Austrian Federal Service for Torrent and Avalanche Control developed a project including avalanche barriers and snowpack stabilizing structures. Now the main parts are finished.
Language of Article: English
Keywords:avalanche, size, recreationalists, killed, injured
Subjects:fracture mechanicsavalanche dynamics
The Alps are a spectacular mountain range over 3,000 metres high with a sharp, steep landscape. In February 1999, a series of low pressure systems persisted that brought continuous heavy snowfall. The result was that in one month, more than twice the amount of snow fell as usually falls during the whole winter from December to April.
How are avalanches created?
Avalanches occur when a large amount of snow and ice or rock falls suddenly down a mountainside. There are two main types of avalanche - dense flow avalanches or 'wet' avalanches, sometimes called slab avalanches, and powder snow or 'dry' avalanches. Most of them happen during or soon after storms. Slab avalanches are usually more deadly than powder snow avalanches but this disaster was a dry avalanche. Avalanches happen when a weak layer of snow can no longer support the weight of the snow above it and the overlying snow cracks and breaks away.
What happened at Galtür and why?
Very high winds and low temperatures meant that exceptionally large amounts of snow were deposited without breaking free. The build-up of snow continued for a week until record levels had been deposited. When the mass gave way, in places a giant 50 metre wall of snow travelled with great force up to 200 kilometres an hour into the small town. It overturned cars, damaged buildings and 31 people were killed. In February 1999 there was simply too much snow that accumulated very quickly and enormous quantities fell on the valley floors. Once the avalanche began it collected more and more snow that ran far out into the valley floor and engulfed the settlement that was built there. The steep, sharp Alpine landscape intensified the effect of the avalanche.
What can be done to reduce the danger of avalanches?
Austria has tried to categorize areas that are in danger from avalanches by creating red zones and yellow zones. In red zones construction of any kind is prohibited. In yellow zones certain safety measures apply and strict building codes are enforced. Although the threat of avalanches is present the buildings are constructed in such a way that people should not be harmed. Galtür is built in a yellow zone. At the time the avalanche struck at 4.00pm many people were returning from the ski slopes and were caught out on the streets rather than in the relative safety of the buildings.
Austria has spent a great deal of money to try to reduce the risks from avalanches -constructing strong, resistant buildings; avalanche barriers on the mountain slopes; planting trees which in themselves break the flow of an avalanche. However, pressure for further development on mountainsides to meet the increased demand from tourists creates tensions between planners, environmentalists and the authorities. If further development continues to take place then the risks from avalanches also increase.
These notes are aimed at students studying for Edexcel (B) Unit 5 - Hazards, though will be suitable also for people studying with different exam boards and at different levels.
They were originally submitted by wackojacko in this thread on TSR Forums.
Article by TSR User on Thursday 15 February 2018