1. THE AVALANCHE HAZARD

2. 2 news clips from 1999, 7.17 mins

3. Avalanche A Definition: A Definition: A mass movement of snow and ice(and/or regolith) down a slope due to structural weakness in the snow cover on that slope, under the pull of gravity. A mass movement of snow and ice(and/or regolith) down a slope due to structural weakness in the snow cover on that slope, under the pull of gravity.

4. Avalanches! Avalanches are common phenomena throughout mountain areas. Avalanches are common phenomena throughout mountain areas. People are increasingly active in mountain areas : recreation and leisure tourism; infrastructure to support tourism; pressure on more easily inhabited land. People are increasingly active in mountain areas : recreation and leisure tourism; infrastructure to support tourism; pressure on more easily inhabited land. Therefore increased RISK of interaction, and increased hazard. Therefore increased RISK of interaction, and increased hazard.

5. What are the main characteristics of avalanches? Distribution over space. Distribution over space. Location : same places each time therefore relatively predictable. Location : same places each time therefore relatively predictable. Frequency: changing through time? Frequency: changing through time? Speed of onset/warning time : little warning. Speed of onset/warning time : little warning. Relative to other hazards? Relative to other hazards?

6. AVALANCHE FREQUENCY and DISTRIBUTION 1 million per year. 1 million per year.

7. A spectrum of hazards (Smith 1992)

8. Impacts Main direct impacts are deaths, injuries, and economic losses to communities affected. Main direct impacts are deaths, injuries, and economic losses to communities affected. Indirect impacts include wider economic losses to tourism industry, transport delays, and wider spatial economic losses. Indirect impacts include wider economic losses to tourism industry, transport delays, and wider spatial economic losses.

9. FATALITIES IN EUROPE AND NORTH AMERICA

10. AVALANCHE TYPES Powder snow avalanches Wet snow avalanches Slab avalanches

11. Powder snow avalanches No warning. Up to 200mph Up to 50 tonnes/m 2 force Occur at any time in season. Example :Galtur, Austria.

12. Wet snow avalanches Usually late in season. Usually late in season. Slow moving (5-15mph). Slow moving (5-15mph). Considerable weight of wet snow (up a million tonnes). Considerable weight of wet snow (up a million tonnes). Example : Odda, Norway. Example : Odda, Norway.

13. Slab avalanches Slab avalanches are most common occurrence. Slab avalanches are most common occurrence. Often started by human error. Often started by human error. Most frequent cause of death amongst skiers, snowboarders, and power-skiers. Most frequent cause of death amongst skiers, snowboarders, and power-skiers. Speeds up to 100mph. Speeds up to 100mph.

14. Origins of avalanches Weather : snowfall is essential ingredient. Weather : snowfall is essential ingredient. Slope : more than 30 o and less than 45 o for starting an avalanche. Slope : more than 30 o and less than 45 o for starting an avalanche. Changes in the snow-pack. Changes in the snow-pack.

15. Contributing factors Heavy rainfall on snow (more likely in Scotland than the Alps!) Heavy rainfall on snow (more likely in Scotland than the Alps!) Deforestation - reducing slope stability Deforestation - reducing slope stability Vibrations - skiers,more dangerous earth movements Vibrations - skiers,more dangerous earth movements Long cold winters then heavy snow falls in spring. i.e. slip plane created. Long cold winters then heavy snow falls in spring. i.e. slip plane created.

16. Changes in the snow-pack Temperature changes in the air can bring about : Temperature changes in the air can bring about : Partial melting in the snow-pack. Partial melting in the snow-pack. Freezing of melt-water in snow. Freezing of melt-water in snow. Changes in snow crystal shapes and sizes. Changes in snow crystal shapes and sizes. Changes in the strength of the snow layers. Changes in the strength of the snow layers.

19. Chamonix & Galtur, 18mins

20. Snow-pack stress Snow lying on a slope is subject to stress : Snow lying on a slope is subject to stress : gravity is pulling it downwards gravity is pulling it downwards adhesion and weight is keeping it “stuck” to the slope. adhesion and weight is keeping it “stuck” to the slope. Often these stresses are delicately balanced, and a slight change can bring about failure, particularly where the snow-pack is under tension. Often these stresses are delicately balanced, and a slight change can bring about failure, particularly where the snow-pack is under tension.

22. Reconstruction of Galtur, 1.41 mins

24. What was important? Speed 200mph : No warning time Speed 200mph : No warning time Weight : three quarters of a million tonnes. Weight : three quarters of a million tonnes. Force : 50 tonnes per square metre, enough to demolish a house. Force : 50 tonnes per square metre, enough to demolish a house. Over 30 people killed, in village, not on ski slopes. Over 30 people killed, in village, not on ski slopes. Why was village constructed in avalanche area? Why was village constructed in avalanche area? What can be done to prevent avalanches like this? What can be done to prevent avalanches like this?

25. What can be done? Stop avalanches before they start. Stop avalanches before they start. Slow them down. Slow them down. Build only in avalanche free areas. Build only in avalanche free areas. Protect buildings. Protect buildings. Protect roads, railways, power lines etc. Protect roads, railways, power lines etc. Artificial avalanche control. Artificial avalanche control. Warnings Warnings

26. Physical structures used to prevent avalanches (Smith 1992)

27. Responses at Galtur, 1.50 mins