Avalanches are falling masses of snow that can reach speeds of up to 300 kph and contain rocks, soil, or ice. They become hazardous when interacting with people and infrastructure. There are two main types - loose snow avalanches which start from a single point and involve powdery snow, and more deadly slab avalanches where a large slab of ice and snow shears away rapidly downhill. Avalanches are caused by heavy snowfall, steep slopes, tree removal, temperature rises, and human activity like off-piste skiing. They cause deaths, injuries, and property damage, which has increased due to growing winter sports resorts. Ways to reduce impacts include closing prone slopes, issuing warnings,

1. Avalanche hazards

2. Avalanches are falling masses of snow that can contain rocks, soil or ice that move downhill at speeds of up to 300 kph. Avalanches are natural phenomena, but become a natural hazard when they interact with people and their surroundings. Avalanches cause deaths and injuries and damage to property. They also impact on transport networks and livelihoods, particularly in tourism

3. Avalanche and snow-related incidents in Europe, spring 1999

4. Two types of avalanche: Loose snow avalanche Starts from a single point Involves loose powdery snow Slab avalanche More deadly A large slab of ice and snow shears away from a hillside and moves rapidly downhill It has immense power Carries rocks and trees

5. Causes of avalanches: Heavy snowfall – this adds weight to earlier snowfalls. Steep slopes – more likely to occur on steep slopes in excess of 30 o Tree removal – enables avalanches to move downhill unimpeded Temperature rise- sudden rises in temperatures and associated melting often lead to avalanches in spring Heavy rainfall – lubricate a slope and trigger an avalanche Human factors – off piste skiing

6. Why a hazard? Avalanches cause deaths, injuries and property damage This has increased over past 50 years due to growth of winter sports resorts In Switzerland an average of 40 people die each year from avalanches

9. What can be done to reduce the impact?

10. 1. Closing avalanche prone slopes and issuing warnings Since the majority of deaths occur amongst recreational skiers, snowboarders etc. restricting such activities at times of high risk is clearly vital. This can be done by closing avalanche prone slopes and issuing warnings This depends on expert knowledge of the snow conditions, daily monitoring of dangerous slopes, and accurate warning systems. 2. Trigger small avalanches under controlled conditions before the snowpack builds to a dangerous state. 3. Controlling avalanche activity. Several measures are used to control Avalanches e.g. stabilising the snow pack in the starting zone. This prevents the snow pack achieving the momentum to begin to move. Planting trees and building snow fences are two common strategies. Other measures may be used to deflect avalanches away from buildings or to slow the rate of movement, thereby reducing the power. 4. Planning where and where not to build in mountain areas is clearly critical to minimising damage to buildings and infrastructure. However, such planning must be based on accurate records of previous avalanche activity, and reinforced by legislation and punishment for infringing the planning laws