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THE AVALANCHE HAZARD. 2 news clips from 1999, 7.17 mins. Avalanche. 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. Avalanches!.

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Avalanche
Avalanche

  • 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.


Avalanches
Avalanches!

  • 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.

  • Therefore increased RISK of interaction, and increased hazard.


What are the main characteristics of avalanches
What are the main characteristics of avalanches?

  • Distribution over space.

  • Location : same places each time therefore relatively predictable.

  • Frequency: changing through time?

  • Speed of onset/warning time : little warning.

  • Relative to other hazards?




Impacts
Impacts

  • 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.



Avalanche types
AVALANCHE TYPES

  • Powder snow avalanches

  • Wet snow avalanches

  • Slab avalanches


Powder snow avalanches
Powder snow avalanches

  • No warning.

  • Up to 200mph

  • Up to 50 tonnes/m 2 force

  • Occur at any time in season.

  • Example :Galtur, Austria.


Wet snow avalanches
Wet snow avalanches

  • Usually late in season.

  • Slow moving (5-15mph).

  • Considerable weight of wet snow (up a million tonnes).

  • Example : Odda, Norway.


Slab avalanches
Slab avalanches

  • Slab avalanches are most common occurrence.

  • Often started by human error.

  • Most frequent cause of death amongst skiers, snowboarders, and power-skiers.

  • Speeds up to 100mph.


Origins of avalanches
Origins of avalanches

  • Weather : snowfall is essential ingredient.

  • Slope : more than 30o and less than 45o for starting an avalanche.

  • Changes in the snow-pack.


Contributing factors
Contributing factors

  • Heavy rainfall on snow (more likely in Scotland than the Alps!)

  • Deforestation - reducing slope stability

  • Vibrations - skiers,more dangerous earth movements

  • Long cold winters then heavy snow falls in spring. i.e. slip plane created.


Changes in the snow pack
Changes in the snow-pack

  • Temperature changes in the air can bring about :

  • Partial melting in the snow-pack.

  • Freezing of melt-water in snow.

  • Changes in snow crystal shapes and sizes.

  • Changes in the strength of the snow layers.



Snow pack stress
Snow-pack stress

  • Snow lying on a slope is subject to stress :

  • gravity is pulling it downwards

  • 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.



What was important
What was important?

  • Speed 200mph : No warning time

  • Weight : three quarters of a million tonnes.

  • Force : 50 tonnes per square metre, enough to demolish a house.

  • Over 30 people killed, in village, not on ski slopes.

  • Why was village constructed in avalanche area?

  • What can be done to prevent avalanches like this?


What can be done
What can be done?

  • Stop avalanches before they start.

  • Slow them down.

  • Build only in avalanche free areas.

  • Protect buildings.

  • Protect roads, railways, power lines etc.

  • Artificial avalanche control.

  • Warnings




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