The avalanche hazard
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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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THE AVALANCHE HAZARD

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The avalanche hazard

THE AVALANCHE HAZARD


2 news clips from 1999 7 17 mins

2 news clips from 1999, 7.17 mins


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?


Avalanche frequency and distribution

AVALANCHE FREQUENCY and DISTRIBUTION

  • 1 million per year.


A spectrum of hazards smith 1992

A spectrum of hazards (Smith 1992)


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.


Fatalities in europe and north america

FATALITIES IN EUROPE AND NORTH AMERICA


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.


Chamonix galtur 18mins

Chamonix & Galtur, 18mins


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.


Reconstruction of galtur 1 41 mins

Reconstruction of Galtur, 1.41 mins


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


Physical structures used to prevent avalanches smith 1992

Physical structures used to prevent avalanches (Smith 1992)


Responses at galtur 1 50 mins

Responses at Galtur, 1.50 mins


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