Digging into the Avalanche Phenomenon Presented at UNBC Feb 8 th - - PowerPoint PPT Presentation

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Digging into the Avalanche Phenomenon Presented at UNBC Feb 8 th - - PowerPoint PPT Presentation

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Digging into the Avalanche Phenomenon Presented at UNBC Feb 8 th 2017 By Laurent Janssen Scope of this presentation Basic knowledge of the Avalanche Phenomenon Basic knowledge of Avalanche Terrain Morphology Basic knowledge of the

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Digging into the Avalanche Phenomenon

Presented at UNBC Feb 8th 2017 By Laurent Janssen

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Scope of this presentation

  • Basic knowledge of the Avalanche Phenomenon
  • Basic knowledge of Avalanche Terrain Morphology
  • Basic knowledge of the life of a snowflake
  • Better appreciate the complexity of the Avalanche Phenomena
  • I will try not to get into backcountry avalanche safety.
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Avalanche definition :

  • Oxford dictionaries: A mass of snow, ice, and rocks falling rapidly

down a mountainside. (en.oxforddictionaries.com)

  • Dictionary.com: a large mass of snow, ice, etc., detached from a

mountain slope and sliding or falling suddenly downward. (www.dictionary.com)

  • Oxford dictionaries: A sudden arrival or occurrence of something in
  • verwhelming quantities.
  • Origin of the word Avalanche: Late 18th century: from French,

alteration of the Alpine dialect word lavanche (of unknown origin), influenced by avaler descend; compare with Italian valanga. (en.oxforddictionaries.com)

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The Avalanche on Television!

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The common avalanche.

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Canadian Snow Avalanche Size Classification

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Size 1

Relatively harmless to people Typically:

  • Mass: 10 tonnes
  • Run: 10 meters
  • Force: 1 kilopascal
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Size 2

Could bury, injure or kill a person Typically:

  • Mass: 100 tonnes
  • Run: 100 meters
  • Force: 10 kilopascals
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Size 3

Could bury or destroy a car, damage a truck, destroy a wood frame house or break a few trees Typically:

  • Mass: 1,000 tonnes
  • Run: 1,000 meters
  • Force: 100 kilopascals
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Size 4

Could destroy a railway car, large truck, several buildings

  • r up to 4 hectares of forest.

Typically:

  • Mass: 10,000 tonnes
  • Run: 2,000 meters
  • Force: 500 kilopascals
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Size 5

Catastrophic Typically:

  • Mass: 100,000 tonnes
  • Run: 3,000 metres
  • Force: 1,000 kilopascals

Huascaran avalanche in Peru, May 31, 1970

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The Avalanche Triangle

The 3 ingredients necessary to produce an avalanche

Trigger Avalanche

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Slope

  • An avalanche happens

when gravitational force becomes greater then friction force.

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Trigger

Natural trigger such as:

  • Extra load : Precipitation (snow or rain)
  • Wind : transporting snow, therefor creating extra load
  • Rapid warming : radiation (sun), weather (frontal)
  • Earthquake
  • Cornice fall

Artificial trigger such as:

  • Skier, snowboarder, snowmobiler, snowshoer….
  • Explosives
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Unstable snow

  • Snow with little or no

cohesion, no strength

  • Snow pack layering
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Avalanche Terrain Morphology

  • The classic avalanche path
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Wind Effect

  • Lee aspect : opposite aspect
  • f the wind direction
  • Cross loaded aspect : perpendicular

aspect to wind direction

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Solar aspect

  • The angle is

everything

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Elevation

  • The air normally gets

cooler as we get higher (in the Troposphere), which will have an influence

  • n the snowpack and

precipitation type…

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Avalanche Terrain Exposure Scale

  • Simple Terrain
  • Challenging Terrain
  • Complex Terrain
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Simple terrain

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Challenging terrain

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Complex terrain

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Avalanche Character or type

As define by Avalanche Canada

Slab avalanches

  • Wind slab
  • Wet slab
  • Storm slab
  • Persistent slab
  • Deep persistent slab

Loose avalanches

  • Loose wet
  • Loose dry

Cornice fall

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Slab Avalanches

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Loose Avalanches (sluff)

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Cornice fall

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The life of a snowflake

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They form in the atmosphere

  • No snowflakes are the same : The exact shape of the final snow

crystal is determined by the precise path it took through the clouds. But the six arms all took the same path, and so each experienced the same changes at the same times

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The most stable form of ice crystal

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Metamorphic processes once on the ground

  • Settlement
  • Rounding
  • Faceting
  • Melting and freezing (crust formation)
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Settlement

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These metamorphic processes are more efficient at warmer temperatures

Clausius Clapayron Equation

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Rounding

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Faceting

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Melting and freezing (crust formation)

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Surface hoar formation

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  • Clear sky
  • Calm or light winds (about 3 mph is best)
  • Open slope exposed to a clear sky (trees
  • r clouds can radiate their own heat and

disrupt the process)

  • Humid air
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Thank you!

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References

  • Avalanche Canada: www.avalanche.ca
  • Oxford dictionary: en.oxforddictionaries.com
  • Dictionary.com: www.dictionary.com
  • McClung and Schaerer, D.McC. and P.S., 2006, The Avalanche

Handbook 3rd ed, Seattle, The Mountaineers Books.

  • Avy Snacks, Sherpa Cinema
  • www.avalanches.org
  • www.snowcrystals.com
  • www.ngdc.noaa.gov/hazardimages