SNOW & AVALANCHES - unibz

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AUTONOME PROVINZ BOZEN - SÜDTIROL PROVINCIA AUTONOMA DI BOLZANO - ALTO ADIGE

Rudi Nadalet – snow & avalanches Free University of Bolzano, 22/04/2015

Rudi Nadalet

SNOW & AVALANCHESSNOW & AVALANCHES


Ripartizione 26 – Protezione antincendi e civileAbteilung 26 – Brand- und ZivilschutzHydrographisches Amt Ufficio idrografico



INTRODUCTIONINTRODUCTION

BASICSBASICS

CLASSIFICATION OF AVALANCHESCLASSIFICATION OF AVALANCHES

CASE STUDIESCASE STUDIES

RISK MITIGATION APPROACHRISK MITIGATION APPROACH

SUMMARYSUMMARY

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Video Pill Lawine


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Definition:Avalanche = a rapidly moving snow masswith volume > 100 m³ and length ≥ 50 m (from EAWS glossary)

Gomagoi, 09/02/2009

BASICSBASICS



i > 25°(58% of South Tyrol)

Mountain region

BASICSBASICS

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Amount of fresh fallen snow (HN) = amount of daily snowfall

Mean yearly amountfor the period 1981-2010

BASICSBASICS



Snow depth (HS) = the measurement from snow surface to ground level

Settlements

BASICSBASICS

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Measurement of fresh fallen snow (by observer)

Snow measurement board

yesterdayesterday tod ayay

BASICSBASICS



Measurement of snow depth (by observer)

Snow measurement stick

BASICSBASICS

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Wind direction & speedSnow depth

(ultrasonic sensor)

Air pressure

Radio data transmission

snow surface temperature(infrared sensor)

Solar panel

Air temperature& humidity

GPRS

Global & reflectedradiance

Measurement of snow depth (by automatic stations)

BASICSBASICS



BASICSBASICS

Properties of snow

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BASICSBASICS

Winter snowpack evolution

The appearance of snow lying on the ground iscompletely different from the well known

hexagonal shape of a snow flake.



BASICSBASICS


Metamorphism changes the shape and the size of the grains.

Metamorphism processes:

• Destructive metamorphism

• Constructive metamorphism

• Melt metamorphism

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Snow profile Temperature

Density

BASICSBASICS




BASICSBASICS

Mechanical properties of snow

Firn 600-830

Pure ice 917

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• Tensile strenght = ca. 1/10 of comp.st.

• Shear strenght f(layer properties)

• Compressive strenght

BASICSBASICS

Shear forces

Tensile forces

Compressive forces Mechanical properties of snow



For slow loading

snow behaves ductile

e.g.

• successive snowfalls of low intensity

• slight rainfall

• slow warming

BASICSBASICS

Behaviour of snow under loading

Viscoelastic material

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For fast loading

snow behaves brittle

e.g.

• skier as an additional load

• explosives

BASICSBASICS


Linear elastic material



Slow Slow loadload

Fast Fast loadload

collapsecollapseForceForce

timetime

collapsecollapse

BASICSBASICS


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1. Destabilizing forces increase2. Stabilizing forces decrease3. Combination of both effects

StabilizingStabilizing forcesforces

DestabilizingDestabilizing forcesforces

RR

FgFgGravitationalGravitational forceforce

frictionfriction

BASICSBASICS

FgFg sinsinφφ FgFg coscosφφ

φφ

Forces on hillslopeTriggering mechanisms

What can happen?



1.Destabilizing forces increasee.g. increase of snow weight

BASICSBASICS

Triggering mechanisms

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BASICSBASICS

Amount of freshfallen snow (HN 3days)= amount of daily snowfalldeposited over 3 days

TR = 30 Years

Triggering mechanismse.g. increase of snow weight



1.Destabilizing forces increasee.g. using artificial avalanche release techniques

BASICSBASICS


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Video Sella Nevea

BASICSBASICS




1.Destabilizing forces increasee.g. additional load throughskier

BASICSBASICS


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2. Stabilizing forces (cohesion, friction force) decrease

BASICSBASICS

e.g. effect of solar radiation on fresh snow




BASICSBASICS

e.g. formation of weak layers

2. Stabilizing forces (cohesion, friction force) decrease


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Video rusty

BASICSBASICS




Parts of an avalanche:Starting zone with potential release areas - initiationTransit zone or track - motionRun out and deposition zone - deposition

CLASSIFICATIONCLASSIFICATION

From: ProAlp Final Meeting ISPRA 2008-12-10

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Starting zone




Starting zone


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09/02/2009, Tauf Lahn Karthaus

Starting zone




Transit zone


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Ground Ground avalancheavalanche

Transit zone




Foto: PAT Foto: PAT -- TrentoTrento

Transit zone


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Transit zone




Transit zone


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Transit zone




Foto: SLF - Davos

Deposition zone


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Deposition zone



Schnals, 25.01.09

Deposition zone


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27 May 2009, Pfunders

Deposition zone




Basic avalanche types


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Loose snow (or point) avalanche





Slab avalanche Key elements

Cohesive layer

Weak layer

Slope angle


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Dynamic of a slab avalanche



Video placa

BASICSBASICS


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Key elements

Cohesive layer

Weak layer

Slope angle


The typical “skier”- avalanche

Slab avalancheentrance

exit





Slab avalanche

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Key elements

Cohesive layer

Weak layer

Slope angle


Slab avalanche




Wet snow avalanche


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Wet snow avalanche




Video Vals



Wet snow avalanche

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Gliding avalanche

“fish mouths”





Gliding avalanche


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Powder snow avalanche




Size 1: sluffminimal danger of burying (danger of falling) snow relocation typically stops before the end of a slope

Size 2: small avalanchecould bury, injure or kill a personsnow avalanche stops typically at the end of a slope

Size 3: medium avalanchecould bury & destroy a car, damage a truck; destroy a small building or break a few treesavalanche could traverse flat terrain (considerably below 30°) over distances < 50 m

Size 4: large avalanchecould bury and destroy a railway car, large truck, several buildings or a piece of forestsnow avalanche traverses flat terrain (considerably below 30°) over distances > 50 mand can reach valley ground

Size 5: very large avalanchecould gouge the landscape; disastrous damage potentialsnow avalanche reaches valley ground; largest runout distance known

Avalanche size


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Gurgllawine - Starting zone




Gurgllawine – Track(s)


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PROVINCIA AUTONOMA DI BOLZANO - ALTO ADIGE

Starting zone ~ 9 haTrack ∆h > 800 m

v ~ 100 km/hp ~ 4-5 kPa





Gurgllawine - Video

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Gurgllawine – Runout





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Pill Lawine

Mixed avalanche form

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Pill Lawine



Rauhjoch 2926 m


fast increase of T

Pill Lawine

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RAMMS Simulation Model

Runout between 1300–1200 m


Pill LawineStarting zone between 2600-2700 m




HAZARD, VULNERABILITY & RISK

R = H ∩ V

HAZARD

VULNERABILITY

RISK

H

V

R

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MEASURES FOR

REDUCTION OF V

RESIDUALRISK

HAZARD

VULNERABILITY

RISK

H

V

R

MEASURES FOR

REDUCTION OF HH

V


RESIDUAL RISK



Hazard zonesplanning

DefenceWorks

Weather forecastAvalanche bulletins

Local avalanchecommissions

PASSIVEACTIVE

TE

MP

OR

AR

YP

ER

MA

NE

NT

AVALANCHE CONTROL


INTEGRATED RISK MANAGEMENT

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Buildings Traffic routes

Winter tourism infrastructures Backcountry sports



Thank you for your attention

Dr. Rudi Nadalet [email protected]

Hydrographic Office of Bolzano/Bozen

SNOW & AVALANCHES - unibz

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