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Key Words: Backcountry, Burial,Force,Obstacle, Risk
ABSTRACT
Thelikelihoodofsevere injury ordeath increaseswhen
avalanchevictimsencounterstrongdestructiveforces
within moving debris,and/orthey impact with injurious
orfatal terrain features such as trees, cliffs,and deep gul-
lies along the avalanche path.This paper proposes a scale
fordetermining the level of potential risk of severe injury
ordeath as these factors vary from one avalanche path to
another.The intent of this risk scale is to provide a deci-
sion-making tool to help both recreationalandprofessional
backcountry travelers determine theneedto minimize site-
specificuncertaintyabout snow stability whencontemplat-
ing travel onto avalanche terrain.
INTRODUCTION
Byfar,thelargest numberofavalanche fatalitiesoccurs
among backcountry skiers and mountaineers.Tragically,
the number of fatalities in these groups is increasing over
the long term.This trend suggests the need for additional
and/orimproved methods and toolsto help backcountry
travelers correctly analyze site-specific avalanche risk.
Conventionalwisdomoncetaughtthatallthatwas
neededfor an avalanche to occur is snow on a slope and a
trigger.Avalanche safety educationand backcountry fore-
castingtechniqueshaveadvanced wellbeyondoffering
suchvague generalities.Overthe years,clearerparam-
etershavebeenidentifiedforobservingelementsof
weather,snowpack, andterrainthatcontribute to avalanche
probabilityon a given slope.
Whilebeing able to forecastavalancheprobability is im-
portant, by its nature any suchforecastinvolves some level
of uncertainty.Given this fact,a modicum ofcaution in
choosinga saferoutein avalancheterrainhasalwaysbegged
the question, "Whatarethepotentialconsequencesof being
caught in an avalanche on thisslope?".The answerde-
pends on threefactors;1) the potential for dynamic forces
withintheavalanche toinjureorkill,2)thenumberof
potentiallyinjuriousand/orfatalterrainfeatureswith
which the avalanchevictim may come into contact on the
ridedown,and 3)the time,skills,and toolsrequired to
conductasuccessful rescueasdeterminedbythefinal
burial depth and/orsize of the search area.
Existing "hazard rating"scales classify the size of
anddestructiveforces forspecific avalanche events and
are usefulforland-use planning.Existing"stabilityrat-
ing"scales classifygeneraltrends insnowpack stability
during timesofuncertaintyand are usefulforassessing
thepotentialforavalanchestooccuroverabroadgeo-
graphicarea.However, neither scale classifiesthe specific
risks presented by the terrain features and configuration of
a given avalanche path.This paper proposes the stepped
AvalancheTerrainRisk(ATR)Scalewhichtheauthors
believe can provide an additional tool to aid backcountry
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travelers in the decision-making process forvariable risk
terrain.
Along with the ATR Scale, advisory recommendations for
minimizinguncertainty andtaking precautions tomaxi-
mizepersonal safetyateach risklevelareoffered.Itis
intended that the ATR Scale and the associated advisories
be usedin conjunctionwith existing"stabilityrating"scales
soastoprovideamorecomplete methodologyforthe
decision-making process in the backcountry.It is hoped
that,used together,the ATR Scale and the stabilityfore-
castwillprovidealogical,structuredapproachtodata
gatheringand routeselection when the possibilityoffa-
tigue,environmentalpressures and/orthe excitementor
confusion ofimmediate circumstance might cloud better
judgment.
DEFINITIONS AND ASSUMPTIONS
"Risk",defined in Webster's New World Dictionary,Col-
legeEdition (1966),is"thechance ofinjury,damage or
loss".The concept of "risk" will be used throughout this
paper with "chance"being expressed in terms of probabil-
ity,with "injury" and "damage" being defined as severe
personal injury,and with "loss" being defined as loss of
life.
A widely documentedreason thatbackcountry travelers
areseverelyinjuredorkilledinavalanches isthatthey
lack the knowledge, skills,and means necessary to recog-
nizepotentiallyweaksnowpackconditions,and/orto
conduct asuccessful rescue afterthe fact.Itwillbeas-
sumed,therefore, that users of the ATR Scale have a basic
avalancheeducation,i.e. theyhave successfullycompleted
a Level 1 (or equivalent) avalanchesafety course, andthat
they are equipped with the basic toolsnecessary forcon-
ductingslopemeasurements,snowstabilitytests,and
avalanche rescue.Italsowill be assumed thatusers are
bothcompetentinaccurately assessingtheirown limits
and capabilities, and that the "goal"of the touring groupis
to minimize risk insofaras this is practical.
AVALANCHEHAZARD AND SNOW STABILITY
RATINGSCALES
Numerous types of rating scales and systems fordescrib-
ing snowstability andpotentialavalanchehazardhavebeen
adopted throughout the world.There has been difficulty
in arriving at a consensus in the wording of these systems.
Different mountain regions appear to have rating scales to
servetheiruniquepurposesandphilosophies.Recent
effortsbyEuropeanandNorthAmericancountriesto
standardize theirstability rating categories and terminol-
ogy into the "Unified Scales" aretestimony to the difficul-
ties encounteredwhentryingto agreeon a universalsystem.
Despite the apparent disparity inrating systems,each is
useful and provides important information.Examples of
some of the variousratingscalesandsystems are described
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