H a z a r d

M a n a g e m e n t

a n d

P u b l i c

Wa r n i n g

below.

AVALANCHE HAZARD RATING SYSTEMS

Several countries including Canadaand Switzerland have
adopted hazardratingsystems which categorizethe effects
on people and property after anavalanchehas started.For
example, the Canadiansystem (Table1), describes the size
ofanavalanche bythe typeand magnitudeofpotential
destructive forces.
Sucha rating systemprovidesusefulinformationfor
engineersandland-usepolicy makers, but does notdirectly
address the question of relative risk ofpotentially severe

Table 1.Canadian Reporting System

Extreme Hazard:Widespreadareas of unstable snow. Ava-
lanches are certain onsomesteepsnow-covered gul-
lies.Large destructiveavalanches possible.
Noneofthesesystemsfullyaddressestheriskofstrong
avalanche forces orpotentiallyinjuriousterrainfeatures
towhichapersonmaybeexposedifcaught inanava-
lanche on a particular slope.For example,the U.S. "Low
Hazard" and "High Hazard" ratings represent two differ-
ent levels of snow strength.Both indicate a potential for
areas of weak snow toexist,and eithercould represent a
high potential risk ora low potential risk of severe injury
or death for backcountry travelers dependingon thelength
of slope orthe number large trees orrock outcrops on the
slopetheyintendtoaccess.Suchgeneral warningsof
potential instability are clearly helpfulin assessing of over-
all snowpack conditions,but backcountry travelers obvi-
ouslyneedtoconsidermorethan thistodeterminethe
level of risk they are facing in any site-specific situation.

AVALANCHE RISK AND DANGER SCALES

Adopted bymost ofEurope at the Meeting of Avalanche
ServicesheldinWildbadKreuth,Bavariain1993,the
Unified Avalanche Risk Scale attempts toidentify poten-
tially hazardous backcountry situations and recommends
action to avoid those situations.More recently avalanche
forecast and information centers in the United States and
Canada have adopted modified versionsof the European
model.The U.S. AvalancheDanger Scaleis representedin
Table3 as an example.While these scales still lack a rank-
ing scale forpotentially injurious orfatal terrain features
on an avalanche slope, they do go a step further than pre-
vious scales by expressing the need for increasinglybetter
evaluation and route selection techniques on higherrisk
slopes.

DIFFICULTY RATING SCALES FOR OTHER TYPES OF
MOUNTAIN RECREATION

In the process of developing a rating scale that addresses
the relative risks specific toa given avalanche slope,the
authors examined various difficulty rating scales that are
commonly used in othermountain activities.The rating
scales used for mountaineering and for rivers were found
tocontainusefulformatsforevaluatingriskspresentin
theirrespectiveenvironmentsaswellasfortheskills
neededto deal with those hazards.These scales are repre-
sented in Table 4 and Table 5 respectively.

Size

1

2

3

4

5

Description

Relatively harmless
to people
Could bury, injure,
or kill a person
Could bury a car,
destroy a small
building, or break
a few trees
Could destroy a
railway car, large
truck, several buildings,
or a forest with an area
up to 4 hectares
Largest snow
avalanches known;
could destroy a village
or a forest of 40 hectares

Typical
Mass

<10t

10²t

10³t

10⁴t

10⁵t

Typical
Path
Length
10 m

100 m

1000 m

2000 m

3000 m

Typical
Impact
Pressure
1 kPa

10 kPa

100 kPa

500 kPa

1000 kPa

SNOWSTABILITYRATINGSCALES

Inpast years,many countries also adopted snowstability
rating scaleswhich attemptedto describe general trends in
overall stability of the snowpack.Typical of thesesystems
arethose of the U.S., Canada,France,andSwitzerland. The
U.S. scaleis presentedin Table 2 as an example.

injuryordeathtobackcountrytravelersattemptingto
negotiate a particular avalanche slope.

Table 2.U.S.Stability Rating Scale

Low Hazard:Mostly stable snow. Avalanchesare unlikely
except inisolatedpocketsonsteepsnow-covered
slopes and gullies.

ModerateHazard:Areasofunstablesnow.Avalanches
arepossibleonsteepsnow-coveredopen slopesand
gullies.

High Hazard:Mostly unstable snow.Avalanchesarelikely
on steep snow-covered open slopes and gullies.

2

TABLE 4.

CLIMBING RATING SCALE

Class 1- Cross-country hiking, hands not needed.

Class 2- Scrambling,hands helpful, rope not needed but
probably carried to assure party safety.

Class 3- Easy climbing,scrambling with use of hands, el-
ementary climbing technique helpful.Rope should be
availableandmaybedesiredbyaninexperienced
climber.

Class4-Roped climbingwithbelaying.Belaysmaybe
anchored usingeither natural anchors or climbing hard-
ware.Some moves may be difficult and could be Class
5 except for the security of short pitches, or natural pro-
tection such as trees, shrubs, and rock horns.