S n o w

C o v e r

S t a b i l i t y,

A v a l a n c h e

I n i t ia t i o n

a n d

F o r e c a s t i n g

REFERENCES

Canadian Avalanche Association. 1995. Observation Guidelines
andRecordingStandardsforWeather,SnowpackandAva-
lanches, Canadian Avalanche Centre, P.O. Box 2759, Revelstoke,
BC, V0E 2S0, Canada.

Jamieson, J.B. and C.D. Johnston, 1993. Rutschblock precision,
techniquevariations andlimitations.JournalofGlaciology
39(133), 666-674.

Jamieson, Bruce and Colin Johnston. 1995. A preliminary field
study of the compression test. Presented at the Public Meeting
of the Canadian Avalanche Association, May 5, 1995. Available
from the Dept. of Civil Engineering at the University of Calgary,
Calgary, Alberta, Canada.

Jamieson, Bruce. 1995. Avalanche Prediction for Persistent Snow
Slabs. PhD thesis, Dept. of Civil Engineering, University of Cal-
gary, Calgary, Alberta, 258 p.

Figure 10 Frequency of skier-triggering for skier-tested slabs

LIMITATIONS&FUTURESTUDIES

This paper only presents limited data. It is not yet clear if
the compression test can identify (and rate) all the weak
layers that can produce slab avalanches. For example, on
level terrain the compression test may miss certain weak
layers such as a poorly-bonded crusts.
Also,the compression scores in this paperare based
on the average numberof taps required tocause failure
inweaksnowpacklayers.Testsinwhichweaklayers
did notfail during the first30tapsare excluded from
the averages (except for the studies of column size). Non-
failures should be included in a mannersimilartothe
wayrutschblockscoresof7areincludedinmedian
rutschblockscores.

Finally,more field studies are required to:

*identify the maximum effective depth forcompression
tests,

*clarifytheeffectofslopeinclinationoncompression
scores,

*bettercorrelatecompressionscoreswithrutschblock
scores and skier-triggering,and

*correlate compressionscores fromstudy sites with the
frequency of skier-triggering on surrounding slopes.

ACKNOWLEDGEMENTS

This ongoing studyispart of aCollaborative Research
and Development Project funded bythe BCHelicopter
andSnowcatSkiing OperatorsAssociation(BCHSSOA)
and Canada's Natural Sciences and Engineering Research
CouncilofCanada.Inadditiontofinancialsupport,
MikeWiegeleHelicopterSkiingandCanadianMoun-
tain Holidays also provided logistical support and a pro-
ductiveenvironmentforfieldstudies.Thanksalsoto
GerryIsraelson,ClairIsraelson,and PeterSchaererfor
advice on the compression test,and toJillHughes,Sue
Gould,Joe Filippone,Greg McAuley and Ken Black for
theirfield work.

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