A v a l a n c h e

C o n t r o l ,

R e s c u e

a n d

E d u c a t i o n

FurtherStudiesontheInfluenceoftheGAZ-EXonaContinentalSnowpack,

GloryBowlSlidePath,TetonPass,Wyoming
Kell yEl der¹andRodNewcomb²

1 _{Earth Resources, Colorado State University, Ft. Collins, CO 80523}

2 _{American Avalanche Institute, Box 308, Wilson, WY 83014}

Keywords:avalanche control,GAZ-EX,ram resistance1992WTD installed two GAZ-EX explodes on Mt.Glory,
followed by two more in 1993. One device is located in the
ABSTRACT^{South Twinslidepath; theother threearein theGlory Bowl}
Thestudyiscentered onthree GAZ-EXinstallationson^{slide path starting zone.The study isbased ondata col-}
Teton Pass,Wyoming.The results reported here support^{lected at the latterthree installations.}
theprevious conclusionsofElderand Newcomb(1994,^{The GAZ-EX was developed in Francefor the maritime}
1995),andpresenttwoyear'sadditional datawithnew^{climateofEurope.Mostoftheinstallationsworld-wide}
results.Transects of depth and ram resistance were com-^{havebeen in the snowclimatesofmaritimesnowpacks,}
pleted at the GAZ-EX sites in 1993,1994,1995 and 1996.^{i.e. Europe andCalifornia. Based on observations in a con-}
Measurements were made at different times each season,^{tinental climate fromfourseasons on Teton Pass,the ra-}
butallmeasurementsweremadeafterasignificant^{dius of influenceand the expectedbehavior may be differ-}
snowpackhadaccumulated andbeforeripeningofthe^{ent in this type of snowpack.}
snowpack changed stratigraphy critical to cold-snow sta-
bility.Two different ram calculations were used foreach^{STUDY SITE}
point; mean and integrated ramresistance. IntegratedramThe GAZ-EX installations that we studied areon the Glory
numberisthesumofallindividuallayerram numbersBowlpathwhichrunsfromabout3050\|mtoabout
afterthey are multiplied bythe depth of the correspond-2150\|m.Theclimate istypicalofintermountainareas
ing layer. Results indicatethata shallowsnowpack is main-where cold temperatures and clearweather periods lead
tained in the blast arearelative to surrounding terrain, and
a weak snowpackdominated exists in the blast region with
increasing strength observed at greater distances from the
blast area. The radius of influence for snow depth is about
10to40\|mfromtheGAZ-EXlegs,depending onyear
and direction, but may be greater in down-slopecases. The
radius of influence for strength is about 10 to 35\|m from
the GAZ-EX legs, dependingon year anddirectionof meas-
urement. Although effective in removing new snow above
the depth hoarbefore it gains strength, the GAZ-EX itself
is noteffective inremoving the depth-hoarsnowpack in
theblastarea.Anopportunitytotesttheeffectofthe
blasting operation on local snowpack properties was pre-
sentedin the 1995seasonwhen mechanical failure pre-
cluded useof GAZ-EX 3. Trends in snowpackproperties at
the two operationalGAZ-EXswere similar to previous years
results, while thesnowpacksurroundingthenonfunctional
unit showed significant differences; both snow depthand
ramresistanceweremuchgreaterwherenoGAZ-EX
activity occurred.

INTRODUCTION

Wyoming State Highway 22 was relocated in 1970,cross-
ing several paths that previously did not affect the route.
Theroute nowcrossestheGloryBowlslidepath which
was initially spanned by a bridge.In January of 1970 the
bridge framework was damaged by a large avalancheand
was removedbefore completion. Avalancheforecastingand
activecontrolbegan inthe winterof1971-1972and has
continued tothepresent.Controldevicesincluded a 75
mmpack howitzer,avalauncher, and a 105 mmrecoiless^{Figure 1.Cross-slope profile of snow depth, integrated ram resistance,}
rifle.With diminishingreservesofmilitaryammunition^{and mean ram resistance through GAZ-EX 4 and 1. The two vertical}
and a desire to reducehazard to motorists on Teton Pass,^{lines represent the locations of the blasters: leftmost is number 4,}
theWyomingTransportationDepartment(WTD)began^{rightmost is number 1. The lines represent smoothed fits of the point}
data; point values are plotted with the last digit of their year of collection
searching foralternative methods of hazard mitigation.In(e.g. 3 is from 1993).

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