I n s t r u m e n t s

a n d

M e t h o d s

measurementsare considered validinlowersectionsofUsing equation2 the snow movement accelerationwas 7.32
the snowpack.Figures 1 and 2,which represents Sensorcm/hr² .Overthe next 18 hours the sensormoved back to
#1 and 2 respectively,indicate no movement.The nega-an angle of 30 degrees.This corresponds toan accelera-
tive angles that areshown in the figures representa deflec-tion of 1.35x10^-2cm/hr^{2 .}
tion greaterthan 90 degrees.Thisis possible due to theThe accelerated creep rate from the explosive was a re-
sensors being mounted plum to the slope.sult of the elasticresponsein thesnowpack.This increased
Though problems were evident in sensors #1 and 2, sen-creep rate after the delivery of the explosive charge could
sor #3 produced the following data at a higher confidencesignal a weakersnowpack.The delivery of an explosive
level.Sensor # 3 monitors the snowpack in the top metercould weaken the snowpack for a short duration.
of the snowpack. As thestorm progressedsensor #3 showedThe ninthstorm of the year arrived on February 22, 1996.
littlemovement.Thesensorwas bentat an angle of35By 1100 hours the Collins study plot had received 45.7 cm
degrees(2degreeslessthan perpendiculartothe slope)of snow with 3.38 cmof water(7% density).The winds
and began to declineat a slow rate until 30 degrees.Thiswere from the northwest at 41 cm/hr².
tendstoindicatethatthestressinthesnowpackwasThe heaviest intensity occurred between 0100 through
decliningduringthestorm.Atabout1130hoursan1500hours.During the storm cycle sensor#3 was moni-
avalanche control team began progressing out to stabilizetored.Figure 4 shows the creep rate began to increase at
the slidepath's around Mt. Baldy.At 1200 hours a explo-0000hours.As the intensity ofthe snowfall increased at
sive charge (2 kg /PETN) tied to a bamboo pole was deto-0600 hours the creeprate also accelerated.At 0615 hours
nated1meterabove thenewsnowsurface tocreate anthecreep rate accelerated dramatically.Increasing from
airblast.This explosive created a class 2 avalanche with33 degrees at 0615 hours to 34 degrees at 0945 hours.This
an crown depth of 46 cm,width of 254 cm and ran 10 m.relates to a snow movement acceleration of 0.124 cm/hr² .
This indicated some instability within the new snow.Over the next hour and half the C&G sensor showed the
At the time the explosive was detonated the creep ratesnowpack stabilizing as the angle of tilt was decreased to
accelerated insensor#3.At1200hoursthe sensorwas31 degrees.This decline in the creep rate correlates to a
bent at an angle of 30degrees and at 1215the angle wasdecreaseinsnowfallintensity.However,at1145hours
32.5 degrees.The sensorstabilized at 32.5 degrees.Referthe creep rate accelerated to 35 degrees at 1215hours and
to Figure 3.slowlyincreasedto 36 degrees at 2200 hours.
From equation 1 the deflection was calculatedas 4.12 cm.This storm cycle producedno natural or artificial releases

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