A v a l a n c h e

D y n a m i c s

a n d

Figure 7

snow wasdeposited on the running surface bythe slide
due to poorslope preparation priorto the slide.
The third slide was on 3/30/96.Again the shear plate
and velocity sensors were used on this slide with the addi-
tionofthedepthgauge and anattempt tocalibratethe
photosensorsfordensitymeasurements.Thisslidewas
triggered on about 28 cm of new snow and conditionswere
drierthan the previousslide.The slidewas larger than
thepreviousslideand had a substantialpowder cloud.
Theleading edge ofthe slidewas movingfast,reaching
speeds up to 12 m/s during a surge, taking about 4 seconds
to pass the shed before runningfar into the runout zone.It
was observedandrecordedthatthe depthgaugewaskicked
up in theinitial wave front of the slide beforesettling down
and riding smoothlyon the slide surface.This slide also
deposited about 15 cm of snow on the plate.For this drier
slide, the S/N ratio was much lower for the majority of the
slide because the normal stress was much larger than the

Figure 8

previousslide,whiletheshearwasaboutthesame
magnitude.Anattemptcalibratetheopticalsensorsto
measure densities was alsotried on thisslide.The data
gives conflictingresults with measurementsof the densities
measured in the deposition afterthe slide.The densities
measured withthe opticalsensorsshow lowerdensities
near the bottom of the slide.This may in part be attributed
to leakageof infraredthroughtheslide surface.Thesensors
at 10.5 cm above the runningsurface measured the density
of about 280 Kg/m³(Figure 9).The data shows that as the
sensorbecameuncoveredataround4secondsthe
reflectanceincreased, increasingthe recorded density. The
measuring of densityusing the opticalsensors requiresfur-
therinvestigation.
Due to the amount ofdeposition uponthe plate there
are doubtsas to whether thesemeasurementsrepresentthe
true shear layerS/N ratios and actual slide depth.Since
the two slides deposited similaramounts of snow though

Figure 9

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