A v a l a n c h e

D y n a m i c s

a n d

D e f e n ce

Figure10. The leadingedgevelocities from K to P point as a function of
releasedball numbers. Theline was derived theoretically by Nohguchi
(1996).

avalanches passed by the station.Figure 12 gives the data
of snow avalanche broke out at 1337 on 29 January 1996. It
is certain that airmovement in the snow cloud has never
beenrevealed forsuch alarge powdersnowavalanche,
velocityofwhichamounted tomorethan 50m/s.Since
we can estimate the velocity of dense part with analyzing
the impact pressuredata andseismic signals, the compari-
son with thedatainFigure12 promises to givea newinsight
about theinternal structure of thepowder snowavalanches.

ACKNOWLEDGMENT

workhasnotcompleted withouttheircooperation.Fur-
thermore all this work would not have been possible with-
out the help of the workshop of our institute who made all
the experimental equipment.We wish to express special
gratitudetothem.ThanksareduetoSapporocityfor
permission to utilize the ski jumpas our experimental field.
Thisworkwaspartlysupportedbythe Grant-in-Aid for
Co-operativeResearchandScienceResearchof theMinistry
of education, Science and Culture, Japan.

REFERENCES

Figure 12. Air velocity in thesnow cloud. This avalanche broke out at Shiai-dani, Kurobe Canyon, at 1337 on
29 January 1996.

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