M o u n t a i n

We a t h e r

a n d

S n o w p a c k

yukigata,"Nichirin" ismainly formed by the accumula-
tion of debris piled up on a circle by avalanches. The cir-
cle-shaped remaining snow persists longerthan the sur-
rounding snowpack.Therefore,I conclude that the topo-
graphicalorigin of this positive type yukigata is landslide
terrain where avalanches are apt to occur.
Forsuch complex topography a graphic display of the
slope gradient (i.e., the derivative of elevation), especially
its bird's-eye view (Fig.8b) is more informative than a dis-
playofelevations.Theareabetween thescarpand the
hummockymassofdebreisisarc-shaped.Therateof
changeof slope (i.e., the Laplacian)was negative hereand
thus it is concave terrain.
A cross section of "Nichirin" was made from 1:10,000
scale.Elevationsweredetermined every10malongthe
WNW-direction fall line that goesthrough the centerof
the landslide with the origin of x-axis chosen at elevation
1,600m.The topelevationofthe scarp of the landslide
was about 1,750m and its length was about 80 m.
Comparing the ground photograph (Fig.1) and aerial
photographs (Figs. 4, 5) with the contour lines, slopes and
cross section in Figures 6-9,theradius of"Nichirin" is
about150mand thetopmostedge of"Nichirin"(1,700
m) coincided with the hummocky mass of debris of past
landslides.Furthermore,the lowestborderoftheland-
slide was estimated to be at least 1,650 m from the rate of
change of the cross section.

4.2 Hane-uma

Fromthe photograph ofyukigata,"Hane-uma" taken in
thespring (Fig.2),we can recognize manytracksofre-
maining snow at his mane, where snow blocks spilled and
dropped down, andseveral slipover tracks on the remain-
ing snow below his abdomen. On the contour map drawn
fromthe digital elevation map (Fig.10),there is a blank
area at the cliff that correspond to the mane of the horse.
From the bird's-eye view of slope gradient near "Hane-
uma" (Fig. 11),the body of the horse is on slopes of more
than35degrees,and inthecircumference gentle slope
spreads.Thistopographysuggeststhattheyukigata
"Hane-uma" is mainly formed by the denudationof snow-
packbyavalanches.Smallamountsofremaining snow
melt away earlierthan the surrounding snowpack.
Combining slope contour lines of more than 35 degrees
and the cliff, the resulted outline (Fig.12) is similar to that
ofyukigata"Hane-uma" (Fig.13).Therefore,Iconclude
that the topographicalorigin of this negative type yukigata
iscliffterrainandsteepslopeswherefull-depthava-
lanchesareapt totakeplace. ThetotallengthofHane-
uama was about 600 mand its width was about 200m.
The white part between the tail and the rearleg (Fig.
13)is a gentle inclination ranging from20 to25degrees
(Fig. 12). Dotted lines in Fig. 12 do not follow the drawing
rule stated above. This is because, in addition to slopes of
the avalanche site,plants,trees and runout distances of
avalanches are important issues.

5CONCLUDINGREMARKS

Yukigatas are strongly associated with accumulation and
melting of snowpack and micro topography. In the case of
the positive type yukigata,"Nichirin",land slide terrain
and avalanche release due to abrupt terrain created by

Fig. 4 Winter aerial photograph of theYukigata, "Nichirin"(thesun)
in Shimizu. Photographed by National Research Institute for Earth
Scienceand Disaster Prevention, March 1 1964. A curved scarp is at
(a) andhummocky mass of debris is at (b).

Fig. 5 Fall Aerial photographof the Yukigata, "Nichirin" (the sun) in
Shimizu. Photographedby Agriculture andForestry Section, Shiowa
Town Office, Fall, 1994. Trucks and curved scarp are at (A) and
hummocky mass of debis is at (B).

77