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Key Words: Yukigata, Snowpack, Avalanche,Landslide,To-
pography, DEM
ABSTRACT
Yukigatas are complex patterns on mountainsides formed
by combinations ofbright domains covered with remain-
ing snow and dark domains of ground or trees. A positive
type (bright) yukigata shows its pattern on the hillside as
remaining snow anda negativetype (dark) yukigata shows
its pattern as groundor trees. Theformation mechanism of
yukigatasiscloselyrelatedtosnowpack,snowmeltand
topography.
In this paper, I analyzetwo representativeyukigatas, one
positive and one negative, with aerial photographs and a
DigitalElevationModel (DEM).Then, I examinetherelation
between the origin of yukigatas and topography.
The positive type yukigata called "Nichirin" (the sun)
formsonlandslideterrain thathasan abrupt change in
slope.Avalanchedebris piles up below the steep slope in
an area thatis circular in shape. Thenegativetype yukigata
called "Hane-uma" (galloping horse) formsundera cliff
onsteepslopesof35degreesormore.Full-depthava-
lanches are apttotakeplace these denuding thatslope.
Thus,the formation of these two yukigatas is mainlydue
to topography that causes avalanche release.
1 INTRODUCTION
Whenseasonal snow retreats on a mountain, complex pat-
ternsappearin spring.Combinationsofbrightdomains
covered with snow and dark domainsof ground ortrees
form these patterns.WeJapanese, havelooked upon some
of these patterns as shapes of old farmers, animals such as
oxen and horses, agricultural utensils, Chinese characters
and others,and have called them "yukigata", which liter-
ally means "snow shape" (Japanese Society ofSnow and
Ice,1990;Nohguchiet al.,in print).Yukigatas are classi-
fiedintotwotypesdepending onwhethertheshape is
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bright or dark; the former are thepositive type andthelatter
are the negative type.
Long ago, yukigatas were broadly and practically used
asagriculturalcalendarsinthesnowyregions.Now,
yukigatas are mostlyforgotten, because modern technolo-
gies, especiallyweather forecasting have replacedthe role
of yukigatas. In Japanover threehundredsfamousyukigatas
have been handeddown from generation to generation by
oral tradition (Tabuchi, 1981) of which more than eighty
are in Uuonuma County,Niigta Prefecture (Endo, private
letter). Tabuchi'sstudy of yukigatasis comparableto Wilson
A. Bentley's pioneeringstudy of snow crystals (Bentleyand
Humphreys,1931).However,wecannotidentifyand
delineatemostofthem.Thisisbecause,fewyukigata
inventorieshavebeen accumulated bynaturalscientist,
except Tabuchi.
The formation mechanismof yukigatas is closely related
tosnowpack,snowmeltand topography. Inthispaper,I
analyze two representativeyukigatas, onepositive and one
negative,with aerial photographs and a Digital Elevation
Model(DEM).Then,Iexamine therelationbetween the
origin of yukigatas and topography.
2 TWO YUKIGATAS
2.1 Yukigata, "Nichirin" (the sun)
This yukigatais locatedon thewest slopeof Nomio-kashira
Mt. (1,843 m) south of the famous Ushiga-take Mt. (1,961.5
m) in Shimizu, ShiozawaTown, Minami-uonuma County,
NiigataPrefecture(Hayashi,1985;Yamada,1995a;
Yamada,1995b).As is expressed in its name, it is a circle-
shaped, positive type yukigata (Fig. 1).
From distant views of this yukigata,I conclude that it
originates because of landslide topography. By decipher-
ing fall andwinter aerial photographsand by terrain analy-
sis,I determined the topographical origin of this yukigata
and related it to snowpack phenomenon.
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