Title. Author(s)HUJIOKA, Tosio; SHIMIZU, Hiromu; AKITAYA, Eiji; NARI. CitationPhysics of Snow and Ice : proceedings = 雪氷の物理学 : 論文集.

Transcription

1 Title Oservtion of Creep Rte of Snow on Mountin Slopes Author(s)HUJOKA, Tosio; SHMZU, Hiromu; AKTAYA, Eiji; NAR CittionPhysics of Snow nd ce : proceedings = 雪氷の物理学 : 論文集 ssue Dte 1967 Doc URL Type ulletin Note nterntionl Conference on Low Tperture Science. Cryoiology. (August, 14-19, 1966, Spporo, Jpn) File nformtion 2_p pdf nstructions for use Hokkido University Collection of Scholrly nd Ac

2 Oservtion of Creep Rte of Snow on Mountin Slopes, Teshio District, Hokkido* Tosio HUZOKA, HiromuSHMzU, Eiji AKTA YA nd Hideki NARTA iii Jlil!1< ~!!f 7)( <fl. tkletl-~l'1\. nx: E ~ ~ The nstitute of Low Tperture Science Hokkido University, Spporo, Jpn Astrct The creep rtes of snow covers on mountin slopes were mesured to determine the stress distriution in the snow cover in Teshio District, Hokkido. Mesurents were mde on the snow cover of the north nd south slopes of ridge running from est to west on which the Avlnche Reserch Sttion of the nstitute of Low Tperture Science ws estlished in Although oth slopes hve pproximtely the sme ngle of uniform inclintion, out 35, with no trees, they gretly differ in vlnche hzrd wise. Every yer mny vlnches occur on the south slope, ut none re seen on the north slope. n totl four sites for oservtion were selected, i. e., the upper prt nd middle prt on the south nd north slopes of the ridge respectively, to mesure the creep of snow cover on the slope. At ech site, verticl cut plne ws mde in the snow cover y n electriclly heted wire lid in prllel with the contour line of the slope. An iron r mrker ws plced on the ground eforehnd s the se line to mesure the mount of creep of snow cover. An oservtion snow wll ws mde perpendiculrly to the cut plne every two weeks t ech site. The strtifiction of snow lyers nd distriution of snow density, tperture, hrdness, shpe of snow prticle, prticle size nd free wter content were lso mesured on the snow wll.. ntroduction Every winter hevy snowflls cover the northern.hlf of Jpn where 22 million people live. Economic losses cused y snow dmges prticulrly y vlnches hve incresed with industril development. Thus, Snow Dmge Section of the nstitute of Low Tperture Science ws estlished in 1963 to study the physicl chrcteristics of snow covers nd the dynmics of vlnches. Avlnche hzrd districts in Jpn lie etween 36 nd 46 ltitude. The southern prt of this district hs wrm wether; the tperture is nerly oce even in mid-winter. The ~nowcover is generlly very deep nd wet throughout the winter. Most of the vlnches re of the surfce or ground type of wet snow. The northern prt, on the other hnd, hs cold wether in winter with rther light weight dry snow. The tperture grdient in the snow cover chnges the snow prticles into depth hor which mkes the snow cover wek mechniclly. Avlnches re of the ground or surfce type of dry snow in winter nd of wet snow in erly spring. Now, in the Teshio District, mny vlnches occur on mountin slopes every winter. For instnce in Jnury, 1961, n iron ridge under the jurisdiction of the Jpnese Ntionl Rilwys ws destroyed y n vlnche ner the Avlnche Reserch Sttion. * Contriution No.897 from the nstitute of Low Tperture Science.

3 1178 T. HUZOKA ET AL p 3p m B , Fig. 1. Profile of experiment slopes., M /, F + :+ 6 '" Q e, \' J..... '" " J '~"'" '1." 1-8 Q d 1 G ''/-'" R'... ~~ ) 6 4 Q- 2 - <1 o - l! - : C C i e Ce C '35.YV.1 2,, l X 1 1 J.5 1.4, 1 : 2 G. g/cm3, X 1 2 4, \'. '. "..., /... Fig. 2. Physicl chrcteristics of snow t site B, Ferury' 23, 1966! i , R g/ 2,, 2 4 X 1 3

4 CREEP RATE OF SNOW ON SLOPES Physicl Chrcteristics of Snow Covers The physicl chrcteristics nd the creep rtes of the snow cover were mesured on the south nd north slopes of the ridge on which the Avlnche Reserch Sttion ws estlished in The profile of the slopes is illustrted in Fig. 1. The numerls, ', nd. the rrows with the letters A, B, C nd D in the figure show the ngles of inclintion nd the oservtion sites on the slopes respectively. At ech oservtion site snow pit ws mde nd the strtifiction of snow lyers, distriution of snow density, tperture, hrdness, shpe of the snow prticle, prticle size nd,free wter content were mesured every two weeks. The ir tperture, wind direction, wind velocity nd solr rdition were recorded utomticlly in the Sttion throughout t~e winter. Exmples of the physicl chrcteristics of the snow cover t site Bnd D on 23rd nd 24th of Ferury of the winter of re illustrted in Figs. 2 nd 3 in M F ~ q -1 -? -i -'1-1 -~ -7 -~ --- ~ _ T, - ~ /" '\ /, \.. ti " () o Q Q Q cd To G 1... R.. >~ ~:: Zl Zl Zl Q :... ::1 o 2 o.1 c R, g/ Fig. 3. Physicl chrcteristics of snow t site D, Ferury 24, 1966

5 118 T. HUZOKA ET AL. which the nterntionl Clssifiction* of snow ws used. The letter symols M, F, D, R, T nd T re the depth of the snow cover perpendiculr to the ground, grin shpe, grin size, snow hrdness, snow tperture nd ir tperture respectively. The snow hrdness ws mesured y Kinosit's hrdness guge. The grin size D is expressed in the figures y the letter symols,, c, d nd e which re defined in the nterntionl Clssifiction s follows; <.5 mm,.5 ~ < 1. mm, 1. ~ c < 2. mm, 2. ~ d < 4. mm, nd e24. mm. Some modified grphic symols of the snow prticle shpe of the nterntionl Clssifiction were used in Figs. 2 nd 3. The squre represents depth hor crystls of solid type which hs the shpe of hexgonl thick plte or hexgonl short prism reported in this ook y Akity (1966). The nterntionl Clssifiction defines the squre symol to e snow grins with fit fcets which show distinct sprkling effect in Fig. 4. Snow profile t site S, Ferury 23, 1966 * Commission of Snow nd ce of the nterntionl Assocition of Hydrology (1951, 1954).

6 CREEP RATE OF SNOW ON SLOPES ll81 right sunlight. The depth hor crystls of solid type hs the sme chrcteristic fetures s those ove defined. The solid circle in the nterntionl Clssifiction represents snow of rounded grin, nmely, the grins of compct snow nd grnulr snow. n this pper the solid circle is used only for the grnulr snow trnsformed y wet metmorphosis nd the white circle is newly introduced to represent grins of the compct snow metmorphosed through the dry process.. Creep Rte of Snow nd Principl Axis of Stress The creep profile of the snow cover ws otined t four sites A, B, C nd D in Fig. 1. n lte utumn n iron r of 4 m length ws fixed to the ground of ech site long the contour line, nd t the oth ends of the r moo poles were put verticlly in the ground s the mrkers of the site. n winter snow pits were mde t the moo poles nd the snow cover ws cut verticlly y n electriclly heted wire long the verticl plne determined y two plum lines t the oth ends of the iron r. This rtificil plne crevice hd width of out 1 mm t first nd chnged its shpe nd width ccording to the creep movent of snow lyers throughout the winter seson. Figure 4 shows the snow profile t site B on 23 rd Ferury, The pit wll ws coloured y ink to mke the snow strtifiction visile. There cn e seen two :. :. :. :: : : ::" 13 H F Fig. 5. Creep movents of two rtificil crevices in the snow cover, t site B, from Jnury 27 to April 7, The displcents of the intersections of crevices nd oundries of snow lyers give the displcent vectors shown y the dotted line on the figure

7 1182 T. HUZOKA ET AL. H 12 o 11 /' ' Fig. 6. Distriution of principl stresses t site B, Ferury 23, 1966

8 CREEP RATE OF SNOW ON SLOPES 1183 crevices of which the lower one ws cut on 27th Jnury nd the upper one ws mde on 9th Ferury long the verticl plum line of the photogrph. The displcent of the crevice from the verticl plum line just ove the iron r ws mesured every two weeks nd the results t site B in the winter seson of re illustrted on Fig. 5. The solid lines represent the crevices nd when it ws open the uphill side surfce of the crevice is indicted in the figure. The dotted lines in the figure show the displcent of the oundries of snow lyers. Hefeli (1963) proposed geometricl method to find out the directions of the principl stresses from the displcent vector of snow within the snow cover. And once these directions re determined the corresponding vlues cn e esily e clculted if the creep deformtion in the ove lying snow tkes plce homogeneously. Figure 6 is one of the results of the stress distriution in the snow cover t site B on 23rd of Ferury, Clcultions were crried out under the ssumption tht the crevice ws filled with uniform nd continuous snow. References 1) AKTAYA, E Some experiments on the growth of depth hor. n Physics of Snow nd ce, Prt 2 (H. URA, ed.), Low Tp. Sci., Spporo, ) HAEFEL, R Stress trnsformtions, tensile strength, nd rupture processes of the snow cover. n ce nd Snow (W. D. KNGERY, ed.), M.. T. Press, Cmridge, Mss., ) SCHEFER, V., KLEN, G. nd DE QUERV AN, M Entwurf einer interntionlen Schneeklssifiktion usgereitet durch ds Komitee fur Schneeklssifiktion. lugg, ntern. Assoc. Sci. Hydrol., Pul. 32, ) SCHEFER, V., KLEN, G. nd DE QUERV AN, M The interntionl clssifiction for snow (with specil reference to snow on the ground). The Commission on Snow nd ce of the nterntionl Assocition of Hydrology. Technicl Morndum, 31, Associte Commitee on Soil nd Snow Mechnics, Ntionl Reserch Council, Ottw, Cnd.