ABSTRACT. A detail ed investigation h as been carried out on the dynamics of an Alpine valley glacier of r elatively simple shape a nd the results are considered in relation to the development of secondary structures. I ce veloc ity reaches a maximum near the top of a small ice fall (40 m a-I) which also coincides approximately with the eq uilibrium li ne. Flow lines converge in the accumu la tion area but a re roughl y parallel in the ablation a rea. The " regional " strain-rate pattern is ra the r complex. Approxima te longitudinal extension is evident in the accumul ation area and strain-rates reach high va lues at the south margin and in the ice fall (up to 0. 12 a-I). I n the a bla tion area, strain-ra tes are comparatively small and in general indicate longitudinal compression. " Local" deformation rates obtained in th e a rea beneath the ice fall and along a flow line near one of th e margins reveal com plex patterns of deformation within small a reas.T here is no clear relationship between foliati on and strain-rates (and by ana logy stresses), except in the case of longitudinal foli a tion in marginal a r eas which, if actively developing, li es approximately parallel to a direction of maximum sh ear strain-rate . It is more important to consider the rela tionship of this st ructure to stra in history. R esults from this study indicate that, regardless of the initia l o ri entation of th e foliation in r elation to the strain ellipse, it attains approx imate parallelism with the long axis of the ellipse as deformation progresses.It is also shown that many foliati ons originate from pre-existing layered structures such as stratifi cation or crevasse traces. This problem is discussed particularly with reference to a n a rcuate foliation which originates in the ice fa ll and is beli eved to represent tensional veins, subsequently subj ected to compressive strain within and below the ice fall. RESUME. DYllamiqlle et structure du glacier de Gries en Suisse. U ne etude approfondie a ete effectu ee sur la dynamique d'un glacie r d e vallee a lpin de forme relativeme nt simple et les resultats sont consideres en rapport avec le developpement de st ru ctures secondaires. La vitesse de la g lace a tteint son maximum (40 m a-I ) au voisinage d'une petite chute qui coin cide approximativement avec la linge d'equilibre. Les lignes de courant convergent dans la zon e d'accumulation, mais d emeurent en r evanch e a peu pres paralleles dans la zone d 'a blation. La distributio n "regionale" des vitesses de deformation est assez complexe. L es d eformations de traction plus ou moins longitudinales sont evid entes da ns la zon e d'accumulation e t les vitesses de deformati o n atteignent des valeurs elevees sur la rive sud et dans la chute du glacier (jusqu'a 0,12 a -I) . Dans la zone d'ablation, les vitesses de deformation sont comp¥.ativement faibl es et indiquent en general une com pressio n longitudina le . L es vitcsses de deformation "locales" observees dans la zone situee au-dessous de la chut e du glacier, de mem...

A detailed investigation has been carried out on the dynamics of an Alpine valley glacier of relatively simple shape and the results are considered in relation to the development of secondary structures. Ice velocity reaches a maximum near the top of a small ice fall (40 m a−1) which also coincides approximately with the equilibrium line. Flow lines converge in the accumulation area but are roughly parallel in the ablation area. The “regional” strain-rate pattern is rather complex. Approximate longitudinal extension is evident in the accumulation area and strain-rates reach high values at the south margin and in the ice fall (up to 0.12 a−1). In the ablation area, strain-rates are comparatively small and in general indicate longitudinal compression. “Local” deformation rates obtained in the area beneath the ice fall and along a flow line near one of the margins reveal complex patterns of deformation within small areas.There is no clear relationship between foliation and strain-rates (and by analogy stresses), except in the case of longitudinal foliation in marginal areas which, if actively developing, lies approximately parallel to a direction of maximum shear strain-rate. It is more important to consider the relationship of this structure to strain history. Results from this study indicate that, regardless of the initial orientation of the foliation in relation to the strain ellipse, it attains approximate parallelism with the long axis of the ellipse as deformation progresses.It is also shown that many foliations originate from pre-existing layered structures such as stratification or crevasse traces. This problem is discussed particularly with reference to an arcuate foliation which originates in the ice fall and is believed to represent tensional veins, subsequently subjected to compressive strain within and below the ice fall.