Uniaxial compressive creep tests were performed on polycrystalline samples of glacier ice at stresses ranging from 0.06 bar to 1.0 bar under conditions similar to those actually occurring in a temperate glacier. Tests were conducted in an ice tunnel on the Blue Glacier, Mt Olympus, Washington, U.S.A., thus ensuring that the temperature remained at the pressure melting point.The flow law proposed as an appropriate one-dimensional flow law for temperate glacier ice is a polynomial expression containing linear, cubic and fifth-order terms. This law provides a good fit to the data and is also consistent with the quasi-viscous creep data of Glen (1955).

The initial state of stress in fallen snow is calculated by considering incremental gravity loading of the accreting snow slab. It is then postulated that slab avalanche release is initiated by a reduction of shear strength on a critical layer to a value below that of the existing shearing stress. The manner of top tensile failure, side shear failure, and either buckling or shear compression fa.ilure at the lower end of the stab is then described. These results provide avalanche dimensions that are lower bounds on those occurring naturally.A recent paper on snow slab failure by Perla and LaChapelle [1970] provides an avalanche model falling into four parts: (1) shear failure at the snow-ground or snow-snow interface, (2) tensile failure at the slab top, (3) shear failure at the slab sides, and (4) compression failure at the slab bottom (Figure 1).The physical reasons for the shear failure at the snow-ground or the snow-snow interface were dealt with by Perla and LaChapelle [1970]; the subsequent behavior is a consequence of this initial shear degeneration. Unfortunately the Perla and LaChapelle model could not be developed into a complete theory, because no adequate way of predicting the stress distribution in the snow slab prior to avalanching appeared to be available. Therefore only arguments relating to order of magnitude were used to examine the consequences of the model. In spite of this restriction the results proved encouraging. , 1963] is used to determine the initial state of stress in fallen snow; thus in nature it corresponds most closely to conditions for soft-slab avalanches originating in new-fallen snow. The basic analysis is for uniform cover of a plane surface of constant slope, but the effect of curvature is examined by considering uniform accretion on a spherical surface. Nonuniform coverage is also investigated. In the present paper a method of incremental analysis developed for accreting bodies [Brown and GoodmanThe shear stresses over a part of the interface are then released, and the subsequent forms Copyright ¸ 1972 by the American Geophysical Union. 457O of failure at the top, sides, and bottom are described. The bottom failure can be due to buckling or fracture [Hae[eli, 1963]. Both modes are examined. The consequences of the theory are slab dimensions (length and breadth) in terms of the thickness, slope, snow density, and mechanical properties. These dimensions are consistent with observed slab behavior and suggest that the Perla-La-Chapelle approach is valid. One concept of metamorphosis involves a shear strength degeneration along a layer. This layer may be located at the ground-snow interface, at an interface between new and old snow, or at some other surface in the snow thickness.

Surface defo rma tions in th e neighborhood of a crevasse field were measured over short (3 m) gage lengths in order to study fl ow conditions associated wi th crevasse formation. The results obtained were unusual in that they were in consistent with large-scale resu lts found by previous workers. It was conclud ed that the presence of mall-scale surface effects, such as fractures, potholes and hea led crevasses give rise to small-scale deformation fields with large spatial and temporal variations and that there is a lower limit of gage length below which deformation measurements pertinent to regional flow phenomena cannot be made. This lower limit is appa ren tl y a n order of magnitude greater than the spacing of the feat ures which give rise to localized effects. RESUME. M esures de diformations a petite echelle a. la slliface d'wI glacier. Les deform a ti ons de la surfa ce dans le voisinage d ' un e zone de crevasses ont e te mesurees sur de court es longueu rs (3 m) en vue d 'etudier les conditions d 'ecoul ement associees a la forma tion des crevasses. Les resultats obten us on t ete etranegs en ce sens qu'i1s n'etaien t pas cohe rents avec les resultats a grande echell e obten us par les precedents c herc heurs. On e n conclut que la presence d'effets de surface a petite echelle tels q ue fractures, marmites et c revasses cicatrisees donn e naissance a des champs de deformation a petite echell e avec de grandes va ri a ti ons dans l'espace et da ns le temps et qu'il y a un e limite infe ri eure des longueurs mesurees en dessous de laq ucll e les mesures de defo rma tion convenabl es pour le phe nomene d 'ecoul em ent d 'ensembl e ne peuvent plus etre faites. Cette limite inferi eure est a ppa rement d ' un ordre de grandeur supe rieur a I'espacem ent des accid ents qui donnent naissa nce a d es effets loca lises. ZUSAMMENFASSUNG. Engmaschige D ejormatioTlslllessllllgeTl mif eiller Gletscheroberjidche. Die Oberflachende-formationen in der Nachbarschaft eines Spa ltengebietes wurden in kUI'zen Absta nden (3 m) gemessen, um die mit der Spaltenbildung verbundenen Fliessvorgange zu u ntersuchen. Die e rha ltenen R esulta te waren insofern ungewohnlich, a ls sie mit den Ergebnissen weitmaschiger Messungen fruherer Autoren nicht ubereinstimmten. Es wurde geschlossen, dass das Vorhandensein kl einteiliger Erscheinungen an d er Oberflache, wie Bruche, Gletschertopfe und wieder geschlossene Spa lten, fein strukturierte Deformati ons-feld er mit grossen ra umlichen und zeitli chen Schwankungen bewirkt und dass es ein e untere Grenze fur di e M essabstande gibt, unter der Deform atio nsmessungen in A bhangigkeit von regionalen Fliesserscheinungen w cht durchgefuhrt werden ko nnen. Diese untere Grenze ist sichtli c h um eine Ordnung grosser a ls die Dimension der E rscheinunge n, welche ortliche Effekte hervorrufe n. THE study of crevasse formation and propagation provides information on the overall flow of the glacier and the tensile properties of glacier ice. The earliest theoretical contribution was that of Hopkin...

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