Full crystallographic orientation (<i>c</i> and <i>a</i> axes) of warm, coarse-grained ice in a shear-dominated setting: a case study, Storglaciären, Sweden

Abstract. Microstructures provide key insights into understanding the mechanical behavior of ice. Crystallographic preferred orientation (CPO) develops during plastic deformation as ice deforms dominantly by dislocation glide on basal plane, modified and often intensified dynamic recrystallization. CPO patterns in fine-grained have been relatively well characterized understood experiments nature, whereas “warm” (T>-10?C), coarse-grained, natural remain enigmatic. Previous microstructural studies coarse-grained limited to c-axis orientations using light optical measurements. We present first study a axes c such application cryo-electron backscatter diffraction (EBSD) do so shear-dominated setting. done this developing new sample preparation technique constructing composite sections, allow us use EBSD obtain representative, bulk draw attention well-known issue interlocking grains complex shape suggest that grain sampling bias large, branching crystals appear multiple times island thin sections may result typical multimaxima CPOs previously identified warm, has subjected prolonged shear. combined from samples highly sheared Storglaciären more comprehensive picture microstructure yield pronounced cluster sub-normal shear plane elongate or split normal direction concomitant girdle parallel with maximum perpendicular direction. This pattern compares produced subsampling datasets laboratory at high homologous temperatures up strains ?1.5. Shear margin are much higher than those experimental work. At lower strain rates, recrystallization, particularly boundary migration, effective represents small, final fraction history. A is reported previous work be due sizes related presence single host several section.