Ice crystallographic evolution at a temperate glacier:Glacier de Tsanfleuron, Switzerland

Ice crystallographic measurements have been made on eight cores retrieved from temperate Glacier de Tsanfleuron. Switzerland. Cores are aligned approximately along a flow-parallel transect, allowing a stratigraphic model of crystallographic evolution at the glacier to be constructed. Results indicate the presence of four crystallographic units at the glacier. Unit 1 composed of homogeneous, fine-grained ice with a uniform fabric, is located within c. 20 m of the ice surface in the accumulation area of the glacier. Crystal growth within this unit occurs in the absence of significant stresses, and its rate is closely described by an Arrheniustype relationship. Unit 2 ice, characterized by the local development of coarser crystals, forms after some decades of Arrhenius growth, marking the initial influence of processes of dynamic recrystallisation. Unit 3 ice, characterized by an abrupt increase in minimum crystal size, occurs at a depth of c. 33m throughout the glacier. In the accumulation area, this increase coincides with the first evidence of systematic fabric enhancement, interpreted in terms of dynamic recrystallisation. Unit 4 ice, characterized by large, interlocking grains with a multi-modal girdle fabric, develops within c. 10m of the glacier bed. Here, the measured minimum crystal size is consistent with a steady-state balance between Arrhenius processes of grain growth and strain-related processes of grain-size reduction. These changes are interpreted in terms of the effects of intense, continuous deformation in this basal zone.