Ice crystallographic evolution at a temperate glacier: Glacier de Tsanfleuron, Switzerland
Published:January 01, 2000
Jean-Louis Tison, Bryn Hubbard, 2000. "Ice crystallographic evolution at a temperate glacier: Glacier de Tsanfleuron, Switzerland", Deformation of Glacial Materials, Alex J. Maltman, Bryn Hubbard, Michael J. Hambrey
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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 Arrhenius-type 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. 33 m 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. 10 m 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.
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Deformation of Glacial Materials
The flow of glacier ice can produce structures that are striking and beautiful. Associated sediments, too, can develop spectacular deformation structures, and examples are remarkbly well preserved in Quaternary deposits. Although such features have long been recognized, they are now the subject of new attention from glaciologists and glacial geologists.
This collection of papers addresses how the methods for unravelling deformation structures evolved in recent years by structural geologists can be used for glacial materials, and the opportunities offered to structural geologists by glacial materials for studying deformation in rocks.