Laboratory studies of flow properties and associated crystal structure in Holocene and Wisconsin ice
Ice mechanical experiments in uniaxial compression and in simple shear configurations were carried out at 0.2 MPa octahedral shear stress and - 5 °C on ice core samples deposited as snow during the Wisconsin and Holocene periods. Tested samples were selected from ice cores drilled in South Greenland...
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| Format: | Thesis |
| Language: | English |
| Published: |
1995
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| Online Access: | https://eprints.utas.edu.au/21945/ https://eprints.utas.edu.au/21945/1/whole_WangWeiLi1995_thesis.pdf |
| Summary: | Ice mechanical experiments in uniaxial compression and in simple shear configurations were carried out at 0.2 MPa octahedral shear stress and - 5 °C on ice core samples deposited as snow during the Wisconsin and Holocene periods. Tested samples were selected from ice cores drilled in South Greenland (Dye 3), Ellesmere Island, Canada (Agassiz Ice Cap) and East Antarctica (Law Dome Ice Cap), with an aim to finding the reasons for different flow rates between Wisconsin ice and Holocene ice. These different flow rates, reported by some glaciologists, were inferred from field measurements of borehole closure and inclination. The ice test samples were analysed for crystal size and orientation fabric, and soluble and insoluble impurity concentrations. The experiments, in two different stress configurations, gave coincident results. With the progression of strain, the deformation of the Wisconsin ice and of the Holocene ice tended to reach a constant tertiary (steady state) flow rate. Ice with a c-axis fabric pattern compatible with the applied stress configuration (small circle girdle pattern for compression and single maximum pattern for shear) reached steady state flow directly, without passing through a minimum creep stage. For the steady state tertiary flow, there was no evidence found of any significant difference between the flow rates of Wisconsin and Holocene ice. Crystal size and the presence of impurities (in the concentrations found in the different ice samples) seemed not to affect the ice flow rates at the temperature and stress tested. The ice flow rates were found to be determined mainly by crystal orientation fabric pattern. It is concluded therefore, that the more rapid flow measured in some field projects for the Wisconsin ice is primarily due to enhanced crystal orientation strength. |
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