The tertiary creep of polycrystalline ice: experimental evidence for stress-dependent levels of strain-rate enhancement

• Published in: Journal of Glaciology
• Main Authors: Treverrow, A, Budd, WF, Jacka, TH, Warner, RC
• Format: Article in Journal/Newspaper
• Language: English
• Published: International Glaciological Society 2012
• Subjects: Earth Sciences; Physical Geography and Environmental Geoscience; Glaciology; Journal of Glaciology
• Online Access: http://www.igsoc.org/journal/; https://doi.org/10.3189/2012JoG11J149; http://ecite.utas.edu.au/78600

Laboratory creep deformation experiments have been conducted on initially isotropic laboratory-made samples of polycrystalline ice. Steady-state tertiary creep rates, ∈ ter , were determined at strains exceeding 10% in either uniaxial-compression or simple-shear experiments. Isotropic minimum strain rates, ∈ min , determined at ∼1% strain, provide a reference for comparing the relative magnitude of tertiary creep rates in shear and compression through the use of strain-rate enhancement factors, E , defined as the ratio of corresponding tertiary and isotropic minimum creep rates, i.e. E = ∈ ter / ∈ min . The magnitude of strain-rate enhancement in simple shear was found to exceed that in uniaxial compression by a constant factor of 2.3. Results of experiments conducted at octahedral shear stresses of τ o = 0.040.80 MPa indicate a creep power-law stress exponent of n = 3 for isotropic minimum creep rates and n = 3.5 for tertiary creep rates. The difference in stress exponents for minimum and tertiary creep regimes can be interpreted as a τ o stress-dependent level of strain-rate enhancement, i.e. E α τ 1/2 o . The implications of these results for deformation in complex multicomponent stress configurations and at stresses below those used in the current experiments are discussed.