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Closure of deep boreholes in ice sheets: a discussion
Authors: Talalay PG and Hooke RL
Year: 2007
Periodical/Journal: Annals of Glaciology
Volume: 47
Number: 1
Page Range: 125-133
Abstract: The most frequently used relation between ice deformation rate, &epsi, and stress, T, is the power law, commonly called Glen's flow law, E = ATn, in which A is an ice stiffness parameter and n is an empirical constant. A can be estimated from the simple exponential relation A = EA0eQ/RT, where A0 is a constant independent of temperature; E, commonly called the enhancement factor, depends on ice crystal orientation, impurity content and other factors; Q is the activation energy for creep; R is the universal gas constant; and T is the absolute temperature. Laboratory experiments yield values of A0 = 9.514 MPa-3a-1 for secondary creep. Typical borehole closure experiments then give E = 0.16. This low value probably results from the fact that, when deforming into a borehole, ice is subject to stresses that are inconsistent with the preferred orientation of c axes that has developed over many years under a stress configuration with no borehole present. Closure data from Vostok hole 3G yield E = 0.7. This higher value may reflect a unique stress environment yielding fabrics that are somewhat better oriented for borehole closure.
DOI: 10.3189/172756407786857794
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