The role of grain size evolution in the rheology of ice: implications for reconciling laboratory creep data and the Glen flow law

Abstract. Viscous flow in ice is often described by the Glen law – a non-Newtonian, power-law relationship between stress and strain rate with exponent n ? 3. The attributed to grain-size-insensitive dislocation creep; however, laboratory field studies demonstrate that deformation can be strongly dependent on grain size. This has led hypothesis at sufficiently low stresses, controlled boundary sliding, which explicitly incorporates size dependence of rheology. Experimental find neither creep (n 4) nor sliding 1.8) have exponents match value 3 law. Thus, although provides an approximate description glaciers sheets, its functional form not explained single mechanism. Here we seek understand origin using “wattmeter” model evolution ice. wattmeter posits balance mechanical work required for growth dynamic reduction. Using wattmeter, calculate two end-member cases: (1) 1-D shear zone (2) as function depth within sheet. Calculated sizes both data core observations interior sheets. Finally, show variations conditions result effective intermediate creep, consistent = ± 0.5 over range rates found most natural systems.