Laboratory study of tidally modulated glacier flow through ice friction experiments

Improved understanding of controls on glacier flow is critical for predictions of glacier-dynamic contributions to sea level and glacier response to climate change. The nonlinear character of glacier ice and subglacial till, in which material properties can depend on stress, strain rate, and strain history, poses a particular challenge for physically realistic modeling, and for interpretation of observational datasets. In particular, the physics of tidally modulated glacier motion is poorly understood, and knowledge of ice deformation properties under tidal loading conditions is limited. Using a new, custom-designed and fabricated, servo-controlled biaxial loading apparatus we are exploring the frictional and internal deformation behaviors of periodically loaded ice sliding on rock. The apparatus is fit with a liquid-medium cryostat that can control temperature steadily for weeks at a time, allowing us to make measurements at glaciologically relevant loading rates and frequencies. We will present preliminary results from a series of double-direct shear experiments in which a central piece of ice slides between two rock samples. In the experiments a constant normal stress and periodic (sinusoidal) loading stress are applied to mimic tidal loading of glaciers. Thus with a single experiment we will measure both the solid-solid friction and anelastic properties of the ice. The planned experimental conditions are P = 1 atm, T = ~0 to -20°C, and f = 10^-5 - 1 Hz. Applying well established methods from the field of rock mechanics, we will provide frequency-dependent material properties of ice and ice-on-rock deformation at realistic frequencies experienced by tidewater glaciers in Antarctica and elsewhere. The values obtained from this study will provide better constraints for next generation modeling of glacier and ice-stream response to external forcing. The results will be compared with field observations to infer characteristics of the bed interface and the material in the bulk glacier.