Laboratory Study of Substrate Control and Cryoseismicity of Glacier Basal Motion
One of the most devastating potential impacts of climate change is sea-level rise. Current forecasts predict sea level to rise by as much as a meter by the end of this century. Such a magnitude would inundate some of the world's most populated areas, but uncertainties in the predictions need to be lowered. Well-constrained sea-level projections that can provide guidance to infrastructure protection and planning are dependent in part on accurately modeling the rate that glacier ice is transported from snow accumulation zones to the oceans by fast-moving bodies of ice called ice streams. Controls on ice-stream flow rates, particularly those influencing processes at the hard-to-access base of ice streams, are poorly constrained by observation. To shed light on these important controls, the project team will conduct laboratory experiments that isolate and constrain particular sliding behaviors. The experiments aim to identify which factors (e.g., temperature, water pressure, velocity, amplitude of forcing) control the sliding response so that outcomes can be scaled up from the laboratory to the ice-stream scale and provide better predictive power to ice-sheet simulation models.
To isolate the ice-stream basal sliding process, the project team will conduct friction experiments of materials at cryogenic conditions. The team will apply the mathematical framework of rate- and state-dependent friction that has been successfully used for decades in rock mechanics to describe earthquake phenomena. Building on the team's past measurements of ice-on-rock frictional dependence on normal stress, temperature, sliding velocity, and driving stress oscillation, this project will extend the parameter space to include till-layer thickness and pore-fluid saturation under drained and undrained conditions. Coupling among frictional melt, lubrication, and pore pressure will complicate the forcing and may greatly increase the range of behaviors. The experiments will test the rate-state friction formulation's ability to describe this full range of observed behaviors, from stick-slip events to slow slip and tremor to steady aseismic creep. In addition to measuring frictional shear stress, the team will implement acoustic characterization techniques to record acoustic emissions and ultrasonic wave propagation properties during deformation. Although direct comparability to seismic data from the field is unlikely, observations of how experimental conditions influence waveform properties such as the polarity, frequency, and shape can help in the interpretation of cryoseismic datasets. The results will also provide basal slip and bed deformation constitutive relations and parameters for use in ice-sheet models that are vital for predicting changes in ice-sheet systems.