Subglacial Slip and Seismicity

Fast ice streams and outlet glaciers are the dominant contributor to expected future sea-level rise. They are able to achieve such high surface velocities predominantly by sliding on their beds, but basal processes and conditions are hard to access and are thus under-constrained, as well as poorly represented, in ice sheet models. The majority of ice stream bed area is likely underlain by wet, deformable sediment, or till, but few experiments have probed the sliding behavior of polycrystalline ice on soft beds under the range of relevant subglacial conditions. Implementing the double direct shear configuration and other techniques long used to measure the frictional properties of fault gouge, we add precise cryogenic temperature control and the ice interface to apply these methods to glacier basal sliding behaviors. Using velocity stepping, slide-hold-slide, and shear stress oscillation experiments in the framework of rate-state friction, we explore the effect of temperature, normal stress, ice and till grain size/composition, and layer thickness on frictional parameters. These parameters determine behaviors such as whether the interface undergoes stable sliding or stick-slip motion, allowing us to address the conditions that contribute to the subglacial seismicity or steady-slip observed in West Antarctic ice streams. A recent publication presents the first evidence of velocity-weakening friction of ice-on-till sliding, that at slightly subfreezing temperatures (Saltiel et al., Seismological Research Letters 2021). By freezing transducers in the ice sample, we measured and analyzed acoustic emissions from stick-slip cycles, comparing waveform characteristics from ice on hard and soft beds at a range of subglacial temperatures. Machine learning classification algorithms find that its possible to decipher the bed type from waveforms, offering the potential to monitor bed conditions from remotely sensed subglacial seismicity (Saltiel et al., Annals of Glaciology 2024).

Collaborators: Christine McCarthy, Ben Holtzman, & Jacob Tielke (LDEO Rock and Ice Mechanics Lab); Tim Creyts (LDEO); Heather Savage (UC Santa Cruz)