Hydrologic forcing of subglacial sediment properties and impact on glacier dynamics
We demonstrate that temporally coincident collection and joint interpretation of high-quality differential GPS (supported by two consecutive GEF loans of four Leica 1200 receivers, which form the basis of this report), repeat seismic amplitude-versus-offset (AVO) and continuous ground-penetrating radar (GPR) data is well suited to characterising the spatiotemporal dynamics of the subglacial processes controlling the flow instability of the Grubengletscher, Valais, Switzerland. We find that basal motion of the Grubengletscher occurs principally by subglacial sediment deformation during much of the day in summer, although hydrologically-induced sliding events are common in the afternoon. The highest glacier flow velocities occur during these sliding events, as opposed to those measured during times of sediment deformation which are relatively slow and invariable. We conclude that hydrological processes are a governing control on basal mechanical processes at the Grubengletscher during the summer. More generally our study demonstrates that an integrated geophysical approach is well suited not only to characterising at a snapshot in time coupled hydrological and mechanical properties of the glacier bed, but also to monitoring changes in those properties over time. From this fundamental glaciological processes can be inferred, which may well hold true at outlet glaciers from Polar ice masses as they do for the Grubengletscher as a possible small-scale analogue.
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