EEPS Colloquium: Dougal Hansen

Experimental insights into subglacial sediment flux and basal slip

Rapid glacier motion is commonly facilitated by ice sliding over water-saturated sediment beds. These sediments, known as “till”, are mobilized during slip—deforming due to traction exerted at the ice-bed interface or becoming entrained in basal ice and transported downslope as a “frozen fringe.” The resultant sediment flux transforms the evolving subglacial landscape, modulating basal friction, water flow pathways, and catchment-wide erosion rates. Despite their importance, however, the temporal scales and fundamental dependencies of these processes remain underconstrained, limiting the predictive abilities of modeling efforts. In this talk, I will present experimental results obtained with custom devices designed to closely simulate these hidden basal processes. Specifically, I examine long-standing assumptions concerning i) the deformation and transport of basal till and ii) the infiltration of glacier ice into sediment pore spaces. In the case of the latter, I also demonstrate how the presence of ice-rich basal debris controls friction for many soft-bedded glaciers and ice streams, which are the primary drivers of ice mass flux to global oceans. This work not only provides fresh perspectives on processes currently driving large-scale change in the cryosphere but also marks the first instance of real-time observation of these sediment flux processes in such environments.

EEPS Colloquia are made possible by the William C. Ferguson Fund.