Subglacial processes and their control on ice dynamics and landscape evolution

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The objective of this proposal is to observe and quantify the strong interaction between mechanical processes and hydrological conditions present beneath weak-bedded valley glaciers.  A field study will be initiated at a small valley glacier in the St. Elias Mountains of Yukon Territory, Canada to determine mechanical and hydrological conditions at the glacier bed.  The bed will be accessed using a hot-water drill, and arrays of instruments will be installed to allow (1) interpretation of field records with the aid of a numerical model of subglacial hydromechanical behaviours and (2) use of the data to constrain more general numerical models of glacier dynamics.  Ice deformation and surface flow rates will be measured by repeat borehole inclinometry and GPS survey techniques, and meltwater production rates calculated from automated weather station data and accumulation/ablation measurements will aid in quantifying changes in subglacial drainage system characteristics.  Instrument data will be used to improve an interpretation model of subglacial processes, with a long-term goal of improving the treatment of the basal boundary condition for general ice-dynamics models.   Basal processes greatly influence many aspects of glacier behaviour.  Glaciers that are underlain by soft, deformable sediments move by some combination of ice deformation, sediment deformation and basal sliding.  These last two components of flow are often collectively called "basal motion" and can contribute greatly to the motion of ice masses.  Basal motion is the dominant flow mechanism of some glaciers, gives rise to some unstable behaviours of tidewater and surging glaciers and plays an important role in the dynamics and mass balance of ice sheets.  In addition, effective erosion at the base of the ice allows glaciers to carve cirques and valleys into mountainsides and to deliver vast quantities of sediment to drainage basins.  Because high subglacial water pressures facilitate both glacier sliding and sediment deformation, basal motion is strongly influenced by hydrological conditions at the glacier bed.  An improved knowledge of basal processes is thus key to understanding both the dynamic behaviour of ice masses and their effect on the landscape.