Discrimination of the flow law for subglacial sediment using in situ measurements and an interpretation model

• Published in: Journal of Geophysical Research. F. Earth Surface 2006-03, Vol.111 (F1), p.n/a
• Main Authors: Kavanaugh, Jeffrey L., Clarke, Garry K. C.
• Format: Article
• Language: English
• Subjects: Earth sciences; Earth, ocean, space; Exact sciences and technology; subglacial hydrology; subglacial instrumentation; subglacial mechanics
• ISSN: 0148-0227; 2156-2202
• DOI: 10.1029/2005JF000346

Subglacial hydrological and mechanical processes play a critical role in determining the flow characteristics and stability of glaciers and ice sheets. To study these processes, we have measured simultaneously basal water pressure, pore water pressure, sediment deformation, glacier sliding, and sediment strength beneath Trapridge Glacier, Yukon Territory, Canada. To interpret these data, we have developed a simple hydromechanical model of processes beneath a soft‐bedded alpine glacier. The glacier bed is divided into soft‐bedded regions that are hydraulically connected to the subglacial drainage system, soft‐bedded but hydraulically unconnected regions, and hard‐bedded regions. Each region is represented as a one‐dimensional column. The columns are coupled by a simple ice dynamics model that accounts for water‐pressure‐driven changes in basal shear stress distribution. Synthetic responses for subglacial instruments are calculated from the modeled basal conditions, providing a framework for improving interpretation of field records. The model is used to determine which of several till flow laws best represents conditions beneath Trapridge Glacier. Investigated are linear‐viscous, nonlinear‐viscous, nonlinear‐Bingham, and Coulomb‐plastic tills. Pore water pressures, sediment deformation profiles, and sliding rates are calculated for each flow law. Comparison of synthetic and field instrument responses suggests that till behavior is best represented as Coulomb‐plastic. Model results also suggest that the ploughmeter is the most diagnostic in situ indicator of till behavior currently available and that using long‐term observations of sediment deformation profiles in regions of varying pore water pressure can result in an underestimation of flow law nonlinearity.