PLOWING OF SUBGLACIAL SEDIMENT

Mechanical conditions at the base of Trapridge Glacier, Yukon Territor y, were investigated using a ''ploughmeter''. We describe the physical characteristics and the theory of this new instrument as well as its operation. Observational results reveal variations in ploughmeter resp onse that might be attributed to spatial variability in subglacial pro cesses or spatial variation in sediment granulometry. Quantitative ana lysis of the interaction of the ploughmeter with the basal layer yield s estimates of rheological parameters. If the sediment is assumed to b ehave as a Newtonian viscous fluid, the estimated effective viscosity is 3.0 x 10(9)-3.1 x 10(10) Pa s; if it is assumed to behave as an ide al plastic solid, the estimated yield strength is 48-57 kPa. In both c ases, the estimated shear resistance of subglacial material is compara ble to but somewhat less than that required to balance fully the appli ed basal shear stress.