Mechanical and hydraulic properties of till beneath Bakaninbreen, Svalbard

Bakaninbreen, Svalbard, was in the late phase of a prolonged surge during 1995-96. In order to investigate the nature of the basal mechanical and hydraulic regime, sets of tilt sensors equipped with pore-pressure sensors were installed into the basal till layer. Water-pressure transducers were also installed in the boreholes above the ice-till interface. During 1995, the measured mean strain rate in the till was 0.44 a-1 up-glacier of the surge front, while down-glacier the rate was 0.04 a-1. Our interpretation indicates that deformation was the dominant component of basal motion. Strain rates fluctuated strongly, and periods of both positive (down-glacier) and negative (up-glacier) strain occurred. No consistent relationship was apparent between effective pressure and strain rate within the basal till layer. The viscosity of the basal sediments ranged from 1.3 × 1012 to 3.4 × 1012 Pa s. Such high values suggest that the till layer beneath Bakaninbreen may be partially frozen. Analysis of simultaneous measurements of pore-water and borehole water pressure suggests the hydraulic diffusivity of the till layer ranges from 1.2 to 5.0 × 10-6 m2 s-1, and the hydraulic conductivity from 3.2 × 10-7 to 7.7 × 10-8 m s-1.