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 x 10(12) to 3.4 x 10(12) 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 he hydraulic diffusivity of the till layer ranges from 1.2 to 5.0 x 10(-6) m(2) s(-1), and the hydraulic conductivity from 3.2 x 10(-7) to 7.7 x 10(-8) m s(-1).