The use of borehole inclinometry in determining basal sliding and internal deformation at Haut Glacier d'Arolla, Switzerland

A series of boreholes were drilled with high-pressure hot water across a section of Haut Glacier d'Arolla, Switzerland, in summer 1995. Twenty-three of the boreholes were profiled with a digital inclinometer soon after drilling, and 14 were re-profiled up to 6 weeks later to determine changes in the longitudinal shape of boreholes with time. In addition to the main surveys, three boreholes were surveyed 14 times each to assess the accuracy and reproducibility of inclinometry measurements. These repeat surveys suggest that caution is needed in the interpretation of short-term borehole displacement measurements, and that the reoccupation of boreholes from one year to the next may be a better way to determine patterns of internal deformation and basal sliding. The annual scale may also have advantages in providing more long-term insight into glaciological processes than short-term (single season) measurements.