The image shows a drag spool or "slidometer" to be placed in the borehole. The sharp tip is pounded into the sediment and connected by a cable to a potentiometer. As the glacier slides or the sediment deforms, the potentiometer is turned and a voltage is registered by the data logger. Using these instruments, we can determine the sliding rate of the glacier.
The image is a close-up of the slidometer. Other sensors include ploughmeters (used to study ice-bed coupling), and turbidity, conductivity and water pressure sensors (used to study residence times of water and the subglacial drainage system).
Blake, E. W., and G. K. C. Clarke. 1991. Subglacial water and sediment samplers. Journal of Glaciology, 37(125), 188-190.
Blake, E. W., G. K. C. Clarke, and M. C. Gérin. 1992. Tools for examining subglacial bed deformation. Journal of Glaciology, 38(130), 388-396.
Blake, E. W., U. H. Fischer, and G. K. C. Clarke. 1994. Direct measurement of sliding at the glacier bed. Journal of Glaciology, 40(136), 595-599.
Fischer, U. H., and G. K. C. Clarke. 1994. Ploughing of subglacial sediment. Journal of Glaciology, 40(134), 97–106.
Stone, D. B., and G. K. C. Clarke. 1996. In situ measurements of basal water quality and pressure as an indicator of the character of subglacial drainage systems. Hydrological Processes, 10(4), 615-629.
Stone, D. B., G. K. C. Clarke, and E. W. Blake. 1993. Subglacial measurement of turbidity and electrical conductivity. Journal of Glaciology, 39(132), 415-420.