Fibre-optic strain sensing on an alpine glacier

Abstract. In-situ measurements of ice deformation are constrained by the spatial resolution of discrete sensors, leaving fundamental questions about small-scale ice rheology unresolved. Here we present the first application of fibre-optic Distributed Strain Sensing (DSS) in a glacier setting, deployed at Chessjengletscher, a small polythermal glacier in the Swiss Alps. We compare Brillouin and Rayleigh DSS techniques in a borehole drilled to 38.4 m depth, alongside Raman distributed temperature sensing. Both methods resolve highly variable strain rates at the sub-metre scale — detail unattainable with conventional tiltmeters or inclinometry. Fitting observed strain profiles to a plane-strain deformation model supports a near-linear ice rheology for temperatures within 1 °C of the pressure melting point, consistent with recent laboratory experiments on temperate ice. Corresponding rate factors align closely with accepted values – though likely tempered by incomplete borehole freeze-in, which decouples the cable from ice deformation over portions of the column and introduces uncertainty into our displacement estimates. Brillouin offers a simpler field workflow and kilometre-scale measurement range compatible with remote deployment while Rayleigh provides superior spatial resolution but requires a demanding calibration procedure ill-suited to autonomous field use, though it shows promise for laboratory-scale deformation experiments. DSS represents a step change in englacial deformation measurement with direct implications for the study of ice rheology, glacier dynamics, and hazard assessment at alpine and ice-sheet scales.