Temperature sensitivity of snow viscoplasticity: Evidence from controlled creep experiments

Snow is a warm, porous material whose densification under its own weight is highly temperature-dependent. Despite decades of research, reported activation energies for snow viscoplasticity remain highly scattered, ranging from 40 to 600 kJ mol-1. We quantified the temperature dependence of snow viscoplasticity using in-tomograph creep experiments with a newly developed thermo-mechanical cell. This design allows accurate load and temperature control, micrometric displacement measurement, and microstructural evolution monitoring via X-ray tomography. To disentangle microstructural evolution and temperature effects on the compression rate, we used a state-of-the-art viscoplastic model. We conducted five experiments on centimetre-scale samples of decomposing and fragmented precipitation particles with initial densities ranging from 278 to 320 kg m-3 under an applied stress of 1.25 kPa. Each experiment comprised five temperature steps from -6 to -18°C, each lasting one day, and resulted in a mean final vertical strain of 4%. We show that the viscoplastic response follows a two-regime Arrhenius law, with activation energies Qh = 126 ± 6 kJ mol-1 for temperatures above -13 ± 1°C and Ql = 51 ± 18 kJ mol-1 below. This temperature sensitivity matches that reported for polycrystalline ice but is greater than that used in detailed snowpack models.