How to model crevasse initiation? Lessons from the artificial drainage of a water-filled cavity on the Tête Rousse Glacier (Mont Blanc range, France)

Abstract. Crevasses play a crucial role in glacier-related hazards by facilitating water intrusion into the ice body and potentially triggering the collapse of large ice masses. However, the stress conditions governing their initiation and propagation remain uncertain. In particular, there is ongoing debate regarding the most relevant stress invariants to define fracture initiation (the failure criterion) and the corresponding failure strength, i.e. the stress threshold beyond which crevasses form. Laboratory estimates are hampered by the difficulty of reproducing natural glacier conditions, while in situ studies encounter uncertainties when converting strain or strain rate into stress estimates. This study investigates crevasse initiation processes by analyzing the artificial drainage of a water-filled cavity on Tête Rousse Glacier in 2010. Using the finite element code Elmer/Ice, we simulate the drainage and subsequent cavity refilling over three consecutive years. Given the well-constrained cavity geometry and water levels, stress fields are inferred directly from the force balance, removing the need to convert deformation data into stress estimates. Simulated stress distributions are compared with a pattern of circular crevasses mapped around the cavity after the first drainage event. Our results suggest that crevasse initiation is best explained by assuming a non-linear viscous mechanical response of ice (Glen's flow law, n = 3), rather than a linear viscous or linear elastic response. Additionally, by evaluating four failure criteria commonly used in glaciology, we show that the maximum principal stress criterion, with a stress threshold of 100 to 130 kPa, provides the best match to the observed crevasse field.