Simulating cracks in glacier ice by means of the phase field method

Calving is still a poorly understood process, hence a physically based calving law has not yet been found. Large ice sheet models are using simplified parameterisations to describe calving, which are tuned by observational data. Therefore the demands for the development of physically based models for calving are large.

Calving is facilitated by fracture formation and propagation, which description is the objective of fracture mechanics. Based on the fundamental theory for fracture proposed by Griffith a numerical approach has been developed to describe cracks: the so-called phase field method. This method represents the state of a material, whether it is intact or broken, by means of an additional continuous scalar field. The advantage of the phase field method is its simple numerical implementation and the avoidance of explicit representation of crack faces as well as costly remeshing.

This work adjust the phase field method for fracture to simulate fracture in glacier ice. Thereby the ice rheology is considered by using a viscoelastic material description where a nonlinear viscosity, based on Glen’s flow law, is taken into account. Furthermore finite strain theory is used to capture the large deformations occurring in ice shelves and floating glacier tongues.

The developed theoretical framework is utilized to simulate crack initiation and propagation at ice rises. Here the calving front geometry of the 79N Glacier in Greenland is used to validate the proposed model by comparing the simulated crack paths to satellite imagery.