Breaking Better: modelling rifts of the Ross Ice Shelf using extended finite elements

Abstract:

Useful representation of through-cutting rifts is a long standing challenge in ice shelf and ice sheet system modelling. Upstream of the calving front, rifts disconnect the ice continuum, affecting stress transmission in a time-dependent manner as the features continue to develop. In this work, we present a framework for explicit representation of rifts in an ice shelf model and use this to argue that ice shelf stresses cannot be accurately represented or understood if rifts are ignored.

Our approach applies linear elastic fracture mechanics to simulate rifts. We use the extended finite element method in elastic sub-domains on which we impose stress fields by calculating equivalent nodal forces. The stress fields are retrieved from modelled ice flow (for example, from ISSM) or deduced from (otherwise) smoothed velocity fields using constant rheological properties. In both cases, remotely observed viscous deformation is used as a proxy from which stresses are derived and care is taken regarding the length of the observational interval. This approach has been verified using synthetic fields and analytical solutions. The case studies presented here serve as validation.

We preform a careful examination of splay rifts responding to propagation of nearby branches, rifts interacting with each other and rifts interacting with structural boundaries, all near the front of the Ross Ice Shelf in West Antarctica. We find that discontinuities caused by rifts modify the stress field in important ways, directing further propagation and modifying local flow and thus, how we interpret remotely sensed flow and strain rate fields.