Bounds on the calving cliff height of marine terminating glaciers

Abstract

Increased calving and rapid retreat of glaciers can contribute significantly to sea level rise, but the processes controlling glacier retreat remain poorly understood. We seek to improve our understanding of calving by investigating the stress field controlling tensile and shear failure using a 2‐D full‐Stokes finite element model. Using idealized rectangular geometries, we find that when rapidly sliding glaciers thin to near buoyancy, full thickness tensile failure occurs, similar to observations motivating height‐above‐buoyancy calving laws. In contrast, when glaciers are frozen to their beds, basal crevasse penetration is suppressed and calving is minimal. We also find that shear stresses are largest when glaciers are thickest. Together, the tensile and shear failure criteria map out a stable envelope in an ice‐thickness‐water‐depth diagram. The upper and lower bounds on cliff height can be incorporated into numerical ice sheet models as boundary conditions, thus bracketing the magnitude of calving rates in marine‐terminating glaciers.Key PointsWe simulated tensile and shear failure within idealized glaciers using a full‐Stokes ice dynamics modelSurface and basal crevasses intersect when rapidly sliding glaciers thin to buoyancy, and shear failure occurs when ice thickness is largeTensile and shear failure mechanisms together provide lower and upper bounds on permissible ice thickness for any given water depth