Advanced fracture mechanics modelling of glacial calving
Author(s)
Clayton, Theo
Type
Thesis
Abstract
Sea level rise primarily occurs from glacial mass loss from ice sheets, through ice-berg calving and meltwater production. However, iceberg calving from meltwater driven hydrofracture remains poorly understood. A stress-based phase field simulation is proposed to model surface and basal crevasse propagation in ice sheets and ice shelves. The model incorporates: a constitutive description of nonlinear viscous ice rheology; a phase field formulation capturing complex fracture patterns; and a poro-damage approach representing crevasse meltwater pressures. Crevasse depth predictions are compared to analytical solutions with good agreement for appropriate idealisations. The influence of firn material properties on longitudinal stress and crevasse depth are explored. Novel analytical solutions for longitudinal stress are derived considering depth-dependent density and Young’s modulus, used subsequently in fracture mechanics studies to determine the contribution of firn to crevasse growth compared to homogeneous ice. The largest crevasse depth reductions were for shallow crevasses in thin glaciers, with Young’s modulus being more influential. However, for near-terminus crevasses in ice shelves, firn density increased penetration depth, with differences observed in ice shelves up to a kilometre in thickness. A phase field model based on the Mohr-Coulomb failure criteria is proposed for subaerial cliff calving, where failure stresses are decomposed into maximum shear stress and pressure components. Free slip glaciers are prone to mode I failures away from the terminus, whereas glaciers frozen to the bedrock are vulnerable to full thickness cliff failure beyond a critical thickness. This is dependent on cohesion, and damage initiation sites depend on internal friction. For tidewater glaciers, iceberg detachment occurs above a critical glacier free-board, with ice slumping above the oceanwater height. Stability envelope diagrams are produced based on critical conditions for cliff failure from multiple simulations. The understanding of crevasse behaviour in glaciers alongside the required conditions for iceberg calving are thereby enhanced.
Version
Open Access
Date Issued
2024-09-11
Date Awarded
2025-08-01
Copyright Statement
Attribution-Non Commercial-No Derivatives 4.0 International Licence (CC BY-NC-ND)
Advisor
Wadee, Ahmer
Martínez-Pañeda, Emilio
Publisher Department
Department of Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)