Ice viscosity governs hydraulic fracture that causes rapid drainage of supraglacial lakes

TL;DR

This study introduces a novel computational model showing that viscous deformation in ice significantly influences hydrofracture propagation, leading to rapid supraglacial lake drainage, especially under warming conditions, impacting sea level rise predictions.

Contribution

The paper develops a two-scale numerical model that incorporates viscous deformation and thermo-hydro-mechanical processes to better understand glacier hydrofracture dynamics.

Findings

Viscous deformation dominates fracture propagation over elastic effects.

Rapid lake drainage is likely without refreezing as temperatures rise.

Model aligns with observational data from 2008 lake drainage event.

Abstract

Full thickness crevasses can transport water from the glacier surface to the bedrock where high water pressures can open kilometre-long cracks along the basal interface, which can accelerate glacier flow. We present a first computational modelling study that describes time-dependent fracture propagation in an idealised glacier causing rapid supraglacial lake drainage. A novel two-scale numerical method is developed to capture the elastic and viscoelastic deformations of ice along with crevasse propagation. The fluid-conserving thermo-hydro-mechanical model incorporates turbulent fluid flow and accounts for melting/refreezing in fractures. Applying this model to observational data from a 2008 rapid lake drainage event indicates that viscous deformation exerts a much stronger control on hydrofracture propagation compared to thermal effects. This finding contradicts the conventional assumption that elastic deformation is adequate to describe fracture propagation in glaciers over short timescales (minutes to several hours) and instead demonstrates that viscous deformation must be considered to reproduce observations of lake drainage rate and local ice surface elevation change. As supraglacial lakes continue expanding inland and as Greenland Ice Sheet temperatures become warmer than -8 degree C, our results suggest rapid lake drainages are likely to occur without refreezing, which has implications for the rate of sea level rise.