Greenland’s firn hydrofractures


Ice-penetrating radar observations of firn water storage in Northwest Greenland. Radar observations in 2011 show an ice blob that had refrozen in the porous firn beneath the ice slab (left, Culberg et al., 2022, link). Non-dimensional analysis of maximum effective stress as a function of water height within the crevasse (right). The poromechanical model shows that it is impossible to hydrofracture firn as pore pressure takes around 80% of the hydrostatic stress. Read the paper here. 

On the Greenland Ice Sheet, hydrofracture connects the supraglacial and subglacial hydrologic systems, coupling surface runoff dynamics and ice velocity. Over the last two decades, the growth of low-permeability ice slabs in the firn above the equilibrium line has expanded Greenland’s runoff zone, but the vulnerability of these regions to hydrofracture is still poorly understood. Observations from Northwest Greenland suggest that when meltwater drains through crevasses in ice slabs, it is stored in the underlying relict firn layer and does not reach the ice sheet bed. Here, we use poromechanics to investigate whether water-filled crevasses in ice slabs can propagate vertically through a firn layer. We find that the firn layer reduces the system’s vulnerability to hydrofracture because much of the hydrostatic stress is accommodated by a change in pore pressure, rather than being transmitted to the solid skeleton. This result suggests that surface-to-bed hydrofracture will not occur in ice slab regions until all pore space proximal to the initial flaw has been filled with solid ice.

Gas migration and sediment mechanics

Photoporomechanics: fluid injection into cohesionless (left) and cohesive (right) granular media. Read the paper here and here. 

Gas migration through a soft, liquid-saturated granular material involves a strong coupling between the motion of the gas and the deformation of the material. This process is central to many natural and industrial systems, such as methane venting from lake and ocean sediments, enhanced oil/gas recovery, and geological carbon sequestration. We employ photoporomechanics to study fluid-induced deformation and fracture of granular media, with a focus on its underpinning grain-scale mechanics. We build a two-phase poroelastic continuum model to rationalize the crossover from pore invasion to fracturing regimes.

discrete Element Modeling of coupled multiphase flow and granular mechanics

Discrete element modeling on invading fluid morphology with different wettabilities: fractures (left), frictional fingers (middle) and capillary invasion (right). Read the paper here. 

Granular materials are part of our everyday life (e.g. sand, rice, coffee, and corn), and they can exhibit both solids-like and liquid-like properties. We examine, for the first time, how wet granular materials transition from liquid-like to solid-like states (a jamming transition) under immiscible fluid displacement (e.g. water displacing oil). In particular, we developed a hydromechanical computational model coupling two-phase flow at the pore scale with grain mechanics. We find that the affinity of the grains to one fluid compared to the other (i.e. wettability) defines the character of the granular pack deformation, resulting in a beautiful array of patterns ranging from expanding cavities to capillary fractures and frictional fingers.