A numerical study of hydrologically driven glacier dynamics and subglacial flooding

Abstract

A hydrologically coupled flowband model of 'higher order' ice dynamics is used to explore perturbations in response to supraglacial water drainage and subglacial flooding. The subglacial drainage system includes interacting 'fast' and 'slow' drainage elements. The fast drainage system is assumed to be composed of ice-walled conduits and the slow system of a macroporous water sheet. Under high subglacial water pressures, flexure of the overlying ice is modelled using elastic beam theory. A regularized Coulomb friction law describes basal boundary conditions that enable hydrologically driven acceleration. We demonstrate the modelled interactions between hydrology and ice dynamics by means of three observationally inspired examples: (i) simulations of meltwater drainage at an Alpine-type glacier produce seasonal and diurnal variability, and exhibit drainage evolution characteristic of the so-called 'spring transition'; (ii) horizontal and vertical diurnal accelerations are modelled in response to summer meltwater input at a Greenlandtype outlet glacier; and (iii) short-lived perturbations to basal water pressure and ice-flow speed are modelled in response to the prescribed drainage of a supraglacial lake. Our model supports the suggestion that a channelized drainage system can form beneath the margins of the Greenland ice sheet, and may contribute to reducing the dynamic impact of floods derived from supraglacial lakes.

Modelling channelized surface drainage of supraglacial lakes

“…Because the drainage of lakes along the ice-bed interface can affect ice dynamics (e.g. Das and others, 2008;Pimentel and Flowers, 2011;Bartholomew and others, 2011;Kingslake and Ng, 2013), the location and evolution of supraglacial lakes have implications for the future dynamic response of the ice sheet to atmospheric warming. Figure 1 shows that supraglacial lake water can also flow supraglacially into other lake basins (e.g.…”

The annual glaciohydrology cycle in the ablation zone of the Greenland ice sheet: Part 1. Hydrology model

“…Annual surface ablation is distributed through time to yield a surface ablation rate, _ a s , using a sine function to represent the melt-season solar insolation history (cf. Pimentel and Flowers, 2010):…”

Sensitive response of the Greenland Ice Sheet to surface melt drainage over a soft bed

“…Current theoretical understanding of GrIS basal hydrology calls on the evolution of the subglacial drainage system from low to high hydraulic efficiency, to accommodate for melt supply variability over the ablation season [19][20][21] , although limited direct observations of the basal environment do not fully verify this model [22][23][24] . Moreover, the representation of an evolving subglacial drainage system in numerical models is challenging, and currently necessitates major simplifications such as reduced spatial dimensions 23,[25][26][27][28] , application on idealized domains 25,29 or disregarding feedbacks on ice flow 30 . Significantly, these dynamic processes are yet to be realistically incorporated into studies aiming to forecast future sea-level rise [31][32][33] .…”