Water/Falls: Coupling stochastic calving and subglacial hydrology at Sermeq Kujalleq (Store Glacier)

Calving glaciers (lake-terminating or tidewater) represent a key uncertainty in future glacier projections, particularly for the ice sheets, where they are responsible, respectively, for around 40% of ice mass loss (Greenland), and nearly 100% (Antarctica). Accurately modelling these glaciers into the future is therefore crucial for being able to forecast future mass loss and the associated sea-level rise. Yet, long-term predictions of the evolution of these systems remain extremely challenging, as both calving and subglacial hydrology, to which these glaciers are highly sensitive, are difficult and/or expensive to model at longer timescales.

One possible solution to better model long-term calving is to represent it as a stochastic process based on the theory of self-organised criticality. Calving can be typified by two types of self-organisation around, respectively, ice cliffs (serac-style events) and ice tongues (full-thickness events). We show that both modes of calving can be influenced by subglacial hydrology.

Here, we therefore present recent work building on the calving implementation of the stochastic crevasse-depth calving function in the open-source ice-flow model, Elmer/Ice, allowing significant improvements in long-term predictions of calving rates and styles. We couple the new calving implementation with the version of the Glacier Drainage System (GlaDS) subglacial hydrology model available in the Elmer/Ice code and present results from a Greenlandic tidewater glacier, Sermeq Kujalleq (Store Glacier). This allows us to explore the interaction of calving, subglacial hydrology, and meltwater plumes, and also provides useful insight for similar future modelling efforts. Using the capabilities of the Elmer/Ice model to resolve the full 3D stress field and allow unconstrained terminus geometries gives us unparalleled insight into the melt-driven serac calving that results from undercutting of the terminus. Furthermore, the subglacial hydrology modelled by GlaDS can directly influence full-thickness calving through increased basal water pressure promoting fractures near the base of the glacier. Consequently, we show that coupled hydrology-calving modelling promotes increased calving in summer when water pressures are high compared to winter.