Katarzyna L P Warburton , Colin R. Meyer, Aleah Nicholson Sommers 

The sliding speed of glaciers depends strongly on the water pressure at the ice-sediment interface, which is controlled by the efficiency of water transport through a subglacial hydrological system. The least efficient component of the system consists of 'distributed' flow everywhere beneath the ice, whereas the 'channelised' drainage through large, thermally eroded conduits is more efficient. To understand the conditions under which the subglacial network channelises, we perform a linear stability analysis of distributed flow, considering competition between thermal erosion and viscous ice collapse. The calculated growth rate gives a stability criterion, describing the minimum subglacial meltwater flux needed for channels to form, but also indicates the tendency to generate infinitely narrow channels in existing models. We demonstrate the need to include lateral heat diffusion when modeling melt incision to resolve channel widths. We also show that low numerical resolution can suppress channel formation and lead to overestimates of water pressure. The linear stability results are used to predict the character of subglacial hydrological networks without recourse to numerical modeling.