Channelization of subglacial water flow: stability and channel distribution

The sliding speed of glaciers is related to the water pressure at the ice-sediment interface, which is controlled by the efficiency of water transport through a subglacial hydrological system. These hydrological networks transition from inefficient 'distributed' flow in a thin sheet everywhere beneath the ice to 'channelized' drainage through large thermally eroded conduits. Understanding the conditions under which subglacial flow will channelize, and the location and extent of the resulting channels, will allow for better predictions of ice sheet dynamics.

We first perform a linear stability analysis of the distributed system, taking into account melting of the ice from both geothermal and dissipative heating, countered by the collapse of channels from the viscous flow of the ice above. We then consider the non-linear growth and eventual size of channels in the unstable case, and quantify the distributions of channels that develop beneath different glacier geometries. We find that subglacial water pressure initially increases with meltwater availability, but once the channelization threshold is reached, even small channels can efficiently drain water from the glacier bed.