Subglacial drainage by groundwater–channel coupling, and the origin of esker systems: part II—theory and simulation of a modern system

The observations from Breidamerkurjo¨ kull reported in Part I are used as a basis for a theory of coupled channel/groundwater flow that suggests that the large scale geometry of the hydraulic system self-organises as a consequence of coupling between groundwater and channel flow. The pattern of channel/esker distribution is largely determined by winter conditions and the sedimentary characteristics of eskers are largely determined by summer conditions, when large discharges of surface meltwater penetrate to the bed in the terminal zone. A simulation model is developed to explore evolution of the channel/groundwater system during a period of glacier growth. It suggests that as the glacier grows, channel/esker frequencies will increase as will the proportion of the melt flux discharged by channel flow, that groundwater impacts can extend to depth, that low water-pressure bulbs will extend downwards beneath channels, that groundwater upwelling towards channels are strong enough to create widespread conditions for liquefaction and that pressure shocks can occur as the channel system reorganises itself.